Effects of tallow in diets based on corn silage or alfalfa silage on digestion and nutrient use by lactating dairy cows

Six multiparous Holstein cows (average 31 days in milk; 36.3 kg/d of milk) fitted with ruminal cannulas were used in a 6 x 6 Latin square with 21-d periods to investigate the effects of diets that varied in forage source and amount of supplemental tallow. Isonitrogenous diets in a 2 x 3 factorial arrangement were based on either high corn silage (40:10 corn silage to alfalfa silage, % of dry matter) or high alfalfa silage (10:40 corn silage to alfalfa silage, % of dry matter) and contained 0, 2, or 4% tallow. Intakes of dry matter and total fatty acids were lower when cows were fed the high corn silage diet. Tallow supplementation linearly decreased dry matter intake. Milk yield was unaffected by diet; yields of milk fat and 3.5% fat-corrected milk were higher for the high alfalfa silage diet but were unaffected by tallow. Milk fat percentage was higher for the high alfalfa silage and tended to decrease when tallow was added to the high corn silage diet. Contents of trans-C18:1 isomers in milk fat were increased by high corn silage and tallow, and tended to be increased more when tallow was fed in the high corn silage diet. Ruminal pH and acetate:propionate were lower when high corn silage was fed. Ruminal acetate:propionate decreased linearly as tallow increased; the molar proportion of acetate was decreased more when tallow was added to the high corn silage diet. Ruminal liquid dilution rates were higher for the alfalfa silage diet; ruminal volume and solid passage rates were similar among diets. Total tract apparent digestibilities of dry matter, organic matter, crude protein, starch, energy, and total fatty acids were unaffected by diet. Digestibilities of neutral detergent fiber, acid detergent fiber, hemicellulose, and cellulose were lower when high corn silage was fed. The high alfalfa silage diet increased intakes of metabolizable energy and N, and increased milk energy and productive N. Tallow decreased the amount of N absorbed but had few other effects on utilization of energy or N. Tallow linearly increased concentrations of nonesterified fatty acids and cholesterol in plasma; cholesterol was increased by high alfalfa silage. Overall, forage source had more pronounced effects on production and metabolism than did tallow supplementation. Few interactions between forage source and tallow supplementation were detected except that ruminal fermentation and milk fat content were affected more negatively when tallow was fed in the high corn silage diet.     

Ruminal temperature may aid in the detection of subacute ruminal acidosis

The objective of this study was to investigate the relationship between ruminal pH and ruminal temperature and to develop a predictive equation that can aid in the diagnosis of subacute ruminal acidosis (SARA). Six rumen-fistulated lactating Holstein dairy cows (639 ± 51 kg body weight) were used in the study. Cows were randomly allocated to 1 of 2 dietary treatments: control (% of dry matter, 40% corn silage, 27% mixed haylage, 7% alfalfa hay, 18% protein supplement, 4% ground corn, and 4% wheat bran) or SARA total mixed ration (% of dry matter, 31% corn silage, 20% mixed haylage, 5% alfalfa hay, 15% protein supplement, 19% ground wheat, and 10% ground barley) and were fed daily at 0700 and 1300 h. The experiment consisted of 1 wk of adaptation followed by 1 wk of treatment. Ruminal pH and ruminal temperature were simultaneously and continuously recorded every minute for 4 d per week using the same indwelling electrode. Subacute-acidotic cows spent more time (min/d) below ruminal pH 5.6 and a greater time above 39.2°C than control cows. Ruminal pH nadir had a negative relationship with its corresponding ruminal temperature (R² = 0.77). Therefore, ruminal temperature may have potential to predict ruminal pH and thus aid in the diagnosis of SARA.     

Microbial Protein Synthesis in Rumens of Cows Fed Dried Whole Whey

Two rumen-fistulated Holstein cows, weighing approximately 550 kg, were in an experiment with switchback design to evaluate effects of consuming large amounts (38% of total ration dry matter) of dried whole whey on synthesis of microbial protein in the rumen. Cows were fed total mixed rations of (dry matter) 45% corn silage, 10% alfalfa hay, and 45% concentrate mix. The concentrate mix was primarily corn and soybean meal (control) or 85% dried whole whey. Dry matter intakes averaged 16.4 and 15.3 kg/day for control and whey diets. Diaminopimelic acid nitrogen as percent of bacterial nitrogen was similar for both diets (.61 and .63% for control and whey diets). Likewise, aminoethylphosphonic acid nitrogen as percent of protozoal nitrogen was similar for both diets (.17 and .19% for control and whey diets). For the control diet, total ruminal nitrogen was estimated to be 45% bacterial and 27% protozoal. Bacteria and protozoa accounted for 52 and 22% of the total ruminal nitrogen in the cows fed the whey diet. Ruminal fluid volume (33.8 and 39.2 liters for control and dried whey diets) and dilution rates (10.2 and 12.8% h) were higher for dried whey. Ruminal ammonia (5.0 and 3.4 mg/dl) was lower for dried whey. Butyrate (16.5 and 24.4 moles/100 moles total volatile fatty acids) was higher, whereas propionate was lower (32.4 and 23.2 moles/100 moles total volatile fatty acids) when cows were fed dried whey. Bacterial synthesis appeared to be increased when cows were fed a diet containing large amounts of dried whey.     

Influence of addition of yeast culture supplement to diets of lactating cows on ruminal fermentation and microbial populations

Six ruminally fistulated Holstein cows were utilized in a randomized block design to examine effects of yeast culture supplement on ruminal metabolism and apparent digestibility. Cows were fed a diet of 40% corn silage and 60% concentrate (DM basis). Treatments were control (supplement without yeast cells) and yeast culture supplement. Treatment periods were 6 wk. Ruminal pH, ammonia, molar proportions of acetate and isovalerate, and acetate: propionate ratio were lower and molar proportions of propionate and valerate higher in cows receiving yeast. The concentration of anaerobic bacteria tended to be higher and cellulolytic bacteria concentrations were greater in cows fed yeast than in cows receiving control diet. Supplemental yeast did not affect molar proportions of isobutyrate or butyrate, total VFA, or viable yeast concentrations in ruminal fluid. Ruminal liquid dilution rate and total tract apparent digestibilities were not different between treatments. Rate of disappearance of cellulose in vitro was lower in cows receiving yeast. Less variation in ammonia concentrations and microbial numbers suggest that ruminal fermentation was more stable in cows receiving yeast culture supplement.     

Effect of ruminal ammonia-nitrogen concentration on protein degradation in situ

Two experiments were conducted to determine the effect of ruminal ammonia-nitrogen concentration on rate of ruminal protein degradation. In Experiment 1, four Holstein steers were fed a basal diet of corn grain and corn silage at hourly intervals. Continuous intraruminal infusions of solutions containing sodium bicarbonate and either sodium chloride or ammonium chloride resulted in ruminal ammonia-nitrogen concentrations that averaged 4.8 and 17.3 mg/dl. Ruminal fluid pH, fluid volume, and turnover rate of fluid and molar percentage of acetate, propionate, and butyrate were similar across treatments, reflecting steady state conditions. Rates of nitrogen and dry matter disappearance from polyester bags containing soybean protein supplements with 10.2 or 50.1% soluble nitrogen were not affected by increase of ruminal ammonia-nitrogen concentrations from 4.8 to 17.3 mg/dl. In Experiment 2, Holstein steers were fed twice daily a basal diet of urea-supplemented corn grain and corn silage. Polyester bags containing soybean protein supplements were placed in the rumen at -4, 0, or 4 h with reference to feeding and incubated from 1 to 12 h. Peak ruminal ammonia-nitrogen concentrations occurred during different periods of incubation for each treatment. Ruminal ammonia-nitrogen concentrations ranged from 3 mg/dl at 6 h postfeeding to 46 mg/dl at 1 h postfeeding. Nitrogen and dry matter disappearance rates during 0 to 1 and 1 to 12 h of incubation did not differ among treatments.     

Alteration of rumen fermentation, milk fat synthesis, and nutrient utilization with mineral salts in dairy cows

The ability of mineral salts to alter rumen fermentation, rumen fluid dilution rate, milk fat synthesis, and nutrient utilization was investigated in dairy cows fed a high-concentrate, milk-fat depressing diet. Four rumen-fistulated Holstein cows were in a 4 X 4 Latin square design. Treatments consisted of: 1) basal (25% corn silage: 75% concentrate on a dry matter basis), 2) basal + 2.0% sodium chloride, 3) basal + 2.0% sodium bicarbonate, and 4) basal + 2.4% limestone. Addition of limestone to the basal diet reduced dry matter intake but increased efficiency of dietary nutrient utilization for milk synthesis. Sodium bicarbonate increased synthesis of milk fat. Sodium chloride also tended to increase milk fat synthesis whereas limestone had no effect. Milk yields (kg/day) and milk fat (%) for the four treatments were 1) 29.5, 2.40; 2) 29.3, 2.66; 3) 28.9, 3.26; and 4) 29.2, 2.32. Rumen fluid pH, dilution rate (%/hour), and molar percentage of acetate and propionate were: 1) 5.98, 10.3, 49 and 39; 2) 6.02, 12.4, 55 and 32; 3) 6.16, 12.2, 58 and 25; and 4) 5.92, 10.7, 51 and 38. Limestone was totally ineffective in altering ruminal pH, fluid dilution rate, molar percentages of acetate and propionate, and synthesis of milk fat. Improved feed efficiency for milk production after addition of limestone was related to an increase in starch digestion compared to the basal ration (95 versus 88%).     

Whole rolled sunflower seeds with or without additional limestone in lactating dairy cattle rations

Thirty lactating Holstein cows were in a continuous trial from 21 to 120 days postpartum to evaluate diets containing whole, rolled sunflower seeds with or without additional limestone. Cows were fed individually total mixed rations of (dry matter) 47% corn silage, 9% alfalfa hay, and 44% concentrate. Concentrates were corn and soybean meal (control); corn, soybean meal, and 22% sunflower seeds; or corn, soybean meal, and sunflower seeds plus 3.5% additional limestone. Milk yield (32.2, 32.0, and 32.8 kg/day) was similar among rations. Yield of 4% fat-corrected milk was lower for cows fed sunflower seeds without additional limestone (30.2, 28.1, and 30.2 kg/day) because of lower milk fat percentages (3.57, 3.19, and 3.51). Milk protein percentage tended to be lower for cows fed sunflower seeds with additional limestone (3.01, 2.97, and 2.90). Milk, flavor score was acceptable but tended to be lower for milk from cows fed sunflower seeds with additional limestone (8.4, 8.5, and 7.9). Milk fat from cows fed sunflower seed rations contained less carbon-14:0, 16:0, and 16:1 fatty acids but more carbon-18:0. Dry matter intakes were 21.0, 18.4, and 20.0 kg/day. Dry matter digestibilities, body weight changes, and ruminal volatile fatty acid concentrations were similar among treatments. Total cholesterol in blood serum was elevated in cows fed sunflower seed rations. Insoluble salts of fatty acids were increased in ruminal fluid dry matter from cows fed sunflower seeds but were not increased further by additional limestone. Concentrations of nonesterified carbon-18:1 fatty acids in ruminal fluid dry matter were lower for cows fed sunflower seeds with additional limestone.     

Effects of brown midrib 3 mutation in corn silage on productivity of dairy cows fed two concentrations of dietary neutral detergent fiber: 3. Digestibility and microbial efficiency

The effects of digestibility of corn silage neutral detergent fiber (NDF) and dietary NDF content on ruminal digestion kinetics, site of nutrient digestion, and microbial N production efficiency were evaluated with eight multiparous high producing dairy cows in a duplicated 4 x 4 Latin square design with 21-d periods. Experimental diets contained corn silage from a brown midrib (bm3) hybrid or its isogenic normal control at two concentrations of dietary NDF (29 and 38%). The NDF digestibility estimated by a 30-h in vitro fermentation was higher for bm3 corn silage by 9.4 units (55.9 vs. 46.5%). Neither ruminal nor total tract NDF digestibility was affected by corn silage treatment. The bm3 corn silage diet decreased starch digestibility in the rumen and in the total tract, but increased postruminal starch digestibility compared with control diet. The bm3 corn silage diets increased microbial N flow to the duodenum and tended to decrease ruminal ammonia concentration. Microbial efficiency was greater for cows fed bm3 corn silage in spite of lower ruminal pH. Higher efficiency of microbial nitrogen production might be attributed to faster passage rate of NDF for cows fed bm3 corn silage compared with those fed control corn silage. Higher in vitro NDF digestibility might predict enhanced NDF fragility and ease of NDF hydrolysis in vivo. Enhanced in vitro NDF digestibility does not necessarily result in increased NDF digestibility either in the rumen or in the total tract, but possibly increases rate of passage and DMI, improving efficiency of microbial N production.     

Corn grain endosperm type and brown midrib 3 corn silage: ruminal fermentation and N partitioning in lactating cows

Interactions of endosperm type of corn grain and the brown midrib 3 mutation (bm3) in corn silage on ruminal fermentation and microbial efficiency of lactating dairy cows were evaluated. Eight ruminally and duodenally cannulated cows (72 +/- 8 d in milk; mean +/- SD) were used in a duplicated 4 x 4 Latin square design experiment with a 2 x 2 factorial arrangement of treatments. Treatments were corn grain endosperm type (floury or vitreous) and corn silage type (bm3 or isogenic normal). Diets contained 26% neutral detergent fiber and 30% starch. Increasing ruminal starch digestibility by replacing vitreous corn grain with floury grain reduced mean and minimum ruminal pH. Brown midrib 3 corn silage reduced mean and minimum ruminal pH and increased total volatile fatty acid concentration. Ruminal pH was positively associated with rate of valerate absorption. Although floury endosperm reduced acetate:propionate ratio in both control and bm3 corn silage diets, it had a greater effect on reducing acetate:propionate ratio for control silage compared with bm3 corn silage. Nonammonia N flow to the duodenum did not differ among treatments and no effects of treatment were detected for microbial N and nonammonia, nonmicrobial N flow. Although treatment effects on ruminal fermentation and ruminal pH were observed, few interactions of treatment were detected and treatments did not affect flow of N fractions to the intestines.     

Brown midrib sorghum in diets for lactating dairy cows.

In Experiment 1, 16 Holstein cows were assigned to one of four diets in replicated 4 x 4 Latin squares with 4-wk periods to measure dietary effect on short-term lactational performance. Additionally, 3 fistulated cows were assigned to the same diets in a 3 x 4 Youden square design with 4-wk periods to measure ruminal rate and extent of fiber digestion, fractional passage rate of fiber, ruminal pH, and concentration of volatile fatty acids. Diets comprised 65% of brown midrib (BMR) forage sorghum, standard forage sorghum, alfalfa or corn silages and 35% concentrate. Experiment 2 was conducted with 30 Holstein cows in early lactation to evaluate the same BMR sorghum hybrid in a 10-wk study with 35.3% standard sorghum, BMR sorghum, or corn silages as dietary treatments. Milk production was significantly higher for brown midrib than for standard sorghum in Experiment 1. Ruminal pH and acetate to propionate ratio did not differ among diets. The fractional passage rate of silage was not significantly different among the forages. In situ extent of ruminal fiber digestion was significantly higher for BMR than for standard sorghum, but rate of fiber digestion was not different. Similarly, in Experiment 2, in vitro extent of fiber digestion was significantly higher for BMR sorghum than for standard sorghum. Dry matter intake and body condition score were not significantly different between cows fed BMR and standard sorghum, but cows fed BMR sorghum resulted in long-term milk production greater than cows fed standard sorghum and similar to cows fed corn silage.     

Pigeon peas as a supplement for lactating dairy cows fed corn silage-based diets

Holstein rumen-cannulated cows [n = 7; initial body weight (BW) 640.56 ± 71.43 kg] were fed a corn silage basal diet with 1 of 3 concentrates (C = control; P10 = 10% pigeon peas; P20 = 20% pigeon peas). Cows were randomly assigned to treatments in a replicated 3 × 3 Latin square and individually fed using Calan gates. Each experimental period was 21 d with 7 d for adaption and 14 d for sample collection. Ruminal fluid samples were taken the last day of each experimental period and analyzed for pH, ammonia, long-chain fatty acids, and volatile fatty acids (VFA). Consecutive a.m. and p.m. milk samples were taken during the last 2 wk of the 21-d period and analyzed for fat, protein, long-chain fatty acids, and somatic cell count. Dry matter intake (kg/d) was reduced during the second period and was greater for P10 diets. Milk protein was greater for cows fed P20 compared with P10. Energy-corrected milk was greater for cows fed the control diet compared with P10. Treatment had no effect on milk yield. Ruminal fluid pH decreased over sampling times; however, pH remained at or above 5.5. Diets did not affect ruminal fluid pH; however, pH was different for sampling periods. Ruminal ammonia decreased until 8 h postfeeding at which time it peaked consistent with changes in ammonia concentrations that usually peak 3 to 5 h postfeeding on diets high in plant proteins. Dietary treatments altered ruminal fluid VFA with reduced concentrations of acetate and greater concentrations of propionate for control diet, resulting in reduced acetate:propionate ratio. Isobutyrate exhibited an hour by treatment interaction, in which isobutyrate decreased until 8 h postfeeding and then tended to be greater for P10 than for other treatments. Animals fed the P10 diet had greater concentrations of ruminal isovalerate. Ruminal cis-9,trans-11 and trans-10,cis-12 conjugated linoleic acid (CLA) isomers were not affected by dietary treatments. The P10 diet had greatest ruminal synthesis of cis-9,trans-11, but control cows had greatest ruminal synthesis of trans-10,cis-12. Milk CLA isomers were similar among treatments. Trends were observed for greater cis-9,trans-11 and trans-10,cis-12 for the P10 diet. Pigeon peas may be used as a protein supplement in dairy diets without affecting milk production, dry matter intake, or ruminal environment when they replace corn and soybean meal.     

A buffer value index to evaluate effects of buffers on ruminal milieu in cows fed high or low concentrate, silage, or hay diets.

Our objective was to develop a buffer value index that would incorporate alterations in both ruminal fluid pH and buffering capacity as indicators of the influence of dietary buffering and alkalinizing agents on ruminal acid-base status. This index was evaluated using ruminal fluid from four lactating Holstein cows fed either sorghum silage or alfalfa hay in high or low concentrate diets. Ruminal fluid was incubated in vitro for 1, 2, 3, 4, or 5 h with no buffer or with 7.1 g of either NaHCO3, sodium sesquicarbonate, or a multielement buffer added per liter of ruminal fluid. Ruminal fluid pH was lower for diets based on high concentrate or alfalfa; buffering capacity between pH 5 and 7 was greater for high concentrate diets but was not affected by forage type. Ruminal fluid pH was higher for sesquicarbonate than for NaHCO3, the multielement buffer, or the control; however, ruminal fluid H+ concentration was similar between sesquicarbonate and NaHCO3, and both were lower than for the multielement buffer. Hydrogen ion concentration for the multielement buffer was lower than for the control. Buffering capacity was highest for NaHCO3, followed by sesquicarbonate, the multielement buffer, and the control. The buffer value index, which accounted for alterations in both H+ concentration and buffering capacity, was highest for NaCHO3, followed by sesquicarbonate, the multielement buffer, and the control. The poor response to the multielement buffer may be attributable to our relatively short incubation interval (less than 5 h). Dietary buffers increase both ruminal fluid pH and buffering capacity; both of these responses are beneficial.(ABSTRACT TRUNCATED AT 250 WORDS)     

Corn silage management III: effects of hybrid,maturity, and processing on nitrogen metabolism and ruminal fermentation

Two experiments were conducted to evaluate the effects of maturity and mechanical processing of two hybrids of whole plant corn silage on DM and OM digestibility, nitrogen metabolism, ruminal fermentation, and milk production and composition in lactating Holstein cows. In the first experiment, Pioneer hybrid 3845 whole plant corn was harvested at hard dough, one-third milkline, and two-thirds milkline with a theoretical length-of-cut of 6.4 mm. At each stage of maturity, corn was harvested with (1-mm roll clearance) and without (15.9-mm roll clearance) mechanical processing using a John Deere 5830 harvester with an on-board kernel processor. In the second experiment, Pioneer hybrids 3845 and Quanta were harvested at one-third milkline, two-thirds milkline, and blackline stages of maturity with and without mechanical processing. The theoretical length-of-cut was 12.7 mm. Total tract DM and OM digestibilities were lower for cows fed diets containing processed corn silage in experiment 1, and tended to be lower for cows fed diets containing unprocessed corn silage in experiment 2. Ruminal acetate concentrations were greater and ruminal propionate concentrations were lower 2 and 6 h after feeding for cows fed diets containing corn silage harvested at physiological maturity in experiment 2. This was due to decreased digestion of starch at advanced maturities in experiment 2. Ruminal pH tended to decline rapidly after feeding for cows fed hybrid Quanta (2 h) compared to hybrid 3845 (5 h) corn silage based diets. Ruminal acetate concentrations decreased and ruminal propionate concentrations increased 2 and 6 h after feeding for cows fed diets containing hybrid Quanta corn silage compared to hybrid 3845 corn silage. This was related to a greater starch concentration in the corn silage, greater starch intake, and increased rate of starch digestion for cows fed hybrid Quanta corn silage-based diets. Microbial nitrogen flow was lower and feed nitrogen flow was greater for cows fed diets containing hybrid Quanta corn silage. The lower microbial nitrogen flow was due to lower microbial nitrogen concentration and nonammonia nitrogen flow to the duodenum. Milk fat and protein concentrations had a strong quadratic relationship with forage NDF intake as a percentage of body weight. When forage NDF intake as a percentage of body weight dropped below 0.70%, there was a rapid decline in milk fat and protein concentrations.     

Effects of forage particle size,forage source,and grain fermentability on performance and ruminal pH in midlactation cows

Our study investigated the effects of, and interactions between, forage particle size, level of dietary ruminally fermentable carbohydrate (RFC), and level of dietary starch on performance, chewing activity, and ruminal pH for dairy cows fed one level of dietary NDF. Twelve cows (48 DIM) were assigned to six treatments in a replicated 6 x 6 Latin square. Treatments were arranged in an incomplete 2 x 2 x 2 factorial design. Factors were: dry cracked shelled corn (DC, low RFC) or ground high-moisture corn (HMC; high RFC), finely chopped or coarse silage, and alfalfa silage as the only forage or a 50:50 ratio (DM basis) of alfalfa and corn silage. Diets combining HMC with only alfalfa silage were not included in the experiment. Diets were fed for ad libitum intake as a TMR with a concentrate:forage ratio of 61:39. Diets based on only alfalfa silage and diets based on a mix of alfalfa and corn silage averaged 18.6 and 15.8% CP, 25.8 and 24.7% NDF, 17.7 and 14.8% ADF, and 29.1 and 37.3% starch, respectively. Mean particle sizes were 5.3, 2.7, 5.6, and 2.8 mm for coarse alfalfa, fine alfalfa, coarse corn silage, and fine corn silage, respectively. Decreasing forage particle size decreased DMI (23.3 vs. 21.6 kg) and organic matter intake (22.0 vs. 20.2 kg). Increasing RFC decreased DMI (22.8 vs. 21.0 kg) and organic matter intake (21.5 vs. 20.0 kg). Decreasing forage particle size increased energy-corrected milk for alfalfa based diets (34.9 vs. 37.4 kg). Percentage of milk fat decreased with decreasing forage particle size (3.07 vs. 2.90%) and increased level of RFC (3.04 vs. 2.57%). Percentage of protein increased when corn silage partially replaced alfalfa silage (2.84 vs. 2.90%) but decreased when HMC replaced DC (2.90 vs. 2.84%). Apparent total tract digestibility of DM (66.7 vs. 68.5%), OM (65.9 vs. 70.7%), and starch (88.9 vs. 93.4%) increased when level of RFC was increased. Increasing level of RFC decreased mean ruminal pH from 5.82 to 5.67 and decreased minimum pH. Hours per day at which pH was <5.8, and area <5.8, increased when corn silage partially replaced alfalfa silage (2.6 vs. 4.4 h and 8.9 h x pH vs. 11.4 h x pH) and decreased further when level of RFC was increased (4.4 vs. 6.4 h and 11.4 h x pH vs. 14.3 h x pH). Decreasing forage particle size in HMC diets increased hours and area <5.8, but for DC diets, the effect of forage particle size depended on forage source. Interactions were found between level of physically effective fiber, forage source, and level of RFC on production and pH, complicating the inclusion of these effects in dairy ration formulation and evaluation.     

Effects of brown midrib 3 mutation in corn silage on productivity of dairy cows fed two concentrations of dietary neutral detergent fiber: 2. Chewing activities

The effects of digestibility of corn silage neutral detergent fiber (NDF) and dietary NDF content on chewing activities were evaluated with eight multiparous high producing dairy cows in a duplicated 4 x 4 Latin square design with 21-d periods. Experimental diets contained corn silage from a brown midrib (bm3) hybrid or its isogenic normal control at two concentrations of dietary NDF (29 and 38%). The NDF digestibility estimated by 30-h in vitro fermentation was higher for bm3 corn silage by 9.4 units (55.9 vs. 46.5%). Feeding behavior of animals and ruminal pH were monitored continuously for 4 d in each period by a computerized data acquisition system. Ruminal digesta were evacuated twice per period to determine the ruminal NDF pool and its turnover rate. There was no effect of NDF digestibility on total chewing time either per day or per kilogram of NDF intake, or on ruminating time either per day or per kilogram of NDF intake. Although bm3 treatments increased the turnover rate of NDF in the rumen, they increased dry matter intake and had no effect on ruminal NDF pool size. Total chewing time and ruminating time per day were related positively to NDF intake and ruminal NDF pool size, but were not related to ruminal turnover rate of NDF. These results provide no evidence that enhanced NDF digestibility decreases the physical effectiveness of NDF of corn silage.     

Ration digestibilities and ruminal characteristics in steers fed chickpeas

Twenty-four Holstein steers were used in a 5-d digestion trial to evaluate chickpeas as a substitute for corn and soybean meal. Total mixed diets contained (dry basis) 51% concentrate mix, 33% corn silage, and 16% alfalfa hay. Concentrate mixes contained 0, 50, and 100% chickpeas in place of corn and soybean meal. Ad libitum intakes of DM were not different between diets. Digestibilities of DM, NDF, ADF, hemicellulose, cellulose, lignin, and gross energy were not different among diets. Digestibilities of protein, fat, and ash were greater for steers fed 100% chickpeas than 0% chickpeas. Fecal N was lower and absorbed N was higher for steers fed 100% chickpeas. Ruminal acetate and acetate:propionate ratio were lower and ruminal propionate was higher for all steers fed diets containing chickpeas. Ruminal ammonia and pH were similar for all treatments.     

Rumen volatile fatty acid production and nutrient utilization in steers fed a diet supplemented with sodium bicarbonate and monensin

Effects of feeding dietary supplements of monensin and sodium bicarbonate singly or in combination on production of rumen volatile fatty acids, nitrogen balance, and rumen water kinetics were studied. Four rumen fistulated steers were fed a diet (50% concentrate mix and 50% corn silage) ad libitum in a 4 X 4 Latin square design (21-day periods) with a 2 X 2 factorial arrangement of treatments. Sodium bicarbonate increased feed intake, water intake, rumen pH, fluid dilution rate, and decreased both molar proportion and production rate of propionate in the rumen. Alteration of the ratio of acetate to propionate reflects the large decrease in propionate production relative to the small increase in acetate production. In contrast, monensin did not alter significantly rumen fluid dilution rate or ruminal pH but did decrease the molar proportion of acetate and increase that of propionate. Monensin increased production of both acetate and propionate in the rumen; however, the large increase in propionate production appears to account for more of the increase in molar proportion of propionate in the rumen. Increases in total volatile fatty acid production per kilogram of dry matter consumed with monensin supplementation appears to result from decrease in feed intake, thereby increasing ruminal retention time of dry matter and potentially the extent of digestion. Efficiency of nitrogen utilization was not altered by either sodium bicarbonate or monensin.     

Impact of feeding a raw soybean hull-condensed corn steep liquor pellet on induced subacute ruminal acidosis in lactating cows

We used four ruminally cannulated, multiparous Holstein cows (690 kg; 21 kg/d milk) in a 2-period crossover design to determine the impact of feeding a raw soybean hull-corn steep liquor pellet (SHSL) on induced subacute ruminal acidosis (SARA) in lactating cows. Cows were fed control [30% alfalfa hay, 15% corn silage, 34% corn, 9% whole cottonseed, 5% soybean meal (SBM)] or SHSL (20% of diet DM) diets as TMR. SHSL replaced 6.2% alfalfa hay, 3.7% corn silage, 6.6% corn, and 3.3% SBM. Periods were 15 d (10 d adaptation, 2 d for prechallenge measures, and 3 d of SARA challenge). Cows were fed once daily at a common DMI dictated by the cow consuming the least. Cows were fasted 12 h before the first SARA challenge. For each of the three SARA challenges, cows were offered 75% of their daily diet at 0600 h. The remaining 25% of diet DM was replaced by ground corn, which was mixed with the orts that remained 2 h after feeding and placed into the rumen. Ruminal pH declined linearly with time after feeding, and this decrease was greater during the SARA challenges. Ruminal lactate increased linearly with repeated SARA challenges. Concentrations of total ruminal VFA increased linearly after feeding, and increases were greater when cows were challenged. No differences were observed due to SHSL inclusion. The model induced SARA, but partial replacement of alfalfa, corn silage, corn, and SBM by SHSL did not influence responses to SARA challenges.     

Effects of sarsaponin on digestion and passage rates in cattle fed medium to low concentrate

Four dairy cows with duodenal cannulae were fed diets consisting of sorghum silage (67% of dietary dry matter) at 85% of ad libitum intake with 0 (control diet) or 44 ppm (dry matter) sarsaponin (sarsaponin diet) in a crossover experiment. Digestion coefficients for organic matter were low but increased by addition of sarsaponin both in the rumen (43.7 versus 32.4%) and total tract (52.1 versus 48.2%). Digestibilities of starch and nitrogen in the rumen and total tract and passage rates of fluid, concentrate, and silage tended to be greater for the sarsaponin diet. Extent of ruminal digestion of organic matter was related to passage rate of concentrate (correlation .81) and fluid (correlation .75). In a second study, diets contained 50% concentrate either with or without sarsaponin added at 44 ppm. Ruminal pH for animals given sarsaponin tended to be lower 4, 8, and 12 h after feeding. In situ rate constants of dry matter disappearance tended to be greater with the control diet for corn, alfalfa, and prairie hay and lower for milo and soybean meal. Lag time of digestion tended to be longer with the sarsaponin diet for corn, milo, soybean meal, and corn gluten meal but shorter for alfalfa and prairie hay. Although sarsaponin may increase ruminal digestion of medium to low concentrate diets, in situ data indicate that effects may differ with type of feed.     

Effects of limestone on starch digestion in Holstein steers

Eight calcitic and three dolomitic limestones were examined for particle size and reactivity with hydrochloric acid at pH 3.5 and 5.5. Reactivity was higher in calcitic than dolomitic limestone. Within calcitic limestones, reactivity was highly related to particle size. A highly reactive limestone was selected for use in two digestion trials with Holstein steers. In Trial 1, 4 steers (approximately 300 kg) were fed diets consisting of 40% corn silage and 60% concentrate (DM basis) with .62 or 2.34% limestone in a single reversal trial with 3-wk experimental periods. Added limestone affected only starch digestibility, which increased from 91.3 to 93.2%. Fecal pH increased from 5.7 to 6.4 by limestone addition. In trial 2, four rumen and duodenally cannulated steers (approximately 475 kg) were fed the same diets in the same design. Limestone addition increased fecal pH from 5.7 to 6.5. There were no effects of limestone on rumen or total tract digestion of starch or other nutrients. Limestone addition had no effect on rumen pH, buffering capacity, or VFA concentrations. Addition of a highly reactive limestone to diets containing high amounts of starch had little effect on starch digestion in either the rumen or lower gastrointestinal tract.