Effects of lactation length and weaning-to-service interval on subsequent farrowing rate and litter size in landrace and yorkshire sows in Thailand

The aim of the present study was to investigate the influence of lactation length (LL) on weaning-to-service interval (WSI), and the effect of LL and WSI on the subsequent farrowing rate and litter size among purebred Landrac e and Yorkshire sows under tropical conditions. The variation in litter wei ght at weaning (LWW) was also studied. Data were analyzed from three purebr ed sow herds located in the central part of Thailand, including sows weaned during the period from January 1993 to December 1996. Data were analyzed w ith analysis of variance using SAS(R) software. The procedure MIXED was use d for analysis of the continuous outcome variables (namely LL, LWW, WSI, nu mber of total born and number of live born piglets). The GLIMMIX macro was used for analysis of the categorical outcome variable, farrowing rate (FR). In the statistical analyses, WSI was grouped into 7 groups, when it was an independent variable, as follows: 1 to 4, 5, 6, 7, 8, 9 to 10, and 11 to 2 1 days. Lactation length was grouped into 4 groups as follows: 17 to 24, 25 to 27, 28 to 30 and 31 to 35 days. Parities were grouped into 4 groups as follows: 1, 2, 3+4, and 5 to &. Landrace sows had significantly higher LWW (P < 0.001) compared with Yorkshire sows (56.1 vs. 53.6 kg). The LL was sig nificantly (P < 0.05) shorter during the cool season than during the other seasons while no difference was found in LWW between the hot and the cool s eason. The LL had no effect on WSI, FR and litter sizes. The FR was signifi cantly lower when the WSI was 7 to 10 days than when the WSI was 1 to 6 day s. An increase in WSI between Days 9 to 10 and Day 21 resulted in a signifi cant increase in FR. Subsequent litter size decreased by about 0.5 piglets when the WSI increased from 1 to 5 days to 6 to 7 days. Thereafter, litter size increased as the WSI increased from 9 to 10 days to 21 days. (C) 2000 by Elsevier Science Inc.