Milk production response to varying protein supply is independent of forage digestibility in dairy cows.
The aim of this experiment was to examine whether the positive response in milk production to increased crude protein (CP) supply in dairy cows was dependent on the digestibility of the forage. Forty-eight lactating Danish Holstein cows were used in a 4 × 4 Latin square design experiment with 4 rations: (1) high digestibility and high CP concentration (HdHp), (2) high digestibility and low CP concentration (HdLp), (3) low digestibility and high CP concentration (LdHp), and (4) low digestibility and low CP concentration (LdLp). All rations contained 30% corn silage, 25% grass-clover silage, and 45% concentrate on a dry matter (DM) basis. Different digestibilities were obtained by replacing a high-digestible grass-clover silage combined with a high-digestible corn silage with a low-digestible grass-clover silage combined with a low-digestible corn silage. Organic matter digestibilities were 79.8 and 74.7% in the high- and low-digestibility rations, respectively. Dietary CP concentration in the ration was increased by substituting barley and sugar beet pulp with rapeseed meal and soybean meal, whereby CP increased from 13.9 to 14.0% (Lp) to 15.7 to 16.0% (Hp). All cows were offered 3 kg of the same concentrate per day in the automatic milking system in addition to the mixed ration. Every feeding period lasted 3 wk, and DM intake and milk yield were measured in the last week in each period, and milk samples for determining milk composition, including fatty acid content, and blood samples were taken during the last 3d of each period. Dry matter intake increased by 2.2 kg/d on Hd compared with Ld and by 0.7 kg/d on Hp compared with Lp. The positive effect on DM intake was reflected in the energy-corrected milk (ECM) yield, as a higher ration digestibility increased the ECM yield by 1.7 kg/d and a higher CP concentration increased it by 1.2 kg/d. We detected no interaction between forage digestibility and CP concentration on milk production. Reduced digestibility was accompanied by an increase in the plasma level of glucose, suggesting that other nutrients were limiting to milk production. In conclusion, milk production responses to dietary CP supply appeared independent of forage digestibility.
Department of Animal Science, AU Foulum, Aarhus University, DK 8830 Tjele, Denmark. Electronic address: Lene.Alstrup@agrsci.dk.
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L
Alstrup
Department of Animal Science, AU Foulum, Aarhus University, DK 8830 Tjele, Denmark.
M R
MR
Weisbjerg
Department of Animal Science, AU Foulum, Aarhus University, DK 8830 Tjele, Denmark.
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L
Hymøller
Department of Food Science, AU Foulum, Aarhus University, DK 8830 Tjele, Denmark.
M K
MK
Larsen
Department of Animal Science, AU Foulum, Aarhus University, DK 8830 Tjele, Denmark.
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P
Lund
Department of Veterinary Clinical and Animal Sciences, Faculty of Health and Medical Sciences, University of Copenhagen, DK 1870 Frederiksberg C, Denmark.
M O
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Nielsen
D000818:Animals; D001786:Blood Glucose / Q000378:metabolism; D002087:Butyrates / Q000097:blood; D002417:Cattle / Q000502:physiology*; D002784:Cholesterol / Q000097:blood; D004032:Diet / Q000662:veterinary; D004041:Dietary Fats / Q000032:analysis; D004044:Dietary Proteins / Q000008:administration & dosage*; D004063:Digestion; D005227:Fatty Acids / Q000032:analysis; D005260:Female; D001467:Hordeum; D007774:Lactation; D019344:Lactic Acid / Q000097:blood; D007785:Lactose / Q000032:analysis; D000455:Medicago sativa; D008892:Milk / Q000737:chemistry* / Q000378:metabolism*; D008894:Milk Proteins / Q000032:analysis; D006109:Poaceae; D012820:Silage / Q000032:analysis*; D029921:Trifolium; D014280:Triglycerides / Q000097:blood; D014508:Urea / Q000097:blood; D003313:Zea mays; D005723:gamma-Glutamyltransferase / Q000097:blood
D001786:Blood Glucose; D002087:Butyrates; D004041:Dietary Fats; D004044:Dietary Proteins; D005227:Fatty Acids; D008894:Milk Proteins; D014280:Triglycerides; D019344:Lactic Acid; D014508:Urea; D002784:Cholesterol; D005723:gamma-Glutamyltransferase; D007785:Lactose
corn and grass clover silage; mammary nutrient supply and extraction; milk fatty acids