Heritability of Herd-life and Relationship between herd-life and Milk Production, Type and Fertility Traits of Holstein Cows in Japan

全国的データを用いて，在群期間の遺伝率および初産泌乳形質，体型形質，および繁殖形質との遺伝相関の推定を行った．データは，社団法人家畜改良事業団に1975年から集積された1993年9月以前に誕生した雌牛の誕生，淘汰，泌乳，および社団法人日本ホルスタイン登録協会で集積された体型と血統記録である．在群期間は誕生から96ヵ月までの打ち切りデータとした．計算機の制約からすべてのデータを用いた遺伝的パラメータの推定は困難であった．そこで，同じ牛群コードをもつ記録が同一サブセットに無作為に分割されるように，遺伝率およびデータ数の限られる体型形質との遺伝相関の推定には10個，データの多い形質の遺伝相関推定には100個のサブセットを作成し，その中の10個のサブセットを用いて，制限最尤法（REML）により分散成分の推定を行った．在群期間の遺伝率は0.07と低い値が推定された．在群期間と初産泌乳形質における遺伝相関の推定値は，0.08から0.16と低いが正の関係が認められた．初産泌乳形質の向上させながら，在群期間に対する改善が可能であると考えられた．体型形質との遺伝的関連では，体の大きい個体を選抜することは負の関係にある在群期間の改良を妨げとなる恐れがあるが，正の比較的大きな遺伝相関がある肢蹄（0.37）や乳器（0.34）などを用いた間接選抜は有効であることが示唆された．在群期間と初産分娩月齢においては小さい負の値が認められ，初産から2産の分娩間隔における遺伝相関の推定値は小さい正の傾向を示したが，2産から3産の分娩間隔は0.15とやや高くなった．Heritability of herd-life (HL) as a longevity trait, and correlations between HL and productive traits in the first lactation, type traits, and reproductive traits were estimated from nationwide data collected by Livestock Improvement Association of Japan and Holstein Cattle Association of Japan. Each dataset on milk production and reproductive traits was randomly divided into 100 subsets. Ten subsets of the 100 subsets were used for analysis. Each dataset on type traits were randomly divided into 10 subsets. Heritabilities and genetic correlations were estimated with AIREMLF90. The heritability estimates for HL were low (0.07±0.002). The genetic correlations between HL and milk production traits were also low and estimated to be 0.08 from 0.16. Milk production is not effective in indirect selection for HL and the selection for increase milk production at first lactation did not have a genetic adverse effect on HL. Moreover, it was thought that correspondence by the management was effective for the improvement of HL with low heritability. The genetic correlations between HL and body capacity, strength, body depth, and rump width were negative and consistent over the subsets. While those between HL and feet and legs (0.37) and between HL and udder traits such as mammary system (0.32), fore udder attachment, rear udder height, udder cleft and udder depth were positive. Selections by udder traits and feet and legs were more effective for long HL than by other type traits, but selection for large body size tends to reduce cows’ HL. Reproductive traits of first calving interval (CI1) in first lactation, second calving interval (CI2) in second lactation, and age at first calving (AFC) were used in the study. Heritability estimates for CI1 (0.06), CI2 (0.05), and AFC (0.12) were low. The genetic correlations between HL and fertility traits (AFC, CI1) were low, except for that between HL and CI2 (0.15)