-The objective of this study was to relate farm feeding practices in different production systems to milk fatty acid (FA) composition on the scale of round tankers. Milks from 10 collection rounds in the French department of the Haute-Loire (10 to 36 herds per collection round) were sampled twice and three times during winter and grazing periods, respectively. The collection rounds were principally characterised by the forage system (grass or maize silage). Nine variants of milk production conditions were defined: four for the winter feeding period (W1 to W4) and five for the grazing period (G1 to G5). Over the year rumenic acid was positively correlated with vaccenic acid (r = 0.99), all the other trans and c11 isomers of C18:1, oleic acid (r = 0.79), linolenic acid (r = 0.82) and eicosapentaenoic acid (C20:5n-3, EPA). The milk fat from cows grazed on grass had a higher proportion of total trans FA (including trans C18:1, non-conjugated C18:2 and c9t11-CLA) and total cis C18:1, and a lower proportion of medium-chain saturated FA (−9.50 g·100 g −1 for C16:0 between G5 vs. W1) and monounsaturated FA (mainly c9-C16:1) than that from grass silage-based (and concentrate-supplemented) diets. Also, C18:0, c9t11-CLA (r = 0.65), t11c15-C18:2, C18:3n-3 (r = 0.68) and EPA (r = 0.64) were positively linked to permanent grassland forages (green or conserved) on the scale of the year. During winter, trans (t6+7+8, t10, t12 and t13+14) and cis (c12, c13 and t16+c14) isomers of C18:1 were positively correlated with the proportion of maize silage in the diet (r = 0.47 to 0.91). The wide range of milk FA composition from the rounds observed in this study was closely linked to the variants in feeding and husbandry conditions. Our data confirm the strong effect of nutritional factors on milk FA composition of tanker milk shown in experimental trials. round tanker milk / farm feeding and husbandry practices / trans, conjugated and n-3 fatty acids / grassland / dairy cow Résumé -Variabilité des acides gras de laits de collecte en fonction des pratiques alimentaires et des conduites d'élevage dans une zone française de semi-montagne. L'objectif de cette étude était, à l'échelle de laits de tournées, d'établir des relations entre les pratiques d'alimentation et les conduites d'élevage de différents systèmes de production et la composition en acides gras (AG) de ces laits. Les laits de 10 tournées dans le département français de la Haute-Loire (10 à 36 troupeaux par tournée) ont été prélevés, respectivement, deux et trois fois pendant l'hiver et la période de pâ-turage. Neuf variants des conditions de production des laits ont été définis : quatre pour la période hivernale (W1 à W4) et cinq pour la période de pâturage (G1 à G5). Au cours de l'année, l'acide ruménique était positivement corrélé à l'acide vaccénique (r = 0.99), à l'ensemble des autres isomères trans et c11 du C18:1, aux acides oléique (r = 0.79), linolénique (r = 0.82) et EPA. La matière grasse laitière provenant du pâturage avait une proportion plus élevée en AG...

The aim of this work was to study the variability in the composition of bulk milk mixtures of fat-soluble compounds (vitamins A and E, carotenoids, and terpenoids) and assess the links with milk production conditions. Milk from 10 collection trips in the French department of the Haute-Loire (10 to 36 herds per trip) was sampled in the tanker twice during the winter period and 3 times during the grazing season. The collection trips differed in their altitude (440 to 1,150 m) and the forage system (grass or based on corn silage). Vitamins A and E, carotenoids, and terpenoids of the 50 tanker loads of milk were analyzed. Data of milk production conditions in the 204 farms made it possible to constitute indicators for the collection trip and to define 50 mean herds. The relationships between mean herd characteristics (breed, stage of lactation, and feed) and milk characteristics were investigated. The constituents of tanker loads of milk were comparable to those observed in milk produced by groups of animals receiving contrasting diets (rich in concentrate or corn silage vs. pasture). The characteristics of the milk differed according to the period; those produced at grazing were more yellow (1.02 +/- 0.4; mean of difference) and richer in beta-carotene, lutein, vitamin E (2.0 +/- 1.2, 0.23 +/- 0.12, and 6.1 +/- 5.0 mug/g of fat, respectively), and sesquiterpenes (2.7 +/- 2.5) than winter. The variations observed for beta-carotene, lutein, and vitamin E were linked to the proportion of grazed grass or grass silage in the forage (r = 0.66, 0.69, and 0.51, respectively), unlike the vitamin A content. During grazing, 20 of the 32 terpenoids identified were associated with the proportion of permanent grassland available for grazing or cut. These results show that feeding is an effective way to modify the quality of dairy products, even in the case of bulk tank milk mixtures. Dairy plants could market different milks, which would contain specific compositions.

The ability of near-infrared spectroscopy to trace cow feeding systems and farming altitude was tested on 486 bulk milk samples from France and northwestern Italy. Milks were grouped into feeding systems according to the main forage in the diet. Partial least square discriminant analysis correctly classified 95.5, 91.5, and 93.3% of pasture versus maize silage, hay, and fermented herbage feeding systems, respectively. Discrimination was slightly less successful when diets with large proportions of the nondominant forage were included in each group. Near-infrared spectroscopy correctly discriminated no-pasture from pasture milk, even with only 30% of pasture in the diet (5.4% cross-validation error), and the error stabilized when pasture exceeded 70% (2.5% error). Near-infrared spectroscopy did not reliably trace milk geographic origin when the feeding system effect was isolated from the altitude effect. These findings may be usefully exploited for the authentication of dairy products.

-A study was conducted to verify whether bulk milk produced according to specific conditions of production would lead to distinctive cheeses. Milk from two groups of farms that mainly differ in their level of intensification of dairy cow and forage area management was processed into cheese in the same Cantal dairy plant, during 4 periods of 3 consecutive days each. The milk chemical composition differed little between the two producing groups whereas the differences were greater between the processing periods because of the combined effects of the season, the mean lactation stage of the herds and cow feeding. Major chemical and microbiological differences were noted in ripened cheeses according to the cheesemaking period, especially between cheeses made in the winter and in the summer. The cheesemaking period and ripening time (6, 13 and 23 weeks) accounted for most of the variance noted in all the sensory characteristics of the cheeses, whereas the production system had a far lesser impact. With regards to odour and aroma, the spring and winter cheeses differed from the autumn and summer ones. With time, the cheeses became softer and melted more and tasted saltier and more pungent. The stronger characteristics were enhanced whereas milder flavours lost power, a trend that was more marked in the winter cheeses. On average, the cheeses made from the more extensive farms were more elastic and slightly less bitter and pungent. They were also characterised by their globally less intense odour and aroma characteristics. The differences between the two production systems were noticeable in cheeses made in the winter or spring and the most significant after 13 weeks of ripening. For other periods or other ripening time, the cheeses made from the 2 groups of farms were very close.

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