Agriculture is responsible for a great share of the anthropogenic sources of greenhouse gases that, by warming the earth, threaten its biodiversity. Among greenhouse gas emissions, enteric CH₄ from livestock is an important target to slow down climate changes. The CH₄ is originated from rumen fermentation and its concentration is affected by several factors, including genetics and nutrition. Ruminants have an extraordinary symbiosis with microorganisms (bacteria, fungi, and protozoa) that ferment otherwise indigestible carbohydrates, from which they obtain energy to grow and continue actively producing, among other products, volatile fatty acids, CO₂ and H₂. Detrimental ruminal accumulation of H₂ is avoided by methanogenesis carried out by Archaea methanogens. Importantly, methanogenesis is not the only H₂ sink pathway. In fact, other bacteria can reduce substrates using metabolic hydrogen formed during carbohydrate fermentation, namely propionate production and reductive acetogenesis, thus lowering the CH₄ produced. Although the complexity of rumen poses challenges to mitigate CH₄ production, the emergence of sequencing techniques that allow the study of microbial communities, gene expression, and metabolome are largely contributing to unravel pathways and key players in the rumen. Indeed, it is now recognized that in vivo emissions of CH₄ are correlated to microbial communities, and particularly with the abundance of methanogens, several bacterial groups, and their genes. The goal of CH₄ mitigation is to work in favor of the natural processes, without compromising rumen function, animal health, and productivity. Notwithstanding, the major challenge continues to be the feasibility and affordability of the proposed solutions.

This work aimed to determine and compare the effect of elevation and season on the productivity and the nutritive value of pastures in the Azores (Terceira Island). Forage was collected and analysed for dry matter (DM), crude protein (CP), neutral detergent fibre (NDF), acid detergent fibre (ADF), acid detergent lignin (ADL), ether extract (EE), mineral ash (Ash), dry matter digestibility (DMD) and organic matter digestibility (OMD). The net productivity (NP) was higher in the low elevation pasture A (1.80 g m⁻²), lower in pasture B (0.98 g m⁻²) and peaked in the winter in both pastures A (3.57 g m⁻²) and B (2.33 g m⁻²) and during the summer in the high elevation pasture C (2.15 g m⁻²). The soil chemical proprieties varied significantly among the three pastures. The highest soil pH, available P, K, Ca and Mg were recorded in pasture A. Positive correlations were observed between all soil parameters analysed and NP, except for the OM content. The DM, PB and EE changed significantly with elevation, while all nutritive parameters (except CP, EE and Ash) increased significantly along the growth season. Environmental factors influenced the nutritive parameters and productivity, suggesting that climate change might have significant impacts on forage production and quality.

Copyright © INRA, EDP Sciences, 2005.The objective of this study was to observe the effect of supplementation with vegetable oils (VO) on the fatty acid profiles and conjugated linoleic acid (CLA) content of milk fat. Twelve dairy cows in mid lactation fed on pasture were blocked by body weight, milk production and days in lactation and randomly allocated from blocks to 3 treatments repeated in a Latin square design with periods of 28 day duration. The treatments were as follows: cows on pasture supplemented with 5 kg concentrate per head per day (C), supplemented with 4.5 kg concentrate + 0.5 kg sunflower oil per head per day (SFO) and supplemented with 4.5 kg concentrate + 0.5 kg soybean oil per head per day (SBO). The animals were grazed as a group and were stocked at 2.5 heads per hectare. The treatments had no effect on milk yield or protein yield and content, but decreased milk fat yield and content (P < 0.05). Milk fat from the cows supplemented with VO had a lower concentration of short and medium chain fatty acids (P < 0.05) and a higher concentration of long chain fatty acids (P < 0.05). The addition of VO to the diet also resulted in a reduction in saturated and an increase in unsaturated fatty acids of milk fat (P < 0.05). The hypercholesterolemic fatty acids in milk fat (i.e. C12:0, C14:0 and C16:0) decreased while the concentration of oleic and linoleic acids increased with VO (P < 0.05). There was no effect on linolenic acid. Finally, the inclusion of VO in the diet increased (P < 0.05) the contents in milk fat of the various cis/trans isomers of oleic acid (including trans-vacenic, TVA) and of CLA which increased by 61%

International audienceTwelve dairy cows 130 days in milk were sorted by milk production and body weight and assigned to three feeding regimens in a 3 × 3 Latin-square design, in order to study the effects of diet on milk fatty acid (FA) composition. The cows were fed a total mixed ration (TMR) consisting of corn silage (60%) and concentrate (40%) on dry matter basis, or grazed pasture, without (P) or with 5 kg*d-1 concentrate as a supplement (SP). Supplemented grazing dairy cows produced significantly more milk than the cows on the TMR and P diets (P < 0.05). The supplementation of grazing dairy cows with a low fat concentrate did not significantly affect the milk fat FA profile. The pasture diet, with a supplement or not, decreased the concentration of saturated FA (P < 0.05) and increased the concentration of unsaturated FA (P < 0.05), of milk fat as compared to the TMR diet. The reduction in medium-chain FA was offset in large part by increases in long-chain FA (mainly oleic acid). The concentrations of conjugated linoleic acid (CLA) (P < 0.05) and trans-vaccenic acid were higher (P < 0.05) in the milk fat from the grazing cows. The results showed substantial variation among individual cows within treatments on milk fat content of CLA. Significant correlations were found for individual cow's milk fat CLA content across diets. Overall, this study indicates that the concentration of CLA in milk fat is enhanced by the dietary intake of pasture and that moderate low fat concentrate supplementation of grazing dairy cows increases performance without compromising the FA profile of milk fat.Effet du régime alimentaire sur la composition en acides gras de la matière grasse du lait chez la vache. Douze vaches laitières, en lactation depuis 130 jours, ont été réparties en trois lots sur la base de la production laitière et du poids vif. Elles ont reçu trois régimes alimentaires, selon un carré latin 3 × 3, afin d'étudier leurs effets sur la composition en acides gras (AG) du lait. Les trois régimes étaient une ration complète (TMR) composée d'ensilage de maïs et de concentré (respectivement 60 % et 40 % sur la base de la matière sèche), de l'herbe pâturée sans complémentation (P), ou de l'herbe pâturée complémentée avec 5 kg par jour de concentré (SP). Les vaches laitières complémentées au pâturage (SP) ont produit significativement plus de lait que celles qui ne disposaient que du pâturage ou qui recevaient la ration complète. Le pâturage, complémenté ou non, a diminué la concentration de la somme des AG saturés et a augmenté celle des AG insaturés (P < 0,05) dans les lipides du lait. La réduction de la concentration des AG à chaîne moyenne a principalement été compensée par une augmentation de celle des AG à chaîne longue (acide oléique surtout). La concentration de l'acide linoléique conjugué (CLA) dans les lipides du lait, et celle de l'acide trans-vaccénique ont été plus élevées (P < 0,05) quand les vaches étaient au pâturage que quand elles recevaient le TMR. Les résultats ont montré une variation notable entre vaches et intra régime de la teneur en CLA des lipides du lait, ainsi que des liaisons significatives individuelles entre les régimes. Notre étude a montré que la teneur en CLA des lipides du lait est accrue par l'ingestion d'herbe fraîche et qu'une complémentation modérée en concentré augmente la production laitière sans compromettre le profil en AG