The high nutritional value of legumes also impacts on other aspects of production including ewe lactation and lamb survival. Ewes were found to produce 25% more milk when grazing on legumes compared to grass, which consequently improved lamb weaning weights (Kenyon and others 2010 ; Hutton and others 2011 ) and is associated with improved triplet survival (Keithly and others 2011 ). Interestingly, lamb survivability is related to PUFA content as thermogenesis, which uses brown adipose tissue (BAT) as an energy source, is mainly fueled by linoleic acid. Grazing ewes on forages high in linoleic acid, throughout the latter stage of gestation and during early lactation, could influence the amount of BATs present in their lambs. This is thought to improve lamb survivability, because the transfer of linoleic acid from the ewe to its lamb via the placenta or milk could be used as an energy source within BATs. This could enable lambs to withstand harsher environmental conditions during the early stages of life due to the use of BATs during thermogenesis (Keithly and others 2011 ).

Lambs grazing on legumes typically grow faster than grass‐fed lambs, partially due to a more rapid rate of digestion, which allows for higher feed intakes (Fraser and Rowarth 1996 ; Fraser and others 2004 ; Speijers and others 2004 ). As legumes have a higher ratio of crude protein (CP) to water‐soluble carbohydrates (WSC), dietary protein utilization is more efficient than for lambs grazing on grass (Fraser and others 2004 ; Merry and others 2006 ). Furthermore, some forage species contain condensed tannins (CTs), which reduce protein degradation in the rumen, resulting in enhanced nitrogen utilization as more dietary proteins are absorbed in the intestinal tract of the host animal. Additionally, forages containing CTs have a direct anthelmin effect that has reduced worm burdens in lambs grazing on plantain and chicory (Woodfield and Easton 2004 ).

When evaluating alternative methods to improve the nutritive value of meat, it is crucial that production characteristics such as growth and carcass yield are not compromised. Under ordinary grass‐based systems, animals often grow slower than those fed concentrates (O'Sullivan and others 2003 ; Webb and O'Neill 2008 ; Winichayakul and others 2008 ). However, this can be improved by strategically using plant varieties that more appropriately meet seasonal nutrition requirements (Brown 1990 ). The use of high‐value forages such as Brassica rapa (turnip), Brassica napus (rape), Cichorium intybus (chicory), red clover, Trifolium repens (white clover), Lotus corniculatus (birdsfoot trefoil), Onobrychis viciifolia (sainfoin), Hedysarum coronarium (sulla), Plantago lanceolata (plantain), and alfalfa can achieve high postweaning live‐weight gains in lambs, often in excess of 250 g/d throughout summer and autumn (Fraser and others 2004 ; Golding and others 2011 ). Furthermore, legumes are of increasing interest for sustainable farming in terms of nitrogen utilization (Humphreys 2005 ; Høgh‐Jensen and others 2006 ) and are particularly relevant for areas subject to leaching (Høgh‐Jensen and others 2006 ).

Feeding and finishing systems influence growth characteristics, carcass quality, and meat quality, including fatty acid composition. In some regions the accessibility and cost of feeding supplements is uneconomical (Cosgrove and others 2004 ; Kenyon and Webby 2007 ), but can be compensated for by the ability to grow high‐quality forages (Kenyon and Webby 2007 ). Climate and topography tend to dictate plant selection, which may range from high‐performing species on fertile developed land, or alternatively consist of native species that thrive on steep undeveloped hill country (Ådnøy and others 2005 ; Lind and others 2009 ).

In the meat industry, production varies globally and is reliant on factors that influence the cost and efficiency of rearing an animal from birth to slaughter. With contrasting diets across continents and even within countries, it is vital that we understand the effects of management practices on the nutritional value, consistency and palatability of meats, and the environmental sustainability of production (McCartney and others 2008 ).

CLA production has also been reported to rise with grass‐finishing (Table 3 ), but this is not routinely measured and findings have been inconsistent (Knight and others 2003 ). Since CLA isomers differ in structure and function, these findings may not be directly comparable, and could depend on the isomer found.

Health recommendations suggest that PUFA:SFA ratios should be at least 0.4, which is a challenge to achieve in ruminants, even with forage‐based diets. Some studies have achieved a more desirable PUFA:SFA ratio by increasing PUFAs levels, which consequently decreased SFAs as a proportion of TFAs (Mir and others 2002 ; Aurousseau and others 2004 ; Noci and others 2007 ). In contrast, other studies have reported minimal changes to the PUFA:SFA ratio when PUFAs were elevated, because SFA levels remained unchanged (Santos‐Silva and others 2002 ; Realini and others 2004b ).

Dietary source can influence the fatty acid profiles of animals more significantly than genotype (Bas and Morand‐Fehr 2000 ; Garcia and others 2008 ). In general, the more concentrate in the diet, the more SFAs that will be present in meat. This is especially evident during the later stages of growth when animals deposit more adipose tissue (Arsenos and others 2006 ). Pasture finishing produces higher quantities of n ‐3 fatty acids than concentrate‐fed animals, which improves both the PUFA:SFA and n ‐6: n ‐3 ratios (Wood and Enser 1997 ; Gatellier and others 2005 ; Rochfort and others 2008 ). For example, Kasapidou and others ( 2012 ) found an n ‐6: n ‐3 ratio of 8.9 in the meat of concentrate‐fed animals, compared to a more desirable 0.9 for grass silage‐fed animals (Table 2 ).

To achieve the recommended daily adult intake in New Zealand and Australia, red meat needs to contain 30 mg of EPA and DHA per 100 g cooked serving (or 135 g raw) (Ponnampalam and others 2014b ). A trial conducted at Massey Univ., determined that grass‐fed beef supplies approximately 2% of this, or 4% to 5% at maximum EPA and DHA levels. If 100% conversion of DPA is assumed, this increases to 7% to 11%. Knight and others ( 2003 ) suggested typical genetic selection and management practices would not improve the quantity of n ‐3 fatty acids that significantly contribute to the daily requirement (greater than 20%). Yet, a number of trials conducted in Australia, suggest this can be achieved when animals are grazed on high‐quality pastures (Ponnampalam and others 2006 ).

Species and cultivar variances in fatty acid content

Although many studies have explored the influence of grass and clover on the PUFA contents of meat, alternative finishing species such as herbs and legumes (except clover) have been studied to a lesser extent. As herbages can be a cheap and sustainable source of fatty acids, there may be an opportunity to breed plants that have increased levels of desirable fatty acids. However, when doing this, it is important to note that the PUFA content is significantly reduced in muscle and adipose tissues, due to biohydrogenation in the rumen. However, intermediates of the biohydrogenation process also have useful properties for improving human health (Dhiman and others 2005; Dewhurst and others 2009).

Lipids make up 8% of leaf dry matter and 22% to 25% of chloroplasts on a dry matter basis. Most leaf tissues are composed of complex lipids such as phospholipids and glycolipids. Esterified lipids contribute two‐thirds of total lipids and represent 5% of leaf dry matter. The esterified lipids in forages are approximately one‐third simple lipids, half galactolipids, and the remaining portion is phospholipids (Boufaïed and others 2003). The building block of n‐3 PUFAs, linolenic acid, is synthesized by de novo plants (Dewhurst and others 2003c) and contributes 55% to 66% of the TFA content of grasses (Elgersma and others 2003a). The combination of palmitic, linoleic, and α‐linolenic acids contributes 75% to 93% of TFAs (Meľuchová and others 2008). Although these remain the predominant fatty acids in most forage plants, their concentrations vary between species. Dewhurst and others (2001) noted minor compositional differences between the fatty acids found in grasses such as Festuca arundinacea (fescue). However, in other plant species, such as chicory which has high TFA contents, the fatty acid compositions were highly variable. Boufaïed and others (2003) also found individual fatty acids varied greatly between cultivars, with some variation attributed to differences in maturity date.

Although forages are naturally high in linolenic acid, biohydrogenation means this is not necessarily reflected in muscle tissue. In addition, differences in fatty acid concentrations are more obvious in phospholipids than in TAGs, when comparing grass‐ and concentrate‐fed lambs (Bas and Morand‐Fehr 2000; Aurousseau and others 2004; Sinclair 2007). Aurousseau and others (2004) found lambs grazing on pasture had up to 3 times more linolenic acid than those fed concentrate, which was evident in the neutral lipids and even more so in the phospholipids. Relationships between fatty acid content in pastures and the rate of biohydrogenation are still being determined, so it is unknown whether improvements in the lipid compositions of plants would be replicated in muscle tissue.

Recent studies have investigated the influences of grazing animals on botanically diverse pastures on the fatty acid composition of meat (Sinclair 2007). “Botanically diverse” typically refers to mixed pastures of native origin and can include a range of grass, legume, and herb species. Differences in composition are especially apparent when animals graze on diverse pastures in mountainous areas, compared with those grazed in monoculture lowlands (Ådnøy and others 2005). Lourenço and others (2007a) found botanically diverse pastures accumulated more biohydrogenation intermediates in the rumen and an elevated PUFA content in the IMF. This suggests rumen biohydrogenation was partially inhibited and PUFAs were further desaturated and elongated. This could also have been due to the lower IMF levels that were found in the botanically diverse treatment group (Lourenço and others 2007a).

Compared to composite grass swards, mixed leguminous pastures produce significantly higher proportions of linoleic and α‐linolenic acids in the abomasum and subcutaneous fats, but not in the rumen (Lourenço and others 2007a, b). This suggests that there may be greater duodenal flow of PUFAs, which agrees with other findings suggesting that reduced lipolysis occurs (Lourenço and others 2008). Lourenço and others (2008) found higher PUFA contents in IMF of lambs grazed on pastures that contained high quantities of white clover and alfalfa, compared to those on perennial ryegrass. Similarly, Ponnampalam and others (2012a) indicated that alfalfa has the potential to improve the linolenic acid and vitamin E contents in the muscles of lambs, compared to lambs fed senescent ryegrass pasture, or concentrate supplements during the finishing period. However, Dierking and others (2010) found no significant differences when steers grazed on leguminous species were compared to those grazed on tall fescue, tall fescue + red clover, or tall fescue + alfalfa. These conflicting findings were thought to occur due to a short feeding duration and lower percentage of clover in the sward (Dierking and others 2010).

There is considerable interest in red clover due to its ability to forgo rumen biohydrogenation, which increases the proportion of PUFAs in animal tissues (Dewhurst and others 2003a, 2003b; Lee and others 2003a, 2003b; Lourenço and others 2007b; Dierking and others 2010; Faria and others 2012). High consumption of red clover tends to inhibit lipolysis as a result of elevated activity of the enzyme polyphenol oxidase (PPO) in the rumen (Lee and others 2007b, 2009; Lourenço and others 2008). PPO converts phenols into quinones, which reduces proteolysis by binding to proteins (Faria and others 2012) and prevents lipolysis by forming complexes with polar lipids (Lee and others 2004).

Biohydrogenation may also be influenced by the presence of tannins or other secondary compounds and has led some researchers to investigate the influence of CTs on fatty acid profiles (Ponnampalam and others 2012a). Although CTs are present in a number of plant species, research has mainly focused on the supplementation of tannins in concentrate diets. High dietary concentrations of CTs reduce the activity of ruminal bacteria, which limits biohydrogenation (Vasta and others 2007, 2008, 2009a; Patra and Saxena 2011). Furthermore, in vitro studies have established high CTs levels can cause a reduction in Butyrivibrio proteoclasticus, a bacterium commonly found in the gastrointestinal systems of animals, which are known to convert vaccenic acid to stearic acid in the final step of biohydrogenation (Vasta and others 2010). However, if replicated in vivo, animal performance would be limited at such high CT levels, thus further work is required to measure the effects of CTs at levels below 4.5% dry matter (Vasta and others 2010). Studies have also evaluated the impact of CTs on CLA production, but this is difficult to measure because CLA can be synthesized endogenously in muscle via Δ‐9 desaturase (Vasta and others 2007, 2009b), the levels of which vary across muscle types (Poulson and others 2004).

Pastures such as red clover or others that contain CTs are of considerable interest for pasture‐based finishing, as significant compositional differences can be created in meat and milk, by selecting specific plant species for animals to graze. However, further studies are required to evaluate the effectiveness of this approach in the field as many of the studies to date have been carried out in vitro, or with ensiled forage, and therefore little is known about the variability within a species, especially under different grazing conditions. It is also possible that there are other plant species that could have unique characteristics with the potential to influence biohydrogenation and the uptake of PUFAs.

When assessing the impacts of animal diet on fatty acid composition, time on the diet is also an important factor to consider. Studies suggest that the composition of fatty acids in lamb muscle will continue to change until about 42 d after the change in diet and not change markedly thereafter (Griswold and others 2003; Aurousseau and others 2007a, b; Bessa and others 2008). With short feeding durations, the fatty acid profile of lamb still resembles that resulting from the pretreatment diet (Scerra and others 2011). While short feeding durations would be advantageous for some lamb finishing systems in terms of the costs associated with feeding, a sufficiently long duration is required for tissue deposition to occur and hence significant changes in muscle and adipose tissue fatty acid composition.