Meta-analysis for effects of breed and climatic zone in reproduction traits of pig

Abstract

Objective of this study was to reveal effects of breed and climatic zone and their interaction for reproduction traits of sows by meta-analysis. A data set included 2097 averages of reproduction traits extracted from 205 published articles. Climatic zone of a test place was classified into temperate, tropical and subarctic zone according to Köppen’s climate classification. Traits in study were 12 traits including total number of piglets born, number of born alive, number of stillborn, number of weaned, age at first farrowing, farrowing rate, average birth weight, average weaning weight, litter weight at birth, litter weight at weaning, farrowing interval and weaning to service interval. Statistics software used for the analysis was MIXED/SAS procedure with a random effect of research article, where residuals were assumed to have heterogeneous variance between known and unknown parity, and the residual variances were weighted by number of records. Test of statistical significance showed that effects of climatic zone, breed, country and parity were significant in most of traits in study, however effect of operation (experiment, breeding vs commercial farms) was significant in a few traits. Global breeds such as Landrace and Large White showed high performance in most of reproductive traits. Their high performance was not restricted only in temperate and subarctic zone, but also in tropical zone compared with other breeds. Results of crossbreds showed their high performance of reproductive traits even at climatic zone out of thermal neutral zone such as subarctic and tropical zone, and their higher reproductive performance was considered to be due to heterosis effect.Alternate abstract:本研究は，ブタの繁殖形質に関するメタ分析により品種と気候帯の効果およびそれらの交互作用について明らかにすることを目的に行った．データには205論文の2097件の形質平均値を使用した．試験地をケッペンの気候区分に従い温帯，熱帯，亜寒帯に分類した．分析対象形質は，生存産子数，離乳産子数，離乳時平均体重，離乳時一腹体重，分娩率，分娩間隔などの12形質である．分析には統計ソフトウェアSASを使用した．SAS分析プロセジャーは，研究論文データに共通な変量効果を含む混合モデルMIXEDである．分析モデルでは，標本数を誤差分散に対する重みづけ値として考慮した．主効果に対する有意性検定の結果，多くの繁殖形質で気候帯，品種，産次数の効果が有意性を示した．一方，経営体の効果は少数の形質で有意性がみられた．本分析の結果，改良種として世界の広い地域で飼養されているランドレース種と大ヨークシャー種の高い繁殖能力が示された．この高い能力は，品種の原産地である温帯に留まらず，熱帯においても若干の低下はあったもののみられ，これらに亜寒帯を加えた3地域で示された．また，西洋種間交雑種に代表される交雑種では，温度環境が熱的中性圏以外の温度ストレスがかかる地域においてヘテローシス効果により高い能力が示された．