EFFECTS OF ECG DOSAGE AND BREED VARIABILITY ON ESTRUS INDUCTION IN QUEEN CATS

The current study aimed to compare the efficacy of two different equine chorionic gonadotropin (eCG) doses in inducing estrus, and to evaluate the responsiveness of various cat breeds to eCG treatment. Twenty-five mature domestic queens, aged 1–2 years, and six mature tomcats were utilized in this trial, which was conducted at a private clinic in Al-Ramadi Governorate, Iraq, from July to October 2024. All animals were examined twice via ultrasonography, two weeks apart, to confirm non pregnant and anestrus status. The queens were allocated into two experimental groups: the first group (n=20; comprising 5 individuals from each breed— Himalayan, Orange, Persian and Shirazi) was administered 100 IU of eCG, while the second group (n=5, mixed breeds) received 200 IU of eCG. Estrus was monitored through behavioral changes and vaginal cytology. Parameters such as the onset of estrus, mating interval, estrus duration, and conception rates were recorded daily. Conception was confirmed via ultrasonography on days 30 and 40 post-mating, and litter size was recorded after kittening. The findings revealed no significant variance between the two eCG doses in terms of estrus induction (100% in both groups) or conception rates (75.00% vs. 80%). Similarly, no significant variances were detected in the onset of estrus (2.48 ± 1.21 vs. 2.00 ± 0.82 days), estrus to mating interval (11.78 ± 1.17 vs. 8.50 ± 1.29 days), or estrus duration (12.72 ± 3.69 vs. 11.25 ± 0.95 days). However, a significant increase (P≤0.05) in litter size was observed in the 100 IU group (3.45 ± 0.27) compared to the 200 IU group (2.80 ± 0.15). When comparing responses by breed, all breeds exhibited optimal estrus rates. Additionally, Shirazi cats demonstrated a significantly longer (P≤0.05) onset of estrus compared to other breeds. The estrus-to-mating interval was prolonged across all breeds, with no significant differences observed. Additionally, pregnancy rates were significantly higher (P≤0.05) in Shirazi and Himalayan breeds compared to Orange and Persian breeds. Furthermore, Persian and Himalayan queens produced significantly larger (P≤0.05) litters than Shirazi and Orange queens. In conclusion, a single dose of 100 IU eCG is sufficient to induce fertile estrus within several days post-injection, resulting in higher conception rates and litter sizes. The prolonged estrus-to-mating interval observed may be attributed to social factors or a lack of male interest due to seasonal effect. Shirazi cats exhibited a superior response to eCG, with higher conception rates, while Persian and Himalayan breeds demonstrated larger litter sizes. These findings highlight the influence of breed-specific factors on reproductive outcomes following eCG treatment.