The approach has attracted positive comments, and it is hoped that production
losses associated with sub-clinical infections will not be a deterrent to the long term
implementation of this strategy by the livestock producers.
3 Mastitis Control in Dairy Cows
Mastitis, an inflammatory response of the mammary gland, usually caused by
bacterial pathogens, is one of the most important endemic infectious diseases to
affect dairy cattle. Mastitis has an impact on animal production, animal welfare and
the quality of milk produced. Mastitis is typically recognised by clinical signs
expressed as abnormalities in the milk and the udder. Infection can affect one or
more of the four mammary quarters of the cow’s udder. The disease is usually local
but, in acute cases, may trigger systemic signs of pyrexia, anorexia and depression.
Severe clinical mastitis may terminate with the cow’s death or agalactia of the
infected quarter(s), leading to premature culling. Based on the epidemiology of the
causative bacterial pathogen, bovine intramammary infections can be categorised
as contagious or environmental in origin. Contagious mastitis can be described as
intramammary infection transmitted from cow to cow, wherein the primary reser-
voir of pathogens is infected quarters. Uninfected quarters are mainly exposed to
contagious pathogens during the milking process. The bacteria responsible for such
infections include streptococci (Streptococcus agalactiae,Streptococcus dysgalac-
tiae), coagulase positive staphylococci (Staphylococcus aureus), coagulase nega-
tive staphylococci (CNS) andCorynebacterium bovis. On the other hand, the
primary reservoir of pathogens responsible for environmental mastitis is the dairy
cow’s environment. Uninfected quarters may be exposed at any time during the
cow’s life, including during milking, between milkings and during the dry period
(the dry period, typically 40–50 days long, is the phase of milking cessation that
precedes the next calving). The primary pathogens are Gram-negative bacteria,
mainly Enterobacteriaceae (Escherichia coli, Klebsiellasp., Enterobactersp.,
Serratiasp.,Proteussp. andPseudomonassp.), environmental streptococci (mainly
Streptococcus uberis) and enterococci (Enterococcus faecalis) (Oliver 1998 ).
Intramammary infection of the dairy cow is much less common than 40 years
ago due to the implementation of udder health strategies. One such dairy health
programme is the five-point plan introduced in the UK in the early 1970s. At that
time, the vast majority of mastitis cases in the British herd were caused by
contagious pathogens, principallyS. aureusandS. agalactiae. The plan advocated
treating and recording all cases of clinical mastitis, performing post-milking disin-
fection of all teats immediately after every milking, instituting dry cow therapy
(DCT) of all cows at the end of every lactation, culling of chronic cases of mastitis
and carrying out regular milking machine maintenance. As a consequence of the
application of this control plan, the incidence of mastitis caused by contagious
pathogens has decreased markedly (Jones and Ohnstad 2002 ). For example, at the
Institute for Animal Health (UK) herd, 43% of mastitis cases were caused by
124 H. Benchaoui