Portal de Periódicos da CAPES

THYROID HORMONE CONCENTRATIONS: SOME KINETIC PARAMETERS OF TRIIODOTHYRONINE AND METABOLIC RATE IN 'DOUBLE-MUSCLED' CATTLE

1982; Canadian Science Publishing; Volume: 62; Issue: 2 Linguagem: Inglês

10.4141/cjas82-045

1918-1825

R. A. Strath, J. A. Basarab, James R. Thompson, R. T. BERG,

Birth, Development, and Health

Serum triiodothyronine (T 3 ) and thyroxine (T 4 ) concentrations were determined in 43 cattle of a Beef Synthetic (SY) breed group and 44 cattle of a 'double-muscled' (DM) breed group at the University of Alberta. Animals within the DM breed group were categorized as phenotypically normal, moderate or extreme based on the degree of phenotypic expression of the 'double-muscling' trait. Serum T 3 concentration was significantly influenced by the degree of phenotypic expression of the double-muscling trait with phenotypically extreme-muscled DM animals demonstrating an increased T 3 concentration as compared with phenotypically normal DM and SY cattle. Serum T 3 concentrations in the phenotypically moderate-muscled DM cattle were intermediate. A nonsignificant trend was observed for the phenotypically extreme-muscled DM cattle to have an elevated serum T 4 concentration as compared with the other phenotypes. The phenotypically moderate-muscled DM and normal SY cattle tended to be intermediate to phenotypically extreme- and normal-muscled DM cattle in serum T 4 concentrations. In another study, some kinetic parameters of T 3 were determined in three normal- to moderate-muscled, 19-mo-old DM bulls and three of their extreme-muscled DM half-siblings. The extreme DM cattle exhibited a significantly increased T 3 pool size and a trend towards an increased T 3 irreversible loss as compared with their half-siblings. The total T 3 entry rates in extreme DM cattle and normal- to moderate-muscled cattle were not observed to be significantly different. The metabolic rate of four normal- to moderate-muscled DM bulls and four of their extreme-muscled DM half-siblings were compared. The metabolic rate of the extreme-muscled DM cattle was significantly (P < 0.05) higher than that of their half-sibling carriers. The increased serum T 3 concentration, the larger T 3 pool size and the elevated irreversible loss combined with the higher metabolic rate in the extreme DM cattle suggest that this heavily muscled animal type is relatively hyperthyroid. Key words: Thyroxine, triiodothyronine, metabolic rate, double-muscling, cattle