POSTNATAL THYROXINE STATUS OF PIGLETS IN RESPONSE TO PRENATAL THYROXINE INFUSION OF THE SOW

Fifteen pregnant primiparous sows were infused intravenously with eith er 0 (T(4)0), 25 (T(4)25), or 50 (T(4)50) mg thyroxine (T4) d-1 betwee n days 102 and 112 of gestation. Piglets were observed for the birth t o suckling interval (BTS) during the first 6 h of life. At 6 h, pre-de termined piglets were subjected to a cold challenge, consisting of exp osure to an environment of 5-degrees-C for 2 h. Rectal and skin temper atures of piglets were recorded from birth to 8 h of life. Body weight s of piglets and their plasma-T, 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 p iglet plasma-T, concentrations were observed as a consequence of the p renatal treatment of the sows. BTS was not influenced by treatment. Pi glets of all groups had similar rectal temperatures within 2 min of bi rth (P > 0.05). During cold exposure, the rectal and skin temperatures of all the piglets decreased (P > 0.05). It can be concluded that pre natal 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.