Growth and serum thyroid hormone and insulin-like growth factor I (IGF-I) responses to natural passive immunization against somatostatin in the lamb

The colostral transfer of maternal humoral immunity against somatostatin (SRIF) was examined as a mechanism of improving growth performance of the lamb. Lambs were the offspring of 15 ewes actively immunized against an SRIF-ovalbumin conjugate (SI; 14 male, 7 female) and of 13 ewes actively immunized against ovalbumin (C; 10 male, 5 female). At 5 d of age, lambs were removed from the ewes and received a 50:50 mixture of whole cow's milk and milk replacer ad libitum. At 46 d of age lambs were weaned and provided with an 18% crude protein pelleted grower ration ad libitum. Lamb weight was recorded and blood samples were obtained at regular intervals from 5 to 46 d of age and at 102 d of age. From 5 to 46 d of age, immunization increased growth rate of male (P < 0.001) but not female lambs. Serum thyroxine (T4) was lower (P < 0.001) in male than in female lambs. Serum triiodothyronine (T3) was higher (P < 0.05) in SI male than in C male lambs. SI female lambs initially demonstrated higher serum T3 levels tha...