Soy Phytoestrogens and Reproduction:
Progress Report

Soybean meal contain estrogenic compounds called phytoestrogens that have been shown to effect reproductive function in animals. Soybean meal makes up a significant percentage ( 20%) of most swine diets. This research is concentrating on the effects of these compounds on swine reproduction. In vitro studies with swine ovarian granulosa cells indicate that phytoestrogens have the ability to decrease follicular cell atresia potentially leading to more follicle recruitment and ovulations, thus potentially increasing litter size. A swine feeding study is underway. Prepubertal gilts were assigned to two diet treatment groups: 1) standard soybean meal; and 2) low phytoestrogen soy protein concentrate. Parameters under examination are body weight, feed consumption, backfat, serum reproductive hormones, vulva diameters, first estrus, estrous cycle length, success of breeding, and litter size. Body weight, crown-rump length, and anogenital distance will be measured on offspring within 24 h of farrowing. Breeding success and litter size will then be examined for two subsequent gestations to determine if the possible effects of phytoestrogens are permanent or only occur when the animals are fed these soy compounds. Reproductive performance of offspring will also be followed over the following year. Since swine also have a great potential for being a model for human cardiovascular health studies, plasma HDL, LDL, total cholesterol, triglycerides, glucose, and insulin are also being measured. First trial gilts are just reaching breeding age. Preliminary results show increases in frame (length, p<0.05; girth p<0.10) as well as an increase (p<0.05) in blood glucose for the soybean meal fed animals suggesting a phytoestrogen effect on growth and metabolism.

Progress:

Soy products contain estrogenic compounds called phytoestrogens that have been shown to affect reproductive function in animals. Our overall objective was to determine the effects of soy-related phytoestrogens on animal reproductive function. Rat feeding studies have found that dietary soy protein affects histological reproductive parameters in female rats. Uterine epithelium and larger follicle numbers were dependent on soy phytoestrogens. In vitro studies with swine ovarian granulosa cells indicate that phytoestrogens, especially daidzein, have the ability to decrease follicular cell atresia. Increased use of phytoestrogens in the swine diets could lead to more follicle recruitment and ovulations, thus potentially increasing litter size.