Consequences of long-term inbreeding accumulation on preweaning traits in a closed nucleus Angus herd1

Abstract

The effect of individual and dam (maternal) inbreeding was quantified for preweaning traits in an Angus nucleus herd that has been closed to outside breeding for 70 yr. The effectiveness of 5 models (linear, quadratic, exponential, Michaelis-Menten, and Rumford-Newton) was evaluated for describing the effect of inbreeding on growth traits, hock length (HL), and scrotal circumference (SC). Pedigree information and production records were retrieved for 10,938 animals 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 observed 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 inbreeding effects. Genetic gain from selection at an intensity equivalent to 0.25 can be nullified by an inbreeding accumulation 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 maternal inbreeding. At current inbreeding accumulation levels in this herd, 7 generations of inbreeding accumulation will be necessary to nullify the genetic progress from 1 generation of selection in growth traits.

Conservation priorities of genetic diversity in domesticated metapopulations: a study in taurine cattle breeds

“…Figs. S2, S3, and S4) with high fitness (high fertility and long life history) in a challenging environment, but with relatively low annual output; on the other side of the spectrum are breeds with low fitness (e.g., Dobson et al 2007) and inbreeding depression (e.g., Carrillo and Siewerdt 2010) but high annual output in a favorable environment where environmental pressures are managed through intervention strategies such as providing high-quality feeds, artificial housing, or disease management. Our results clearly demonstrate high neutral diversity in the first group and suggest their potential for economically and environmentally sustainable agriculture.…”

Population Structure and Genetic Variability of Angus and Nellore Herds

“…Since 1965 breeding has been managed to prevent crossings between closely related animals. However, the inbreeding coefficient increased until the 1980s as a result of cumulative inbreeding (Carrillo & Siewerdt, 2010). In contrast, the Nellore herd shows no evidence of inbred mating, possibly due to the lack of pedigree information at the time.…”

“…A number of studies have documented inbreeding depression in bovine traits (Mc Parland et al, 2007;Carrillo & Siewerdt, 2010;Santana et al, 2012). However, less experimental work has been conducted on the effects of inbreeding and other parameters (e.g.…”

Prioritization based on neutral genetic diversity may fail to conserve important characteristics in cattle breeds

“…In wild and laboratory populations, traits related to fitness are often of this latter kind (Barker 2000). Formal studies in livestock are lacking, but the general finding that reproduction and fitness traits in cattle are more susceptible than production traits to inbreeding depression (Carrillo & Siewerdt 2010) may be consistent with differences in genetic architecture.…”