A total of 146 nulliparous gilts at two centres were assigned to lactation lengths of 10, 25 or 40 days and maintained on the same weaning regime for up to five parities.
The interval between weaning and conception tended to be shorter for the 40-day treatment with little difference between the 10- and 25-day treatments. The data from all parities were pooled on the basis of an assumed herd structure giving the number of litters produced per sow per year aa 2·63, 2·37 and 2·18 for the 10-, 25- and 40-day treatments respectively.
The number of pigs born alive per litter remained more or less static with successive parities on the 10-day treatment but increased on the 40-day treatment with differences between treatment s reaching or approaching significance in parities 4 and 5. Although this trend was reflected in the number of pigs weane d per litter, the differences between lactation treatments were non-significant as a result of higher post-natal mortality in the larger litters of the longer lactating sows.
Consequently sows on the 10-day treatment reared the highest number of pigs per year, 22·4 compared with 20·2 and 19·8 for 25- and 40-day lactations respectively.
Data are also presented on changes in sow live weight.
A high culling rate and an extended interval betwee n weaning and conception were experienced at one centre in parity 1. The possible reasons and effect on subsequent litter size are discussed.