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

Abstract Economic losses due to contagious agalactia (CA) in small ruminant herds are mainly associated 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 production losses caused by CA, 46 primiparous lactating Valle del Belice ewes were monitored after experimental infection. Sixty days after lambing, two ewes were each experimentally infected with a single dose of 10 8  CFU/ml of a live Mycoplasma agalactiae strain in both teats by intracanalicular route. Three days after inoculation, the infection was spread manually by the milkers dipping their hands in the pooled milk from the experimentally infected ewes 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 milk data, collected from each ewe, were used to design individual lactation curves in order to estimate the impact of CA infection. Individual milk samples were screened for the presence of M. agalactiae as well other pathogens which cause mastitis in small ruminants comprising Staphylococcus aureus , coagulase negative-staphylococci (CNS), Corynebacterium spp. and Streptococcus spp. No pathogens were detected in the milk of 10 (22%) of the 46 ewes kept with the experimentally infected sheep. There was a reduction of 17% in milk output of 19 (41%) ewes from which M. agalactiae was isolated; the 17 (37%) remaining ewes had a similar drop in milk production but recovered quickly within 2–3 weeks, so the final losses were estimated to be 3%. The infected milk showed a significantly higher somatic cell count when mycoplasma excretion in milk was >10 3 CFU/ml. Percentages of milk protein and casein were higher in milk excreting M. agalactiae due to concentration, in contrast the percentage of lactose in the milk was significantly lower. No significant effect of M. agalactiae was found on the percentage of milk fat. In conclusion, the loss of milk following CA infection is variable and probably related to the degree of exposure and capacity of the individual ewe to resist the pathogen.