Postnatal thyroxine status of piglets in response to prenatal thyroxine infusion of the sow

Abstract

Fifteen pregnant primiparous sows were infused intravenously with either 0 (T40), 25 (T425), or 50 (T450) mg thyroxine (T4) d−1 between days 102 and 112 of gestation. Piglets were observed for the birth to suckling interval (BTS) during the first 6 h of life. At 6 h, pre-determined piglets were subjected to a cold challenge, consisting of exposure to an environment of 5 °C for 2 h. Rectal and skin temperatures of piglets were recorded from birth to 8 h of life. Body weights of piglets and their plasma-T4 concentrations were measured until 4 wk of age. Infusion with T4 increased the sow's plasma-T4 levels (P < 0.05) during the entire infusion period. No postnatal differences in piglet plasma-T4 concentrations were observed as a consequence of the prenatal treatment of the sows. BTS was not influenced by treatment. Piglets of all groups had similar rectal temperatures within 2 min of birth (P > 0.05). During cold exposure, the rectal and skin temperatures of all the piglets decreased (P > 0.05). It can be concluded that prenatal priming of sows with T4 does not influence BTS, thermoregulatory capability or subsequent performance of piglets, probably because of low rates of transport of thyroxine across the placenta. Key words: Thyroxine, thermoregulation, temperature, cold, piglet