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

A practice becoming more common in Australasia is to extend the lactation cycle beyond the traditional 10 months, even up to 20 months. Whereas there are particular advantages to the dairy farmer, the question is how does such an extended system affect the composition and quality of dairy products? This lead to an investigation by M.J. Auldist and co-workers which was published in the Journal of Dairy Science, Volume 93 of 2010, pages 1401 to 1411; the title being: Composition, coagulation properties, and cheesemaking potential of milk from cows undergoing extended lactations in a pasture-based system.

Extending the lactation length of dairy cows has attracted much attention 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, to for example maintain concentrated calving systems because of labour limitations and utilizing peak pasture quality and production. Lactation lengths longer than 10 months provide cows with more time to cycle and conceive after birth of the calf and such systems may therefore be more suitable for high-producing Holstein-Friesian cows. However, before extended lactations can be recommended it should be established whether the milk of such cows is suitable for manufacturing of high-quality dairy products. This was the intention of the trials discussed in the present article.

The composition of the milk of cows entering the second half of a 22-month lactation was examined in detail and compared with the milk of cows in a traditional 10-month lactation. Coagulation properties were measured on two occasions and Cheddar cheese was made on a pilot scale. The results showed that milk from cows on the extended treatments had higher concentrations of fat and protein than milk from cows on the 10-month cycle when similarly managed and at the same time per year. However, the ratio of casein to true protein was not affected by lactation length and also not the proportions of individual caseins. The increase in milk solids in the extended treatments resulted in more rapid coagulation and in a firmer curd in one of the two occasions. The extended treatments furthermore yielded more cheese per 100kg milk, but the composition of organoleptic properties showed very little difference.

The results suggested that farmers of pasture-based systems can evaluate the practicality and viability of extended lactations without being concerned about the quality of manufactured products. The implications are that even although in South Africa we do not employ extended systems, we nevertheless have circumstances on the eastern seaboard where such systems may be considered. The results of this study is therefore promising.