In situ and in vitro studies with a 3 x 2 x 5 factorial arrangement of treatments with an added untreated control evaluated three enzyme preparations, two levels of enzyme, and five moisture conditions of grass forage. Enzyme preparations predominantly contained cellulase and xylanase and will be designated as enzyme 1 (E1), enzyme 2 (E2), and a 50:50 combination of E1 and E2 (E1E2). The five moisture conditions included fresh, wilted, dried and rehydrated to fresh, dried and rehydrated to wilt, and dried grass. Addition of the high level of E1E2 to dried grass improved (P < .05) in vitro DM (43.5 vs 38.7%) and NDF (31.1 vs 26.0%) disappearance (48 h incubation) compared with the control treatment. Also, IVDMD was greater (P < .05) for the low level of E1 applied to wilted grass compared with the control. No other enzyme application improved in situ or in vitro disappearance of substrate over the control. In vivo responses of enzyme treatments found most likely to be effective from degradability studies were measured using four ruminally cannulated steers in a 4 x 4 Latin square experiment. Treatments examined were E1 applied to fresh forage, then dried; E1 applied to wilted forage, then dried; E1E2 applied to dry forage immediately before feeding (E-dry), and untreated forage (control). All forage treatments were harvested as dry hay. Total diet and hay DM intakes were greater (P < .05) for the E-dry than for the control diet. Rate of in situ NDF disappearance and total tract DM and NDF digestibility were greater (P < .05) for the E-dry than for the other treatments. Ruminal fluid ammonia N concentration, total VFA concentration, and pH were not altered (P > .10) by dietary treatment. Ruminal particulate passage rate was greater (P < .05) and ruminal retention time was shorter (P < .05) for the E-dry than for the control treatment. Data from this study suggest that addition of fibrolytic enzymes to grass hay before feeding has the potential to enhance intake and digestion.
Fifty-six multiparous Holstein cows were assigned at 3 wk prepartum to rations based on grass silage with 1) corn distillers grains to provide 86 and 90% of estimated required metabolizable Lys and Met, respectively; 2) a blend of blood meal, fish meal, and meat and bone meal as amino acid (AA) sources to provide 112 and 103% of required metabolizable Lys and Met, respectively; 3) ruminally protected Lys and Met added as a top-dressing to ration 1 to provide 27 g/d of Lys and 8 g/d of Met as available AA at the duodenum postpartum; and 4) ruminally protected AA for 8 wk postpartum as a top-dressing to ration 1 to provide 40 g/d of Lys and 13 g/d of Met as available AA at the duodenum. Cows fed rations 3 and 4 were offered 13.5 g/d of duodenally available Lys and 4 g/d of duodenally available Met for 3 wk prepartum. The total length of the study was 43 wk. Cows fed ration 4 consumed 3 to 4 kg more dry matter than did cows fed the other three rations, and milk yield and the percentage of milk protein and fat were significantly increased during the first 8 wk of lactation. In early lactation, cows fed ration 3 had a greater milk fat percentage but similar dry matter intake, protein percentage, and yield of 4% fat-corrected milk compared with cows fed ration 2. The concentrations of blood serum glutamic oxaloacetic transaminase, serum glutamic pyruvic transaminase, triglyceride, and nonesterified fatty acids were lower for cows fed ration 4 during the first 8 wk of lactation than they were for cows fed the other three rations. The mammary arteriovenous difference of whole blood AA indicated that Met along with His and Arg may be the most limiting AA for milk yield.
Four multiparous late-lactation Holstein cows were fed a basal ration designed to be co-limiting in intestinally absorbable supplies of methionine and lysine. Cows were supplemented with no amino acids, lysine by abomasal infusion to 140% of the calculated intestinally absorbable requirement, methionine by abomasal infusion to 140% of requirement, or both amino acids in a 4 x 4 Latin square design with 28-d periods. Unsupplemented cows consumed 23.8 kg/d of dry matter and produced 36.9 kg/d of milk containing 3.70% fat, 3.22% protein, and 4.82% lactose. Cows ate less dry matter and produced less milk and milk lactose, and tended (P = .06 or .08) to produce less milk protein when abomasally infused with methionine alone or together with lysine. Infusion of lysine alone resulted in production values numerically between those of unsupplemented cows and those cows supplemented with methionine alone or together with lysine. Evaluation of the results with two metabolic models of dairy cows indicated that performance of unsupplemented cows may have been limited by delivery of metabolizable or digestible protein, or intestinally absorbable lysine, isoleucine, or histidine, depending on the metabolic model used to evaluate animal performance. Regardless, results are consistent with those using nonruminant species, which have shown that imbalanced profiles of intestinally absorbable amino acids are associated with reduced dry matter intake and animal performance. Results also show that negative effects on performance of lactating dairy cows can occur if methionine is supplied at levels substantially in excess of calculated intestinally absorbable requirements, either alone or together with lysine.
Dairy cows, 20 at each of two sites, were used to determine responses to ruminally protected Lys and Met in a full lactation study. Cows were fed corn silage twice daily for ad libitum intake and a concentrate four times daily in proportion to milk production. At Truro, cows were fed 2.7 kg/d of alfalfa and timothy hay DM at 0600 and at 1500 h. At Fredericton, cows were fed 2.7 kg of timothy silage DM at 0600 h and 2.7 kg of alfalfa hay DM at 1500 h. Diets were designed to meet, but not to exceed, recommendations for ruminally degradable CP and intestinally digestible protein. Ten cows at each site were fed ruminally protected L-Lys.HCl (19 g/d) and DL-Met (6.5 g/d). Cows fed AA at each site produced more milk, lactose, protein, and fat; milk protein and fat percentages were also higher. No time x treatment interactions occurred for any production parameter. In spite of similar production responses between sites, cows fed AA consumed more DM at Truro, but those at Fredericton did not. Thus, gross efficiency of utilization of dietary N for milk N was increased with AA at Fredericton but not at Truro. However, considering the increased intake of CP by cows fed AA at Truro, an event that would have been expected to depress efficiency of utilization of dietary N, the lack of difference at Truro between treatments can be interpreted as an improvement, relative to expectations, because of AA feeding. High producing dairy cows fed a diet that was adequate in CP responded to ruminally protected Lys and Met primarily with increased production of milk protein and fat throughout the full lactation.
Four multiparous Holstein cows were fed a basal diet balanced with the Cornell Net Protein and Carbohydrate System (CNCPS). Diets were formulated to be co-limiting in intestinally absorbable supplies of methionine, lysine, and isoleucine. Cows were supplemented with no amino acids (control); lysine and methionine in a ruminally protected form; isoleucine by abomasal infusion; or lysine, methionine, and isoleucine in a 4x4 Latin square arrangement of treatments with 28-d periods. Performance of cows on all treatments was lower than expected due to low intake of DM that could have been caused by the high fiber level of the basal diet. This high fiber level was likely responsible for the high daily chewing times for cows fed all diets, which was consistent with the high ruminal pH values. Intake of DM and its components were not influenced by any treatment. Milk protein percentage tended to be higher when cows were fed diets supplemented with ruminally protected lysine and methionine; however, production of milk, milk fat, and milk lactose were not affected by any treatment. Cows tended to have a higher milk lactose proportion and tended to produce more milk and milk lactose when they were abomasally infused with isoleucine alone. However, when cows were supplemented with all three amino acids, milk production and composition did not differ from that of cows fed the unsupplemented diet. Use of the CNCPS to evaluate the performance of the cows fed the unsupplemented diet suggested that these cows may have been colimited by intestinally absorbable supplies of lysine, isoleucine, and methionine in addition to metabolizable protein. Evaluation of the unsupplemented diet with an alternate model, Shield, suggested that cows fed the unsupplemented diet may have been colimited by intestinally absorbable supplies of lysine, isoleucine, and arginine. Results suggest that enhanced delivery of intestinally absorbable isoleucine may stimulate milk lactose synthesis.
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