AUTHOR=Knap Pieter W. , Knol Egbert F. , Sørensen A. Christian , Huisman Abe E. , van der Spek Dianne , Zak Louisa J. , Granados Chapatte Ana , Lewis Craig R. G. 

TITLE=Genetic and phenotypic time trends of litter size, piglet mortality, and birth weight in pigs

JOURNAL=Frontiers in Animal Science

VOLUME=Volume 4 - 2023

YEAR=2023

URL=https://www.frontiersin.org/journals/animal-science/articles/10.3389/fanim.2023.1218175

DOI=10.3389/fanim.2023.1218175

ISSN=2673-6225

ABSTRACT=Litter size in pigs has increased steadily since 1990. Because of unfavourable genetic correlations to piglet mortality, survival traits belong in the breeding goal next to litter size. Unbalanced breeding programmes that neglected this requirement have produced increased mortality levels, attracting negative public attention. Balanced breeding does not have this disadvantage, but public opinion is largely unaware of that. We present long-term time trends of these traits as realized in commercial breeding. The data includes (i) phenotypes of litter size, piglet birthweight, and piglet mortality, as used in routine breeding value estimation; and (ii) the GBLUP estimated breeding values so obtained. Piglet mortality  and birthweight (2009-2022) phenotypes were related to litter size by recording year. Estimated breeding values (EBVs) for the mortality traits were regressed on those for litter size by birth year (2012)(2013)(2014)(2015)(2016)(2017)(2018)(2019)(2020)(2021)(2022). Average litter size is very weakly correlated to the mortality (R 2 ≤0.06) and birthweight (0.07≤R 2 ≤0.26) traits, and those correlations are unfavorable (antagonistic) within each year. However, all traits analyzed here show favorable simultaneous phenotypic and genetic trends over time: the antagonisms are neutralized by balanced breeding. Above the annual mean litter size level, farrowing and lactation mortality rates increased with increasing litter size in every year (unfavorable), but the annual intercepts increased and the slopes decreased from 2001 to 2022 (favorable). Average litter birthweight decreased with litter size in every year (unfavorable), but the annual intercepts increased and the slopes decreased from 2009 to 2022 (favorable). The within-litter birthweight variation coefficient increased with litter size in every year (unfavorable), but the annual intercepts decreased from 2009 to 2022 (favorable). The proportion of low birthweights (e.g. < 0.9 kg) for a given litter size is decreasing over time, and the critical birthweight level (below which lactation mortality increases strongly) is 3 clearly population-dependent and changes over time too. The increases in litter size and piglet survival rates due to balanced breeding policies lead to reduced total numbers of dead piglets (e.g. per country, per year) coinciding with a certain pig production volume (i.e. with a certain total number of weaned piglets).