2010-Carrilo_and_Siewerdt - Consequences of long-term...

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J. A. Carrillo and F. Siewerdt nucleus Angus herd Consequences of long-term inbreeding accumulation on preweaning traits in a closed doi: 10.2527/jas.2009-1897 originally published online Oct 9, 2009; 2010.88:87-95. J Anim Sci http://jas.fass.org/cgi/content/full/88/1/87 the World Wide Web at: The online version of this article, along with updated information and services, is located on www.asas.org by on April 11, 2011. jas.fass.org Downloaded from
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ABSTRACT: The effect of individual and dam (ma- ternal) inbreeding was quantified for preweaning traits in an Angus nucleus herd that has been closed to out- side breeding for 70 yr. The effectiveness of 5 models (linear, quadratic, exponential, Michaelis-Menten, and Rumford-Newton) was evaluated for describing the ef- fect of inbreeding on growth traits, hock length (HL), and scrotal circumference (SC). Pedigree information and production records were retrieved for 10,938 ani- mals and analyzed in an animal model that included the fixed effects of year of birth, age of the dam, sex, and age at weaning (for traits measured at weaning). Average individual and maternal inbreeding in the herd were 0.068 and 0.066, respectively, for all animals; in the last calf crop these values were 0.120 for the calves and 0.121 for their dams. Inbreeding depression was ob- served for BW at birth (WB), weaning weight (WW), BW adjusted to 205 d of age (W205), ADG, HL, and SC. The effect of maternal inbreeding was smaller than for individual inbreeding for WB, WW, W205, and ADG. Nonlinear prediction was done more effectively by the exponential and Michaelis-Menten models. Quadratic polynomials were an inadequate descriptor of inbreed- ing effects. Genetic gain from selection at an intensity equivalent to 0.25 can be nullified by an inbreeding ac- cumulation of 0.187 (WB), 0.056 (WW), 0.068 (W205), 0.065 (ADG), or 0.092 (SC). Inbreeding accumulation of 0.018 is required to nullify genetic gain for HL; this particular prediction is valid for non-inbred cows due to an observed interaction between individual and ma- ternal inbreeding. At current inbreeding accumulation levels in this herd, 7 generations of inbreeding accumu- lation will be necessary to nullify the genetic progress from 1 generation of selection in growth traits. Key words: beef cattle, growth, inbreeding depression, nucleus herd, scrotal circumference ©2010 American Society of Animal Science. All rights reserved. J. Anim. Sci. 2010. 88:87–95 doi:10.2527/jas.2009-1897 INTRODUCTION Inbreeding is the consequence of mating related indi- viduals. In diploid species, inbred individuals will carry 2 copies of the same allele that are identical by descent (i.e., from a common ancestor), through DNA replica- tion (Malécot, 1969). Genetic management of livestock should contemplate not reaching levels of inbreeding in future generations where it would be possible to ob- serve a reduction in biological performance or a threat to the sustainability of selection programs. Reproduc- tion and fitness traits are usually more sensitive to in- breeding accumulation than growth and morphological traits (McParland et al., 2007). Inbreeding depression
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2010-Carrilo_and_Siewerdt - Consequences of long-term...

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