Determination of milk production losses in Valle del Belice sheep following experimental infection of Mycoplasma agalactiae

Abstract

tEconomic losses due to contagious agalactia (CA) in small ruminant herds are mainlyassociated with significant reductions in or complete loss of dairy production, mortality,abortions, ill thrift, early culling and costs of control. With the aim of estimating milk pro-duction losses caused by CA, 46 primiparous lactating Valle del Belice ewes were monitoredafter experimental infection. Sixty days after lambing, two ewes were each experimentallyinfected with a single dose of 108CFU/ml of a live Mycoplasma agalactiae strain in both teatsby intracanalicular route. Three days after inoculation, the infection was spread manuallyby the milkers dipping their hands in the pooled milk from the experimentally infectedewes just before milking each of the uninfected sheep. The milk yield was recorded daily(morning and evening) for 12 weeks: 5 weeks before and 7 weeks after infection. Daily milkdata, collected from each ewe, were used to design individual lactation curves in order toestimate the impact of CA infection. Individual milk samples were screened for the presenceof M. agalactiae as well other pathogens which cause mastitis in small ruminants compris-ing Staphylococcus aureus, coagulase negative-staphylococci (CNS), Corynebacterium spp.and Streptococcus spp. No pathogens were detected in the milk of 10 (22%) of the 46 eweskept with the experimentally infected sheep. There was a reduction of 17% in milk out-put of 19 (41%) ewes from which M. agalactiae was isolated; the 17 (37%) remaining eweshad a similar drop in milk production but recovered quickly within 2–3 weeks, so the finallosses were estimated to be 3%. The infected milk showed a significantly higher somaticcell count when mycoplasma excretion in milk was >103CFU/ml. Percentages of milkprotein and casein were higher in milk excreting M. agalactiae due to concentration, in con-trast the percentage of lactose in the milk was significantly lower. No significant effect ofM. agalactiae was found on the percentage of milk fat.In conclusion, the loss of milk following CA infection is variable and probably related tothe degree of exposure and capacity of the individual ewe to resist the pathogen.