Repeated high doses administration of eCG in cows submitted to an ovum pick-up experimental protocol: plasmatic eCG binding rate follow up

This study performed plasma eCG binding rates assay on 8 cows submitted to repeated and high doses eCG administration in an ovum pick-up experimental protocol (de Roover et al., Abs.). The cows were divided in two groups. For each cow, blood samples were taken three times a week, before and during the period of treatments. Cows of the first group received 10 injections of eCG (2000UI; 4x1000 UI; 5x2000 UI) while cows of the second group received 5 eCG treatments (2000 UI).Statistical analysis of results was made using the "SAS General Linear Model Procedure (GLM)" with binding rate considered as dependent variable and animals, treatment, and stade (before or after treatment) as independent variables. A significative (p<0.01) difference was found between binding rates before and after the treatment in either the first or the second group. The two treatments were found to induce a significative (p<0.001) increase in binding rates when compared with values obtained before treatments. Even if all cows responded to treatments by a binding rate increase, the effect of the treatment differed significantly (p<0.01) from one cow to another which could be explained by a large individual variability.

From this experiment, we conclude that production of eCG antibodies is a wide response in the cows herein presented and repeatedly submitted to high doses of eCG. This immune response appeared after three to five injections and binding rates remained elevated over weeks following the latest injection. Special care should be given to this active immunisation -that could explain refractoriness to treatments- if such repeated administrations high doses of eCG were applied in usual protocols.