	Instituto Nacional de Tecnología Agropecuaria	Estación Experimental Agropecuaria Balcarce

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GENETIC COMPONENTS FOR SLAUGHTER AND MEAT QUALITY TRAITS IN THE ANGUS-HEREFORD CROSSING

E.L. Villarreal*, L.M. Melucci and C.A. Mezzadra.*Email:evillarreal@balcarce.inta.gov.ar

Unidad Integrada Balcarce (Estación Experimental Agropecuaria Balcarce, INTA Facultad de Ciencias Agrarias, Universidad Nacional de Mar del Plata), 7620 Balcarce, Argentina

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Introduction

British breeds are predominant for beef production in the temperate region of Argentina. Breeding female productivity may be enhanced through crossing, better yet when using F1 females with sires of a third breed. This latter scheme may impact favourably on the fattening calve performance and on its carcass and meat quality.

The impact of crossbreeding on the fattening process efficiency depends on the correct use of genetic potential of the breeds and crosses.

This report deals with the genetic and phenotypic components of slaughter and meat quality traits determining the beef production aptitude of the Angus and Hereford breeds and their crosses under grazing conditions.

Materials and Methods

Animals. 355 steers born on 4 years and weaned in early autumm, belonging to a dialell crossbreeding experiment involving Angus and Hereford breeds, and Limousin as terminal breed. All possible genetic groups were generated. Number of sires within breeds varied from 4 to 18.

Management. Fattening started on april every year. Steers grazed cultivated pastures under two feeding regimes: R₁= pasture grazing + autumn-winter supplementation with maize silage; R₂= pasture grazing only. Steers were fattened until 6-8 mm ultrasound back fat thickness was achieved, and then were slaughtered in a commercial abbatoir.

Data collection. The following measurements were performed: Ultrasound (Pie Medical 200 machine, 3.5 MHz) back-fat thickness (UFT) and m.longissimus dorsi area (ULDA) over the 12th-13th rib interval; slaughter weight (SW); hot carcass weight (HCW) and dressing percentage (DP=HCW/SW*100); kidney fat weight (KFW) and percentage (KFP=KFW/(HCW+KFW)*100).

The 12th-13th rib steak from the left half carcass was removed after 24h cooling at 0-50C and was stored at -180C. At the laboratory, actual fat thickness (AFT) and actual m.longissimus dorsi area (ALDA) were determined on each steak, as well as the cooking water loss proportion (WL), ultimate pH (pH), colour readings in the L*a*b* colour space, Warner-Bratzler shear force (WB) and the longissimus muscle ether extract percentage (EE).

Data analyses. Mixed models (PROC MIXED, SAS) were used to estimate direct and maternal additive genetic and individual heterosis effects. Fixed effects included breed Group (G), birth Year (Y), feeding Regime (R) and YxR interaction. Sire within breed or cross was included as a random effect. Age at slaughter (a) was included as covariate. Contrasts to estimate genetic effects were used according to Malik (1984).

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Results and Discussion

For the slaughter traits:

Heterosis was significant for almost all the slaughter traits, which showed hybrid vigour figures ranging from 1.5% (DP) to 19.6% (KFP).

AFT was the only slaughter trait showing no heterosis effect, but with significant differences of +1.5 and -1.0 mm between Angus and Hereford, for direct and maternal effects, respectively.

Limousin crosses weighed more at slaughter and had heavier carcasses, more longissimus dorsi muscle area and less subcutaneous fat depth and kidney fat proportion than backcrosses.

For the meat quality traits:

When considering the genetic effects, heterosis and both direct and maternal effect differences were found to be not different from zero.

Limousin crosses showed a slightly greater pH and smaller WB shear force and ether extract content than backcrosses.

Table 1. ANOVA results and significance of estimated effects^A

^A:* (p<0.05)
^B:SW=slaughter weight; UFT=ultrasound fat thickness; ULDA=ultrasound longissimus dorsi area; AFT=actual fat thickness; ALDA=actual longissimus dorsi area; HCW=hot carcass weight; KFW=kidney fat weight; DP=dressing percentage; KFP=kidney fat percentage; WL=cooking water loss proportion; pH=ultimate pH; L*=brightness; a*=redness; b*=yellowness; WB=Warner-Bratzler shear force; EE=ether extract
^C:G= breed or cross group effect; Y= year of birth effect; R=feeding regime effect; YxR=interaction effect; a= age at slaughter effect
^D:estimate±se; h^o_AH =individual heterosis; g^o_A g^o_H =difference between direct additive effects; g^m_A g^m_H =difference between maternal additive effects; LF₁ PF₁=difference between combined Limousin crosses and combined backcrosses

Conclusions

Angus and Hereford breeds show very similar slaughter performance and meat quality traits. Nearly no additive or maternal differences were detected. Heterosis was important for slaughter traits but not for meat quality traits.

Three-breed (Limousin terminal sired) steers performed higher than backcrosses for both slaughter and meat quality traits, showing also higher leanness and muscling.

(FONCYT Project # 08-04156; UNMDP Project # A040)