Increase of plasma eCG binding rate after administration of repeated high dose of eCG to cows

Abstract

-Equine chorionic gonadotrophin (eCG) is still used to promote follicular growth in cattle and, more recently with an increased frequency of administration, in ovum pick-up protocols. The aim of this experiment was to verify the possible effect of high frequency of administration on the immune response to eCG. The profiles of eCG binding rate, in the blood of two groups (A, B) of 4 primiparous cross breed beef cows (3-3.5 years old) submitted weekly for 5 to 10 weeks to repeated high doses (1 000-2 000 IU) of equine chorionic gonadotrophin, are presented in this paper. A sensitive radiometric method was used to detect antibodies in plasma. The profiles clearly indicated a marked increase of eCG binding rate after 3 to 5 injections of the exogenous hormone to the females. The statistical analysis of the results established that treatments induced a significant increase (P < 0.01) in binding rates after 6 and 3 injections in group A and B respectively. These binding rates remained elevated for at least 1 week following the last injection and decreased afterwards. The values of plasma binding rates following repeated eCG administration differed significantly between groups (0.90 ± 1.04 and 1.04 ± 0.11 for groups A and B before treatment versus 11.77 ± 0.92, 6.70 ± 0.85 for groups A and B after treatment, P < 0.01) and from one cow to another (P < 0.01) with some cows presenting no significant immune response while others were more reactive against the hormone (at least 3 injections).cow / eCG / antibody Reprod. Nutr. Dev. 41 (2001) 207-215 207

Consequences of eight consecutive applications of equine chorionic gonadotropin on ovarian follicle development and ovulation in bos indicus cows

“…eCG's effect after repetitive use (revised by DRION et al, 1998;ROY et al, 1999a;DRION et al, 2001). the positive effect of eCG on follicle development has not been completely determined.…”

“…the eCG administration can increase the concentration of anti-eCG antibodies after the first use (ROY et al, 1999b;MaNtOVaNI, 2010) and some studies have reported an additive effect of subsequent treatments (ROY et al, 1999a;DRION et al, 2001). Furthermore, most studies have concluded that there is an animal individuality to the immune response against eCG (DRION et al, 2001;MaNtOVaNI, 2010).…”

“…the production of anti-eCG antibodies has been reported in goats, sheep, cows, and rabbits (ROY et al, 1999a;ROY et al, 1999b;DRION et al, 2001;thEaU-ClEMENt et al, 2008, respectively). these antibodies are responsible for reducing the interaction of eCG with FSh and lh receptors (MaUREl et al, 2003).…”

“…Conversely, eCG was not beneficial when used in Holstein and post-partum Nellore cows that were in a good BCS (ERENO et al, 2007;pUllEY et al, 2013) however, due to a heterologous origin, a high molecular weight, high degree of glycosylation and longer half-life, eCG becomes a potentially immunogenic molecule when injected in cattle (DRION et al, 2001). thus, animals that undergo successive treatments with eCG appear to become refractory to this molecule, not effectively responding to the treatment (DRION et al, 2001).…”

“…as a consequence a delay could occur in the lh surge and ovulation, reducing the females' fertility. Some studies report antibody production from the first eCG application while others claim that there is an additive effect in repeated applications (ROY et al, 1999a;DRION et al, 2001;MaNtOVaNI, 2010).…”