Effects of diets containing gossypol on ovarian histology, function and fertility in prepubertal beef heifers

Forty-five crossbred beef heifers (weight = 268.3 +/- 5.7 kg) were used to determine the effects of dietary gossypol on ovarian morphology, erythrocyte fragility and fertility. Heifers were randomly assigned to 1 of 3 isonitrogenous dietary treatments. The diet consisted of rice mill feed and milo supplemented with soybean meal (n = 13; control), cottonseed meal (n = 16; low supplementation) which supplied 6.1 g free gossypol animal(-1) day(-1), or whole cottonseed (n = 16; high supplementation) which supplied 13.7 g free gossypol animal(-1) day(-1). The heifers were group-fed each diet for 64 days and were maintained on similar but separate fescue pastures overseeded with wheat. After 64 days, 4 heifers from each diet were confined and fed their respective diets. On Day 10 following estrus, each animal was unilaterally ovariectomized, and the ovary containing the corpus luteum was removed. The remaining ovary was removed 6 to 12 hours after detection of estrus in the next cycle. Erythrocyte fragility increased (P < 0.02) in heifers receiving gossypol compared with that of the controls. Cyclicity in the heifers was 81.3, 68.8 and 38.4% for high, low and control diets, respectively, at the end of the 64-day treatment period. First service conception rate, as determined by palpation per rectum, was similar among treatments (58.3, 33.3, 33.3% for high, low and control groups, respectively). Weight gain increased (P < 0.03) in control heifers compared with that of heifers receiving gossypol. Gross ovarian morphology and histology were similar for all heifers. Although gossypol produced mild toxicosis in heifers, no adverse reproductive effects could be detected from gossypol intake.