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Factors associated with fertility of nulliparous dairy heifers following a 10‐day fixed‐time artificial insemination program with sex‐sorted and conventional semen
Author(s) -
Noonan EJ,
Kelly JC,
Beggs DS
Publication year - 2016
Publication title -
australian veterinary journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.382
H-Index - 59
eISSN - 1751-0813
pISSN - 0005-0423
DOI - 10.1111/avj.12430
Subject(s) - semen , artificial insemination , sire , insemination , estrous cycle , fertility , zoology , biology , sperm , gynecology , andrology , medicine , pregnancy , population , genetics , environmental health
Objective To examine factors associated with fertility on dairy farms that used a common fixed‐time artificial insemination ( FTAI ) program in yearling heifers. Methods Records were analysed from 954 yearling heifers on 10 south‐west Victorian dairy farms that used a common FTAI program, involving the insertion of a 1.9‐g progesterone‐releasing device for 10 days; 2 mg oestradiol benzoate at insertion; 500 µg cloprostenol on day 7; and FTAI 48 h after device removal. Weight, age, expression of oestrus, sire, semen type (frozen sex‐sorted or frozen conventional) and timing of insemination were examined for their relationship with first‐service conception rates. Results Heifers over 300 kg body weight were 1.18‐fold more likely to express oestrus during the FTAI program. For every extra 1 kg, there was a 1.5% increase in the likelihood of expressing oestrus. First‐service conception rates were 40.3% and 56.0% for sex‐sorted and conventional semen, respectively, and were significantly higher when oestrus was expressed. The difference was greater for sex‐sorted semen (3.4‐fold) compared with conventional semen (1.5‐fold). The interval from device removal to insemination varied between 47 and 51.4 h and had no significant effect on conception rates. However, there was a trend towards a higher conception rate for sex‐sorted semen when inseminations were performed >50 h after device removal. Conclusions Increased fertility was associated with larger heifers and heifers that expressed oestrus, particularly when sexed‐sorted semen was used. Variation in the timing of AI with respect to device removal between 47 and 51.4 h did not adversely affect conception rates.