@article{oai:obihiro.repo.nii.ac.jp:00000264,
 author = {Kawahara, Takayoshi and 河原, 孝吉 and Gotoh, Yusaku and 後藤, 裕作 and Hagiya, Koichi and 萩谷, 功一 and 山口, 諭 and 鈴木, 三義},
 issue = {1},
 journal = {日本畜産学会報, Nihon Chikusan Gakkaiho},
 month = {},
 note = {application/pdf, 本分析では，ホルスタイン集団に関して，選抜の4径路の遺伝選抜差と世代間隔から産乳形質の遺伝的改良の現状と将来の予測を行った．データは，北海道において1976年1月から2001年6月までに乳期を終了した305日2回搾乳の検定記録であり，複数記録・単形質アニマルモデルを使用して育種価を推定した．乳量，乳脂量および乳タンパク質量の遺伝標準偏差（σGm，σGfおよびσGp）は，各々514，18および12kgと仮定した．種雄牛の父（SB）と母（DB）径路の世代間隔は，最近4年間（1993から1996年）において各々平均7.78と4.95年であった．雌牛の父（SC）と母（DC）径路の世代間隔は，最近4年間（1995から1998年）において各々平均7.98と4.49年であった．SBとDB径路の遺伝選抜差は，乳量，乳脂量および乳タンパク質量に関して，各々平均2.19σGmと1.69σGm，2.28σGfと1.85σGfおよび2.95σGpと2.14σGpであった．SC径路の遺伝選抜差は，乳量，乳脂量および乳タンパク質量に関して各々平均1.57σGm，2.40σGfおよび2.18σGp，DC径路の遺伝選抜差は，すべての形質で0.10σG以下であった．雌牛の期待選抜反応量は，実現選抜反応量に対し，乳量，乳脂量および乳タンパク質量で各々157％，193％および167％高いことが予測された．しかし，実際には，産乳形質以外にも選抜圧が加えられる可能性があるので，産乳形質の実現選抜反応量は，期待選抜反応量よりも低いと推察された．, The objectives of this study were to examine the effects of genetic selection differential (GSD) and generation interval (GI) that affect actual genetic gain per year and to predict genetic changes in the future for milk production of Hokkaido Holstein cows and progeny test bulls in Japan. The data for estimation of breeding values consisted of 305-d (240-d) records of Holstein cows that produced milk with 2 times milking from 1976 through 2001. The data included 5,012,423 records of 1,687,142 cows for milk and fat yields, and 3,574,169 records of 1,306,174 cows for protein yield. A single trait animal model with repeated records for prediction of breeding values included herd-year-parity subclass as fixed management group effects, age and month of calving within each birth year group as fixed effects, linear regression on inbreeding, random permanent environment effects of cows, random additive genetic effects of animals, and random residual effects. The GI was calculated as an interval of the birth dates between progeny and its parent and was expressed in years. The GSD was estimated as the difference between estimated breeding value (EBV) of a parent and mean EBV of cows which were contemporary with the parent. Then, GI and GSD were averaged on each birth year of progeny for four paths of selection : sires of bulls (SB), dams of bulls (DB), sires of cows (SC), and dams of cows (DC). Genetic standard deviations (σGm, σGf and σGp) for milk, fat and protein yields were estimated based on the assumption that the accuracy of selection (square root of reliability) is equal to the correlation of predicted and true breeding values. The GI for SB and DB paths decreased steadily over the years and had dropped to 7.78 and 4.95yr in the last four years (1993 through 1996), respectively. The GI for SC and DC paths were 7.98 and 4.49yr in the last four years (1995 through 1998), respectively. The GSD for SB and DB paths were 2.19σGm and 1.69σGm for milk yield, 2.28σGf and 1.85σGf for fat yield, and 2.95σGp and 2.14σGp for protein yield in the last four years (1993 through 1996), respectively. The GSD of protein yield for SB and DB paths increased dramatically from 1985. The GSD of SB and DB paths for imported bulls taken into progeny test was higher than domestic produced bulls in the 1980’s, the difference of GSD between both bulls decreased in the 1990’s. The GSD for the SC path in the last four years (1995 through 1998) were 1.57σGm for milk yield, 2.40σGf for fat yield, and 2.18σGp for protein yield. The GSD in DC path had no large changes and were below 0.10 σG for all traits. The annual genetic gain expected in the future for protein yield (0.30σGp/yr) was greater than for fat and milk yields by +0.03σGf/yr and +0.08σGm/yr, respectively. Those expected annual genetic gains correspond to 157% for milk, 193% for fat, and 167% for protein with higher genetic progress than the actual genetic changes per year in the last four years. However, because indications of the possibility that selection on traits other than milk production have been intensified in the cow population of Hokkaido region, it was predicted that the actual genetic changes for milk production is smaller than the expected genetic changes.},
 pages = {1--10},
 title = {北海道のホルスタイン雌牛集団において産乳形質の年当たり遺伝的改良量に影響を及ぼす遺伝選抜差と世代間隔},
 volume = {75},
 year = {2004}
}