RESUMO
The aim of the study was to determine the luteolytic dose of cloprostenol administered directly into the corpus luteum (CL; intra-luteal treatment, ILT) in dairy cattle. Cows of two control groups were treated with 500⯵g of cloprostenol (Estrumate®) intramuscularly (IM-500) or via ILT with 0.2â¯mL of physiological solution (ILT-0). Cows of four experimental groups were treated by ILT with cloprostenol in doses 5, 25, 50 and 100⯵g (ILT-5, -25, -50 and -100 groups). Progesterone concentrations (P4) and size of CL were evaluated to assess luteolysis at 0, 0.5, 1, 2, 4, 8, 24 and 48â¯h or at 0, 24 and 48â¯h after ILT, respectively. Cows in the ILT-0 and -5 groups were unaffected by ILT. The P4 concentrations were less in cows of the IM-500, as well as ILT-25, -50 and -100 groups at 48â¯h subsequent to ILT. The size of the CL was less in cows of IM-500, as well as ILT-25, -50 and -100 groups at 48â¯h after ILT. There were P4 concentrations of about 1â¯ng/mL 48â¯h after ILT in cows of the IM-500, as well as ILT-50 and -100 groups. In conclusion, the cloprostenol dose of 50⯵g administered intra-luteally is a luteolytic dose in cows.