Wang C T, Dickerson G E
Anim. Sci. Dept., Univ. of Nebraska, Lincoln 68583-0908.
J Anim Sci. 1991 Nov;69(11):4338-47. doi: 10.2527/1991.69114338x.
A deterministic computer model of a purebreeding sheep production system was used to simulate effects on life-cycle efficiency from genetic changes in lambing rate (LB), fertility (FERT), precocity of fertility (PREC), and estrus season length (ES) under annual (Y), 4-mo (A), and 73-d (S) breeding intervals. Ewes and lambs of a 1,000-ewe flock were fed to requirement through five yr, beginning with ewe lambs at the optimal breeding season and accumulating feed input (TDN) and market lamb equivalent weight of output (EBW), including cull ewes and wool. For annual lambing, improvement in cost (TDN/EBW equivalence) per 10% increase in genetic potential was -9.8, -8.2, -1.3, and -.8% for LB, FERT, PREC, and ES, respectively. For the A and S lambing intervals, corresponding gains in TDN efficiency were -19 for FERT and -9% for LB when ES was 72 d, but only -6 and -5% when ES was 192 d. Increasing PREC by 10% improved cost -3% under accelerated systems when ES was 72 d, but less than -1% when ES was 192 d. Cost reduction from 10% longer ES under A and S breeding intervals was greater when other reproductive performance was low (-11 and -17%) rather than high (-2 and -3%). Reduction in costs for A and S vs Y lambing intervals was greatest with long ES and was greater with low (-43 and -53%) than with high reproductive performance (-20 and -24%). When ES was 72 d, A and S intervals would reduce costs for high (-9 and -11%) but increase costs for low reproductive traits. Corresponding increases in CP/TDN required in diet would reduce gains in TDN/EBW only slightly. These results should aid in development of optimum selection criteria for stocks used for pure or rotation crossbreeding or as maternal parents of terminal crosses.
利用一个纯种绵羊生产系统的确定性计算机模型，模拟了在年度（Y）、4个月（A）和73天（S）的繁殖间隔下，产羔率（LB）、繁殖力（FERT）、繁殖早熟性（PREC）和发情季节长度（ES）的基因变化对生命周期效率的影响。一个拥有1000只母羊的羊群中的母羊和羔羊在五年内按照需求进行饲养，从处于最佳繁殖季节的母羊羔羊开始，累计饲料投入（可消化总养分，TDN）和市场羔羊等效产出重量（育成母羊体重，EBW），包括淘汰母羊和羊毛。对于一年生羔羊，遗传潜力每提高10%，成本（TDN/EBW等效值）的改善分别为：LB为-9.8%、FERT为-8.2%、PREC为-1.3%、ES为-0.8%。对于A和S繁殖间隔，当ES为72天时，FERT的TDN效率相应提高-19%，LB提高-9%；但当ES为192天时，仅分别提高-6%和-5%。当ES为72天时，在加速系统下，PREC提高10%可使成本降低3%；但当ES为192天时，降低幅度小于1%。在A和S繁殖间隔下，当其他繁殖性能较低（-11%和-17%）而非较高（-2%和-3%）时，ES延长10%带来的成本降低幅度更大。与Y繁殖间隔相比，A和S繁殖间隔的成本降低在ES较长时最大，且在繁殖性能较低时（-43%和-53%）比在较高时（-20%和-24%）更大。当ES为72天时，A和S间隔对于繁殖性能较高的情况会降低成本（-9%和-11%），但对于繁殖性状较低的情况会增加成本。日粮中所需粗蛋白/TDN的相应增加只会略微降低TDN/EBW的提高幅度。这些结果应有助于为用于纯种或轮回杂交或作为终端杂交母本的种群制定最佳选择标准。
