Live weight loss and its components in Romney ewes subjected to L-thyroxine therapy and a low plane of nutrition. Part I. Effects on live weight, carcass weight and carcass composition

Abstract

1. An experiment involving fifty Romney ewes of known history is described. These ewes were randomized to ten treatment groups of five ewes so that group mean live weights were approximately equal. The average live weight of the ewes was 147 lb. at selection and 135.5 lb. at the beginning of the 28-day experimental period. Three levels of L-thyroxine implants, viz. 150, 210 and 270 mg. were used on six groups of ewes, three of which (LT: NP, MT: NP, HT: NP) were on a normal plane of nutrition and three (LT: LP, MT: LP, HT: LP) on a low plane of nutrition. One group of ewes (DT: LP) was daily injected with 5 mg. L-thyroxine; one group of ewes (CB) was slaughtered at the commencement of the 2 8-day experimental period; one group of ewes (C:NP) was maintained for 28 days on a normal plane of nutrition and did not receive thyroxine therapy, and another group of ewes (C:LP) was on a low plane of nutrition for 28 days and was not treated with thyroxine.2. Live-weight losses of up to 24.4 lb. for the low thyroxine (150 mg.) low-plane group of ewes (LT:LP) and 30.0 lb. for the three surviving ewes of the DT: LP group were recorded at the end of the 28-day experimental period. The daily injection of 5 mg. L-thyroxine treatment had to be modified because of two deaths.