Reduced rates of embryo survival have been shown to be associated with both low levels of food intake and high concentrations of progesterone (P4) in peripheral circulation and high levels of intake with low P4 concentrations.

There is evidence that P4 is transferred from the ovarian vein to the ovarian artery and a branch of this artery supplies the oviduct and upper uterine horn. Thus, P4 profiles in the peripheral circulation may not be indicative of the pattern of P4 supply to the uterus. Since undernutrition results in a reduced LH pulse frequency, which in turn can reduce the secretion of P4, it was postulated that the effect of undernutrition on embryo survival could be mediated through changes in the profiles of LH and so of P4 secretion. It was further suggested that the effects of undernutrition on P4 profiles in the ovarian venous plasma may differ from the effects on jugular venous profiles, and that it is the latter which determines embryo survival rates.