Broiler growth rates increased by over 400% from 1957 to 2005 从1957年到2005年，肉鸡生长速度增加了超过400％
The following text and images are quoted from a poultry science journal [1]: M.J. Zuidhof, B.L. Schneider, V.L. Carney, D.R. Korver, F.E. Robinson, Growth, efficiency, and yield of commercial broilers from 1957, 1978, and 2005. Poultry Science, Volume 93, Issue 12, 2014, Pages 2970-2982
Abstract
The effect of commercial selection on the growth, efficiency, and yield of broilers was studied using 2 University of Alberta Meat Control strains unselected since 1957 and 1978, and a commercial Ross 308 strain (2005). Mixed-sex chicks (n = 180 per strain) were placed into 4 replicate pens per strain, and grown on a current nutritional program to 56 d of age. Weekly front and side profile photographs of 8 birds per strain were collected. Growth rate, feed intake, and measures of feed efficiency including feed conversion ratio, residual feed intake, and residual maintenance energy requirements were characterized. A nonlinear mixed Gompertz growth model was used to predict BW and BW variation, useful for subsequent stochastic growth simulation. Dissections were conducted on 8 birds per strain semiweekly from 21 to 56 d of age to characterize allometric growth of pectoralis muscles, leg meat, abdominal fat pad, liver, gut, and heart. A novel nonlinear analysis of covariance was used to test the hypothesis that allometric growth patterns have changed as a result of commercial selection pressure. From 1957 to 2005, broiler growth increased by over 400%, with a concurrent 50% reduction in feed conversion ratio, corresponding to a compound annual rate of increase in 42 d live BW of 3.30%. Forty-two-day Feed Conversion Ratio FCR decreased by 2.55% each year over the same 48-yr period. Pectoralis major growth potential increased, whereas abdominal fat decreased due to genetic selection pressure over the same time period. From 1957 to 2005, pectoralis minor yield at 42 d of age was 30% higher in males and 37% higher in females; pectoralis major yield increased by 79% in males and 85% in females. Over almost 50 yr of commercial quantitative genetic selection pressure, intended beneficial changes have been achieved. Unintended changes such as enhanced sexual dimorphism are likely inconsequential, though musculoskeletal, immune function, and parent stock management challenges may require additional attention in future selection programs.”
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From 1957 to 2005, broiler growth rates increased by over 400%, with a concurrent 50% reduction in Feed Conversion Ratio FCR. The claim that broiler 42-d live BW was increasing at a compounded rate of 3.1% [2] has held up to scrutiny. The current study confirms that the rate of increase in 42-d live BW from 1957 to 2005 was 3.30% per year, compounded for 48 yr. Similarly, FCR to 42 d of age has decreased by 2.55% per year, also in a compounding manner. The net result was that over a period of almost 50 yr, the broiler industry has been able to reduce the amount of feed required to produce chicken meat by one-half, and breast meat by 67%. Because feed accounts for approximately two-thirds of the cost of producing chicken, the resulting savings to consumers is substantial.
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To counter a surprisingly widespread popular misunderstanding of the underlying mechanisms behind rapid broiler growth, it is important to note the basis for this transformative change in productivity. Modern chickens grow quickly because they have tremendous genetic potential to grow. Traditional selection methods—breeding efficient and robust birds with high growth rates—have been a particularly successful strategy in poultry because of high reproductive rates and short generation times. There have been lessons along the way. Unintended consequences to selection have proven challenging for the broiler industry, and will likely continue to emerge in spite of a high level of diligence manifested through comprehensive balanced selection programs. Many unintended changes such as increasing sexual dimorphism are not likely to become problematic, but musculoskeletal biomechanics, changes in immune response, and implications of huge growth potential for the welfare of breeding stock will undoubtedly challenge primary meat-type poultry breeders for the foreseeable future.
本研究探讨了商业筛选对肉鸡生长、效率和产量的影响，使用了自1957年和1978年以来未经选择的2种亚伯达大学肉品控制品系以及一种商业Ross 308品系（2005）。每个品系的混合性别雏鸡（每个品系n = 180）被放置在4个重复笼子中，并按照当前营养计划生长到56天。收集每个品系8只鸡的每周正面和侧面照片。对生长率、饲料摄入量和饲料效率的指标，包括饲料转化率、剩余饲料摄入量和剩余维护能量需求进行了表征。使用非线性混合Gompertz生长模型来预测体重和体重变异，有利于随后进行随机生长模拟。从21天到56天龄期间，对每个品系的8只鸡进行了解剖，以表征胸肌、腿肉、腹部脂肪垫、肝脏、肠道和心脏的异速生长。使用新颖的非线性协方差分析来测试假设，即由于商业选择压力的影响，异速生长模式已经发生变化。从1957年到2005年，肉鸡生长率增加了超过400%，同时饲料转化率降低了50%，相应的42天活体重增长复合年增长率为3.30%。与此同时，42天的饲料转化率在同一48年期间每年减少2.55%。由于遗传选择压力，肌肉中胸肌的生长潜力增加，而腹部脂肪减少。从1957年到2005年，雄性42天时的胸小肌产量比雌性高30％，雌性高37％；胸大肌产量在雄性和雌性中分别增加了79％和85％。在几乎50年的商业数量遗传选择压力下，实现了预期的有益变化。增强的两性异形等意外变化可能无关紧要，但肌肉骨骼、免疫功能和种鸡管理方面的挑战可能需要在未来的选择计划中额外关注。
从1957年到2005年，肉鸡生长速度增加了超过400％，同时饲料转化率减少了50％。肉鸡42天存活体重以复合速率3.1％增长（Barton，1994）的说法经受住了审查。本项研究证实，从1957年到2005年，肉鸡42天活体体重的增长率为每年3.30％，复合增长48年。同样，饲料转化率到42天龄也以每年2.55％的复合方式降低。净结果是，在近50年的时间里，肉鸡行业已经成功将生产鸡肉所需的饲料量减少了一半，胸肉减少了67％。因为饲料约占生产鸡肉成本的三分之二，因此对消费者的节省是相当可观的。
为了消除人们对快速肉鸡生长背后机制的普遍误解，需要指出这种生产力转型的基础。现代鸡之所以能够快速生长，是因为它们具有巨大的遗传潜力。传统的选择方法——培育高生长率、高效率和强健的鸟类——在家禽业中特别成功，因为家禽繁殖速度快，代际间隔短。这一过程中也存在一些教训。选择的无法意料之后果对肉鸡行业构成了挑战，尽管通过综合平衡的选择计划表现出的高度勤勉性可能会继续出现。许多无法意料的产生的变化，如两性异形增加，不太可能成为问题，但肌肉骨骼生物力学、免疫反应的变化以及巨大生长潜力对繁殖肉禽福利的影响无疑会在可预见的未来挑战主要的肉禽育种者。
Reference
- M.J. Zuidhof, B.L. Schneider, V.L. Carney, D.R. Korver, F.E. Robinson,
Growth, efficiency, and yield of commercial broilers from 1957, 1978, and 2005. Poultry Science, Volume 93, Issue 12, 2014, Pages 2970-2982 - N. Barton. Breeding meat type poultry for the future targets for selection, limits to performance and market requirements for chicken. Proc. 9th European Poultry Conference, World’s Poultry Science Association, UK Branch, Andover, Hants, UK (1994), pp. 33-38
