Effect of variation in proportion of cornmeal and steam-rolled corn in diets for dairy cows on behavior, digestion, and yield and composition of milk

Sixty-six lactating multiparous Holstein cows (113+/-46 DIM) housed in a free-stall facility were blocked and assigned randomly to one of three treatments to evaluate the effects on animal performance from feeding cornmeal, cornmeal mixed with steam-rolled corn in a ratio of 1:1 on dry matter basis, or steam-rolled corn. The only difference in the dietary ingredients was the type of corn, which was included in the total mixed ration (TMR) at 17% of dry matter. The densities (g/L) of cornmeal and steam-rolled corn were, respectively, 635 and 553. Diets were fed as TMR and were formulated according to the Cornell Penn Miner Dairy nutrition model. The TMR consisted of 40% forage and 60% concentrate on dry matter basis. The first 2 wk of the 8-wk study was a preliminary period, and data collected during this period were used as covariate in statistical analysis of production data collected during wk 6 to 8. Treatment diets were fed from wk 3 to 8. Total tract digestibilities of dry matter, organic matter, crude protein, starch, and neutral detergent fiber were not significantly different among treatments. Cows fed TMR containing steam-rolled corn had higher body condition and ruminated longer. However, feeding cornmeal and steam-rolled corn together did not improve dry matter and nutrient digestion, milk yield, 3.5% fat-corrected milk yield, and percentage and yield of fat, crude protein, true protein, and lactose in milk, and milk urea nitrogen. In conclusion, feeding steam-rolled corn improved animal body condition and rumination. Partial or complete substitution of cornmeal by steam-rolled corn in diets for lactating dairy cows did not improve dry matter and nutrient digestion, milk yield, and milk composition.     

Response of lactating dairy cows to steam-flaked sorghum, steam-flaked corn, or steam-rolled corn and protein sources of differing degradability

Protein sources with different degradabilities were fed to 48 lactating Holstein cows receiving 37 or 39% of dietary dry matter as steam-flaked sorghum (360 g/L), steam-flaked corn (360 g/L), or steam-rolled corn (490 g/L) in a 3 x 2 factorial arrangement of treatments. Cows were fed an alfalfa-based diet with 7% soybean meal or 5% of an animal-marine protein blend and 37 or 39% grain. Although not significant, cows fed flaked grain yielded a mean of 1.5 kg/d more milk than did those fed rolled grain. Gross feed efficiency was not affected by grain processing or protein source, but diets with the animal-marine protein blend had 9% higher estimated net energy for lactation than did diets with soybean meal. The greater gains in body weight and increased digestibility of the diets with the animal-marine protein blend verify the higher energy concentration of those diets. Yield of milk protein was increased by flaked grain or the animal-marine protein blend, and flaked grain increased percentages of lactose and solids nonfat. Increasing the ratio of rumen-degradable starch to rumen-degradable protein increased milk protein content and yield linearly and increased contents of lactose and solids nonfat. A linear response of dry matter, organic matter, crude protein, and starch digestibilities was observed as the ratio of rumen-degradable starch to rumen-degradable protein increased. These data show improved performance of dairy cows fed a high rumen-undegradable protein source with diets high in rumen-degradable starch from steam-processed grains.     

Recombinant bovine somatotropin with lactating cows fed diets differing in energy density

Sixty-four Holstein cows (32 primiparous) were assigned randomly at parturition to one of two diets differing in forage:grain ratio and were further assigned to either control or treatment with recombinant bST. A full lactation study was conducted. Total mixed rations consisted of alfalfa silage, high moisture ear corn, soybean meal, and vitamin and mineral supplements. Percentages of forage in the diet (dry basis) for the high and medium energy diets were wk 1 to 12, 38.2 and 58.2; wk 13 to 26, 48.2 and 68.2; and wk 27 to 44, 68.2 and 88.2. Injection of a saline placebo or 20.6 mg/d per cow of bST started at wk 13 and stopped at wk 43 of lactation. Administration of bST increased 305-d milk yield by 19.9 and 18.3% for multiparous cows fed high and medium grain diets and by 13.0 and 5.9% for primiparous cows fed the same diets. Body weight gain during lactation tended to be lower for cows treated with bST, and body condition scores were significantly lower for those treated with bST and fed the medium energy diets. Daily injection of bST did not change concentrations of glucose or urea in blood or beta-hydroxybutyrate in plasma. Multiparous cows had a transitory increase in plasma FFA concentration immediately after bST treatment started. Milk composition, health, and reproductive parameters observed were not adversely affected by bST administration. Cows fed low energy diets during bST administration in the first lactation did not produce as much milk as controls when compared during the first 10 wk of their second lactation.     

Effects of grain processing and bovine somatotropin on metabolism and ovarian activity of dairy cows during early lactation

This study compared the effects of exogenous bovine somatotropin (bST) on the metabolism and ovarian activity of cows fed diets differing in ruminally degradable starch. Twenty-four multiparous and eight primiparous Holstein cows in early lactation were divided into four groups and fed diets containing 39% grain as steam-flaked sorghum or steam-rolled corn with or without bST for 90 d in a 2 x 2 factorial design. Flaked sorghum improved energy status of cows during early lactation, tending to increase plasma glucose and insulin. Administration of bST decreased plasma urea nitrogen and increased nonesterified fatty acids (NEFA). Plasma levels of beta-hydroxybutyrate (BHBA) and hepatic concentrations of triglycerides were not altered by treatments. Temporal changes in plasma glucose, urea nitrogen, NEFA, and BHBA were detected in a quadratic manner and insulin increased linearly with time, but treatments did not affect postpartum changes in these metabolites. There were greater decreases in body weight and net energy balance in cows on bST during the first 7 wk of treatment. Cows receiving bST took longer to reach the nadir of negative energy balance, and bST tended to delay the period to reach a positive energy balance. Follicular populations and incidence of cystic ovaries were not affected by treatments, but cows receiving bST had fewer double ovulations. Flaked sorghum increased plasma progesterone during the early luteal phase of the first two postpartum estrous cycles. Feeding more ruminally degradable starch improved the energy status and luteal activity of cows in early lactation.     

Effects of corn processing and supplemental hay on rumen environment and lactation performance of dairy cows grazing grass-legume pasture

The effect of corn processing (9 kg of dry matter/d of ground dry shelled or 9 kg of dry matter/d of steam rolled) and supplemental hay (0 or 3.2 kg of dry matter/d of alfalfa hay) on milk yield and composition, rumen environment, and starch utilization by lactating cows grazing grass-legume pasture was studied. Twelve rumen cannulated, multiparous Holstein cows in early lactation (95 d in milk), were assigned to a 4 x 4 Latin square design replicated three times. Treatments were ground shelled corn-based concentrate, ground shelled corn-based concentrate plus alfalfa hay, steam-rolled, corn-based concentrate, or steam-rolled, corn-based concentrate plus alfalfa hay. Supplements were fed in equal proportions twice daily. Cows fed steam-rolled corn tended to have higher percentage of milk protein and lower milk urea nitrogen concentrations than cows fed shelled corn. Milk yield was not affected by corn processing or hay supplementation. Intake of pasture forage but not total dry matter intake was reduced by hay supplementation. Starch plus free glucose digestibility in the total tract was not affected by grain processing; however, starch plus free glucose digestibility tended to increase with hay supplementation. Supplemental hay increased starch plus free glucose digestibility through changes in rumen digestion kinetics. Hay supplementation reduced the liquid rate of passage, and tended to reduce particulate turnover. Rumen degradability of pasture forage organic matter tended to be higher for cows fed supplemental hay. Supplemental hay in these diets had a greater impact on starch utilization than corn processing.     

Production performance,nutrient digestibility,and milk fatty acid profile of lactating dairy cows fed corn silage- or sorghum silage-based diets with and without xylanase supplementation

The objective of this study was to evaluate the effects of supplementing xylanase on production performance, nutrient digestibility, and milk fatty acid profile in high-producing dairy cows consuming corn silage- or sorghum silage-based diets. Conventional corn (80,000 seeds/ha) and brown midrib forage sorghum (250,000 seeds/ha) were planted, harvested [34 and 32% of dry matter (DM), respectively], and ensiled for more than 10 mo. Four primiparous and 20 multiparous Holstein cows were randomly assigned to 1 of 4 diets in a replicated 4 × 4 Latin square design with a 2 × 2 factorial arrangement of treatments and 19-d periods. Treatment diets consisted of (1) corn silage-based diet without xylanase, (2) corn silage-based diet with xylanase, (3) sorghum silage-based diet without xylanase, and (4) sorghum silage-based diet with xylanase. The xylanase product was supplemented at a rate of 1.5 g of product/kg of total DM. Corn silage had higher concentrations of starch (31.2 vs. 29.2%), slightly higher concentrations of crude protein (7.1 vs. 6.8%) and fat (3.7 vs. 3.2%), and lower concentrations of neutral detergent fiber (36.4 vs. 49.0%) and lignin (2.1 vs. 5.7%) than sorghum silage. Xylanase supplementation did not affect DM intake, milk yield, milk fat percentage and yield, milk protein percentage and yield, lactose percentage and yield, and 3.5% fat-corrected milk yield. Cows consuming corn silage-based diets consumed 13% more DM (28.8 vs. 25.5 kg/d) and produced 5% more milk (51.6 vs. 48.9 kg/d) than cows consuming sorghum silage-based diets. Milk from cows consuming sorghum silage-based diets had 16% greater fat concentrations (3.84 and 3.30%) than milk from cows consuming corn silage-based diets. This resulted in 8% greater fat yields (1.81 vs. 1.68 kg/d). Silage type did not affect milk protein and lactose concentrations. Xylanase supplementation did not affect nutrient digestibility. Cows consuming corn silage-based diets showed greater DM (77.3 vs. 73.5%), crude protein (78.0 vs. 72.4), and starch (99.2 vs. 96.5%) digestibilities than cows consuming sorghum silage-based diets. In conclusion, xylanase supplementation did not improve production performance when high-producing dairy cows were fed corn silage- or sorghum silage-based diets. In addition, production performance can be sustained by feeding sorghum silage in replacement of corn silage.     

Milk production and nutrient digestibility by dairy cows when fed exogenous amylase with coarsely ground dry corn

The digestibility of starch provided by coarsely ground corn is often low, which reduces the digestible energy (DE) concentration of the diet. We hypothesized that adding exogenous amylase to diets based on coarsely ground dent corn would increase dietary DE resulting in greater milk production. Total-tract nutrient digestibility was measured in a partially replicated Latin square experiment (6 cows and 4 periods) with a 2 × 2 factorial arrangement of treatments. Diets had 26 or 31% starch with or without exogenous amylase (amylase was added to the concentrate mixes at the feed mill). In the low and high starch diets, coarsely ground dry corn (mean particle size = 1.42 mm) provided 43 and 62% of total dietary starch (corn silage provided most of the remaining starch). No treatment interactions were observed. High starch diets had greater dry matter (DM), organic matter, and energy digestibility than low starch diets, and diets with amylase had greater neutral detergent fiber digestibility than diets without amylase. Digestibility of starch averaged 88% and was not affected by treatment. A long-term (98-d) lactation study with 48 Holstein cows (74 d in milk) was conducted using 3 of the diets (low starch diets with and without amylase and the high starch diet without amylase). Addition of amylase to a diet with 26% starch did not affect intake, milk yield, milk composition, body weight, or body condition. Cows fed the diet with 31% starch had greater DM and DE intakes; yields of milk, fat, and protein; and feed efficiency than those fed diets with 26% starch. Milk composition was not affected by starch concentration. Adding exogenous amylase to a lower starch diet did not make the diet nutritionally equivalent to a higher starch diet.     

Lactational evaluation of recombinant bovine somatotropin with corn and barley diets

Forty-eight Holstein cows were randomly assigned to receive diets containing corn or barley as the primary energy concentrate from wk 4 through 44 postpartum. During wk 14, cows from each grain source group were randomly assigned to receive 0 (control), 10.3, 20.6, and 30.9 mg/cow per d of recombinant bST injected wk 15 through 44 postpartum. Grain source exerted no significant effect on production parameters and efficacy of bST, although milk production tended to be higher with corn diets. Milk production (24.2, 29.2, 31.7, and 29.5 kg/d) and 4% FCM (21.9, 26.2, 28.1, and 28.0 kg/d) were higher for cows injected with bST, and DM intakes (20.9, 22.8, 22.0, and 23.3 kg/d) increased slightly. Percentages of milk fat (3.47, 3.28, 3.39, and 3.52) and protein (3.48, 3.44, 3.44, and 3.38) varied. Lactose, SCC, and body weights were similar for bST and dietary treatments. Diet or bST had no detectable affect on health or reproduction. Injection of bST wk 15 through 44 increased milk production 21 to 31% relative to control animals. Limiting bST use to the latter two-thirds of lactation resulted in an 8 to 17% increase in total yield with only a 0 to 5% increase in lactational DM intake.     

Comparison of feeding corn silages from leafy or conventional corn hybrids to lactating dairy cows

Three corn hybrids (Pioneer 36F30, Mycogen TMF2450, and Mycogen TMF2404) were compared for yield and quality traits, and lactation performance and apparent digestibility by Holstein cows. The three corn silages were harvested at a target of 33 to 35% dry matter. Before harvest, six corn plants were randomly selected for plant fractionation. Grain-to-stover ratios were 0.92, 0.70, and 0.95 for the 36F30, TMF2450, and TMF2404 corn plants, respectively. Fifty-two multiparous Holstein cows were placed on a 120-d lactation trial after a 21-d covariate diet. Cows were blocked by calving date and randomly assigned within block to one of three dietary treatments, containing approximately 40% (dry matter basis) corn silage. Milk yield, milk components, and dry matter intake did not differ among dietary treatments. In vitro true and neutral detergent fiber digestibilities were numerically higher for TMF2404 than the other corn silage hybrids. Apparent total-tract crude protein and neutral detergent fiber digestibilities, as measured by acid insoluble ash, were higher for TMF2450 than the other two hybrids, but starch digestibility was not different between the corn silage dietary treatments. Although small differences in nutrient content and digestibility existed among corn silage hybrids, inclusion of these leafy hybrids in lactating cow diets at 40% of the dietary dry matter did not have a significant impact on lactation performance of dairy cattle.     

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.     

Effects of substitution of different levels of steam-flaked corn for finely ground corn on lactation and digestion in early lactation dairy cows

Eight multiparous Holstein cows, 4 of them fitted with rumen cannulas, were used to test the effects of substitution of steam-flaked corn (SFC) for equal amounts of finely ground corn (FGC) in diets on feed intake and digestion, blood metabolites, and lactation performance in early lactation dairy cows. Cows were fed 4 diets in a replicated 4 × 4 Latin square design. The fistulated cows formed 1 replicate. Each experimental period lasted for 3 wk. The 4 diets contained 0, 10, 20, or 40% SFC and 40, 30, 20, or 0% FGC (dry matter basis), respectively. The milk protein content and yield, milk solid nonfat content and yield, plasma glucose concentration, and dry matter intake increased as the proportion of SFC increased in diets. Apparent total tract digestibilities of dry matter, organic matter, neutral detergent fiber, acid detergent fiber, and average ruminal fluid NH₃-N concentration decreased with increasing levels of SFC. The ruminal fluid pH was not affected by the substitution of SFC for FGC. The 20% SFC substitution improved digestion of crude protein, yield of fat-corrected milk, milk lactose content, fat, and fat yield. The 40% SFC substitution increased urea concentration in both plasma and milk. It was concluded that 20% of SFC substitution for FGC appeared to be an appropriate level in diet for early lactation dairy cows.     

Effects of feeding diets composed of corn silage and a corn milling product with and without supplemental lysine and methionine to dairy cows

Formulating diets with high inclusion rates of a feed that provides necessary nutrients at lower-than-market prices for those nutrients should increase income over feed costs if the feed is not detrimental to yields of milk and milk components. The objective of this study was to determine whether cows fed a diet composed of approximately 53% corn silage, 44% corn milling product (68% dry matter, 21% crude protein, 37% neutral detergent fiber, and 9% starch) and 3% minerals (CMP) would have similar productivity as cows fed a control diet of predominantly corn silage, alfalfa silage, corn grain, and soybean meal. Based on the National Research Council (2001) dairy model, the CMP diet was inadequate in metabolizable methionine and extremely low in metabolizable lysine. A third treatment (CMP+AA) was the same as the CMP diet but was supplemented with rumen-protected lysine and methionine. Twenty-one Holstein cows were used in a replicated Latin square (28-d periods) design to evaluate production responses to the 3 diets. Diets were formulated to contain the same concentration of net energy for lactation and metabolizable protein (MP) based on the National Research Council model, but diets with CMP contained more neutral detergent fiber (38.3 vs. 31.4%) and less starch (21.6 vs. 30.5%) than the control diet. Lysine as a percent of MP was 6.5, 6.0, and 6.8 for the control, CMP, and CMP+AA diets, respectively, and methionine was 1.8, 1.8, and 2.3% of MP, respectively. Dry matter intake was not affected by diet (24.3 kg/d), but milk yield was lower for cows fed either CMP diet than for those fed control (36.0 vs 38.1 kg/d). Milk fat concentrations were normal and not affected by diet (3.7%). Milk protein concentration was greater for cows fed CMP+AA than for cows fed the other 2 treatments (3.19 vs. 3.11%); however, milk protein yield was greatest for cows fed the conventional diet. The concentration of methionine in plasma was significantly greater for cows fed CMP+AA than for cows fed the other diets. Plasma lysine concentrations were greater for cows fed the conventional diet than for those fed the other 2 diets. Plasma concentrations of several essential AA were lower for cows fed either CMP diet. Based on calculated energy balance, diets contained similar concentrations of net energy for lactation, but cows fed CMP diets partitioned more energy toward body energy reserves than did control cows, perhaps because supply of specific AA limited milk synthesis.     

Influence of a reduced-starch diet with or without exogenous amylase on lactation performance by dairy cows

The objective of this trial was to determine lactation performance responses in high-producing dairy cows to a reduced-starch versus a normal-starch diet and to the addition of exogenous amylase to the reduced-starch diet. Forty-five multiparous Holstein cows, 68 ± 29 d in milk and 696 ± 62 kg of body weight (BW) at trial initiation, were randomly assigned to 1 of 3 treatments in a completely randomized design; a 2-wk covariate adjustment period with cows fed the normal-starch diet was followed by a 10-wk treatment period with cows fed their assigned treatment diets. The normal-starch total mixed ration did not contain exogenous amylase (NS−). The reduced-starch diets, formulated by partially replacing corn grain and soybean meal with whole cottonseed and wheat middlings, were fed without (RS−) and with (RS+) exogenous amylase addition to the total mixed ration. All diets contained 50% forage and 19.8% forage neutral detergent fiber (dry matter basis). Starch and neutral detergent fiber concentrations averaged 27.0 and 30.9%, 22.1 and 35.0%, and 21.2 and 35.3% (dry matter basis) for the NS−, RS−, and RS+ diets, respectively. Expressed as a percentage of BW, dry matter intake was greater for cows fed RS− than for cows fed NS− or RS+. Intake of neutral detergent fiber ranged from 1.09 to 1.30% of BW among the treatments, with that of RS− being 21% greater than that of NS−. Milk yield tended to be greater for cows fed NS− compared with the RS diets. Milk fat content and yield were unaffected by treatment. Milk protein content and yield were greater for cows fed NS− compared with the RS diets. Concentrations of milk urea nitrogen were greater for cows fed RS diets compared with the NS− diet. Body weight, BW change, and body condition score were unaffected by treatment. Feed conversion (kg of milk/kg of dry matter intake) was 10% greater on average for cows fed NS− than for cows fed the RS diets, and tended to be 6% greater for cows fed RS+ compared with RS−. Feeding a reduced-starch diet formulated by partially replacing corn grain and soybean meal with a wheat middlings and whole cottonseed mixture compared with a normal-starch diet without addition of exogenous amylase to either diet reduced milk and component-corrected feed conversions. Addition of exogenous amylase to a reduced-starch diet was of minimal benefit in this study.     

Low doses of bovine somatotropin during the transition period and early lactation improves milk yield, efficiency of production, and other physiological responses of Holstein cows

The objectives of this experiment were to determine whether low doses of bovine somatotropin (bST) during the transition period and early lactation period improved dry matter intake (DMI), body weight (BW), or body condition score (BCS); provoked positive changes in concentrations of somatotropin, insulin, insulin-like growth factor-I (IGF-I), glucose, nonesterified fatty acids, and Ca; or improved milk yield (MY) response without obvious adverse effects on health status. Eighty-four multiparous Holstein cows completed treatments arranged in a 2 x 3 x 2 factorial design that included prepartum and postpartum bST, dry period (30 d dry, 30 d dry + estradiol cypionate, and 60 d dry), and prepartum anionic or cationic diets. Biweekly injections of bST began at 21 +/- 3 d before expected calving date through 42 +/- 2 d postpartum (control = 0 vs. bST = 10.2 mg of bST/d; POSILAC). At 56 +/- 2 d in milk, all cows were injected with a full dose of bST (500 mg of bST/14 d; POSILAC). During the prepartum period and during the first 28 d postpartum, no differences in mean BW, BCS, or DMI were detected between the bST treatment group and the control group. During the first 10 wk of lactation, cows in the bST treatment group had greater mean MY and 3.5% fat-corrected milk yield and lower SCC than did cows in the control group. When cows received a full dose of bST, an increase in milk production through wk 21 was maintained better by cows in the bST group. Mean concentrations of somatotropin, IGF-I, and insulin differed during the overall prepartum period (d -21 to -1). During the postpartum period (d 1 to 28), cows in the bST group had greater mean concentrations of somatotropin and IGF-I in plasma. Concentrations of Ca around calving did not differ because of bST treatment. Results suggest that changes in concentrations of blood measures provoked by injections of bST during the transition period and early lactation period resulted in improved metabolic status and production of the cows without apparent positive or negative effects on calving or health.     

Effect of exogenous amylase on lactation performance of dairy cows fed a high-starch diet

Exogenous amylase supplementation can increase starch and fiber digestibility in lactating dairy cows. We evaluated the effect of exogenous amylase supplementation on diets with high starch concentration (32% of dry matter). Twenty-eight Holstein cows (171 ± 80 d in milk, 4 primiparous) received a standard diet for 14 d and then a treatment for 63 d, in a covariate-adjusted randomized block design with repeated measures over time. Treatments were amylase [0.5 g of Ronozyme RumiStar (DSM Nutritional Products, Basel, Switzerland) per kg of total mixed ration dry matter] or control. The diets contained (% of dry matter): 39.4% corn silage, 11.2% rehydrated and ensiled mature corn grain, and 11.7% finely ground mature corn. Amylase increased milk yield (32.3 vs. 33.0 kg/d) and reduced dry matter intake (20.7 vs. 19.7 kg/d), increasing feed efficiency (1.52 vs. 1.63). Amylase also increased milk lactose synthesis (1.49 vs. 1.56 kg/d) and plasma glucose concentration (59.3 vs. 68.6 mg/dL). Secretions of milk fat and protein did not differ. Although milk urea N did not differ, amylase reduced the concentration of urea N in blood, suggesting an increase in ruminal starch degradation. However, the total-tract apparent digestibility of starch (96.3% of intake) and neutral detergent fiber (44.4% of intake), ruminal fermentation profile, and microbial yield estimated by urinary allantoin excretion did not differ. Cows fed amylase sorted in favor of long feed particles and against short particles, had shorter chewing activity (780 vs. 699 min/d), and had fewer meals per day (11.5 vs. 9.7). Amylase improved the feed efficiency of lactating cows fed a high-starch diet; the enzyme increased milk yield and reduced intake.     

Performance of dairy cows fed diets formulated at 2 starch concentrations with either canola meal or soybean meal as the protein supplement

This study was designed to evaluate the effects of substituting corn grain with nonforage fiber sources in diets containing soybean meal (SBM) or canola meal (CM) as the primary protein source. Sixteen Holstein cows were assigned to a replicated 4 × 4 Latin square design with 4 periods of 28 d each. Treatments were arranged as a 2 × 2 factorial with 2 protein sources (SBM and CM) and 2 dietary starch concentrations (21 and 27% dry matter, DM). Diets were formulated to contain 16.5% CP, and the 21% starch diets were obtained by replacing corn grain with soybean hulls and beet pulp. Protein source × starch interactions were observed for DM intake (DMI), milk fat and protein concentrations, milk protein yield, milk urea nitrogen, and feed efficiency. Cows fed CM diets had a higher DMI when dietary starch concentration was 27% compared with 21%, but those cows had DMI similar to that of cows on SBM diets regardless of the starch concentration. Milk fat percentage was decreased in cows fed CM with 27% starch compared with cows fed CM with 21% starch and cows fed SBM with 27% starch. Milk protein percentage and yield and milk lactose percentage were least in cows fed CM with 21% starch compared with the other 3 diets, but feed efficiency was greater for cows fed CM with 21% starch. Milk urea nitrogen was least in cows fed CM with 27% starch compared with the other 3 diets. Cows fed diets with 27% starch produced 2.5 kg/d more milk and 1.9 kg/d more energy-corrected milk compared with cows fed 21% starch. Digestibility of DM and organic matter was higher in cows fed SBM diets than in cows on CM diets, and cows fed 27% starch showed greater DM and organic matter digestibility than cows on 21% starch. Digestibility of neutral detergent fiber and acid detergent fiber was greater in diets with SBM than in those with CM. Molar proportion of acetate was the lowest for cows fed CM with 21% starch compared with cows fed SBM with 21% starch, with the remaining cows fed being intermediate and similar. However, propionate was highest for cows fed CM with 21% starch than for cows fed SBM with 21% starch, but the remaining treatments were intermediate and similar. Isobutyrate was greater for cows fed CM with 21% starch, which resulted in the lowest acetate:propionate ratio compared with cows fed the remaining treatments. Overall, we confirmed that the interaction of protein with starch in CM diets can sustain similar cow performance as with the SBM diets. Those making decisions about starch concentration and protein source should consider feed price when SBM or CM and different starch levels are being formulated in diets for lactating dairy cows.     

Production of dairy cows fed distillers dried grains with solubles in low- and high-forage diets

The objective of the study was to investigate the effects of dietary forage and distillers dried grains with solubles (DDGS) concentration on the performance of lactating dairy cows. Twelve Holstein cows were blocked by parity and milk production and assigned to replicated 4 × 4 Latin squares with a 2 × 2 factorial arrangement of treatments. Diets were formulated to contain low forage [LF; 17% forage neutral detergent fiber (NDF)] or high forage (HF; 24.5% forage NDF) and DDGS at 0 or 18% of diet dry matter. The forage portion of the diet consisted of 80% corn silage and 20% alfalfa hay (dry matter basis). A portion of the ground corn and all of the expeller soybean meal and extruded soybeans from 0% DDGS diets were replaced with DDGS to formulate 18% DDGS diets. Overall, we found no interactions of forage × DDGS concentrations for any of the production measures. We observed no effect of diet on dry matter intake. Milk yield was greater when cows were fed LF diets compared with HF diets (43.3 vs. 41.5 kg/d). Milk fat concentration (3.03 vs. 3.38%) was lower for cows fed LF diets compared with HF diets, whereas protein concentration (3.11 vs. 2.98%) and yield (1.34 vs. 1.24 kg/d) were greater for cows fed LF diets compared with HF diets. Yields of fat, total solids, energy-corrected milk, and feed efficiency were not affected by diets. Cows partitioned equally for milk, maintenance, and body reserves. Replacing starch from ground corn and protein from soybean feeds with DDGS at either 17 or 24.5% of forage NDF concentration in the diet was cost-effective and did not affect the production performance of lactating dairy cows.     

Effect of dietary energy and previous bovine somatotropin on milk yield, mastitis, and reproduction in dairy cows.

Thirty multiparous lactating Holstein cows were blocked according to time of calving and assigned to a 2 x 3 factorial arrangement of treatments in a randomized complete block design to evaluate the effects of two dietary energy concentrations either without or with bST (20.6 mg/d per cow) administered to cows that had not or had received bST during the preceding lactation. Subcutaneous injection of bST began 28 to 35 d postpartum and continued for 39 wk. The dietary energy concentration x bST interaction was not significant for any response variable. Compared with DMI of control cows, DMI was higher for cows receiving bST, being 1.6 and 2.4 kg/d higher for cows receiving bST for one and two lactations, respectively. Milk, fat, and protein yields were higher for cows receiving bST than for controls. Those receiving bST for a second lactation also produced more milk than controls until wk 20; thereafter, milk yields were similar to those of controls. Somatotropin administration had no adverse effect on udder health. Cows receiving bST tended to ovulate less regularly than controls, which may be attributed to their higher milk yield. However, BW gains during lactation were similar for all treatments, indicating that bST-treated cows built energy reserves for the subsequent lactation. Although energy concentrations of the diets had no significant impact on yield, the higher energy diet tended to depress milk fat concentration. Administration of bST to dairy cows for a second, consecutive lactation yielded responses similar for the first 20 wk of the study to those receiving bST for the first time. However, after wk 20, milk yield was less than that by cows receiving bST for the first lactation but similar to that of control cows.     

Effects of bovine somatotropin on milk yield and composition in Holstein cows in advanced lactation fed low- or high-energy diets

The objective of this study was to evaluate the response of Holstein cows to bovine somatotropin (bST) during advanced lactation and its relationship to energy intake. Twenty-four lactating Holstein cows averaging 21 kg of milk/d, and 292 d in milk were assigned to one of three treatment groups in a randomized block design. Blocks were based on the 14 d of pretreatment milk production, and treatment groups were balanced for days in milk. Treatment 1 was a low-energy diet (1.49 Mcal/kg of dry matter) without bST injection; treatment 2 was the low-energy diet plus injection of 500 mg of bST every 14 d; and treatment 3 was a high-energy diet (1.71 Mcal/kg of dry matter) with bST injections as in treatment 2. Treatment was divided into two periods (1 to 49 and 50 to 98 d) to determine if response to bST and energy changed with time on treatment. Results showed that bST significantly (P < 0.05) increased milk, fat-corrected milk, and fat and protein yields; and feed efficiency (fat-corrected milk per dry matter intake) for both periods. Milk yield responses to bST were greater for cows fed the low-than the high-energy diet in both periods. These data show that bST injections for cows in advanced lactation increased performance, but excessive energy diminished the bST response.     

Ruminal fermentation and intestinal flow of nutrients by lactating cows consuming brown midrib corn silages.

Rumen characteristics and digestive kinetics of brown midrib corn silage were evaluated with five late-lactation (221 DIM +/- 20 d) multiparous cows fitted with ruminal and duodenal cannula. Dietary treatments were applied by using a single reversal design with two 21-d periods where either brown midrib (BM3) or isogenic (ISO) corn silage were included in a total mixed ration formulated to be 40% concentrate and 60% corn silage on a dry matter (DM) basis. Rumen and total tract digestibilities of DM, organic matter, neutral detergent fiber, acid detergent fiber, starch, and N were determined and rumen characteristics evaluated. Apparent rumen DM and organic matter digestibilities were greater for the BM3 corn silage (7.1 and 4.7 percentage units, respectively). Dietary intake and duodenal flow of starch were greater and rumen and total tract starch digestibilities were lower for BM3 corn silage diets than ISO corn silage diets. However, more starch (1.1 kg/d) was apparently digested and absorbed postruminally in cows fed the BM3 corn silage diets. Duodenal flow of neutral detergent fiber was 0.9 kg/d lower, and ruminal (15.9 percentage units) and total tract digestibilities (4.4 percentage units) were higher for BM3 treatment compared with the ISO treatment. Digestive patterns of ADF were similar for the BM3 and ISO treatments. Ruminal pH was lower in the cows fed the BM3 corn silage than those fed the ISO corn silage. As a result of a tendency for decreased N excretion in urine and slight increases in N intake due to increased DM intake, N balance tended to be greater for the BM3 treatment compared with the ISO treatment. These results may partially explain the benefits of feeding BM3 corn silage to cows during early lactation, as the observed increases in fiber component digestibility and improved N economy may combine to enhance DM intake and better support the nutritional demands of milk production for the high producing dairy cow.