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Physiological Mechanisms in Nutritionally-Induced Differences in Ovarian Activity of Mature Ewes¹

University of Wisconsin,^,4 Madison

Abstract

One hundred twenty-eight mature white face ewes were placed on either maintenance or gaining rations (minimum of 51 days duration). They were then assigned to a factorially-designed experiment for one estrual cycle in which the two ration groups were subdivided into those receiving and those not receiving sodium propionate, giving four final nutritional regimes. Nutritional differences were studied in the following: ovarian stimulation and pituitary gonadotrophic hormone potency of ewes slaughtered in early estrus; increase in gonadotrophin content of pituitary glands resulting from ovariectomy in spayed ewes; ovarian stimulation and pituitary potency determined for ewes under exogenous progesterone suppression; and ovarian response to exogenous gonadotrophin (PMS) in ewes under exogenous progesterone.

Ovariectomy increased pituitary FSH concentration, but nutritional differences did not affect gonadotrophin-producing ability of the glands. Grain feeding did not increase pituitary gonadotrophin concentration, but did increase pituitary weight and consequently total FSH and LH potency. Grain feeding increased follicular fluid weight significantly but not the response of the ovary to PMS. Sodium propionate produced no significant increase in ovarian follicular fluid.

Larger animals (independent of fatness and length) had larger pituitaries and greater follicular fluid weight. This was true whether variation in carcass weight was that existing between ewes within feeding groups or whether produced by grain feeding.

It is postulated that flushing in ewes is associated with increased rates of protein synthesis.

¹ Paper No. 902 from the Division of Genetics and from the Department of Meat and Animal Science. No. 362. Published with the approval of the Director of the Wisconsin Agricultural Experiment Station.

² Present address: U. S. Range Livestock Experiment Station, Miles City, Montana.

³ Authors wish to express appreciation to the Upjohn Company for a genenerous supply of PMS and to E. I. DuPont de Nemours and Company for furnishing sodium propionate (Impedex). Appreciation is also expressed to B. R. Baumgardt, Dept. of Dairy Science, for assistance in planning this experiment.

⁴ Department of Genetics, Meat and Animal Science, and Zoology.