SUB CLINICAL MASTITIS: A THREAT TO DAIRY FARMERS

By-

J B Rajesh, Malsawmtluangi Ralte, Hridayesh Prasad, Kalyan Sarma and Chethan G E

Department of Veterinary Medicine

College of Veterinary Sciences and Animal Husbandry

Central Agricultural University

Selesih PO, Aizawl, Mizoram: 796015

Corresponding author: LEOVET@GMAIL.COM

In 2005, India’s contribution was 1/10th global milk production, but as of now we are contributing 1/6th global milk output. On an average India’s growth in milk production is 4% per annum and it is 2.1% for other countries. India is leading in the whole world in total milk production and it accounts for 19% of total milk production of the world with 150 million tones of milk production every year. The white revolution, operation flood and the technology mission on dairy development brought a steady increase in milk production and consumption in India. Per capita availability of milk in India is 337 gram/day and average world per capita availability of milk is 229 gram/day.

Mastitis is the infection to intra mammary tissue and it can be clinical or subclinical mastitis (SCM). In the clinical forms of mastitis, inflammation is characterized grossly by swelling, heat, redness, pain and disturbed function, whereas the existence of inflammation in the absence of gross signs is referred to as subclinical mastitis. Presence of an infection without apparent systemic involvement or inflammatory changes in udder is described as subclinical mastitis. But in some cases abnormal milk for a brief period or inflammatory changes in udder can be noticed. It is worth to mention that SCM is more common than clinical mastitis. Clinical mastitis is alarming to a farmer in a dairy herd and treatment is given immediately to control it. Subclinical Mastitis causes sub optimal performance in production without identifiable lesions. Subclinical mastitis, which cannot be identified without a laboratory or field test, mostly remains unnoticed by the farmers. The loss of an individual farmer was largely dependent upon the prevalence of subclinical mastitis in the herd.

Many infective agents have been implicated as causes of mastitis in cattle. They are bacteria, fungi, mycoplasmas and viruses. The bacterial pathogens alone accounts for about 90% of mastitis cases. Apart from bacteria, yeast, fungi and moulds have been isolated. In India, Staphylococci have been reported as the chief aetiological agents of both clinical and sub-clinical bovine mastitis. Escherichia coli have been reported as the predominant coliform organisms encountered in bovine mastitis.

The pathological changes in glandular tissues ranges from very mild to severe form, from per acute to chronic form and from subclinical to gangrene. Mastitis is the most common and the most expensive disease of dairy cattle throughout the world. In terms of economic loss it is the most important disease which the dairy industry has to contend. The loss is mainly from decrease in milk production and deterioration of quality of milk, expenses and therapeutic loss due to antibiotic contaminated milk and extra labour. Most estimates show that on the average an affected quarter suffered a 30 % reduction in productivity and an affected cow was estimated to lose 15 % of its production for lactation. Mastitis causes an annual loss of Rs. 72 billion in India as per 2009 estimation and about 60% of this constituted loss from SCM.

Comparatively the literature on the incidence of subclinical mastitis is fewer than that on the incidence of clinical mastitis because clinical mastitis attracted more attention of a dairyman. But due to the economic importance, SCM is recognised as a herd problem and the loss is nearly three times that of clinical mastitis, whereas clinical mastitis is an individual problem. Mastitis has been investigated over 100 years but progress in its control has been not yet satisfactory. The reasons for this are complex. Mastitis is caused by several types of infections, each with a different etiology. The high incidence of udder disease is enough evidence that the present methods of control, based mainly on the treatment of the clinical cases are ineffective.

Bovine mastitis is one of the stumbling blocks in achieving self sufficiency in milk production in many countries including developed countries throughout the world. This led to one of the greatest challenges to the veterinary profession. To meet these challenges, more cows of better genetic makeup shall have to be raised and the dairy farmers will be forced to further intensify herd management. Increase in herd size, intensification, complacency and ignorant of the control measures necessary to achieve sufficiently high standards of husbandry, hygiene and milk practices will ensure that mastitis remains an enzootic disease.

The subclinical form is detectable mainly by tests applied to the milk for the demonstration of products of inflammation and by the changes in chemical compositions. A quarter Somatic Cell Count (SCC) threshold of >200,000 cells/ml is considered to have subclinical mastitis. Most often the SVCM goes undetected and the continuing effects on milk yield cause economic loss. Another aspect of SCM is maintenance of reservoir of infection within the herd apart from the low production potential.

Infected quarters and infected teat sores and dissemination of pathogens from cow to cow by hands and clothes of milkers and milking equipment remained the major sources of pathogens. The possibility of control by simple practical hygienic measures like hand and udder washing with disinfectant solutions and use of paper towels or individual clothes, and teat-dipping immediately after milking coupled with use of antibiotic therapy for eliminating established infection of subclinical mastitis and clinical mastitis was highly emphasized.

There are two main essentials for an effective control scheme:

(1) a method of preventing or greatly reducing the rate at which new infections occur, i.e. reducing the number of new cases of subclinical and clinical mastitis

(2) Methods of eliminating infections, i.e. reducing the duration of infections.

The loss due to subclinical mastitis can be reduced by treating the cases with sensitive antibiotics and associate medicaments. The discarded milk can be pasteurized and can be fed to calves. Periodic screening of the herd is a measure to identify the cows with SCM. Chronic cases should be culled and disposed off. Effective managemental practices can be adopted to control the infection.

Organisms transferred by direct contact with environmental sources could be reduced by proper maintenance of stalls and yards, but there appeared to be no practical means of eliminating this mode of transfer. The use of clean fresh bedding materials and semi-permanent smooth surfaces would reduce the degree of contamination and the potential risk of new infections.

Heavy reliance on the use of antibiotics will continue to control mastitis as there are no prophylactic vaccines against the ailment, nor are there any preventive measures which are fully dependant. The obstacle in effective control of bovine mastitis is due to the emergence of resistant bacterial strains to various antimicrobial agents, due to their wide and indiscriminate usage, high monetary involvement in the treatment of cases caused by such drug resistant pathogen with newer antibiotics and the undesirable antibiotic residues in milk. However, the selection of most favourable drugs to meet the resistance properties of infective organisms is most essential.