author(s)
Harjyote Singh, Sanjay Agarwal, Padamveer Singh, Sharad Kumar, Pawan Kumar Verma, Sudhir Kumar

abstract
The aim of this study was to investigate the effects of hCG (Chorulon®, 1500 I.U.) administration on day 4 of the estrous cycle. Healthy and normal cyclic repeat breeder cross bred cows (n= 12) aging 4-7 years were used in this study. Animals with pre-ovulatory follicle of ≥ 10 mm were bred artificially. The plasma progesterone was estimated using RIA kit. Ultrasonography and blood collection was done on day 0, 4, 14 of estrous cycle. Pregnancy diagnosis was confirmed at day 45 post breeding. Preovulatory follicle had the largest diameter among all the days of estrous cycle. There was no significant difference in diameter of follicle between control and treatment group and within the control group. Diameter and area of the corpus luteum increased in treatment group. There was no significant difference in diameter and area of corpus luteum between control and the treatment group. No accessory corpus luteum was formed in cows of control group, whereas, two accessory corpora lutea were induced in the treatment group. Plasma progesterone concentration on day 14 was significantly high in comparison to day 0, 4 of the estrous cycle within treatment and control group. The pregnancy rate was Nil in control group, while 16.66% in treatment group. It was concluded that there was no significant effect of hCG administration on diameter of dominant follicle. The diameter and area of corpus luteum increased post hCG administration. The accessory corpus luteum could be produced by hCG administration on day 4 of the estrous cycle, which is lesser in size. 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.