Biology of Reproduction, Vol 1, 264-271, Copyright © 1969 by Society for the Study of Reproduction

Effect of Nutrient Intake on Ovulation in Mice and Sheep

¹ C.S.I.R.O., Division of Animal Physiology, Cunningham Laboratory, Mill Road, St. Lucia, Queensland, Australia

The effects of undernutrition and realimentation on numbers of ovulations or embryos were studied in mice of different ages and weights subjected to a number of management regimens. Experiment 1 was 3 x 2 x 3 x 2 factorial design with two mice per treatment. The factors were: age at beginning of experiment (3, 5, or 7 weeks); whether intake was restricted or not; amount of feed offered during realimentation (1.25, 2.5, or 5.0 g/day) ; and dose of PMS (0.2 or 2.0 IU). Realimented mice had compensatory growth and produced more gonadotropin-induced ovulations than controls. The design of Exp 2 was 2 x 3 x 2 x 3 factorial with six mice per treatment. The factors were: low or high plane of nutrition; subsequent increase, decrease or no change in the plane of nutrition; injected 24 or 48 hr after the change in nutrition with 0.5, 1.5, or 4.5 IU of HCG. Most ova were obtained by injection with gonadotropin 24 hr after commencing realimentation thus indicating that endogenous gonadotropin was released soon after the ration was increased. Experiment 3 was 3 x 2 x 2 x 2² factorial with eight mice per treatment. The factors were: age of mice at beginning of experiment (18, 25, or 32 days); rate of gain during realimentation (rapid or slow); introduction of male 1 or 8 days after realimentation began; severe or mild cold stress each morning or afternoon after introduction of the male. Mating patterns and fecundity were influenced by the age of the mice when undernutrition began and by the rate of growth during subsequent realimentation. Mice in which growth was restricted as adults and which were then allowed food ad libitum had higher fecundity than either normal colony mice that had never been restricted, or restricted mice that were realimented at a moderate rate of growth. Severe stress reduced the number of embryos by about 6%.