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Histology and genetic control of intramuscular fat deposition and desaturation

Valenzuela, Jose L. (2020) Histology and genetic control of intramuscular fat deposition and desaturation. PhD thesis, Murdoch University.

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There is an increasing world demand for food production. Contemporaneously the market seeks assurance in terms of provenance, quality, and healthiness. While consumers demand tasty, highly and fine marbled meat, its healthiness has become extremely important.

An important component of the organoleptic characteristics and level of healthiness is the quantity of intramuscular fat of the meat and its fatty acid composition. Higher intramuscular fat content, measured as marbling, results in better tenderness, juiciness and flavour, and is often healthier due to a higher content of UFA and MUFA, i.e. oleic acid. The intramuscular fat quantity, measured as marbling, is part of the quality grading and pricing of the carcase.

This thesis examines the deposition of intramuscular fat, contributing to the understanding, and consequently the improvement, of marbling and fat desaturation. The different areas examined are (a) genetics of marbling and fat desaturation, (b) nature of marbling and possibilities of measuring in live animals and (c) similarities between marbling and muscular dystrophy in human, and opportunities for translation of scientific findings between the two species.

One of the simplest ways of assessing the level of desaturation of the fat is measuring its melting temperature (Tm). Fats with higher proportions of unsaturated fatty acids melt at lower temperatures. Current techniques are practical and repeatable and can be done in conjunction with some DNA tests. Here I validate the measurement of Tm of fat obtained in the process of DNA extraction. Using this method, we proved the effects of the breed on the Tm for Red Wagyu (Akaushi) and Black Wagyu, as well as individual differences among Black Wagyu bulls.

I evaluated the effect of breed-specific haplotypes in Bota19 over Tm, establishing the importance of these haplotypes in the inheritance of the trait. I show synteny between the region that contains these haplotypes in cattle and an important region in Hosa 17 involved in some muscular dystrophies. Additionally, these ancestral haplotypes also proved to be practical and successful in the confirmation of the post mortem identity.

The lack of knowledge and deep understanding of intramuscular fat deposition is a big limitation. The inability to reliably measure the trait in live animals limits its measurement and analysis to the carcass stage, and even then, the traditional measurements of marbling are still not objective, reliable and repeatable.

I analysed and described marbling at a microscopic level, designing a microscopic scoring system for marbling. We defined areas suitable for fat and muscle biopsies and measured their Tm and marbling. Later, I compared and validated the results against the muscle commonly used for marble score (Longissimus dorsi), showing similarities on histology, marble score and Tm of the surrounding fat. This gives the opportunity for the development of a test to monitor marbling and fat desaturation throughout the animal’s life.

Following the previously established genetic relation between marbling and muscular dystrophy, a histological comparison of the two processes was made, revealing common features. Due to the histological commonalities between marbling and human muscular dystrophy, and the relation between the areas of the genome involved in fat and muscle metabolism in both species, I proposed the translation of scientific findings from one species to the other. For example, I observed fat acting as an invasive tissue, which could also be a factor in muscular dystrophy.

An example of a practical way of performing farm trials was presented, as an alternative to achieve statistical significance with small sample size and minimal interference in production systems, allowing beef farmers to team up with scientists to generate practical knowledge, and to minimise the number of animals needed for research with live animals.

This thesis provides new information that could lead to the development of practical techniques to establish more effective and efficient production systems, favouring grass-feeding and shorter feeding times, with the consequent improvement on animal welfare and reduction of the environmental impact.

Item Type: Thesis (PhD)
Murdoch Affiliation(s): College of Science, Health, Engineering and Education
Supervisor(s): Lloyd, Sally, Dawkins, Roger, Harper, Richard and Dell, Bernard
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