Effect of supplementing rumen-protected methionine,lysine, and histidine to low-protein diets on the performance and nitrogen balance of dairy cows

Lowering the dietary protein content can reduce N excretions and NH₃ emissions from manure and increase milk N efficiency of dairy cows. However, milk yield (MY) and composition can be compromised due to AA deficiency. Methionine and Lys are known as first limiting EAA for dairy cows, and recently His is also mentioned as limiting, especially in grass-based or low-protein diets. To examine this, a trial was conducted with a 3-wk pre-experimental adaptation period (diet 16.5% crude protein), followed by a depletion period of 4 wk, in which 39 cows (average ± standard deviation: 116 ± 29.3 d in milk, 1.8 ± 1.2 lactations, 638 ± 73.2 kg of body weight, and 32.7 ± 5.75 kg MY/d) received a low-protein diet (CTRL) (14.5% crude protein). Then, taking into account parity, His plasma concentration, and MY, cows were randomly assigned to 1 of 3 treatment groups during the rumen-protected (RP) AA period of 7 wk; (1) CTRL; (2) CTRL + RP-Met + RP-Lys (MetLys); (3) CTRL + RP-Met + RP-Lys + RP-His (MetLysHis). Products were dosed, assuming requirements for digestible (d) Met, dLys, and dHis being, respectively, 2.4%, 7.0%, and 2.4% of intestinal digestible protein. In the cross-back period of 5 wk, all cows received the CTRL diet. During the last week of each period, a N balance was conducted by collecting total urine and spot samples of feces. Total feces production was calculated using the inert marker TiO₂. Statistical analysis was performed with a linear mixed model with cow as random effect and data of the last week of the pre-experimental period used as covariate for the animal performance variables. No effect of supplementing RP-Met and RP-Lys nor RP-Met, RP-Lys, and RP-His on feed intake, milk performance, or milk N efficiency was observed. However, the plasma AA profile indicated additional supply of dMet, dLys, and dHis. Nevertheless, evaluation of the AA uptake relative to the cow's requirements showed that most EAA (exclusive Arg and Thr) were limiting over the whole experiment. Only dHis was sufficiently supplemented during the RP-AA period due to an overestimation of the diet's dMet and dLys supply in the beginning of the trial. The numerically increased milk urea N and urinary N excretion when RP-Met, RP-Lys, and RP-His were added to the low-protein diet suggest an increased catabolism of the excess His.     

Histidine dose-response effects on lactational performance and plasma amino acid concentrations in lactating dairy cows: 2. Metabolizable protein-deficient diet

The objective of this experiment was to determine the effect of increasing digestible His (dHis) levels with a rumen-protected (RP) His product on milk production, milk composition, and plasma AA concentrations in lactating dairy cows fed a metabolizable protein (MP)-deficient diet, according to the National Research Council dairy model from 2001. The companion paper presents results on the effect of increasing dHis dose with a MP-adequate basal diet. Twenty Holstein cows, of which 8 were rumen-cannulated, were used in a replicated 4 × 4 Latin square design experiment with four 28-d periods. Treatments were a control diet supplying 1.8% dHis of MP or 37 g/d (dHis1.8) and the control diet supplemented RP-His to provide 2.2, 2.6, or 3.0%, dHis of MP, or 53, 63, and 74 g/d (dHis2.2, dHis2.6, and dHis3.0, respectively). Histidine dose did not affect dry matter intake, but milk yield increased quadratically and energy-corrected milk yield increased linearly with increasing dHis dose. Histidine dose had a quadratic effect on milk fat concentration but did not affect milk fat yield. Lactose concentration decreased linearly, whereas lactose yield increased linearly with increasing dHis dose. There was a tendency for a linear increase in milk true protein concentration, and milk true protein yield increased linearly with dHis dose. Further, plasma His concentration increased linearly with increasing dHis dose and calculated apparent efficiency of His utilization decreased quadratically with increasing dHis supply. Histidine had minor or no effects on rumen fermentation. In the conditions of this experiment, RP-His supplementation of an MP-deficient corn silage-based diet increased milk yield linearly up to a dHis supply of 63 g/d (or 2.6% dHis of MP) and increased feed efficiency, energy-corrected milk yield and milk true protein yield linearly up to a dHis supply of 74 g/d (or 3.0% dHis of MP) in lactating dairy cows.     

Lactational performance and plasma and muscle amino acid concentrations in dairy cows fed diets supplying 2 levels of digestible histidine and metabolizable protein

The objective of this experiment was to investigate the effect of dietary levels of digestible histidine (dHis) and MP on lactational performance and plasma and muscle concentrations of free AA in dairy cows. A randomized block design experiment was conducted with 48 Holstein cows, including 20 primiparous, averaging (±SD) 103 ± 22 d in milk and 45 ± 9 kg/d milk yield at the beginning of the experiment. A 2-wk covariate period preceded 12 experimental wk, of which 10 wk were for data and sample collection. Experimental treatments were (1) MP-adequate (MPA) diet with 2.1% dHis of MP (MPA2.1), (2) MPA with 3.0% dHis (MPA3.0), (3) MP-deficient (MPD) diet with 2.1% dHis (MPD2.1), and (4) MPD with 3.0% dHis (MPD3.0). Actual dHis supply was estimated at 64, 97, 57, and 88 g/d, respectively. Diets supplied MP at 110% (MPA) and 96% (MPD) of NRC 2001 dairy model requirements calculated based on DMI and production data during the experiment. Dry matter intake and milk yield data were collected daily, milk samples for composition and blood samples for AA analysis were collected every other week, and muscle biopsies at the end of covariate period, and during wk 12 of the experiment. The overall DMI was not affected by dHis or MP level. Milk yield tended to be increased by 3.0% dHis compared with 2.1% dHis. Milk true protein concentration and yield were not affected by treatments, whereas milk urea nitrogen concentration was lower for MPD versus the MPA diet. Milk fat concentration was lower for MPD versus MPA. There was a MP × dHis interaction for milk fat yield and energy-corrected milk; milk fat was lower for MPD3.0 versus MPD2.1, but similar for cows fed the MPA diet regardless of dHis level whereas energy-corrected milk was greater for MPA3.0 versus MPA2.1 but tended to be lower for MPD3.0 versus MPD2.1. Plasma His concentration was greater for cows fed dHis3.0, and concentration of sum of essential AA was greater, whereas carnosine, 1-Methyl-His and 3-Methyl-His concentrations were lower for cows fed MPA versus MPD diet. Muscle concentration of His was greater for cows fed dHis3.0 treatment. The apparent efficiency of His utilization was increased at lower MP and His levels. Overall, cows fed a corn silage-based diet supplying MP at 110% of NRC (2001) requirements tended to have increased ECM yield and similar milk protein yield to cows fed a diet supplying MP at 96% of requirements. Supplying dHis at 3.0% of MP (or 86 and 96 g/d, for MPD3.0 and MPA3.0, respectively) tended to increase milk yield and increased plasma and muscle concentrations of His but had minor or no effects on other production variables in dairy cows.     

Effects of feeding rumen-protected methionine pre- and postpartum in multiparous Holstein cows: Lactation performance and plasma amino acid concentrations

Objectives were to evaluate the effect of feeding rumen-protected methionine (RPM) in pre- and postpartum total mix ration (TMR) on lactation performance and plasma AA concentrations in dairy cows. A total of 470 multiparous Holstein cows [235 cows at University of Wisconsin (UW) and 235 cows at Cornell University (CU)] were enrolled approximately 4 wk before parturition, housed in close-up dry cow and replicated lactation pens. Pens were randomly assigned to treatment diets (pre- and postpartum, respectively): UW control (CON) diet = 2.30 and 2.09% of Met as percentage of metabolizable protein (MP) and RPM diet = 2.83 and 2.58% of Met as MP; CU CON = 2.22 and 2.19% of Met as percentage of MP, and CU RPM = 2.85 and 2.65% of Met as percentage of MP. Treatments were evaluated until 112 ± 3 d in milk (DIM). Milk yield was recorded daily. Milk samples were collected at wk 1 and 2 of lactation, and then every other week, and analyzed for milk composition. For lactation pens, dry matter intake (DMI) was recorded daily. Body weight and body condition score were determined from 4 ± 3 DIM and parturition until 39 ± 3 and 49 DIM, respectively. Plasma AA concentrations were evaluated within 3 h after feeding during the periparturient period [d ?7 (±4), 0, 7 (±1), 14 (±1), and 21 (±1); n = 225]. In addition, plasma AA concentrations were evaluated (every 3 h for 24 h) after feeding in cows at 76 ± 8 DIM (n = 16) and within 3 h after feeding in cows at 80 ± 3 DIM (n = 72). The RPM treatment had no effect on DMI (27.9 vs. 28.0 kg/d) or milk yield (48.7 vs. 49.2 kg/d) for RPM and CON, respectively. Cows fed the RPM treatment had increased milk protein concentration (3.07 vs. 2.95%) and yield (1.48 vs. 1.43 kg/d), and milk fat concentration (3.87 vs. 3.77%), although milk fat yield did not differ. Plasma Met concentrations tended to be greater for cows fed RPM at 7 d before parturition (25.9 vs. 22.9 µM), did not differ at parturition (22.0 vs. 20.4 µM), and were increased on d 7 (31.0 vs. 21.2 µM) and remained greater with consistent concentrations until d 21 postpartum (d 14: 30.5 vs. 19.0 µM; d 21: 31.0 vs. 17.8 µM). However, feeding RPM decreased Leu, Val, Asn, and Ser (d 7, 14, and 21) and Tyr (d 14). At a later stage in lactation, plasma Met was increased for RPM cows (34.4 vs. 16.7 µM) consistently throughout the day, with no changes in other AA. Substantial variation was detected for plasma Met concentration (range: RPM = 8.9–63.3 µM; CON = 7.8–28.8 µM) among cows [coefficient of variation (CV) > 28%] and within cow during the day (CV: 10.5–27.1%). In conclusion, feeding RPM increased plasma Met concentration and improved lactation performance via increased milk protein production.     

Effects of polymerization of casein and sources of lysine on amino acid bioavailability among calves fed liquid-based diets

Two experiments were conducted to evaluate the bioavailability of AA between polymerized and less polymerized or unpolymerized sources of AA. In the first experiment, 6 bull calves (53.8 ± 0.6 kg of body weight) were bottle-fed milk replacer that contained 0, 60, or 120 additional grams of AA from casein or acid hydrolyzed casein every 12 h. Plasma essential AA increased linearly with increasing intake of casein from either source. Branched-chain amino acids accounted for 74% of increases in essential AA, regardless of source of AA. Concentrations of nonessential AA increased linearly with increased intake of AA from acid hydrolyzed casein but only tended to increase in response to casein. Also, the rate of increase in total plasma AA concentration in response to acid hydrolyzed casein (4.3 µM increase per g of supplemental AA) tended to be 145% greater than casein (3.0 µM per g of supplemental AA). In a separate experiment, 6 additional bull calves (52.1 ± 0.9 kg of body weight) were bottle-fed milk replacer that contained 0, 4.8, or 9.6 additional grams of Lys from ε-polylysine or Lys-HCl each 12 h to measure Lys bioavailability between a polymerized and unpolymerized source of Lys. Plasma Lys concentrations increased linearly in response to greater Lys intake from Lys-HCl (slope = 13.51 µM/g Lys,), but plasma Lys concentrations did not change in response to increased intake of Lys from ε-polylysine. Plasma concentrations of Thr, Met, Glu, and Gln decreased linearly with increasing ε-polylysine intake, whereas concentrations of His, Val, Leu, and Ile increased linearly with increasing ε-polylysine intake. Data from these experiments suggest that the form of AA provided to calves should be considered when formulating diets to meet AA requirements.     

Histidine dose-response effects on lactational performance and plasma amino acid concentrations in lactating dairy cows: 1. Metabolizable protein-adequate diet

The objective of this experiment was to determine the effect of increasing digestible His (dHis) doses on milk production, milk composition, and plasma AA concentrations in lactating dairy cows fed diets that meet or exceed their energy and metabolizable protein (MP) requirements. In a companion paper (Räisänen et al., 2021) results are presented on the effect of increasing dHis dose with an MP-deficient basal diet. In this experiment, 16 Holstein cows (72 ± 15 d in milk) were used in a replicated 4 × 4 Latin square design experiment with four 28-d periods. Treatments were as follows: (1) control, total mixed ration (TMR) with 1.8% dHis of MP (TMR1; dHis1.8); (2) a different TMR with 2.2% dHis (TMR2; dHis2.2); (3) TMR2 supplemented with rumen-protected His (RP-His) to supply 2.6% dHis (dHis2.6); and (4) TMR2 supplemented with RP-His to supply 3.0% dHis of MP (dHis3.0). Estimated dHis intakes calculated at the end of the experiment were 46, 58, 69, and 79 g/d for dHis1.8, dHis2.2, dHis2.6, and dHis3.0, respectively. Contrasts were used to compare TMR1 with TMR2 and to test the linear and quadratic effects of RP-His inclusion rate on TMR2. We detected no effects of TMR or dHis dose on dry matter intake or milk yield, whereas energy-corrected milk (ECM) yield was quadratically increased, being greatest for cows on treatment dHis2.6. Milk true protein and lactose concentrations and milk true protein yield were not affected by TMR or dHis dose. Milk fat concentration and yield increased quadratically, and lactose yield tended to increase quadratically with increasing dHis dose. Calculated apparent efficiency of His utilization decreased quadratically with increasing dHis supply. Further, plasma concentration of His was greater for cows on TMR2 compared with TMR1. When an MP-adequate diet was fed to dairy cows, milk true protein concentration and yield were not affected by dHis supply, but milk fat and ECM yields of dairy cows were optimized at dHis supply of 69 g/d or 2.65% of MP.     

Histidine deficiency has a negative effect on lactational performance of dairy cows

A 10-wk randomized complete block design experiment with 24 Holstein cows was conducted to investigate the long-term effects of feeding a His-deficient diet on lactational performance of dairy cows. Cows were blocked by days in milk, milk yield, and parity, and randomly assigned to 1 of the following 2 treatments: (1) His-adequate diet [HAD; providing +166 g/d over metabolizable protein (MP) requirements, according to the National Research Council (2001) and digestible His (dHis) supply of 68 g/d, or 2.5% of MP requirements] and (2) His-deficient diet (HDD; +37 g/d over MP requirements and dHis supply of 49 g/d, or 1.9% of MP requirements). Both HAD and HDD were supplemented with rumen-protected (RP) Met and Lys supplying digestible Met and digestible Lys at 2.4 and 2.4% and 7.2 and 7.1% of MP requirements, respectively. At the end of the 10-wk experiment, HDD was supplemented with RPHis (HDD+RPHis; total dHis supply of 61 g/d, or 2.4% of MP requirements) for an additional 9 d. Dry matter intake (DMI; 25.4 and 27.1 kg/d, standard error of the mean = 0.41), yields of milk (37.6 and 40.5 kg/d, standard error of the mean = 0.62), protein and lactose, energy-corrected milk, and milk and plasma urea-N were decreased by HDD compared with HAD. Feed and energy-corrected milk feed efficiencies, milk fat, protein and lactose concentrations, body weight, and body condition score of the cows were not affected by treatment. Apparent total-tract digestibility of dry and organic matter, crude protein, and neutral detergent fiber, and excretion of urinary N and urea-N were decreased by HDD compared with HAD. Concentration of plasma leptin tended to be decreased for HDD compared with HAD. Plasma concentrations of EAA (His, Leu, Lys, Val) and carnosine decreased and total EAA tended to be decreased in cows fed HDD compared with HAD. Muscle concentrations of free His, Leu, and Val decreased and Gly and β-alanine tended to be increased by HDD compared with HAD. Cows fed HDD had a lower blood hemoglobin concentration than cows fed HAD. At the end of the 10-wk study, the 9-d supplementation of HDD with RPHis (i.e., HDD+RPHis) increased DMI and plasma His, and tended to increase energy-corrected milk yield and plasma carnosine, compared with HDD. In conclusion, feeding a diet deficient in dHis supplying adequate MP, digestible Met, and digestible Lys affected negatively lactational performance of dairy cows. These results confirm our previous findings that low dietary His supply can impair DMI, yields of milk and milk protein, and blood hemoglobin in dairy cows.     

Effects of increased doses of lysine in a rumen-protected form on plasma amino acid concentration and lactational performance of dairy cows fed a lysine-deficient diet

The objective of these studies was to determine the effects of feeding a novel rumen-protected Lys (RP-Lys) product on plasma AA, lactational performance, and Lys bioavailability. To evaluate RP-Lys on lactation performance a corn-based diet (42.5% of corn silage and 21.9% of corn and corn by-products, on DM basis) was formulated to be Lys deficient but adequate in Met, energy, and metabolizable protein. Thirty-six lactating Holstein cows were fed either a Lys-deficient control diet (CON) with no added RP-Lys, or diets containing 0.3% of RP-Lys (0.3RP-Lys) or 0.6% of RP-Lys (0.6RP-Lys) for 8 wk. There were no effects on dry matter intake (mean ± SD; 26.1 ± 0.58 kg/d), milk yield (37.9 ± 0.72 kg/d), or milk composition to the RP-Lys supplementation. No effect was observed on plasma AA concentrations except for His. Plasma His was linearly reduced by Lys feeding (42.6, 41.2, 30.0 ± 4.09 μM, for CON, 0.3RP-Lys, and 0.6RP-Lys, respectively). Calculated efficiency of Lys utilization decreased linearly with RP-Lys supplementation. In the companion study, 3 rumen-cannulated lactating dairy cows were used in a 3 × 3 Latin square design to assess the bioavailability of the RP-Lys. Free Lys (HCl-Lys), RP-Lys, and water were administered separately by postruminal bolus dosing. The Lys bioavailability was assessed by the ratio of area under the curve of Lys plasma concentration for RP-Lys compared with HCl-Lys and discounted for the area under the curve for water bolus dose. The estimated bioavailability of the RP-Lys was 24.4% ± 4.61. In summary, increased supplemental doses of Lys had no effect on Lys plasma concentration and lactational performance when fed to dairy cows on a corn-based diet, although altered Lys as % of essential AA was observed. However, the lack of effects should be considered in light of the lower-than-expected bioavailability of the RP-Lys.     

Responses to graded postruminal doses of histidine in dairy cows fed grass silage diets

Five Finnish Ayrshire cows were used in a 4 x 4 Latin square experiment designed to study the effects of graded doses of postruminal His infusion on milk production, arterial concentrations, and mammary uptakes of plasma amino acids (AA) as well as utilization of added His. Grass silage (16.9% CP) was given ad libitum with 8 kg of cereal-based concentrate per day (11.3% CP). Treatments were abomasal or duodenal infusions of 250 g of glucose/d in combination with 0, 2, 4, or 6 g of His/d. Infusions did not affect dry matter intake (mean 18 kg/d). Infusion of His increased milk yield linearly from 27.0 to 28.8 kg/d, protein yield from 861 to 919 g/d and lactose yield from 1345 to 1457 g/d. Milk fat yield and content changed in a cubic manner (1240, 1167, 1296, and 1177 g/d and 4.60, 4.16, 4.60, and 4.09). Infusion of His had no influence on milk protein or lactose concentrations. Arterial Lys and His concentrations increased linearly, but other AA concentrations were unaffected as well as calculated arteriovenous differences and mammary AA uptakes. The extraction of His decreased linearly with an increasing amount of His. The utilization of added His (28%) was not affected by the level of infusion, and mammary AA uptake seemed to be regulated by an inverse relationship between arteriovenous difference of essential AA and calculated mammary plasma flow. This experiment confirmed that His is the first-limiting AA on grass silage-cereal based diets.     

Nitrogen utilization,whole-body urea-nitrogen kinetics,omasal nutrient flow,and production performance in dairy cows fed lactose as a partial replacement for barley starch

The objective of this study was to determine whether the partial replacement of barley starch with lactose (fed as dried whey permeate; DWP) affects N utilization, whole-body urea kinetics, and production in dairy cows. Eight lactating Holstein cows were used in a replicated 4 × 4 Latin square design with 28-d periods. Four cows in one Latin square were ruminally cannulated and used to determine dietary effects on whole-body urea kinetics and N utilization. Cows were fed a barley-based diet that contained 3.6% (dry matter basis) total sugar (TSG; designated control), or diets that contained 6.6, 9.6, or 12.6% TSG. Dietary TSG content was increased by the replacement of barley grain with DWP (83% lactose). Diets were isonitrogenous (～17.3% crude protein), and starch contents of the control, 6.6, 9.6, and 12.6% TSG diets were 24.3, 22.2, 21.2, and 19.1%, respectively. Whole-body urea kinetics were measured using 4-d infusions of [¹⁵N¹⁵N]-urea with concurrent total collections of feces and urine. Dry matter intake (mean = 26.7 kg/d), milk yield (mean = 34.9 kg/d), and milk protein and fat contents were unaffected by diet. Ruminal ammonia-N concentration decreased linearly as TSG content increased, whereas ruminal butyrate concentration increased linearly as TSG content increased. Urinary excretion of total N and urea-N changed quadratically, whereas urinary excretion of total N (% of N intake) tended to change quadratically as TSG content increased. Fecal N excretion linearly increased as TSG content increased. A quadratic response was observed for total N excretion as TSG content increased. Milk N and retained N were not affected by diet. As TSG content increased, we observed quadratic responses in the omasal flow of fluid-associated and total bacterial nonammonia N, endogenous production of urea-N, urea-N recycled to the gastrointestinal tract, and urea-N returned to the ornithine cycle. Dietary TSG content did not affect the anabolic utilization of recycled urea-N or the proportion of recycled urea-N that was used for bacterial growth. Our results indicate that feeding DWP did not influence dry matter intake, milk yield, or milk composition. Feeding DWP decreased ruminal ammonia-N concentration, but this did not result in positive responses in milk protein secretion or N balance. The quadratic response in omasal flow of total bacterial nonammonia N indicated that including TSG beyond 9.6% of diet dry matter might depress ruminal microbial protein synthesis.     

Effects of feeding wheat or corn-wheat dried distillers grains with solubles in low- or high-crude protein diets on ruminal function,omasal nutrient flows,urea-N recycling,and performance in cows

A study was conducted to determine the effects of including either wheat-based (W-DDGS) or corn-wheat blend (B-DDGS) dried distillers grains with solubles as the major protein source in low- or high-crude protein (CP) diets fed to dairy cows on ruminal function, microbial protein synthesis, omasal nutrient flows, urea-N recycling, and milk production. Eight lactating Holstein cows (768.5 ± 57.7 kg of body weight; 109.5 ± 40.0 d in milk) were used in a replicated 4 × 4 Latin square design with 28-d periods (18 d of dietary adaptation and 10 d of measurements) and a 2 × 2 factorial arrangement of dietary treatments. Four cows in one Latin square were ruminally cannulated for the measurement of ruminal fermentation characteristics, microbial protein synthesis, urea-N recycling kinetics, and omasal nutrient flow. The treatment factors were type of distillers co-product (W-DDGS vs. B-DDGS) and dietary CP content [15.2 vs. 17.3%; dry matter (DM) basis]. The B-DDGS was produced from a mixture of 15% wheat and 85% corn grain. All diets were formulated to contain 10% W-DDGS or B-DDGS on a DM basis. No diet effect was observed on DM intake. Yields of milk, fat, protein, and lactose, and plasma urea-N and milk urea-N concentrations were lower in cows fed the low-CP compared with those fed the high-CP diet. Although feeding B-DDGS tended to reduce ruminal ammonia-N (NH₃-N) concentration compared with feeding W-DDGS (9.3 vs. 10.5 mg/dL), no differences were observed in plasma urea-N and milk urea-N concentrations. Additionally, dietary inclusion of B-DDGS compared with W-DDGS did not affect rumen-degradable protein supply, omasal flows of total N, microbial nonammonia N (NAN), rumen-undegradable protein, and total NAN, or urea-N recycling kinetics and milk production. However, cows fed the low-CP diet had lower N intake, rumen-degradable protein supply, ruminal NH₃-N concentration, and omasal flows of N, microbial NAN, and total NAN compared with those fed the high-CP diet. Feeding the low-CP compared with the high-CP diet also resulted in lower endogenous urea-N production, urea-N recycled to the gastrointestinal tract, and urea-N excretion in urine. In summary, our results indicate that both W-DDGS and B-DDGS can be included as the major protein sources in dairy cow diets without compromising nutrient supply and production performance. However, feeding the low-CP diet lowered omasal flows of microbial protein and metabolizable protein, which, in turn, resulted in lower milk production compared with feeding the high-CP diet.     

Alfalfa pellet-induced subacute ruminal acidosis in dairy cows increases bacterial endotoxin in the rumen without causing inflammation

A study was conducted to determine if subacute ruminal acidosis (SARA) induced by feeding alfalfa pellets results in increases in free bacterial lipopolysaccharide (LPS) in rumen fluid and peripheral blood, and acute phase proteins in plasma, and to determine the effect of alfalfa pellet-induced SARA on feed intake, rumen fermentation characteristics, milk production and composition, and blood metabolites. Eight lactating Holstein cows, 4 of which were ruminally cannulated, were used in a 6-wk experiment and were fed once daily at 0900 h. During wk 1, cows received a diet containing 50% of DM as concentrate and 50% of DM chopped alfalfa hay. Between wk 2 and wk 6, alfalfa hay was gradually replaced with alfalfa pellets at the rate of 8% per week to reduce rumen pH. Rumen pH was monitored continuously in the ruminally cannulated cows using indwelling pH probes. Rumen fluid and peripheral blood were sampled 15 min before feed delivery and at 6 h after feed delivery. Based on adopted threshold of SARA of at least 180 min/d below pH 5.6, SARA was induced from wk 3 onwards. Replacing 40% of alfalfa hay with alfalfa pellets quadratically increased the DMI from 18.1 kg/d in wk 1 to 23.4 kg/d in wk 6. This replacement linearly decreased milk yield (32.7 vs. 35.9 kg/d) and milk fat percentage and yield (2.32 vs. 3.22%, and 0.77 vs. 1.14 kg/d, respectively), but increased milk protein percentage and yield (3.80 vs. 3.04%, and 1.23 vs. 1.07 kg/d, respectively). This gradual replacement also linearly increased the daily averages of total volatile fatty acids (90 to 121.9 mM), acetate (53.9 to 66.8 mM), propionate (21.5 to 39.6 mM), and osmolality (277.7 to 293.8 mmol/kg) in the rumen and decreased the acetate to propionate ratio from 2.62 to 1.73. Replacing alfalfa hay with alfalfa pellets linearly increased blood lactate from 1.00 mM in wk 1 to a peak of 3.46 mM in wk 5. Induction of SARA in this study increased free rumen LPS concentration from 42,122 endotoxin unit (EU)/mL in wk 1 to 145,593 EU/mL in wk 6. However, this increase was not accompanied by an increase in LPS (<0.05 EU/mL) and in acute phase proteins serum amyloid-A, haptoglobin, and LPS-binding protein in peripheral circulation. Results suggest that SARA induced by alfalfa pellets increased LPS in the rumen without causing translocation of LPS and an immune response.     

Production performance and nitrogen metabolism in dairy cows fed supplemental blends of rumen undegradable protein and rumen-protected amino acids in low- compared with high-protein diets containing corn distillers grains

Feeding corn dried distillers grains with solubles (DDGS) in low crude protein (CP) diets could limit N waste in lactating cows. However, it also could possibly reduce metabolizable AA supply, especially Lys, and compromise milk production. Therefore, the objective of this study was to evaluate the effects of feeding supplemental blends of rumen undegradable protein (RUP) and rumen-protected (RP) AA in a low compared with high CP diet containing corn DDGS on milk production and selected measures of N utilization. Six multiparous Holstein cows (619.3 ± 49.8 kg of body weight; 26.8 ± 6.2 d in milk) were subjected to a split-plot, 3 × 3 Latin square design (21-d periods) with dietary CP content [low (14.6%; LP) or high (16.6%; HP)] as the whole-plot factor, and blend of RUP and RP-AA [control (CON), no supplement; blend A (0.11 kg/cow per d); or blend B (0.45 kg/cow per d)] as the sub-plot factor. All diets contained 10% corn DDGS; blends of RUP and RP-AA were top-dressed during morning feeding. There was no dietary CP content × supplemental blend interaction for all measured variables. Nutrient (dry matter, organic matter, neutral detergent fiber, acid detergent fiber, and CP), milk and milk component yields, and feed and apparent N efficiency did not differ for cows fed the low- compared with the high-protein diet. However, apparent total-tract CP digestibility, blood and milk urea-N concentrations, and urinary excretion (g/d) of N and urea-N were lower for cows fed the low-protein compared with the high-protein diet. There was no supplemental blend effect on nutrient intake and apparent total-tract digestibility, and milk and milk component yields. Except for a tendency for total urinary purine derivative excretion and microbial N flow to be lower for cows fed blend B compared with CON but not blend A, there was no supplemental blend effect on measures of N utilization. Both dietary CP content and supplemental blend of RUP and RP-AA had a marginal effect on the plasma free AA profile. In summary, reducing dietary CP content in diets containing corn DDGS had no effect on lactation performance, possibly accounting for the lack of a positive response following the provision of supplemental blends of RUP and RP-AA. However, reducing dietary CP content resulted in a decrease in blood and milk urea-N concentrations, and urinary excretion of N and urea-N, suggestive of an improvement in the efficiency of N use.     

Prediction of ammonia emission from dairy cattle manure based on milk urea nitrogen: relation of milk urea nitrogen to urine urea nitrogen excretion

The objectives of this study were to assess the relationship between urinary urea N (UUN) excretion (g/d) and milk urea N (MUN; mg/dL) and to test whether the relationship was affected by stage of lactation and the dietary crude protein (CP) content. Twelve lactating multiparous Holstein cows were randomly selected and blocked into 3 groups of 4 cows intended to represent early [123 ± 26 d in milk (DIM); mean ± standard deviation], mid (175 ± 3 DIM), and late (221 ± 12 DIM) lactation stages. Cows within each stage of lactation were randomly assigned to a treatment sequence within a split-plot Latin square balanced for carryover effects. Stage of lactation formed the main plots (squares) and dietary CP levels (15, 17, 19, and 21% of diet dry matter) formed the subplots. Graded amounts of urea were added to the basal total mixed ration to linearly increase dietary CP content while maintaining similar concentrations of all other nutrients among treatments. The experimental periods lasted 7 d, with d 1 to 6 used for adjustment to diets and d 7 used for total collection of urine as well as milk and blood sample collection. Dry matter intake and yields of milk, fat, protein, and lactose declined progressively with lactation stage and were unaffected by dietary CP content. Milk and plasma urea-N as well as UUN concentration and excretion increased in response to dietary CP content. Milk and urine urea-N concentration rose at increasing and decreasing rates, respectively, as a function of plasma urea-N. The renal urea-N clearance rate differed among lactation stages and dietary CP contents. The relationship between UUN excretion and MUN differed among lactation stages and diverged from linearity for cows in early and late lactation. However, these differences were restricted to very high MUN concentrations. Milk urea N may be a useful tool to predict the UUN excretion and ultimately NH₃ emission from dairy cattle manure.     

Effect of feeding hydrolyzed feather meal and rumen-protected lysine on milk protein and energy utilization in late-lactation Jersey cows

Hydrolyzed feather meal (HFM) is a feed that is high in rumen undegradable protein; however, it is low in Lys compared with other high rumen undegradable protein sources. Additionally, processing methods differ by facility, which affects AA composition and protein digestibility. The objective of this study was to use lactating dairy cows to determine the effects of feeding 2 sources of HFM that differed by the amount of blood they contained and also to study the effects of supplementing rumen-protected (RP) Lys when these sources of HFM are fed. In this study, 12 multiparous Jersey cows were enrolled in a triplicated 4 × 4 Latin square with 4 periods 28 d in length. Cows were fed 2 total mixed rations that differed by source of HFM. The HFM was included at 4.5% of the diet dry matter, and one source was produced with the addition of poultry blood. Cows were randomly assigned to 1 of 4 treatment sequences. Treatments were as follows: HFM without added blood and no RP-Lys, HFM with added blood and no RP-Lys, HFM without blood and with RP-Lys (22 g of digestible Lys), and HFM with added blood and RP-Lys. The source of HFM containing blood tended to increase dry matter intake (18.3 vs. 17.3 ± 0.72 kg/d), and increased milk yield (20.5 vs. 18.4 ± 1.31 kg/d) and protein yield (0.788 vs. 0.694 ± 0.040 kg/d). The inclusion of RP-Lys did not affect milk or protein yield. In cows fed HFM containing blood, plasma concentration of Lys (82.1 vs. 70.8 ± 4.06 μM) and His (27.8 vs. 17.9 ± 3.15 μM) was higher. The addition of RP-Lys had no effect on the concentration of either plasma Lys or His. Gross energy intake tended to increase for HFM containing more blood (81.4 vs. 77.3 ± 3.29 Mcal/d); however, no difference was observed for intake of digestible energy (52.0 ± 2.20 Mcal/d) or metabolizable energy (46.4 ± 2.02 Mcal/d). Similar to dry matter intake, N intake increased with the inclusion of HFM containing blood, but crude protein digestibility decreased (61.6 vs. 66.0%). Results of this study highlight that source of HFM can be a factor that affects milk production and that this in part is due to differences in the profile of AA. Additionally, the observation that plasma His and milk protein increased with the consumption of HFM containing more blood suggests that His may have played a role in increasing milk and milk protein yield.     

Effect of tea saponins on milk performance,milk fatty acids,and immune function in dairy cow

This study investigated the effects of tea saponins (TSP) on milk performance, milk fatty acids, and blood immune function in dairy cows. A total of 20 early-lactation Holstein cows (days in milk = 66.4 ± 16.8 d; parity = 1.75 ± 0.91; and milk yield = 36.3 ± 7.32 kg/d; mean ± standard deviation) were randomly divided into 4 homogeneous treatment groups, with TSP added at 0, 20, 30, and 40 g/d per head, respectively. All cows had 2 wk of adaptation and 6 wk of treatments. Feed, milk, and blood were sampled and analyzed weekly. At the end of the experimental period (wk 6), the dry matter intake and yields of energy-corrected milk, milk, and milk protein, fat, and lactose in the cows fed TSP showed a quadratic response, with the lowest values in cows fed TSP at 40 g/d. The milk fat content of cows fed TSP increased linearly. Significant interactions for treatment by week were found in milk C16:1 cis-9 and C18:1 cis-9, with the highest values at wk 2, 3, and 4 in the cows fed TSP at 40 g/d. The levels declined quickly after 4 wk of feeding to values similar to those for other TSP treatments and the control at wk 5 and 6. Plasma malondialdehyde concentration decreased as the supplement level of TSP increased. The concentration of superoxide dismutase increased as the supplement level of TSP increased. The plasma concentration of tumor necrosis factor-α increased as the supplement level of TSP increased. In summary, this study showed that an intermediate dose of TSP (20 and 30 g/d) had no significant effect on feed intake, but the supplementation of 40 g/d TSP decreased feed intake, resulting in a lower milk yield. The energy-corrected milk of cows fed 40 g/d TSP declined at first but increased after 3 wk of feeding, indicating the potential adaptation to high doses of TSP supplements in dairy cows. The supplementation of TSP could reduce oxidative stress in cows and improve the immunity of dairy cows during 6 wk of feeding.     

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.     

Lactation performance and amino acid utilization of cows fed increasing amounts of reduced-fat dried distillers grains with solubles

The use of a solvent-extraction process that removes corn oil from distillers grains produces a reduced-fat co-product (RFDG). To determine the optimal concentration of RFDG in mid-lactation diets, 22 multiparous and 19 primiparous Holstein cows were used in a completely randomized design for 8 wk, including a 2-wk covariate period. The RFDG was included at 0, 10, 20, and 30% of the diet on a dry matter basis, replacing soybean feedstuffs. Increasing RFDG in diets had no effect on dry matter intake (23.1 kg/d) or milk production (35.0 kg/d). Milk fat percentage increased linearly from 3.18 to 3.72% as RFDG increased from 0 to 30% of the diet. Similarly, milk fat yield tended to increase linearly from 1.08 to 1.32 kg/d. Milk protein percentage (2.99, 3.06, 3.13, and 2.99% for diets with RFDG from 0 to 30%) responded quadratically, whereas protein yield was not affected by treatment. Milk urea N decreased linearly from 15.8 to 13.1 mg/dL. The efficiency of N utilization for milk production was not affected by including RFDG (26.1%), whereas the efficiency of milk production (energy-corrected milk divided by dry matter intake) tended to increase linearly with increasing RFDG in the diet. Similarly, concentrations of plasma glucose increased linearly. Arterial Lys decreased linearly from 66.0 to 44.8 μM/L, whereas arterial Met increased linearly from 16.5 to 29.3 μM/L. Arteriovenous difference of Lys decreased linearly from 42.6 to 32.5 μM/L, whereas that of Met was unaffected. The extraction of Lys by the mammary gland increased linearly from 64.3 to 72.2%, whereas that of Met decreased linearly from 71.6 to 42.7%. Feeding up to 30% of RFDG in a mid-lactation diet supported lactation performance similarly to cows fed the soybean protein-based diet (0% RFDG).     

Use of dietary feather meal to induce histidine deficiency or imbalance in dairy cows and effects on milk composition

Removing His from a postruminal AA infusion decreases milk protein and increases milk fat content. Feather meal is an inexpensive protein source, high in rumen undegradable protein but low in His. The objective of our study was to investigate dietary feather meal as a method for creating a His deficiency or imbalance to alter milk composition. Four dietary treatments were fed for 4 wk each to 8 multiparous mid-lactation Holstein cows in a replicated 4 × 4 Latin square design. A standard-protein control diet (SP-C) was formulated to provide 3,100 g/d of metabolizable protein (MP). Feather meal was added to the control diet either to replace the MP isonitrogenously (SP-FM) or to increase the MP supply to 3,484 g/d (HP-FM). As an isonitrogenous control for HP-FM, a high-protein diet (HP-C) was formulated with His-adequate protein sources to provide the same MP content as HP-FM. Dry matter intake tended to decrease when feather meal was fed. Predicted flows of digestible His, Met, and Lys, and plasma concentrations of these AA were reduced on both feather meal diets. Predicted flows of total digestible essential AA were not different between HP-FM and SP-C. We concluded that the DMI depression on HP-FM prevented an imbalance of excess AA over His, and created a deficiency of His, Met, and Lys compared with SP-C. Milk production decreased on the 2 feather meal treatments, partly explained by a tendency for DMI to decrease. Milk yield was lowest on SP-FM at 30.3 kg/d and highest on HP-C at 37.9 kg/d. Milk fat yield was not affected by diet but protein and lactose yields were both lower with feather meal. Protein yields were 860 and 998 g/d, whereas lactose yields were 1,384 and 1,561 g/d for SP-FM and HP-FM, respectively. This resulted in a higher fat content and lower protein percentage on FM diets. The ratio of solids-not-fat:fat in milk was lowest on SP-FM at 2.11 compared with 2.56 on SP-C. Adding feather meal to the diet by replacing MP isonitrogenously was more effective at lowering the solids-not-fat:fat ratio than increasing the MP content with an imbalanced protein source.     

Plasma essential amino acid concentration and profile are associated with performance of lactating dairy cows as revealed through meta-analysis and hierarchical clustering

Our aim was to explore whether changes in plasma essential AA (EAA) concentration ([EAA]_p) or profile (defined here as the molar proportion of individual [EAA]_p relative to the total [EAA]_p) may serve as an indicator of the EAA status of a cow. We undertook a meta-analysis with the objectives to determine if different plasma EAA profiles exist among cows and to explore the association of [EAA]_p or the profile of EAA with lactating cow performance and measures of N utilization. We hypothesized the existence of differences in [EAA]_p and different plasma EAA profile for cows with greater milk output, feed efficiency, and greater N use efficiency (NUE; milk true protein-N:N intake) compared with cows with lower milk output, feed efficiency, and lower NUE. The data set included 22 feeding trials and 96 dietary treatments. First, a mixed-effect model analysis was used to predict [EAA]_p in response to the categorical fixed effect of EAA, continuous fixed effect of National Research Council model-predicted metabolizable protein (MP) supply, continuous fixed effect of body weight, the fixed effect of EAA and MP supply interaction, the fixed effect of EAA and body weight interaction, and the random effect of study. Then, residuals of the model were standardized based on Z-score and clustered using the hierarchical method (Euclidean distance and Ward's minimum variance method) resulting in 2 clusters. Finally, a fixed-effect model was used to evaluate the significance with which clusters were associated with [EAA]_p, cow performance, feed efficiency, and NUE. The total concentration of [EAA]_p was lower (784 vs. 983 µM) and the concentration of each EAA was on average 22 µM lower for cows in cluster 1 compared with cluster 2 with the smallest and greatest difference found for Met (4 µM) and Val (59 µM), respectively. The percentage difference in [EAA]_p was the smallest for Thr (?5.3%) and the greatest for Leu (?37.1%). There was no difference between clusters for Arg, His, and Met molar proportions; however, cows in cluster 1 had a lower molar proportion of Leu and a tendency for lower molar proportion of Val compared with cows in cluster 2. Additionally, cows in cluster 1 had greater molar proportions of Ile, Lys, and Thr and a tendency for greater molar proportion of Phe compared with cows in cluster 2. The fixed-effect model analysis indicated that cows in cluster 1 had higher milk energy output (+3.2 Mcal/d), true protein yield (+87 g/d) and fat yield (+236 g/d), feed efficiency (milk Mcal:dry matter intake; +8% unit), and a tendency for greater MP efficiency (Milk true protein/MP supply; +2.3% unit) than cows in cluster 2. These results suggested greater use of EAA by the mammary gland (as reflected by greater milk protein synthesis) and lower hepatic catabolism of AA (as reflected by a tendency to greater MP efficiency) in cows of cluster 1 compared with cluster 2. Our findings should be evaluated further, including whether the relative molar proportions of plasma EAA might serve as a holistic indicator of the EAA status of cows as related to their productivity, feed efficiency and N utilization.