Effects of Fasting on Oestrus and Ovulation in the Oestrous Rabbit

Abstract

The effect of fasting on the persistence of oestrus was examined in 28 New Zealand white rabbits. Oestrus was terminated in 14 out of 14 fasted rabbits within 6 days of feed removal. Only 4 out of 14 control rabbits became anoestrous in this time and another 4 out of 14 were continuously in oestrus for more than 72 days.To study the effect of fasting on ovulation, 40 rabbits which displayed oestrus on 2 successive days were divided between a control (normal feed) and a fasted group. Forty hours after feed removal, all rabbits were mated and after a further 24 hr they were autopsied. Number of ovulations was 9·85 in the control and 7·05 in the fasted group (P < 0·001). Control ovaries contained an average of 1·55 more follicles :> 1 mm diameter (n.s.). Fresh blood follicles were present in the ovaries of 3 out of 20 control and 12 out of 20 fasted rabbits (P < 0·01). Adrenal weights showed little difference between the groups and total corpus luteum weight adjusted for the covariate corpus luteum number was greater in the control animals (P < 0·05).It is concluded that fasting, probably acting to impair synthesis or release of pituitary follicle stimulating hormone or both thereby affects follicle development or maintenance or both. Failure of oestrus occurs within a few days, and animals which mate after a period of fasting shed fewer ova and more of their residual follicles are haemorrhagic. INTRODUOTIONThe influence on reproductive performance of high planes of nutrition and of chronic undernutrition have been studied in a wide range of mammalian species. The effects of acute and severe undernutrition have received little attention. In the pig, McGillivray et al. (1962) found that gilts fasted from approximately mid-cycle showed oestrus at the expected time but produced fewer ova than control gilts. Undernutrition in the female rat quickly causes anoestrus, with the ovaries lacking mature follicles (Marrian and Parkes 1929;Mulinos and Pomerantz 1940), while in the guinea pig, oestrus and ovulation may be delayed by undernutrition (Papanicolaou and Stockard 1920). Starvation in the cyclic hamster for more than one oestrous cycle prevents antral follicular development and stimulates interstitial hypertrophy (Printz and Greenwald 1970). The effects of fasting on oestrus and ovulation in the rabbit have not previously been investigated. As the rabbit normally requires mating to induce ovulation, it was necessary as a first step to obtain some information on the time for which oestrus would persist in fasted rabbits. It was then possible to plan an experiment to examine the effects of fasting on ovulation, using a fasting period which could be expected to have little effect on oestrus.

Ovarian hormones and fasting differentially regulate pituitary receptors for estrogen and gonadotropin-releasing hormone in rabbit female

“…Consequently, these two types of females could, theoretically, use different behavioral and neuroendocrine strategies to deal with nutritional challenges in the environment. Although several studies in rabbit (Brecchia et al, ; Edey and Casida, ) and in another reflex ovulatory, shrews, (Gill and Rissman, ) found a reduction in fertility and sexual receptivity following fasting, little is known about the specific neuroendocrine modifications underlying the effects observed. Yet, it has been reported that in fasted rabbits plasma E2 shows a lower pulse frequency and amplitude than in rabbits fed ad libitum, GnRH‐dependent LH secretion decreases, free fatty acid and plasma corticosterone concentrations increase, while lower levels of leptin, insulin, and triiodothyronine are observed (Brecchia et al, ).…”