Cellular defense mechanisms in the udder and lactation of goats.

Migration of neutrophils into mammary tissue provides the first immunological line of defense against bacteria that penetrate the physical barrier of the teat canal. Evasion of neutrophil defenses provides an opportunity for invading bacteria to become established. Depletion of neutrophils results in a dramatic increase in susceptibility to intramammary infection. Numerous cytoplasmic particles are shed from the apical surface of mammary secretory cells during milk secretion in goats. Only those counting methods that are specific for deoxyribonucleic acid can distinguish cell-like particles from somatic cells and thereby give reliable estimates of somatic cell numbers in goat milk. Unlike in milk from dairy cows, the somatic cell count in goat milk is influenced by the presence of nucleated cytoplasmic particles, stage of lactation, parity, and caprine arthritis-encephalitis. Investigations indicate that a dry period is necessary for optimal milk production in dairy cows but may not be necessary in goats. However, in many other respects regulation of bovine and caprine lactation seems to be quite similar. Studies have demonstrated additive galactopoietic effects of growth hormone and frequent milking in both species and a recently isolated chemical feedback inhibitor of lactation seems effective across both species. Increasing lactational performance has the potential for decreasing milk somatic cell counts in late lactation.