MVSc

The objective of the present study is to evaluate the fertility in repeat breeding cattle with prolonged oestrum after oestrus induction and subsequent treatment with GnRH and hCG. Detailed data of cross bred cows and heifers belonging to University Livestock Farm, Mannuthy and those presented at Artificial Insemination Centre, attached to the Department of Animal Reproduction, College of Veterinary and Animal Sciences, Mannuthy were collected. Repeat breeding animals with a history of prolonged oestrum were randomly selected and allotted into four groups of ten animals in each. Group I repeat breeding animals were subjected to induction of oestrus using 25 mg dinoprost, a PGF2 alpha analogue (Lutalyse) and insemination was done twice at an interval of 24 h on detection of proper signs of oestrum. In group II, oestrus induction was done using 25 mg Dinoprost on tenth day of cycle and 10 μg Buserelin a GnRH analogue (Receptal) was administered 48 h after PGF2 alpha administration. In group III, oestrus was induced using 25 mg Dinoprost on tenth day of cycle and 1500 IU hCG (Chorulon) was administered 48 h after PGF2 alpha administration. Both group II and III repeat breeding animals were inseminated twice at an interval of 24 h on detection of proper signs of oestrum. Group IV repeat breeding animals were subjected to insemination during natural oestrum.

A total of 817 animals were screened of which 21.91 per cent animals were repeat breeders, out of which 26.26 per cent animals showed prolongation of oestrual signs. Among the 193 farm animals investigated, 19.17 per cent were repeaters out of which 21.62 per cent of animals showed prolonged oestrum. The duration of prolonged oestrum ranged from 32 to 96 h with a mean of 65.65  2.57 h. Out of 40 repeat breeding animals showing prolonged oestrum selected for the study, 35 per cent animals exhibited oestrus length between 30-48 h, 45 per cent between 48-72 h, and 20 per cent between 72 and 96 h. The intensity of oestrum was found to be higher in 77.5 per cent, medium in 20 per cent and low in 2.5 per cent animals.

All the 30 repeat breeding animals in group I, II, III subjected to PGF2 alpha administration responded to the treatment by exhibiting oestrus signs, and hence the efficacy was 100 per cent. The time taken for induction of oestrus in group I, II and III were 52.7  2.99 h, 51.7  2.68 h and 52.0  2.68 h respectively. The duration of oestrus in groups I, II and III were 68.6  3.75 h, 38.6  3.75 h and 37.4  3.75 h respectively. Physical changes in the reproductive tract of repeat breeding animals showing prolonged oestrum were more pronounced during natural oestrum than during induced oestrum.

The conception rate during induced oestrum in group I, II, III and control group were 50, 40, 40 and 30 per cent respectively. Overall conception rate for three consecutive oestrus in group I, II, III and control group were 60, 60, 50 and 40 percentage respectively. It can be recommended that induction of oestrus using prostaglandin could be employed for enhancing the conception rate in repeat breeding animals with the history of prolonged oestrum.