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Genetic analyses of tropical adaptive traits were conducted for two tropically adapted genotypes, Brahman (BRAH)andTropicalComposite(TCOMP).Traitsincludedtickscores(TICK),faecaleggcounts(EPG),buffalo fly-lesion scores (FLY), rectal temperatures under hot conditions (TEMP), coat scores (COAT), coat colour on a light to dark scale (COLOUR), navel scores (NAVEL) and temperament measured as flight time (FT). The data comprised adaptive measures recorded at specific times on 2071 heifers comprising 966 BRAH and 1105 TCOMP. The genetic correlations of these adaptive traits with heifer growth, scanned carcass, pubertal measures and steer growth and carcass traits were estimated. BRAHrecordedsignificantly(P <0.05)lowerTICK,EPG,FLYandTEMPthandidTCOMP.BRAHalsohadsignificantly sleekercoats,lightercoatcolour,morependulousnavelsandmoredociletemperamentthandidTCOMP.Theheritabilityof TICK and FLY was low (<20%), that of EPG, TEMP, NAVEL and FT was moderate (20-50%) and that of COAT and COLOURhigh(>50%).Ingeneral,phenotypiccorrelationsbetweentheseadaptivetraits werelowandgeneticcorrelations were non-significant, implying trait independence. Genetic correlations between EPG and weight traits (0.29 to 0.44) indicated a positive relationship, implying no deleterious effect of worms on the growth at a genetic level, especially in TCOMP. The negative genetic correlations between COAT and body-condition score across genotypes (-0.33 to -0.48) indicated genetic advantage of sleek coats in tropics. A positive genetic correlation between COAT and the age at the first- observed corpus luteum (0.73) in BRAH indicated that BRAH with sleeker coats were genetically early maturing. Further, sleekercoatsweregeneticallyindicativeoflowerweightsandlowerfatcoveratpubertyinBRAH.Thescannedfatmeasures atrumpandribsitesforfeedlotsteersshowedstronggeneticcorrelation(0.50-0.58)withheiferTEMP,indicatinggenetically fatter animals had genetically lower heat tolerance. In BRAH, a positive genetic association between heifer COLOUR and scanned fat measures in steers (0.50-0.54) implied increased fatness in genetically darker animals. Further, in BRAH, a strong negative genetic correlation (-0.97) was observed between steer retail beef yield and heifer TEMP, indicating a favourable genetic association. In general, genetic correlations between adaptive traits and other economic traits were genotype specific. Further, it can be concluded that selection for productive and pubertal traits in tropical beef cattle genotypes would not adversely affect their tropical adaptability.

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