黒毛和種繁殖肥育一貫経営農家経営におけるDNAマーカー情報活用による肥育牛販売収益上昇額の推定 Potential profitability increase of Japanese Black cattle (Wagyu) by raising marbling and carcass weight through planned mating based on DNA testing of QTL alleles

黒毛和種繁殖肥育一貫経営農家経営において，BMSナンバーや枝肉重量（CW）に関与するQTLアリル型情報はどの程度収益上昇に活用できるかを，初期QTLアリル頻度 （p），計画年数 （T），DNAタイピング料金（CTYP），使用する精液差額（SEM），種雄牛と繁殖雌牛の割合（R (s/d)）を変化させて検討した．その結果，BMSナンバーに関わるQアリルを1個持つことで得られるBMSランク上昇分（ΔBMSQTL）を1.0，BMSナンバー1ランク上昇分の枝肉単価（CWPBMS）を150円/kg, CWを440 kg, CWに関わるQアリルを1個持つことで得られる枝肉重量上昇分（ΔCWQTL）を20 kg, 黒毛和種去勢枝肉単価（CWPU）を1,900円/kgとした場合，QTLアリル型情報は，黒毛和種繁殖肥育一貫経営農家の経営に充分活用できると考えられた．また，以下のことが明らかになった．QTLアリル型情報を経営に活用する際，集団におけるpの頻度，SEMおよびT数が重要であり，CTYPとR (s/d)　の重要性は低かった．CTYPが5千円/頭，SEMが1万円程度以下で，1頭当たり1万円程度の収益上昇を確保するためには，pの頻度は，BMSナンバーでは0.6〜0.7以下，CWでは0.4〜0.5以下であることが示唆された．繁殖雌牛集団のQTLアリル型情報は，pの頻度が0.5〜0.7程度の範囲内，T数がBMSナンバーで6年以上，CWで8年以上であれば，収益上昇に貢献できることが明らかになった．

We predicted the potential profitability increase of Japanese Black cattle (Wagyu) at cow-calf fattening farms by the use of planned mating, based on DNA testing of QTL alleles, to increase Beef Marbling Standards (BMS) scores and carcass weight (CW). The following assumptions and scenarios were adopted. (1) Q (excellent) to q (ordinary) allele additive substitution effect : 1.0 for BMS score (ΔBMSQTL) and 20 kg for CW (ΔCWQTL). (2) A rise of \150/kg in dressed carcass price when the BMS score increases by 1 (ΔCWPBMS). (3) CW = 440 kg (CW). (4) Price of CW (CWPU) : \1,900/kg. (5) The DNA typed sires (QQ type) were used to breed dams (Hardy-Weinberg population). (6) The age at first calving and the productive lifetime of dams (N : number of dams) were 3 and 8 (or 9) years, respectively. (7) The replacement rate for cows was ⅙N. Calves not for replacement (⅚N) and cows over 8 (or 9) years (⅙N) were moved for fattening and slaughter. (8) The planned time horizon (T) was 15 years. (9) Priority sequence of dams for slaughter : qq→Qq→QQ. (10) Frequency of the Q allele in the population = 0.1, 0.3, 0.5, 0.7, 0.9. [Scenario 1] : Sires were known for DNA type (QQ) : CTYP = \0, SEM ≥ \0. [Scenario 2] : Sires were DNA typed and selected (QQ) : CTYP > \0, SEM ≥ \0. [Scenario 3] : Dams were DNA typed, CTYP > \0 and sires were known for QQ type : CTYP = \0, SEM ≥ \0. To increase profitability, the Q allele frequency in population, SEM, and the number of T are more important than CTYP and R (s/d). The Q allele frequency is required to be less than 0.6∼0.7 for the BMS score and less than 0.4∼0.5 for CW in order to retain around \10,000 of ΔVind on the condition that the cost of DNA diagnosis, including patent fees, is \5,000/head or less and that the semen price difference is \10,000/head or less. In addition, it is more effective to use planned mating for dams and sires (Scenario 3) than those of sires (Scenarios 1 & 2) based on information on QTL alleles if the Q allele frequency for the BMS score is in the range of 0.5∼0.7 at over 6 year (T) or if it is over 8 year (T) for CW to retain around \10,000 of ΔVind.