Bioscientifica Proceedings

The pre-ovulatory LH surge triggers luteinisation of follicle tissue, but subsequent development of corpora lutea to full size is independent of LH up to around day 12 of pregnancy. Thereafter, severe (pharmacological) inhibition of LH secretion for 3 to 5 days will result in luteal failure and loss of pregnancy. It is unlikely that nutritional circumstances will have a similar effect, although scenarios with severe undernutrition have hardly been studied during early pregnancy. Milder levels of pre- and postmating undernutrition (around maintenance requirements), do affect luteal tissue development, but whether this is related to variation in LH is not clear as studies are equivocal, and there are indications that other nutrition related factors, like IGF-1 and insulin, may mediate these effects. A high plane of nutrition seems to increase progesterone secretion by the ovaries, even though systemic progesterone is reduced at the same time. Since there is direct transfer of progesterone from ovarian veins to the uterus, this may explain why a high plane of nutrition may actually benefit embryo survival and pregnancy, although very early during luteal formation (first days after mating), secretion by the ovaries may be overridden by systemic clearance of progesterone on a high feed level. Direct measurement of progesterone secretion by the ovaries is poorly understood as is the transfer of progesterone to the uterus and effects of specific nutrition related mediators such as IGF-1 and insulin on these processes.

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