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Pituitary and Ovarian Function in Ewes Fed on Two Nutritional Levels¹

University of Wisconsin, Madison

Abstract

A total of 96 mature ewes was used in an experiment to determine the effect of longterm feeding a high-energy ration (grain) on ovarian and pituitary activity. The animals were studied at four stages of the estrous cycle (days 1, 4, 10 and 16). Grain-fed ewes, when compared with ewes receiving only hay, were heavier and had a higher plasma glucose level and lower concentration of plasma freefatty acids. The adrenal weight, pituitary weight and ovulation rate were greater for this group also. Follicular fluid weight and the number of large follicles were greater in grain-fed animals at all stages. Both follicular traits were greatest at day 10. Volume of the largest follicle was greatest at day 1. Luteal weight and progesterone content of the luteal tissue increased between days 4 and 10 and remained high at day 16. Although the bio-assays were not entirely valid, pituitary LH concentration appeared higher in grain-fed ewes at all stages of the cycle. LH concentration was lowest at day 1 and increased to day 16. FSH concentration also appeared to increase from day 1 to day 10 and then remain high through day 16. Feed had no apparent effect on FSH concentration. Rumen action on the high-energy ration presumably leads to an abundance of propionic acid, which through gluconeogenesis results in elevated plasma glucose levels. Probably less gluconeogenesis from protein is then required, allowing an increase in body protein. It is suggested that persistently elevated plasma glucose levels, via hypothalamic stimulation, lead to greater gonadotropin production and subsequent greater ovarian activity.

¹ Paper No. 1071 from the Genetics Laboratory and No. 442 from the Department of Meat and Animal Science. Published with the approval of the Director of the Agricultural Experiment Station. This investigation was supported in part by a grant from the Ford Foundation and in part by Public Health Service Training Grant No. 1 T1 HD 104-01, from the National Institute of Child Health and Human Development.

² The grain ration contained 50% cracked shelled corn, 30% whole oats, 10% linseed meal and 10% wheat bran.