Mastitis continues to be a major cause of economic loss to the national dairy herd and I suspect that, combined with teat injuries, it is one of the greatest aggravations to the herdsman.

Mastitis also has welfare implications for the affected cow. Although the incidence of infections caused by Staphylococcus aureus, Streptococcus agalactiae and Strep. dysgalactiae has decreased and the national mastitis cell count has fallen, this has been matched by a rise in the number of cases caused by Escherichia coli and Strep.

AMastitis Surveillance Scheme carried out on 144 herds in England from 1994 to 1996 showed that an average herd of 100 cows would have 43 cases of mastitis each year, defining a ‘case’ of mastitis as one quarter affected on one occasion. There is, of course, tremendous variation in the severity of mastitis, ranging from a few clots needing only one course of treatment, to an acute case in which the cow dies. However, the average cost of a case of mastitis, based on the antibiotics used, milk discarded, reduction in quality and the reduced milking potential and increased cell count of the cow for the remainder of the lac­tation, has been estimated at approximately £90 for each case at 1998 values. Even at 35 cases per 100 cat­tle per annum, with approximately 2.6 million cows in Great Britain, this is a cost to the national herd of £82 million per year or £31 for every cow in your herd! Other surveys have shown an incidence of over 50 cases per 100 cows per year, which means that the overall cost would rise to £45 per year for every cow in your herd, viz an average of £4500 every year lost in mastitis alone for a 100 cow herd!

Mastitis, Yield and Milk Flow Rates

Milk yields have increased considerably over the past 35 years. Approximate UK average figures increased from 3320 litres per cow in 1960 to 5500 litres in 1996. In addition, ‘easy’ milking cows have been selected to achieve faster parlour throughputs.

Both factors lead to more open teat ends and therefore an increased risk of mastitis. For example, it has been shown that over the past 40 years milk flow rates from the teat end have doubled from 0.8 kg to 1.6 kg per quarter per minute, and this increased flow rate has produced a twelve-fold increase in susceptibility to mastitis. The situation is still changing and as yields increase, milk flow rates will rise and it is likely that susceptibility to mastitis will increase even further. This does not mean that the incidence of mastitis will increase, of course, but it does mean that we need to learn to understand the disease and to house, manage and milk our cows in such a way that mastitis is minimised. It is the understanding of mastitis that this chapter sets out to give.