Genetics of steer daily and residual feed intake in two tropical beef genotypes, and relationships among intake, body composition, growth and other post-weaning measures

Abstract

Abstract. Genetic parameters for Brahman (BRAH) and Tropical Composite (TCOMP) cattle were estimated for steer production traits recorded at weaning (WEAN), 80 days post-weaning (POSTW), feedlot entry (ENTRY) and after $120 days feedlot finishing (EXIT). The TCOMP was 50% Bos indicus, African Sanga or other tropically adapted Bos taurus, and 50% non-tropically adapted Bos taurus. Data involved 2216 steers, comprising 1007 BRAH by 53 sires and 1209 TCOMP by 50 sires. Individual daily feed intake (DFI) and residual feed intake (RFI) were assessed on 680 BRAH and 783 TCOMP steers over an~70-day feedlot test. Other traits were liveweight (LWT), average daily gain (ADG), ultrasonically scanned rump (SP8) fat depth, rib (SRIB) fat depth, M. longissimus area (SEMA) and intra-muscular fat % (SIMF), body condition score (CS), hip height (HH), flight time (FT) and serum insulin-like growth factor-I concentration (IGF-I).BRAH were significantly (P < 0.05) lighter at ENTRY and EXIT, and had lower DFI (10.8 v. 13.2 kg/day) and RFI (-0.30 v. 0.17 kg/day), greater SP8 (5.8 v. 5.1 mm) but similar SRIB at ENTRY, lower SRIB (8.2 v. 8.9 mm) but similar SP8 at EXIT, and greater HH than TCOMP. Heritabilities for DFI, RFI, LWT, ADG, scanned body composition, HH and IGF-I measures, across measurement times, were generally in the 20 to 60% range for both genotypes. Genetic variance for RFI was 0.19 (kg/day) 2 in BRAH and 0.41 (kg/day) 2 in TCOMP, suggesting a clear potential to genetically change RFI in both genotypes. Trait variances and genetic correlations often differed between the genotypes, supporting the use of genotypespecific parameters in genetic evaluation. The genotype differences may be associated with evolutionary changes that have occurred in B. indicus as a part of their adaptation to tropical environments.Measures with potential to be used as genetic indicators of DFI were LWT measures in BRAH and TCOMP, ADG at ENTRY in TCOMP, and SP8 and SIMF at ENTRY in BRAH. Measures with potential to be genetic indicators of RFI were HH and ADG at ENTRY in BRAH, and IGF-I in both genotypes. Taller and faster-growing BRAH steers at ENTRY had genetically lower RFI. IGF-I was negatively genetically correlated with RFI whether IGF-I was measured at POSTW, ENTRY or EXIT. SRIB fatness at EXIT was strongly positively genetically correlated with RFI in TCOMP but only lowly correlated in BRAH. Fatness at ENTRY was lowly and negatively genetically correlated with RFI. The results emphasise the need for a population-specific understanding of trait relationships and of trait differences between measurement times if genetic indicator traits are to be utilised in genetic evaluation of RFI.

Importance of adaptation and genotype × environment interactions in tropical beef breeding systems

“…Genetic associations exist between growth traits and body composition attributes such as retail beef yield, fat depth and marbling (the review of Burrow et al, 2001 and references therein; Reverter et al, 2003a andWolcott et al, 2009) and feed efficiency (Robinson and Oddy, 2004;Barwick et al, 2009a). Genetic and phenotypic associations also exist between growth and reproductive attributes (Burrow et al, 1991;Burrow, 2001 and references therein).…”

“…Barwick et al (2009a) found that in steers grown under commercial backgrounding and grain-finishing environments, G 3 E interactions were indicated by the presence of significant genotype 3 cohort effects, with the mean cohort performance for a trait assumed to be the measure of environment level. Significant genotype 3 cohort effects existed for many measures at and before the steers entered the feedlot, indicating the differences evident in Brahmans and Tropical Composites could change under different environmental conditions.…”

Erratum to: Genetics of heifer performance in 'wet' and 'dry' seasons and their relationships with steer performance in two tropical beef genotypes

“…In the feedlot, they were fed a standard finisher ration of 12.2 MJ ME/kg DM energy density, 16.25% crude protein (w/w) and 87% DM for an average of 119 days to a finished average liveweight of 568 kg. Other details of the management of steers are given by Barwick et al (2009).…”

“…Heifers born and managed together at 'Belmont' represented 34 BRAH and 26 TCOMP sires. Other details of sire and dam groups in the TCOMP genotype, and of the BRAH and TCOMP sires used are given by Barwick et al (2009). Briefly, the 50% tropically adapted component of the TCOMP is approximately one-half derived from the Bos indicus Brahman and one-half from African Sanga (Frisch et al 1997) (24% Africander) or other adapted Bos taurus (2% N'Dama, through the Senepol).…”

“…The TCOMP is 50% derived from tropically adapted and 50% from nontropically adapted breeds. Barwick et al (2009) presented results from this study for daily (DFI) and residual feed intake (RFI), body composition, growth and other post-weaning measures of feedlot-finished steers. This paper reports on the genetics of heifer post-weaning performance in 'wet' (between December and May) and 'dry' (between June and November) seasons; and on relationships between this and the performance of their steer half-sibs.…”