ARS | Publication request: N UTILIZATION IN ALFALFA HAY VERSUS ALFALFA SILAGE BY HOLSTEIN COWS: MILK PROTEIN SECRETION AND MICROBIAL N FLOW ESTIMATED FROM PURINE DERIVATIVE EXCRETION

Submitted to: Journal Dairy Science Supplement
Publication Type: Abstract Only
Publication Acceptance Date: July 17, 1996
Publication Date: N/A

Technical Abstract: Twelve multiparous Holstein cows were assigned to 3 replicated 4 x 4 Latin squares to evaluate N utilization in alfalfa conserved as silage (AS) vs hay (AH). Diets were arranged as a 2 x 2 factorial and contained (DM basis) either 75% forage (F) and 24% high moisture corn (C) or 55% F and 40% C. Milk and milk protein secretion were increased (P < .01) by increased dietary C; increased dietary C elicited a greater response in milk protein secretion on AS than AH diets (F x C level, P < .10). Purine derivative (PD) excretion and microbial N (MN) flow responded similarly; increasing in response to dietary C (P < .01), more so on AS than AH diets (P < .05). Results suggested that milk protein secretion was driven by MN supply in alfalfa-based diets, and that preservation of alfalfa as silage resulted in a deficiency of rumen fermentable energy vs N availability for MN synthesis. 75AH 75AS 55AH 55AS P > F Item 24C 24C 40C 40C SE F C FxC Milk, kg/d 29.6 28.2 31.6 31.8 .7 .35 <.01 .26 Milk protein, .96 .90 1.06 1.07 .02 .22 <.01 .09 kg/d PD 552 473 603 568 11 <.01 <.01 .05 excretion, mmol/d bacterial .604 .713 .570 .666 .001 <.01 .01 .55 N:purine, g/mmol MN flow,g/d 317 308 333 362 8 .22 <.01 .02