Teat length bioassays of a range of legume swards and comparisons between temporary infertility, teat length, and uterine weight responses

Abstract

Teat length bio-assays were performed with both wethers and ovariectomised ewes on three occasions during 1963, using injected stilboestrol dipropionate and a range of pasture swards. Various statistical transformations to improve the precision, by obtaining better linear relations and stabilizing variances, were attempted. No advantage was gained over that obtained by regression of teat length increase against log (dose + k). Thirty-five days rest was adequate to regain sensitivity to further oestrogen stimulation. Uterine weight assays, performed at the same time on the same animals, were found to be more precise than teat length assays. Stilboestrol equivalent potency was higher on thirteen swards by teat length response than by uterine weight, and on four swards the reverse was true. On one occasion on red clover, confidence limits for the two responses failed to overlap. Comparisons with temporary infertility were made on two occasions. In the autumn comparison, significant teat length responses were obtained on lucerne, which showed no indication of affecting fertility. In the spring, teat length tended to overestimate red clover potency by about the same amount that uterine weight bioassays underestimated it.