An investigation was taken up to study the relationship of preovulatory follicle size at the time of first postpartum AI and CL biometry with conception using transrectal ultrasonography in 70 parous Graded Murrah buffaloes maintained under rural conditions. POF sizes were measured ultrasonographically and grouped in to small preovulatory follicle (SPF), medium preovulatory follicle (MPF) and large preovulatory follicle (LPF). Serum progesterone concentration at the time of AI and pregnancy status was negatively correlated indicating that when progesterone level declined to < 0.3 ng/ml (basal level) at the time of AI, the chances of the animal becoming pregnant was increased. The size of the POF was positively correlated to the size of the CL on day 10 in pregnant buffaloes. The overall POF diameter at the time of estrum was 12.31 ± 0.29 mm (Range 9 to 16 mm) in Graded Murrah buffaloes and 50 % of the buffaloes had POF size > 12 -14 mm. They conceived only if the POF diameter was more than 9 mm at the time of AI however there was no significant correlation between the POF size at the time of AI and conception. Thus, it was concluded that physiological maturity rather than the diameter of the follicle influenced the fertility in Graded Murrah buffaloes under field conditions.

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