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Aust Vet J. 2008 Sep;86(9):341-51. doi: 10.1111/j.1751-0813.2008.00335.x.

Effects of increasing days of exposure to prepartum transition diets on milk production and milk composition in dairy cows.

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1
Veterinary Clinical Studies, University of Sydney, NSW, Australia.

Abstract

OBJECTIVE:

To evaluate the effects of length of exposure to prepartum transition diets on milk yield, fat and protein production.

DESIGN:

Prospective cohort study. The number of days that the cows were fed the prepartum transition diets was the exposure of interest.

PROCEDURES:

Holstein and Holstein x Jersey cows (n = 1008) were enrolled. Diets given in the far-off dry period (from end of lactation until approximately 3 weeks before expected parturition) consisted of ad libitum access to perennial ryegrass pastures. Prepartum transition diets included perennial ryegrass pasture, ryegrass silage, cereal hay, grain, grain by-product, protein meals, BioChlor, sodium monensin, virginiamycin or tylosin, MgSO(4), trace elements and vitamins. On a dry matter basis, these contained 16.0% crude protein, 4.2% rumen undegradable protein, and 9.9 mJ metabolisable energy/kg. Diets provided an estimated metabolisable protein balance of 286 g/day and dietary cation anion difference of -150 meq/kg dry matter. Statistical models controlled for effects of herd, calving day, breed, age and gestation period.

RESULTS:

Increasing length of exposure to the prepartum transition diets significantly increased the 4.0% fat- and 3.2% protein-corrected milk yield and milk-protein yield as a linear and quadratic effect. The optimal duration of exposure to the prepartum transition diets was 25 days for fat- and protein-corrected milk production and 22 days for milk protein production. Milk-fat percentage decreased significantly and linearly with increasing exposure to the prepartum transition diets; however, milk-fat yield or milk-protein percentage did not vary significantly with duration of exposure to the diets.

CONCLUSIONS:

Increasing exposure to prepartum transition diets increased milk and milk-protein yields and decreased the milk fat-percentage, but not the milk-protein percentage or milk-fat yield.

[Indexed for MEDLINE]

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