Abstract:
Proc. Assoc. Advmt. Anim. Breed. Genet. Vol13 EARLY RESULTS OF THE GENETIC RELATIONSHIP BETWEEN POSTWEANING GROWTH AND CARCASE INTRAMUSCULAR FAT IN STEERS D. J. Johnston', A. Reverter', D. Perry', J. M. Thompson' and R. W. Dicker4 vlity), Department 1 NSW 2370 The Cooperative Research Centre for the Cattle and `Animal Genetics and Breeding Unit' , *NSW Agriculture, Animal Science, University of New England, 4NSW Agriculture, Agricultural Research and Advisory SUMMARY British breed steers grown out for the Korean and Japanese relationship between postweaning growth and intramuscular dorsi muscle. The results showed postweaning average positively correlated genetically with IMF. The study also parameters for average daily gain traits measured over short Keywords: Postweaning growth, intramuscular fat, genetic Beef Industry (Meat Beef Industry Centre, Armidale, NSW 235 Station, Glen Innes, of markets were used to estimate the genetic fat percent (IMF) in the m. longissimus daily gain was moderately heritable, and highlighted problems in estimating genetic periods. correlation INTRODUCTION The level of marbling in beef carcases is an important specification for some domestic and export markets. With the availability of marbling estimated breeding values (EBVs), Australian beef producers can consider genetic and non-genetic methods to improve marbling. The aim of this study was to better understand the genetic and phenotypic relationship between marbling and early postweaning growth. MATERIALS AND METHODS Data from the Cooperative Research Centre for the Cattle and Beef Industry (CRC) straightbreeding project was used, the design and management of the project were outlined by Robinson (1995). In brief, the project entailed a designed progeny test for carcase and meat quality traits from four temperate breeds (Angus, Hereford, Shorthorn, and Murray Grey) and three tropically adapted breeds (Brahman, Belmont Red and Santa Gertrudis). The data in this study were on temperate breed steers that were backgrounded to an average liveweight of 400 kg prior to finishing for the Korean or Japanese export markets. Within a year and season (autumn and NSW, for grow-out. Liveweights were weights being used in this study. These grow-out. The middle weight coincided at an average liveweight of 300 kg. The the intake group was 400 kg. spring), taken at weights with the end of animals were assembled at Glen Innes, several stages throughout the grow-out were at t!he start, the middle, and at the moving of the domestic market groups the grow-out weight was taken when the in northern with three end of the to finishing average of * AGBU is a joint institute of NSW Agriculture and the University of New England 349 Proc. Assoc. Advmt. Anim. Breed. Genet. Vol I3 After grow-out the steers were finished on pasture or grain to either the Korean (280 kg carcase) or Japanese market (320 kg carcase) endpoints. At slaughter, a sample of the m. longissimus dorsi muscle was taken between the 1203th ribs. Samples were freeze dried and intramuscular fat percent predicted by near infra-red (NIR) spectroscopy. Growth traits considered were: initial grow-out weight (IWT), average daily gain from start to the mid-weight (ADG12), average daily gain from mid-weight to final weight (ADG23), and average daily gain from initial to final (ADG13). Variance components were estimated by REML using VCE4.0 (Groeneveld and Garcia Cortts 1998). The first analysis included IWT, ADG13 and IMF run in a three trait model. For the growth traits, the model included a fixed effect for herd of originljbackground nutrition levelllyear)(season. A covariate of age at the start of grow-out was included for IWT and ADG13. The model for IMF included two fmed effects, the first modelled the pre-finishing backgrounding regimes: herd of originllbackground nutrition 1evelijyear)lseason and a second defined a comparable group of animals: herd of origin){kill code, where kill code grouped all animals from same CRC intake, finish-market destination, killed on the same day at the same abattoir. A covariate of carcase weight was included. The second analysis was performed where the grow-out period was considered as two separate traits (ADGl2 and ADG23) and were included with IWT and IMF in a four trait model. For growth traits, the model included a fixed effect for herd of origin))background nutrition 1evel)jyear))season. A covariate of age was included for IWT and ADG12. A covariate of mid-weight was included for ADG23. IMF was modelled as above. For both analyses, additive genetic and residuals were modelled as random effects. The analysis included a relationship matrix using up to five generations of pedigree. A total of 193 sires had progeny recorded. RESULTS AND DISCUSSION Trait statistics are presented in Table 1. The steers had an average initial weight (IWT) of 270 kg at 324 days of age. On average, the steers were backgrounded for 186 days (days13) and grew at 0.66 kg/day. When the grow-out period was partitioned, the first period was on average 69 days (days12) and the second period 119 days (days23). Heritabilities and correlations are presented in Table 2. IWT and IMF were moderately heritable, with a lower estimate for ADG13. Genetic correlations were positive between the three traits, with IMF and ADG13 being moderately correlated (r&).32). The results were in general agreement with estimates reviewed by Koots et al (1994a,b), who reported a heritability of 0.32 for yearling gain and a weak positive genetic relationship between post weaning gain and marbling score. Phenotypic correlations were close to zero. This was due to negative residual correlations between the traits. This has ramifications for the grow-out management of feeder cattle, particularly those destined for markets requiring marbling. 350 Proc. Assoc. Advmt. Anim. Breed. Genet. Vol13 Table 1. Raw trait statistics Variable Initial wt (kg) age (d) days12 (d) adg 12 (kg/d) mid wt (kg) days23 (d) adg23 (kg/d) days1 3 (d) adg 13(kg/d) imf (%) carcase wt (kg) Number 1593 1839 1427 1427 1839 1749 1749 1510 1510 1332 1830 Mean 270.3 324 68.7 0.71 308.5 118.9 0.70 186.2 0.66 5.47 302.6 Std 45.0 29.0 39.9 0.39 40.9 31.2 0.29 54.9 0.22 2.01 34.4 Min. 128 227 9 0.02 172 85 0.01 104 0.01 I .48 195.5 Max. 415 417 110 1.95 428 200 1.63 252 1.37 16.26 445.5 Table 2. Heritabilities (on diagonal) diagonal) for IWT, ADG13 and IMF and correlations (genetic above, phenotypic below IWT ADG13 IMF IWT (kg) 0.44 0.05 -0.03 ADG13 (kg/cl) 0.12 0.28; -0.0 I IMF (%) 0.12 0.32 0.42 When grow-out was split into two periods, the genetic parameters estimated were quite different (Table 3). Gain in the first period (ADG12) had an inflated heritability, was negatively correlated with initial weight (IWT) and was slightly negatively correlated with gain in the second period and IMF. However, gain in the second period was positively correlated with initial weight and with IMF. Mukai et al (1995) reported a genetic correlation of 0.24 between mid-end test gain for bulls on test and steer marbling score. These results showed that gain over a short period was an u:nreliable genetic measure of growth. In this study the animals were recently weaned and relocated from their property of origin. Therefore it is likely that the genetic parameters estimated from the early gain over a relatively short period were confounded with carry over maternal effects and possibly compensatory gain effects during the first few weeks postweaning. Table 3. Heritabilities (diagonals) ADG12, ADG23 and IMF and correlations (genetic above, phenotypic below) for IWT, IWT ADG12 ADG23 IMF IWT (kg) 0.44 -0.01 0.22 -0.03 ADGl2 (kg/d) -0.32 0.48 -0.06 0.02 ADG23 (kg/d) 0.34 -0.12 0.27 -0.04 IMF %) 0.12 -0.09 0.44 0.4 I 351 Proc. Assoc. Advmt. Anim. Breed. Genet. Vol13 These early positive and zero between the finishing intramuscular results could gain period fat. showed the genetic relationship between postweaning gain and marbling was be considered in selection programs. However, the phenotypic correlation was and marbling. Further work will be done to investigate the effect of gain during and any interactions with regime (pasture vs. grain) on the relationship with ACKNOWLEDGEMENTS We thank Cattle and Beef Industry CRC for assistance, in particular Peter Kamphorst and staff at the Agricultural Research and Advisory Station, Glen Innes for cattle management, and Andrew Blakely, and his staff, for their processing of the chemical fats. REFERENCES Groeneveld E.and Garcia Cartes, A. (1998) Proc. 6th Wrld Congr. Genet. Appl. Livest. Prod. 27:455 Koots, K.R., Gibson, J. P., Smith, C. and Wilton, J.W. (1994a) Anim. Breed. Abstr. 62:33 1 Koots, K.R., Gibson, J. P., and Wilton, J.W. (1994b) Anim. Breed. Abstr. 62:825 Mukai, F., Oyama, K. and Kohno, S. (1995) Livest. Prod. Sci. 44:199 Robinson, D.L. (1995) Proc. Aust. Assoc. Anim. Breed. Genet. 11:541 352