Estimating body composition using CT scans of cross-bred lambs fed at 2 feeding levels and 2 stages of maturity to inform predictive growth models.

Livestock producers would benefit from more precise predictions of the growth response from nutrients consumed. Previously published models are often limited by the realities of data collection and are unable to account for alterations to body composition, due in part to the response of visceral organs to an alternate diet. The computerized tomography (CT) scanning of lambs enables the analysis of changes in body composition of individual animals over time, potentially supporting better model development and testing. The aim of this experiment was to develop a repeatable method for the analysis of live lamb body composition using CT scans. A secondary aim was to compare the data collected from CT scanning during a feeding trial to 2 predictive lamb growth models. Cross-bred lambs were fed 2 feeding levels at 2 stages of maturity, with CT scans at the beginning and end of each 8-wk feeding period. The CT scan-derived values for body composition taken at the beginning of feeding periods were used as inputs for 2 existing lamb growth models. Predictions of body composition were compared with CT scan-derived values at the end of feeding periods. The CT scan analysis method used a proportion of images from each lamb to reduce manual image editing. The method was developed by comparing the estimated mass and volume of empty body components using all available CT scans to estimated values using a reduced number of scans from 12 lambs. The CT scan-derived lean tissue mass aligned with model predictions at the end of each feeding period, however, CT scan-derived fat mass was greater than predictions by both models especially for the high feeding level at the later stage of maturity. These results highlight that the analysis of body composition using CT scans requires further validation, particularly for the viscera, and that models likely require refinement to better predict the efficiency of energy utilization by different tissues. The use of live animal CT scans can provide more accurate predictions of the growth of saleable products than measuring liveweight alone and will enable ruminant growth models to better adapt to different genetics and changing diets than comparative slaughter. To replicate the current data using comparative slaughter would require 4 times the animals, as individual lambs were CT scanned 4 times in this study, demonstrating the potential value of CT scanning in live animal research.

Predictive growth models are unable to properly account for the effects of changes to body composition on the energetic efficiency of lamb growth and improving these models has been limited by the realities of data collection. By tracking changes in individual animal body composition, it is likely that better predictions of the effects of genetics, nutrition, and management on lamb growth can be made. The computerized tomography (CT) scanning of lambs enables the analysis of changes in body composition over time, potentially supporting better model development and testing. A repeatable method for analyzing lamb CT scans was developed and results were compared with 2 existing lamb growth models. Lean tissue mass derived from CT scans aligned with model predictions but fat mass estimated using CT scans was greater than model predictions, particularly for lambs fed at later stages of maturity. Further verification is needed by combining CT scanning and comparative slaughter, especially with respect to the weight of internal organs and the stomach and intestinal contents to better inform predictive growth models.

Level of feeding and stage of maturity affects diet digestibility and protein and fat deposition in cross-bred lambs.

Metabolizable energy intake is the key determining factor for the expression of an animal's genetic potential for growth, and current predictive growth models are not capable of accounting for all the nutritional variation that is commonly observed. The current study was designed to investigate energy transactions as lambs grow using CT scanning to assess body compositional changes at two levels of intake and two stages of maturity, and compare results to predictive equations. A pelleted diet was provided to cross-bred lambs (n = 108) at approximately 2.5 and 3.5% of liveweight (LW) in dry matter when the lambs were approximately four (31.8 ±â€…0.3 kg LW) and eight (40.5 ±â€…0.3 kg LW) months of age. A digestibility trial was run sequentially using 10 lambs of the same genetic and nutritional history fed at the same feeding levels to determine the digestibility of the diet. In the first feeding period, metabolizable energy intake was 15.3 ±â€…0.03 and 9.5 ±â€…0.03 MJ ME/d for high and low feeding levels respectively, resulting in higher rates of empty body gain for high feeding level lambs (197.7 ±â€…7.8 vs. 72.8 ±â€…8.2 g/d; P < 0.001). In the second feeding period, metabolizable energy intake was 15.2 ±â€…0.01 and 12.0 ±â€…0.01 MJ ME/d for high and low feeding levels respectively, resulting in higher rates of empty body gain for high feeding level lambs (176.3 ±â€…5.4 vs. 73.9 ±â€…5.3; P < 0.001). Lambs at later stages of maturity retained proportionately more energy as fat for every unit of retained energy compared to younger lambs (95.4 ±â€…0.40 vs. 90.0 ±â€…0.42%; P < 0.001). Lambs fed the lower feeding level in period two also retained proportionately more energy as fat for every unit of retained energy than lambs at the higher feeding level (97.1 ±â€…0.36 vs. 94.0 ±â€…0.37%; P < 0.001) which is hypothesized to be because of the rapid response of visceral lean tissue to changes in nutrition. There were no significant interactions between treatments in the first and second feeding periods, indicating an absence of a compensatory gain response to a nutritional restriction in the first feeding period. This experiment highlights the significance of a changing feed supply and the subsequent effects on body composition and the partitioning of energy to lean and fat tissue deposition. For improvements in the accuracy of predictive ruminant growth models it is necessary to gain a greater understanding of the different tissue responses over time to changes in nutrition.

Understanding animal responses to changes in nutrition will assist to create more efficient red meat production systems. Complex interactions exist due to the quality, physical characteristics and level of feeding of the diet, and the nutritional history of the animal. The resultant changes to body composition and the partitioning of energy to tissues has important implications for producers. A replicated trial used CT scans of live animals to investigate body compositional changes at different stages of animal maturity and different feeding levels. Given that fat deposition has been shown to increase at greater energy intake, it was expected that the contribution of fat to empty body gain would be smaller at lower feeding levels; however, lambs at later stages of maturity and lower levels of intake deposited greater amounts of fat as a proportion of empty body gain. Results are likely confounded by the response of visceral lean tissue mass to changes in nutrient supply. Irrespective of this, nutritional history had no effect on the rate or composition of gain at different levels of feeding, potentially demonstrating an inexistence of compensatory growth. A greater understanding of lean tissue responses to dietary changes is necessary for the increased precision of predictive growth models.

A Cross-Sectional Study of Commercial Ewe Management Practices for Different Sheep Breeds across Southern Australia.

The management of ewes across southern Australia may vary with breed and can change over time and, as such, a greater understanding of producer management practices and the motivations that influence these practices is required. A cross-sectional study was performed by telephone interview with sheep producers managing Composite, Maternal, Merino or shedding ewe breeds mated in either spring, summer, or autumn. The surveyed producers were a unique subset of southern Australian producers. A large proportion of the surveyed producers followed current best practice guidelines for ewe mating and lambing nutritional management; however, some producers did not align with these targets. Further, some producers did not see the value in attaining the current recommendations. Pregnancy scanning was widely practiced, likely an artefact of the recruitment process; however, a few producers did not utilize this information for nutritional management at lambing time. Finally, most producers were active in their search for new information, seeking information regularly from a wide range of sources and reported making management changes within the last five years. Further work is required to understand why some producers are not adopting best practice where possible and to understand current barriers for adoption. Management guidelines for all sheep breeds are required to best manage sheep across southern Australia.

Mating Conditions and Management Practices Influence Pregnancy Scanning Outcomes Differently between Ewe Breeds.

Sheep production in southern Australia may vary by breed, time of year, production output (wool, meat, or both), region and seasonal influence. Sheep producers with flocks of approximately 300-500 ewes (n = 58) were recruited across southern Australia to take part in a survey and mating variables were collected from over 30,000 ewes between October 2020 and August 2021. A Bayesian Network (BN) was developed to identify the interrelatedness and most influential variable on pregnancy and fetal number (of pregnant ewes) outcomes under different scenarios. The BN analysis indicated a low association between the variables explored, however, were breed dependent. In wool-based breeds a mating liveweight of 60-69.5 kg predicted the lowest non-pregnant and greatest number of fetuses, and in shedding ewes 70-79.5 kg predicted the lowest non-pregnant rate and 90-99.5 kg the greatest number of fetuses. Pregnancy rate and fetuses per ewe were optimized at ram percentages of 1.5% for Composite and Merino ewes and 2% for Maternal ewes. A mating BCS 4 resulted in greatest pregnancy rate and number of fetuses across all breeds. Curvilinear relationships between mating liveweight, BCS and ram percentage were observed with pregnancy rate and fetal number. Practically, reproductive potential is best managed on a breed basis and with consideration of all variables explored.

The quality and mineral composition of the longissimus lumborum and semimembranosus muscles from lambs fed perennial or annual wheat forage with or without lucerne.

This study compared the effect of a novel perennial wheat forage and a conventional annual wheat forage, fed to lambs with or without lucerne, on the quality and mineral profile of the longissimus lumborum and semimembranosus muscles. This involved 48 Poll Dorset × Merino ewe lambs, 12 per treatment, managed for 28 days within individual pens. Consumer sensory panel scores showed 'good eating quality' for all samples irrespective of diet, a conclusion supported by the shear force, cooking loss, particle size, and intramuscular fat results. Drip loss was affected by a significant interaction between diet and muscle. The ultimate pH of meat from lambs fed annual wheat was highest. Comparable colour stability and purge results suggested that diet did not impact on lamb retail-potential. Sodium, sulphur and zinc concentrations were higher in the meat from lambs fed annual wheat, compared to perennial wheat. Overall, these outcomes support the use of perennial wheat as a forage for lamb production.

The effect of forage-types on the fatty acid profile, lipid and protein oxidation, and retail colour stability of muscles from White Dorper lambs.

The aim of this study was to evaluate the effect of different forage-types on lamb meat quality parameters. White Dorper lambs that had grazed five forage-types, were slaughtered commercially. At 24h post-mortem, the m. longissimus lumborum (LL) was removed from one side, sliced into three equal sub-samples, vacuum packaged and assigned to ageing periods (5, 12 or 40days); the other side of LL was aged for 5days. The m. adductor femoris was used for fatty acid analysis. Lambs fed chicory+arrowleaf clover had the highest concentration of health claimable omega-3 fatty acids and the lowest omega-6:omega-3 fatty acid ratio. Forage-types with higher vitamin E content showed lower lipid oxidation levels independent of ageing period. Forage-type and ageing period did not influence the redness, yellowness, chroma or reflectance ratio (630nm÷580nm) of displayed meat. Chicory+arrowleaf clover gave the best results to improve the fatty acid content of lamb meat.

The effect of forage type on lamb carcass traits, meat quality and sensory traits.

The aim of this study was to evaluate the effect of different forage-types on lamb carcass, meat quality and sensory attributes. Sixty-two, White Dorper lambs finished on bladder clover, brassica, chicory+arrowleaf clover, lucerne+phalaris or lucerne, were slaughtered at a commercial abattoir. At 24h post-mortem, the m. longissimus thoracis et lumborum (LL) was removed from the left side and sliced into three equal sub-samples, vacuum packaged and randomly assigned to ageing periods (5, 12 or 40days) and the right side was aged for 5days. The m. semimembranosus and m. adductor femoris were removed and, the former was then aged for 40days. Lambs fed chicory+arrowleaf clover or lucerne had a higher dressing percentage and fat depth. Bladder clover gave the highest level of glycogen in the LL. No sensory or other meat quality trait differences were found between the treatments. In general, no treatments showed any unfavourable effect on the traits examined.