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Decreasing the share of protein contributed by animal-based foods is recommended to move towards more sustainable and healthier diets. This study aimed to assess the potential environmental impacts of diets with a lower share of animal protein. The diets were modeled to include the minimum share of animal protein in total protein that met nutrient requirements and did not increase costs. The new diets also minimized the difference in the quantity of food from those of observed (OBS) diets. They were modeled for five adult subpopulations (defined by sex and age) using mathematical optimization. The model was created by combining the INCA2 database (to model OBS diets in the French population) and a database of 207 food items to adjust nutritional and price parameters. All modeled diets satisfied nutritional and cost constraints. A low-animal-protein (LAP) diet was identified for each subpopulation by progressively decreasing the share of animal protein by steps of 5% until the recommended quantity of protein and/or consumption constraints were no longer satisfied. Potential environmental impacts of the LAP diets in eight impact categories were calculated using life cycle assessment and life cycle inventories from Agribalyse® 3.0. A LAP diet for the entire population was calculated as a weighted mean of the subpopulations' LAP diets. The share of animal protein decreased from 70% in the OBS diet to 50% in the LAP diet. Compared to the OBS diet, the LAP diet decreased five environmental impacts: climate change (greenhouse gas emissions), acidification (emissions of acidifying compounds) and land occupation (all by more than 30%), cumulative energy demand (by 23%) and marine eutrophication (by 13%). Conversely, it increased three environmental impacts: freshwater eutrophication and water use (both by ca. 40%) and biodiversity damage potential (potential loss of species associated with land use) (by 66%). These results suggest that decreasing the share of animal protein to 50% is compatible with nutritional requirements, affordability and consumption constraints, but would have mixed effects on the environment.

The availability of baseline emission data across various livestock systems is an essential component of identifying suitable mitigation strategies for the future. However, the comparative CH4 emissions of different livestock species, particularly those that represent key small ruminants globally (sheep (Ovis aries) and goats (Capra hircus)), have not been explored in the context of diet digestibility and growth potential of the animal. This study aimed to generate baseline data through comparing weaned lambs and goat kids in relation to (1) growth performance, (2) enteric methane emissions, (3) and diet in vivo digestibility of a common medium-digestibility diet that reflects the pasture type that the animals might be expected to graze. Ten castrated lambs (Welsh Mountain breed) and ten goat kids (Cashmere × Boer crossbreed) of an equivalent age postweaning (c. 12 months) (avg. starting weight of 15 kg ± 0.86, and 26 kg ± 1.02, respectively) were offered a grass-nuts diet ad libitum whilst housed in individual pens. Dry matter intake (DMI) of feed was monitored daily throughout an 8-week growth stage, whilst liveweight was assessed weekly. Enteric CH4 emissions of each animal were recorded for 72 h in methane collection chambers. We found significantly higher liveweight gains for the sheep compared to goats (163 and 84 g/day for lambs and kids respectively; SED = 12.8; P < 0.001), as well as higher DMI (1299.8 vs 881.8 g/day; SED = 64.7; P < 0.001). DM intake was comparable between species on a metabolic liveweight (W0.75) basis. The sheep also produced higher daily CH4 emissions (26.3 g/day, and 19.4 g/day, respectively; SED = 3.02; P < 0.01) than goats. However, no effect of species was observed on CH4 emissions per kg W0.75 or per kg DMI. The proportion of methane energy excreted expressed as a proportion of diet gross energy (Ym) was similar for both species (4.9 and 4.6% CH4 E/gross energy intake for lambs and kids, respectively; SED = 0.46), as were apparent whole-tract in vivo DM digestibility, although the sheep had a better feed conversion ratio (FCR) than the goats (6.6 g DMI/ g W0.75 gain and 11.5 g DMI/g W0.75 gain, respectively; SED = 1.58; P < 0.05). Here, we found that sheep were more efficient than goats when offered an identical diet of grass nuts, giving a higher weight gain than the goats (resulting in a lower FCR), whilst also producing similar CH4 emissions to the goats on a metabolic LW basis.

Reducing dietary CP concentration can reduce feeding costs and N excretion in dairy production but may negatively impact productivity and efficiency. This study investigated the impact of reduced dietary CP concentration, across early, mid- and late-lactation stages in primiparous and multiparous lactating cows, on productivity, feed and energy use efficiency and CH4 emission parameters. Twenty-four Holstein-Friesian (12 primiparous, 12 multiparous) cows were allocated to three experimental total mixed rations containing 12.2, 15.1 or 18.1% CP (LCP, MCP and HCP, respectively; DM basis), in a continuous study across lactation (days 1-305). Digestibility and gas exchanges were measured in metabolism units and indirect open-circuit respiration calorimeter chambers during early, mid- and late-lactation. Data were analysed using a linear mixed model, with repeated measures, with CP concentration, stage of lactation, parity and their interactions as fixed effects, and a random effect of cow fitted as the subject and stage of lactation as the repeated measure. When compared with LCP treatment, MCP and HCP had higher DM intake (DMI) (+1.9 and +3.0 kg/d), milk yield (+5.5 and +7.7 kg/d), energy corrected milk yield (ECMY) (+5.0 and +7.1 kg/d), and feed efficiency (ECMY/DMI, +0.13 and +0.15 kg/kg; milk solids/DMI, +16 and +20 g/kg; milk energy output (EL)/DMI, +0.40 and 0.46 MJ/kg). Digestible energy intake (DEI)/gross energy intake (GEI), metabolisable energy intake (MEI)/GEI, MEI/DEI and milk energy output adjusted for zero energy balance (EL(0))/MEI were higher in HCP (+0.02, +0.03, +0.02, and +0.06 MJ/MJ) than LCP while there were no differences between LCP and MCP for DEI/GEI, or between MCP and HCP for MEI/DEI and EL(0)/MEI. Methane production per digestible DMI and ECMY were lower for MCP (-3.2 and -3.1 g/kg) and HCP (-3.8 and -3.4 g/kg), when compared with LCP. Methane energy per GEI, DEI and MEI were lower for the MCP (-0.007, -0.011 and -0.014 MJ/MJ) and HCP (-0.007, -0.014 and -0.017 MJ/MJ) than LCP. The significant interaction between CP concentration and stage of lactation on milk yield and ECMY showed that treatment differences (increased values in MCP or HCP vs LCP diets) reduced as lactation progressed. A diet containing 15.1% CP (DM basis) may be sufficient to maintain milk production and feed efficiency while reducing CH4 yield and intensity. However, regression analysis suggests that productivity may increase further between 15 and 18% CP (DM basis) but the response to dietary CP may depend on the stage of lactation.

Cow-calf contact (CCC) systems have become increasingly popular calf−rearing systems to promote positive welfare; however, weaning and separation may cause distress. This preliminary study aimed to investigate the interaction between weaning and CCC on the physiological health, performance, and behaviour of dairy cows and calves. Three systems were compared: conventional, pasture-based Irish system (CONV; 18 pairs), cow and calf separated ≤ 2 h postbirth, cows milked twice-a-day, calves artificially reared indoors; full-time access system (FT; 14 pairs), dam and calf allowed constant, pasture-based, unrestricted access and cows milked twice-a-day; and part-time access system (PT; 18 pairs), unrestricted access at night indoors, cows grazed outdoors by day while calves remained indoors, cows milked once-a-day (0800 h). All calves were weaned at 8 weeks of age; FT and PT pairs underwent a 7 d gradual weaning and separation process (PT cows switched to twice-a-day milking) while CONV calves were gradually weaned over 12 d. Clinical health scores (2x/week), blood samples (1x/week; analysed for physiological markers of health and performance), BW (1x/week), body condition score (1x/week; cows only), and behaviour (1 d/week; scan sampling 3x/d; 24 total observations) were taken the week before (preWS) and after (postWS) the weaning and separation process. The PT cows had higher body condition scores (3.18 ± 0.034) than CONV (2.95; FT cows were similar to both, 3.05) and lower non-esterified fatty acids (NEFA; 0.40 ± 0.038 mmol/L) than the FT cows (0.58 mmol/L; CONV cows were similar to both, 0.48 mmol/L) across both time-points. All calves preWS had lower summed clinical health scores (0.91 vs 1.25 ± 0.131; P = 0.017), beta-hydroxybutyrate (0.07 vs 0.39 ± 0.023 mmol/L; P < 0.001), and globulin (12.0 vs 14.5 ± 0.929 g/L; P = 0.010) than postWS. After weaning and separation, the FT (0.36 mmol/L; P < 0.001) and PT (0.34 mmol/L; P = 0.001) calves had higher NEFA than CONV calves (0.13 mmol/L). Calf weekly average daily gain (ADGw) was similar preWS (0.9 ± 0.142 kg/d), but CONV calves had higher ADGw postWS than FT (0.42 kg/d) and PT calves (0.40 kg/d). All calves performed more (P = 0.009) positive behaviours preWS (4.6 ± 6.37%) compared to postWS (2.3 ± 3.38%). Our results suggest the applied CCC slightly worsened cow and calf health, performance, and behaviour around weaning and separation.

Sustainable food systems encompass nutrition, the environment and socioeconomics, each aspect requiring unique assessment and consideration. This is especially important in the dairy industry, since livestock contributes 14.5% of global greenhouse emissions while also contributing 49% to global calcium supply and 12% to global protein supply. This necessitates strict measurement to ensure science-based decision-making while producing sustainably, ensuring adequate nutrient supply. This review aimed to identify and evaluate existing measures of sustainability with the goal to generate recommendations for future sustainability measurements. From a nutritional perspective, it identified existing measures such as nutritional life-cycle analysis, hybrid nutrient-rich food index, nutrient-rich food adjusted for adequate intake and nutrient deficiencies, as well as the priority micronutrient density score, as methods which consider broader nutrient profiles and utilise more recent research, and therefore serve as a basis for future models. Major limitations exist in the incorporation of bioavailability or the food matrix effect in such measures, as well as food-group-specific indices. The Prospective Urban Rural Epidemiology healthy diet score also provides promise in serving as an updated version of current dietary guidelines. Environmentally, the life cycle analysis approach forms a detailed basis for environmental footprint assessment, although the practical application thereof in modern agriculture may be cumbersome and may warrant the use of simpler metrics. However, the complexity of sustainability assessments due to differing production methods and system boundaries makes comparisons difficult, which justifies either standardised or contextualised indices. Lastly, socioeconomics which are often measured only via retail price with a focus on economics also deserves consideration of affordability at consumer and producer level by evaluating the effect of the production system on the local and global economy, producer affordability and the potential to improve livelihoods. In conclusion, a localised and holistic measure of sustainability is warranted which is both sector and context-specific and reported in sufficient detail to prevent the masking of poor results due to single metric expressions.

Feeding ruminants with agro-industrial by-products represents an effective strategy to implement circular economy principles in animal husbandry. Olive tree leaves discarded during olive oil production are a natural source of compounds that may influence ruminant metabolism and product quality. In this study, an in vivo feeding trial evaluated the effect of dietary olive tree leaves on the rumen microbial community, animal performance and milk quality in dairy sheep. Two groups of 10 grazing Comisana ewes were supplemented with 800 g/head/d of a control pelleted concentrate (CTRL) or a concentrate containing 28% of dried olive leaves (LEAVES) for 30 days. After the adaptation period, individual milk was collected weekly and analysed for gross composition, fatty acids and renneting properties. Individual rumen liquor collected on the last day of the trial was analysed for microbial and fatty acid profiles. Moreover, the effect of olive tree leaves inclusion on dietary nutrient degradability of the LEAVES concentrate was tested in vitro. In vitro data indicated that olive leaves did not affect the rumen degradability of NDF and protein compared to CTRL. Regarding the in vivo trial, milk yield was comparable between groups, but LEAVES milk showed a greater protein percentage. Dietary olive leaves marginally affected the rumen microbiota: the Catenisphera genus was more abundant in the rumen of the LEAVES group, and Mogibacterium was found only in rumen of LEAVES ewes. The rumen liquor of LEAVES ewes showed a greater content of c9 18:1 and t6-8 18:1. Fatty acids mainly involved in biohydrogenation were found at a comparable content in the rumen of CTRL and LEAVES groups. Despite this, both dietary polyunsaturated fatty acids (c9c12 18:2 and c9c12c15 18:3) and fatty acids mainly originated from rumen biohydrogenation (trans 18:1 and 18:2 isomers) were found at a greater percentage in the LEAVES milk. Dietary olive leaves increased total monounsaturated fatty acids, polyunsaturated fatty acids, polyunsaturated fatty acids n-3 and polyunsaturated fatty acids n-6 and reduced saturated fatty acids in comparison with the CTRL diet. Among the health-promoting fatty acids, c9 18:1, c9t11 18:2, 22:5 n-6 and 22:6 n-3 were greater in the LEAVES milk. Consequently, LEAVES milk showed a lower atherogenic and thrombogenic index and a smaller hypercholesterolemic potential. Our results confirm the viability of the use of agro-industrial by-products rich in bioactive compounds in animal diets as a strategy to improve the circularity of animal production and product quality without modification to animal performance.

Grazing multispecies swards can have multiple benefits for the productivity and environmental sustainability of ruminant production systems. However, few studies have determined the effect of different sward-type systems on co-grazed cattle and sheep performance. The objective of this study was to determine the effect of different sward type systems: (1) a sown Lolium perenne (PRG) sward (receiving 170 kg of N/ha per year); (2) a pre-existing permanent pasture (PP) (receiving 135 kg N/ha per year); (3) a sown 6 species sward (6SP) with Lolium perenne, Phleum pratense, Trifolium pratense, Trifolium repens, Cichorium intybus and Plantago lanceolata (receiving 70 kg N/ha per year); and 4) a sown 12 species sward (12SP) with Dactylis glomerata, Lotus corniculatus, Onobrychis viciifolia, Achillea millefolium, Petroselinum crispum, Sanguisorba minor in addition to the 6SP listed above (receiving 70 kg N/ha per year); on the animal performance of co-grazed cattle and sheep. In 2020 and 2021, each sward-type system (9 ha) was rotationally co-grazed from April to November by dairy cross heifers (n = 20 per treatment per year, turned out at 395 ± 15 days of age, mean ± SD) and ewes (n = 22 ewes per treatment per year) plus lambs. Heifer live weight was recorded monthly, and heifers were drafted for slaughter when their estimated fat class on the EUROP grid scale reached 3-. Lamb live weight was recorded fortnightly, and lambs were drafted for slaughter at 42 kg (lambing to weaning), 44 kg (weaning to September) and 46 kg (after 1 September) to obtain a target carcass weight of 21 kg. Average daily gain (ADG) from turnout to slaughter was higher for heifers grazing the 6SP sward (1.09 kg/day) compared to all other sward types (12SP (0.99 kg/day), PRG (0.92 kg/day), and PP swards (0.92 kg/day); P < 0.001)). Lamb ADG from birth to slaughter in the 6SP (393 g/day) and 12SP (363 g/day) were greater than the PP (305 g/day; P < 0.001) or PRG swards (292 g/day; P < 0.001). Carcass dressing percentage was higher for lambs grazing the 6SP (48.5%) and 12SP (48.6%) compared to lambs grazing the PRG (44.7%; P < 0.001) and PP swards (44.6%; P < 0.001). Lambs grazing the 6SP and 12SP had a reduced number of grazing days from turnout to slaughter (82 and 93 days respectively) compared to the lambs grazing the PPG and PP swards (133 and 127 days respectively; P < 0.01). Overall, co-grazing multispecies swards improved heifer and lamb production performance at lower nitrogen fertilisation rates, potentially mitigating the environmental impact of beef and sheep production systems.

Greenhouse gas (GHG) emissions from livestock ruminants, particularly methane (CH4), nitrous oxide, and indirectly ammonia (NH3) significantly contribute to climate change and global warming. Conventional monoculture swards for cattle feeding, such as perennial ryegrass or Italian ryegrass, usually require substantial fertiliser inputs. Such management elevates soil mineral nitrogen levels, resulting in GHG emissions and potential water contamination. Mitigating the environmental footprint of these farming practices requires sustainable alternative feeding strategies for cattle production. Multispecies grassland swards (grass + legumes or legumes + herbs) represent a promising alternative to monoculture grassland swards for cattle nutrition due to their reduced nitrogen requirements, excellent herbage yield, and polyphenolic compounds (tannins, formononetin, luteolin, quercetin, and acteoside) which may have positive effects on animals. This study investigated the effects of selected multispecies grassland swards (plant blends) on in vitro ruminal fermentation and DM digestibility. Three experimental blends of plants cultivated without fertilisers were utilised: (1) perennial ryegrass (PRG) + red clover (RC), (2) chicory (C) + red clover (RC), and (3) Tonic plantain (PLA) + red clover (RC). The control blend included perennial ryegrass (PRG), and red clover (RC) cultivated with fertiliser. The in vitro trial showed a reduction in CH4 production and ruminal NH3 concentration (by 14.7 and 28.8%, respectively; P < 0.01) in the PLA+RC blend compared to the control. This plant blend also increased propionate concentration (P < 0.05) and reduced acetate and butyrate concentrations and the acetate-propionate ratio (P < 0.01). Additionally, the total protozoal and methanogen counts were mostly reduced by the PLA+RC blend (P < 0.01) among all blends investigated. In conclusion, the Tonic plantain and red clover blend (PLA+RC) cultivated without fertilisers have the potential to be utilised as a sustainable alternative feed source for climate-friendly cattle production, aligning with the aims of the European Climate Care Cattle Farming project.