Fresh grass in the cow diet improves the rheological and nutritional properties of butter. However, the relationship between the proportion of fresh grass in the diet and these properties is still unknown. The objective of the study was to determine the relationship between the proportion of fresh grass in the diet and the properties of milk and butter. Four groups of 2 cows were fed 4 isoenergetic diets characterized by increasing amounts of fresh grass (0, 30, 60, and 100% dry matter of forage) according to a Youden square design. Energy levels were similar among all diets. Thus, no effect of mobilization was observed and the results were only due to the proportion of fresh grass in the diet. Milk yield linearly increased with the proportion of fresh grass in the diet (+0.21 kg/d per 10% of grass). Fat yield remained unchanged. Thus, by effect of dilution, increasing the proportion of fresh grass in the diet induced a linear decrease in fat content. Milk fat globule size decreased by 0.29 mum when the proportion of grass reached 30% in the diet. Increasing the proportion of fresh grass in the diet induced a linear increase in unsaturated fatty acids percentages at the expense of saturated fatty acids. Relationships were +0.38, +0.12, +0.05 and -0.69 points/10% of fresh grass in the diet for C18:1 trans-11, C18:2 cis-9,trans-11, C18:3n-3, and C16:0, respectively. These modifications in fatty acid composition, and in particular in the spreadability index, C16:0/C18:1, were responsible for linear decreases in final melting temperature and solid fat content in butter fat, perceived in sensory analysis by a linear decrease in firmness in mouth. The nutritional value of butter was also linearly improved by the proportion of fresh grass in the diet by halving the atherogenicity index.

Five dairy cows were arranged in a 5 x 5 Latin square design to compare the effects of two amounts of either duodenal glucose or ruminal propionic acid (C3) on milk yield and composition. Treatments consisted of a grass silage-based diet supplemented with glucogenic nutrients either infused in the rumen as a mixture of volatile fatty acids (control) or pure C3 (1.72 and 3.45 Mcal/d) or in the duodenum as glucose (1.72 and 3.45 Mcal/d). Treatments were isoenergetic and isonitrogenous and contained 100 and 115% of energy and protein requirements according to INRA (1989), respectively. Only C3 treatments significantly modified ruminal volatile fatty acid composition and linearly increased C3 percentage (up to 25.5%). Both treatments substantially decreased milk fat yield and content, and linearly increased milk and protein yields. Although no significant differences between glucose and C3 were highlighted for milk yield and composition, it seems that mechanisms involved in milk fat decrease are different. Indeed, whereas C3 treatments decreased fatty acid production in an homogeneous way, short- and long-chain fatty acids decreased and medium-chain fatty acid production increased with glucose treatments. A bibliographical study confirmed that increasing glucogenic precursors (GP) supply curvilinearly increase milk yield, linearly increase milk protein content (+ 0.04% per Mcal of GP) and curvilinearly decrease milk fat content (- 0.14% per Mcal of GP). Thus, it appears important to account for the nature of energy supplied by the ration in formulation.

This review summarizes the recent developments in understanding of the relationships between the diet of animals and the sensory quality of dairy products. Feeding dairy cattle with maize silage by comparison with hay or grass silage leads to whiter and firmer cheeses and butter and sometimes to differences in flavour. Major differences in sensory characteristics were observed between cheeses made with milk produced by cows on winter diets (based on hay and grass silage) or turned out to pasture in the spring. Conversely, preserving grass as silage, by comparison with hay, has no major effect on cheese sensory characteristics, except on colour, the cheese being yellower with grass silage. Several recent experiments have shown a significant effect of grass botanical composition on cheese texture and flavour. These effects are due to the presence in milk of specific molecules directly introduced by feeding (carotenes, terpenes) or produced by the animals (plasmin, fatty acids) under the effect of specific diets.

The nutritional and rheological properties of butter depend on the fatty acid composition of milk. Therefore, feeding oilseeds rich in unsaturated fatty acids is likely to affect butter properties. The aim of this trial was to examine to what extent feeding the linolenic acid-rich cruciferous plant camelina can affect the fatty acid composition of dairy products and the properties of butter. A control diet composed of 60% corn silage-based ration and completed with high-energy and nitrogenous concentrates was compared with 2 experimental diets designed to provide the same amount of polyunsaturated fatty acids via either camelina seed (630 g/d, CS diet) or camelina meal (2 kg/d, CM diet). The diets were isoenergetic and isonitrogenous. The trial followed a double 3 x 3 Latin-square design with 4-wk periods on 6 Holstein dairy cows. The camelina diets tended to decrease dry matter intake but did not have a significant effect on milk production. They generated a slight decrease in milk protein and a strong decrease in milk fat yield and content. The CM diet led to a stronger decrease in fat content. Camelina generated a greater proportion of monounsaturated fatty acids, notably C18:1 trans isomers, including trans-10 and trans-11 C18:1, which increased by 11.0- and 2.6-fold, respectively, with the CM diet. Camelina also led to an increase in conjugated linoleic acids, particularly rumenic acid, cis-9, trans-11 C18:2. Camelina did not affect parameters of buttermaking except churning time with milk from CM fed cows, which was longer. The butters of camelina diets were softer at all temperatures tested, especially with the CM diet. In conclusion, feeding camelina can modify milk fatty acid profile and butter spreadability.

The aim of this experiment was to compare the effects of increasing amounts of extruded linseed in dairy cow diet on milk fat yield, milk fatty acid (FA) composition, milk fat globule size, and butter properties. Thirty-six Prim'Holstein cows at 104 d in milk were sorted into 3 groups by milk production and milk fat globule size. Three diets were assigned: a total mixed ration (control) consisting of corn silage (70%) and concentrate (30%), or a supplemented ration based on the control ration but where part of the concentrate energy was replaced on a dry matter basis by 2.1% (LIN1) or 4.3% (LIN2) extruded linseed. The increased amounts of extruded linseed linearly decreased milk fat content and milk fat globule size and linearly increased the percentage of milk unsaturated FA, specifically alpha-linolenic acid and trans FA. Extruded linseed had no significant effect on butter color or on the sensory properties of butters, with only butter texture in the mouth improved. The LIN2 treatment induced a net improvement of milk nutritional properties but also created problems with transforming the cream into butter. The butters obtained were highly spreadable and melt-in-the-mouth, with no pronounced deficiency in taste. The LIN1 treatment appeared to offer a good tradeoff of improved milk FA profile and little effect on butter-making while still offering butters with improved functional properties.

The objective of this study was to examine the synthesis and composition of milk produced by dairy cows that secrete either small milk fat globules (SMFG) or large milk fat globules (LMFG), and to study their response to diets known to alter milk composition. Four groups of 3 multiparous dairy cows were assigned to 2 isoenergetic feeding treatments: a corn silage treatment supplemented with soybean meal, and fresh pasture supplemented with cereal concentrate. The 4 groups comprised 2 groups of 3 dairy cows that produced SMFG (3.44 microm) and 2 groups of 3 dairy cows that produced LMFG (4.53 microm). The SMFG dairy cows produced higher yields of milk, protein, and calcium. Nevertheless, their milk had lower fat and protein contents. Both SMFG and LMFG cows secreted similar amounts of milk fat; therefore, higher globule membrane contents in milk fat were observed in SMFG cows. Higher calcium mineralization of the casein micelles in SMFG cows suggests that it may be possible to improve cheese-making properties even if the lower protein content may lead to lower cheese yields. The SMFG cows secrete milk fat with a higher concentration of monounsaturated fatty acids and a lower concentration of short-chain fatty acids. They also have a higher C18:1/C18:0 ratio than LMFG cows. This suggests that SMFG cows have more significant fatty acid elongation and desaturation. The pasture treatment led to an increase in milk and protein yields because of increased energy intake. It also resulted in lower milk fat yield and fat and protein contents. The pasture treatment led to a decrease in milk fat globule size and, as expected, an increase in monounsaturated and polyunsaturated fatty acid contents. However, it induced a decrease in the protein content, and in calcium mineralization of casein micelles, which suggests that this type of milk would be less suitable for making cheese. This study also shows that there is no correlation between the cows, based on milk fat globule size and diet. These results open up possibilities for improving milk fat quality based on milk fat globule size, and composition. The mechanisms involved in milk fat globule secretion are still to be determined.

We conducted two trials to study the effect of graded amounts of glucose infused into the duodenum on milk yield and composition as well as on plasma metabolites, using diets based on grass silage. In trial 1, four fistulated Holstein cows were arranged in a 4 x 4 Latin square design and received 0, 750, 1500, and 2250 g of glucose/d in the duodenum. In trial 2, five fistulated Holstein cows were arranged in a 5 x 5 Latin square design and received 0, 250, 500, 1000, and 2000 g/d of glucose. In both trials, cows were fed a basal diet of 38% grass silage, 10% dehydrated alfalfa, 49% energy concentrate, and 3% oil meal. The treatments (feed plus infusion) were isoenergetic and isonitrogenous. Increased amounts of glucose increased milk yield up to 2.4 and 1.6 kg/d in trials 1 and 2, respectively. Lactose content was not affected, while fat yield and content decreased linearly. The decrease in milk fat resulted from a reduced yield of C18, probably caused by a lower mobilization of fat. The glucose treatments significantly affected the profiles of medium-chain fatty acids, by enhancing the elongation process (up to C14). Glucose infusions induced an asymptotic response of protein yield (linear increase up to 1000 g of glucose, after ceiling). It appears that with poor postruminal starch diets, such as grass silage-based diets containing 35 to 40% of concentrate, the glucose supply to the mammary gland may be limiting for milk synthesis.

Milk protein secretion is changed by increasing the proportion of energy, mainly as propionic acid, or the availability of AA. Whether associative effects exist between energy nature and protein amounts is unknown. Therefore, ruminal isoenergetic infusions of low or high propionate mixtures were combined factorially with duodenal infusion of sodium caseinate or control. Four ruminally and duodenally fistulated Holstein cows were used. The diet was limited and consisted of 70% forage and 30% concentrate. Caseinate infusion increased milk yield and protein and casein contents and decreased milk fat content; curd yields and coagulation properties of milk were improved. The infusion of propionic acid caused a large increase in rumen propionate. Milk yield tended to decrease, and milk fat decreased, but protein, casein, and curd yields were unchanged; milk-coagulating properties were improved. No interaction existed between energy and protein amounts. Alteration of VFA had little effect on milk composition, but increasing the protein supply to the duodenum increased milk protein.