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  • Author: WILLIAM HANSEL x
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Hysterectomy of pseudopregnant rats consistently increased the duration of vaginal dioestrus and the interval between ovulations. These observations suggested that the presence of the nongravid rat uterus limits the life span of pseudopregnancy corpora lutea.

Neither aqueous nor ether extracts of bovine endometrium collected at several stages of corpus luteum function significantly affected the life span of corpora lutea in hysterectomized pseudopregnant rats.

Vasopressin decreased the duration of vaginal dioestrus and hastened ovulation in hysterectomized, but not in intact, pseudopregnant rats, suggesting that it hastened luteal regression after hysterectomy.

Oxytocin failed to shorten the period of luteal function in the hysterectomized rat. Ovarian weight in intact and hysterectomized rats was increased by this means.

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The mean interval to the first observed post partum oestrus was 14 days in milked cows. In contrast, none of eleven nursed animals showed behavioural oestrus by Day 30 post partum, although two ovulated before that time. Only one of seven anaemic animals (haemoglobin levels of 9 to 10 g/100 ml) showed behavioural oestrus by Day 22 post partum; two others ovulated, but showed no signs of oestrus. Thyroprotein-fed cows also had prolonged periods of post partum anoestrus.

Pregnancy corpora lutea were quite degenerate by Day 7 post partum. At Day 14 post partum, they were approximately 9·0 mm in diameter and remained at this size, at least to Day 30. There was an increase in follicular size following parturition. At Day 7, the mean diameter of the largest follicle was 9·6 mm; at Day 14, it was 11·3 mm; at Day 30, the largest follicle averaged 13·0 mm.

Neither the presence of suckling calves, nor anaemia delayed uterine involution. Caruncular tissue sloughed and was expelled from the uterus between Day 7 and Day 14 post partum. Regeneration of the surface epithelium over the caruncles occurred by growth from the surrounding tissue, and was complete in a majority of animals slaughtered at Day 30 post partum.

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There was a non-significant rise in pituitary lh concentration from Day 7 post partum (2·07 μg/mg fresh anterior pituitary) to Day 30 post partum (2·62 μg/mg). Neither nursing of calves nor anaemia caused a significant change in pituitary lh content. Both control and thyroprotein-fed non-post partum cows had significantly higher levels of pituitary lh, 7·4 μg and 6·9 μg respectively, than did the post partum cows.

There was no detectable tsh in pituitaries of five of six thyroproteinfed cows. tsh concentration ranged from 2·0 to 9·5 mu nih-tsh-b3/mg fresh pituitary in the remaining animals, but there were no significant differences between any of the groups. Thyroprotein-fed animals also had significantly lower thyroid cell heights than all other groups.

Adrenal data indicate a positive correlation exists between progesterone and cortisol in the same gland (r = 0·67, P<0·01). The only group difference of significance was that the nursed group had a significantly lower adrenal progesterone than did the milked group (0·63 versus 1·76 μg/g). Cortisol content was also lower in the nursed animals, but not to a significant extent.