Milk market suitability

of beta-casein found in the milk of dairy breeds originating in northern European such as the Holstein, Friesian, Ayrshire and British Shorthorn. A2 beta-casein is found predominantly in the milk of Channel Island cows, Guernsey and Jersey, in Southern French breeds, Charolais and Limousin, and in the Zebu original cattle of Africa [Truswell, 2005]. Interest in ‘A2’ milk, produced by cows that only have alpha-2 casein and no alpha-1 casein, was generated in the early-mid 1990s when concerns were raised by researchers about a breakdown product of alpha-1 casein, beta-casomorphin-7 (BCM-7), could be associated with type I diabetes and may also be a risk factor for coronary heart disease [Truswell, 2005].

Amino acids

Csapo et al. (2011) and Lim et al. (2020) found that the amino acid (AA) profile of milk did not differ significantly between breeds, and that the higher concentrations of essential AA concentrations in Jersey milk compared to Holstein milk were a function of the higher protein level of Jersey milk.

Minerals

Differences between breeds in the mineral concentration of milk have been well studied. Lim et al. (2020) found that the concentrations of calcium, phosphorus and zinc were higher in Jersey milk than in Holstein milk, while the potassium concentration was lower. However, for cows of any particular breed, mineral concentrations in milk also vary widely between individual cows within a herd, and between herds [Cerbulis and Farrell, 1976; Rodriguez et al., 2001].

Milk market suitability

When respondents to the Jersey Australia survey were asked to give their level of agreement with the statement ‘Jerseys provide access to more milk markets than other breeds’, 67% agreed or strongly agreed, 12% disagreed or strongly disagreed, and 21% were unsure.

Milk composition influences the processing attributes of milk i.e. casein micelle size, heat stability, buffering capacity, rennet coagulation time and ethanol stability [Chen et al., 2016]. Studies are inconsistent as to whether Jersey milk has better heat stability than Holstein milk. The higher levels of protein and fat found in Jersey and Guernsey milks results in higher cheese yields and a deeper yellow colour. Jersey milk, with its lower ratio of casein to fat, may be more suitable for bloomy rind cheeses, while Brown Swiss milk, with its higher ratio of casein to fat, may be more suitable for aged hard cheese [Wendorrf and Paulus, 2011]. While Jersey milk is supplied around the world into liquid milk and powdered milk markets, there are also opportunities to differentiate Jersey milk in cheese, butter and other products.

Fatty acids from a human health perspective

There is increasing interest in the potential human health benefits that may be gained from consuming bioactive fatty acids such as α-linolenic acid (ALA; 18:3 c9,c12,c15), conjugated linoleic acids (CLAs), and vaccenic acid (VA; 18:1 t11), from milk and dairy products [Bainbridge et al., 2016]. Higher dietary intakes of ALA has been associated with decreased inflammation, neurological disorders and cardiovascular disease, CLAs have been shown to have anticarcinogenic effects and VA has been found to have anti-carcinogenic effects and reduce cardiovascular disease. Higher dietary intakes of several saturated fatty acids in milk have also been found to have human health benefits. Palmitic acid (16:0), Stearic acid (18:0) and very-longchain saturated fatty acids (>22 carbon atoms) have been associated with decreased insulin sensitivity, reduced cardiovascular disease and lower the risk of diabetes respectively. However, a moderate-high dietary intakes of myristic acid (14:0) have been associated with higher plasma high-density lipoprotein level, a risk factor for cardiovascular disease. Branched-chain fatty acids (BCFA) have also been found to have anti-carcinogenic properties and help improve pancreatic function. BCFAs are unique in that they are only synthesised in the cell walls of rumen bacteria

and protozoa. Their use as potential biomarkers for rumen function has therefore been suggested [Fievez et al., 2012]. The content and profile of BCFA in milk fat depends on the activity and composition of the rumen microbial population, which is a function of diet and cow breed.

The bioactive fatty acid profile of milk is influenced by animal genetics, stage of lactation, diet and environment. Bainbridge et al. (2016) compared the fatty acid profile of milk (g/100g FA) and the concentration of fatty acids in milk (g/kg milk) by stage of lactation and breed in Holstein, Jersey and HJ crossbred cows fed the same diet. They found that stage of lactation was the predominant factor affecting the FA content of milk. However, there were also differences between breeds (Table 4). The content of OBCFA and BCFA in milk fat from Jersey cows increased at each time point, whereas the content of OBCFA in Holsteins did not differ across the lactation. Overall, milk from Jersey cows had a greater content of n-6 FA than Holsteins and crossbreds (0.81 vs. 0.70 and 0.70 g/kg milk, respectively) resulting in higher n-6:n-3 ratio when compared to Holsteins and crossbreds at 5 DIM.

Table 4. Content (g/kg milk) of odd and branched-chain fatty acids (OBCFA) in milk from three breeds of dairy cow over four time points; 5 days in milk (DIM), 95 DIM, 185 DIM, 275 DIM [Bainbridge et al., 2016].