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The design of swine breeding programs for the tropics requires knowledge of genetic parameters for economically important traits determined under tropical conditions. A literature review found a total of 468 heritability (h 2 ) estimates, 368 genetic correlations and 254 phenotypic correlations for 35 traits across 117 peer-reviewed articles published from 1974 to 2009 and covering tropical Africa, Southeast Asia, the Caribbean and Latin America. A model that incorporated between and within study variance component was used to obtain weighted means and variances for all parameter estimates. Weighted means and standard errors of direct and maternal heritability, common litter effects and the correlation between direct and maternal effects are given for various reproduction, growth and carcass traits. The weighted means and confidence intervals for the genetic and phenotypic correlations between the trait groups are also given. Weighted least-squares analyses of the h 2 estimates were performed by fitting a number of fixed effects and covariates for each trait as appropriate for the data. Breed, data origin, estimation method, data age and location of study were found to be significant (Po 0.05) for majority of the traits analysed. These results indicate the relevance of having local, population-specific genetic parameter estimates for the tropics. The weighted mean estimates of genetic parameters presented here are recommended for use when reliable estimates are not available for a specific tropical pig population. This is quite appropriate because it uses the vast resource of published genetic parameter estimates effectively.

Mandell, I. B., Campbell, C. P., Quinton, V. M. and Wilton, J. W. 2006. Effects of skeletal separation method and postmortem ageing on carcass traits and shear force in cull cow beef. Can. J. Anim. Sci. 86: 351‐361. Sixty-six cull cow carcasses were subjected to skeletal separation methods for improving beef tenderness as evaluated using shear force. Forty-one carcasses were used to evaluate the effect on longissimus muscle shear force from skeletal separation at various sites including: (1) the 11th thoracic vertebra, (2) the 12th thoracic vertebra, and (3) the 6th thoracic and 5th lumbar vertebrae. Longissimus muscle steaks from the posterior and anterior loin and posterior rib were aged for 2, 7, 14, and 28 d. Twenty-five carcasses underwent skeletal separation processing in the round with severing of the ischium and the junction between 4th/5th sacral vertebrae. Semimembranosus, semitendinosus, biceps femoris, vastus lateralis, and rectus femoris muscles were processed into steaks and aged for 2, 7, 14, and 28 d. Skeletal separation techniques involving thoracic and lumbar vertebrae decreased (P < 0.04) shear force in the posterior rib and anterior loin but not in the posterior loin. Shear force continued to decrease (P < 0.01) as postmortem ageing duration increased. The semimembranosus was the only muscle in the round in which shear force decreased (P < 0.01) with skeletal separation. Postmortem ageing for at least 14 d decreased (P < 0.06) shear force in semimembranosus and vastus lateralis steaks while there were no further decreases in shear force after 7 d ageing for semitendinosus and rectus femoris steaks. Skeletal separation increased (P < 0.10) sarcomere length in all muscles studied. Skeletal separation techniques have the potential to improve tenderness in the longissimus and semimembranosus muscles, which may increase utilization of cull cow beef.

Economic values or weights measure the net economic gain per unit genetic increase of a given trait. These were derived for sow productivity traits for use as weighting factors in a dam line selection index used by purebred or nucleus dam line breeders. The profit function approach was used in order to provide flexibility to alternative production systems, market requirements or population trait levels. The approach accounted for constraints on perinatal survival rate imposed by larger birth litter sizes. The effect of accounting for these constraints was to reduce the economic value of birth litter size as the population average increased; without this, the economic weight for litter size was constant. Weights for the other traits were not affected. Economic weights were calculated for both the 100 kg finished pig and the 25 kg feeder pig market, and for a range of average birth litter sizes, with constant values for all other traits, using average market conditions, prices and costs in Canada as an example. The relative importance of litter size for the finished pig market decreased from 64% of the total breeding value when average litter size was 8 pigs to 29% when average litter size was 20 pigs, whereas that of perinatal survival increased from 17% to 42%, and that of survival to weaning increased from 7% to 18%. The relative importance of litter size for the feeder pig market also decreased from 45% to 15% as average litter size increased from 8 to 20 pigs, whereas that of piglet weaning weight increased from 22% to 41%, that of perinatal survival increased from 12% to 22% and that of survival to weaning increased from 5% to 9%. The relative importance of age at puberty and weaning to conception interval were both less than 8% of the total in both markets at all litter sizes. These results show that economic weights for litter size designed for populations with relatively small litter sizes should be reduced when the average litter size becomes large and more emphasis should be placed on other traits, particularly perinatal survival.

A herd of purebred Hampshire and a herd of purebred Duroc pigs were created between 1987 and 1989 and subsequently selected on an index of growth rate and backfat from 1989 to 1995. Strict rules were put in place to promote rapid turnover of generations and allow only minimal culling for structural soundness. In 1990, 1991, 1993 and 1994, a number of sows coming from the Hampshire and Duroc selection lines were bred using frozen semen collected from a sample of control boars born in 1988 and 1989. Estimates of genetic trend based on single trait animal model analyses of age at 100 kg and backfat estimated rates of response to selection of approximately –1.4 and –0.4 days and –0.5 and –0.3 mm backfat per annum in Durocs and Hampshires, respectively. These were close to the original predictions based on the index employed for Durocs, but somewhat less than expected for Hampshires. Comparison of progeny of selected versus control boars was consistent with significant selection responses having been achieved, though estimates of the magnitude of the response had high standard errors. During the period of the trial, both the Hampshire and Duroc herds went from slightly below average on the Canadian National Genetic Evaluation Program to become the number one herds within their breed for the sire line index based on backfat and growth. The trial demonstrated that selection indexes based on estimated breeding values can be used effectively to achieve genetic progress. Key words: Pig breeding, selection index, estimated breeding values, selection response

The theory and use of best linear unbiased prediction in genetic evaluation are well developed. However, there has been little empirical checking of its efficacy in practice. The objective here was to use a large body of Canadian pig performance records to check on the predicted benefits of BLUP in genetic evaluation. Phenotype records were available on fat depth and on days to 100 kg on some 65 000 progeny born in 1994 and 1995 from parents evaluated before 1994. Rank correlations between parent and progeny in data were calculated within herd-year-season to avoid effects due to differences in these factors. Computer simulation studies were also run to check on the predicted results. The simulation results confirmed the expectations on the higher correlation of mid-parental EBV than of mid-parental phenotype with progeny genotype and a regression (of progeny phenotype on mid-parental EBV) of unity when all relevant pedigree and performance data were used. In the data analysis, the (rank) correlations with progeny phenotype were consistently higher (36 and 27%) for mid-parental BLUP genetic evaluation than for mid-parental phenotypes, confirming the superiority of the BLUP evaluations over phenotypes. However, the regression of progeny phenotype on mid-parent BLUP EBV was usually less than the predicted value of unity. Simulation results suggest that either the base population heritability was lower than that used in the evaluation or that the information used was incomplete. Key words: Best linear unbiased prediction, EBV, pigs, performance, selection

Data on more than 1.3 million pigs of four breeds in four regions of Canada were used to estimate genetic changes in fat depth and growth rate from 1976 to 1993. Analysis was by a multi (two)-trait best linear unbiased prediction (BLUP) animal model within breed and across regions. The genetic changes were measured as the changes in average estimated breeding value (EBV) over years.The across-breed average total phenotypic changes from 1976 to 1993 were− 3.9 mm in fat depth (26% of the mean) and− 17 d in age at 100 kg (9% of the mean). The multi-trait BLUP estimates of the genetic trends were similar to single-trait BLUP estimates. The mean EBV and the changes were similar for the four regions. The changes were larger in the Landrace and Yorkshire breeds than in the Duroc and Hampshire. The overall genetic trends were − 1.44% of the mean yr−1 in fat depth and − 0.36% of the mean yr−1 in age at 100 kg. The trend for age at 100 kg increased over time as better methods of deriving the EBV were implemented. The current rates of pig improvement in Canada are good and yield large economic benefits. However, they could be improved to recoup the full gains possible through the Canadian Swine Improvement Program. Key words: Canadian pigs, performance testing, genetic trends