Composition, coagulation properties, and cheesemaking potential of milk from cows undergoing extended lactations in a pasture-based dairying system.

Extending the lactation length of dairy cows beyond the traditional 10 mo toward lactations of up to 22 mo has attracted interest in the pasture-based seasonal dairying systems of Australia and New Zealand as a way of alleviating the need for cows to conceive during peak lactation, such as is required to maintain seasonally concentrated calving systems. Lactation lengths longer than 10 mo instead provide cows with more time to cycle and conceive after parturition and may therefore be more suitable systems for high-producing Holstein-Friesian cows. Before recommending such systems there is a need to evaluate the effects of long lactations on the suitability of milk for manufacture of high-quality dairy products. In the current experiment, the composition of milk from cows entering the second half of a 22-mo lactation was examined in detail and compared with that from cows undergoing a traditional 10-mo lactation. On 2 occasions, coagulation properties were measured using low amplitude strain oscillation rheometry, and Cheddar cheese was made in 250-L pilot-scale vats. Results showed that milk from extended lactations had higher concentrations of fat and protein than cows undergoing 10-mo lactations under similar management conditions and at the same time of year. The ratio of casein to true protein was not affected by lactation length and neither were the proportions of individual caseins. The increase in milk solids during extended lactations translated into a more rapid rate of coagulation and ultimately a firmer curd on one of the two occasions. Milk from extended lactations yielded more cheese per 100 kg of milk, and there were few differences in the composition or organoleptic properties of the cheese. These data are the first to show that pasture-based dairy industries could embrace the use of extended lactations without compromising the core business of producing high-quality dairy products.

Managing diet quality for Cheddar cheese manufacturing milk. 1. The influence of protein and energy supplements.

The effects of supplementing cows' diets with protein and energy on milk composition and the composition and yield of Cheddar cheese were investigated. This research addresses the problems of seasonal reduction in the capacity of cheese curds to expel moisture as observed in parts of south-eastern Australia. Milk was collected from cows offered a basal diet of silage and hay supplemented with different sources and levels of dietary protein and energy. The protein supplements were sunflower, canola, cottonseed meal and lupin, and the energy supplements were maize grain, oats, wheat and barely. This milk was used to manufacture Cheddar cheese on a pilot scale. Cheese moisture content was dependent on the source and level of dietary protein and energy. Milk from cows offered the lupin protein supplements and wheat energy supplements consistently produced cheese with a lower moisture content and moisture in fat-free matter. Milk from these supplemented diets had increased casein concentrations and higher proportions of alpha S2-casein than milk from the poor quality control diet. Cheese yield was directly related to the total casein concentration of milk, but was not influenced by differences in casein composition. Supplementing the cows' diets increased the inorganic P, Mg and Ca concentrations in milk. A low inorganic P concentration in milk from cows offered the control diet was caused by a low intake of dietary P. These findings showed that changes in the mineral and casein composition of milk, associated with diet, could influence the composition of Cheddar cheese.

Managing diet quality for cheddar cheese manufacturing milk. 2. Pasture v. grain supplements.

The effects of supplementing a basal diet of silage and hay with increasing amounts of harvested spring pasture, or with lupin and wheat, on the composition of milk and the consequent effects on cheese composition and yield were investigated in an indoor feeding study. Milk was collected from five groups of eight cows in mid lactation offered different diets and manufactured into Cheddar cheese on a pilot scale. Milk from cows given the lupin-wheat (LW) and the high pasture level (HP) diets produced low moisture cheese. Cheese produced with milk from cows given the control diet was high in moisture content compared with that made with milk from cows offered the LW diet. Cheese yields from the milk of cows offered the HP and LW diets were greater than from the milk of cows on the control diet, and were associated with the higher casein concentrations of these milks. Casein number was higher in milk from diets supplemented with pasture but was not an indicator of the functional properties of milk that affected cheese moisture. The proportion of beta-casein in milk from cows offered the HP diet was higher and that of gamma-casein lower than in milk from cows given the LW supplement, although cheese moisture content was similar with both diets. Milk from cows offered the HP diet had a greater inorganic P concentration than that from cows given the LW diet, although the dietary intake of P was higher for the LW diet. The significance of the effect of dietary P intake on the concentration of inorganic P in milk and hence its suitability for cheesemaking was apparent when dietary P intake was low, as shown in milk produced by cows offered the control diet.

Effects of somatic cell count and stage of lactation on raw milk composition and the yield and quality of Cheddar cheese.

The effects of somatic cell count and stage of lactation on the yield and quality of Cheddar cheese were investigated. Cheese was manufactured in a pilot scale factory using milk of low bulk milk cell count (BMCC) from herds in early (LE) and late (LL) lactation, and milk of high BMCC from herds in early (HE) and late (HL) lactation. The deleterious effect of an elevated BMCC on product yield and quality in late lactation was clear. Cheese made from LL milk was significantly superior to that made from HL milk for most yield and quality characteristics measured. Stage of lactation also affected cheese yield and quality, as evidenced by the lower recovery of fat and poorer flavour score for cheese from LL milk compared with that manufactured from LE milk. The observed differences could be explained largely by differences in raw milk composition. We conclude that the effect of stage of lactation was magnified by an elevated BMCC, and that many of the problems encountered when processing late season milk could be overcome by containing mastitis at this time.

Seasonal influences on Cheddar cheese manufacture: influence of diet quality and stage of lactation.

The influence of diet quality and stage of lactation on Cheddar cheese moisture and yield were segregated and the effects of other potential variables (cow breed, milk protein genotype, age and level of mastitis) were minimized. An experiment was conducted using milk of cows in mid lactation or late lactation fed on high or low quality diets. Increased moisture in cheese was largely due to the influence of cow diet. Milk from cows given high quality diets produced lower moisture cheese. Cheese yield was influenced by diet and stage of lactation. Cows in late lactation fed on high quality diets always gave milks yielding the most cheese. Fat and protein recovery in cheese was not influenced by diet or stage of lactation. The results suggest that low quality diets may induce changes in the complex interactions of milk proteins and other components that affect cheesemaking.