List of references:

6.1. Essential books (text books)

• Veterinary Clinical Epidemiology: A Problem- Oriented Approach (1995)/ by Roland D. Smith, 2^nd ed. CRC Press, Inc.
• Livestock Health and Housing (1979): David Sainsbury and Peter Sainsbury. Cassell Ltd, London.
• Essential Environmental Science (1996): Simon Watts and Lyndsay Halliwell. TJ Press (Padstow_ Ltd, Padstow, Cornwall.

6.3. Recommended books

• Farm animal and the environment (1992): Clive Philips and David Piggsins. C.A.B. International. UK.
• Disinfection in Veterinary and Farm Animal Practice (1987): A.H. Linton, W.B. Hugo and A.D. Russell. MacMillan Indial Ltd, Bangalore.
• Veterinary Epidemiology (1995): Michael Thrusfield, Blackwll Science Ltd.
• Risk Assessment and Management Handbook (1996): Rao V. Kollurn, Steven M. Bartell, Robin M. Pitdlado and R. Scott Stricoff. McGraw- Hill Inc, USA