Effect of variable interservice interval on conception in crossbred cows

Abstract

Reducing number of services per conception holds the key for profitable dairying. The widely considered estrous cycle length of 21 d has been refuted, a change that can seriously implicate fertility. The present investigation evaluated association amongst interservice interval (ISI, the period intervening two successive inseminations) and services per conception alongwith certain cow related variables (age, lactation number, days in milk to AI, days in milk at conception, age at conception and 305 d lactation yield). Data on 768 ISIs (range: 17 to 24 d) from 1,479 AIs (600 in normal; 879 in repeat breeders) in 193 lactating Jersey crossbred cows conceiving to different number of inseminations, was utilized. The ISI data in form of average, immediately prior to conception and pattern (regular – if ISI between AIs was of same duration; irregular – if ISI between AIs was of different durations) was considered for analysis. Nearly 84% of ISI ranged from 19 to 22 d, merely 22.6% being of 21 d (overall average of 20.3±0.44 d). Correlation matrix revealed a solitary, significant and negative relation of ISI, both average and prior to conception, with services per conception. The ISI of ≥21 d culminated consistently into more number of pregnant cows as well as lesser services per conception. The forward selection regression model predicted reduction in ISI by 0.17 d with each additional insemination. Irregular pattern of ISI was also unfavourable for conception. The probable mechanisms for variable ISI in light of conception have been exhaustively elaborated, which could pave potential future studies aiming reduced reproductive wastage.