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K. J. COOPER

It is established that food deprivation has a marked adverse effect on vaginal cytology and ovarian weight in the rat. This is generally attributed to an impaired secretion of pituitary gonadotrophins (Piacsek & Meites, 1967; Howland, 1971a; Negro-Vilar, Dickerman & Meites, 1971). Recently, Howland (1971b, c, 1972) has examined the ability of the underfed rat to exhibit the compensatory ovarian hypertrophy following unilateral ovariectomy that is known to occur in the fully fed animal (Benson, Sorrentino & Evans, 1969). He concluded that compensatory hypertrophy was not evident in rats which had been subjected to a period of severe dietary restriction. Further, the report of Howland (1971b) indicates that, although hypertrophy of the remaining ovary may not result from hemicastration, the gonadal atrophy usually associated with food deprivation can be prevented by unilateral ovariectomy.

The influence of a reduced food allowance on the compensatory response was examined by Howland (1971b, c)

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K. J. COOPER and N. B. HAYNES

Summary.

The presence of a male from the afternoon of pro-oestrus to the following morning resulted in significant increases in anterior pituitary and uterine weights both in female rats on an unrestricted food intake and in underfed females. A significant decrease in pituitary lh content was apparent in the underfed group exposed to males. A trend towards an increased number of ovulations was found in females of both groups subjected to the presence of a male when compared to control animals but the difference did not reach significance.

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K. J. COOPER and N. B. HAYNES

Summary.

The effect of dietary restriction on the oestrous cycle of rats was modified by the time of feeding. There was a significant decrease in the cyclic activity in a group of rats fed at 17.00 hours when compared with a group fed at 12.00 hours (P<0·01).

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K. J. COOPER and N. B. HAYNES

Summary.

The effect of dietary restriction on the oestrous cycle of Wistar strain rats was modified by the presence of the male. In the absence of the male, increasing irregularity of oestrous cycle with a significant lengthening of the cycle (P<0·01) was observed with increase in the degree of inanition. The presence of the male had a significant effect (P<0·01) on the cyclic behaviour of rats on the lowest planes of feeding, bringing these animals into oestrus earlier than expected.

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K. PURVIS, K. J. COOPER and N. B. HAYNES

Summary.

Continuous pairing of underfed female rats, each with the same male rat under conditions which prevented bodily contact, significantly lowered the frequency of oestrus and increased the number of females which ceased to show cyclic activity when compared to underfed females not exposed to males or to those exposed to different males each day for 15 hr (P<0·01).

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K. J. COOPER, K. PURVIS and N. B. HAYNES

It is established that male proximity can influence the oestrous cycle of the underfed rat even when physical contact between the sexes is prevented; the lengthened cycles characteristic of underfeeding becoming significantly shorter (Cooper & Haynes, 1967; McNeilly, Cooper & Crighton, 1970). More recently, it has been shown that exposure for 15 hr/day to different male rats can elicit a greater and more sustained response from the female than continuous exposure to the same male partner (Purvis, Cooper & Haynes, 1971). This work, however, did not distinguish between two possibilities, namely, whether the stimulating effect of discontinuous association was a result of periodic removal and reintroduction of the stimulus or of regular alteration of the stimulus by the use of different males. The object of the

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A. M. SCOFIELD, K. J. COOPER and G. E. LAMMING

There are several reports of pregnancy in intersex pigs (Følger, 1932; Schmied, 1941; Albertsen, 1951; Petersen, 1952; Smidt, 1962; Hulland, 1964; van Logtestijn, 1968; Cox, 1968) but only four workers appear to have slaughtered intersexes during pregnancy (Table 1). During the course of experiments which have involved the slaughter of about 200 Large White × Landrace pigs at known times after mating, three intersexes have been encountered. Two of these were pregnant at slaughter and the other had previously borne a litter. None of the pigs showed any external signs of their condition. In each case, the ovary appeared normal and was on the left. In two pigs, the right gonad was an ovotestis and in the other (BG), only testicular tissue was present. The ovarian portion of the ovotestis was roughly hemispherical in shape. Other observations and measurements of their reproductive tracts are given in Table 2. As
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MAXINE GRIFFITHS, K. J. COOPER and D. B. CRIGHTON

It is established that stimuli associated with the presence of a sexually mature male can influence the oestrous cycle of the underfed rat (Cooper & Haynes, 1967). This effect is still present when physical contact between the sexes is prevented, the lengthened and irregular cycles characteristic of undernutrition becoming significantly shorter (McNeilly, Cooper & Crighton, 1970; Purvis, Cooper & Haynes, 1971). A similar response to the proximity of the male has been demonstrated in the mouse, the lengthened and irregular oestrous cycles usually observed when mice are grouped not being found in the presence of a male (Whitten, 1957). Castration of the male prevented the acceleration of oestrous behaviour, but the stimulus value of the male for the female returned following androgen therapy (Bronson & Whitten, 1968). The object of the work

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K. J. COOPER, N. B. HAYNES and G. E. LAMMING

Summary.

The reproductive capacity of the female rat as determined by cyclic behaviour, ovulation rate and number of viable foetuses after 19 days of pregnancy has been studied in relation to nutrient intake. Reproductive capacity decreased with increase in the degree of nutrient restriction imposed, but unrestricted feeding for 12 hr immediately before the estimated time of ovulation significantly increased the ovulation rate (P<0·05) though not the number of viable foetuses of underfed rats.

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A. S. McNEILLY, K. J. COOPER and D. B. CRIGHTON

Dietary restriction in the rat has been shown to affect the oestrous cycle, increasing the length of the di-oestrous period and producing a reduction in the cellular content of the vaginal smear (Mulinos & Pomerantz, 1940). Cooper & Haynes (1967) demonstrated that the introduction of a male to the cage of a female rat subjected to dietary restriction resulted in a shortening of the cycle regardless of the stage at which the male was introduced. In those animals which failed to mate at the first oestrus after introduction of the male (detected by the vaginal smear technique), the subsequent cycle again appeared to be of shorter duration than those before the introduction of the male, indicating that the female continued to respond to the presence of the male. The present