Effects of increasing dosages of zeranol implants on lamb growth, carcass characteristics, blood hormones, and nitrogen metabolism

Effects of weaning on total and free iodothyronines in lambs

BACKGROUND

Weaning is a crucial period in the management of lambs, resulting in physiological and mental challenges, that may have prolonged effects on lamb's health and welfare.

HYPOTHESIS/OBJECTIVES

To evaluate the effect of weaning on total and free triiodothyronine (T3, fT3) and thyroxine (T4, fT4) concentrations in serum of lambs by enzyme immunoassay. Animal and methods: The study was performed on two groups of 17 clinically healthy Comisana cross-bred lambs (7 males and 10 females) with or without weaning at 10 weeks of age. Serum samples were collected at the age of 8 weeks, 24 h and 2 weeks after weaning in the experimental group and at similar times in the non-weaned control group. Enzyme immunoassay was performed. Statistical analysis was done by one-way analysis of variance.

RESULTS

Compared to control animals, weaned animals showed significantly decreased T3 and elevated T4 concentrations two weeks after weaning with higher concentrations in both males and females in contrast to 24 h after weaning. Body weight (BW) was significantly restored in both females (11% increase) and males (6%) two weeks after weaning as compared to 24 h after weaning. No gender effects were shown for total and free iodothyronine changes. Significant positive correlations were observed between BW and T4 concentrations in both females (r = 0.692) and males (r = 0.856), fT3 concentrations in males (r = 0.968) and fT4 concentrations in females (r = 0.862).

CONCLUSION AND CLINICAL IMPORTANCE

Total iodothyronines could represent an indicator of their different metabolic activity with their magnitude altered two weeks following weaning.