豚の閉鎖集団における近交度の予測

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タイトル別名
  • Prediction of Rate of Inbreeding in Closed Pig Herds
  • ブタ ノ ヘイサ シュウダン ニ オケル キンコウド ノ ヨソク

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Considering the reduction in additive genetic variance due to selection, a method for predicting the rate of inbreeding (ΔF) and response to selection (R) in closed pig herds was developed. Using the method, numerical computations were carried out to evaluate the effects of population size on ΔF and R under three different types of selection; selection based on index including only individual record (IP), selection based on index including individual and full-sibs records (IP+HS), and selection based on index including individual, full-sibs and half-sibs records (IP+FS+HS). Population size considered was the combination of Nm=5, 10, 15, 20, 30 and 60 boars, and Nf=60, 120, 180, 240, 300, 360, 420 and 480 sows. Each sow was assumed to produce two progeny of each sex eligible for selection. Thus the proportion selected was Nm/2Nf for male and 1/2 for female. The initial heritability (h20) was assumed to be 0.1, 0.3 or 0.5. The results obtained were summarized as follows: 1) The rate of reduction in additive genetic variance of selected trait was larger with higher h20 and larger amount of information from relatives. 2) The predicted ΔF was always higher than that expected from random choice of parents. The larger value of ΔF was found under selection with higher intensity and larger amount of information from relatives. 3) For a fixed number of boars, an increase in the number of sows led to an increase in ΔF under selection based on IP+FS+HS. This paradoxical result is ascribed to the fact that the reliability of information from half-sibs increases with an increase in the number of available half-sibs (4Nf/Nm), and so more offspring are likely selected from a family with higher half-sibs mean. 4) For a given intensity of selection, selection based on IF+FS+HS always gave the largest cumulative response. However, this was not true when the selection methods were compared at the same level of inbreeding. For example, in populations with Nf=120 and h20=0.3, selection based on IP achieved a larger response than that based on IP+FS+HS, when the comparison was made at ΔF_??_2%. These results emphasize the importance of choice of population size in establishing closed pig herds.

収録刊行物

  • 日本畜産学会報

    日本畜産学会報 68 (3), 318-324, 1997

    公益社団法人 日本畜産学会

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