Abstract
Genetic relationships between growth and carcass traits in South African Large White pigs were estimated. Genetic parameters for growth and carcass traits were generated using a maternal effects model in ASREML. Data analysed were on 13 703 pigs from 28 herds tested between 1990 and 2007, and 4 128 carcasses from 21 herds evaluated between 1993 and 2007. The traits included in the study were backfat thickness (BFAT), test period weight gain (TPG), lifetime weight gain (LTG), test period feed conversion ratio (FCR), age at slaughter (AGES), lean percentage (LEAN), drip-free lean percentage (DLEAN), drip loss percentage (DRIP), carcass length (CRLTH), dressing percentage (DRESS), eye muscle area (AREA) and carcass fat (CFAT). Heritability estimates for growth traits ranged from 0.24 ± 0.03 for FCR to 0.45 ± 0.04 for BFAT, while those for carcass traits ranged from 0.14 ± 0.06 for DRIP to 0.55 ± 0.0.08 for AREA. Maternal genetic effects were significant in most traits, and were negatively correlated with direct heritabilities. Genetic correlations among growth traits ranged from –0.14 ± 0.08 between BFAT and LTG to –0.99 ± 0.01 between TPG and FCR, and LTG and AGES. For carcass traits, genetic correlations ranged from –0.02 ± 0.20 between DRIP and CRLTH to 0.99 ± 0.01 between LEAN and DLEAN. There is substantial genetic variation in growth and carcass traits; hence faster genetic improvement may be achieved through selection. Growth performance and carcass characteristics can be improved through selection for reduced backfat thickness and increased daily weight gain. Keywords : Genetic selection, growth traits, carcass traits, correlations
Highlights
The South African Pig Performance Testing Scheme is conducted to extend and improve the national pig herd by means of scientifically founded and proven methods and practices
Fast genetic progress may be expected if genetic selection is aimed at reducing backfat thickness
These moderate heritability estimates indicate the existence of substantial genetic variation in this population, which may result in genetic improvement if direct selection is applied on the traits
Summary
The South African Pig Performance Testing Scheme is conducted to extend and improve the national pig herd by means of scientifically founded and proven methods and practices. Growth performance, with little emphasis on output parameters such as carcass yield and quality (Visser, 2004). Input and output parameters have been central to pig improvement programmes (Visser, 2004; Dube, 2012). This is in accordance with the general trend in the pig industry, where selection objectives have changed from performance traits to carcass yield and quality (Suzuki et al, 2005; Van Wijk et al, 2005). Meat quality parameters are important from the consumer viewpoint, the inputs used during the rearing of pigs remain important
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