author(s)
Harjyote Singh, Sanjay Agarwal, Padamveer Singh, Sharad Kumar, Pawan Kumar Verma and Utsav Sharma

abstract
The present study was designed to investigate the effects of hCG (Chorulon®, 1500 I.U.) administration on day 5 of the estrous cycle, inducing formation of accessory corpus luteum, thus preventing early embryonic mortality due to possible luteal insufficiency, monitoring the size of preovulatory follicle (day 0), dominant follicle (day 5), subsequent corpus luteum, formation of accessory corpus luteum vis-à-vis progesterone profile and pregnancy rate in repeat breeder cross-bred cows. Healthy and normal cyclic repeat breeder cross bred cows (n= 12), “White side negative”, BCS between 3 and 4, 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, 5, 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 on various days of observation between and within control and treatment groups. Diameter and area of the corpus luteum increased in treatment group. There was no significant difference in diameter of corpus luteum, while area of corpus luteum differed significantly with control group. No accessory corpus luteum was formed in cows of control group. The formation and retention of 3 accessory corpora lutea were obtained in treatment group. The diameter and area of accessory corpus luteum was lesser than the diameter and area of corpus luteum present on the same day. Plasma progesterone concentration on day 14 was significantly high in comparison to day 0, 5 of the estrous cycle within treatment and control 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, while 50% in treatment group. It was concluded that there was no significant effect of hCG administration on diameter of pre-ovulatory or 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 5 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.