Cytoplasmic inheritance has limited importance on early calf growth traits in a closed breeding nucleus Angus herd

The importance of cytoplasmic inheritance was investigated in an elite Angus herd closed to outside breeding for almost 70 years. Data included full pedigree information on 10,841 animals and phenotypes on up to 7986 animals on body weights collected at birth (WB) and weaning (WW), hock length (HL) measured at birth, and scrotal circumference (SC) measured at weaning. Body weights adjusted to 205 days (W205) were obtained. Each animal was traced back to one of 18 founder cows, from distinct female lineages. Data were analyzed with an animal model that included contemporary group and the random effects of animal, maternal, permanent environment, and cytoplasmic line. The ratios of cytoplasmic variances to phenotypic variances ranged from 0.00 ± 0.00 (WB) to 0.01 ± 0.01 (SC) indicating very small participation in the determination of genetic and phenotypic variability. In contrast genetic maternal variances had ratios to the phenotypic variances ranging from 0.04 ± 0.05 (SC) to 0.19 ± 0.03 (WB) and were typically 50-fold the cytoplasmic variances. The observed ranges for cytoplasmic breeding values (kBV) for W205, SC, and HL were of 2.62 kg, 0.252 cm, and 0.054 cm, respectively, suggesting that a small but not negligible amount of genetic gain could be amassed by including kBV for body weight traits in a selection index. Selection for cytoplasmic effects can lead to increased inbreeding by focusing selection on few maternal lines. Rapid exhaustion of what little cytoplasmic genetic variation is present will happen unless new variation is created by mutations.