Radford H M, Nancarrow C D, Mattner P E
J Reprod Fertil. 1978 Sep;54(1):49-56. doi: 10.1530/jrf.0.0540049.
Two groups, each of 7 crossbred beef cows, which were suckling or not suckling calves, were fed a high quality food ad libitum for 3 months post partum. The non-suckling cows experienced regular ovarian cycles from 10--33 days post partum while the suckling cows did not do so until at least 14 weeks post partum. There was little difference between the groups in growth rate or in plasma glucose concentration. The plasma prolactin concentrations in the non-suckling cows showed a seasonal trend which paralleled ambient temperature and daylight hours; in the suckling cows this trend was less evident. Plasma LH concentrations were lower in suckling cows before Day 30 post partum but were similar thereafter. Most suckling cows also failed to experience oestrus or to exhibit LH release in response to an injection of oestradiol benzoate at about 6 weeks post partum. This failure, together with the earlier lower levels of LH in the suckling cows, is considered to be indicative of malfunction of the hypothalamic mechanism normally responsible for the establishment and maintenance of cyclic ovarian function.
