Thyroid hormones and daily gain in cattle. Relationships between plasma total thyroxine, free thyroxine, triiodothyronine and average daily gain during the first year of life in Belgian blue and Friesian cattle

Abstract

Link to this article: http://journals.cambridge.org/abstract_S0003356100010394How to cite this article: J. Fabry (1983). Thyroid hormones and daily gain in cattle. Relationships between plasma total thyroxine, free thyroxine, triiodothyronine and average daily gain during the rst year of life in Belgian blue and Friesian cattle. ABSTRACTCorrelation between circulating thyroid hormones and live-weight gain during the first year of life were observed in four trials on cattle of the two main Belgian breeds: Belgian Blue and Friesian. Thyroid hormones assayed and considered as potential predictors of growth rate were: thyroxine (T 4 ), triiodothyronine (T 3 ) and free thyroxine (FT 4 ). Triiodothyronine uptake (T,U), thyroid stimulating hormone (TSH) and free thyroxine index (FTI) were also estimated.' No significant correlation was found between live-weight gain and T 4 or T 3 in 13 Belgian Blue heifers (trial 1). In 49 bulls submitted to a performance test, T 4 and FTI increased from 3 to 12 months whilst T 3 U decreased (trial 2). Significant correlations between live-weight gain and T 4 and between live-weight gain and FTI were obtained from samples taken between 66 and 95 days. Live-weight gain was correlated with T 3 U when animals were between 96 and 125 days, and 126 to 155 days of age. It is possible that the interaction between total T 4 and T,U is important in controlling growth. In 13 young calves, beef merit, expressed as live-weight gain in 1 year, was highly correlated with T 4 concentration at 8 to 10 days of age (trial 3). T 3 and FT 4 did not seem to be directly associated with the growth processes. In trial 4, live-weight gains of 42 young animals housed on a commercial farm were negatively correlated with T 4 and with FTI. The conflicting results encountered may perhaps be explained by the lack of information on the use of anabolic preparations in field conditions. T 4 concentration and FTI may be considered as potential parameters for the estimation of beef merit but the results are insufficient to draw definite conclusions.