Effect of Age and Different Doses of GnRH and PGF2α Analogue on Oesturs Synchronization and Conception Rate of Crossbreed Heifers

Abstract

Forty-eight crossbreed heifers were artificially inseminated within 10-20 hours after standing heat to evaluate the effects of different doses of hormones and age on reproductive performance synchronized with GnRH and PGF2α. On day 90 after artificial insemination, the conception rate was confirmed by rectal palpation. There were significant differences (<I>P</I><0.05) in oesturs response in maximum doses (1.5 ml GnRH used in group III) of the hormone-treated group. The conception rate was significantly higher (<I>P</I><0.05) in the highest treatment group (1.5 ml, 66.67%) than in low treatment groups (1 ml and 1.3 ml; 42.85% and 44.44%; respectively) in morning synchronization protocol (83.33%). The effect of different doses of the hormone on conception rates was statistical significance on the age of crossbreed heifers (<I>P</I><0.05), time of initiation of ovsynch (<I>P</I><0.05), time of insemination (<I>P</I><0.05), semen placement (<I>P</I><0.05), body condition score (<I>P</I><0.05), retrieve to natural oesturs and subsequent pregnancy rate (<I>P</I><0.05). On the other hand, there was no significant (<I>P</I>>0.05) effect on conception rate by the onset of oesturs and duration of oesturs. The highest oesturs rate and conception rate was observed at 75.00% and 66.67%; respectively by administration of maximum doses of the hormone of body condition score (3) 69.23% of crossbreed heifer. When 1.5 ml GnRH was used in group III, the conception rate was observed higher at 25-30 months of age (77.78%) which were inseminated in the site of the deep cervix (77.77%) with frozen-thaw semen by experience inseminator at 10-14 hours (75%) after the onset of oesturs and naturally retrieve of oesturs on conception rate (75%). It was concluded that the age of the heifers, doses of the hormone, Body Condition Score (BCS), time of initiation of synchronization protocol, time of AI, semen placement and retrieve to oesturs naturally were the most important factors to get maximum oesturs response and conception rate of crossbreed heifers. So, it may be suggested that to achieve the desired rate of oesturs and conception, the farmers should inseminate their crossbreed heifers (BCS, 3 out of 5) with maximum doses of hormone in the deep cervix by technically sound and skilled inseminator at 10-14 hours after onset of oesturs in morning synchronization protocol. GnRH and PGF2α analogs could successfully induce oesturs response and improve the fertility of a dairy herd. Therefore, ovsynch protocol for crossbreed heifers is needed for further work involving a large number of animals for a definite conclusion.