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Grasslands cover around 25% of the global ice-free land surface, they are used predominantly for forage and livestock production and are considered to contribute significantly to soil carbon (C) sequestration. Recent investigations into using 'nature-based solutions' to limit warming to2 °C suggest up to 25% of GHG mitigation might be achieved through changes to grassland management. In this study we evaluate pasture management interventions at the Rothamsted Research North Wyke Farm Platform, under commercial farming conditions, over two years and consider their impacts on net CO

The objective was to assess the impact of replacing a permanent pasture with a reseeded pasture on system productivity and product quality in the first year of establishment under commercial conditions management. Dairy cows were allocated to treatment based on pasture availability at the start of the season following standard commercial practices. Seventy autumn-calved cows grazed a high sugar grass pasture (14.1 ha reseeded in September 2015) and 55 grazed a permanent pasture (12.1 ha) from April to June 2016. Pastures snip samples were taken to assess nutritional composition every two weeks. Milk production and composition was measured on 4th May and 10th June. A slightly higher content of water soluble carbohydrate was observed in May on the reseeded sward (27.1 vs. 25.8%) coinciding with a higher milk yield (24.6 vs. 22.9 L d-1 per cow), lactose content (4.41 vs. 4.34%), and a lower somatic cell account (59,400 vs. 113,300 cell mL-1), compared to the permanent pasture. Pasture varied in nutritional value across the study. In June, no differences in milk production or composition were observed. However, the reseeded sward was estimated to produce 12.3% more milk per ha than the permanent pasture during the experimental period (113.8 vs. 101.3 L ha-1 d-1), driven by the greater carrying capacity of the sward (5 vs. 4.5 LU ha-1). This farm case study shows the potential of a reseeded pasture to outperform permanent pasture even in the first year of establishment at a farm system scale.

Forage type and management influences the nutritional quality and fatty acid composition of ruminant milk. Replacing grass silage with red clover (RC; L.) silage increases milk fat 18:3-3 concentration. Red clover has a higher polyphenol oxidase (PPO) activity compared with grasses, which has been suggested to decrease lipolysis and . The present study characterized the abundance and fatty acid composition of esterified lipid and NEFA before and after ensiling of grass and RC to investigate the influence of forage species, growth stage, and extent of fermentation on lipolysis. A randomized block design with a 2 × 3 × 4 factorial arrangement of treatments was used. Treatments comprised RC or a mixture of timothy ( L.) and meadow fescue ( Huds.) harvested at 3 growth stages and treated with 4 levels of formic acid (0, 2, 4, and 6 L/t). Lipid in silages treated with 0 or 6 L/t formic acid were extracted and separated into 4 fractions by TLC. Total PPO activity in fresh herbage and the content of soluble bound phenols in all silages were determined. Concentrations of 18:3-3 and total fatty acids (TFA) were higher (0.001) for RC than for grass. For both forage species, 18:3-3 and TFA content decreased linearly (0.001) with advancing growth stage, with the highest abundance at the vegetative stage. Most of lipid in fresh RC and grass herbage (97%) was esterified, whereas NEFA accounted for 71% of TFA in both silages. Ensiling resulted in marginal increases in TFA content and the amounts of individual fatty acids compared with fresh herbages. Herbage total PPO activity was higher (0.001) for RC than grass (11 vs. 0.11 μkatal/g leaf fresh weight). Net lipolysis during ensiling was extensive for both forage species (660 to 759 g/kg fatty acid for grass and 563 to 737 g/kg fatty acid for RC). Formic acid application (0 vs. 6 L/t) resulted in a marked decrease ( = 0.026) in net lipolysis during the ensiling of RC, whereas the opposite was true ( = 0.026) for grass. In conclusion, results suggest that formic acid addition during the ensilage of RC decreases lipolysis . For both plant species, total PPO activity was not associated with the extent of lipolysis . However, bound phenols formed via PPO activity appear to have a role in protecting lipid and protein against degradation in grass and lowering proteolysis of RC during ensiling.

Polyphenol oxidase (PPO) activity in red clover (Trifolium pratense) has been reported to reduce both proteolysis and lipolysis, resulting in greater N use efficiency and protection of PUFA across the rumen. Although high levels of PPO have been reported in grasses such as cocksfoot (orchard grass; Dactylis glomerata), no in vivo research has determined whether grass PPO elicits the same response as red clover PPO. To test the hypothesis that silage ensiled from grass with high levels of PPO protects N and PUFA across the rumen, 6 steers with ruminal and duodenal cannulas were offered cocksfoot silage (CO; high-PPO grass), perennial ryegrass silage (PR; Lolium perenne; low-PPO grass), or red clover silage (RC; high-PPO control) at 16 g DM/kg BW daily with the experiment consisting of two 3 × 3 Latin squares with 21-d periods, consisting of 12 d of diet adaptation, 6 d of duodenal marker infusion, 2 d of duodenal sampling, and 1 d of ruminal sampling. All silages were well preserved, with DM of 34.4, 55.3, and 45.4% for CO, PR, and RC. Activity of PPO in silages was low due to deactivation but was greater in CO than either PR or RC (0.15 vs. 0.05 and 0.08 μkatal/g DM). Protein-bound phenol (mg/g DM) as a measure of the degree of oxidation and an indication of PPO protection was greatest for RC (15.9) but comparable for PR (10.1) and CO (12.2). Biohydrogenation of C18 PUFA was significantly lower on RC compared to the 2 grass silages with CO greater than PR. Despite lower levels of total fatty acid intake and subsequent duodenal flow, CO resulted in greater levels of phytanic acid and total branched and odd chain fatty acids in duodenal digesta than RC or PR. Ruminal ammonia concentration was greatest for RC, with no difference between the grasses. Duodenal flow of microbial N and efficiency of microbial protein synthesis were lowest for CO and comparable for RC and PR. The CO (high-grass PPO) did not result in elevated levels of C18 PUFA escaping the rumen or improve efficiency of total N transfer through the rumen compared to PR. The RC resulted in a greater flow of N and nonmicrobial N to the duodenum than the 2 grasses with PR greater than CO.

Because of the potential benefits to human health, there is interest in increasing 18:3n-3, 20:5n-3, 22:6n-6, and cis-9,trans-11 CLA in ruminant foods. Four Aberdeen Angus steers (406 ± 8.2 kg of BW) fitted with ruminal and duodenal cannulas were used in a 4 × 4 Latin square experiment with 21-d periods to examine the potential of fish oil (FO) and linseed oil (LO) in the diet to increase ruminal outflow of trans-11 18:1 and total n-3 PUFA in growing cattle. Treatments consisted of a control diet (60:40; forage:concentrate ratio, on a DM basis, respectively) based on maize silage, or the same basal ration containing 30 g/kg of DM of FO, LO, or a mixture (1:1, wt/wt) of FO and LO (LFO). Diets were offered as total mixed rations and fed at a rate of 85 g of DM/(kg of BW(0.75)/d). Oils had no effect (P = 0.52) on DMI. Linseed oil had no effect (P0.05) on ruminal pH or VFA concentrations, whereas FO shifted rumen fermentation toward propionate at the expense of acetate. Compared with the control, LO increased (P0.05) 18:0, cis 18:1 (Δ9, 12-15), trans 18:1 (Δ4-9, 11-16), trans 18:2, geometric isomers of 9,11, 11,13, and 13,15 CLA, trans-8,cis-10 CLA, trans-10,trans-12 CLA, trans-12,trans-14 CLA, and 18:3n-3 flow at the duodenum. Inclusion of FO in the diet resulted in greater (P0.05) flows of cis-9 16:1, trans 16:1 (Δ6-13), cis 18:1 (Δ9, 11, and 13), trans 18:1 (Δ6-15), trans 18:2, 20:5n-3, 22:5n-3, and 22:6n-3, and decreased (P0.001) 18:0 at the duodenum relative to the control. For most fatty acids at the duodenum, responses to LFO were intermediate of FO and LO. However, LFO resulted in greater (P = 0.04) flows of total trans 18:1 than LO and increased (P0.01) trans-6 16:1 and trans-12 18:1 at the duodenum compared with FO or LO. Biohydrogenation of cis-9 18:1 and 18:2n-6 in the rumen was independent of treatment, but both FO and LO increased (P0.001) the extent of 18:3n-3 biohydrogenation compared with the control. Ruminal 18:3n-3 biohydrogenation was greater (P0.001) for LO and LFO than FO, whereas biohydrogenation of 20:5n-3 and 22:6n-3 in the rumen was marginally less (P = 0.05) for LFO than FO. In conclusion, LO and FO at 30 g/kg of DM altered the biohydrogenation of unsaturated fatty acids in the rumen, causing an increase in the flow of specific intermediates at the duodenum, but the potential of these oils fed alone or as a mixture to increase n-3 PUFA at the duodenum in cattle appears limited.

Diet composition can be estimated in free-ranging animals by the use of n-alkane and long-chain fatty alcohol concentrations in feces. However, this technique involves relatively laborious and costly analytical techniques. Two spectroscopy techniques were investigated as a way of determining whether dietary differences are likely, thus indicating whether the more expensive and labor-intensive techniques for more detailed analysis are justified. Fourier-transform infrared spectroscopy (FTIR) and front-face fluorescence emission spectroscopy (lambda(excitation) = 380 nm, lambda(emission) = 600 to 760 nm) were used to analyze fecal samples collected from 2 different breeds of cattle and sheep (4 groups in total, n = 6 per group) grazing moorland plants in 2 grazing sessions. These fecal samples were also analyzed for alkane and alcohol concentrations. Fourier-transform infrared spectra, particularly in the alkane regions, demonstrated clear separation between animal species. Fluorescence emission spectra showed similar separation; fluorophores were most likely chlorophylls and their derivatives. Multivariate analysis of all 3 data sets showed similar variation within and between groups of cattle and sheep, indicating differences in diet selection particularly between species, but also between breed and grazing session. Both spectroscopy methods showed utility in suggesting differences in diet composition that would be worth investigating using more detailed chemical analyses. Of the 2 techniques, the FTIR spectroscopy gave the better comparative results, being able to detect differences in sampling months that were detected with alkanes and alcohols that the fluorescence emission spectroscopy did not detect.

Two experiments were carried out to determine the effects of feeding grass silages differing in their water-soluble carbohydrate content, with or without red clover silage, on the efficiency of nutrient use. High-sugar grass, control grass, and red clover were ensiled in laboratory silos for use in an in vitro experiment (Exp. 1). For an in vivo experiment (Exp. 2), the same forage types were baled and ensiled. All silages were well preserved; within experiments the grass silages had similar composition, except for greater (P0.05) water-soluble carbohydrate concentrations in the high-sugar than the control grass silage. In Exp. 1, high-sugar grass, control grass, and red clover silages were fed alone or as mixtures (30:70, 50:50, or 70:30 on a DM basis, respectively) of each grass with the red clover silage to a simulated rumen culture system. There were no significant differences in microbial N flow or efficiency of microbial protein synthesis between individual forages. However, the corresponding values for the 70:30 ratio of high-sugar grass:red clover silage were greater (P0.05) than for the red clover silage. The value for the efficiency of N use (g of microbial N/g of feed N) was greater (0.86; P0.05) for high-sugar grass silage than the control grass silage. In addition, the high-sugar grass:red clover silage mixtures all gave greater (P0.05) values for the efficiency of N use than red clover silage alone; this difference was not achieved with the control grass mixture. Experiment 2 was an incomplete Latin square design conducted with 6 Here-ford x Friesian steers (163 +/- 5.9 kg of BW) with rumen and duodenal cannulas fed the following 5 silage diets: high-sugar grass silage; control grass silage; high-sugar grass and red clover silage (50:50 DM basis); control grass and red clover silage (50:50 DM basis); and red clover silage. Rumen NH3-N concentration was lowest (P0.05) with the high-sugar grass silage. Microbial N flows to the duodenum and efficiency of microbial protein synthesis were greater (P0.05) for steers fed the high-sugar grass silage than for control grass and red clover silages, and mixing red clover with grass silages increased (P0.05) these values compared with red clover silage alone. In both experiments, the efficiency of incorporation of silage N into microbial N was more than 20% greater (P0.05) for high-sugar grass than for control grass silage. These data suggest that grass silage with high-sugar content provides a forage-based strategy for balancing N and energy supply and improving the efficiency of use of grass silage N in the rumen.

The experiment investigated the digestion of lipids from different forage silages in beef steers. Six Hereford x Friesian steers prepared with rumen and duodenal cannulas were given ad libitum access to a high-sugar grass silage, control grass silage, red clover silage, or mixtures of the red clover and each of the grass silages (50:50, DM basis). The experiment was conducted as an incomplete 5 x 5 Latin square, with an additional randomly repeated sequence. Total fatty acid and C18:3n-3 concentrations were greater (P0.05) for the high-sugar grass silage than the control grass silage or the red clover silage. Dry matter and total fatty acid intake were less (P0.05) for steers fed the control grass silage than for steers fed the other diets. Duodenal flow of C18:3n-3 was greater (P0.05), and flows of C18:0 and total C18:1 trans were less (P0.05), for the red clover silage compared with the 2 grass silage diets, with the mixtures intermediate. These results were supported by a reduction (P0.05) in biohydrogenation of C18:3n-3 for the red clover silage, with the mixtures again being intermediate. Flows of total branched- and odd-chain fatty acids were greater (P0.05) for the high-sugar grass silage diet, possibly as a result of greater microbial flow, because these fatty acids are associated with bacterial lipid. Duodenal flows of the chlorophyll metabolite, phytanic acid, were greater (P0.05) for animals fed the high-sugar grass silage treatments compared with the other treatments. These results confirm the potential for modifying the fatty acid composition of ruminant products by feeding red clover silage.

Lee, M.R.F., Scott, M.B., Evans, P., Richardson, R.I., Kim, E.J., Veberg Dahl, A., Lundby, F., Scollan, N.D. (2010). The potential of a plant extract to provide fluorescent chlorophyll derivatives to act as markers of faecal contamination on carcasses. Advances in Animal Biosciences. Proceedings of the British Society of Animal Science Annual Conference, 'Food, Feed, Energy and Fibre from Land - A Vision for 2020', Queen's University, Belfast, Northern Ireland, 12-14 April 2010, p132.

Belanche, A., Lee, M.R.F., Moorby, J.M., Scott, M., Newbold, C. J. (2010). Effect of forage species, ryegrass water soluble carbohydrate concentration, and red clover polyphenol oxidase activity on in vitro rumen efficiency of nitrogen utilization. Advances in Animal Biosciences. Proceedings of the British Society of Animal Science Annual Conference, 'Food, Feed, Energy and Fibre from Land - A Vision for 2020', Queen's University, Belfast, Northern Ireland, 12-14 April 2010, p203.

Conjugated linoleic acid (CLA) has been associated with numerous health benefits in animal models including modulation of immune response and fat deposition (Lock & Bauman, 2004). The most predominant CLA in ruminant products (meat and milk) is cis-9 trans-11 with traces of other isomers such as trans-10 cis-12 which can be increased according to dietary regimes such as increasing the proportion of concentrate in the diet (Sackmann et al. 2003). More recent findings into the health benefits of CLA in humans have found the trans-10 cis-12 isomer to be more potent than cis-9 trans-11 (Tholstrup et al. 2008). Whilst it has been reported that acidic methylation during analysis of milk fat results in isomerisation of cis-9 trans-11 (Lee & Tweed, 2008) little information is available on the effect of different methylation regimes on the increasingly important trans-10 cis-12 isomer. This study investigated the isomerisation of esterified and un-esterified trans-10 cis-12 CLA during three methylation regimes.

Dietary conjugated linoleic acids (CLA) offer significant health benefits for man, and ruminant products are the major dietary sources (Bauman et al., 2001). The synthesis of CLA in the ruminant animal occurs either directly in the rumen or in the tissue from trans -vaccenic acid (TVA), formed primarily as intermediate products of ruminal biohydrogenation of linoleic acid (C18:2) to stearic acid (C18:0). Within the rumen, the pattern of biohydrogenation and the products formed appear to differ between the particle rich and the liquid fractions of the rumen (Singh and Hawke, 1979), with biohydrogenation occurring primarily on small particles. The aim of this study was to investigate whether the pattern of CLA and TVA formation differs in these fractions.

Forages are a rich source of beneficialn-3PUFAs (?-linolenic acid; C18:3n-3) and may be a useful means of modifying the fatty acid composition of ruminant products. Altering the fatty acid composition of ruminant products is difficult due to the biohydrogenation action of rumen micro-organisms, which hydrogenate the PUFAs into monounsaturated and saturated fatty acids. Little information is available on biohydrogenation of PUFAs in forages hence this study investigated this in steers fed on perennial ryegrass, red or white clover silages or combinations thereof.