GENETIC PARAMETERS AND CORRELATIONS BETWEEN FEED EFFICIENCY AND GROWTH TRAITS FOR BORAN CATTLE IN KENYA

Abstract

Selection for increased body weight leads to heavier animals which have higher feed and maintenance costs, ultimately reducing the profitability of beef enterprises. Measures of feed efficiency such as residual feed intake (RFI) and feed conversion efficiency (FCE) require individual animal feed intake records, leading to higher cost of production. Kleiber index (KI) and relative growth rate (RGR) are derived from already existing performance data. However, their genetic parameters and genetic correlations with growth traits are not known. This study aimed to estimate genetic parameters for feed efficiency and their genetic correlation with growth traits as well as investigating the impact of direct-maternal genetic correlation on estimated breeding values on weaning weight by analysing 2184 records of body weight adjusted (WA) to 205 (WA205), 365 (WA365) and 550 days (WA550), daily growth rate from birth to weaning (ADGB-205), yearling (ADG205-365) and 550 days (ADG365-550), Kleiber Index and relative growth rate at 205 days (KI205, RGR205), 365 days (KI365 and RGR365) and 550 days (KI550 and RGR550) via Bayesian inference in THRGIBBSF90 Software. Direct heritability estimates for ADG ranged from 0.12 to 0.27. Estimates for WA were in range of 0.05±0.05 at 205 days to 0.10±0.05 at 550 days. Estimates for KI were 0.13±0.05 at 205 days to 0.29±0.05 at 550 days. For RGR, estimated direct heritability at 205 days was 0.21±0.05, 0.19±0.04 at 365 days and 0.33±0.05 at 550 days. Genetic correlations between growth rate and feed efficiency traits were low at all ages. The direct-maternal genetic correlations for WA, ADG, KI and RGR at 205 days were between -0.30 and 0.90. The genetic correlations between WA365 and ADG were moderate to high (0.45 to 0.67) while WA550 had a low, positive (0.17±0.09) and negative (-0.30±0.08) genetic correlation with ADG205-365 and ADG365- 550, respectively. The association between KI365 and RGR365 was strong and positive (0.78±0.04) while the genetic correlations between KI365 and RGR550 at 365 and 550 days were low (-0.34 to 0.02). Direct-maternal genetic correlation for weaning weight was strong and negative (-0.49±0.03), leading to significant re-ranking of animals for direct (rrank=0.827) and maternal breeding values (rrank=0.221) estimated by the model fitting direct-maternal genetic correlation and those without. KI and RGR had substantial heritability estimates, implying potential for improvement through selection. The genetic correlations of KI and RGR with growth traits and the direct-maternal genetic correlation indicate antagonistic relationships, therefore, a weighted index which also accounts for direct-maternal genetic effect should be implemented.