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Effect of Exogenous Thyroxine on the Interval from Weaning to Estrus of the Primiparous Sow^1,2,

University of Nebraska³, Lincoln 68583-0908

Abstract

A total of 159 primiparous sows were fed 0 (C) or 675 mg/d of thyroprotein (TP) from d –2 until d 14 postweaning. Sows received 8 (LE) or 14 (HE) Meal of ME/d during a 28-d lactation period. Plasma levels of 3,5,3'-triiodothyronine (T₃) and 3,5,3',5'-tetraidothyronine (T₄) were determined for d –4, –2, 0, 1, 2, 3, 5 and 7 postweaning. Sows consuming LE lost more weight and backfat during lactation (P < .01) than HE sows. Litters of sows consuming LE gained less weight than litters of sows consuming HE (P < .01). Thyroprotein increased plasma levels of both T₃ and T₄ (P < .01), whereas energy intake had no effect (P > .10) on either of the two hormones. The response to thyroid hormone was not consistent across days postweaning (TP x day, P < .01). Feeding TP increased T₄ (P < .01) on all days, and T₃ was increased (P < .05) on d 0, 2 and 3 postweaning. Thyroid hormones rose markedly following weaning regardless of TP level. Percentage of sows in estrus by d 7 postweaning for LE-C, LE-TP, HE-C and HE-TP were 80, 78, 92 and 90, respectively. Energy restriction during lactation resulted in fewer sows returning to estrus by d 7 (P < .03) than those fed HE. However, feeding TP postweaning had no effect on return to estrus, suggesting that the effect of dietary energy restriction during lactation on the interval from weaning to first estrus is not mediated through postweaning thyroid hormone concentrations.

¹ Published as paper no. 8567. Journal Series Nebraska Agric. Res. Div.

² The technical assistance of Georgette A. Caddy, Ruth M. Diedrichsen, Joy L. Kovarand Ken A. Pearson and manuscript preparation by Diana J. Smith is gratefully acknowledged.

³ Dept. of Anim. Sci.