The effect of level of diet intake after mating on the serum concentration of thyroxine, triiodothyronine, growth hormone, insulin and glucose, and embryonic survival in the gilt

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Abstract
Two experiments were undertaken to determine whether there was a relationship between embryo survival and the blood serum concentration of thyroxine (T4) triiodothyronine (T3), growth hormone (GH), insulin (INS), glucose (Glc) and progesterone (P4), as influenced by diet intake. In exp. 1, serum concentrations of T4, T3, INS, Glc and P4 were measured in samples collected at 0.0 (preprandial), 0.33, 0.67, 1.0, 1.5, 2.0, 3.0, 5.0 and 7.0 h (postprandial) on days 7, 11, 15 and 25 of gestation. In exp. 2, 16 control (C) gilts gained 0.49 ± 0.04 kg d−1, while 19 restricted (R) gilts were fed at the same level, except from days 1 to 10 after mating, when diet intake was restricted to 50% of the C gilts. The R gilts from days 0–10 and days 10–20 gained −0.01 ± 0.05 kg d−1 and 0.59 ± 0.06 kg d−1, respectively. Gilts were bled at 5 h postprandial on days 1, 4, 7, 9, 11, 13, 15, 20 and 25, and eight samples were collected on days 7, 11, 15 and 25, from 0–5 h postprandial. Embryo survival was expressed as a percentage of the number of corpora lutea. In exp. 1, T4 and T3 concentrations on day 7 were greater than those on days 11 and 15 (and day 25 for T4). The INS profile was not affected by day of gestation, while Glc profiles differed for days 7 and 25. In exp. 2, a day-of-gestation effect was observed for T4 and T3, with elevated levels on days 1 and 4. Postprandially, T4 increased by 20 min and remained constant, while T3 peaked at 1.5 h; GH showed no change; and INS peaked at 1 h. The INS peak for R gilts was lower on day 11, and GH concentration was lower for R gilts on days 7, 11 and 15. Correlations were only consistently significant between T4 and T3, and between INS and Glc, and for days 1–11 for progesterone with T4 and T3. Correlations of hormone concentrations with embryo survival were generally not significant. These results show that T4 and T3, GH and INS responded differently to the day of early gestation and to diet intake. There were no changes in hormone concentration that could be associated with embryo survival. Key words: Pregnant gilts, diet intake, metabolic hormones

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