Human chorionic gonadotrophin administration in the treatment of repeat breeder cows

Many repeat breeder cows that fail to conceive tend to have low progesterone concentrations in the early and mid luteal phases (Rajamahendran and Sianangama, 1992). To prevent embryonic losses during early stages of pregnancy in repeat breeder cows, human Chorionic Gonadotrophin (hCG) can be used to strengthen the corpus luteum and to form the accessory corpus luteum. This in turn will increase the level of endogenous progesterone to avoid early embryonic death in repeat breeder cows. Studies using ultrasound imaging in heifers and cows have shown oestrous cycles characterized by two waves (Rajamahendran and Taylor, 1990) and three waves (Sirois and Fortune, 1988) of follicular growth. These waves culminate in the emergence of atleast one large follicle on the day of oestrus and insemination (day 0), at 7 and occasionally 14 days after oestrus or insemination. Reports also indicate that these large follicles possess luteinizing hormone receptors and would respond to human Chorionic Gonadotrophin (hCG). Based on this principle a study has been undertaken to evaluate the use of hCG to induce ovulation of large follicles present either at the time of insemination (day O-oestrus) or 7 or 14 days after insemination and to study the effect of such treatments on oestrous cycle length and pregnancy rates in repeat breeder cows.