The effect of anaesthesia on milk yield and maintenance of lactation in the goat and rat.

Abstract

SUMMARY The effect of anaesthesia on lactation was studied in the lactating goat and the lactating rat. Cyclopropane was used in the goat. All goats were milked once daily in the morning. The experimental and the control periods started on Monday and ended on Saturday; the control period was usually followed immediately by the experimental period. Average milk yields in eight experimental periods in three goats ranged from 91·4 to 108·3%, with a mean of 101·4±1·84% (s.e.) of those in the corresponding control periods. The increase in intramammary pressure, which occurred 30–40 sec. after the start of milking of the contralateral teat in the normal lactating goat, was not observed during milking under anaesthesia. Lactating rats were anaesthetized with sodium pentobarbitone. Six or eight pups were placed with the mother to suckle the teat for 2 hr. in the morning. This suckling regime was continued for 5 days. No increase in the body weight of litters was obtained when the litter suckled under anaesthesia. When oxytocin was injected into the anaesthetized mother, a gain in litter weight was observed during the experimental period, although it was smaller than in the controls. In conclusion, a species specificity in the importance of the milk ejection response for the removal of milk has been demonstrated. The fact that milk secretion continued normally in the goat milked under the anaesthesia suggests that the secretion of the pituitary hormones concerned with the maintenance of milk secretion continues in the absence of the milking stimulus. In the rat, although milk secretion was maintained at a subnormal level by oxytocin replacement under anaesthesia, it was not possible to draw a final conclusion as to whether the suckling stimulus is dispensable for the maintenance of milk secretion.