The epidemiology of subfertility in non-seasonal calving dairy herds in the Camden region of New South Wales: description of population and incidence.
OBJECTIVE
To describe biographic, reproductive, production and disease characteristics of 965 Holstein cows from 10 non-seasonal calving dairy herds in the Camden region of New South Wales, and to describe the incidence of subfertility, that is, conception requiring > 2 inseminations, in this population.


METHODS
A retrospective epidemiologic study.


METHODS
Computer records were used to determine biographic, reproductive, production and disease characteristics in all lactations that commenced between 1 July 1995 and 30 June 1996 and resulted in conception during that lactation. Differences in these characteristics among herds and between primiparous and multiparous cows were examined. The lactational incidence of subfertility for lactations commencing during the study period was determined.


RESULTS
Ten herds with appropriate records and management structures entered the study. Herd size ranged from 86 to 203 lactating cows. Nutritional and reproductive management of these herds was typical of smaller pasture-based herds within the study region. Records from 1320 cows were available, of which 965 were considered suitable for descriptive analysis. Monthly variations in number of cows calving were noted, with number of lactations commenced by primiparous and multiparous cows peaking in January and October, respectively. Significant (P < 0.001) inter-herd differences for all reproductive, disease and milk production outcomes were detected for both the entire population and within primiparous and multiparous subgroups. Of 1041 cows submitted for insemination, 76 failed to conceive. The lactational incidence rate (LIR) of subfertility in all lactations was 21.1% (95% CI 19-24%). and among all cows conceiving was 22.8% (95% Cl 20-25%). The LIR of subfertility in primipara was 24.1% (95% Cl 19-28%) and varied widely between herds (10%-40%). The LIR of subfertility in multipara was 22.2% (95% Cl 20-25%) and also varied widely between herds (7%-46%).


CONCLUSIONS
Parity and herd of origin should be considered in any further analyses of these data.
Moss
N
N
University Veterinary Centre, Faculty of Veterinary Science, The University of Sydney, Camden, New South Wales.
Lean
I J
IJ
Reid
S W J
SW
Hodgson
D R
DR
D000818:Animals; D002417:Cattle; D002418:Cattle Diseases / Q000453:epidemiology*; D003612:Dairying; D005260:Female; D015994:Incidence; D007246:Infertility / Q000453:epidemiology / Q000662:veterinary*; D007774:Lactation; D009517:New South Wales / Q000453:epidemiology; D010298:Parity; D011996:Records / Q000662:veterinary; D012098:Reproduction; D012189:Retrospective Studies; D012621:Seasons