Abstract
Thermoneutral and norepinephrine-induced changes in thermogenesis, plasma metabolite (glucose, NEFA), and hormone (cortisol, triiodothyronine, T3; thyroxine, T4) concentrations were measured in newborn Angus (A; n = 5), Brahman (B; n = 10), A x B (n = 7), B x A (n = 8), Tuli (T) x A (n = 7), and T x B (n = 9) calves. Norepinephrine-induced peak metabolic rates are reflective of brown adipose tissue function. At birth each calf was fed colostrum and fitted with an indwelling jugular catheter. Heat production was measured by indirect calorimetry and blood samples collected prior to and following norepinephrine infusion at 35 jig- kg-I-min-1 for 4 min. Calves bom to B dams were 12.9% lighter than calves bom to A dams. Weight-specific therrnoneutral metabolic rates (TMR) were similar for all calf breed types and averaged 28.5 cal-kg-I-min-1. Calves bom to B dams had lower (P <.0001) weight-specific peak metabolic rates (PMR) than calves bom to A dams. However, the magnitude of the reduction for PMR was sire breed dependent (sire x dam interaction; P < .00 1). The B matemal reduction in PMR was greatest for T-sired calves (34.3% decrease in TB vs TA), intermediate for B-sired calves (1 5.3% decreased in BB vs BA) and lowest for A-sired calves (4. 1 % decrease in AB vs AA). Peak tympanic temperatures were significantly correlated with PMR (r = .46) and reflected treatment differences found in PMR. At birth, plasma NEFA (P < .001), cortisol (P <.10), and T3 (P <.01) concentrations were higher in calves bom to B dams than A dams. Moreover, plasma T4 concentrations were 28.6% higher in calves bom to B dams than A dams at birth and following norepinephrine infusion. These results suggest that calves bom to B dams have lower nonshivering therrnogenic capabilities than calves bom to A dams, which may be a contributing factor to higher neonatal mortality in calves of Bos indicus breeding.
Mostyn, Paul Curtis (1995). Genotypic influences on norepinephrine-induced change in thermogenesis and plasma constituents in newborn calves. Master's thesis, Texas A&M University. Available electronically from
https : / /hdl .handle .net /1969 .1 /ETD -TAMU -1995 -THESIS -M676.