Influence of dietary Mirex and nutritive restriction on cottontail rabbit reproductive physiology

Physiological and reproductive characteristics of captive cottontail rabbits (Sylvilagus floridanus) after ingestion of 20 ppm Mirex or under the influence of 25 percent nutritive restriction were examined in three experiments. A 2 X 2 factorial design was employed in Experiment I in which 29 females were treated for 11 weeks with Mirex and nutritional restriction. Mirex treatment ceased for 3 weeks while the rabbits were in outdoor enclosures for mating purposes. Mirex treatment induced hepatic microsomal enzyme activity as evidenced by shorter barbiturate-induced sleeping times and greater liver weights. Nutritional restriction reduced body, carcass, kidney, and ovarian weights, femur bone marrow fat, and the proportion of rabbits which ovulated or conceived, but did not significantly affect corpora lutea or fetal numbers. Twenty males were treated with Mirex for 6 weeks in Experiment II. Decreased feed intake and increased eye lens weights were observed in Mirex-treated rabbits in both Experiment I and II. Mirex treatment did not adversely affect the reproductive characteristics examined in either experiment. In Experiment III, 38 females were fed either ad libitum or restricted diets for 6 weeks after which one-half of the rabbits in each group were placed on the opposite diet for 3 weeks while in outdoor enclosures. Rabbits restricted nutritionally in the pens had less femur and tibia bone marrow fat, but tended to breed sooner than ad libitum rabbits. Ovarian weights and numbers of corpora lutea or fetuses were not significantly affected by nutritive > restriction. However, nutritional restriction reduced the proportion of rabbits which ovulated or conceived.