Genetics of adaptive traits in heifers and their relationship to growth, pubertal and carcass traits in two tropical beef cattle genotypes

摘要

Genetic analyses of tropical adaptive traits were conducted for two tropically adapted genotypes, Brahmann(BRAH) and Tropical Composite (TCOMP). Traits included tick scores (TICK), faecal egg counts (EPG), buffalo fly-lesionnscores (FLY), rectal temperatures under hot conditions (TEMP), coat scores (COAT), coat colour on a light to dark scalen(COLOUR), navel scores (NAVEL) and temperament measured as flight time (FT). The data comprised adaptive measuresnrecorded at specific times on 2071 heifers comprising 966 BRAH and 1105 TCOMP. The genetic correlations of thesenadaptive traits with heifer growth, scanned carcass, pubertal measures and steer growth and carcass traits were estimated.nBRAHrecorded significantly (P < 0.05) lower TICK, EPG, FLY and TEMPthan did TCOMP.BRAHalso had significantlynsleeker coats, lighter coat colour, more pendulous navels and more docile temperament than did TCOMP. The heritability ofnTICK and FLY was low (<20%), that of EPG, TEMP, NAVEL and FT was moderate (20–50%) and that of COAT andnCOLOUR high (>50%). In general, phenotypic correlations between these adaptive traits were low and genetic correlationsnwere non-significant, implying trait independence. Genetic correlations between EPG and weight traits (0.29 to 0.44)nindicated a positive relationship, implying no deleterious effect of worms on the growth at a genetic level, especially innTCOMP. The negative genetic correlations between COAT and body-condition score across genotypes (–0.33 to –0.48)nindicated genetic advantage of sleek coats in tropics. A positive genetic correlation between COAT and the age at the firstobservedncorpus luteum (0.73) in BRAH indicated that BRAH with sleeker coats were genetically early maturing. Further,nsleeker coats were genetically indicative of lower weights and lower fat cover at puberty in BRAH. The scanned fat measuresnat rumpand rib sites for feedlot steers showed strong genetic correlation (0.50–0.58) with heiferTEMP,indicating geneticallynfatter animals had genetically lower heat tolerance. In BRAH, a positive genetic association between heifer COLOUR andnscanned fat measures in steers (0.50–0.54) implied increased fatness in genetically darker animals. Further, in BRAH, anstrong negative genetic correlation (–0.97) was observed between steer retail beef yield and heifer TEMP, indicating anfavourable genetic association. In general, genetic correlations between adaptive traits and other economic traits werengenotype specific. Further, it can be concluded that selection for productive and pubertal traits in tropical beef cattlengenotypes would not adversely affect their tropical adaptability.