Milk Somatic Cells and Lactation in Small Ruminants

Abstract

The milk somatic cell count (MSCC) is the basis for abnormal milk control programs. The current legal MSCC limit for bulk tank milk for goats and sheep in the United States is 1000 and 750×103/ml, respectively. Milk somatic cell counts for goats are higher than MSCC for cows and sheep. The MSCC for goats free from intramammary infection (IMI) range from 270 to 2,000×103/ml. Cell counts for sheep are similar to cows and range from 10 to 200×103/ml. Neutro-phils comprise the major cell type in milk from uninfected goats and constitute 45 to 74% of the MSCC, compared with 2 to 28% for sheep and cows. The macrophage is the major cell type in milk from cows and sheep. Milk secretion in goats and sheep is largely apocrine in nature and cytoplasmic particles, similar in size to milk somatic cells, are normal constituents of their milk. Concentrations of cytoplasmic particles in sheep milk average 15×103/ml, while goat milk averages 150×103/ml. Therefore, to obtain accurate MSCC for goats, only cell counting procedures specific for DNA should be used. While IMI significantly increases MSCC for goats and sheep, noninfectious factors such as parity, stage of lactation, season and milk yield have been related to increased MSCC. An increase in MSCC for goats has been shown to decrease milk and fat yields. Intramammary infusion of antibiotics at dry-off and postmilking teat dipping in goats decreased the rate of new IMI and MSCC. Thus, mastitis control practices shown to be efficacious in cows are also effective in goats.