Effects of the method of conservation of timothy on nitrogen metabolism in lactating dairy cows.
Six ruminally and duodenally cannulated lactating primiparous Holstein cows were used to study the effects of different methods of conservation of timothy on N metabolism. Cows were assigned randomly to 2 replicated 3 x 3 Latin squares (35-d periods). Because of missing data from 2 cows, data were analyzed as a 3 x 4 Youden square. Diets contained a similar concentrate (44% of total ration on a dry matter basis) plus first-cut timothy conserved as hay, or as restrictively (formic) or extensively fermented silage (inoc). Crude protein contents were 10.4, 13.6, and 14.8% for hay, formic, and inoc, respectively. Hay and formic had a high soluble carbohydrate content (> or =8.0% of dry matter) and formic and inoc had a high soluble protein content (> or =8.0% of dry matter). Haying and restricting fermentation resulted in increased efficiency of partition to milk N (30.9, 28.2, 24.7% of N intake for hay, formic, and inoc, respectively). Despite a 14% lower N intake with hay, no effects of treatments were detected on microbial protein synthesis and apparent intestinal digestion of essential AA. Haying reduced feed protein degradation in the rumen, whereas this effect was not observed when restricting fermentation in the silage. Haying and restricting fermentation induced a lipogenic fermentation pattern in the rumen (4.55, 4.23, and 3.78 ratio of acetate to propionate for hay, formic, and inoc), but no effects on milk fat yield and plasma glucose were observed. Whole-body protein metabolism was unaffected by treatments.
Martineau
R
R
Département des Sciences Animales, Université Laval, Québec, Québec, Canada G1K 7P4.
Lapierre
H
H
Ouellet
D R
DR
Pellerin
D
D
Berthiaume
R
R
D000821:Animal Feed; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D002417:Cattle / Q000378:metabolism / Q000502:physiology*; D004040:Dietary Carbohydrates / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism; D004044:Dietary Proteins / Q000008:administration & dosage / Q000032:analysis / Q000378:metabolism; D005260:Female; D005285:Fermentation; D005511:Food Handling / Q000379:methods*; D007774:Lactation / Q000378:metabolism*; D008892:Milk / Q000737:chemistry*; D009584:Nitrogen / Q000378:metabolism*; D031784:Phleum; D014176:Protein Biosynthesis; D011897:Random Allocation; D012417:Rumen / Q000378:metabolism*; D012820:Silage
D004040:Dietary Carbohydrates; D004044:Dietary Proteins; D009584:Nitrogen