Browsing by Author "Van Der Westhuizen, R. R."
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- ItemGenetic variance components for residual feed intake and feed conversion ratio and their correlations with other production traits in beef bulls(South African Society for Animal Science, 2004) Van Der Westhuizen, R. R.; Van Der Westhuizen, J.; Schoeman, S. J.Feeding costs of animals is a major determinant of profitability in livestock production enterprises. Genetic selection to improve feed efficiency aims to reduce feeding cost in beef cattle and thereby improve profitability. This study estimated genetic (co)variances between weaning weight and other production, reproduction and efficiency traits. Traits included residual feed intake (RFI), feed conversion ration (FCR), growth (average daily gain (ADG), weaning weight (WW) and shoulder height (SHD)), reproductive (scrotum circumference (SCR)) and profitability traits measured in growth tests of young bulls. The only genetic correlations of significance with WW were those with SHD (0.50) and ADG (0.28). Weaning weight serves as no indication of an animal's production, owing to low genetic correlations with other traits (reproduction or feedlot post-weaning growth efficiency). The heritability estimated for FCR was 0.34 and for RFI 0.31 with a genetic correlation estimate of 0.75 between them. The estimated genetic correlation of profitability (Rand-value) with FCR and RFI were -0.92 and -0.59, respectively. The genetic correlations and expected correlated responses between RFI and FCR with Rand-value suggest that indirect selection for Rand-value through direct selection for FCR and/or RFI will result in slower genetic progress in Rand-value than direct selection. However, where the Rand-value cannot be calculated and/or direct selection for Rand-value is not possible, it would be better to select indirectly for Rand-value through the use of FCR rather than RFI.
- ItemNon-genetic factors affecting growth performance and carcass characteristics of two South African pig breeds(South African Society for Animal Science, 2011) Dube, B.; Mulugeta, S. D.; Van Der Westhuizen, R. R.; Dzama, K.A study was conducted to establish non-genetic factors affecting growth and carcass traits in Large White and Landrace pigs. This study was based on 20 079 and 12 169 growth and 5 406 and 2 533 carcass data collected on performance tested pigs between 1990 and 2008 from Large White and Landrace breeds respectively. The traits analyzed were backfat thickness (BFAT), test period gain (TPG), lifetime gain (LTG), feed conversion ratio (FCR), age at slaughter (AGES), lean percentage (LEAN), drip-free lean percentage (DLEAN), drip loss (DRIP), dressing percentage (DRESS), carcass length (CRLTH) and eye muscle area (AREA). Significant effects were determined using PROC GLM of SAS. Herd of origin, year of testing and their interaction significantly affected all traits. Most traits were not affected by season of testing in both breeds, while all traits in both breeds were significantly affected by sex. Testing environment (station, farm) affected all growth traits except for LTG. Backfat thickness and AGES increased with increasing total feed intake, while other traits decreased as total feed intake increased. Improved test centre management did not compensate for pre-test underperformance. Castrates produced higher carcass yields of lower quality than females, while performance testing showed the best results when done at testing centres. This study showed the importance of adjusting for fixed effects when performing genetic evaluations in the two pig populations.