Ruminal degradation of dried brewers grains, wet brewers grains, and soybean meal

A series of trials was conducted to determine the ruminal degradation of nitrogenous compounds and dry matter of soybean meal, wet brewers grains, and dried brewers grains. In situ and in vitro estimates of degradation were positively correlated but yielded different absolute values for measures of ruminal degradation. Ruminal digestion of protein, predicted from in situ data, was 42, 73, and 83% for brewers dried grains, brewers wet grains, and soybean meal. Drying of wet grains at either 50 or 150 degrees C increased resistance to ruminal digestion equally. Measurements of flow of dry matter and nitrogen of feed origin to the duodenum were made in vivo for diets containing either brewers dried grains or soybean meal. Negative apparent digestibility of nitrogen in the rumen for a 13% crude protein, brewers dried grains ration indicates the potential for using a non-protein nitrogen supplement with this ration. Resistance to digestion of nitrogen from brewers dried grains occurred only in the rumen. Amino acid patterns delivered to the small intestine and digestion of duodenal contents were similar for diets containing brewers dried grains or soybean meal.     

Prediction of duodenal nitrogen supply from degradation or organic and nitrogenous matter in situ

The contribution of different feedstuffs to nitrogen reaching the duodenum was evaluated in situ. Dacron bags containing barley grain, corn grain, wheat silage, corn silage, alfalfa hay, rye grass, whole cottonseeds, or soybean meal were suspended in the rumens of three dairy cows fed roughage and concentrate diets. The effective degradability of the nitrogenous and organic matter of feedstuffs was calculated from their residues after incubation in the rumen for 3, 6, 9, 12, 24, 36, or 48 h. The duodenal nitrogen content at ruminal outflows of 2, 5, or 8%/h was calculated as the sum of undegradable dietary nitrogen and potential microbial nitrogen (assuming 32 g N/kg ruminally degradable organic matter). Comparison of the in situ estimates with previously reported in vivo measurements of duodenal nitrogen in cattle fed diets with similar ingredients to the tested feedstuffs yielded a linear relationship (r2 = .887). The dacron bag technique appears to hold promise for the prediction of nitrogen flow to the duodenum.     

Effects of source of protein and carbohydrate on ruminal fermentation and passage of nutrients to the small intestine of lactating cows

Four early lactation multiparous Holstein cows were used in a 4 x 4 Latin square to investigate the effects of source of protein (fish meal or soybean meal) and carbohydrate (corn or barley) on ruminal fermentation, flow of nutrients to the small intestine, and animal performance. The treatments, arranged in a 2 x 2 (protein x carbohydrate) factorial were: 1) corn plus soybean meal; 2) corn plus fish meal; 3) barley plus soybean meal; and 4) barley plus fish meal. Dry matter and starch intakes were greater when corn was fed than when barley was fed. Barley-based diets were more extensively degraded in the rumen than corn-based diets and therefore provided more energy for microbial growth. However, passage of amino acids and starch to the duodenum was greater for corn-based diets than barley-based diets, because of the greater intake and lower ruminal degradability of the corn-based diets. Microbial protein constituted a larger portion of the total N and had a greater influence on the pattern and quantity of amino acids that passed to the duodenum than did protein from fish meal or soybean meal, which escaped ruminal degradation. Feeding corn-based diets increased production of milk and milk protein compared with feeding barley-based diets.     

Forestomach and whole tract digestibility for lactating dairy cows as influenced by feeding frequency

Three lactating Holstein cows, averaging 510 kg and fitted with T-type duodenal cannulae in the proximal duodenum, were in a 3 X 3 Latin-square experiment to measure digestion in forestomachs and whole tract of feed nitrogen and neutral detergent fiber components as influenced by frequency of feeding. Cows were fed one diet containing 65% chopped grass legume hay, 26% cracked corn, and 8% soybean meal. Mixed ration was fed either once daily, four times daily, or the concentrate portion of the diet was fed once daily and the forage portion four times. Ytterbium, as ytterbium chloride, was included with diets to allow calculation of flow rates of duodenal and fecal dry matter. Assayed ratios of nitrogen to diaminopimelic acid in ruminal bacteria and duodenal digesta or fecal bacteria and feces were used to calculate duodenal and fecal bacterial nitrogen flows respectively. Ratios of nitrogen to diaminopimelic acid in ruminal and fecal bacteria averaged 4.15 and 2.38 g/mmol. Apparent digestibility of organic matter in the forestomachs and whole tract averaged 43.7 and 66.4%. Forestomach and whole tract digestibility of cellulose, hemicellulose, and lignin averaged 56.1, 52.0, 14.7, and 58.7, 58.5, and 16.8. Bacterial nitrogen flows averaged 255 and 91 g/day at the duodenum and in the feces. Bacterial nitrogen yield in the rumen averaged 36.6 g/kg organic matter apparently digested in the forestomachs. Frequency of feeding had no effect on almost all measures and components of rumen and whole tract metabolism and digestion. For these intakes, frequency of feeding had little effect on feed intake and nutrient utilization.     

Effects of source and amount of protein on ruminal fermentation and passage of nutrients to the small intestine of lactating cows

Four Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square to investigate the effects of source (corn gluten meal or soybean meal) and amount (14.5 or 11.0%) of CP on ruminal fermentation, passage of nutrients to the small intestine, and animal performance. Cows wee fed for ad libitum intake a diet of 60% corn silage and 40% concentrate on a DM basis. The treatments, arranged in a 2 x 2 (source x amount of CP) factorial, were 1) 14.5% CP, soybean meal; 2) 11.0% CP, soybean meal; 3) 14.5% CP, corn gluten meal; and 4) 11.0% CP, corn gluten meal. Digestion in the rumen of OM, starch, ADF, and NDF was not affected by source or amount of CP in the diet. Total VFA and NH3 concentrations in ruminal fluid were increased by feeding diets that contained 14.5% CP or soybean meal. FLows of non-NH3 N and amino acids to the duodenum were greater in cows fed the 14.5% CP diets because of a greater flow of non-NH3 nonmicrobial N to the duodenum. Larger amounts of lysine passed to the duodenum when cows were fed soybean meal compared with corn gluten meal. Microbial N flow to the duodenum and efficiency of microbial growth were not affected by treatments, suggesting that ruminal NH3 concentration was not limiting for maximal microbial protein synthesis. Feeding 14.5% CP diets increased the production of milk (29.5 vs. 26.8 kg/d) and milk protein compared with 11.0% CP diets, possibly because of greater passage of amino acids to the small intestine. Feeding soybean meal to cows increased production of milk protein compared with feeding corn gluten meal, possibly because more lysine passed to the small intestine.     

Effect of dietary soybean meal and fish meal on protein digesta flow in Holstein cows during early and midlactation

Six lactating cows were fitted with ruminal and duodenal cannula to measure protein digesta flow to the duodenum during early and midlactation. Diets were composed of corn grain, corn silage, and orchardgrass hay plus supplemental fish meal or soybean meal. Diets contained 15.5% CP and 20.7 ADF. Cobalt-EDTA and Yb were used as liquid and particulate digesta markers and cytosine was used as microbial marker. Corrected organic matter digestibilities in the stomachs were 48.4, 49.8, 44.9, and 53.2% for fish meal and soybean meal diets and early and midlactation, respectively. Preduodenal degradabilities were 47.2, 65.8, 56.7, and 56.2% for fish meal and soybean meal diets and early and midlactation, respectively. Nitrogen recoveries at the duodenum were 93.2 and 84.3% for fish meal and soybean meal diets. Intake of amino acids was greater when cows were fed the soybean meal diet, but total flows of amino acids to the duodenum were similar for both diets. Greater quantity of protein escaping ruminal degradation in cows fed fish meal compared with soybean meal was counterbalanced by less microbial synthesis in the rumen.     

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.     

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 diet nitrogen and forage nitrogen insolubility on performance of cows in early lactation

Thirty-six Holsteins were allotted at parturition to six treatments to measure effects of diet nitrogen and increased insolubility of silage nitrogen on performance and ruminal, plasma, and milk constituents during the first 100 d of lactation. Diets contained 40% concentrate and 60% silage in dry matter. The six silage treatments were untreated corn silage (low nitrogen); untreated corn silage and untreated alfalfa silage (1:1); untreated corn silage and formaldehyde and formic acid-treated alfalfa silage (1:1); ammonia-treated corn silage (low nitrogen); treated corn silage and untreated alfalfa silage (1:1); or treated corn silage and treated alfalfa silage (1:1). Diets containing ammonia-treated corn silage had higher hot water-insoluble nitrogen and diets containing formaldehyde and formic acid-treated alfalfa had higher autoclaved rumen fluid-insoluble and hot water-insoluble nitrogen that their respective untreated silage diets. Dry matter intake, daily yields of milk and its constituents, ruminal NH3 nitrogen, and plasma urea nitrogen were lower for cows consuming low nitrogen diets containing only corn silage compared with cows consuming high nitrogen diets containing alfalfa. Dry matter intake and milk protein yields were greater for cows consuming treated alfalfa compared with untreated alfalfa in the diet. Daily 4% fat-corrected milk yields tended to be higher for diets containing treated alfalfa than untreated alfalfa. Cows fed diets containing NH3-treated corn silage had similar milk, fat, and protein yields compared with diets containing untreated corn silage and urea in the concentrate.     

Effect of ruminal protein degradation of blood meal and feather meal on the intestinal amino acid supply to lactating cows

Four lactating cows fitted with ruminal cannulae and T-type cannulae in the proximal duodenum and terminal ileum were utilized to measure protein degradation in the rumen and amino acid flow to and absorption from the small intestine. Soybean meal, blood meal, feather meal, and a 50-50 combination of blood meal and feather meal provided 50% of the protein in diets that contained 50% grain mix, 40% corn silage, and 10% alfalfa pellets on a DM basis. Ruminal degradation of dietary CP was 53, 43, 32, and 37% for diets containing soybean meal, blood meal, feather meal, and the combination of meals. Cows fed the latter two diets also had lower ruminal NH3 concentrations and efficiency of bacterial protein synthesis compared to those fed the soybean meal diet. Total tract N digestibility was lower for diets containing feather meal (63.4%) and a combination of meals (66.3%) than the soybean meal diet (78.5%). Total amino acid flow to the duodenum was 19.3 and 15.6% higher for cows fed the feather meal and combined meal diets, respectively, compared with the soybean meal diet. Total amino acid absorption from the small intestine was higher as well as absorption of individual amino acids for the combined meal diet compared with the soybean meal diet. Absorption of individual amino acids, expressed as a percentage entering the duodenum, was lowest for the feather meal diet. Results from this study show that feeding a combination of blood meal and feather meal instead of soybean meal can increase intestinal supply and absorption of amino acids in dairy cattle.     

Effect of source of rumen-degraded protein on production and ruminal metabolism in lactating dairy cows

Twenty-eight (8 with ruminal cannulas) lactating Holstein cows were assigned to seven 4 × 4 Latin squares in a 16-wk trial to study the effects on production and ruminal metabolism of feeding differing proportions of rumen-degraded protein (RDP) from soybean meal and urea. Diets contained [dry matter (DM) basis] 40% corn silage, 15% alfalfa silage, 28 to 30% high-moisture corn, plus varying levels of ground dry shelled corn, solvent- and lignosulfonate-treated soybean meal, and urea. Proportions of the soybean meals, urea, and dry corn were adjusted such that all diets contained 16.1% crude protein and 10.5% RDP, with urea providing 0, 1.2, 2.4, and 3.7% RDP (DM basis). As urea supplied greater proportions of RDP, there were linear decreases in DM intake, yield of milk, 3.5% fat-corrected milk, fat, protein, and solids-not-fat, and of weight gain. Milk contents of fat, protein, and solids-not-fat were not affected by source of RDP. Replacing soybean meal RDP with urea RDP resulted in several linear responses: increased excretion of urinary urea-N and concentration of milk urea-N, blood urea-N, and ruminal ammonia-N and decreased excretion of fecal N; there was also a trend for increased excretion of total urinary N. A linear increase in neutral detergent fiber (NDF) digestibility, probably due to digestion of NDF-N from lignosulfonate-treated soybean meal, was observed with greater urea intake. Omasal sampling revealed small but significant effects of N source on measured RDP supply, which averaged 11.0% (DM basis) across diets. Increasing the proportion of RDP from urea resulted in linear decrease in omasal flow of dietary nonammonia N (NAN) and microbial NAN and in microbial growth efficiency (microbial NAN/unit of organic matter truly digested in the rumen). These changes were paralleled by large linear reductions in omasal flows of essential, nonessential, and total amino acids. Overall, these results indicated that replacing soybean meal RDP with that from urea reduced yield of milk and milk components, largely because of depressed microbial protein formation in the rumen and that RDP from nonprotein-N sources was not as effective as RDP provided by true protein.     

Protein degradation in rumen and amino acid absorption in small intestine of lactating dairy cattle fed heat-treated whole soybeans

Four lactating Holstein cows fitted with rumen cannulae and T-type cannulae in proximal duodenum and terminal ileum were used to measure protein degradation in the rumen and amino acid flow and absorption in the small intestine. Soybean meal, whole soybeans, and whole soybeans extruded at 132 and 149 degrees C provided 50% of the protein in diets that contained 51% grain, 36% corn silage, and 13% alfalfa hay (dry matter). Spot samples of digesta were collected from duodenum and ileum during 96 h, and lanthanum was an indigestible marker to estimate flow and digestibility of nutrients. With diaminopimelic acid as a microbial marker, apparent degradations of dietary crude protein in the rumen were 73, 80, 66, and 60% for diets containing soybean meal, whole soybeans, and whole soybeans extruded at 132 and 149 degrees C. Because of the extensive degradation of protein with the raw soybean diet, less total amino acids reached the duodenum, and because of decrease of availability, absorption from the small intestine (g/day) was lowest with this diet. Feeding diets containing extruded whole soybeans increased availability of total essential amino acids in the small intestine compared with diets containing soybean meal and whole soybeans. Absorption from the small intestine (g/day and percent entering) of individual amino acids was generally higher for extruded whole soybean diets.     

Effects of calcium salts of fatty acids and protein source on ruminal fermentation and nutrient flow to duodenum of cows.

Four Holstein cows fitted with ruminal and duodenal cannulas were used in a 4 x 4 Latin square to investigate the effects of calcium salts of long-chain fatty acids (fat) and source of protein (fish meal or soybean meal) on ruminal fermentation, flow of nutrients to the small intestine, and animal performance. Cows were fed for ad libitum intake a diet of 30% alfalfa haylage, 20% corn silage, and 50% concentrate on a DM basis. Treatments, arranged in a 2 x 2 (fat x protein) factorial, were 1) soybean meal, no fat; 2) soybean meal, fat; 3) fish meal, no fat; and 4) fish meal, fat. Intake of DM was not affected by fat or protein source, but feeding fat decreased the amount of OM truly digested in the rumen. Starch intake was decreased, but flow of starch to the duodenum was not altered by feeding fat. Nonammonia N and microbial N flows to the duodenum were not affected by treatment comparisons. However, efficiency of microbial growth was increased by feeding fat, but not by source of protein. Passage of amino acids to the duodenum was not affected by source of protein, probably because fish meal contributed only 17% of the total dietary CP, and microbial N constituted about 50% of the NAN passing to the duodenum; this had an equalizing effect on the pattern and quantity of amino acids that passed to the duodenum. Feeding fat or different sources of protein did not alter milk production. Milk fat percentage was increased, and protein percentage was decreased when fat was fed, but yields of milk fat and protein were not different.     

Influence of dietary protein sources on the amino acid profiles available for digestion and metabolism in lactating cows

Six lactating Holstein cows, fitted with T-type cannulas in the proximal duodenum, were used in a replicated 3 x 3 Latin square design to determine influence of supplemental protein on amino acid profiles of duodenal chyme and plasma. Protein sources were blood meal, corn gluten meal, and cottonseed meal, which furnished approximately 46% of the total protein in corn-grain corn silage diets. Markers were 15N to estimate rumen bacteria and chromic oxide to estimate nutrient flow. Dry matter intake was lowest on blood meal. Duodenal flow of N exceeded N intake 23% on blood meal and corn gluten meal. Percentages of organic matter and protein digested in the rumen were 56.5, 41.8; 61.2, 53.4; and 50.6, 56.2 for the respective diets. Variation in patterns of amino acids flowing to the duodenum, but not in coccygeal blood, closely reflected dietary differences with six of eight essential amino acids highest for the same treatment in both diet and duodenal chyme. Essential amino acids in least abundance for milk production, measured by mammary extraction coefficients, differed among diets. We conclude that supplemental protein source influences greatly the quantity and pattern of amino acids available for digestion in lactating dairy cows.     

Dehydrated Alfalfa in Dairy Cow Diets

The objective of Experiment 1 was to determine protein degradation in the rumen and amino acid supply to and absorption of amino acids from the intestine of lactating dairy cows receiving supplements of soybean meal or a combination of dehydrated alfalfa and corn gluten meal. Four lactating Holstein cows, fitted with ruminal, duodenal, and ileal cannulae, were used in a switchback experiment. Two diets consisting of 50% corn silage and 50% concentrate were fed. One diet contained soybean meal and the other contained a mixture of dehydrated alfalfa and corn gluten meal. It was estimated that 76% of the dietary protein was degraded in the rumen with the soybean meal diet compared with 62% with the dehydrated alfalfa:gluten meal diet. Flow of total amino acids to the duodenum was 13% higher for the dehydrated alfalfa:gluten meal than for the soybean meal diet.Experiment 2 consisted of two trials. The objective of Trial 1 was to measure rumen fermentation products in lactating dairy cows fed diets where dehydrated alfalfa, with or without urea, replaced 40% of the concentrate. The objective of Trial 2 was to measure milk production, milk composition, and plasma amino acids of dairy cows in early lactation fed the same diets as in Trial 1. Milk production was 34.7, 33.4, and 32.8 kg/d and milk fat was 3.48, 3.58, and 3.63% for the three diets, control, dehydrated alfalfa, and dehydrated alfalfa with urea.     

Influence of protein supplementation of alkaline hydrogen peroxide-treated wheat straw on ruminal microbial fermentation

A dual flow continuous culture system was used to determine the effects of four protein sources (soybean meal, Ca-ligno-sulfonate treated-soybean meal, blood meal, and feather meal), supplied individually or in combination in diets composed predominantly of alkaline hydrogen peroxide-treated wheat straw, on ruminal microbial fermentation and amino acid flow. Diets containing blood meal had lower organic matter and fiber digestion, NH3 N and VFA concentrations, and CP degradation but higher non-NH3 N, dietary N, total amino acid, and essential amino acid flows. Feather meal fed alone or combined with other sources was not different from the blood meal diet in organic matter and fiber digestion. Combining treated soybean meal and blood meal resulted in similar organic matter and fiber digestibilities compared with the soybean meal diets. This combination was similar to the treated soybean meal diet in VFA concentration, non-NH3 N, and essential and total amino acid flows; however, amino acid profile was different with this combination, showing higher histidine and leucine flows. Results from this study suggest that amino acid profiles of digesta leaving the rumen may be manipulated by choice of protein supplement when diets containing a low protein, highly fermentable feedstuff such as alkaline hydrogen, peroxide-treated wheat straw are fed.     

Effect of rumen ammonia concentration on in situ rate and extent of digestion of feedstuffs

Three dry Holstein cows fitted with rumen fistula were fed a 7.4% crude protein diet consisting of 47.4% corn, 50% cottonseed hulls, and 2.6% minerals and vitamins during a 44-d experiment. Treatments consisted of rumen infusion, 0, 33, 67, and 100 g/d of urea nitrogen applied in a four period Youden Square design. Increasing urea infusion increased rumen fluid ammonia nitrogen from 4.3 to 25.0 mg/dl. Estimated effective dry matter degradation based on in situ rates of digestion were increased from 67.9 to 74.4% for corn and 77.5 to 80.3% for soybean meal with maximums at 100 g/d infused urea nitrogen. Up to 67 g/d infused nitrogen increased dry matter degradation of corn gluten feed from 67.0 to 71.4% and cottonseed meal dry matter degradation from 56.7 to 60.1%. Alfalfa hay dry matter and neutral detergent fiber degradation were not increased by urea infusion. Minimum rumen ammonia required in feeds in this trial were pooled with literature data and suggest that lowest ammonia concentrations required for maximal digestion was a function of the rumen fermentability of the diet or feed. The equation: minimum ammonia concentration (mg/dl) = .452 fermentability % - 15.71, accounted for 50% of the variation in minimum ammonia requirements. We conclude that rumen ammonia concentrations required for maximum digestion are not constant but rather are a function of fermentability of the diet.     

Varying protein and starch in the diet of dairy cows. I. Effects on ruminal fermentation and intestinal supply of nutrients

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 ruminal fermentation, nutrient passage to the small intestine, and nutrient digestibility. For this purpose, 6 multiparous Holstein cows fistulated in the rumen and duodenum that averaged 73 d in milk were used in a 6 × 6 Latin square 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 protein (about 14, 16, and 18%) were combined into 6 treatments. On a dry matter (DM) basis, diets contained 25% corn silage, 20% alfalfa silage, 10% cottonseed, 26.7 to 37% corn grain, and 4 to 13.5% protein supplement. Intakes and digestibilities in the rumen and total tract of DM, organic matter, acid and neutral detergent fiber were unaffected by treatments. Increasing dietary CP from 14 to 18% decreased the intake and apparent ruminal and total tract digestion of starch, but increased the proportion of starch consumed by the cows that was apparently digested in the small intestine. At 14% CP, starch intake and total tract digestion were higher for the AMB diet than for the SBM diet, but the opposite occurred at 16% CP. Across CP sources, increasing CP in the diet from 14 to 18% increased the intakes of N and amino acids (AA), and ruminal outflows of nonammonia N, nonammonia nonmicrobial N, each individual AA except Met, total essential AA, and total AA. Across CP percentages, replacing a portion of SBM with AMB increased the intake of Met and Val and decreased the concentration of ammonia N in the rumen, but did not affect the intake of other essential AA or the intestinal supply of any essential AA and starch. The ruminal outflow of microbial N, the proportional contribution of Lys and Met to total AA delivered to the duodenum, and milk yield were unaffected by treatments. 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 without compromising the supply of metabolizable protein if the source and amount of dietary CP and carbohydrate are properly matched.     

Effect of supplemental L-lysine-HCL and corn source on rumen fermentation and amino acid flow to the small intestine

Four lactating Jersey cows fitted with ruminal and duodenal cannulae were used in a 4 x 4 Latin square design trial to determine the effect of supplemental lysine in diets containing dry ground (GC) or steam-flaked (SFC, 360 g/L) corn on ruminal fermentation and amino acid (AA) flow to the duodenum. Supplemental L-lysine-HCL provided 10 g/d of additional Lys to the total mixed rations. There were no interactions between supplemental Lys and corn source. Supplemental Lys increased Lys intake, but did not alter nutrient intake and digestibility or N flow to the duodenum. Intake of dry matter (DM), organic matter (OM), and neutral detergent fiber (NDF) and ruminal digestibility of starch tended to be higher, whereas ruminal digestibility of DM, OM, acid detergent fiber, and NDF was lower for diets supplemented with SFC compared with GC. Whole-tract digestibility was similar for both corn supplements. Ruminal pH and molar proportions of volatile fatty acids were not affected by supplemental Lys or corn source; however, ruminal NH(3) concentrations were lowest when SFC was fed. Intake of N tended to be higher and the flow of total N and individual AA to the duodenum was higher for diets supplemented with SFC. There was a trend for increased flow of microbial N for diets supplemented with SFC. Supplemental L-lysine-HCL did not alter ruminal fermentation, flow of amino acid to the small intestine, or nutrient digestibility, but feeding SFC reduced ruminal fiber digestion and increased microbial protein synthesis and flow of amino acid to the duodenum.     

Site and extent of nutrient digestion in lactating dairy cows fed alfalfa protein concentrate or soybean meal

In vivo and in situ trials were conducted to investigate the utilization of alfalfa protein concentrate as a protein supplement for lactating dairy cows. In the in vivo trial, four Holstein cows fitted with ruminal, duodenal, and ileal cannulae were used in a crossover experiment to measure site and extent of nutrient digestion. Isonitrogenous and isoenergetic diets containing alfalfa protein concentrate or soybean meal were fed four times daily. Sixty percent of dietary total N was provided by the test proteins. Ruminal ammonia and total VFA concentrations were lower in cows fed alfalfa protein concentrate. Fractional digestion coefficient of organic matter (52 vs. 43%) and degradation of dietary protein (57 vs. 47%) in the rumen were slightly lower in cows fed alfalfa protein concentrate. The ratio of amino acid flow to the small intestine to dietary intake of amino acid was higher in cows fed alfalfa protein concentrate. In the in situ trial, rate of N disappearance (2.4 vs. 9.5%.h-1) and potential protein degradability (35 vs. 68%) were lower for alfalfa protein concentrate. Results suggest that alfalfa protein concentrate may be more resistant to ruminal degradation than soybean meal and could be utilized as a relatively undegradable protein source for milk production.