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Yield, butterfat, protein, lactose and solids-not-fat of milk from mature dams (n = 128) representing eight Bos taurus and Bos indicus X Bos taurus breed types were evaluated approximately 60, 105 and 150 d postpartum. Breed type was a significant source of variation in milk yield at each stage of lactation. Average 24-h milk yields (kg) were: Hereford, 7.3; Red Poll, 9.1; Hereford X Red Poll, 9.1; Red Poll X Hereford, 9.1; Angus X Hereford, 8.6; Angus X Charolais, 9.3; Brahman X Hereford, 7.3 and Brahman X Angus, 8.3. Daily yields of Brahman X Angus dams increased as lactation progressed, while production levels of other breed types remained approximately the same or declined. Hereford-Red Poll crosses showed significant heterosis in 24-h milk production and component yields at 150 d. Breed type effects also were significant for lactose yield throughout lactation. Sex of calf influenced (P less than .05) milk yield at 60 and 105 d postpartum and yield of protein and solids-not-fat at 105 d. Mastitis caused a reduction (P less than .01) in percentage of lactose but had no effect on milk yield. Residual correlations between yield traits and preweaning average daily gain were all positive and significant, with values ranging from .22 to .45. Breed type was a major source of variation in milk traits of beef-type Bos taurus and Bos indicus X Bos taurus dams.
Daley et al. (Sun,) studied this question.