Reproductive Performance of Purebred Swedish Landrace and Swedish Yorkshire Sows: II. Effect of Mating Type, Weaning-to-first-service Interval and Lactation Length

Abstract

The objective of this retrospective study was to investigate the effect of mating type [natural mating (NM) versus artificial insemination (AI)], weaning-to-first-service interval (WSI) and lactation length on some reproductive traits of purebred Swedish Landrace (L) and Swedish Yorkshire (Y) sows. Data analysed comprised farrowings during the period 1994-1997 from 19 Swedish nucleus herds and included 20 275 litters from 6989 purebred sows (3598 L and 3391 Y). Analysis of variance was used for the statistical analysis of quantitative data. Logistic regression analysis was applied for binary data using the GLIMMIX macro in the SAS program. The response variables analysed were litter size, WSI, farrowing rate and remating rate. Explanatory variables included in the analyses were mating type, lactation length, sow breed, boar breed, parity, herd-year combination within breed and month of the year. The effect of WSI on subsequent fertility performance (i.e. litter size, farrowing rate and remating rate) was also analysed. Compared with AI, NM resulted in significantly larger litters (0.2 total born per litter; P<0.001; 0.3 born alive per litter; P<0.001), and lower remating rate (1.6%-units; P<0.01). The difference between NM and AI varied according to sow breed, parity number and month of the year. Subsequent litter sizes decreased by about one piglet when WSI increased from 4 to 10 days. Thereafter, litter size increased as the WSI increased from 10 to 20 days. Farrowing rate decreased gradually when WSI increased from 4 to 7 days, but an increase in WSI from day 9 to day 20 resulted in an increase in farrowing rate. A longer lactation period led to a shorter WSI and a larger subsequent litter size for both breeds.