author(s)
Harjyote Singh, Sanjay Agarwal, Padamveer Singh, Sharad Kumar, Pawan Kumar Verma and Anil Kumar Pandey

abstract
The present study was aimed to determine the effects of hCG (Chorulon®, 1500 I.U.) administration at day 6 of the estrus cycle on follicular and luteal dynamics, progesterone (P₄) concentration and conception rate in repeat breeder cross-bred cows. Twelve healthy and normal cyclic repeat breeder cross bred cows (n= 12) were used in this study. The plasma progesterone was estimated using RIA kit. Ultrasonography and blood collection was done on day 0, 6, 14 of estrous cycle. There was no significant difference in diameter of follicle between and within control and treatment groups. There was no significant difference in diameter and area of the corpus luteum between control and treatment group. No accessory corpus luteum was formed in cows of control group. The formation and retention of one accessory corpora lutea was obtained in treatment group. Progesterone concentration was significantly high on day 14 in treatment group in comparison to control group. The pregnancy rate was Nil in control group, whereas, 16.66% in treatment group. It was concluded that there was no significant effect of hCG administration on diameter of pre-ovulatory or dominant follicle, diameter and area of corpus luteum, however, the diameter and area of corpus luteum increased post hCG administration. The accessory corpus luteum could be produced by hCG administration on day 6 of the estrous cycle. After hCG administration there was significant rise in progesterone concentration, may be due to accessory corpus luteum formation or stimulatory effect on existing corpus luteum.