We hypothesised that taxonomical and phytochemical diversity of plants species and their spatial arrangement across the paddock (i.e., functionality of plant diversity; Garret, 2022), would alter metabolomic and lipidomic profiles of beef and the post-prandial metabolomic profiles of human consumers. Our results suggest that metabolomic profiles of beef and human consumers are indeed altered by the type of sward that cattle were grazing. While changes in the metabolomic profile of human plasma was more subtle due to the limited detection of metabolites [(in house metabolite library of AgResearch (Lincoln, New Zealand)], approximately 30% of the metabolites detected were affected in their relative abundances based on raw P-values, and several unknown compounds differed by treatment-sward. These effects have never been reported, making this study the first of its kind, supporting the original hypothesis of Gregorini et al. (2017) that states “We are what we eat eats!”.
Metabolomic profiles of the three treatments-swards differed and this affected cattle metabolism. Enrichment ratios suggest that pathways associated with linoleic fatty acid metabolism and eicosapentaenoic acid were upregulated in cattle grazing AMS compared with PRG or CMS, indicating increased presence of polyunsaturated fatty acids in the AMS swards. Eicosapentaenoic acid is an omega-3 fatty acid usually found in fatty fish such as salmon but also in pasture-raised land animals and has several health benefits including antidepressant activities and prevention of coronary heart disease thrombosis – blood clots, and arterial plaque formation (Russell & Bürgin-Maunder, 2012). Eicosapentarnoic acid is a long-chain fatty acid (FA), that is synthesised from alpha linolenic acid (ALA), the main omega-3 FA in plants, by the enzyme delta-15-desaturase. Alpha-linolenic acid is also an essential omega-3 FA with pleiotropic actions that have anti-inflammatory, anti-depressant, neuroprotective and cardio-protective outcomes (Blondeau et al., 2015). While ALA is reported to reduce circulating LDL-C, (Blondeau et al., 2015) point out that many of the positive responses have been reported from chronic ALA supplementation, which is supported by others who have reported subtle changes to plasma, EPA and omega-3 FA after 4 weeks consumption of either grain- or pasture-finished beef, or 6 months consumption of eggs and chicken meat enriched with algae-sourced omega PUFA (McAfee et al., 2011; Stanton et al., 2020). Therefore, the short-term nature and potentially low dosage of the current study may not have captured this response as responses to omega FA in human consumers.
The AMS also increased the relative abundance of pantothenic acid (PA; vitamin B5) in beef. Vitamin B5 is an essential nutrient involved in the synthesis of coenzyme A – needed for FA synthesis and degradation. Supplementation of PA reduced cholesterol levels by 17% after 4 weeks in people suffering from dyslipidaemia (high LDL, TGL, and total cholesterol) (Chen et al., 2015). The long-term supplementation of PA is inversely correlated to CRP levels and has been suggested to reduce low-grade inflammation associated with early stages of heart disease (Chen et al., 2015). In addition, 3-hydroxybenzaldehyde (3HBA) also increased in beef produced with the AMS. Benzaldehydes are commonly found in nature and 3HBA has a OH group at the meta position of the phenol ring and it is a potent intracellular antioxidant (Bortolomeazzi et al., 2007; K.-Y. Chen et al., 2021). Research in mice has identified that 3HBA is vaso-protective by preventing angiogenesis, and adenosine diphosphate - a platelet agonist – thrombosis formation (Kong et al., 2016), in addition to antimutagenic (Gustafson, 2000), cytotoxic (Tseng et al., 2001), and antibacterial functions(Chen et al., 2021) and can even influence flavour (Bortolomeazzi et al., 2007). Vitamin B5 and 3HBA have vaso-protective, anti-inflammatory and ‘heart-healthy’ roles were upregulated by the AMS beef, which could have human health benefits compared with traditional -status quo- PRG beef, highlighting the need for longer-term human health studies.
Our results suggest that human metabolism following a single meal of beef produced from different treatment-swards is altered. Gamma tocopherol (vitamin E) was elevated in the AMS sward, and this increased the circulating concentrations of gamma-tocopherol in people following the consumption of AMS beef. Gamma tocopherol is the second most common form of vitamin E, a lipophilic molecule (second to α-tocopherol) but as 1 of 8 isomers, it is the most effective anti-inflammatory, due to its ability to inhibit cyclooxygenase and 5-lipoxygenase activity, and antioxidant through capture of lipophilic electrophiles (Jiang et al., 2001). The content of gamma tocopherol was observed to be numerically greater in relative abundance of the chicory plant compared with all other plants or plant mixes. eported gamma tocopherols are present in Chicorium spinosum (spiny chicory), which belongs to the same family Ateraceae as the C. intybus used in the current study. Research of γ-tocopherol has also indicated that it is superior to α-tocopherol in its ability to reduce cancer cell growth, trapping of reactive N-species through formation of 5-nitro-γ-tocopherol (Jiang et al., 2022).
The human results also presented five different (P-values < 0.1) features between treatments. These were 3-hydroxymethylglutarate (HMG), indoxyl sulphate, arginine, oxoadipate, and D-sedoheptulose, with their FDR locating them as ‘hypothetically possible’. Compared with people eating PRG and CMS beef, AMS participants had greater relative abundance of HMG, arginine and oxoadipate, while indoxyl sulphate and D-sedoheptulose declined (Fig. 6). Therefore, we conjecture that these differences can add to the positive effects of AMS to humans. Indoxyl sulphate, is produced from the breakdown of tryptophan by colon microbes – and may reflect exogenous intake of phenols and indoles (Evenepoel et al., 2009; Schepers et al., 2010). In patients with chronic kidney disease, it is considered a uremic toxin, but as it is also reported to vary considerably between individuals and increases with the consumption of meat when compared to a vegetarian diet (Patel et al., 2012). Accumulation of indoxyl sulphate is also associated with additional side effects in the kidneys, bones, and cardiovascular system (Evenepoel et al., 2009; Schepers et al., 2010). Arginine is an amino acid required help build muscle and rebuild tissue. The body also convert this amino acid into the chemical nitric oxide, which is a vasodilator (Preli et al., 2002). These results not only need further investigation, but also highlight the need for longer-term human health studies.
Metabolomic profiling offers an insight into changes in biochemical pathways and small metabolites fundamental to basic metabolism. While changes in the relative abundance of metabolites indicate that some pathways may be upregulated or downregulated in response to the inclusion of functionally diverse AMS swards, further analysis in other laboratories with broad metabolomic and lipidomic libraries are needed to identify, quantify and compare our current results. The untargeted LCMS/MS analyses revealed 267 metabolites in human plasma differed by treatment, while we were unable to identify these lipids, they still prove our hypothesis that sward composition influences consumer metabolism. There is a need to continue developing diverse pasture systems based on metabolomic profiling of livestock which consume such feeds and the human consumer.
Beef finishing and performance
Several interactions between treatment and date were identified across plant and animal measurements. While cattle were allocated similar amounts of herbage and estimated DMI was similar across treatment, DMI of the CMS cattle was numerically less than PRG or AMS and this most likely explains the lower LW and LWG achieved from this treatment. Furthermore, CMS herbage contained lower quantities of CP, greater content of NDF, ADF and DMD tended to be the less than AMS or PRG, which likely explain the reduced performance of CMS cattle. Plasma concentrations of NEFA declined 29% compared with AMS or PRG. The plasma concentrations of NEFA reflect fatty acids produced in the liver from adipose reserves within the animal. Therefore, the lower concentration of NEFA in the CMS treatment may reflect lower caloric intake and rumen digesta outflow, reducing nutrient supply to the host animals and thereby average LWG.
Treatment by time interactions for livestock performance (LW and LWG) were observed across all treatments reflecting seasonal variation of plant growth and chemical components such as CP and ME content. The AMS diet contained less CP and was generally lower in WSC and DMD compared with PRG counterparts and reduced the nutritional value of the diet during late summer compared with PRG and CMS. However, the chemical composition and growth of the AMS sward was favourable for liveweight growth and performance during late Spring and early Summer (November-January), which maintained average LWG and LW of the cattle grazing this sward when averaged across the experimental period. Further evaluation of the seasonal variation of growth and chemical composition of diverse diets requires further evaluation at the farm system-level to understand performance outcomes and profitability at greater scale.
Carcass characteristics and beef quality were assessed using Silver Fern Farms Eating Quality System. Meat colour increased in cattle that grazed the AMS swards, compared with those grazing PRG or CMS. Meat colour of the chilled rib eye muscle area was scored against a set of colour reference standards with scores increasing relative to the darkness of the meat colour. Meat colour reflects myoglobin levels and ultimate pH as postmortem glycolysis decreases muscle pH, resulting in a brighter colour of meat that is preferred by consumers. If the ultimate meat pH is high, the meat proteins will associate with more water in the muscle and therefore fibres will be tightly packed resulting in meat which is ‘tough’. However, the ultimate pH in AMS cattle was similar to PRG or CMS cattle. In addition, the numerical difference between the treatments was minor (0.2–0.3) and did not alter the overall grade of the carcass, thus this difference may not be meaningful in terms of marketability, but nonetheless requires further study.
The results of this study indicate that animal performance can be enhanced using AMS when used strategically throughout the finishing period. Further development of the plant species and their level of inclusion in the sward along with consideration of their seasonality relative to animal finishing and requirements are needed to further evaluate and develop a more consistent response in both performance and metabolomic profiles. It is also worth noting that the limited number of animals used in this study is likely also a factor in the response and studies with a greater number of animals and replication across mobs (as opposed to the individual animal used currently) will provide a better indication of the animal response.