3. Results
The frequency distributions of serviced females by the non-return to service, first reservice, and second or later reservice were 88.6, 9.7, and 1.7%, respectively. The means (± estimated S.E. or S.E.M.) of farrowing rate and PBA in 115,442 service records and 93,867 farrowing records were 81.3 ± 0.11% and 10.1 ± 0.01 pigs, respectively. Of 21,575 not-pregnant services in the 115,422 service records, 8392 females were culled for various reasons (e.g. anestrus, reproductive failure, or lameness).
The number of preceding services, parity, lactation length, and WMI groups were associated with farrowing rate and PBA (P < 0.05). Farrowing rate decreased by approximately 18% with each service (P < 0.05). Sows with lactation length of 0–13 days had ≥ 15% lower farrowing rates and ≥ 0.4 fewer PBA than those with lactation length ≥ 14 days (P < 0.01). Additionally, the two-way interaction of the number of services × WMI with farrowing rate was found (P < 0.05; Table 1). In the non-return to service group, sows with WMI 7–12 days had the lowest farrowing rate, while sows with WMI 0–6 days had the highest farrowing rate (P < 0.05). In the first and second or later reservice groups, no differences between the WMI groups were found in farrowing rate.