Estimates of phenotypic and genetic parameters and responses to selection in growth traits in three beef cattle breeds raised under ranch conditions in Botswana

Abstract

The study estimated phenotypic and genetic parameters and responses to selection of growth traits in three beef cattle breeds raised under ranch conditions in Botswana. Weights at birth (BW), at weaning (7 month; (WW) and 18 month (18MW) were obtained for Brahman (n = 841), Bonsmara (n = 926) and Tuli (n = 403) breeds from 1997 to 2008 inclusive from the Department of Agricultural Research, Botswana. Sex, age of dam, month of birth and year of birth significantly affected (P<0.05) performance of growth traits. Birth weight did not differ (P > 0.05) between breeds, (26.0±0.97kg, 26.5±2.38kg, 32.1±2.29kg for Tuli, Brahman and Bonsmara, respectively). Weaning weight was significantly higher (P < 0.05) in Bonsmara (215±10.9kg) than Tuli (144±5.00kg). At 18MW Bonsmara (323±15.0kg) and Brahman (303±18.4kg) had significantly high weights than the Tuli (221±6.62kg). Heritability estimates for BW, WW and 18MW, respectively did not differ (P > 0.05) between breeds, but were highest for Bonsmara (0.36±0.12, 0.69±0.08 and 0.64±0.08) and lowest in Tuli (0.21±0.11, 0.36±0.12 and 0.21±0.12) with Brahman being intermediate 0.57 ± 0.11, 0.53 ± 0.10 and 0.45 ± 0.10). Greater phenotypic and genetic correlations were observed in WW and 18MW for Bonsmara and Brahman. No response to selection was observed for all the traits in the three breeds under study. This may imply that under ranch conditions in Botswana the breeds have reached their potential for growth, not necessarily due to genetic but environmentally driven.