The effect of hot climate and undernutrition on fertility and blood composition of dairy cows
Three experiments were conducted with dairy cows in Venezuela, to study the effect of certain environmental factors on the fertility of cattle. One experiment investigated the levels of total proteins, albumin and globulins in non-lactating Guernsey cows adapted to a tropical climate. Levels of albumin (mean) were much lower than those reported for cattle in temperate climates. There were no significant differences (P < 0.05) between the means for those proteins in the cows under restricted feeding regime and those of the ad libitum group. There was a highly significant (P < 0.01) negative correlation (r = - 0.9687) between the means of albumin and globulin concentrations. No significent difference in any plasma proteins (P 0.05) were found between cows that conceived and those that did not conceive in regard to levels of blood proteins. The second experiment investigated the possibility that a particular globulin in blood responsible for the transport of steroids (sex hormone binding globulin) might be related to fertility. Experiments showed the existence of a specific binding protein in blood similar to that reported for other species but the levels were unchanged by undemutrition or by different days of the oestrous cycle and they were not related to subsequent reproductive performance. A third experiment was performed to measure the concentrations of various reproductive hormones in blood, and the oestrus behaviour and reproductive performance of cows which viere fed either ad libitum or were on restricted rations. The incidence and length of the oestrous cycle in the well fed animals did not differ from those reported from other climatic zones. The incidence of ancestrous animals was high in the group receiving restricted rations. The levels of LH and progesterone were similar to those reported from other parts of the world and not affected by nutrition. Levels of oestrogen were depressed by undernutrition.