Progeny test data used to estimate breeding values (EBVs) of sires for carcase traits may come from measurements taken on animals that have been slaughtered over time based on individual animal market suitability. Confounding between genetic effects and age can result. However, in the current study appropriate adjustment for growth rate resulted in highly accurate sire EBVs for both the slaughtering criteria, namely liveweight, and for a second trait (e.g. a carcase trait) regardless of the genetic correlation between the two traits.

The performance of sires across flocks and years are likely to vary due to factors such as interactions with the environment, differences in ewe genotypes, errors in recording, non-random mating, and preferential treatment of progeny. Research in other breeds and species has shown that these sire by flock-year interactions typically account for less than 5% of the phenotypic variance. This paper examines the significance of sire by flock-year effects for weight traits in Poll Dorset sheep. The results demonstrate that while the sire by flock-year effects explained between 2 and 4% of the phenotypic variance, they significantly improved the fit of the model and resulted in a direct-maternal genetic correlation closer to zero. However, heritabilities were reduced significantly by up to 50%, indicating that sire by flock-year effects may be removing too much genetic variation for traits with maternal effects. On balance however, it seems advisable to include sire by flock-year interaction effects in the across flock evaluation.

Data from four hundred and seventy-eight mixed sex Angus weaners of known pedigree were used to examine the relationship between two measures of temperament, visual crush score and electronically measured flight time. Weaners were measured in four Angus seedstock herds in NSW. At each property animals were assessed for both crush score and flight time on two separate occasions (on average 73 days apart) with temperament being measured twice on each occasion. A significant relationship bet ween crush score and flight time existed both within and across measurement time. The results showed significant differences in both flight time and crush score between herds, but the repeatability of the traits was high, ranging from 58 to 65% within a measurement time and 31 and 44% across measurement times. Both traits were lowly heritable but all estimates had large standard errors. The study has shown both traits could be used as measures of temperament in Angus cattle and may able to be changed by selection.

Significant genetic change has occurred in many domestic livestock species and is evident in most Australian beef breeds across a range of economically important traits and selection indexes. Large variation in rates of gain is apparent across breeds, and even larger differences between herds within breeds. Reasons for these differences are examined and results show the selection differential of sires was the key factor explaining the across herd differences in genetic progress for all breeds. Validating genetic trends is important to ensure change is reported accurately. Evidence is presented that show the estimated genetic trends are real and key assumptions used in genetic evaluations are examined, in particular the accuracy of the assumed genetic parameters. The paper identifies opportunities which exist to increase rates of gain across the beef industry, including improvements to the genetic evaluation system, increased levels of performance recording, clearer breeding objectives, and adoption of new technologies.

This paper reports two of the short and longer term outcomes of dystocia for the cow. Calving interval (a measure of cow fertility) may be increased by up to 42 days following a difficult calving. Cow survival may also be reduced, though farmers rarely identify a difficult calving as a cause of a culling or death of a cow more than a month after calving. We investigated the varying culling rates for cows following differing degrees of calving difficulty, particularly cows culled soon after calving, or later than 21 days after calving. Any degree of calving difficulty reduces cow survival and fertility, depending on the severity of dystocia.

Meat quality measures, including objective measures of tenderness (shear force and compression), were taken on 2 muscles ['M. longissimus thoracis et lumborum' (LTL) and 'M. semitendinosus' (ST)] from 7566 from temperate (TEMP) and tropically adapted (TROP) beef cattle breeds. Animals were finished to 1 of 3 market carcass weight end-points (220, 280, or 340 kg) either on pasture or in a feedlot, and in 2 different geographic regions for TROP. Both the phenotypic and genetic expression of the traits were estimated at each market weight and for each finishing regime. Heritabilities and correlations between the traits were estimated for TEMP and TROP separately. Smaller additive variances and heritabilities were observed for temperate breeds compared with tropically adapted breeds for most of the traits studied. For TROP, the heritability of traits measured on the ST muscle [compression (ST_C), shear force (ST_SF), and L* Minolta lightness value (ST_L*)] was 0.27, 0.42, and 0.16, respectively, and for traits measured on the LTL muscle [compression (LTL_C), shear force (LTL_SF), L* Minolta lightness value (LTL_L*), a* Minolta redness value (LTL_a*), cooking loss% (LTL_CL%), and consumer assessed tenderness score (LTL_TEND)] 0.19, 0.30, 0.18, 0.13, 0.20, and 0.31, respectively. For TEMP, the heritability of traits measured on the ST muscle [ST_C, ST_SF, ST_L*, a* Minolta redness value (ST_a*), cooking loss % (ST_CL%)] was 0.12, 0.11, 0.17, 0.13, and 0.15, respectively, and of traits measured on the LTL muscle (LTL_C, LTL_SF, LTL_L, and LTL_TEND) were 0.08, 0.09, 0.17 and 0.18 respectively. Genetic correlations were moderate to high for tenderness measures (shear force and compression) between muscles for the same tenderness measure (e.g. LTL_SF and ST_SF was 0.46 for TROP) and within a muscle for the different measures (e.g. LTL_SF and LTL_L* for TROP was -0.40). The genetic relationship between LTL_SF and LTL_TEND was -0.79 and -0.49 for TROP and TEMP, respectively. Finishing system affected the phenotypic expression of all traits. Pasture-finished, compared with feedlot-finished, animals had higher shear force and compression measures, darker meat colour, and lower sensory tenderness scores for both TEMP and TROP. For TROP, heifers had higher shear force and compression measures, lower sensory tenderness scores, and darker meat colour (lower L* values) than steers. Genetic correlations between markets were genera;;y high and close to unity with the exception of the ST_L*, LTL_L*, ST_C, and ST_SF for TEMP. Geographic region had little effect on the phenotypic and genetic expression of meat quality traits for TROP. Genetic correlations between finishing regimes for all traits were positive and close to unity, with the exception of ST_C and LTL_SF for TEMP, and LTL_L* and LTL_CL% for TROP. Genetic improvement of meat quality traits is a possibility for tropically adapted breeds given the moderate heritabilities, adequate phenotypic variance, generally favourable genetic correlations between traits, and little evidence of genotype by environment interactions.

Improved female reproductive performance (FRP) of beef breeds in northern Australia is an important means to increase profitability. However selection to improve FRP has proved difficult due to low heritabilities and late expression of traits. One trait that may influence maiden calving performance is age at puberty. Several studies have shown age at puberty is heritable in beef cattle, particularly in 'Bos taurus' breeds (e.g. Gregory et al. 1995), but limited studies (and numbers) exist for 'Bos indicus' genotypes. Vargas et al. (1998) reported, from a small study, a heritability for age at puberty in Brahmans of 0.42. However the relationship between age at puberty and subsequent measures of female fertility are inconclusive. Some studies show a favourable relationship between improved pregnancies and earlier age at puberty (Morris et al. 2000). However several others (e.g. Dow et al. 1982) have observed no relationship. The aim of this study was to estimate the heritability of FRP traits and the genetic correlation with age at puberty in 2 tropically adapted genotypes raised in northern Australian environments.

The CRC for Cattle and Beef Quality was established in 1993 to identify the genetic and non-genetic factors affecting beef quality and other production traits of economic importance. Providing feed for cattle is the single largest input cost in beef production enterprises. Advances in computing and electronics has allowed the development of reliable automatic feed intake recorders making it easier to measure feed intake, and this in association with increased producer demand for a means of selecting on the basis of efficiency, has led to increased research in feed efficiency. Understanding genetic variation in feed efficiency and providing the tools for genetic improvement in the efficiency of feed utilization can have a major impact on profitability. Progress of research within the CRC, and internationally, for beef cattle feed efficiency has been regularly reviewed and published (Archer et al. 1999; Herd et al. 2003a; Arthur et al. 2004; Arthur and Herd 2005, 2006). This paper summarises the CRC's major contributions to new knowledge and applications for genetic improvement of growth and feed efficiency.

The theory relating genetic difference between the sexes, genotype x sex interaction and thegenetic correlation between the sexes is described by Eisen and Legates (1966), wheregenotype x sex is considered a special case of genotype x environment interaction. It followsfrom this that a genetic correlation of less than one between the sexes is evidence both ofgenotype x sex interaction and of genetic difference between the sexes. By extension, this alsoholds for similar traits in different environments. Here, we present genetic correlations forcorresponding measures of steer and heifer growth and live body composition for two tropicalgenotypes that are important to beef production in tropical and sub-tropical Australia. The dataare from a project described by Burrow et al. (2003). The correlations provide insight into thepossible magnitude of genotype x environment and genotype x sex interactions whenenvironments differ markedly for the sexes. As in industry, steers were run in a more benignenvironment and finished in a feedlot, while heifers were run in typically harsher, tropicalenvironments.

Costs associated with feeding represent one of the major inputs for beef cattle producers.Arthur et al. (2001) and Robinson and Oddy (2004) demonstrated that net feed intake (NFI: defined as feed eaten, less what is expected based on the animal’s growth rate and body weight) was heritable (h 2 = 0.18 to 0.51). Robinson and Oddy (2004) estimated geneticcorrelations of daily feed intake (FI) and NFI with body composition traits and reported that animals with lower NFI produced leaner carcases. Given the high costs of FI measurement, there is interest in indirect means of predicting genetic merit for NFI. Moore et al. (2005) reported a moderate positive correlation (r g = 0.54) between NFI and blood plasma levels of IGF-I (IGF-I) measured post-weaning in Angus seedstock cattle. Johnston et al. (2002) found a genetic correlation of 0.56 between IGF-I concentration and NFI in feedlot tested cattle. These experiments examined NFI in predominantly Bos taurus breeds. As part of a larger study described by Burrow et al. (2003), genetic parameters for FI and NFI were estimated for two genotypes of tropically adapted cattle. This paper presents the initial findings of this research, including the genetic relationships of FI and NFI with steer production traits and IGF-I measurements, taken from weaning to feedlot exit.