14 February 2011

5 minute read

The beef industry is competing in a global food market, and to continue to thrive it needs to produce beef efficiently and become more customer-focused. Increased globalisation, reduced commodity prices and increasingly sophisticated, health-conscious consumers are motivating the beef-chain to produce beef and beef products that are more diverse, traceable, nutritious and of consistent quality. This approach could help to maintain or increase beef consumption, stimulate product differentiation and add-value across the food chain. Increased health consciousness among consumers is driving a growing preference for healthier, more nutritious and more functional food products. In beef, considerable attention is focused on quality of the fat in beef.

Previous studies have suggested that there are opportunities for increasing the content of fats such as the omega-3 (n-3) poly unsaturated fatty acids (PUFA), because they are known to be beneficial to human health. Important n-3 fatty acids include alpha linolenic acid (C18:3n-3), eicosapentaenoic acid (EPA), docosapentaenoic acid (DPA) and docosahexaenoic acid (DHA).

Our research has demonstrated that producing animals off grass, which is high in the n-3 fatty acid, linolenic acid, increases the content of n-3 fatty acids in the meat relative to producing beef from intensive concentrate systems (Figure 1).

This is an important point for grass fed beef and helps to make beef an even more attractive product to consumers.

Grass feeding not only enhances the content of beneficial n-3 PUFA in the meat but it also delivers other useful components such as the antioxidants, vitamin E, carotenoids and the derivatives of pigments such as chlorophyll which help to improve colour, shelf life and sensory attributes of the meat. These positive aspects of grass feeding offer considerable scope to help create product differentiation in increasingly competitive markets. Maximising delivery of n-3 PUFA in grass through to meat (and hence to man) is central to this project.

The overall objective of the project is to investigate key factors infl uencing the delivery of benefi cial lipids (fats) from plants (forage) through to beef muscle.

Activities are focused on:

1. examining the degree of variation in both total lipid and individual fatty acids in perennial ryegrass with a view to establishing the potential to breed grasses for a higher content of n-3 PUFA and hence the opportunity to deliver more n-3 PUFA into the animal and ultimately to man;



2. beef production studies examining the effect of “lifetime” nutritional feeding strategies and in particular length of time on “grass” and the inclusion of plant oils in the diet of beef cattle on the fatty acid composition of beef, colour, shelf-life and sensory attributes of the meat.

The studies examining the fat composition of different grasses involve a total population of 190 genetically different plants. We have measured the fatty acid composition of 96 plants in two cuts (June and September 2008). In both cuts genotype significantly influenced total lipid, amount C18:3n-3 and proportion of C18:3n-3 in the total lipid. Importantly, the data suggest that the genotypes behaved similarly across cuts. In cut 1 and 2, total lipid ranged between 15.9-31.5 and 15.5-35.0 mg/g freeze dry matter, respectively. In cut 1 and 2, C18:3n-3 ranged between 10.4-22.1 and 9.8-24.2 mg/g freeze dry matter, respectively. In cut 1 and 2, the proportion of C18:3n-3 in total lipid ranged between 0.56-0.71 and 0.52-0.67, respectively. Genetic markers for fatty acids are currently being determined. Heritability for proportion of C18:n-3 was high ≈ 0.71. These results are encouraging and provide evidence of significant genetic variation in fatty acid content in this population.

We have also investigated the effect of feeding n-3 rich plant extracts on further enhancing the n-3 fatty acid content of beef. The study used a plant extract developed from the liquid fraction extracted from fresh lucerne (Medicago sativa L.), and then heat-treated and dried (referred to as PX). The lipid in the PX has a high degree of rumen protection. The study compared feeding steers PX on top of grass silage relative to feeding straw and concentrate. Effects of additional vitamin E within the concentrate were also investigated. The study used forty Belgian-Blue × Holstein steers (≈ 400 kg liveweight) which had been only been fed on forage (grazing and/or grass silage). The animals were then fed on one of five diets:

1. grass silage ad libitum (GS),
2. grass silage ad libitum plus 75 g PX/dry matter intake (DMI;GS-LPX),
3. grass silage ad libitum plus 150 g PX/DMI (GS-HPX),
4. barley straw and control concentrate (40:60 on a DM basis; S-CC), and
5. barley straw and concentrate with PX (25 per cent in concentrate on a DM basis) (40:60 on a DM basis; S-PXC) and additional vitamin E (≈ 300 mg/kg).

Diets were fed to achieve similar liveweight gain across all treatments, averaging ≈ 1.1 kg/day. Total fatty acids were not different averaging ≈ 2500 mg/100 g muscle which is equivalent to 2.5 per cent fat in the muscle (Table 1).

Feeding grass silage relative to concentrate (compare GS and S-CC) resulted in a doubling of the amount of 18:3n-3 in muscle and higher amounts of benefi cial EPA and DHA. Incremental PX on grass silage resulted in additional deposition of C18:3n-3 and longer chain derivatives EPA and DHA. All the diets resulted in good levels of vitamin E in the muscle (greater than 3 mg/kg muscle). Small differences in TBARS (which is a measure of the stability of the fat in the meat) were noted, indicating that treatments had little negative effect on oxidative stability of the fat.

These results confi rm the positive effects of feeding grass based diets and also show that feeding the n-3 rich plant extract, PX, results in further increases C18:3n-3 and increased the longer chain derivatives EPA and DHA. Within the concentrate treatments PX also increased C18:3n-3 and EPA. This provides a potential feeding strategy to further increase n-3 fatty acids in beef. A second feeding study has recently commenced.

This project underpins the importance of grass feeding in delivering beef with benefi cial levels of n-3 PUFA and is developing strategies to further enhance these fatty acids in beef.