title: Effects of the m gene for muscular hypertrophy on birth weight and growth to one year of age in beef cattle.
abstract: 182 calves, mostly Angus but also of Hereford and Shorthorn breeding, born in the University herd, were studied, including 55, born during Spring 1970, genotypically distributed as 8 mm, 33 m+ and 14 ++. Eighteen of the 24 homozygotes (mm) had the typical double-muscled conformation at birth (mmY); in the remainder, the typical bulging muscles usually manifested themselves within one month after birth. Averaged over sexes, mmY calves were 4.4 kg heavier (P less than 0.05) than the Angus (++) breed average of 26.6 kg. Compared within-sires, mmY calves were 4.0 kg heavier than m+. Heterozygotes (m+) were 0.4 kg heavier than the normal (++) average. Estimating differences between mm, m+ and ++ for post-natal traits was confined to the 1970 calves because experimental conditions were controlled. Double-muscled (mm) calves had a higher (+7%) 180-day weight compared with normal (++) calves. After weaning at approximately 180 days, until yearling age, bulls and heifers received diets with roughage:concentrate ratios of 75:25 and 70:30, respectively. The post-weaning growth rate of mm calves was depressed (-17%) due to a reduced (-11%) feed intake compared with non-mm controls. Homozygotes had a lower (-4%) liveweight at 365 days, compared with ++ animals. Least squares estimates of the difference (m+ - ++) at birth, 180 days and 365 days were -1.0 +/- 1.0 kg, +7.3 +/- 4.5 kg and +7.3 +/- 6.3 kg, respectively.
mesh_terms: D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D001724:Birth Weight; D001835:Body Weight; D002417:Cattle / Q000235:genetics* / Q000502:physiology; D002418:Cattle Diseases / Q000235:genetics*; D005799:Genes, Dominant; D006128:Growth; D006984:Hypertrophy / Q000662:veterinary; D009132:Muscles / Q000473:pathology; D009135:Muscular Diseases / Q000235:genetics / Q000662:veterinary*