Seasonal variations in prolactin, growth hormone and thyroid hormones and the prolactin surge at ovulation do not affect litter size of ewes during pregnancy in the oestrous or the anoestrous season.
Injection of bromocriptine from 5 days before until 5 days after mating clearly suppressed the periovulatory prolactin surge in ewes in the anoestrous and oestrous season but did not change the litter size significantly. Progesterone, GH, TSH or thyroid hormone concentrations were not influenced by the bromocriptine treatment. The progesterone concentrations were lower during the first weeks after mating in the anoestrous season compared to the oestrous season, while there was no difference between pregnant and non-pregnant ewes. During later gestation this seasonal difference was only observed in the non-pregnant ewes. At the same time there was a clear difference between pregnancy and non-pregnancy in both seasons. The prolactin, GH and thyroid hormone values also varied significantly during gestation. Since these patterns are identical in pregnant and non-pregnant ewes, the fluctuations are due to environmental factors and not to pregnancy or altered progesterone concentrations. In the anoestrous season prolactin, GH, T4 and T3 levels were higher than in the breeding season, while rT3 showed the opposite pattern. The TSH concentration did not differ between the two seasons. These results suggest that seasonal variations in prolactin, GH and thyroid hormones or the periovulatory prolactin surge do not affect litter size of ewes during pregnancy in the oestrous or the anoestrous season.
Buys
N
N
Laboratory of Comparative Endocrinology, Catholic University of Leuven, Belgium.
Peeters
R
R
De Clerck
B
B
Van Isterdael
J
J
Kühn
E R
ER
Decuypere
E
E
D000818:Animals; D001971:Bromocriptine / Q000494:pharmacology; D004971:Estrus; D005260:Female; D013006:Growth Hormone / Q000097:blood; D008098:Litter Size; D010060:Ovulation / Q000502:physiology; D010908:Pituitary Hormones, Anterior / Q000097:blood*; D011247:Pregnancy; D011270:Pregnancy, Animal / Q000502:physiology*; D011388:Prolactin / Q000097:blood; D012621:Seasons; D012756:Sheep / Q000097:blood / Q000502:physiology*; D013963:Thyroid Hormones / Q000097:blood*; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D014285:Triiodothyronine, Reverse / Q000097:blood
D010908:Pituitary Hormones, Anterior; D013963:Thyroid Hormones; D014284:Triiodothyronine; D001971:Bromocriptine; D014285:Triiodothyronine, Reverse; D011388:Prolactin; D013006:Growth Hormone; D013974:Thyroxine