Sire breed, litter size, and environment influence genetic potential for lamb growth when using sire breeding values

Lamb growth can be optimised with genetic selection using sire Australian sheep breeding values, however, breeding value expression has been shown to be reduced with poor nutrition. It was therefore hypothesised that the genetic potential for lamb growth would also be reduced, where production factors such as multiple births limit growth. Live weights at birth, weaning, and post-weaning were collected from more than 18,000 lambs produced over five years and eight locations of the Sheep Cooperative Research Centre Information Nucleus Flock experiment, and the impact of environment, production factors, and genotype was determined using mixed effects regression. The genetic potential for lamb growth was moderated by environment, multiple births, and sire type (p < 0.05). Twin lambs achieved 76% of the expected weight gain at weaning and 58% post-weaning. For triplet lambs weight gains were drastically less at approximately 30% of the expected gain at the same time points. Lambs born to maternal sires consistently had the poorest response to genetic selection, achieving approximately half the expected weight gain. Hence, producers need to temper expectations for growth based on genetic selection, or employ mitigation strategies such as precision feeding, the use of alternate breeds, or place emphasis on the genetic merit of other desirable traits

Selection for leanness decreases meat aerobicity

The Australian lamb industry uses Australian Sheep Breeding Values for reduced postweaning subcutaneous fat depth (PFAT) to select for leanness and increased lean meat yield. Selection for reduced PFAT results in increased loin muscle weight (Gardner et al 2010) potentially leading to lower oxidative capacity in muscle (Greenwood et al 2006). Isocitrate dehydrogenase activity (ICDH) is an accepted indicator of aerobic metabolism, and therefore we hypothesise that selection for reduced PFAT results in a decrease in ICDH levels

Effects of different ageing methods on colour, yield, oxidation and sensory qualities of Australian beef loins consumed in Australia and Japan

This study investigated the effect of three ageing methods (dry, wet and stepwise wet-then-dry) and ageing time on pH, colour, yield, lipid and protein oxidation and eating quality of beef loins using Meat Standards Australia (MSA) sensory protocol with 900 and 540 consumers in Australia and Japan, respectively. Australian beef loins (Longissimus thoracis et lumborum) at four days post mortem were subjected to wet ageing (boneless; for 7, 21, 35 or 56 days), dry ageing (bone-in; for 35 or 56 days) or a wet-then-dry ageing method (bone-in; 21 days wet ageing followed by 35 days dry ageing). The pH was higher in dry aged than wet aged beef loins (P < .001). Instrumental measurement of surface colour of trimmed dry and wet aged steaks showed significant differences in a*, b* and hue angle. Weight loss was higher in dry aged primals (P < .001), however, total water content was similar among the two ageing methods (P = .934). Retail yield did not differ between 35 and 56 days dry aged primals. Lipid (TBARS) and protein (total carbonyl content) oxidation between the dry and wet aged samples differed depending on the ageing time. When comparing the wet-then-dry and 56 days dry aged samples, only pH and retail yield differed. Australian and Japanese consumers rated dry aged steaks significantly higher (P < .001) than the wet aged counterparts for tenderness, juiciness, flavour, overall liking and weighted palatability scores. The wet-then-dry steaks were also rated higher than the 56 days wet aged steaks for flavour, overall liking and palatability within the Japanese sensory panels. The Japanese consumers also consistently rated all MSA sensory attributes lower (P < .001) than the Australian consumers. The results from this study show dry ageing provides a value adding opportunity for the meat industry in both domestic and export markets

Consumer perceptions of meat redness were strongly influenced by storage and display times

Lamb (n = 79) meat colour was scored by 879 untrained consumers using a scale of 0 (brown) to 100 (red). This consumer colour score (CCS) was obtained on m. longissimus lumborum (loin) and m. semimembranosus (topside), stored for short (5–7 days), medium (33–35 days), and long periods (110–112 days) and a retail display time of up to 4 days. Consumers perceived topside to be less red initially and changed from red to brown more rapidly when stored for the long-storage period (p 0.05). CCS and the instrument measure oxy/met (reflectance of light at wavelengths 630 nm and 580 nm) had a low correlation coefficient of 0.33 (p < 0.01). The propensity for lamb growth and leanness indicated by sire breeding values for lamb weight, eye muscle depth, eye muscle fat depth, and loin intramuscular fat had varied and inconsistent effects on CCS. Therefore, even the selection on CCS

Prediction of sheep carcass traits from early-life records using machine learning

Currently hot carcass weight (HCW) and fat score jointly indicate the price grid for sheep meat in Australia. However, experts in the field believe that soon, yield and quality traits such as intramuscular fat (IMF), greville rule fat depth (GRFAT), computed tomography lean meat yield (CTLEAN), and loin weight (LW) are likely to play a role in pricing. Having an accurate prediction of these traits earlier in the life of an animal will allow sheep producers to adjust their management practices in order to achieve the target market requirements. Management, genetics, pasture and climate factors, influence these traits directly and epistatically. Traditional prediction methods may not be powerful enough to capture complex interactions while avoiding overfitting. In this case, learning algorithms that can learn from the current data to predict the animal's future performance offers promise. In this study, five different types of Machine Learning (ML) algorithm, namely Deep Learning (DL), Gradient Boosting Tree (GBT), K-Nearest Neighbour (KNN), Model Tree (MT), and Random Forest (RF) were employed to predict HCW, IMF, GRFAT, LW and CTLEAN and their performances were compared against linear regression (LR) as the gold standard of multinomial prediction. Four scenarios representing different numbers of weight recordings-from a total of 9 weight measures taken between birth (WT1) and pre-slaughter (WT9)- were used to inform the algorithms and all models were trained and tested under equal conditions with identical training and testing sets. Selection of the most effective subset of predictor features were completed via greedy stepwise search among all the available features jointly with expert opinion. In predicting all the traits, RF was superior while LR and KNN showed the lowest prediction performance. When using the final model for predicting on an independent test set, the scenario with the most accurate prediction performance differed across traits. IMF and GRFAT were most accurately predicted when using birth, weaning, and pre-slaughter weights, while the most accurate scenario for HCW, LW and CTLEAN utilised weaning, six monthly weight measures after weaning and pre-slaughter weight. Across all scenarios the least accurate prediction was for IMF

Extreme bilateral polydactyly in a wild‐caught western grey kangaroo

Polydactyly is a congenital malformation resulting from an autosomal dominant mutation manifesting as supernumerary digits of the hands or feet. It is most commonly reported in humans and domestic mammals, though there have also been isolated examples across a range of wild vertebrate species. Here we report a case of extremely unusual bilateral preaxial polydactyly on the pectoral limbs of a male western grey kangaroo (Macropus fuliginosus) from the South West region of Western Australia, in which two supernumerary digits were present on each manus. A supernumerary digit I on each manus was rudimentary in morphology without extrinsic muscular connections. However, supernumerary digit II present on each manus had fully developed extrinsic and intrinsic muscular connections, suggesting that these digits possessed normal function in flexion and extension. An alternative hypothesis is that the two supernumerary digits are both representatives of the most radial digit I, though this would then require the true digit I to have taken on the appearance of digit II by acquiring an additional phalanx and modified muscular attachments. The carpal bones exhibited a number of subtle differences in morphology when compared to normal pentadactyl individuals. The presence of a distal, rather than proximal, epiphysis on the first metacarpal was unexpected but further investigation suggested that this characteristic is perhaps more variable (in this species at least) than has been previously recognized. This case provides an unusual example to be considered within the broader context of limb development

Multiple births limit the advantage of using high growth sires

The Australian lamb industry uses breeding values to select for progeny with increased post-weaning weight at 150 days (PWWT). Accurate weight prediction is essential to provide age estimates for lambs to reach target weights, to underpin breeding values, and for assessing the influence of growth rate on factors such as intramuscular fat and myoglobin concentration of lamb muscle. As growth curves can be biased when predicting weights at the edge of the available weight data, the key aim was to develop a population based random regression model to predict lamb PWWT. This fit was compared to an individual based Brody curve fit with comparable results confirming the rigour of the model. The PWWT results were then used to assess the impact of factors such as lamb birth-type rear-type and sire PWWT breeding value on lamb weight. Multiple births were hypothesised to limit the progeny of high PWWT sires from reaching their full weight due to nutritional restriction pre-weaning. Weight data totalling 164,797 observations was collected from 17,525 lambs across eight sites and five years of the Sheep Cooperative Research Centre Information Nucleus Flock. A Bayesian linear mixed model was fitted to the live weight data with fixed effects for site, year of birth, gender, birth type-rear type, age of dam, sire type, darn breed within sire type, sire PWWT as a covariate and random terms for sire, dam by drop and individual. Lamb PWWT was then analysed in a linear mixed model of similar structure. In line with our hypothesis, the weight of singles, twins and triplets at 150 days increased by 9.43, 6.67 and 3.68 kg across the 23 kg PWWT range (P<0.05) confirming that multiple births limit the full expression of weight potential

Selection for lean meat yield in lambs reduces indicators of oxidative metabolism in the longissimus muscle

Selection for increased lean meat yield using Australian Sheep Breeding Values for reduced post-weaning c-site fat depth (PFAT) and increased post-weaning eye muscle depth (PEMD) reduces the oxidative capacity of muscle. Isocitrate dehydrogenase (ICDH) activity and myoglobin concentration were measured in 3178 and 5580 lambs, respectively, to indicate oxidative capacity. In the progeny of sires with a reduced PFAT, ICDH activity and myoglobin concentration were reduced by 0.46 μmol/min/g tissue and 0.67 mg/g tissue across the 5 and 6 mm PFAT ranges respectively. In the progeny of sires with an increased PEMD, ICDH activity and myoglobin concentration were reduced by 0.50 μmol/min/g tissue and 0.49 mg/g tissue across the 7 and 6 mm PEMD ranges respectively. However, the sites at which the lambs were raised had a larger impact on oxidative capacity than genetic or other production factors

Selection for reduced PFAT decreases isocitrate dehydrogenase activity

The Australian lamb industry uses Australian Sheep Breeding Values to select for reduced subcutaneous fat depth (PFAT) and increased lean meat yield. Selection for reduced PFAT increases oin muscle weight, with muscularity associated with reduced muscle aerobicity. As isocitrate dehydrogenase activity (ICDH) is a good indicator of oxidative metabolism, we hypothesised that selection for reduced PFAT would decrease ICDH. ICDH was measured within the loin muscle of 13971ambs and data was analysed using a linear mixed effects model (SAS) with fixed effects for site, kill group within site, sex, birth type-rear type, age of dam, sire type and dam breed within sire type, and random terms for sire and dam. Within this model, covariates such as PFAT, intramuscular fat percentage (IMF) and weight of short loin fat and muscle were included individually to assess their phenotypic association with ICDH. Aligning with our hypothesis, selection for reduced PFAT decreased ICDH by 0.52 µmol/min/g tissue over the 4 unit PFAT range. However, neither short loin muscle nor fat weight demonstrated strong associations with ICDH. This contrasts with the premise of our initial hypothesis that selection for negative PFAT would decrease ICDH via its impact on whole body muscularity and the associated effect on muscle aerobicity. Alternatively, ICDH was strongly associated with IMF, with a 4% decrease in IMF aligning with a 0.84 µmol/min/g tissue reduction in ICDH. Selection for negative PFAT strongly reduces IMF, and when both covariates were used concurrently within the ICDH model, PFAT was not significant. This may imply that the impact of PFAT on ICDH is delivered via its negative impact on IMF, and appears to be independent of whole body adiposity or muscularity