Summary -Dairy cows belonging to 3 different genetic types (Holstein, Montbéliarde and Tarentaise) were fed, according to a 3 x 3 latin square experimental design, 3 different types of forage (ryegrass silage, cocksfoot regrowths and maize silage). The proportion of concentrate in the diet, and the energy and nitrogen contents were similar between ail 3 feeding treatments. The milk yielded by these cows was used in the manufacture of Saint-Nectaire cheeses, under controlled technology manufacturing conditions which were identical from one production to another. Cheeses manufactured from grass silage milk have a more yellow curd than cheeses made from cocksfoot regrowlh or maize silage milk. Cocksfoot regrowlh milk cheeses are more sticky and less firm than the others; they achieve a global score which is 0.6 to 1 point higher (P < 0.05) than those of other cheese types. Cheeses manufactured from milk yielded by Montbéliarde and Tarentaise cows were better rated than those made from Holstein milk. The various reasons for these differences are discussed in relation to the chemical composition of the feeds.

Two groups of eight multiparous cows with different calving periods (November or February) were managed in the same way during lactation. During four 4 week experimental periods distributed over 12 months, the cows were fed on a diet composed of hay and concentrate (70[ratio ]30) in a restricted and controlled amount which varied according to their lactation stage, so as to cover the animals' requirements correctly. The animals' average lactation stage varied according to period from 26 to 298 d. Milk from each group was processed on two occasions during each period to make Saint-Nectaire-type cheese; the cheesemaking conditions were the same throughout. Lactation stage had an important effect on milk fat, protein and calcium contents but not on the casein[ratio ]protein ratio or phosphorus content. The milk pH and the urea content were higher in late lactation. The calcium concentration of milk was higher in late lactation but the soluble fraction was higher in early lactation. Despite higher protein contents, the maximal firmness of the coagulum of late-lactation milk was not different from that of early or mid-lactation milks. pH was higher in cheeses from late-lactation milks compared with those from early and mid-lactation milks. Cheeses from early lactation milks were more yellow than the others and had a lower dry matter fat content. In sensory analysis the odour of cheeses from early and late-lactation milks was less pleasant than that of those from mid-lactation milks. Cheeses from late-lactation milks were more melting and less firm than those from early or mid-lactation milks. Their taste was more intense and more persistent. At tasting, they were less appreciated than the others. These differences were linked to increased proteolysis in the cheeses made with late-lactation milks.

Summary -Fifty-Iour lactating multiparous cows were used in a 3 x 3 latin square trial. During each 3-week period cows were offered a diet composed either 01 perennial ryegrass silage (11 kg dry matter/dl, or second-cutting cocksloot hay (13 kg dry matter/dl or maize silage (11 kg dry matter/dl. Each diet was supplemented with a mixture 01 barley, soya-bean meal and urea in proportions calculated to keep the overall rations isocaloric and isonitrogenous. The cows led grass silage yielded, respectively, 0.4 (P> 0.05) and 1.9 kg/d (P < 0.01) more milk than those led maize silage or hay, but their milk was signilicantly poorer in proteins and caseins. This result is Iinked to a distribution 01 ingested energy in lavour 01 milk yield rather than the deposition 01 body reserves with the grass silage-based diets. The casein/protein ratio, calcium concentration, pH and rheological characteristics 01 the milk were not signilicantly different between the types 01 lorages. dairy cow / coagulation property / milk composition 1 feeding Résumé -Effet de la nature de la ration de base sur la composition chimique du lait et son aptitude à la coagulation.

Seize vaches multipares en milieu de lactation ont été utilisées dans un essai en carré latin 2 x 2. Pendant chaque période de 3 semaines, les animaux ont reçu une ration à base de fourrage de prairie naturelle offerte soit sous forme de foin récolté au premier cycle, soit sous forme d'herbe verte, issue de la même parcelle et pâturée en deuxième cycle. Le lait de ces vaches a été transformé en fromages de Saint-Nectaire, dans des conditions technologiques de fabrication contrôlées et identiques d'une fabrication à l'autre. La production laitière a été supérieure avec l'herbe pâturée (+ 1,8 kg/j, P < 0,01). La teneur en urée du lait a été supérieure avec le foin, et la teneur en calcium légèrement inférieure. Les autres constituants chimiques du lait, son pH et ses caractéristiques rhéologiques ont été voisins dans les deux traitements. La plupart des caractéristiques physiques et sensorielles des fromages ont été semblables dans les deux traitements. Les fromages ont cependant été plus fermes et plus acides lorsque le fourrage était offert sous forme de foin. fromage / alimentation / caractéristique sensorielle / vache laitière Summary-Effect of forage type (hay or grazing) on milk cheesemaking ability. Sixteen muftiparous dairy cows in mid-lactation were used in an experiment with a 2x 2 Latin-square design. During each 3-week period, the cows were offered a diet composed of native mountain grassland given as hay (first eut) or grazed (second eut of the same plot). The milk yielded by these cows was used in the manufacture of Saint-Nectaire cheeses, under controlled technology manufacturing conditions which were identical from one production ta another. Milk yield was higher at pasture (+ 1.8 kg/day, P < 0.01). Urea content was higher with hay (+ 5.6 mg/100 mL, P < 0.01), and calcium content was slightly lower (-0.05 g/kg, P < 0.05). Other chemical contents (fat, protein, casein), pH and renneting properties of milk were similar in bath treatments, as most of the chemical (dry matter, fat in dry matter, pH) and sensory characteristics (taste, odour, colour) of the cheeses. However, cheeses were firmer and more acid when forage was given as hay. cheese / feeding / sensory characteristic / dairy cow

Summary — Forty-two lactating multiparous cows were used in a changeover design with two periods of 4 weeks. During each period cows were offered an isocaloric diet composed either of grass silage (12 2 kg dry matter/day) or hay ( 12.5 kg dry matter/day). Hay and grass silage were harvested the same day (7 June) in the same field of native mountain grassland. Each diet was supplemented with the same quantity of a mixture of barley and soya bean meal in proportions calculated to keep the overall rations isonitrogenous. The cows fed grass silage yielded 0.7 kg/day (P < 0.05) more milk than those fed hay, but their milk was significantly poorer in fat (-1.2 g/kg), proteins (-1.0