Effect of stage of lactation on the immune competence of goat mammary gland.

The present research was undertaken to evaluate the effect of stage of lactation on immune competence of the goat mammary gland. The prevalence and etiology of intramammary infections and cytokine pattern were studied in individual caprine milk during lactation. A total of 1,200 caprine milk samples were collected during early, mid, and late lactation (less than 40 d, from 110 to 130 d, and more than 200 d in lactation, respectively) and analyzed for milk quality, bacterial cell load, and cytokine pattern. Contagious and environmental pathogens associated with intramammary infection were isolated from caprine milk. Nutritional components of caprine milk were affected by stage of lactation; fat, protein, casein, and whey protein increased along with lactation due to the lowest milk yield. Lactose content showed an opposite trend, with a reduced percentage passing from early to late lactation. The impaired rheological properties detected in early and late lactation milk were associated with a modification of milk quality. An impairment of microbial quality was detected at the end of lactation as a consequence of a major susceptibility of mammary gland to infections. The percentage of bacteriologically positive caprine milk samples was 44% throughout lactation. The incidence of bacteria associated with intramammary infection was different according to the stage of lactation with a major prevalence of Staphylococcus aureus, Enterobacteriaceae, Staphylococcus hyicus, and Streptococcus uberis in early lactation milk, Staphylococcus chromogenes, Streptococcus bovis, and Staphylococcus epidermidis in mid lactation, and Pseudomonas aeruginosa and Staphylococcus caprae in late lactation milk. The higher values of IL-1β, tumor necrosis factor-α, and IL-6 were ascribed to the major prevalence of Staphylococcus aureus at the beginning of lactation, whereas a higher level of IL-10 was detected in mid-lactation caprine milk and correlated with Staphylococcus chromogenes. Monitoring the cytokine pattern in milk helps to understand the immune status of the mammary gland, its ability to cope with bacteria, and the evolution of infections.