Relationship between plasma concentrations of thyroid hormones and physiological state of beef cow/calf pairs

Abstract Text:

Triiodothyronine (T₃) and thyroxine (T₄) are important mediators of energy expenditure, growth, and thermogenesis.  The prohormone T₄ is converted to the biologically active form, T₃.  Relationships between concentrations of T₃ and T₄ in cows and their offspring have not been defined.  Spring calving, Angus cow/calf pairs (n = 27) were used to evaluate the relationship between plasma concentrations of T₃, T₄, and T₄:T₃ in cattle of different physiological ages.  Calves were weighed at birth and bulls were castrated by banding.  Weights of cows and calves were recorded at 48 and 97 d post partum and blood samples were collected at 97 d post partum.  Plasma concentrations of T₃ and T₄ were quantified by RIA.  Triiodothyronine, T₄, and the ratio of T₄ to T₃ (T₄: T₃) were analyzed with PROC CORR and PROC MIXED (SAS Inst. Inc.).  Plasma concentrations of T₄ did not differ between cows (P = 0.17, 40.5 ± 7.4 ng/ml) and calves (59.2 ± 7.4 ng/ml).  Concentrations of T₄ in cows and their calves were not correlated (P = 0.40).  Concentrations of T₃ tended to be greater in calves (P = 0.06; 1.99 ± 0.17 ng/ml) compared with cows (0.88 ± 0.17 ng/ml).  Concentrations of T₃ in plasma were correlated (r = -0.43, P = 0.03) between cows and their calves.  Plasma concentrations of T₄:T₃ in cows were greater (P < 0.001; 49.0 ± 9.3) compared with calves (31.3 ± 9.3) and T₄:T₃ was not correlated between cows and their calves (P = 0.83).  The T₄: T₃ in calves was correlated with T₃ (r = 0.45, P = 0.02) in their dams and tended to be positively correlated with T₄ (r = 0.38, P = 0.06) in their dams.  Concentrations of T₄ in calves and T₃ in cows were not correlated (P = 0.87).  Average daily gain of calves was not correlated with T₄, T₃, or T₄: T₃ in cows or calves (P ≥ 0.12).  Concentrations of T₃ tended to be greater in calves compared with their dams; however, concentrations of T₄ were similar.  These results indicate thyroid function in cows and their calves was related as plasma concentrations of T₃ were negatively correlated.  Production efficiency of beef cows and calves may be enhanced by identifying individuals with greater metabolic efficiency.

Keywords: Thyriod hormone, beef cattle, metabolism