Body Composition of Lactating and Dry Holstein Cows Estimated by Deuterium Dilution

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Abstract
In 3 experiments patterns of water turnover and body composition estimated by deuterium oxide were studied in Holstein cows. In the first experiment, 4 lactating cows were infused with deuterium oxide, and blood samples were taken during 4-d collection. Milking was stopped; cows were reinfused with dueterium oxide and resampled. Slopes of deuterium oxide and resampled. Slopes of deuterium oxide dilution curves indicated lactating cows turned water over more rapidly than nonlactating cows. In the second experiment with the same 4 cows,during 4-d collection, deuterium oxide concentrations in milk, urine, and feces showed dilution patterns similar to deuterium oxide in blood. Sampling milk may be an alternative to sampling blood. In the third experiment, 36 Holstein cows were fed 55, 65, or 65% alfalfa, smooth bromegrass, or equal parts of each forage as total mixed rations; remaining portions of rations were a grain mixture. Body composition was estimated at -1, 1, 2, 3, 4, and 5 mo postpartum. Empty body water, protein, mineral, fat, and fat percentage decreased from prepartum to postpartum. First calf heifers contained less empty body water, protein and mineral than older cows. Cows fed diets with 55% forage had more body fat than those fed diets with 75% forage. Cows fed alfalfa-based diets had more gastrointesitnal fill regardless of grain than cows fed diets that contained alfalfa and smooth broomegrass. Gastrointesitnal fill of cows increased from prepartum to 5 mo postpartum.