CELLULAR DEFENSE-MECHANISMS IN THE UDDER AND LACTATION OF GOATS

Migration of neutrophils into mammary tissue provides the first immuno logical line of defense against bacteria that penetrate the physical b arrier of the teat canal. Evasion of neutrophil defenses provides an o pportunity for invading bacteria to become established. Depletion of n eutrophils results in a dramatic increase in susceptibility to intrama mmary infection. Numerous cytoplasmic particles are shed from the apic al surface of mammary secretory cells during milk secretion in goats. Only those counting methods that are specific for deoxyribonucleic aci d can distinguish cell-like particles from somatic cells and thereby g ive reliable estimates of somatic cell numbers in goat milk. Unlike in milk from dairy cows, the somatic cell count in goat milk is influenc ed by the presence of nucleated cytoplasmic particles, stage of lactat ion, parity, and caprine arthritis-encephalitis. Investigations indica te that a dry period is necessary for optimal milk production in dairy cows but may not be necessary in goats. However, in many other respec ts regulation of bovine and caprine lactation seems to be quite simila r. 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 s pecies. Increasing lactational performance has the potential for decre asing milk somatic cell counts in late lactation.