BUSERELIN ALTERS THE DEVELOPMENT OF THE CORPORA-LUTEA IN CYCLIC AND EARLY POSTPARTUM COWS

Changes in proportions of luteal cells after buserelin treatment were studied in the corpus luteum (CL) that was present at the time of trea tment (CLP) and in the buserelin-induced CL (CLI) of cyclic and acycli c postpartum cows. On d 0 of the experimental period, eight cyclic (Cy c-sal) cows were injected with saline, whereas eight cyclic (Cyc-bus) cows and eight acyclic (Acyc-bus) cows were treated i.m, with 8 mu g o f buserelin. On d 3 or 6, ovaries were collected and stained using his tological techniques. As determined with the point-counting method, th e number of nuclei in the CLP was similar on d 3 in Cyc-bus and Cyc-sa l groups but was lower (treatment x day, P <.001) in the Cyc-bus group than in the Cyc-sal group on d 6. The volume of the CLP was similar o n d 3 in the two groups but was greater (treatment x day, P <.04) in t he Cyc-bus than in the Cyc-sal group on d 6. The number of nuclei in t he CLI was greater(P <.001) in cyclic than in acyclic cows on d 3 and 6 after treatment. The volume of the CLI was lower(P <.001) in cyclic than in acyclic cows on d 3 and 6. Buserelin did not change the profil e of progesterone in cyclic cows from d 0 to 6, but concentrations of progesterone increased (P <.01) in acyclic cows 3 to 6 d after buserel in treatment. Results indicate that buserelin increased the number of large luteal cells (LLC), as indicated by the smaller number of nuclei , and the volume of the CLP but did not influence the concentration of progesterone in cyclic cows within 6 d. Buserelin-induced CL had a gr eater number of LLC and a greater volume in acyclic than in cyclic cow s.