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N. B. HAYNES

Summary.

Daily or more frequent samples of cervical mucus were collected from forty-two gilts and analysed for Na and K. In five gilts, sampled through several oestrous cycles, the K level exceeded that of Na for short periods during oestrus. The ovarian status of twenty animals indicated that the K peak occurred approximately 40 hr before ovulation but with some individual variations. Two of these animals did not show a K peak, and had never ovulated. The results differed in twelve gilts on a restricted feed level, the K level generally being in excess of Na. A K peak occurred in two immature gilts after injection of deoxycorticosterone.

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K. Purvis and N. B. Haynes

Summary. Testosterone levels were significantly higher in males, regardless of sexual experience, exposed to the odour of urine from females than in those exposed to saline or kept in ordinary groups.

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N. B. HAYNES and G. E. LAMMING

Summary.

Unilateral ovariectomy of mature female rats 62 to 88 hr after copulation resulted in a significant reduction in embryo survival in the ipsilateral uterine horn when compared to the contralateral horn. The effect was not apparent when oestradiol-17β was injected into the ovarian site at the time of ovariectomy.

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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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N. B. HAYNES and G. E. LAMMING

Summary.

Fructose and other carbohydrates have been identified in sow uterine flushings. The carbohydrate content has been shown to vary with the stage of the cycle.

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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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I. J. SHEARER, K. PURVIS, G. JENKIN and N. B. HAYNES

Summary.

A double isotope derivative assay and a simple competitive protein-binding assay were used to measure peripheral plasma progesterone levels during the pig oestrous cycle. In view of the similarity between the results, the more convenient protein-binding method was employed to determine progesterone levels during prepuberty, the oestrous cycle, early and late pregnancy, parturition and lactation. Peripheral plasma oestradiol-17β levels were measured during the oestrous cycle, early pregnancy and around the time of parturition.

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C. M. Howles, J. Craigon and N. B. Haynes

Summary. Two groups of 6 rams were kept under constant photoperiod consisting of short days (8 h light (L): 16 h dark (D); Group S) and long days (16 h L:8 h D; Group L) from 4 to 38 months of age. Five other rams were reared under a photoperiod representative of that occurring naturally (Group N). Testis size and plasma prolactin concentrations were obtained weekly. These data were subjected to time series analysis. The results indicated that there were persistent periodic excursions in both parameters measured. In Group N, the average cycle length for both testis volume and plasma prolactin was about 1 year and the peaks in plasma prolactin preceded those in testis volume by about 18 weeks. Rams from Group L also showed rhythmical changes in these parameters with periodicities of around 35 weeks and it is suggested that these cyclic changes may constitute true endogenous circannual rhythms; again the prolactin peaks preceded those of testis volume by about 18 weeks. Overall, rams from Group S had excursions of testis growth of a similar magnitude to those of Group L but the changes were less regular than those of Group L. Plasma prolactin was significantly lower in Group S than in Group L and there was little evidence for rhythmicity. It is proposed on the basis of the temporal relationship between peaks of prolactin and testis volume in Groups N and L, that prolactin may play a role in the timing of the reproductive cycle in the ram.

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C. M. Howles, G. M. Webster and N. B. Haynes

Summary. Two groups of 6 rams were maintained under constant photoperiodic conditions consisting of short days (8 h light: 16 h dark; Group S) and long days (16 h light; 8 h dark; Group L) from 4 to 20 months of age. Five other rams were reared under a photoperiod representative of that occurring naturally (Group N). Testis size, plasma testosterone and prolactin concentrations were monitored weekly and sexual behaviour tests were carried out at regular intervals. Over the treatment period Groups S and L did not differ in terms of testis growth or plasma testosterone. Both groups had a phase of testis growth and increased testosterone followed by a decline and the temporal patterns for the two groups were equivalent. Sexual behaviour was slower to develop in Group L than in Group S, indicating that photoperiod can affect the development of sexual behaviour irrespective of peripheral plasma testosterone concentrations. Plasma prolactin levels showed a cyclic variation in Group L and were significantly higher overall than in Group S rams. This, together with a trend towards negative correlations between prolactin concentrations and sexual behaviour in Group L, indicates that prolactin may be involved in the effect of photoperiod on sexual behaviour. The presence of a cycle of testicular growth and of hormone concentrations in young animals under constant photoperiod tentatively suggests that these cycles are endogenous. The constant photoperiod did, however, affect the animals because the cycles which occurred in Groups S and L were out of phase with those of Group N by about 4 months.