MVSc

The present research work was undertaken to evaluate different oestrus synchronization protocols and to recommend a better and more consistent timed artificial insemination (TAI) protocol for improving fertility in postpartum dairy cows. The study was performed in 30 crossbred cows at day 40 postpartum belonging to University Livestock Farm, Mannuthy during the period from July 2007 to May 2008. Efficacy of various synchronization protocols for inducing oestrus and ovulation and conception rate in the experimental and control groups were determined.

In Group I, 20µg of GnRH analogue (Buserelin) was administered intramuscularly on day 40 postpartum followed by 500µg of PGF2α analogue (Cloprostenol) on day 7 intramuscularly and a second dose of 10µg GnRH was administered on day 9 followed by TAI at 24th and 32nd hours. In Group II, 20µg of GnRH analogue was administered intramuscularly on day 40 postpartum followed by 500µg of PGF2α analogue intramuscularly on day 11 and a second dose 10µg GnRH analogue was administered on day 13 followed by TAI at 24th and 32nd hours. In Group III, induction of oestrus was done by administering PGF2α analogue 500µg intramuscularly on day 40 postpartum. A second dose of PGF2α analogue was administered on day 11, followed by TAI at 72nd and 80th hour. In Group IV, cows with a palpable functional CL on day 40 postpartum were administered 500µg PGF2α analogue and were inseminated at observed oestrus. Cows inseminated during first natural post partum oestrus formed the control group (Group V). In the experimental and control groups serum progesterone was estimated on day 40 postpartum, on days of hormone administration and during oestrum. Pregnancy diagnosis was done by rectal palpation of genitalia at 60 days after AI in all groups and the data were subjected to statistical analysis.

Response to oestrus synchronization was 83.33, 33.33, 66.67 and 100 per cent in Group I to IV respectively. The time taken for induction of oestrum was 52.50 ± 0.99, 52.33 ± 0.71, 52.83 ± 1.40 and 53 ± 0.97 h respectively in Group I to IV but there was no significant difference between the groups. The duration of oestrus in Groups I to V were 37.33 ± 0.71, 35.67 ± 0.88, 40.50 ± 0.76, 38.83 ± 0.83 and 39.83 ± 0.48 h respectively.

The percentage of animals showing high, medium and low intensities of oestrum respectively were 0, 33.33 and 50 in Group I, 0, 33.33 and 0 in Group II, 33.33, 33.33 and 0 in Group III, 83.33, 16.66 and 0 in Group IV, 83.33,16.66 and 0 in Group V.

The mean serum progesterone level on day 0, 7, 9 and observed oestrum for those conceived in Group I were1.56 ± 0.69, 5.00 ± 0.94, 0.55 ± 0.09 and 0.36 ± 0.06 ng/ml. For those animals in Group I that did not conceive, the corresponding values for the same days were 0.36 ± 0.01, 0.76 ± 0.61, 0.40 ± 0.11 and 0.32 ± 0.08 ng/ml respectively. In Group II, the mean serum progesterone level on day 0, 11, 13 and observed oestrum for the conceived were 0.49 ± 0.23, 1.59 ± 0.59, 0.35 ± 0.13 and 0.88 ± 0.13 ng/ml respectively and those that did not conceive had mean serum progesterone level 0.99 ± 0.44, 0.35 ± 0.20, 0.31 ± 0.07 and 0.88 ± 0.21 ng/ml respectively. In Group III, the mean serum progesterone level on day 0, 11 and observed oestrum for the conceived were 0.83 ± 0.19, 3.05 ± 0.38 and 0.33 ± 0.10 ng/ml respectively and for the non conceived the corresponding values were 0.20 ± 0.05, 0.34 ± 0.11 and 1.39 ± 0.01 ng/ml respectively. The conceived animals in Group IV had mean serum progesterone level 2.77 ± 0.38 and 0.46 ± 0.12 ng/ml respectively on day 0 and observed oestrum while for those that did not conceive the corresponding values were 1 and 0.5ng/ml respectively. In the control group those that conceived had serum progesterone levels 1.30 ± 0.29 and 0.55 ± 0.08 ng/ml on day 40 and observed oestrum and the corresponding values for those that did not conceive were 1.6 ± 0.85, 0.685 ± 0.235 ng/ml respectively.

The conception rates after synchronization in Groups I to V were 66.66, 33.33, 66.66, 83.33 and 66.66 per cent respectively. The overall conception rate in Groups I to V were 83.33, 83.33, 66.66, 83.33 and 66.66 per cent respectively.

The mean calving to conception interval for the experimental groups was 53.84 ± 2.31 days whereas the corresponding values for the control and herd were 95 ± 6.19 and 200.78 ± 15.97 days respectively.

The present study revealed that treatment with GnRH and PGF2α during early post partum period was useful for reducing the intercalving interval in a herd. Similarly single PGF2α administration on confirmation of a functional CL by clinical examination was useful and more economical for individual animals and small herds. Hence it is recommended that Ovsynch and PGF2α protocol could be suitably employed for reducing the intercalving period in post partum dairy cows.