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Texas Agricultural Experiment Station, Texas A&M University,3, College Station 77843
Abstract
Milk production was measured in fourteen Quarter Horse mares at seven stages of a 150-d lactation period. Mares were divided into two groups of seven and fed diets containing either soybean meal or soybean meal and urea as nitrogen supplements. Rations were isocaloric, contained approximately 12.5% crude protein and were fortified with vitamins and minerals. Daily milk yield was estimated by the weigh-suckle-weigh method and milk composition was determined from samples taken by hand milking. Average daily milk yield ranged from 11.8 kg in early lactation to 9.8 kg in late lactation. Differences (P<.01) in milk yield due to number of previous lactations were observed. Also, diet influenced (P<.01) milk yield, with mares fed soybean meal producing an average of 1.2 kg more milk/d than mares fed urea as part of the N supplement. Further, stage (day) of lactation influenced (P<.01) daily milk yield. The largest mean daily milk yield was measured at approximately 30 d postpartum, but the predicted lactation curve was linear (P<.05) over the range of observations in this study. Average percentages of total solids, protein and fat over the 150-d lactation were 10.5, 2.1 and 1.3, respectively. All components decreased significantly with advancing lactation. There was a trend toward a positive association between milk yield and solids content of the milk, but it was not significant. Milk yield was not significantly related to fat content of the milk. However, milk yield and protein content were correlated (r = .23; ( P<.05). As expected, solids content of the milk was positively associated with percentages of protein (r = .59; P<.01) and fat (r = .44; P<.01). Relationships among milk components were similar after adjustment for days in milk. However, yield of milk and composition were unassociated (P>.05) when days in milk were held constant.
1 Technical Article 16259, Texas Agr. Exp. Sta.
2 Dairy Section, Dept. of Anim. Sci.
3 Dept. of Large Anim. Med. and Surgery.
4 Horse Section, Dept. of Anim. Sci.
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