Growth and Development of the Major Carcass Tissues in Beef Calves from Weaning to Slaughter Weight, with Reference to the Effect of Plane of Nutrition

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Abstract
Thirty-six half-sib Hereford steer calves were used to determine the effect of plane of nutrition on the growth and development of beef calves from weaning to slaughter weight. The experimental design permitted comparison of data on both an age- and a weight-constant basis. Feed efficiency was greatest during the initial phase of the feedlot period and greatly favored the high-level steers over the age-constant moderate steers. On a weight-constant basis, however, little difference was noted in efficiency. Carcass grade and dressing percent also favored the high-level steers. The longissimus dorsimuscle matured faster at the 6th and 9th thoracic vertebrae than at the 12 th. Moreover, this muscle developed in a curvilinear fashion with increased animal age and by the mid-point of the postweaning feedlot period had attained 87% of its potential size. In all cases ribeye area favored the high-level steers. Lean deposition reached its maximum rate during the early part of the feedlot test and diminished as the animals approached maturity. By the H1 slaughter period the high and moderate calves had accumulated 86 and 78%, respectively, of their ultimate carcass lean. The average age of these calves was 10.8 months. The high-level steers produced more total lean than did the age-constant moderate steers, but no significant difference was noted in lean content when the calves were compared on a weight-constant basis. Rate of lean deposition favored the high-plane calves in all comparisons, however. Fat accumulation was most rapid during the latter half of the feeding period and showed a sharp increase after lean production began to subside. Thus, the lean: fat ratio became smaller and less desirable as the feedlot period was extended past this point. Experimental steers weighed approximately 355 kg. and were almost 11 months old at this time. Significant differences in fat content were obtained only with the H2-M2 comparison. Skeletal development was accomplished early in life and was related more to animal age and duration of feeding time than to the nutritional treatments imposed. The high-plane steers had attained about 96% of their mature scale by the H1 period. No significant difference in total bone content was noted between calves slaughtered at the same age. However, on a weight-constant basis, the moderate calves averaged 2 kg. (per side) more none than did the high-level calves. Copyright © 1965. American Society of Animal Science . Copyright 1965 by American Society of Animal Science

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