. 1993. Postnatal thyroxine status of piglets in response to prenatal thyroxine infusion of the sow. Can. J. Anim. . Fifteen piegnant primiparous sows were infused intravenously with either 0 (T10), 25 (T425), or 50 (Ta50) mg thyroxine (To) I-'infusion de To a accru (P < 0,05) les niveaux plasmatiques de la"truie durant toute la dur6e de I'infusion. Toutefois, le traitement pr6natal des truies n'a pas laiss6 de diff6rences clans les concentrations plasmatiques de T.1 chez les porcelets. Il n'avait pas non plus d'effet sur la durde de I'intervalle nalssance-premibre t6t6e. Dans tous les groupes, les porcelets avaient les mdmes temp6ratures rectales dans les 2 minutes suivant la naissance (P < 0,05). L'exposition au fioid a caus6 une baisse non significative des temp6ratures rectales et cutan6es chez tous les porcelets. Ces observations portent ir conclure que I'administration de To d la truie gestante n'influe pas sur I'intervalle naissance-piemibre t6t6e, sur l'aptitude thermor6gulaturice ou sur les performances ult6rieures des porcelets, vraiiemblablement d cause du faible taux de migration de [a thyroxine ) travers le placenia.

The effect of administering thyrotropin-releasing hormone (TRH) before farrowing on the ability of their newborn piglets to withstand a cold challenge was studied. Sows received intravenous infusions of TRH (5 µg kg^–1; TRH group) or physiological saline (0.9% NaCl; control group) from day 105 of gestation until farrowing. The plasma concentrations of thyroxine and triiodothyronine increased in sows treated with TRH. There were no differences in thyroxine and triiodothyronine between pigs born to sows in the TRH group and those of the control group. The rectal temperature of piglets born to TRH-treated sows decreased less than that of piglets born to controls as a consequence of a 1-hour cold challenge. Piglets born to sows in the TRH group had higher body weights at birth, and by day 28 they were an average 600 g heavier than those born to sows in the control group. Summarizing, prenatal maternal treatment with TRH appears to increase piglets’ resistance to cold as well as to have beneficial effects on birth and weaning weights.