This study evaluated the changes of cows’ milk fat fatty acids (FA) after transition from pasture to a total mixed ration (TMR) diet and back to pasture. Eight Holstein cows were used in a 52-d experiment divided into three periods. In period I (PI), cows grazed for 10 d and were supplemented with 5 kg head⁻¹ day⁻¹ of concentrate. On the 11th day, cows were moved to a barn and fed a TMR diet for the next 21 d (PII). On the 32nd day, cows were sent back to pasture for another 21 d (PIII) and received the same supplement of PI. Milk samples were taken on days 10 of PI and 2, 4, 7, 14 and 21 of PII and PIII. Total mixed ratio significantly increased dry matter intake and milk production and decreased milk fat content. Diet significantly affected the concentration of most FA in milk fat. Grazing pasture significantly increased the concentrations of 18:0, 18:1 c9, 18:1 t11, 18:2 c9,t11, 18:2 t11,c15, 18:3 c9,c12,c15, iso and anteiso branched-chain FA and sums of monounsaturated fatty acids (MUFA) and polyunsaturated fatty acids (PUFA). Concentrations of 12:0, 14:0, 16:0, 15:0, 17:0, 18:2 c9,c12 and the sum of saturated fatty acids (SFA) significantly increased with PII diet. Most FA and FA sums took 14–21 d to stabilise in PII and only 4–7 d after transition for pasture. This evolution pattern of milk fat FA suggests that the long historical feeding regimen is a factor that impacts on the time cows take to respond to different diets by changing FA composition, probably as a result of the adaptation time of rumen microbes.

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

Reversing climate change requires broad, cohesive, and strategic plans for the mitigation of greenhouse gas emissions from animal farming. The implementation and evaluation of such plans demand accurate and accessible methods for monitoring on-field CH₄ concentration in eructating breath. Therefore, this paper describes a longitudinal study over six months, aiming to test a protocol using a laser methane detector (LMD) to monitor CH₄ emissions in semi-extensive dairy farm systems. Over 10 time points, CH₄ measurements were performed in dry (late gestation) and lactating cows at an Azorean dairy farm. Methane traits including CH₄ concentration related to eructation (E_CH4) and respiration (R_CH₄), and eructation events, were automatically computed from CH₄ measured values using algorithms created for peak detection and analysis. Daily CH₄ emission was estimated from each profile’s mean CH₄ concentration (MEAN_CH₄). Data were analyzed using a linear mixed model, including breed, lactation stage, and parity as fixed effects, and cow (subject) and time point as random effects. The results showed that Holsteins had higher E_CH₄ than Jersey cows (p < 0.001). Although a breed-related trend was found in daily CH₄ emission (p = 0.060), it was not significant when normalized to daily milk yield (p > 0.05). Methane emissions were lower in dry than in lactation cows (p < 0.05) and increased with the advancement of the lactation, even when normalizing it to daily milk yield (p < 0.05). Primiparous cows had lower daily CH₄ emissions related to R_ CH₄ compared to multiparous (p < 0.001). This allowed the identification of periods of higher CH₄ emissions within the milk production cycle of dairy cows, and thus, the opportunity to tailor mitigation strategies accordingly.