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Selection for litter size at day five after farrowing (LS5) was introduced in 2004 in order to increase number of piglets weaned and reduce piglet mortality in Danish Landrace and Yorkshire. The objective of this study was to investigate selection responses for LS5, total number born (TNB) and mortality (MORT, defined as (TNB-LS5)/TNB), when selection for increasing LS5 was a part of the breeding goal.
Data were collected from nucleus herds recorded from 2004 to 2010, including first litters of 42,807 Landrace sows and 33,225 Yorkshire sows. The heritabilities of TNB, MORT, and LS5 were 0.10, 0.09, and 0.09 in Landrace and 0.12, 0.10, and 0.10 in Yorkshire. The genetic correlations were 0.28 and 0.22 between TNB and MORT, 0.74 and 0.68 between TNB and LS5, and -0.43 and -0.57 between MORT and LS5 in Landrace and Yorkshire, respectively. The results show that the genetic improvement of LS5 was a combination of increased TNB and reduced MORT. During the observation period, the genetic improvement was 1.7 piglets per litter for LS5, 1.3 piglets per litter for TNB and 4.7% for MORT in Landrace, and 2.2 piglets per litter, 1.9 piglets per litter, and 5.9% in Yorkshire. Phenotypic improvement was 1.4 piglets per litter for LS5, 0.3 piglets per litter for TNB, and 7.9% for MORT in Landrace, and 2.1 piglets per litter, 1.3 piglets per litter, and 7.6% in Yorkshire. In addition, genetic gain was evaluated in three phenotypic groups of TNB, representing the 25% smallest litters, the 50% medium litters, and the 25% largest litters. In all three groups, the genetic and phenotypic gains of TNB and LS5 increased while MORT reduced in both populations.
Bjarne Nielsen, Guosheng Su, Mogens S Lund and Per Madsen. Selection for increased number of piglets at day five after farrowing has increased litter size and reduced piglet mortality. J ANIM SCI March 18, 2013 doi: 10.2527/jas.2012-5990