Effects of feeding frequency on ruminal parameters, plasma insulin, milk yield, and milk composition in Holstein cows

Two experiments were conducted to determine the effects of frequency of feeding on ruminal fermentation, blood parameters, milk yield, and milk composition in cows fed a 60% pelleted concentrate and 40% chopped alfalfa hay (DM basis) diet. In Experiment 1, four ruminally cannulated cows were fed concentrates in 12 equal portions at 2-h intervals or in two equal portions at 0500 and 1500 h in a crossover design. In Experiment 2, treatments were as in Experiment 1 plus an additional treatment consisting of a total mixed diet fed at 2-h intervals in a 3 x 3 Latin square design. All treatment periods were 2 wk. In Experiment 1, increased frequency of concentrate feeding tended to result in elevated ruminal pH and increased acetate to propionate ratio. Plasma insulin concentration tended to be higher (1.54 vs. 1.04 ng/ml) and milk fat percentage increased from 2.21 to 2.60% for 2 and 12 times daily feeding, respectively. In Experiment 2, frequency of feeding concentrate or total mixed diet did not affect ruminal and blood parameters or milk yield. In both experiments, milk protein and lactose concentrations were not influenced by feeding frequency. Results suggest that where intake is kept constant, increased feeding frequency will not influence milk yield but could result in elevated milk fat percent in animals fed fat-depressing diets.     

Influence of carbohydrate source and buffer on rumen fermentation characteristics, milk yield, and milk composition in early-lactation Holstein cows

The effects of concentrate to forage ratio and sodium bicarbonate (buffer) supplementation on intake, ruminal fermentation characteristics, digestibility coefficients, milk yield, and milk composition were examined in 4 cannulated Holstein cows (100 +/- 20 d in milk). A 4 x 4 Latin square design with 2 x 2 factorial arrangement of treatments was implemented for 3-wk experimental periods. The 4 treatments were a 50:50 concentrate to forage ratio with 1.2% of dry matter (DM) and without added buffer and a 75:25 concentrate to forage ratio with (1.2% of DM) and without (0% of DM) buffer. The forage component of the ration was a 50:50 mixture of alfalfa and barley and triticale silage, and diets were fed ad libitum as a total mixed ration. Although feed intake was not influenced by treatments, substantial treatment differences were observed for milk yield and milk composition. Cows fed high-concentrate diet had lower ruminal pH, ruminal acetate, and butyrate concentrations, whereas propionate concentrations were significantly elevated. The addition of buffer, at both levels of concentrate inclusion, resulted in elevated total volatile fatty acids and acetate concentrations. We concluded that altering the forage concentrate ratio in the diet of lactation cows influenced milk yield and milk composition, but the addition of buffer to the diet prevented the elevation in trans-C18:1 fatty acids in milk fat, and related milk fat depression, associated with feeding high-concentrate diets.     

Effect of lasalocid on performance of lactating dairy cows

Thirty-two midlactation dairy cows were fed either a typical dairy diet or the same diet plus 340 mg lasalocid/d for 98 d. Diets were 65% forage (alfalfa and corn silage) and 35% concentrate (DM basis). Lasalocid did not affect production of milk (21 kg/d) or FCM (20 kg/d) or milk composition. Dry matter intake was slightly lower for cows consuming lasalocid than for control cows (19.6 vs. 20.6 kg/d). Lasalocid improved energetic efficiency by about 20% during the first 2 wk of the experiment, but treatment effects diminished as the experiment progressed. The period in which lasalocid had significant effects on energetic efficiency was also the period in which lasalocid increased ruminal propionate and decreased ruminal acetate concentrations. On d 7 of the experiment, cows fed lasalocid had lower acetate to propionate ratios as compared with control (3.0:1 vs. 3.7:1). No effect of treatment was observed on ruminal VFA during the remainder of the experiment. These data are interpreted to show that lasalocid improved the efficiency of converting dietary digestible energy into NE1 by altering ruminal fermentation, but this effect was relatively short-lived, since treatment effects on ruminal VFA patterns and energetic efficiency became negligible by 28 d.     

Feeding lactose increases ruminal butyrate and plasma beta-hydroxybutyrate in lactating dairy cows

Ruminal fermentation of lactose increases molar proportions of butyrate, which is metabolized by the ruminal epithelium to beta-hydroxybutyrate (BHBA). To determine the effects of dietary whey, and specifically lactose, on concentrations of ruminal and blood volatile fatty acids (VFA) and blood BHBA, 8 Holstein and 4 Brown Swiss multiparous cows (210 +/- 33 d in milk) were blocked by breed and randomly assigned to one of three 4 x 4 Latin squares. Treatments were control (CON; 7.1% of dietary dry matter [DM] as cornstarch), liquid whey (WHEY; 9.4% of diet DM) containing 70% lactose on a DM basis, low lactose (LOLAC; 7.1% lactose), or high lactose (HILAC; 14.3% lactose). Diets contained 53% forage as corn silage, alfalfa hay, and grass hay (DM basis) and a corn and soybean meal-based concentrate. Average dietary percentage of crude protein and energy density (Mcal/kg net energy for lactation) were 16.8 and 1.47, respectively. Feeding lactose increased DM intake. Milk production and composition were not affected by diet with the exception of decreased urea nitrogen in milk from cows fed lactose. Greater proportions of ruminal propionate were observed in cows fed CON relative to those fed WHEY and LOLAC. Increasing dietary lactose increased proportions of ruminal butyrate and decreased acetate and branched-chain VFA. Concurrent with the increase in ruminal butyrate concentrations, there was an increase in plasma BHBA as lactose in the diet increased. Concentrations of VFA in plasma were not affected by diet with the exception of the branched-chain VFA, which were increased in cows fed LOLAC compared with WHEY. These data indicate lactose fermentation increases proportions of ruminal butyrate and plasma BHBA in lactating dairy cows; however, the observed increase in plasma BHBA is not sufficient to subject cows to ketosis.     

Method of diet delivery to dairy cows: Effects on nutrient digestion,rumen fermentation,methane emissions from enteric fermentation and stored manure,nitrogen excretion,and milk production

This study was conducted to examine the effect of method of diet delivery to dairy cows on enteric CH₄ emission, milk production, rumen fermentation, nutrient digestion, N excretion, and manure CH₄ production potential. Sixteen lactating cows were used in a crossover design (35-d period) and fed ad libitum twice daily a diet [52:48, forage:concentrate ratio; dry matter (DM) basis] provided as forages and concentrates separately (CF) or as a total mixed ration (TMR). For the CF treatment, concentrates were offered first followed by mixed forages 45 min afterward. Method of diet delivery had no effect on DM intake, but neutral detergent fiber (NDF) intake was greater when the diet was delivered as TMR as compared with CF. Apparent total-tract digestibility of DM, crude protein, and gross energy was slightly (1 percentage unit) lower when the diet was offered as TMR than when offered as CF. In contrast, NDF digestibility was greater when the cows were fed TMR versus CF. Although average daily ruminal pH was not affected by method of diet delivery, daily duration of ruminal pH <5.6 was less when the diet was delivered as TMR as compared with CF (0.9 h/d versus 3.7 h/d). Delivering the diet as TMR increased ruminal total volatile fatty acid and NH₃ concentrations, but had no effect on acetate, propionate, or branched-chain volatile fatty acid molar proportions. Yields of milk, milk fat, or milk protein, and milk production efficiency (kg of milk/kg of DM intake or g of N milk/g of N intake) were not affected by the method of diet delivery. Daily production (g/d), yield (% gross energy intake), and emission intensity (g/kg of energy-corrected milk) of enteric CH₄ averaged 420 g/d, 4.9%, and 9.6 g/kg and were not affected by diet delivery method. Fecal N output was greater when the diet was delivered as TMR versus CF, whereas urinary N excretion (g/d, % N intake) was not affected. Manure volatile solids excretion and maximal CH₄ production potential were not affected by method of diet delivery. Under the conditions of this study, delivering the diet as concentrates and forages separately versus a total mixed ration had no effect on milk production, enteric CH₄ energy losses, urinary N, or maximal manure CH₄ emission potential. However, feeding the diet as total mixed ration compared with feeding concentrates and forages separately attenuated the extent of postprandial decrease in ruminal pH, which has contributed to improving NDF digestibility.     

Effects of a proteolytic feed enzyme on intake, digestion, ruminal fermentation, and milk production

The effects of exogenous proteolytic enzyme (EPE) on intake, digestibility, ruminal fermentation, and lactational performance were determined using 8 lactating Holstein cows in a double 4 ×4 Latin square experiment with a 2 ×2 factorial arrangement of treatments. Diets based on barley silage and alfalfa hay as the forage sources were formulated to maintain different forage to concentrate ratios [60:40 vs. 34:66, dry matter (DM) basis]. Four dietary treatments were tested: high forage (HF) without EPE (HF−EPE), HF with EPE (HF+EPE), low forage (LF) without EPE (LF-EPE), and LF with EPE (LF+EPE). The EPE, which contained proteolytic activity but negligible fibrolytic activity, was added to the concentrate portion of the diets after pelleting at a rate of 1.25 mL/kg of DM. Adding EPE to the diet increased total tract digestibilities of DM, organic matter, N, acid detergent fiber, and neutral detergent fiber, with larger increases in digestibility observed for cows fed LF+EPE. Effects of added EPE on in vivo digestibility were consistent with improvements in gas production and degradability of the individual components of the TMR observed in vitro. Ruminal enzymic activities of xylanase and endoglucanase increased with addition of EPE to the diet, which may have accounted for improvements in fiber digestion. However, feeding EPE unexpectedly decreased feed intake of cows, which offset the benefits of improved feed digestibility. Consequently, milk yield of cows fed high or low forage diets decreased with adding EPE. Nevertheless, dairy efficiency, expressed as milk/DM intake, was highest for the LF+EPE diet. Addition of EPE to the diet increased milk fat and milk lactose percentages, but decreased milk protein percentage of cows fed a low forage diet. For cows fed high forage diets, EPE only increased milk lactose percentage. Efficiency of N use for milk production was decreased for both the high and low forage diets when EPE was added to the diet. Mean ruminal pH was lowered when EPE was added a low forage diet, likely due to the increased degradation of forage and concentrate, but there was no effect of EPE on rumen pH when cows were fed high forage diets. Profiles of VFA and microbial yield were not affected by adding EPE to the diets. Adding EPE to a total mixed ration containing alfalfa hay, barley silage, and concentrate improved nutrient digestibility in the total tract, and the response was maximized with a high concentrate diet. However, improvements in digestibility were offset by decreased feed intake, likely due to increased ruminal acidosis.     

Influence of feeding supplements of almond hulls and ensiled citrus pulp on the milk production,milk composition,and methane emissions of dairy cows

Almond hulls and citrus pulp have been fed to dairy cows with variable responses for milk production, but no information exists on their effect on enteric methane emissions. This experiment examined the effects of dietary supplementation with either almond hulls or ensiled citrus pulp on the milk yield, milk composition, and enteric methane emissions of dairy cows. Thirty-two Holstein dairy cows in mid lactation were offered 1 of 3 diets over a 28-d experiment. Twelve cows received a control (CON) diet, 10 cows a diet containing almond hulls (ALH), and 10 cows a diet containing ensiled citrus pulp (CIT). All cows were offered 6.0 kg of dry matter (DM)/d of crushed corn, 2.0 kg of DM/d of cold-pressed canola, and 0.2 kg of DM/d of a mineral mix. In addition, cows fed the CON diet were offered 14.5 kg of DM/d of alfalfa cubes; cows fed the ALH diet were offered 10.5 kg of DM/d of alfalfa cubes and 4.0 kg of DM/d of almond hulls; and cows on the CIT diet were offered 11.5 kg of DM/d of alfalfa cubes and 3.0 kg of DM/d of ensiled citrus pulp. Milk yield was measured daily and milk composition was measured on 4 d of each week. Individual cow methane emissions were measured by a sulfur hexafluoride tracer technique on d 24 to 28 of the experiment. The mean milk yield of cows fed the CON diet (27.4 kg/d) was greater than the mean milk yield of cows fed the ALH diet (24.6 kg/cow per day), whereas the mean milk yield of cows fed the CIT diet (26.2 kg/cow per day) was not different from the mean milk yield from cows fed the other 2 diets. Dietary treatment did not influence the concentrations of milk fat, protein, and lactose or fat yields, but the mean protein yield from cows fed the CON diet (0.87 kg/d) was greater than that from cows fed the ALH diet (0.78 kg/d) but not different to those fed the CIT diet (0.85 kg/d). In general, we found no differences in the proportion of individual fatty acids in milk. The mean pH of ruminal fluid from cows offered the CON diet was not different to the pH in the ruminal fluids of cows offered the ALH or the CIT diets. The mean methane emissions (g/d) and yields (g/kg of DM intake) were not influenced by dietary treatment. These findings indicate that, although almond hulls and ensiled citrus pulp can be used as a low-cost feed supplement, almond hulls did negatively affect milk production and neither inhibited enteric methane emissions.     

Effects of feeding alkaline hydrogen peroxide-treated wheat straw-based diets on digestion and production by dairy cows

Twelve Holstein cows, averaging 34 d postpartum, were used in three replications of a 4 x 4 Latin square design to determine the effects of feeding different levels of alkaline hydrogen peroxide-treated wheat straw on digestion and production responses in lactating dairy cows. Complete mixed diets consisted of 50% concentrate (DM basis) plus varying proportions of treated wheat straw, alfalfa haylage, and corn silage as the forage source. Treatment contained 0 (control), 12.5 (low), 25.0 (medium), or 37.5% (high) treated wheat straw in the diet. Dry matter intakes were 18.5, 17.2, 17.4, and 16.7 kg/d for the four treatments, respectively. Apparent digestibilities of DM and OM were decreased (approximately 4.4 percentage units), and NDF and ADF digestibilities were increased by 9.4 and 3.0 percentage units, respectively, with the high wheat straw diet. Yields of milk and 4% FCM, and SNF percentage did not differ among the treatment groups. Milk fat percentage increased (from 3.07 to 3.32%) and milk protein percentage decreased (from 2.61 to 2.56%) as the proportion of treated wheat straw increased in the diet. Cows fed the higher proportions of treated wheat straw had increased ruminal concentrations of total VFA and molar percentage acetate but a decreased molar percentage propionate, resulting in a greater acetate to propionate ratio. Cows fed the low and medium wheat straw diets had slightly lower DM intakes but production responses were similar to cows fed the control diet containing alfalfa haylage and corn silage as fiber sources.     

Effects of partial mixed rations and supplement amounts on milk production and composition,ruminal fermentation,bacterial communities,and ruminal acidosis

Late-lactation Holstein cows (n = 144) that were offered 15 kg dry matter (DM)/cow per day of perennial ryegrass to graze were randomized into 24 groups of 6. Each group contained a fistulated cow and groups were allocated to 1 of 3 feeding strategies: (1) control (10 groups): cows were fed crushed wheat grain twice daily in the milking parlor and ryegrass silage at pasture; (2) partial mixed ration (PMR; 10 groups): PMR that was isoenergetic to the control diet and fed twice daily on a feed pad; (3) PMR+canola (4 groups): a proportion of wheat in the PMR was replaced with canola meal to produce more estimated metabolizable protein than other groups. Supplements were fed to the control and PMR cows at 8, 10, 12, 14, or 16 kg of DM/d, and to the PMR+canola cows at 14 or 16 kg of DM/d. The PMR-fed cows had a lower incidence of ruminal acidosis compared with controls, and ruminal acidosis increased linearly and quadratically with supplement fed. Yield of milk fat was highest in the PMR+canola cows fed 14 or 16 kg of total supplement DM/d, followed by the PMR-fed cows, and was lowest in controls fed at these amounts; a similar trend was observed for milk fat percentage. Milk protein yield was higher in the PMR+canola cows fed 14 or 16 kg of total supplement DM/d. Milk yield and milk protein percentage were not affected by feeding strategy. Milk, energy-corrected milk, and milk protein yields increased linearly with supplement fed, whereas milk fat percentage decreased. Ruminal butyrate and d-lactate concentrations, acetate-to-propionate ratio, (acetate + butyrate)/propionate, and pH increased in PMR-fed cows compared with controls for all supplement amounts, whereas propionate and valerate concentrations decreased. Ruminal acetate, butyrate, and ammonia concentrations, acetate-to-propionate ratio, (acetate + butyrate)/propionate, and pH linearly decreased with amounts of supplement fed. Ruminal propionate concentration linearly increased and valerate concentration linearly and quadratically increased with supplement feeding amount. The Bacteroidetes and Firmicutes were the dominant bacterial phyla identified. The Prevotellaceae, Ruminococcaceae, and Lachnospiraceae were the dominant bacterial families, regardless of feeding group, and were influenced by feeding strategy, supplement feeding amount, or both. The Veillonellaceae family decreased in relative abundance in PMR-fed cows compared with controls, and the Streptococcaeae and Lactobacillaceae families were present in only minor relative abundances, regardless of feeding group. Despite large among- and within-group variation in bacterial community composition, distinct bacterial communities occurred among feeding strategies, supplement amounts, and sample times and were associated with ruminal fermentation measures. Control cows fed 16 kg of DM of total supplement per day had the most distinct ruminal bacterial community composition. Bacterial community composition was most significantly associated with supplement feeding amount and ammonia, butyrate, valerate, and propionate concentrations. Feeding supplements in a PMR reduced the incidence of ruminal acidosis and altered ruminal bacterial communities, regardless of supplement feeding amount, but did not result in increased milk measures compared with isoenergetic control diets component-fed to late-lactation cows.     

Including 8 hours of access to alfalfa in 1 or 2 grazing sessions in dairy cows fed a partial mixed ration: Effects on intake,behavior, digestion,and milk production and composition

The aim of this study was to evaluate the inclusion of alfalfa grazing during 8 h continuous or partitioned in 2 separated sessions of 4 h after each milking, on nutrient intake, digestibility, ruminal fermentation, feeding behavior, milk production, milk composition, and milk fatty acid profile, in late-lactation cows fed a partial mixed ration (PMR). Twelve dairy cows (193 ± 83 d in milk, 584 ± 71 kg of body weight) were housed in individual outdoor pens and assigned to treatments according to a 3 × 3 Latin square design replicated 4 times. The treatments were as follows: (1) control (T0), cows were fed a total mixed ration (TMR) provided ad libitum 20.0% crude protein (CP), 32.2% neutral detergent fiber (NDF); (2) fed a diet combining a PMR which had the same ingredient composition as the TMR (60% of ad libitum intake) + 1 session of 8 h of pasture (T8), continuous grazing alfalfa (Medicago sativa; 20.6% CP, 35.8% NDF) after the p.m. milking; and (3) PMR (60% of ad libitum intake) + 2 daily sessions of 4 h of access to pasture after each milking (T4+4). The experiment lasted 57 d and was divided into 3 periods of 19 d each. The first 12 d of each period was used for diet adaptation, and the last 7 d was used for data collection. No differences among treatments were observed for any of the productive variables, feeding efficiency, or purine derivatives excretion. Cows in T0 had greater intake and apparent digestibility of dry matter, organic matter, and nonfibrous carbohydrates compared with T4+4 and T8. Compared with T0, alfalfa grazing increased the concentration of C18:1 trans-11 and decreased those of C16:0 and C17:0 in milk fat. Cows in T4+4 consumed 1.1 more kg DM/d of alfalfa and N provided by alfalfa in the diet was 3 percentage points higher compared with T8 cows (266 vs. 229 g/d, respectively). In addition, T4+4 cows had a greater daily range of ruminal pH than T8 (0.73 vs. 0.93), and the highest concentrations of NH₃-N were recorded during the a.m. grazing session while in T8 cows it occurred during the night. In conclusion, including 8 h of alfalfa grazing in T8 and T4+4 treatments allowed the substitution between 35.8 and 38.7% of the total dry matter intake (DMI) of a PMR (with a similar CP concentration to alfalfa) for pasture, maintaining milk solids production and increasing the C18:1 trans-11 of milk fat compared with a TMR in mid late–lactation cows. In an herbage plus PMR diet, splitting the 1 continuous grazing session of 8 h into 2 sessions of 4 h increased the proportion of energy and N provided by alfalfa pasture and reduced PMR intake, without modifying the total nutrient intake or productive performance of cows.     

Effect of dietary concentrate on rumen fermentation, digestibility, and nitrogen losses in dairy cows

The objective of this experiment was to investigate the effect of level of dietary concentrate on rumen fermentation, digestibility, and N losses in lactating dairy cows. The experiment was a replicated 3 × 3 Latin square design with 6 cows and 16-d adaptation periods. Ruminal contents were exchanged between cows at the beginning of each adaptation period. Data for 2 of the diets tested in this experiment are presented here. The diets contained (dry matter basis): 52% (LowC; control) and 72% (HighC) concentrate feeds. Crude protein contents of the diets were 16.5 and 16.4%, respectively. The HighC diet decreased ruminal pH and ammonia concentration and increased propionate concentration compared with LowC. Acetate:propionate ratio was greater for LowC than for HighC. Rumen methane production and microbial protein synthesis were unaffected by diet. Dry matter intake was similar among diets, but milk yield was increased by HighC compared with LowC (36.0 and 33.2 kg/d, respectively). Milk fat percentage and yield and total-tract apparent NDF digestibility were decreased by HighC compared with LowC. More ruminal ammonia N was transferred into milk protein with HighC than with LowC. Urinary N excretion, plasma urea N, and milk urea N concentration were not affected by diet. The ammonia emitting potential of manure was similar between LowC and HighC diets. Increased concentrate proportion in the diet of dairy cows resulted in reduced ruminal ammonia concentration and enhanced ammonia utilization for milk protein synthesis. These effects, however, did not result in reduced urinary N losses and only marginally improved milk N efficiency. Increasing dietary concentrate was not a successful strategy to mitigate enteric methane production and ammonia emissions from manure.     

Effect of fibrous by-products on production and ruminal fermentation in lactating dairy cows

Lactating dairy cows were used in experiments to determine the effects of feeding a combination of fibrous by-products to replace a portion of alfalfa hay or grain. Cows were fed a control diet, consisting of alfalfa hay, corn, soybean meal, and corn silage or one of four treatment diets. In these diets, a combination of soy hulls, corn gluten feed, and wheat midds replaced approximately 30 or 60% of alfalfa hay or 25 or 50% of corn and soybean meal. A 56-d production study used 50 midlactation dairy cows in a randomized complete block design. No differences in milk production or composition among treatments were measured, except for the diet in which 60% of the alfalfa hay was replaced with fibrous by-products. Cows fed this diet had a significantly lower percentage of milk fat compared with other treatments. A fermentation study used five fistulated, multiparous lactating dairy cows in a 5 x 5 Latin square design. Cows were fed one of the five experimental diets used in the production study during five consecutive 14-d periods. Rumen acetate to propionate ratio was highest for the control and 50% concentrate replacement diets (3.27) and lowest for the 60% hay replacement diet (2.78). This shift in ruminal volatile fatty acid profile corresponded to the change in milk fat percentage, measured during the production study. A mixture of fibrous by-products fed as an alternative to hay or grain ingredients could potentially decrease feed costs without a resultant decrease in milk production by mid-lactation dairy cows.     

Influence of carbohydrate source on ruminal fermentation characteristics, performance, and microbial protein synthesis in dairy cows

Eight multiparous Holstein cows (676 ± 57 kg of body weight; 121 ± 17 d-in-milk) were used in a replicated 4 × 4 Latin square design to determine the effects of 4 sources of carbohydrate on milk yield and composition, ruminal fermentation, and microbial N flow to the duodenum. Four cows in one of the Latin squares were fitted with permanent ruminal cannulae. Diets contained (DM basis) 50% forage in combinations of alfalfa hay and barley silage, and 50% concentrate. The concentrate portion of the diets contained barley, corn, wheat, or oats grain as the primary source of carbohydrate. Intake of DM ranged from 24.0 to 26.2 kg/d, and it tended to be lower in cows fed the wheat-based diet compared with those fed the barley-based diet; consequently, milk yield tended to be lower in cows fed the wheat-based diet compared with those fed the barley-based diet. Cows fed the barley- or wheat-based diets had a lower milk fat content compared with those fed the corn-based diet. Ruminal fermentation characteristics were largely unaffected by the source of dietary carbohydrate, with similar ruminal pH and volatile fatty acid and ammonia concentrations for the first 6 h after the morning feeding. Dietary treatment did not affect total tract apparent digestibility of DM, organic matter, and neutral detergent fiber; however, total tract apparent digestibility of starch in cows fed the oats-based diet was higher compared with those fed the corn-and wheat-based diets. Nitrogen that was used for productive purposes (i.e., N secreted in milk + N apparently retained by the cow) tended to be lower in cows fed the wheat-based diet compared with cows fed the barley-, corn-, or oats-based diets. Urinary purine derivative (PD) excretion was similar in cows fed the barley-, corn-, and wheat-based diets; however, purine derivative excretion was higher in cows fed the barley-based diet compared with those fed the oats-based diet. Consequently, estimated microbial N flow to the duodenum was 49 g/d higher in cows fed the barley-based diet compared with those fed the oats-based diet. Improved production performance with corn and barley diets appeared to be due to greater nutrient absorption than in cows fed oats and wheat diets, rather than improved nutrient utilization efficiency.     

Sodium bicarbonate and alfalfa hay additions to wheat silage diets fed to lactating dairy cows

Two experiments were conducted to examine dietary effects of .8% sodium bicarbonate and 1.4 kg/d of alfalfa hay on performance and rumen metabolism of lactating dairy cows fed 50% wheat silage and 50% concentrate (dry basis). In Experiment 1 with 12 midlactation Holsteins in a 4 X 4 Latin square design, intake, milk production, and milk composition were not affected by treatment. Dietary sodium bicarbonate and alfalfa hay did not alter blood, rumen, or fecal pH. Rumen volatile fatty acid pattern was not affected by sodium bicarbonate, but addition of hay resulted in higher molar percentage propionate and lower acetate: propionate ratios. In Experiment 2 with 32 early lactation cows (20 Holsteins and 12 Jerseys) in a complete randomized block design, supplementation of sodium bicarbonate, alfalfa hay, or both did not affect intake, milk production, or milk composition in the first 8 wk of lactation. Blood, rumen, and fecal pH were not affected by treatment. Dietary sodium bicarbonate did not alter ruminal volatile fatty acid profile, whereas addition of hay increased molar proportion acetate and decreased molar proportion butyrate. A shift in rumen fermentation was observed across treatments from wk 1 through 8 postpartum with molar proportions of acetate and butyrate increasing and molar proportion of propionate decreasing.     

Effects of differences in starch content of diets with whole cottonseed or rice bran on milk casein

Forty lactating Holstein cows in early to midlactation were used in a randomized complete block design to measure the effects of the following diets on milk casein. Treatments were four complete rations fed for ad libitum intake consisting of 1) 60% concentrate, 10% alfalfa hay, and 30% corn silage; 2) 45% concentrate, 10% alfalfa hay, 30% corn silage, and 15% whole cottonseed; 3) 60% concentrate, 5% alfalfa hay, 20% corn silage, and 15% whole cottonseed; and 4) 45% concentrate, 10% alfalfa hay, 30% corn silage, and 15% rice bran. Least squares means for daily DM intake all were significantly different and were 3.51, 3.90, 3.28, and 3.74% BW, respectively. Cows fed diet 3 had higher arterial glucose and insulin and venous insulin. Least squares means were significantly different for milk yield, 30.1, 31.4, 28.4, and 31.6 kg/d; for milk protein, 3.30, 3.13, 3.48, and 3.12%; and for casein N, .376, .358, 3.73, and .330, respectively. However, milk protein and casein N yields were similar for all cows. The diet that contained the highest percentage of starch did not result in a significantly higher percentage of casein N in the milk but had the lowest milk production. Both whole cottonseed and rice bran, substituted for concentrate, depressed milk protein percentage.     

Rumen fermentation in lactating cows selected for milk fat content fed two forage to concentrate ratios with hay or silage

Sixteen multiparous cows, including eight rumen fistulated cows, were used in a 4x4 Latin square experiment designed to study dietary effects on rumen and blood parameters and milk production in cows differing in genetic capacity for milk fat content. Diets contained forage to concentrate ratios of 50:50 or 30:70 with either grass hay or silage as the forage. Ruminal fermentation was characterized by a high molar percentage of butyrate, 14 to 17%. Forage to concentrate ratio affected most rumen parameters, with the exception of the molar percentage of propionate (18 to 19%). The silage had a higher fiber degradation rate compared with hay. Compared to hay diets, silage diets had higher ruminal outflow rates, lower acetate:propionate ratios, and greater milk production with no differences in milk composition. Cows selected for low milk fat had higher molar percentages of propionate in the rumen. The low milk fat cows had higher milk production than cows selected for high milk fat but did not differ in milk fat yield. Cows fed the 30:70 diets had higher plasma insulin concentrations in response to a glucose challenge. The low milk fat cows had lower basal concentrations of insulin and lower insulin responses to a glucose challenge. Small changes in nutrient metabolism and supply were sufficient to influence milk production.     

Effects of an enzyme feed additive on extent of digestion and milk production of lactating dairy cows

A study was conducted using lactating Holstein cows with ruminal and duodenal cannulas in a 4 x 4 Latin square design to investigate fibrolytic enzyme supplementation on site and extent of nutrient digestion. The four diets consisted of 45% concentrate, 10% barley silage, and 45% cubed alfalfa hay (dry matter basis) and differed in enzyme supplementation: 1) control cubes, 2) cubes treated with 1 g of enzyme mixture/kg of cubes, 3) cubes treated with 2 g of enzyme mixture/kg of cubes, and 4) both concentrate and cubes treated with 1 g of enzyme mixture/kg of dry matter. The enzyme supplement contained primarily cellulase and xylanase activities. Digestion of organic matter and neutral detergent fiber in the total tract was higher for cows fed the high dosage of enzyme than for cows fed the control cubes. Ruminal digestibility of crude protein was higher, but that of organic matter and neutral detergent fiber was only numerically higher, for cows fed the high dosage of enzyme compared with that of cows fed the control cubes. Higher ruminal digestibility associated with the high dosage of enzyme resulted in more microbial protein synthesis. Milk production increased for cows fed the high dosage of enzyme compared with cows fed the control cubes and effects of the addition of enzyme on milk composition were minimal. The results demonstrated the benefits of using a fibrolytic enzyme additive to enhance feed digestion and milk production by dairy cows. The response to enzyme supplementation was affected more by amount of enzyme than by whether the enzyme was added to forage or concentrate.     

Alfalfa baleage with increased concentration of nonstructural carbohydrates supplemented with a corn-based concentrate did not improve production and nitrogen utilization in early lactation dairy cows

The objective of this study was to investigate the effects of feeding alfalfa baleage with different concentrations of nonstructural carbohydrates (NSC) supplemented with a common corn-based concentrate on performance, ruminal fermentation profile, N utilization, and omasal flow of nutrients in dairy cows during early lactation. Ten multiparous (8 ruminally cannulated) and 8 primiparous Holstein cows were randomly assigned to treatments (high- or low-NSC diet) in a crossover design. The difference in NSC concentration between the 2 alfalfa baleages fed from d 14 to 21 averaged 14 g of NSC/kg of dry matter (DM). Forages and concentrate were offered in separate meals with forages fed once and concentrate offered 3 times daily. Except for the molar proportion of valerate, which was lowest in cows fed the high-NSC diet, no other changes in ruminal fermentation were observed. Omasal flows of most nitrogenous fractions, including bacterial nonammonia N and AA, were not affected by treatments. Apparent ruminal digestibilities of neutral and acid detergent fiber and N were lowest, whereas that of total ethanol-soluble carbohydrates was highest when feeding the high-NSC diet. Postruminal digestibilities of DM, organic matter, fiber, and N were highest in cows fed the high-NSC diet, resulting in no difference in total-tract digestibilities. Total-tract digestibility of total ethanol-soluble carbohydrates was highest in cows fed the high-NSC diet, but that of starch did not differ across treatments. Although milk yield and total DM intake did not differ between treatments, yields of milk fat and 4% fat-corrected milk decreased significantly in cows fed the high-NSC diet. Milk concentration of urea N was lowest, and that of ruminal NH₃-N highest, in cows fed the high-NSC diet. Plasma urea N concentration tended to be decreased in cows fed the high-NSC diet, but concentrations of AA were not affected by treatments, with the exception of Asp and Cys, both of which were lowest in cows fed the low-NSC diet. Feeding diets with contrasting NSC concentrations did not improve milk production, N utilization, or bacterial protein synthesis, possibly because intakes of NSC and DM were similar between treatments. Overall, results from the current study should be interpreted cautiously because of the lack of difference in dietary NSC intake between treatments and reduced N and fiber intakes when feeding the high-NSC diet.     

Performance of dairy cattle fed citrus pulp or corn products as sources of neutral detergent-soluble carbohydrates

The effects of modifying the dietary profile of neutral detergent-soluble carbohydrates (NDSC) on milk production and rumen fermentation were determined. Corn silage and alfalfa hay-based diets were formulated to contain 40% calculated NDSC supplied primarily by dried citrus pulp as a source of neutral detergent-soluble fiber (NDSF), or corn products as sources of starch. Diets were compared within cow with reversal experiments with two periods. In experiment 1, 11 multiparous Holstein cows including three ruminally cannulated animals were individually fed diets containing 23.6% citrus pulp (diet CPD) or 25.3% corn hominy (diet HD) on a dry matter basis. In experiment 2, 184 animals fed as two groups received diets containing 20.5% citrus pulp (diet CPD) or 19.5% cornmeal (diet CMD). Diets CPD provided more dietary NDSF and HD and CMD more starch. In experiment 1, cows fed HD had a greater milk protein percentage (+0.12%), and tended to yield more milk protein (0.08 kg/d) than cows fed CPD. Although ruminal H+ concentrations did not differ between diets, diet x time postfeeding interactions were significant. Ruminal organic acid concentrations did not differ between diets. In experiment 2, cows fed CMD yielded more milk (3.9 kg/d), 3.5% fat- and protein-corrected milk (2.6 kg/d), fat (0.05 kg/d), and protein (0.08 kg/d), whereas cows fed CPD produced greater concentrations of fat (+0.18%), and milk urea nitrogen (0.76 mg/dl). Modifying the proportions of NDSC in the diet can alter milk production and composition, the pattern of ruminal fermentation, and N utilization in dairy cows.     

Nutrient digestion and lactation performance of dairy cows fed combinations of prilled fat and canola oil.

Four combinations of prilled fat and canola oil were fed to 10 lactating Holstein cows in a replicated 5 x 5 Latin square to determine whether mixing plant oil with a rumen inert fat had additive effects on digestive and lactation responses. Five diets of concentrate and corn silage (1:1, DM basis) contained either no added fat (control) or 5% fat comprising 100, 67, 33, or 0% prilled fat and the remainder canola oil. The fat supplement containing 100% prilled fat appeared to be rumen-inert because it caused no changes in ruminal VFA concentration, acetate to propionate ratio, or total tract fiber digestion. Prilled fat increased milk production, FCM, and milk fat percentage but decreased milk protein percentage, including casein content. Increasing canola oil in the fat supplement caused linear declines in ruminal VFA, acetate to propionate ratio, and milk production. Milk production efficiency (weight FCM/weight DMI) exceeded the control diet when fat supplements contained 100 or 67% prilled fat but dropped below control for 33 and 0% prilled fat. This study demonstrates additive effects of combining canola oil with hydrogenated, prilled fat on ruminal fermentation but nonadditive effects on milk production efficiency and milk composition. At low levels of supplementation, plant oils, such as the canola oil used in this study, can inhibit ruminal fermentation but still maintain milk production efficiency.