Graduate Thesis Or Dissertation
 

Hormonal stimulation of breeding activity in different genetic groups of ewe lambs

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  • An investigation of the effects of exogenous gonadotropic treatments on fertility of various genetic groups of ewe lambs were run over a six-year period. Since hormonal treatments varied and the experimental animals were different from one breeding season to the next, each year comprised a separate study. Hormone treatment included the use of Pregnant Mare Serum, progesterone, human chorionic gonadotropin, 17-β-estradiol and crude pituitary extracts on predominantly Willamette and Suffolk ewe lambs. In general, treatment of ewe lambs with various gonadotropins did not increase fertility. The Suffolk lambs, in fact, were adversely affected in that either treatment per se or the handling necessary for treatment caused lower fertility in most cases. In the 1969 study, histological examination of the reproductive tracts of treated and control ewe lambs were made. No differences were observed among breeds or between the various treatment and control groups. Pituitary glands were biologically assayed for LH content. Lutenizing hormone was present in measurable quantities in all pituitary glands assayed. The ewe lambs from a three breed diallel cross were the experimental animals utilized for the 1970 phase of the study. Treatment consisted of three injections of pituitary extract at two-week intervals. Variables measured included ewe birth weight, ewes weight at mating, ewe lamb fertility and lamb birth weight. Heterosis was found to be highly significant for ewe weight at mating and ewe lamb fertility (P<0. 01). This significance was not due to a high positive correlation between the variables. It is due to true heterotic effects. General combining ability was also significant for fertility and ewe weight at mating. Reciprocal effects and breed differences accounted for 31 and 23 percent of the total variation in ewe weight at mating. Fertility of the ewe lambs was not effected by treatment.
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