Progestin treatment for infertility in bitches with short interestrus interval

The purpose of this study was to investigate if the suppression of estrus by the administration of a synthetic progestin, megestrol acetate or clormadinone acetate, could be an effective treatment to infertility in bitches with shortened interestrus periods and previous infertility. Ten bitches of different breeds and ages, with history of infertility and presenting repeated interestrus intervals of less than 4 months, were treated daily either with megestrol acetate (2 mg/kg, n = 8) or clormadinone acetate (0.5 mg/kg, n = 2) orally for 8 days. The treatments were begun within a maximum of 3 days after the onset of clinical signs of proestrus. Estrus was prevented in all animals and appearance of the following proestrus cycle was observed within 2.7 ± 0.6 months (mean ± S.D.) after the beginning of the treatment. When mated during the first post-treatment estrous cycle, bitches became pregnant and whelped normal healthy offspring. No negative side effects were clinically detected over the study period. Our results show that, in bitches with shortened interestrus intervals and previous infertility, suppression of one estrus with synthetic progestins administered at recommended doses, allows fertile breedings on the subsequent cycle, producing litter sizes within the normal range.