Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/9/1998
Publication Date: N/A
Interpretive Summary: Milk somatic cells, which consists of leukocytes and epithelial cells, are used as a parameter for the evaluation of milk quality and as a management tool used by dairymen. Diseases of the mammary gland causes an increase in the milk somatic cell count. While the "Milk Somatic Cell Count" is an accepted and validated procedure for evaluating cow milk, scientists in the Immunology and Disease Resistance Laboratory, USDA-ARS, Beltsville, MD, found that it is not applicable to goat milk. Milk somatic cell counts for uninfected goats are higher than counts for uninfected cows. Factors other than intramammary infection such as stage of lactation, parity and caprine arthritis-encephalitis virus infection contribute to an elevation of milk somatic cell counts for goats. Currently, the somatic cell count limit is one million cells/ml for goat milk and 750 thousand cells/ml for cow milk. There is pressure by regulatory agencies to lower the limit for goat milk to that for cow milk. Lowering the cell count limit below one million would seem inappropriate in light of this present research information, for it would take us into that gray area where the cellular response of infected and uninfected glands would overlap. Lowering the limit would result in the unnecessary dumping of goat milk, place an unfair economic burden on goat dairymen and unjustly drive goat dairymen in "Rural America" out of business. Studies are needed to establish a somatic cell count limit for goat milk.
Technical Abstract: One herd with 138 lactating goats experiencing a high milk Somatic Cell Counts (SCC) was studied. Foremilk was sampled for bacteriology and SCC at two samplings 28 d apart on Dairy Herd Improvement Association (DHIA) test day. Blood samples were obtained for serological analyses of caprine arthritis-encephalitis virus. Bacterial Intramammary infection (IMI) was defined as the same pathogen being isolated twice from the same udder half. Prevalence of IMI was 34%. Most of the pathogens isolated (95.7%) were Staphylococcus spp. Staphylococcus epidermidis was the predominant species (66.7%), and most had similar biochemical profiles. Prevalence of infection by caprine arthritis-encephalitis virus was 94.3%. Composite DHIA SCC averaged 10 6/ml for the first sampling and 1.27 X 10 6/ml for the second. Uninfected right and left udder halves had lower foremilk SCC (1.3 and 1.0 X 10 6/ml) than infected right and left udder halves (1.74 and 1.66 X 10 6/ml). Halves infected by S. epidermidis averaged higher SCC (1.8 X 10 6/ml) than halves infected by other staphylococci (1.5 X 10 6/ml). Milk SCC increased with increasing parity.