Growth Hormone Variability and its Predictive Value in Beef Females

Endocrine influence on metabolism determines the rate and extent of growth of an animal. A thorough understanding of hormones and their influence is necessary to the meat animal industry for advancement of efficient production to supply a growing world demand for food. Many hormones affect metabolism, but growth hormone (GH) appears to have one of the smallest fluctuations in circulating levels. Previous research indicates nonsignificant changes in plasma growth hormone (GH) due to season, circadian rhythm or level of nutrient intake. Factors that have been identified a s influencing GH level are sex, age, roughage content of the diet, breed, estrus and lactation. This study provided for examination of GH levels in beef females over a period of time (8 to 44 mo. of age) not previously reported. The objectives of this study were to examine environmental influences on GH and to evaluate the relationship of GH levels to performance. Continued observation of performance collected for lifetime efficiency studies permitted investigation of relationships to performance in beef cattle that have not been previously examined .Data from 170 female Angus, Charolais and reciprocal cross beef cattle produced in three consecutive calf crops (1970 to 1972) were used in this study of plasma growth hormone (GH) which was a part of a total project investigating efficiency of production. Cattle were assigned randomly within breed to either a dry lot or pasture management regime. Culling criteria were failure to conceive during first breeding season, failure to wean a calf in 2 consecutive year and disabling physical injury. Cattle were maintained until completion of the project in 1979