Effects of supplementing a Saccharomyces cerevisiae fermentation product during the transition period on rumen fermentation of dairy cows fed fresh diets differing in starch content

The objective of this study was to evaluate the effects of supplementing a Saccharomyces cerevisiae fermentation product (SCFP; NutriTek, Diamond V, Cedar Rapids, IA) during the transition period (d −28 ± 3 to 23 ± 3 relative to calving) on rumen fermentation and mRNA abundance of genes in the rumen epithelium of fresh cows (d 1 to 23 ± 3 after calving) fed diets differing in starch content. Eighteen ruminally cannulated multiparous Holstein cows were fed diets with SCFP (n = 9) or without (CON; n = 9) throughout the experiment. All cows were fed a common basal controlled-energy close-up diet (1.43 Mcal/kg, net energy for lactation; 13.8% starch) before calving. Cows within each treatment (CON or SCFP) were fed either a low-starch (LS; 22.1% starch) or high-starch (HS; 28.3% starch) diet during the fresh period. Cows were assigned to treatment after balancing for parity, body condition score, and expected calving date. Rumen pH was measured continuously for 72 h starting on d −10, −3, 1, 7, and 21 relative to calving date. Rumen papillae were collected on d −10 and 21 relative to calving. Supplementation of SCFP had no effect on rumen pH during d −10 to −8, but mean rumen pH tended to be higher (6.64 vs. 6.49) for SCFP cows than for CON cows during d −3 to −1. Feeding SCFP decreased the range of rumen pH variation compared with CON within the HS group during both d 7 to 9 (1.08 vs. 1.38) and d 21 to 23 (1.03 vs. 1.30) after calving. In addition, nadir rumen pH tended to be higher (5.64 vs. 5.44) and duration of pH below 5.8 tended to be shorter (116 vs. 323 min/d) for the SCFP group than for the CON group during d 21 to 23 after calving. Supplementation of SCFP increased the mRNA abundance of insulin-like growth factor-6 (1.10 vs. 0.69) before calving and decreased the mRNA abundance of putative anion transporter isoform 1 (1.12 vs. 2.27) after calving. Nadir rumen pH tended to be higher during d 1 to 3 (5.63 vs. 5.41) for LS cows than for HS cows, but rumen pH was not affected by dietary starch content during other time periods. Dietary starch content had no effect on mRNA abundance of genes in the rumen epithelium after calving. These results suggest that supplementation of SCFP may reduce the range of variation in rumen pH in fresh cows fed HS diets and the duration of subacute ruminal acidosis by the end of the fresh period regardless of dietary starch content and that decreasing dietary starch content during the fresh period may reduce the decrease in rumen pH immediately after parturition.     

Effects of supplementing a Saccharomyces cerevisiae fermentation product during the periparturient period on performance of dairy cows fed fresh diets differing in starch content

The objective of this study was to evaluate the effects of supplementing a Saccharomyces cerevisiae fermentation product (SCFP; NutriTek, Diamond V, Cedar Rapids, IA) during the periparturient period (d ?28 ± 3 to 44 ± 3 relative to calving) on dry matter intake (DMI), milk production, apparent total-tract nutrient digestibility, and postpartum ovarian activity of dairy cows fed fresh diets varying in starch content. From d 28 ± 3 before the expected calving date until d 44 ± 3 after calving, 117 Holstein cows were fed diets with SCFP (SCFP; n = 59) or without (control, CON; n = 58). A common, basal, controlled-energy close-up diet (net energy for lactation: 1.43 Mcal/kg; 13.8% starch) was fed before calving. Cows within each treatment (CON or SCFP) were fed either a low- (LS; 22.1% starch) or high-starch (HS; 28.3% starch) diet from d 1 to 23 ± 3 after calving (fresh period), resulting in 4 treatment groups: LS-CON (n = 30), LS-SCFP (n = 29), HS-CON (n = 28), and HS-SCFP (n = 30). All cows were fed the HS diets from d 24 ± 3 to 44 ± 3 after calving (post-fresh period). Cows were assigned to treatment balanced for parity, body condition score, body weight, and expected calving date. Milk yield was higher for cows fed the LS diets compared with those fed the HS diets during the fresh period (34.1 vs. 32.1 kg/d), whereas DMI and 3.5% fat-corrected milk yield (FCM) were not affected by dietary starch content, and LS cows tended to lose more body condition than HS cows (?0.42 vs. ?0.35 per 21 d) during the fresh period. Overall DMI during the close-up and fresh periods did not differ between SCFP and CON cows. However, SCFP supplementation transiently increased DMI on d 1 (13.0 vs. 11.9 kg/d) and 5 (15.5 vs. 14.1 kg/d) after calving compared with CON. During the post-fresh period, SCFP cows tended to eat less than CON cows (19.8 vs. 20.6 kg/d) but had similar 3.5% FCM (44.9 vs. 43.6 kg/d), resulting in greater feed efficiency for SCFP cows (FCM/DMI; 2.27 vs. 2.13). Neither starch content of fresh diets nor SCFP supplementation affected the interval from calving to first ovulation or the incidence of double ovulation. These findings suggest that feeding low-starch diets during the fresh period can increase milk production of dairy cows during the fresh period, and that supplementation of SCFP may increase feed intake around calving and feed efficiency in the post-fresh period.     

Effects of supplementing yeast culture to diets differing in starch content on performance and feeding behavior of dairy cows

The objectives were to evaluate the effects of a culture of Saccharomyces cerevisiae (YC) on lactation performance of cows fed diets differing in starch content. Fifty-six Holstein cows at 42 d postpartum were blocked by parity and milk production and randomly assigned to 1 of 4 treatments, low starch (23% diet DM) and no YC (LS-control), low starch and 15 g/d of YC (LS-YC), high starch (29% diet DM) and no YC (HS-control), and high starch and 15 g/d of YC (HS-YC). The experiment lasted 14 wk. Blood was sampled twice weekly during the first 5 wk in the experiment. Feeding behavior was evaluated in 2 consecutive days when cows were 33 d in the experiment. On d 92 in the experiment, cows were challenged with 3 kg of corn grain DM immediately before the morning feeding. Blood was sampled in the first 12 h after the challenge. Rumen fluid was collected 5 h after the challenge, and pH, ammonia N, short-chain fatty acids, and lactate concentrations were quantified. Lactation performance was measured daily before and after the challenge. Supplementation with YC increased yields of 3.5% fat-corrected milk and energy-corrected milk by 2.2 and 2.0 kg/d, and the increments were observed in both low- and high-starch diets. Feeding HS tended to decrease milk fat content (LS = 3.88 vs. HS = 3.73%), but increased concentration (LS = 2.87 vs. HS = 3.00%) and yield (LS = 1.11 vs. HS = 1.20 kg/d) of milk true protein. Feeding YC increased yields of fat and true protein in milk by 100 and 60 g/d. Energy balance, body weight, and feed efficiency did not differ with treatments. Feeding HS reduced eating time (LS = 177 vs. HS = 159 min/12 h) and intermeal interval (LS = 103 vs. HS = 82 min), but tended to increase eating rate (LS = 139 vs. HS = 150 g/min). Interactions were detected between level of starch and YC for ruminating time, meal duration, and meal size because within LS, feeding YC increased ruminating time 23 min/12 h, but reduced meal duration 6 min/meal and meal size 0.7 kg/meal. Concentrations of glucose in plasma increased (LS = 62.1 vs. HS = 63.8 mg/dL), whereas those of urea N decreased (LS = 10.1 vs. HS = 9.4 mg/dL) with feeding HS compared with LS in the first 5 wk in the experiment, and the same responses were observed after the challenge with corn grain. After the challenge, rumen pH was less and short-chain fatty acid concentrations were greater in cows fed HS compared with those fed LS; however, supplementing YC to high-starch diets increased rumen pH (HS-control = 5.72 vs. HS-YC = 6.12) and reduced concentrations of lactate in rumen fluid (HS-control = 7.72 vs. HS-YC = 1.33 mM) and haptoglobin in plasma 28%. Feeding YC improved lactation performance irrespective of the level of dietary starch and reduced the risk of subacute rumen acidosis induced by a grain challenge when cows were fed a high-starch ration.     

Effect of supplemental yeast culture and dietary starch content on rumen fermentation and digestion in dairy cows

The objectives of this experiment were to evaluate the effect of feeding a culture of Saccharomyces cerevisiae on rumen metabolism and digestibility when cows are fed diets varying in starch content. Four lactating Holstein cows were assigned to a 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Treatments were low starch (LS; 23% of diet DM) and no yeast culture (YC; LS-control), LS and 15 g of YC/d (LS-YC), high starch (HS; 29% of diet DM) and no YC (HS-control), and HS and 15 g of YC/d (HS-YC). Periods lasted 28 d, with the last 9 d for data collection. Days 20 to 24 were used to determine production, nutrient flow, and digestibility. On d 25, 3 kg of corn grain DM was placed in the rumen 1 h before the morning feeding, and yields of milk and milk components were measured after the challenge. Blood was sampled −1, 3, 7, and 11 h relative to the morning feeding on d 24 and 25. Rumen pH was measured continuously on d 24 and 25. Rumen papillae were collected on d 24 and 28 to quantify mRNA expression of select genes. Supplementing YC increased yields of milk (26.3 vs. 29.6 kg/d), energy-corrected milk (ECM; 26.5 vs. 30.3 kg/d), fat (0.94 vs. 1.08 kg/d), true protein (0.84 vs. 0.96 kg/d), and ECM/dry matter intake (1.15 vs. 1.30) compared with the control but did not affect dry matter intake (22.6 vs. 22.9 kg/d). Cows fed HS had increased milk true protein percentage (3.18 vs. 3.31%) and yield (0.87 vs. 0.94 kg/d) compared with cows fed LS. Feeding HS-YC increased the proportion of dietary N incorporated into milk true protein from 24.9% in the other 3 treatments to 29.6%. Feeding HS increased the concentration of propionate (21.7 vs. 32.3 mM) and reduced that of NH₃-N (8.3 vs. 6.7 mg/dL) in rumen fluid compared with the control, and combining HS with YC in HS-YC tended to increase microbial N synthesis compared with LS-YC (275 vs. 322 g/d). Supplementing YC to cows fed HS reduced plasma haptoglobin and rumen lactate concentrations, increased mean rumen pH, reduced the time with pH <6.0, and prevented the decrease in rumen neutral detergent fiber digestion caused by HS. Cows fed HS had less total-tract digestion of organic matter (73.9 vs. 72.4%) because of reduced acid detergent fiber (57.6 vs. 51.7%) and neutral detergent fiber (60.9 vs. 56.7%) digestibility. Production performance after the challenge was similar to that before the challenge, and YC improved yield of ECM. After the challenge, supplementing YC tended to reduce rumen lactate concentration compared with the control and reduced haptoglobin in cows fed HS. Feeding HS but not YC increased expression in rumen papillae of genes for receptors (FFAR2 and FFAR3) and transporter (SLC16A3) of short-chain fatty acids but did not affect genes involved in transport of Na⁺/H⁺ or water or in inflammatory response. Supplementing YC to dairy cows improved lactation performance in diets containing low or high starch, and mechanisms might be partially attributed to improvements in rumen pH, digestion of fiber, microbial N synthesis, and reduction in acute phase response.     

Effects of pre- and postpartum dietary starch content on productivity,plasma energy metabolites,and serum inflammation indicators of dairy cows

The objective of this study was to evaluate the effects of the starch content of pre- and postpartum diets on productivity, plasma energy metabolites, and serum markers of inflammation of dairy cows during the calving transition period. Eighty-eight primiparous and multiparous cows were randomly assigned to pre- and postpartum dietary treatments balanced for parity and pretrial body condition score at d 28 ± 3 before expected calving date. Cows were fed either a control [Control; 14.0% starch, dry matter (DM) basis] or high-starch (High; 26.1% starch, DM basis) prepartum diet commencing 28 ± 3 d before expected calving date. Following calving, cows were fed either a high-fiber (HF; 33.8% neutral detergent fiber, 25.1% starch, DM basis) or high-starch (HS; 27.2% neutral detergent fiber, 32.8% starch, DM basis) postpartum diet for the first 20 ± 2 d following calving. Cows fed the High prepartum diet had greater DM intake (12.4 vs. 10.2 kg/d), plasma concentrations of insulin (1.72 vs. 14.2 ng/mL), glucose (68.1 vs. 65.0 mg/dL), and glucagon-like peptide-2 (0.41 vs. 0.32 ng/mL) before parturition, but increased plasma free fatty acid concentration (452 vs. 363 µEq/L) and milk fat yield (1.64 vs. 1.48 kg/d) after parturition. Cows fed the HS postpartum diet had lower plasma free fatty acid (372 vs. 442 µEq/L) and serum haptoglobin (0.46 vs. 0.70 mg/mL) concentrations over a 3-wk period after calving. In addition, there was a tendency for interaction between prepartum and postpartum diets for milk yield, where feeding the HS postpartum diet increased milk yield compared with the HF diet for cows fed the Control prepartum diet (40.8 vs. 37.9 kg/d) but not for cows fed the High prepartum diet. These results suggest that management efforts to minimize the change in diet fermentability during the calving transition by feeding the High prepartum diet, the HF postpartum diet, or both did not increase productivity of dairy cows but increased fat mobilization after calving. Our findings also suggest that feeding high-starch postpartum diets can decrease fat mobilization and serum indicators of systemic inflammation and increase milk production even with the transition from a low-starch prepartum diet.     

Effects of rumen-protected glutamate supplementation during the periparturient period on digestibility,inflammation, metabolic responses,and performance in dairy cows

The objective of this study was to evaluate the effects of feeding rumen-protected glutamate during the periparturient period (d ?21 ± 3 to d 21 ± 3 relative to calving) on apparent total-tract digestibility (ATTD), inflammation, metabolic responses, and production performance of dairy cows. Fifty-two multiparous Holstein cows were blocked by parity, body condition score, and expected calving date, and randomly assigned to one of the experimental diets with rumen-protected monosodium glutamate (RP-Glu; intestinally available Glu = 8.8%) or without RP-Glu (control) at d ?21 ± 3 relative to expected calving date. The RP-Glu was fed at 4% and 3% of dietary dry matter, before and after calving, respectively. Prepartum diets contained 17.1% and 16.5% crude protein, and 13.1% and 13.3% starch, and postpartum diets contained 18.8% and 18.3% crude protein, and 22.5% and 22.7% starch on a dry matter basis, respectively for RP-Glu and control treatments. A subset of 19 cows was used to measure ATTD. Cows fed the RP-Glu had greater ATTD of dry matter (70.6 vs. 69.1%), crude protein (75.1 vs. 72.6%), and ether extract (66.0 vs 61.2%) on d 5 ± 1 after calving. Cows fed the RP-Glu also had greater dry matter intake (15.7 vs. 13.7 kg/d) on d 1 after calving. Cows fed the RP-Glu had greater plasma concentrations of Glu (4.60 vs. 3.89 µmol/dL) and insulin-like growth factor-1 (44.2 vs. 30.1 mg/mL), lower serum concentrations of free fatty acids (670 vs. 981 μEq/L) and total bilirubin (0.22 vs. 0.34 mg/dL), and lower plasma 3-methylhistidine concentration (1.28 vs. 1.50 μmol/dL) on d 4 after calving. However, these treatment effects observed between d 1 and d 5 ± 1 immediately after calving did not continue until d 21 after calving. Concentrations of serum amyloid A, serum haptoglobin, and plasma lipopolysaccharide binding protein were not affected by the treatment. In addition, no differences were observed for serum β-hydroxybutyrate concentration and milk yield during the postpartum period between the 2 groups, and cows fed the RP-Glu had a decreased lactose yield. These findings suggest that feeding RP-Glu during the periparturient period can increase digestive capacity and feed intake, and decrease mobilization of body fat and protein immediately after calving without increasing milk production.     

Controlled trial of the effect of negative dietary cation-anion difference on postpartum health of dairy cows

The objective of this study was to assess the effects of feeding negative dietary cation-anion difference (DCAD) dry cow diets on postpartum health. Cows from 4 commercial dairy farms in Ontario, Canada, were enrolled in a pen-level controlled trial from November 2017 to April 2019. Close-up pens (1 per farm), with cows 3 wk before expected calving, were randomly assigned to a negative DCAD [TRT; ?108 mEq/kg of dry matter (DM); target urine pH 6.0–6.5] or a control diet (CON; +105 mEq/kg of DM with a placebo supplement). Each pen was fed TRT or CON for 3 mo (1 period) then switched to the other treatment for the next period, with 4 periods per farm. Urine pH was measured weekly until calving, and body condition score (BCS) was measured at enrollment and at 5 wk postpartum. Data from 15 experimental units [8 TRT and 7 CON, with 1,086 (TRT: n = 681; CON: n = 405) observational units (cows)] that received the assigned diet for >1 wk were included. The incidence of milk fever (MF), retained placenta (RP), metritis, hyperketonemia (blood β-hydroxybutyrate >1.2 mmol/L, measured weekly in wk 1 and 2), clinical mastitis within 30 DIM (MAST), displaced abomasum (DA) within 30 d in milk (DIM), purulent vaginal discharge (PVD, assessed once at wk 5), and number of disease events (≥1 or ≥2) were analyzed with logistic regression models with treatment, parity, BCS, and their interactions, accounting for pen-level randomization and clustering of animals within farm with random effects, giving 10 degrees of freedom to test treatment effects. Multiparous cows fed TRT had greater blood calcium between 1 and 4 DIM than multiparous cows fed CON, and the prevalence of subclinical hypocalcemia (total Ca ≤2.14 mmol/L) was lesser when fed TRT compared with CON (d 1: 73 ± 6% vs. 93 ± 4%; d 2: 65 ± 7% vs. 90 ± 5%), with no differences between treatments detected in primiparous cows. We detected interactions of treatment and BCS at enrollment for MF in multiparous cows and of treatment and parity for ≥2 disease events. Overconditioned (BCS ≥3.75) multiparous cows had reduced incidence of MF when fed TRT (TRT: 2 ± 1%, vs. CON: 13 ± 8%). We detected no treatment effects on RP, metritis, hyperketonemia, or PVD incidence. Cows fed TRT had lesser incidence of DA (1.7 ± 0.7% vs. 3.6 ± 1.6%) and tended to have lesser incidence of MAST compared with CON (1.8% ± 0.6% vs. 4.4 ± 1.4%). No treatment effect was detected on ≥1 disease events (TRT: 38 ± 7%, vs. CON: 42 ± 8%); however, multiparous cows on TRT were less likely to have ≥2 disease events than cows on CON (14 ± 4% vs. 23 ± 6%). Under commercial herd conditions, feeding prepartum diets with negative DCAD improved several measures of postpartum health.     

Effect of dietary supplementation with live-cell yeast at two dosages on lactation performance, ruminal fermentation, and total-tract nutrient digestibility in dairy cows

The experimental objective was to determine the effect of dietary supplementation with live-cell yeast (LCY; Procreatin-7, Lesaffre Feed Additives, Milwaukee, WI) at 2 dosages in high-starch (HS) diets [30% starch in dry matter (DM)] on lactation performance, ruminal fermentation, and total-tract nutrient digestibility in dairy cows compared with HS or low-starch (LS; 20% starch in DM) non-LCY diets. Sixty-four multiparous Holstein cows (114 ± 37 d in milk and 726 ± 74 kg of body weight at trial initiation) were randomly assigned to 32 electronic gate feeders (2 cows per feeder), which were randomly assigned to 1 of 4 treatments in a completely randomized design. A 2-wk covariate adjustment period with cows fed a 50:50 mixture of the HS and LS diets was followed by a 12-wk treatment period with cows fed their assigned treatment diets. The HS diets were fed without (HS0) and with 2 (HS2) or 4 (HS4) g/cow per day of LCY. The LS diet did not contain LCY (LS0) and was formulated by partially replacing dry ground shelled corn with soy hulls. Cows fed LS0 consumed more DM than cows fed HS diets during wk 3, 10, 11, and 12. Yields of actual (44.5 kg/d, on average), fat-, energy-, and solids-corrected milk were unaffected by treatment. Milk fat content tended to be greater for LS0 than for HS0 and HS2 but not different from HS4. Milk urea nitrogen contents were greater for cows fed LS0 than for cows fed the HS diets. Feed conversion (kg of milk/kg of DM intake) was numerically greater for HS diets than for LS0. Ruminal pH was unaffected by treatment. Ruminal molar proportion of acetate was greater, whereas that of propionate was lower, for LS0 compared with HS diets. Dry matter and organic matter digestibilities were greater for HS2 and HS4 than for HS0. Digestibility of neutral detergent fiber was greater for HS4 than for HS0 and HS2. Dry matter, organic matter, and neutral detergent fiber digestibilities were greater for LS0 than for HS diets; starch digestibility was greater for LS0 than for HS0 and HS4. Feeding LS0 increased DM intake and milk fat content, but reduced feed conversions. The addition of 4 g/cow per day of LCY to HS diets tended to increase milk fat content and increased total-tract fiber digestibility in dairy cows.     

Physical effectiveness of corn silage fractions stratified with the Penn State Particle Separator for lactating dairy cows

This study evaluated the physical effectiveness of whole-plant corn silage (CS) particles stratified with the Penn State Particle Separator, composed of 19- and 8-mm-diameter sieves and a pan, for lactating dairy cows. Eight Holstein cows (27.6 ± 2.8 kg/d of milk, 611 ± 74 kg body weight; 152 ± 83 d in milk) were assigned to two 4 × 4 Latin squares (22-d periods, 16-d adaptation), where one square was formed with rumen-cannulated cows. Three CS particle fractions were manually isolated using the 8- and 19-mm diameter sieves and re-ensiled in 200-L drums. The 4 experimental diets were (% dry matter): (1) CON (control): 17% forage neutral detergent fiber (NDF) from CS (basal roughage), 31.5% starch, and 31.9% NDF; (2) PSPan: 17% forage NDF from CS + 9% NDF from CS particles <8 mm, 25.9% starch, and 37.9% NDF; (3) PS8: 17% forage NDF from CS + 9% NDF from CS particles 8 to 19 mm, 25.5% starch, and 38.3% NDF; and (4) PS19: 17% forage NDF from CS + 9% NDF from CS particles >19 mm, 24.9% starch, and 38.8% NDF. Cows fed PS8 had greater dry matter intake and energy-corrected milk yield (22.4 and 26.9 kg/d, respectively) than cows fed CON (20.8 and 24.7 kg/d) and PS19 (21.2 and 24.8 kg/d), but no difference was detected between PSPan (21.6 and 25.8 kg/d) and other treatments. Milk fat concentration was greater for PS8 than CON, with intermediate values for PSPan and PS19. Milk fat yield was greater for cows fed PS8 than CON and PS19, and cows fed PSPan secreted more fat than CON cows but were not different from cows fed the other 2 diets. Cows fed CON had a lower meal frequency than cows fed PSPan, shorter meal and rumination times than PS8, and greater meal size and lower rates of rumination and chewing than the other 3 diets. Total chewing per unit of NDF was higher for PS8 than PSPan, although neither treatment differed from CON or PS19. Cows fed PS19 had higher refusal of feed particles >19 mm than cows fed CON and PSPan. The refusal of dietary NDF and undigested NDF in favor of starch were all greater for PS19 than on the other treatments. Cows fed PS19 had a greater proportion of the swallowed bolus and rumen digesta with particles >19 mm than the other 3 diets. Cows fed CON had the lowest ruminal pH and greatest lactate concentration relative to the other 3 diets. Plasma lipopolysaccharide was higher for cows fed CON and PSPan than for cows fed PS8 and PS19, and serum d-lactate tended to be lower on PSPan than for CON and PS8. In summary, the inclusion of CS fractions in a low-forage fiber diet (CON) reduced signs of ruminal acidosis. Compared with CS NDF <8 and >19 mm, CS NDF with 8- to 19-mm length promoted better rumen health and performance of dairy cows. These results highlight the importance of adjusting CS harvest and formulating dairy diets based on the proportion of particles retained between the 8- and 19-mm sieves.     

Effects of feeding a high-fiber byproduct feedstuff as a substitute for barley grain on rumen fermentation and productivity of dairy cows in early lactation

The objective of the study was to evaluate effects of partial substitution of dietary grain with wheat dried distillers grains with solubles (DDGS) on dry matter intake (DMI), sorting behavior, rumen fermentation, apparent total-tract nutrient digestibility, plasma metabolites, and milk production of dairy cows in early lactation. Sixty-one Holstein cows, including 13 ruminally cannulated cows, were blocked by parity and calving date and assigned to 1 of 2 experimental diets immediately after calving until 12 wk in lactation. The control (CON) diet contained 43% barley silage, 17.3% dry-rolled barley grain, and 39.7% concentrate mix on a dry matter basis, and wheat DDGS replaced dry-rolled barley grain in the DDGS diet. Dietary starch content was 29.2 and 19.1% for CON and DDGS diets, respectively. Despite the 10-percentage-unit difference in dietary starch content, cows fed the DDGS diet did not increase ruminal pH. A significant treatment by parity interaction was observed for DMI; feeding the DDGS diet decreased DMI of multiparous cows compared with CON (20.1 vs. 21.3 kg/d) but increased that of primiparous cows (16.2 vs. 14.7 kg/d). Although milk yield was not affected by treatment, cows fed the DDGS diet had lower apparent total-tract digestibility of starch compared with CON (81.9 vs. 91.2%) and tended to have higher plasma concentrations of nonesterified fatty acids (173 vs. 143 mEq/L). High-fiber byproduct feedstuffs such as wheat DDGS can be used as a partial substitute for grains in diets of dairy cows in early lactation but the substitution may not mitigate rumen acidosis problems and may decrease energy intake of multiparous cows in early lactation.     

Rumen-protected methionine during heat stress alters mTOR,insulin signaling,and 1-carbon metabolism protein abundance in liver,and whole-blood transsulfuration pathway genes in Holstein cows

We investigated effects of rumen-protected Met (RPM) during a heat stress (HS) challenge on (1) hepatic abundance of mTOR, insulin, and antioxidant signaling proteins, (2) enzymes in 1-carbon metabolism, and (3) innate immunity. Holstein cows (n = 32; mean ± standard deviation, 184 ± 59 d in milk) were randomly assigned to 1 of 2 environmental groups, and 1 of 2 diets [total mixed ration (TMR) with RPM (Smartamine M; 0.105% dry matter as top-dress) or TMR without (CON); n = 16/diet] in a split-plot crossover design. There were 2 periods with 2 phases. During phase 1 (9 d), all cows were in thermoneutral conditions (TN; temperature-humidity index = 60 ± 3) and fed ad libitum. During phase 2 (9 d), half the cows (n = 8/diet) were exposed to HS using electric heat blankets. The other half (n = 8/diet) remained in TN, but was pair-fed to HS counterparts. After a 14-d washout and 7-d adaptation period, the study was repeated (period 2) and environmental treatments were inverted relative to phase 2, but dietary treatments were the same. Blood was collected on d 6 of each phase 2 to measure immune function and isolate whole-blood RNA. Liver biopsies were performed at the end of each period for cystathione β-synthase (CBS) and methionine adenosyltransferase activity, glutathione concentration, and protein abundance. Data were analyzed using PROC MIXED in SAS. Abundance of CUL3, inhibitor of antioxidant responses, tended to be downregulated by HS suggesting increased oxidative stress. Heat-shock protein 70 abundance was upregulated by HS. Phosphorylated mTOR abundance was greater overall with RPM, suggesting an increase in pathway activity. An environment × diet (E × D) effect was observed for protein kinase B (AKT), whereas there was a tendency for an interaction for phosphorylated AKT. Abundance of AKT was upregulated in CON cows during HS versus TN, this was not observed in RPM cows. For phosphorylated AKT, tissue from HS cows fed CON had greater abundance compared with all other treatments. The same effect was observed for EIF2A (translation initiation) and SLC2A4 (insulin-induced glucose uptake). An E × D effect was observed for INSR due to upregulation in CON cows during HS versus TN cows fed CON or RPM. There was an E × D effect for CBS, with lower activity in RPM versus CON cows during HS. The CON cows tended to have greater CBS during HS versus TN. An E × D effect was observed for methionine adenosyltransferase, with lower activity in RPM versus CON during HS. Although activity increased in CON during HS versus TN, RPM cows tended to have greater activity during TN. Neutrophil and monocyte oxidative burst and monocyte phagocytosis decreased with HS. An (E × D) effect was observed for whole-blood mRNA abundance of CBS, SOD1 and CSAD; RPM led to upregulation during TN versus HS. Regardless of diet, CDO1, CTH, and SOD1 decreased with HS. Although HS increased hepatic HSP70 and seemed to alter antioxidant signaling, feeding RPM may help cows maintain homeostasis in mTOR, insulin signaling, and 1-carbon metabolism. Feeding RPM also may help maintain whole-blood antioxidant response during HS, which is an important aspect of innate immune function.     

The effects of feeding α-amylase-enhanced corn silage with different dietary starch concentrations to lactating dairy cows on milk production,nutrient digestibility,and blood metabolites

Corn silage is one of the most common ingredients fed to dairy cattle. Advancement of corn silage genetics has improved nutrient digestibility and dairy cow lactation performance in the past. A corn silage hybrid with enhanced endogenous α-amylase activity (Enogen, Syngenta Seeds LLC) may improve milk production efficiency and nutrient digestibility when fed to lactating dairy cows. Furthermore, evaluating how Enogen silage interacts with different dietary starch content is important because the ruminal environment is influenced by the amount of rumen fermentable organic matter consumed. To evaluate the effects of Enogen corn silage and dietary starch content, we conducted an 8-wk randomized complete block experiment (2-wk covariate period, 6-wk experimental period) with a 2 × 2 factorial treatment arrangement using 44 cows (n = 11/treatment; 28 multiparous, 16 primiparous; 151 ± 42 d in milk; 668 ± 63.6 kg of body weight). Treatment factors were Enogen corn silage (ENO) or control (CON) corn silage included at 40% of diet dry matter and 25% (LO) or 30% (HI) dietary starch. Corn silage used in CON treatment was a similar hybrid as in ENO but without enhanced α-amylase activity. The experimental period began 41 d after silage harvest. Feed intake and milk yield data were collected daily, plasma metabolites and fecal pH were measured weekly, and digestibility was measured during the first and final weeks of the experimental period. Data were analyzed using a linear mixed model approach with repeated measures for all variables except for body condition score change and body weight change. Corn silage, starch, week, and their interactions were included as fixed effects; baseline covariates and their interactions with corn silage and starch were also tested. Block and cow served as the random effects. Plasma glucose, insulin, haptoglobin, and serum amyloid A concentrations were unaffected by treatment. Fecal pH was greater for cows fed ENO versus CON. Dry matter, crude protein, neutral detergent fiber, and starch digestibility were all greater for ENO than CON during wk 1, but differences were less by wk 6. The HI treatments depressed neutral detergent fiber digestibility compared with LO. Dry matter intake (DMI) was not affected by corn silage but was affected by the interaction of starch and week; in wk 1, DMI was similar but by wk 6, cows fed HI had 1.8 ± 0.93 kg/d less DMI than LO cows. Milk, energy-corrected milk, and milk protein yields were 1.7 ± 0.94 kg/d, 1.3 ± 0.70 kg/d, and 65 ± 27 g/d greater for HI than LO, respectively. In conclusion, ENO increased digestibility but it did not affect milk yield, component yields, or DMI. Increasing dietary starch content improved milk production and feed efficiency without affecting markers of inflammation or metabolism.     

Replacing ground corn with soyhulls plus palmitic acid in low metabolizable protein diets with or without rumen-protected amino acids: Effects on production and nutrient utilization in dairy cows

We previously observed that diets with reduced starch concentration decreased yields of milk and milk protein in dairy cows fed low metabolizable protein diets. Supplementation of reduced-starch diets with a lipid source may attenuate or eliminate production losses. Our objective was to investigate the effects of partially replacing ground corn with soyhulls plus a palmitic acid-enriched supplement on dry matter (DM) intake, milk yield and composition, plasma AA concentration, and N and energy utilization in cows fed low metabolizable protein diets (mean = −68 g/d balance) with or without rumen-protected Met, Lys, and His (RP-MLH). Sixteen multiparous Holstein cows averaging (mean ± standard deviation) 112 ± 28 d in milk, 724 ± 44 kg of body weight, and 46 ± 5 kg/d of milk in the beginning of the study were used in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments. Each period lasted 21 d, consisting of 14 d for diet adaptation and 7 d for data and sample collection. Diets were fed as follows: (1) high starch (HS), (2) HS plus RP-MLH (HS+AA), (3) reduced starch plus a palmitic acid-enriched supplement (RSPA), and (4) RSPA plus RP-MLH (RSPA+AA). The HS diet contained (DM basis) 26% ground corn and 7% soyhulls, and the RSPA diet had 10% ground corn, 22% soyhulls, and 1.5% palmitic acid. The HS diet averaged (DM basis) 32.6% starch and 4% ether extract, while starch and ether extract concentrations of the RSPA diet were 21.7 and 5.9%, respectively. All 4 diets had (DM basis) 40% corn silage, 5% mixed-mostly grass haylage, 5% grass hay, and 50% concentrate. Diets did not affect DM intake and milk yield. Contrarily, feeding RSPA and RSPA+AA increased yields of energy-corrected milk (47.0 vs. 44.8 kg/d) and milk fat (1.65 vs. 1.50 kg/d) compared with HS and HS+AA. Milk fat concentration tended to decrease when RP-MLH was supplemented to HS, but no change was seen when added to RS (starch level × RP-MLH interaction). Milk and plasma urea N increased, and milk N efficiency decreased in cows fed RSPA and RSPA+AA versus HS and HS+AA. Apparent total-tract digestibilites of crude protein and neutral detergent fiber, as well as urinary urea N and total N excretion, were greater in cows offered RSPA and RSPA+AA than HS and HS+AA. Plasma Met and His concentrations increased with supplemental RP-MLH. Intake of gross energy and digestible energy and the output of urinary and milk energy were all greater with feeding RSPA and RSPA+AA versus HS and HS+AA. In summary, partially replacing ground corn with soyhulls plus palmitic acid in diets supplemented or not with RP-MLH increased milk fat yield and fiber digestibility and maintained DM intake and milk yield, but with decreased milk N efficiency and elevated urinary N excretion.     

Controlled trial of the effect of negative dietary cation-anion difference prepartum diets on milk production,reproductive performance,and culling of dairy cows

Our objective was to assess the effects of feeding negative dietary cation-anion difference (DCAD) prepartum diets on milk production, reproductive performance, and culling. Cows from 4 commercial farms in Ontario, Canada were enrolled in a pen-level controlled trial from November 2017 to April 2019. Close-up pens (1 per farm) with cows 3 wk before calving were randomly assigned to a negative DCAD (TRT; ?108 mEq/kg of dry matter; target urine pH 6.0–6.5) or a control diet (CON; +105 mEq/kg of dry matter with a placebo supplement). Each pen was fed TRT or CON for 3 mo (1 period), and then switched to the other treatment for the next period (4 periods per farm). Data from 15 experimental units (8 pen treatments in TRT and 7 in CON), with a total of 1,086 observational units (cows), were included. The effect of treatment on milk yield at the first 3 milk recording tests of lactation was assessed with linear regression models accounting for repeated measures. The risk of pregnancy at first artificial insemination and culling by 30, 60, and 305 d in milk (DIM) were analyzed with logistic regression models, and effects on time to first AI, pregnancy, and culling were assessed with Cox proportional hazards models. All models included treatment, parity, and their interactions, accounting for pen-level randomization and clustering of animals within farm with random effects, giving 10 degrees of freedom for treatment effects. Multiparous cows fed TRT produced more milk at the first (42.0 vs. 38.8 ± 1.2 kg/d) and second (44.2 vs. 41.7 ± 1.3 kg/d) milk tests. However, multiparous cows fed TRT tended to have 0.2 percentage units less milk fat content at these tests. Although multiparous cows fed TRT tended to have greater energy-corrected milk at the first test (least squares means ± standard error: TRT = 46.1 ± 0.9 vs. CON = 43.8 ± 1 kg/d), there were no differences observed in energy-corrected milk at the second or third tests. In primiparous cows, there was no effect of treatment on milk production. Multiparous cows fed TRT had greater pregnancy to first insemination (TRT = 42 ± 3 vs. CON = 32 ± 4%) and tended to have shorter time to pregnancy [hazard ratio (HR) = 1.20; 95% CI: 0.96–1.49]. In primiparous cows fed TRT, time to pregnancy was increased (HR = 0.76; 95% CI: 0.59–0.99). Culling by 30 DIM tended to be less in TRT (3.3 ± 1.1%) than CON (5.5 ± 1.8%). No effect of treatment on culling by 305 DIM was detected in primiparous cows, but in multiparous cows, the TRT diets decreased the odds of culling (21.3 ± 1.9 vs. 31.7 ± 2.8%) and daily risk of culling to 305 DIM (HR = 0.64; 95% CI: 0.46 to 0.89). Under commercial herd conditions, prepartum negative DCAD diets improved milk production and reproductive performance, and reduced culling risk in multiparous cows. In primiparous cows, TRT diets had no effect on milk yield or culling, but increased the time to pregnancy. Our results suggest that negative DCAD diets should be targeted to multiparous cows.     

Relationship between residual feed intake and digestibility for lactating Holstein cows fed high and low starch diets

We determined if differences in digestibility among cows explained variation in residual feed intake (RFI) in 4 crossover design experiments. Lactating Holstein cows (n = 109; 120 ± 30 d in milk; mean ± SD) were fed diets high (HS) or low (LS) in starch. The HS diets were 30% (±1.8%) starch and 27% (±1.2%) neutral detergent fiber (NDF); LS diets were 14% (±2.2%) starch and 40% (±5.3%) NDF. Each experiment consisted of two 28-d treatment periods, with apparent total-tract digestibility measured using indigestible NDF as an internal marker during the last 5 d of each period. Individual cow dry matter (DM) intake and milk yield were recorded daily, body weight was measured 3 to 5 times per week, and milk components were analyzed 2 d/wk. Individual DM intake was regressed on milk energy output, metabolic body weight, body energy gain, and fixed effects of parity, experiment, cohort (a group of cows that received treatments in the same sequence) nested within experiment, and diet nested within cohort and experiment, with the residual being RFI. High RFI cows ate more than expected and were deemed less efficient. Residual feed intake correlated negatively with digestibility of starch for both HS (r = ?0.31) and LS (r = ?0.23) diets, and with digestibilities of DM (r = ?0.30) and NDF (r = ?0.23) for LS diets but was not correlated with DM or NDF digestibility for HS diets. For each cohort within an experiment, cows were classified as high RFI (HRFI; >0.5 SD), medium RFI (MRFI; ±0.5 SD), and low RFI (LRFI; <?0.5 SD). Digestibility of DM was similar (~66%) among HRFI and LRFI for HS diets but greater for LRFI when fed LS diets (64 vs. 62%). For LS diets, digestibility of DM could account for up to 31% of the differences among HRFI and LRFI for apparent diet energy density, as determined from individual cow performance, indicating that digestibility explains some of the between-animal differences for the ability to convert gross energy into net energy. Some of the differences in digestibility between HRFI and LRFI were expected because cows with high RFI eat at a greater multiple of maintenance, and greater intake is associated with increased passage rate and digestibility depression. Based on these data, we conclude that a cow’s digestive ability explains none of the variation in RFI for cows eating high starch diets but 9 to 31% of the variation in RFI when cows are fed low starch diets. Perhaps differences in other metabolic processes, such as tissue turnover, heat production, or others related to maintenance, can account for more variation in RFI than digestibility.     

Rumen effects of monensin in dry cow diets varying in energy density

Controversy has existed as to whether monensin will provide equal or differential benefits in a higher-energy, lower-roughage close-up diet versus a higher-roughage, lower-energy diet. Our objective was to determine the rumen effects of a controlled-energy, high-fiber diet balanced to meet but not greatly exceed energy requirements during the dry period or a traditional 2-group approach of higher-energy close-up diet. The effects of added monensin in each diet type were determined. Multiparous Holstein cows (n = 17) were fitted surgically with ruminal cannulas. During the first 4 wk of the dry period, all cows were fed a controlled-energy, high-fiber diet (CE) as a total mixed ration for ad libitum intake. During the last 3 wk before calving, half of the cows were switched to a higher-energy, close-up diet until calving (CU), whereas the other half continued to receive the CE diet. Within each dietary group, half of the cows received monensin (MON) supplementation in the diet (24.2 g/t of total dry matter) and half did not (CON). After calving, all cows received the same lactation diet containing monensin (15.4 g/t of dietary dry matter). At 14 d prepartum, dry matter intake was not different across treatments. The weight of rumen contents was greater for cows fed CE. Rumen liquid dilution rate, solids passage rate, pH, total volatile fatty acid (VFA) concentrations, molar proportions of acetate and propionate, and papillae length did not differ among diets. Butyrate percentage tended to be greater for cows fed CE. Postpartum, dry matter intake, mass of rumen contents, solids passage rate, pH, total VFA concentration, molar percentages of propionate and butyrate, and papillae length did not differ among treatments. Liquid dilution rate (16.6, 10.7, 16.0, and 18.2%/h for CE + CON, CE + MON, CU + CON, and CU + MON, respectively) was affected by a diet × monensin interaction. Cows on the CE + CON diet had a greater ruminal proportion of acetate than did cows fed CU + CON, whereas cows fed monensin on either diet were intermediate (diet × monensin interaction). Addition of MON to the CU diet decreased the proportion of propionate (diet × monensin interaction). Cows fed CE had greater mass of rumen contents before parturtition but the high inclusion of wheat straw in the CE diet did not negatively affect rumen papillae length. Monensin inclusion differentially affected liquid passage rate and VFA concentrations.     

An evaluation of an immunomodulatory feed ingredient in heat-stressed lactating Holstein cows: Effects on hormonal,physiological, and production responses

Holstein cows (n = 30) were balanced by days in milk, milk production, and parity (91 ± 5.9 d in milk, 36.2 ± 2.5 kg/d, and 3.1 ± 1.4, respectively) and fed OmniGen-AF (OG; Phibro Animal Health, Teaneck, NJ), an immune stimulant, at 0 g/cow per d for control (CON) or 56 g/cow per d for OG for 52 d on a commercial dairy. At 52 d of the study cows were randomly selected (n = 12) from both groups (6 OG and 6 CON) and housed in environmentally controlled rooms at the Agricultural Research Complex for 21 d at the University of Arizona. Cows were subjected to 7 d of thermoneutral (TN) conditions, 10 d of heat stress (HS), and 4 d of recovery (REC) under TN conditions. Feed intake, milk production, and milk composition were measured daily. Rectal temperatures (RT) and respiration rates (RR) were recorded 3 times per day (600, 1400, and 1800 h). Blood samples were taken on d 7 (TN), 8 (HS), 10 (HS), 17 (HS), and 18 (TN) during the Agricultural Research Complex segment. Cows in HS had higher RR and RT and water intake and lower dry matter intake and milk yield than these measures in TN. There was a treatment × environment interaction with cows fed OG having lower RR and RT and higher dry matter intake during peak thermal loads than CON. However, milk yield did not differ between groups. Cows fed OG had lower milk fat percent than CON (3.7 vs 4.3%) during HS. The SCC content of milk did not differ between treatment groups but rose in both groups during the REC phase following HS. Plasma insulin and plasma glucose levels were not different between groups. However, plasma insulin in both groups was lower during acute HS, then rose across the HS period, and was highest during the REC phase. Plasma cortisol levels were highest in all cows on the first day of HS (d 8) but were lower in cows fed OG compared with CON. However, plasma ACTH concentrations were elevated in OG-fed animals at all times samples were collected. Plasma ACTH was also elevated in cows fed both OG and CON during HS. Feeding OG reduced plasma cortisol during acute but not chronic HS and increased basal plasma ACTH, suggesting that OG treatment may alter the hypothalamic pituitary adrenal axis.     

Saccharomyces cerevisiae fermentation products reduce bacterial endotoxin concentrations and inflammation during grain-based subacute ruminal acidosis in lactating dairy cows

Subacute ruminal acidosis (SARA) is a metabolic disorder in dairy cows that is associated with dysbiosis of rumen and hindgut microbiomes, translocation of immunogenic compounds from the gut lumen into blood circulation, and systemic inflammatory response. In this study we hypothesized that Saccharomyces cerevisiae fermentation products (SCFP) attenuate the increases in ruminal and peripheral bacterial endotoxin concentrations and the inflammation resulting from repeated induction of SARA. Lactating Holstein dairy cows (parity 2 and 3+, n = 32) were fed diets with or without SCFP (all from Diamond V) and subjected to 2 episodes of SARA challenges. Cows received a basal total mixed ration (TMR) containing 34% neutral detergent fiber and 18.6% starch, dry matter (DM) basis. Treatments were randomly assigned to control (basal TMR and 140 g/d of ground corn with no SCFP) or 1 of 3 SCFP treatments: basal TMR and 14 g/d Original XPC (SCFPa), 19 g/d NutriTek (SCFPb-1×), or 38 g/d NutriTek (SCFPb-2×) mixed with 126, 121, or 102 g/d of ground corn, respectively. Treatments were implemented from 4 wk before until 12 wk after parturition. During wk 5 (SARA1) and wk 8 of lactation (SARA2), grain-based SARA challenges were conducted by gradually replacing 20% of DM of the basal TMR over 3 d with pellets containing 50% wheat and 50% barley. Ruminal fluid, fecal, and blood samples were collected weekly during Pre-SARA1 (wk 4, as baseline), Post-SARA1 (wk 7), and Post-SARA2 (wk 10 for blood and wk 12 for rumen and fecal parameters) stages, and twice a week during the challenges SARA1 and SARA2. Rumen papillae samples were taken only during Pre-SARA1 and Post-SARA2. We measured the concentrations of free lipopolysaccharides (LPS) in the rumen fluid and feces; free LPS and lipoteichoic acid (LTA) endotoxins in peripheral plasma; interleukin (IL)-1β and IL-6 in peripheral serum; acute-phase proteins, serum amyloid A (SAA), and LPS-binding protein in peripheral plasma; haptoglobin (Hp) in peripheral serum; and myeloperoxidase (MPO) in rumen papillae. Induction of SARA episodes increased free LPS concentrations in rumen fluid and tended to increase LTA in peripheral plasma. The SARA episodes increased concentration of circulating SAA and tended to increase that of IL-1β compared with Pre-SARA1. Induction of SARA did not affect the concentrations of circulating IL-6, Hp, and MPO. The SCFP supplementation reduced plasma concentrations of LTA and SAA and serum concentration of IL-1β compared with control. Additionally, SCFPb-2× tended to reduce ruminal LPS in second-parity cows compared with control. Overall, SCFP supplementation appeared to stabilize the rumen environment and reduce proinflammatory status, hence attenuating adverse digestive and inflammatory responses associated with SARA episodes.     

Increased super-conditioning temperature of corn grain affects performance,skeletal growth,and blood metabolites in Holstein dairy calves

We aimed to evaluate the effects of feeding super-conditioned corn at different temperatures on intake, growth performance, total-tract starch digestibility, rumen fermentation, blood metabolites, and feeding behavior of dairy calves. Thirty-six Holstein female dairy calves (40 ± 1.72 kg of body weight, ± SD) were randomly assigned to 1 of the following 3 treatments: (1) ground corn (control; CON; n = 12), (2) corn super-conditioned at 75°C (T-75; n = 12), and (3) corn super-conditioned at 95°C (T-95; n = 12). Three mash starter feeds with an identical nutritional composition were blended with 5% chopped alfalfa hay and fed to individually-housed calves from d 3 to 77 of their birth. All calves were fed 4 L/d of pasteurized whole milk twice daily since d 3 to 56, followed by 2 L/d of morning feeding from d 57 to 63 of age. Calves were weaned on d 63 and remained in the study until d 77. The T-75 and T-95 diets increased total-tract starch digestibility compared with the CON diet. Dry matter intake and weaning or final BW were not affected by treatments; however, average daily gain and feed efficiency increased in calves fed T-95 in the overall period. The T-95 diet increased withers height and tended to increase hip height compared with other diets, but feeding behavior did not change throughout the experimental period. Ruminal pH decreased in calves fed the T-95 diet compared with T-75 and CON diets. The molar proportion of ruminal propionate increased, whereas the acetate-to-propionate ratio tended to decrease in calves fed the T-95 compared with CON diet. Calves fed the T-95 diet had the highest blood glucose concentration, whereas a trend for increased insulin concentration was observed in calves fed T-95 compared with other diets. In conclusion, super-conditioning temperature of corn (T-95 vs. T-75 and CON) improved the average daily gain, feed efficiency, and skeletal growth, but did not influence dry matter intake during the first 77 d of age. Finally, the total-tract starch digestibility increased, whereas ruminal pH dropped during the postweaning period as super-conditioning temperature elevated.     

Dietary starch level and rumen-protected methionine,lysine, and histidine: Effects on milk yield,nitrogen, and energy utilization in dairy cows fed diets low in metabolizable protein

Our objective was to investigate the interactions between starch level and rumen-protected Met, Lys, His (RP-MLH) on milk yield, plasma AA concentration, and nutrient utilization in dairy cows fed low metabolizable protein diets (mean = −119 g/d of metabolizable protein balance). Sixteen multiparous Holstein cows (138 ± 46 d in milk, 46 ± 6 kg/d in milk) were used in a replicated 4 × 4 Latin square with a 2 × 2 factorial arrangement of treatments. Each period lasted 21 d with 14 d for diet adaptation and 7 d for data and sample collection. Dietary starch level varied by replacing (dry matter basis) pelleted beet pulp and soyhulls with ground corn resulting in the following treatments: (1) 20% pelleted beet pulp and 10% soyhulls (reduced starch = RS), (2) RS plus RP-MLH (RS+AA), (3) 30% ground corn (high starch = HS), and (4) HS plus RP-MLH (HS+AA). Dietary starch concentrations averaged 12.3 and 34.4% for RS and HS basal diets, respectively. Diets were supplemented with RP-MLH products to supply digestible Met, Lys, and His. Compared with RS and RS+AA diets, HS and HS+AA diets increased yields of milk (37.9 vs. 40.1 kg/d) and milk protein (1.07 vs. 1.16 kg/d) and decreased dry matter intake (25.9 vs. 25.2 kg/d), milk urea N (12.6 vs. 11.0 mg/dL), and plasma urea N (13.3 vs. 11.6 mg/dL). Milk N efficiency was greater in cows fed the HS and HS+AA than RS and RS+AA diets (28.9 vs. 25%), and RP-MLH supplementation improved milk true protein concentration. Starch level × RP-MLH interactions were observed for plasma concentrations of Arg and Lys, with RP-MLH being more effective to increase plasma Arg (+16%) and Lys (+23%) when supplemented to the RS than the HS basal diet. Replacing pelleted beet pulp and soyhulls with ground corn lowered the plasma concentrations of all essential AA except Met and Thr. In addition, the plasma concentrations of His and Met increased with RP-MLH. The apparent total-tract digestibilities of neutral and acid detergent fiber were lower, and those of starch and ether extract greater in cows offered the HS and HS+AA diets than RS and RS+AA diets. Urinary excretion of urea N decreased by replacing pelleted beet pulp and soyhulls with ground corn. Enteric CH₄ production, CH₄ yield, and CH₄ intensity all decreased in the HS and HS+AA versus RS and RS+AA diets. Diets did not affect the intakes of gross energy, metabolizable energy, and net energy of lactation. In contrast, digestible energy intake increased with feeding the RS and RS+AA diets, whereas CH₄ energy decreased in cows fed the HS and HS+AA diets. Supplementation with RP-MLH had no effect on energy utilization variables. Overall, the lack of interactions between dietary starch level and RP-MLH supplementation on most variables measured herein showed that the effects of starch intake and RP-MLH were independent or additive.