Genetic control of equilibrium maintenance efficiency in cattle

Abstract

Twenty-two unmated female Ayrshire twin cattle, that had initially been maintained for prolonged periods on one of six constant feeding levels until an equilibrium weight was attained, were subsequently moved up to higher constant feeding levels including ad libitum. In all, results were obtained for 44 equilibrium periods mostly of 96 weeks duration.For controlled feeding levels, the log^-log,. regression of equilibrium body weight on food intake, within animals, was 0-999 (s.e. 0045). For all results, including mature equilibria, the within-animal regression was 1-014. There was thus no systematic change in an individual's equilibrium maintenance requirement per kg body weight in the range from 25",, to 100",, mature. Efficiency of food utilization for equilibrium maintenance was found to be independent of age also, except for a small increase at advanced ages beyond 8 to 9 years.There were significant differences between animals in equilibrium maintenance efficiency, the genetic coefficient of variation being 6-4%. The most striking result, however, was a within-animal repeatability of 0-7, which meant that almost the same efficiency was re-attained when, after a prolonged period of many years on one constant feeding level, the same animal was allowed to re-establish a new equilibrium on a higher level.Following prolonged periods of food restriction, the animals showed remarkable capacity to recover in body weight even at very advanced ages, but nevertheless substantial stunting of mature weight did occur.

Rate and Efficiency of Gain in Hereford and Angus Bulls From Lines Selected for Rapid Growth on High-Energy and Low-Energy Diets

“…The lines were established in 1963 and selection began in 1964. ln April of 1982April of ,1983April of , and 1984 Es (1978Es ( , 1980, and allowing their weights to reach equilibrium. This approach was based on the finding that body weights of cattle on fixed energy intakes eventually stabilized and remained fairly constant over long periods of time (Taylor et al 1981 .…”

“…Procedures used for carrying out the digestibility trials were as described in an earlier report Maintenance energy requirements were estimated from a subsidiary experiment in which 24 bulls ranging from 280 to 520 kg liveweight were provided enough of the present feed, (70% concentrate, 3O% hay) to satisry their maintenance requirements according to data compiled by van Es (1978Es ( , 1980, and allowing their weights to reach equilibrium. This approach was based on the finding that body weights of cattle on fixed energy intakes eventually stabilized and remained fairly constant over long periods of time (Taylor et al 1981 …”

Prediction model of a joint analysis of beef growth and carcass quality traits

“…In some cases such as the VLVL scheme in heifers and steers, when nutrient restriction has been imposed during backgrounding and feedlot at a level much more severe than what might occur due to seasonal variation in a grazing system or other stresses, a reduction in mature size or permanent stunting has been observed (Taylor et al, 1981). However, the importance of such findings to this subject area is minimal since, while this could occur during periods of extended drought, this type of restriction would never purposely be applied at the field level due to its obvious negative results.…”

Energetic efficiency of protein and body fat retention in crossbred Bos indicus and Bos Taurus × Bos indicus raised under tropical conditions

“…This concept is based on experimental results conducted by Taylor et al (1981) which showed a constant ratio between body mass and feed intake in Ayrshire cattle with body weight varying from 25 to 100% of the weight normally presented by this genetic group at maturity. These authors reported metabolizable energy intakes of 31.2 to 35.6 kcal/kg body mass in animals kept at constant weight for long periods of time, which indicated that all the energy consumed in this period was transformed to heat, that is, it was used for maintenance.…”

“…The maintenance requirement of a certain genetic group is constant in relation to live weight when the animal is in real energetic equilibrium, that is, when its metabolism is stabilized at an intake level regardless of whether this level is above or below maintenance (Taylor et al, 1981). Therefore, the requirements vary with energy intake, due to the support metabolism.…”