Abstract:
1lA RESPONSES TO IODINE SUPPLEMENTATION IN LOW AND HIGH FECUNDITY EWES GRAZING RYEGRASS/CLOVER PASTURE T.N. BARRY* and G.H. DAVIS* Dietary iodine (I) concentrations of 500 pg/kg DM are required to maintain thyroxine (T4) output in ruminants, and 150 Pg/kg DM has been suggested as the minimum dietary concentration to maintain normal levels the present investigations studied of animal production (ARC 1980) responses to 1 ml intramuscular injections of iodised oil (475 mg I) given in mid pregnancy to ewes grazing ryegrass/clover pasture containing loo-200 pg I/kg DM, with non-injected ewes acting as controls. Five flocks of Romney and Booroola x Romney ewes with mean ovulation rates (OR) ranging from 1.5 - 5.2 were used, and productivity studied over two consecutive lambings. In both years, I supplementation had no effect upon lamb birth weight and either post-natal survival or subIn the first year, I supplementation had no sequent growth rate. effect upon embryonic mortality (EM; OR - litter size). In the second year, EM of all control flocks and of I-treated flocks with low OR were as predicted (Hanrahan 19821, but were less than predicted in Itreated flocks where mean flock OR was 3.0 or greater (Fig. 1). l In the flock of control and I-treated ewes with OR of 3.6 and 3.3, plasma hormone concentrations were respectively 71 and 80 n m total T4/1, 52 and 60 p m free T4/l, and 4.1 and 4.6 pg placental lactogen/l It was concluded that I supplements given before mating (P<O.lO) reduce EM in ewes with high OR grazing herbage containing, 100-200 pg I/kg DM* l AGRICULTURAL RESEARCH COUNCIL. (1980) 'The Nutrient Requirements of Ruminant Livestock'. Commonwealth Agricultural Bureau. Slough. UK. l HANRAHAN, J-P. (1982) In 'Proceedings II World Congress on Genetics Applied to Livestock Production'. Madrid. (In Press). Qnvermay Agricultural Research Centre, Mosgiel, New Zealand. l