Source: US National Library of Medicine
Brito AF1, Tremblay GF2, Bertrand A2, Castonguay Y2, Bélanger G2, Michaud R2, Lafrenière C3, Martineau R4, Berthiaume R5.
1. University of New Hampshire, Department of Biological Sciences, Durham 03824.
2. Soils and Crops Research and Development Centre, Agriculture and Agri-Food Canada, Québec City, QC, Canada G1V 2J3.
3. Université du Québec en Abitibi-Témiscamingue, Rouy-Noranda, QC, Canada J9X 5E4.
4. Dairy and Swine Research and Development Centre, Agriculture and Agri-Food Canada, Sherbrooke, QC, Canada J1M 1Z3.
5. Valacta, Dairy Production Centre of Expertise Québec-Atlantic, Sainte-Anne-de-Bellevue, QC, Canada H9X 3R4. Electronic address: email@example.com.
The objective of this study was to investigate the effects of feeding alfalfa baleage with different concentrations of nonstructural carbohydrates (NSC) supplemented with a common corn-based concentrate on performance, ruminal fermentation profile, N utilization, and omasal flow of nutrients in dairy cows during early lactation. Ten multiparous (8 ruminally cannulated) and 8 primiparous Holstein cows were randomly assigned to treatments (high- or low-NSC diet) in a crossover design. The difference in NSC concentration between the 2 alfalfa baleages fed from d14 to 21 averaged 14 g of NSC/kg of dry matter (DM). Forages and concentrate were offered in separate meals with forages fed once and concentrate offered 3 times daily. Except for the molar proportion of valerate, which was lowest in cows fed the high-NSC diet, no other changes in ruminal fermentation were observed. Omasal flows of most nitrogenous fractions, including bacterial nonammonia N and AA, were not affected by treatments. Apparent ruminal digestibilities of neutral and acid detergent fiber and N were lowest, whereas that of total ethanol-soluble carbohydrates was highest when feeding the high-NSC diet. Postruminal digestibilities of DM, organic matter, fiber, and N were highest in cows fed the high-NSC diet, resulting in no difference in total-tract digestibilities. Total-tract digestibility of total ethanol-soluble carbohydrates was highest in cows fed the high-NSC diet, but that of starch did not differ across treatments. Although milk yield and total DM intake did not differ between treatments, yields of milk fat and 4% fat-corrected milk decreased significantly in cows fed the high-NSC diet. Milk concentration of urea N was lowest, and that of ruminal NH3-N highest, in cows fed the high-NSC diet. Plasma urea N concentration tended to be decreased in cows fed the high-NSC diet, but concentrations of AA were not affected by treatments, with the exception of Asp and Cys, both of which were lowest in cows fed the low-NSC diet. Feeding diets with contrasting NSC concentrations did not improve milk production, N utilization, or bacterial protein synthesis, possibly because intakes of NSC and DM were similar between treatments. Overall, results from the current study should be interpreted cautiously because of the lack of difference in dietary NSC intake between treatments and reduced N and fiber intakes when feeding the high-NSC diet.