Duff, Christian J

Clark, Samuel

van der Werf, Julius H

2025-03-07

<pGlobally, particularly in middle and high income countries, intramuscular fat (IMF) and marbling are major determinants of beef quality. Consumers in these markets are also becoming more discerning about the nutrition they obtain from the red meat in their diets, particularly related to the amount and type of fats (e.g saturated, monounsaturated and polyunsaturated), and the links to health outcomes like heart health. ></p> <p>The aim of this thesis was to contribute to the understanding and genetic improvement of meat quality attributes of beef, focusing on intramuscular fat and marbling characteristics. To further extend our knowledge, the proportions of individual fatty acids in the intramuscular fat of beef were specifically examined. </p> <p>In Chapter 3, we compared two technologies used to analyse ultrasound images to predict carcass traits in the live animal, the Pie Medical Esaote Aquila (PIE) and Central Ultrasound Processing (CUP). Each technology was specifically evaluated for their ability to predict carcass traits, including IMF and marbling, for genetic evaluation in Australian Angus cattle. The results indicating that the CUP system, compared to PIE, provides an advantage for genetic evaluation of carcass traits in Angus cattle, particularly for the IMF and associated marbling traits. CUP predicted IMF was more heritable and tended to have stronger correlations with the breeding objective traits of carcass IMF marbling traits, both genetically and phenotypically, compared to PIE. </p> <p>In Chapter 4, accuracy of selection and response to selection for the breeding objective traits of carcase IMF, AUS-MEAT marbling score and Meat Standards Australia (MSA) marbling score were generated by modelling seventeen different phenotyping and genotyping scenarios using selection index theory. The study showed, for Australian Angus breeders, the highest rates of selection accuracy and response (ΔG) will be achieved through using a combination of CUP phenotyping for IMF and genotyping with a reference population of related animals with carcase IMF and marbling score phenotypes. However, the value of ultrasound scan phenotyping diminishes as the Genomic Breeding Value (GBV) prediction accuracy increases, which is mainly a function of the reference population size. </p> <p>In Chapter 5, we examined modifying the definition of Residual Feed Intake (RFI), by including an adjustment for IMF. The secondary aim was to further understand the genetic relationships between feed intake and a range of carcase traits, including IMF and marbling. This study revealed RFI can be redefined to account for traits, other than average daily gain (ADG) and metabolic mid-weight (MMWT), like IMF. However, due to limitations of phenotypic linear regression, and only small amounts of variation in feed intake being explained by the IMF traits, the redefinition of RFI was a suboptimal approach to breeding candidate selection. Furthermore, this study has confirmed the challenges with selecting for both feed efficiency and meat quality traits as they are generally genetically antagonistic. </p> <p>In Chapter 6, we estimated phenotypic and genetic parameters for fatty acid traits of IMF that are prevalent in Australian Angus beef. The conclusion of this study being genetic selection can be applied in Australian Angus breeding programs to modify the fatty acid composition within intramuscular fat. More specifically, Angus cattle breeders can select breeding candidates to change the proportion of fatty acids from saturated (SAT) to healthier unsaturated fatty acids (monounsaturated - MONO and polyunsaturated - PUFA) within the fatty acid profile of beef.</p> <p>In Chapter 7, we continue from the previous chapter by using genomic relationships to estimate phenotypic and genetic correlations between fatty acid traits in IMF and a range of production, eating quality and efficiency traits. The findings show the proportion of fatty acids can be changed from SAT to healthier unsaturated fatty acids (MONO and PUFA) within the intramuscular fat of beef without being detrimental to the common breeding objective traits of liveweight (FW), feed efficiency (RFI), carcase weight (CWT), marbling (CMAU, CMMS, CIMF), or muscling (CEMA). </p> <p>The studies that form this thesis have contributed to the understanding and genetic improvement of meat quality attributes of beef. If the findings from this study are implemented by industry, it can benefit the whole beef supply chain, including the consumer, through genetic selection resulting in beef that has greater eating quality through marbling attributes, and improved health characteristics by modifying the fatty acid profile.</p>

https://hdl.handle.net/1959.11/69197

University of New England

Understanding and Improving Genetics for Meat Quality in Beef Cattle

Thesis Doctoral

Publication