Factors associated with fertility of nulliparous dairy heifers following a 10-day fixed-time artificial insemination program with sex-sorted and conventional semen.
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.
Faculty of Veterinary and Agricultural Sciences, University of Melbourne, 250 Princes Highway, Werribee,, Victoria 3030, Australia.
E J
EJ
Noonan
Warrnambool Veterinary Clinic, Warrnambool, VIC, Australia.
J C
JC
Kelly
Faculty of Veterinary and Agricultural Sciences, University of Melbourne, 250 Princes Highway, Werribee,, Victoria 3030, Australia. dbeggs@unimelb.edu.au.|Warrnambool Veterinary Clinic, Warrnambool, VIC, Australia. dbeggs@unimelb.edu.au.
D S
http://orcid.org/0000-0001-5519-9123
DS
Beggs
D000818:Animals; D002417:Cattle / Q000502:physiology*; D003612:Dairying / Q000379:methods; D004973:Estrus Synchronization / Q000379:methods; D005260:Female; D005298:Fertility / Q000502:physiology*; D005306:Fertilization / Q000502:physiology; D007315:Insemination, Artificial / Q000379:methods / Q000662:veterinary*; D011247:Pregnancy; D012661:Semen / Q000502:physiology*
artificial insemination; conception rates; dairy cattle; oestrus; sex-sorted semen; synchrony