IngentaConnect Effects of increasing days of exposure to prepartum transition di...

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 × 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, MgSO₄, 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.

Aust Vet J 2008;86:341-351

Keywords: dairy cows; milk production; transition nutrition

Document Type: Research article

DOI: 10.1111/j.1751-0813.2008.00335.x

Affiliations: 1: Veterinary Clinical Studies, University of Sydney, NSW, Australia 2: Bovine Research Australasia, PO Box 660, Camden, NSW 2570, Australia;, Email: ianl@dairydocs.com.au 3: Epicentre, Massey University, Palmerston North, New Zealand

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