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. 2018 Dec 12;5(12):180325. doi: 10.1098/rsos.180325

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© 2018 The Authors.

Published by the Royal Society under the terms of the Creative Commons Attribution License http://creativecommons.org/licenses/by/4.0/, which permits unrestricted use, provided the original author and source are credited.

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Figure 5. — Accelerating growth rate of broilers throughout the second half of the twentieth century. The tibiotarsus bone is used as a proxy for skeleton growth, N = 10. Records of tibiotarsus growth rates were obtained from broilers reared in 1964: New Hampshire/Barred Rock cross-breed, USA [32]; 1975: unspecified commercial broilers, Canada [33]; 1991: Vantress/Arbor Acre cross-breed, USA, males [34]; 1992: Cobb, Nigeria [35]; 2000: Ross, Brazil [36]; 2001: unspecified commercial broilers, Turkey [37]; 2002: Ross/Arbor Acre cross-breed, USA [38]; 2009: unspecified commercial broilers, USA [39]; 2012: Ross, Poland [40]. These are compared to the growth rate of the cross-bred red jungle fowl, UK [30]. A smoothing spline with a smoothing factor of 4.35 [41] fitted to the 1964 to 2012 data indicates an increase in the growth rate of broilers from 1964 to present.