Precalving and early lactation factors that predict milk casein and fertility in the transition dairy cow.
Multiparous Holstein cows (n=82) of either high or low genetic merit (GM) (for milk fat + protein yield) were allocated to 1 of 2 diets in a 2×2 factorial design. Diets differed in the ratio of rumen-undegradable protein (RUP) to rumen-degradable protein (37% RUP vs. 15% RUP) and were fed from 21 d precalving to 150 days in milk. This study evaluated the effects of these diets and GM on concentrations of milk casein (CN) variants and aimed to identify precalving and early lactation variables that predict milk CN and protein yield and composition and fertility of dairy cows. It explored the hypothesis that low milk protein content is associated with lower fertility and extended this hypothesis to also evaluate the association of CN contents with fertility. Yields (kg/d) for CN variants were 0.49 and 0.45 of α-CN, 0.38 and 0.34 of β-CN, 0.07 and 0.06 for κ-CN, and 0.10 and 0.09 of γ-CN for high- and low-RUP diets, respectively. Increased RUP increased milk, CN, and milk protein yields. Increased GM increased milk protein and γ-CN yields and tended to increase milk CN yield. The effects of indicator variables on CN variant yields and concentrations were largely consistent, with higher body weight and α-amino nitrogen resulting in higher yields, but lower concentrations. An increase in cholesterol was associated with decreased CN variant concentrations, and disease lowered CN variant yield. A diet high in RUP increased proportion of first services that resulted in pregnancy from 41 to 58%. Increased precalving metabolizable protein (MP) balance decreased the proportion of first services that resulted in pregnancy when evaluated in a model containing CN percentage, milk protein yield, diet, and GM. This finding suggests that the positive effects of increasing dietary RUP on fertility may be curvilinear because cows with a very positive MP balance before calving were less fertile than those with a lower, but positive, MP balance. Prepartum MP balance was important to production and reproductive outcomes, but surprisingly, metabolizable energy balance was not. The hazard of pregnancy in the first 150 d of lactation was 28% lower in cows producing milk with the lowest quartile of protein percentage compared with cows with milk in the upper 3 quartiles. Milk CN percentage was positively associated with improved pregnancy at first service. This study demonstrates the importance of protein metabolism to reproductive performance of the dairy cow.
Scibus, Camden, New South Wales, Australia 2570; Faculty of Veterinary Science, The University of Sydney, Camden, New South Wales, Australia 2570. Electronic address: rachaelr@scibus.com.au.
Rachael M
RM
Rodney
Halltech Services, Orange, New South Wales, Australia 2800.
Jenianne K
JK
Hall
Kimihia Research Centre, PGG Wrightson Seeds Limited, Lincoln, Canterbury, New Zealand 7640.
Charlotte T
CT
Westwood
Animal Nutrition and Health, DSM Nutritional Products, Columbia, MD 21045; Faculty of Veterinary and Agricultural Sciences, The University of Melbourne, Parkville, Victoria, Australia, 3010.
Pietro
P
Celi
Scibus, Camden, New South Wales, Australia 2570; Faculty of Veterinary Science, The University of Sydney, Camden, New South Wales, Australia 2570.
Ian J
IJ
Lean
D000821:Animal Feed / Q000032:analysis; D000818:Animals; D002364:Caseins / Q000008:administration & dosage*; D002417:Cattle / Q000235:genetics / Q000502:physiology*; D004032:Diet / Q000662:veterinary; D004044:Dietary Proteins / Q000008:administration & dosage; D005260:Female; D005298:Fertility / Q000187:drug effects; D007774:Lactation / Q000187:drug effects*; D008892:Milk / Q000737:chemistry*; D008894:Milk Proteins / Q000378:metabolism*; D011247:Pregnancy; D011897:Random Allocation; D012098:Reproduction / Q000187:drug effects*
D002364:Caseins; D004044:Dietary Proteins; D008894:Milk Proteins
casein; fertility; protein degradability