Abstract
This study evaluated phenotypic (rph) and genetic correlations (rg) between 8 feed efficiency traits and other traits of economic interest including weight at selection (WS), loin-eye area (LEA), backfat thickness (BF), and rump fat thickness (RF) in Nellore cattle. Feed efficiency traits were gain:feed, residual feed intake (RFI), residual feed intake adjusted for backfat thickness (RFIb) and for backfat and rump fat thickness (RFIsf), residual body weight gain (RG), residual intake and body weight gain (RIG), and residual intake and body weight gain using RFIb (RIGb) and RFIsf (RIGsf). The variance components were estimated by the restricted maximum likelihood method using a two-trait animal model. The heritability estimates (h2) were 0.14, 0.24, 0.20, 0.22, 0.19, 0.15, 0.11 and 0.11 for gain:feed, RFI, RFIb, RFIsf, RG, RIG, RIGb and RIGsf, respectively. All rph values between traits were close to zero, except for the correlation of feed efficiency traits with dry matter intake and average daily gain. High rg values were observed for the correlation of dry matter intake, average daily gain and metabolic weight with WS and hip height (>0.61) and low to medium values (0.15 to 0.48) with the carcass traits (LEA, BF, RF). Among the feed efficiency traits, RG showed the highest rg with WS and hip height (0.34 and 0.25) and the lowest rg with subcutaneous fat thickness (-0.17 to 0.18). The rg values of RFI, RFIb and RFIsf with WS (0.17, 0.23 and 0.22), BF (0.37, 0.33 and 0.33) and RF (0.30, 0.31 and 0.32) were unfavorable. The rg values of gain:feed, RIG, RIGb and RIGsf with WS were low and favorable (0.07 to 0.22), while medium and unfavorable (-0.22 to -0.45) correlations were observed with fat thickness. The inclusion of subcutaneous fat thickness in the models used to calculate RFI did not reduce the rg between these traits. Selecting animals for higher feed efficiency will result in little or no genetic change in growth and will decrease subcutaneous fat thickness in the carcass.
Highlights
The Brazilian meat industry is one of the most dynamic in the world
Males are selected for yearling weight adjusted to 378 days of age (W378) obtained after feedlot performance testing for 168 days, and females are selected for postweaning weight adjusted to 550 days of age (W550) obtained on pasture
Dry matter intake (DMI), dry matter intake; ADG, average daily gain; BW0.75, metabolic body weight; RFI, residual feed intake; RFIb, residual feed intake adjusted for backfat thickness; RFIsf, residual feed intake adjusted for backfat and rump fat thickness; RG, residual body weight gain; residual intake and body weight gain (RIG), residual intake and gain; RIGb, residual intake and gain using RFIb; RIGsf, residual intake and gain using RFIsf; WS, weight at selection; HH, hip height of males and females at selection; CC, chest circumference of males and females at selection; LEA, loin-eye area; BF, backfat thickness; RF, rump fat thickness. doi:10.1371/journal.pone.0161366.t001
Summary
The Brazilian meat industry is one of the most dynamic in the world. The average annual genetic trends for growth traits reported by Nellore breeding programs in Brazil ranges from 0.15 to 0.61% of the average/year for weaning weight and from 0.15 to 0.77% of the average/ year for postweaning weights, while higher genetic trends are obtained for postweaning weight gain (0.11 to 1.02% of the average/year). This selection has resulted in a genetic trend of 0.33% of the average/year in birth weight and of 0.35% of the average/year in mature cow weight [1]. These figures highlight the intense improvement work of technicians, breeders and companies commercializing genetic material to increase meat production of Nellore cattle, the most representative breed in the Brazilian cattle herd. The objective of this study was to estimate genetic correlations of different feed efficiency traits with growth and carcass traits in Nellore cattle. The selection of beef cattle for feed efficiency will lead to a reduction in production costs, but should not have a negative impact on weight or carcass quality
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