Rumen fermentation and intestinal supply of nutrients in dairy cows fed rumen-protected soy products

Four multiparous lactating Holstein cows that were fistulated in the rumen and duodenum and that averaged 205 d in milk were used in a 4 × 4 Latin square design to evaluate the practical replacement of solvent-extracted soybean meal (SSBM) with soy protein products of reduced ruminal degradability. On a dry matter (DM) basis, diets contained 15% alfalfa silage, 25% corn silage, 34.3 to 36.9% corn grain, 19.4% soy products, 18.2% crude protein, 25.5% neutral detergent fiber, and 35.3% starch. In the experimental diets, SSBM was replaced with expeller soybean meal (ESBM); heated, xylose-treated soybean meal (NSBM); or whole roasted soybeans (WRSB) to supply 10.2% of the dietary DM. Intakes of DM (mean = 20.4 kg/d), organic matter, and starch were unaffected by the source of soy protein. Similarly, true ruminal fermentation of organic matter and apparent digestion of starch in the rumen and total tract were not altered by treatments. Intake of N ranged from 567 (WRSB) to 622 g/d (ESBM), but differences among soy protein supplements were not significant. Compared with SSBM, the ruminal outflow of nonammonia N was higher for NSBM, tended to be higher for ESBM, and was similar for WRSB. The intestinal supply of nonammonia nonmicrobial N was higher for NSBM and WRSB and tended to be higher for ESBM than for SSBM. However, no differences were detected among treatments when the flow to the duodenum of nonammonia nonmicrobial N was expressed as a percentage of N intake or nonammonia N flow. The ruminal outflow of microbial N, Met, and Lys was not altered by the source of soy protein. Data suggest that partially replacing SSBM with ESBM, NSBM, or WRSB may increase the quantity of feed protein that reaches the small intestines of dairy cows. However, significant improvements in the supply of previously reported limiting amino acids for milk production, particularly of Met, should not be expected.     

Selection of barley grain affects ruminal fermentation, starch digestibility, and productivity of lactating dairy cows

The objective of this study was to evaluate the effects of 2 lots of barley grain cultivars differing in expected ruminal starch degradation on dry matter (DM) intake, ruminal fermentation, ruminal and total tract digestibility, and milk production of dairy cows when provided at 2 concentrations in the diet. Four primiparous ruminally cannulated (123 ± 69 d in milk; mean ± SD) and 4 multiparous ruminally and duodenally cannulated (46 ± 14 d in milk) cows were used in a 4 × 4 Latin Square design with a 2 × 2 factorial arrangement of treatments with 16-d periods. Primiparous and multiparous cows were assigned to different squares. Treatments were 2 dietary starch concentrations (30 vs. 23% of dietary DM) and 2 lots of barley grain cultivars (Xena vs. Dillon) differing in expected ruminal starch degradation. Xena had higher starch concentration (58.7 vs. 50.0%) and greater in vitro 6-h starch digestibility (78.0 vs. 73.5%) compared with Dillon. All experimental diets were formulated to supply 18.3% crude protein and 20.0% forage neutral detergent fiber. Dry matter intake and milk yield were not affected by treatment. Milk fat concentration (3.55 vs. 3.29%) was greater for cows fed Dillon compared with Xena, but was not affected by dietary starch concentration. Ruminal starch digestion was greater for cows fed high-starch diets compared with those fed low-starch diets (4.55 vs. 2.49 kg/d), and tended to be greater for cows fed Xena compared with those fed Dillon (3.85 vs. 3.19 kg/d). Ruminal acetate concentration was lower, and propionate concentration was greater, for cows fed Xena or high-starch diets compared with cows fed Dillon or low-starch diets, respectively. Furthermore, cows fed Xena or high-starch diets had longer duration that ruminal pH was below 5.8 (6.6 vs. 4.0 and 6.4 vs. 4.2 h/d) and greater total tract starch digestibility (94.3 vs. 93.0 and 94.3 vs. 93.0%) compared with cows fed Dillon or low-starch diets, respectively. These results demonstrate that selection of barley grain can affect milk fat production and rumen fermentation to an extent at least as great as changes in dietary starch concentration.     

Effects of a subacute ruminal acidosis model on the diet selection of dairy cows

Two experiments were conducted to study the effects of a subacute ruminal acidosis (SARA) model on diet choice in dairy cows. In the first experiment, 25% of the ad libitum dry matter intake (DMI) of the total mixed ration (TMR) was replaced with wheat-barley pellets (WBP, 50% ground wheat, 50% ground barley). Rumen pH was measured continuously via in-dwelling probes in 4 mid to late lactation cows. This diet change reduced rumen pH by 0.14 +/- 0.02 pH units (mean +/- SE) and increased time below pH 6.0, from 319 +/- 36 min(-1) to 641 +/- 36 min(-1). Hence, the nutritional model successfully induced SARA. The second experiment determined if inducing SARA increases the feed preference for long alfalfa hay compared with alfalfa pellets. The 2 wk of inducing SARA were separated by 1 control wk. Four cows on either SARA and control diets were given a choice of 2 feeds, 2 times per d, for 30 min. The preference ratios (PR = Amount of Hay consumed/Amount of Hay + Pellets consumed) for alfalfa hay during two SARA weeks was greater (0.85 +/- 0.03) compared with the control week (0.60 +/- 0.03). In SARA weeks, average rumen pH was 0.23 +/- 0.03 units lower, and time below pH 6.0 and 5.6 was higher compared to control. These results suggest that when given a choice of feeds, dairy cows alter their diet selection to attempt to attenuate SARA.     

Varying protein and starch in the diet of dairy cows. II. Effects on performance and nitrogen utilization for milk production

The main objective of this experiment was to examine the effects of the percentage and source of crude protein (CP) and the amount of starch in the diet of dairy cows on the lactational performance and use of N for milk production. Sixty multiparous Holstein cows were used in a 210-d lactational trial with a completely randomized design with a 2 × 3 factorial arrangement of treatments. Two sources of CP [solvent-extracted soybean meal (SBM) and a mixture of SBM and a blend of animal-marine protein supplements plus ruminally protected Met (AMB)] and 3 levels of dietary CP (means = 14.8, 16.8, and 18.7%) were combined into 6 treatments. On a dry matter (DM) basis, diets contained 25.0% corn silage, 20.0% alfalfa silage, 10.0% cottonseed, 26.7 to 37.0% corn grain, and 4.8 to 13.5% protein supplement, plus minerals and vitamins. Across the 210 d of lactation, the productive response of dairy cows to the source of supplemental CP depended on the concentration of CP in the diet. At 18.7% CP, cows fed SBM consumed more DM and produced more milk, 3.5% fat-corrected milk, fat, and true protein, but had lower efficiency of feed use and body condition score than cows fed AMB. At 16.8% CP, cows fed AMB produced more 3.5% fat-corrected milk, fat, and true protein than cows fed SBM. At 14.8% CP, cows fed SBM consumed more DM but produced less true protein and had lower feed efficiency than cows fed AMB. Across CP sources, cows fed 14.8% CP produced less fat-corrected milk and true protein than cows fed 16.8 and 18.7% CP. Across CP percentages, cows fed AMB produced more fat-corrected milk per kilogram of DM consumed than cows fed SBM. Despite these interactions, improvements in the gross efficiency of N use for milk production were achieved through reductions in the intake of N independently of the source of CP. Data suggest that the intake of N by high-producing dairy cows that consume sufficient energy and other nutrients to meet their requirements can be decreased to about 600 to 650 g daily if the source of RDP and RUP are properly matched with the source and amount of carbohydrate in the diet.     

Effects of monensin on ruminal forage degradability and total tract diet digestibility in lactating dairy cows during grain-induced subacute ruminal acidosis

The effects of monensin premix supplementation on ruminal pH characteristics and forage degradability, and total tract diet digestibility during grain-induced subacute ruminal acidosis (SARA) in lactating dairy cows receiving a total mixed ration were investigated. Six multiparous, rumen-fistulated Holstein cows were used in a 2-treatment, 2-period (5 wk per period) crossover design. During wk 5 (d 29 to 35) of each period, SARA was induced using a grain challenge model, and ruminal pH was measured continuously using indwelling pH probes. Ruminal degradation of corn silage and alfalfa haylage was determined using the in situ (nylon bag) technique, and total tract diet digestibility was determined by total fecal collection during wk 5. Monensin supplementation did not affect dry matter intake, milk yield, and composition, and ruminal pH characteristics under these experimentally induced SARA conditions. Rates of ruminal forage fiber degradability were similar between control and monensin-treated cows; however, monensin supplementation increased total tract fiber digestion. This study indicates that monensin altered total tract nutrient digestion by increasing fiber digestion at postruminal sites.     

Effects of yeast culture and galacto-oligosaccharides on ruminal fermentation in holstein cows

Four nonlactating, ruminally cannulated Holstein cows were used in a 4 x 4 Latin square design, balanced for residual effects, to evaluate the effects of supplementing dairy cow diets with yeast culture (Trichosporon sericeum; YC), galacto-oligosaccharides (GOS), or the mixture of YC and GOS on ruminal fermentation, microbial N supply, in situ degradation, and energy and nitrogen metabolism. Treatments were arranged in a 2 x 2 factorial as follows: 1) basal diet, 2) basal diet plus 10 g/d YC, 3) basal diet plus 2% GOS, 4) basal diet plus a mixture of 10 g/d YC and 2% GOS. Nitrogen losses in urine were lower, and retained N was higher, for cows supplemented with a mixture of YC and GOS. Ruminal pH was lower in cows supplemented with GOS alone compared with other treatments. Total VFA concentration was higher in cows fed control and GOS-supplemented diets than in those fed YC containing diets. The molar proportion of propionate was higher, and the molar proportion of acetate was lower, in cows fed control diets. Microbial N supply was higher in cows fed control diets. There were no major positive effects of supplements observed in this study. However, supplementation of a mixture of YC and GOS had a tendency for synergistic effects on N metabolism and in situ degradation of a soluble fraction of oat straw DM and CP of concentrates compared with supplementation of YC or GOS alone.     

Heat- and lignosulfonate-treated canola meal as a source of ruminal undegradable protein for lactating dairy cows

This experiment used 18 lactating Holstein cows in a 3 x 3 Latin square replicated 6 times to determine the effectiveness of processing with moist heat or moist heat combined with lignosulfonate (LSO3) for increasing the ruminal undegradable fraction of canola meal for use as a protein supplement for lactating dairy cows. Diets were formulated to be isonitrogenous and contained one of 3 forms of canola meal; untreated canola meal (UCM), heat-treated canola meal (HTCM) or heat-and LSO3-treated canola meal (LSO3CM). Total collection of urine and feces was taken from each cow during the last 5 d of each 42-d experimental period. Milk production was greater for cows fed the LSO3CM diet (36.6 kg/d) than for cows fed the UCM diet (34.8 kg/d) but did not differ from cows fed the HTCM diet (35.3 kg/d). Digestibility of crude protein was lower for cows supplemented with LSO3CM and they had reduced concentrations of ruminal ammonia N, blood urea N, and milk urea N compared with cows supplemented with UCM or HTCM. Dry matter intake and apparent digestibilities of neutral and acid detergent fiber were increased in cows fed the LSO3CM diet. Urinary N excretion (as % of N intake) was reduced in cows fed the LSO3CM diet. These results indicate that moist heat combined with LSO3 treatment of canola meal was effective in increasing the proportion of crude protein digested in the lower digestive tract of lactating cows and was therefore used more effectively as a source of protein than UCM or HTCM.     

Effect of sodium laurate on ruminal fermentation and utilization of ruminal ammonia nitrogen for milk protein synthesis in dairy cows

A crossover design trial with 4 ruminally and duodenally cannulated lactating dairy cows was conducted to study the effect of sodium laurate on ruminal fermentation, nutrient digestibility, and milk yield and composition. The daily dose of sodium laurate (0, control or 240 g/cow, LA) was divided in 2 equal portions and introduced directly into the rumen through the cannula before feedings. Ruminal samples (29 in 114 h) were analyzed for fermentation variables and protozoal counts. Sodium laurate had no effect on ruminal pH and total and individual volatile fatty acids concentrations. Ruminal ammonia concentration, ammonia N pool size, and the irreversible loss of ammonia N were unaffected by treatment. Compared to control, protozoal counts were reduced by 91% by LA. Carboxymethylcellulase and xylanase activities of ruminal fluid were decreased (by 40 and 36%, respectively), and amylase activity was not affected by LA compared with control. Flow of microbial N to the duodenum was reduced by LA. Dry matter intake and apparent total tract digestibility of dry matter, organic matter, crude protein, neutral detergent fiber, and acid detergent fiber were not different between the 2 treatments. Milk yield, fat-corrected milk yield, milk fat and protein concentrations and yields, and milk urea N content were not affected by treatment. Sodium laurate did not affect transfer of ruminal ammonia-15N into bacterial or milk protein. In conclusion, LA at approximately 0.3% of the rumen weight reduced ruminal protozoal population and had a negative effect on fibrolytic activities of ruminal fluid and microbial protein flow to the intestine. Treatment had no other significant effects on ruminal fermentation, total tract digestibility, or transfer of ruminal ammonia-15N into milk protein.     

Effect of essential oils on ruminal fermentation and lactation performance of dairy cows

Three experiments (Exp.) were conducted to study the effects of dietary addition of an essential oil product (EO) based on eugenol and cinnamaldehyde (0, control, or 525 mg/d of Xtract 6965; Pancosma SA, Geneva, Switzerland) on ruminal fermentation, total-tract digestibility, manure gas emissions, N losses, and dairy cow performance. In Exp. 1 and 3, the EO supplement was added to the vitamin-mineral premix. In Exp. 2, EO was top-dressed. Experiments 1 and 2 were crossover designs with 20 multiparous Holstein cows each (including 4 and 8 ruminally cannulated cows, respectively) and consisted of two 28-d periods. Intake of dry matter did not differ between treatments. Most ruminal fermentation parameters were unaffected by EO. Concentrations of ammonia (Exp. 1), isobutyrate (Exp. 1 and 2), and isovalerate (Exp. 1) were increased by EO compared with the control. Apparent total-tract digestibility of nutrients was similar between treatments, except total-tract digestibility of neutral-detergent fiber, which was increased or tended to be increased by EO in Exp. 1 and 2. Manure emissions of ammonia and methane were unaffected by EO. Blood plasma and milk urea-N concentrations and urinary N losses were increased by EO compared with the control in Exp. 1, but not in Exp. 2. Average milk yield, 3.5% fat-corrected milk yield, and milk fat, protein, and lactose concentrations were unaffected by treatment. Urinary excretion of purine derivatives, a marker for microbial protein production in the rumen, was greater in cows receiving the EO diet in Exp. 1, but not in Exp. 2. In Exp. 3, 120 Holstein cows were grouped in pens of 20 cows/pen in a 12-wk experiment to study production effects of EO. Dry matter intake, milk yield (a trend for a slight decrease with EO), milk components, milk urea N, and feed efficiency were similar between treatments. Results from these studies indicate that supplementing dairy cows with 525 mg/d of Xtract 6965 had moderate effects on ruminal fermentation, but consistently increased ruminal isobutyrate concentration and tended to increase total-tract digestibility of neutral-detergent fiber. Under the conditions of these experiments, Xtract 6965 fed at 525 mg/d did not affect milk production or composition.     

Effects of feeding dairy cows protein supplements of varying ruminal degradability

Twenty-five (10 ruminally cannulated) Holstein cows averaging 82 +/- 34 d in milk were assigned to 5 x 5 Latin squares (21-d periods) and fed diets supplemented with one of four different proteins to assess effects on production, ruminal metabolism, omasal flow of N fractions, and degradation rates of protein supplements. Total mixed diets contained (dry matter basis) 44% corn silage, 22% alfalfa silage, 2% urea, and 31% concentrate. Five concentrate mixes were fed: 31% high-moisture shelled corn (HMSC; basal); 9% solvent soybean meal (SSBM), 22% HMSC; 10% expeller soybean meal (ESBM), 21% HMSC; 5.5% blood meal (BM), 25.5% HMSC; and 7% corn gluten meal (CGM), 24% HMSC. Diets averaged, respectively, 15.8, 19.1, 19.7, 20.3, and 19.3% crude protein. Feeding the basal diet reduced intake and yield of milk, fat-corrected milk (FCM), and all milk components compared to the protein-supplemented diets. Milk yield was higher for cows fed ESBM and CGM, fat yield was higher for cows fed SSBM and CGM, but FCM and protein yields were not different among cows fed supplemental protein. Based on omasal sampling, mean in vivo estimates of ruminal degradation rate for the crude protein in SSBM, ESBM, BM, and CGM was, respectively, 0.417, 0.179, 0.098, and 0.051/h (computed using passage rates observed for the small particle phase; mean = 0.14/h), and 0.179, 0.077, 0.042, and 0.026/h (computed using a passage rate of 0.06/h). The in vivo degradation rate computed for SSBM at a passage rate = 0.06/h was similar to that estimated using the inhibitor in vitro method. However, in vivo degradation rates computed at passage rate = 0.06/h for ESBM, BM, and CGM were about two, four, and three times more rapid than those estimated by inhibitor in vitro. Experimental proteins fed in this trial will be used as standards for developing in vitro methods for predicting rates of ruminal protein degradation.     

Amylase addition increases starch ruminal digestion in first-lactation cows fed high and low starch diets

The objective of this study was to evaluate the effect of an exogenous amylase preparation on digestion of low- and high-starch diets in dairy cattle. Rumen and total-tract nutrient digestibility were measured in a 4 × 4 Latin square design with 28-d periods using 4 first-lactation cows cannulated at the rumen and duodenum. Corn silage-based diets had 20 or 30% starch, attained by changing the composition of concentrate, with or without addition of an exogenous amylase preparation. Effects of the enzyme additive were observed on ruminal digestibility but not at the total-tract level. Ruminal digestibility of starch increased from 75% in control to 81% with amylase supplementation. This difference in ruminal starch digestion was compensated postruminally, so that the total-tract digestibility of starch was almost complete and did not differ between treatments. The amylase supplement also increased the true ruminal digestibility of organic matter but did not affect microbial N flow to the duodenum. Amylase supplement reduced the proportion of acetate and butyrate and increased that of propionate, particularly in the high-starch diet, where it tended to increase the concentration of total volatile fatty acids in the rumen. Other effects were a higher amylase activity in the solid-associated microbial community and a tendency for lower numbers of protozoa. In contrast, we observed no changes in intake, production, dry matter and fiber (neutral detergent fiber and acid detergent fiber) digestibility, or ruminal digestion, and no or small changes on selected fibrolytic and amylolytic bacteria and on the microbial community in general. We conclude that the exogenous amylase improved starch digestion in the rumen in first-lactation cows with moderate intake and production levels.     

Apparent ruminal synthesis and intestinal disappearance of vitamin B12 and its analogs in dairy cows

The aim of the project was to calculate the apparent synthesis or destruction of cobalamin (vitamin B₁₂) and its analogs in the rumen as well as their apparent intestinal disappearance in dairy cows. Four lactating cows were fed a diet supplemented with cobalt alone (0.76 mg/kg of DM; control) or with cobalt and vitamin B₁₂ (cyanocobalamin, 500 mg/d; treated). In addition to cobalamin, the only biologically active molecule for the cow, 7 analogs were identified in duodenal and ileal digesta: cobinamide, which lacks the base, ribose, and phosphate groups; and 6 other molecules in which the base, 5,6-dimethylbenzimidazole, is replaced by cresol, 2-CH₃-adenine, adenine, 2-CH₃-S-adenine, or 5-OH-benzimidazole, or an unidentified cobamine. Small amounts of cobalamin and cobinamide were detected in the total mixed ration, but apparent synthesis of all forms took place in rumen. During the control period, cobalamin represented 38% of the total amounts of corrinoids produced in rumen. Approximately 11% of the average daily intake of cobalt was used for apparent ruminal synthesis of corrinoids, of which only 4% was incorporated into cobalamin. Only 20% of the supplement of cyanocobalamin was recovered at the duodenal level; cobinamide appeared to be the major product of degradation of supplementary cyanocobalamin in the rumen. During the control and treatment periods, there was an apparent intestinal disappearance of cobalamin and 5-OH-benzimidazole cobamide only; only the apparent intestinal disappearance of cobalamin differed between the 2 periods. Although cobalamin was not the major form synthesized by ruminal microflora and, even if supplementary cyanocobalamin was extensively destroyed by ruminal microflora, based on calculations of apparent intestinal disappearance, cobalamin seems to be the major form absorbed in the small intestine.     

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.     

Effects of a monensin controlled-release capsule or premix on attenuation of subacute ruminal acidosis in dairy cows

The effects of monensin, administered either as a controlled release capsule (CRC) or a premix, on attenuating grain-induced subacute ruminal acidosis (SARA) and on ruminal fermentation characteristics in Holstein cows receiving a total mixed ration were investigated in two experiments. In both experiments, six multiparous, rumen-fistulated Holstein cows were used in a two-treatment, two-period crossover design with 6-wk periods. In Experiment 1, treatments were either a monensin CRC or a placebo CRC. In Experiment 2, treatments were either a monensin premix or a placebo premix. In both experiments, at the beginning of wk 4 SARA was induced in experimental cows for a 10-d period with a grain challenge model, and ruminal pH was measured continuously using indwelling pH probes. The administration of monensin either as a CRC or a premix had no effect on ruminal pH characteristics. Neither monensin CRC nor premix had an effect on ruminal volatile fatty acid concentrations, but reduced the acetate:propionate ratio. Monensin premix-treated cows were observed to have increased milk yield, largely as a result of a higher dry matter intake in monensin-treated cows compared to control cows. Milk fat content and yield were lower in monensin-treated cows compared to placebo-treated cows during SARA. In conclusion, there is no evidence that monensin was efficacious in raising ruminal pH during SARA under the conditions employed in this study.     

Effects of increasing amounts of dietary wheat on performance and ruminal fermentation of Holstein cows

Twelve second-lactation Holstein cows were used in a replicated Latin square design to examine the effects of dietary wheat on lactation performance, ruminal fermentation, and whole-tract nutrient digestibility. Cows were randomly assigned to 1 of 3 diets containing 0, 10, and 20% steam-rolled wheat on a dry matter basis at the expense of steam-rolled barley. Cows were fed and milked twice daily. Six of the cows were ruminally cannulated, and rumen fluid samples were obtained from these cows 18 times during the last 2 d of each period. Treatment did not affect dry matter intake (20.9 kg/d) or yields of milk (36.1 kg/d) or milk components (1.25, 1.10, and 1.67 kg/d for fat, protein, and lactose, respectively). Fat percentage was not different among the treatments but protein content of the milk was reduced by the wheat treatments, and was lower when 10% wheat was included in the diet versus 20%. Cows fed wheat had lower ruminal pH (6.36 vs. 6.44) and greater NH₃-N (11.49 vs. 8.10 mg/dL) and total volatile fatty acids (121 vs. 113 mM) concentrations than cows not fed wheat. The acetate:propionate ratio was lower for cows fed wheat than for those not fed wheat (3.21 vs. 3.36), but was not different between cows fed 10% versus 20% wheat. Wheat feeding did not alter whole-tract apparent digestibility of dry matter, crude protein, acid detergent fiber, and neutral detergent fiber. Results of this study show that up to 20% steam-rolled wheat can be included in the diet of dairy cows without compromising production or causing subacute ruminal acidosis if adequate fiber is provided and the diets are properly formulated and mixed.     

Effects of supplemental hay and corn silage versus full-time grazing on ruminal pH and chewing activity of dairy cows

Grazing young, highly digestible swards with and without supplemental hay or corn silage (5.5 kg of DM/d) offered overnight was tested for its effects on ruminal pH and chewing activity. A double 3 x 3 Latin square arrangement with 6 rumen-cannulated Brown Swiss cows (29 kg/d of milk) was applied. Herbage intake was quantified by controlled-release alkane capsules. Chewing activity was determined using an automatic microcomputer-based system for digital recording of the jaw movements. Except during milking, ruminal pH was measured continuously over 7 d by applying a device consisting of an indwelling pH electrode and a data-recording unit integrated in the cannula's cover. The grazing system had no significant effect on body weight, milk yield or composition (except milk urea), or total DM intake (13.5, 13.8, and 15.7 kg/d with full-time grazing, hay, and corn silage supplementation). No differences occurred for ruminating time per day and time per kilogram of DM intake. Full-time grazing cows spent more time eating per day (+26%) and time per kilogram of DM intake (+31%) than the other cows. Ruminal pH and time with pH <5.8 at night did not differ. Throughout the day, hay-supplemented cows had a significantly lower pH (-0.23) than full-time grazing cows, and the period of pH <5.8 was longer compared with corn-silage fed cows (77 vs. 11 min). Nocturnal supplement feeding gave no advantage over full-time grazing, and supplemental hay led to lower daytime pH.     

Ruminal fermentation and nutrient digestion by dairy cows fed varying amounts of soyhulls as a replacement for corn grain

Five multiparous Holstein cows cannulated in the rumen and duodenum that averaged 63 d in milk were used in a 5 x 5 Latin square design with 14-d periods to evaluate the incremental substitution of soyhulls for corn in the diet. Diets contained 23% alfalfa silage, 23% corn silage, and 54% concentrate on a dry matter (DM) basis. Pelleted soyhulls replaced corn in the concentrate to supply 0, 10, 20, 30, or 40% of the dietary DM. The intakes of DM and organic matter were unaffected by treatments. Intakes of acid detergent fiber and neutral detergent fiber increased linearly, but the intake of nonstructural carbohydrates decreased linearly as soyhulls increased from 0 to 40% of dietary DM. The amount of acid detergent fiber and neutral detergent fiber digested was increased whereas the amount of nonstructural carbohydrate digested was decreased in the rumen, in the lower digestive tract, and in the total digestive tract as soyhulls replaced corn in the diet. Passage to the duodenum of nonammonia N, microbial N, nonammonia nonmicrobial N, total essential amino acids, total nonessential amino acids, and total amino acids were not affected by treatments. Yield of milk (29.5 kg/d) was not affected by treatments in this experiment. In a companion experiment, cows fed the 40% SH diet produced 1.2 kg/day per cow less (P < 0.07) milk than cows fed the control diet which is similar to the 1.3 kg/day per cow less milk produced by cows fed the same 40% SH diet in this experiment. Differences in the source of energy (fiber vs. nonstructural carbohydrates), in the amount of fiber and nonstructural carbohydrates digested, and in the site of digestion in the gastrointestinal tract may cause a shortage of the source and/or amount of energy that is required for maximum milk production in high producing cows when more than 30% of the dietary DM that is supplied as corn is replaced with soyhullss.     

The effects of subacute ruminal acidosis on sodium bicarbonate-supplemented water intake for lactating dairy cows

Four multiparous ruminally fistulated Holstein dairy cows were used in an 8-wk experiment utilizing a repeated measures block design to determine the effects of subacute ruminal acidosis (SARA) on supplemented water intake. Animals were subjected to SARA, which was induced by replacing 25% of the ad libitum intake of the total mixed ration (dry matter basis) with 50:50 wheat:barley pellets utilizing a grain challenge model. Cows had free choice from 2 water bowls. One bowl contained water with sodium bicarbonate (SB) supplemented at 2.5 g/L. The other bowl contained unsupplemented water. Ruminal pH was monitored continuously during the trial using indwelling pH probes. The induction of SARA reduced daily mean ruminal pH and increased the duration when ruminal pH was below 6. The total mixed ration intake by the cows decreased during the SARA periods. The overall preference for SB-supplemented water did not change, as the preference ratio was similar during the control and SARA periods. During the period of greatest ruminal pH depression, total water intake was higher during the SARA periods than during the control periods. During SARA, there was no difference in the preference of a SB water source to unsupplemented water. During the period of day with the most severe ruminal pH depression, the lactating dairy cows subjected to SARA increased their total water intake.     

Technical note: Methodological and feed factors affecting prediction of ruminal degradability and intestinal digestibility of essential amino acids

We hypothesized that ruminal degradability of essential AA (EAA) and the intestinal digestibility of the ruminally undegraded EAA residue in feeds could be evaluated in a meta-analysis. The objective was to characterize methodological factors for ruminal incubation (time of incubation of feed in situ) and method of simulating digestion of the ruminally undegraded AA (incubation of residue in digestive enzymes in vitro or in mobile bags inserted into the duodenum). To increase numbers of observations, feeds were categorized before ANOVA. An approach is described to predict differential ruminal degradability (or undegradability) of individual EAA by normalizing them as a proportion of total AA (TAA) degradability (undegradability) and similarly to normalize the intestinal digestibility of EAA using TAA. Interaction of feed category with individual EAA justifies future studies with a broader range of feeds and more replication within feed to bolster this approach. With broader data, the approach to normalize EAA as a proportion of TAA should allow a better defined EAA library to be integrated with more robust CP databases (that can be updated with specific feed information from more routine laboratory analyses) in dairy supply-requirement models.