Technical note: Recombinant LHRH fusion protein suppresses estrus in heifers

A recombinant luteinizing hormone-releasing hormone (LHRH) fusion protein w as evaluated for its effectiveness in suppression of estrus in heifers. Eig ht heifers were randomly assigned to two equal treatment groups. Treatments consisted of recombinant ovalbumin-LHRH-7 or recombinant ovalbumin (contro l). This recombinant chimeric fusion protein consisted of ovalbumin with se ven LHRH peptides (ovalbumin-LHRH-7). The plasmid for this protein was expr essed in E. coli and was collected and purified as an insoluble protein. On e milligram of the respective proteins was suspended in 2 mL of Z-Max adjuv ant and administered by intramammary injection three times at 7-wk interval s. Luteinizing hormone-releasing hormone antibody binding was elevated in h eifers treated with ovalbumin-LHRH-7 compared to ovalbumin-treated heifers (P < .05). Serum progesterone concentrations (< 1 ng/mL) indicate that the estrous cycle of the four heifers treated with ovalbumin-LHRH-7 was suppres sed for a time period ranging from 60 to 238 d, which was different from co ntrol heifers (P < .01). Serum progesterone for the control heifers continu ed to exhibit cyclic profiles over the experimental period. This preliminar y study in heifers demonstrated that a chimeric LHRH fusion protein induced elevated concentrations of circulating LHRH antibodies that suppressed est rus for an average of 122 +/- 41 d.