Short communicationPresence of Mycoplasma species and somatic cell counts in bulk-tank goat milk
Introduction
Contagious agalactia (CA) is an infectious syndrome caused by several species of mycoplasma, which affects small ruminants. Mycoplasma agalactiae is considered as the classic etiological agent of CA, but other species are now known to cause the disease, especially in goats: Mycoplasma mycoides subsp. mycoides large colony type (MmmLC), Mycoplasma capricolum subsp. capricolum and occasionally Mycoplasma putrefaciens. The clinical signs of CA are the typical triad of mammary, joint and eye symptoms, although respiratory symptoms and occasionally reproductive or other symptoms may appear (Bergonier et al., 1997, Damassa et al., 1992, Gil et al., 2003). However, in endemic areas, clinical outbreaks of the disease are sporadic.
In addition to clinical consequences, CA generates economic costs due to treatments, veterinary assistance and vaccinations, combined with the effects of genetic resource losses via mortality or culling of selected animals affected by the disease (Bergonier et al., 1997, Corrales et al., 2007), but its main effect is on milk production and quality. Intramammary infection causes significant increases in goat milk somatic cell counts (SCC) (Paape et al., 2001, Luengo et al., 2004) and animals with mycoplasma-related mastitis show a large increase in their milk SCC (Poutrel et al., 1996). This effect is not as clear in asymptomatic mycoplasma-infected animals, which could eliminate mycoplasma throughout milk without symptomatology (Bergonier et al., 1997, Contreras et al., 1996). Also, many non-infectious factors are also responsible for variation in SCC in goat milk (Haenlein, 2002, Paape et al., 2007, Raynal-Ljutovac et al., 2007). The increase in bulk-tank milk SCC (BTMSCC) had been demonstrated in CA clinically affected herds in goat (Corrales et al., 2004) and sheep (Gonzalo et al., 2005) but the literature lacks information on the BTMSCC situation for asymptomatically infected herds. In addition, milk producers currently have to comply with the high quality standards demanded by consumers, industry or public health organizations. A legal limit of 1,000,000 cells/ml has been established for goat BTMSCC in the USA (Haenlein and Hinckley, 1995), but only a limit for bovine BTMSCC has been set in the European Union (EU) (Anon, 1992). Instead of an official limit for goat BTMSCC at a EU level, some European countries have set their owns limits for small ruminants BTMSCC (Pirisi et al., 2007). The economic importance of the effects of CA is magnified since the endemic CA areas – such as most Mediterranean countries – have highly productive sheep and goat dairy breeds (Haenlein, 2007). Given that the BTMSCC may be used as a possible surveillance strategy against mycoplasma-related mastitis and also used for the differential payment schemes established by the industry, the present study was designed to determine the effect of the presence of mycoplasmas from the bulk-tank milk on the BTMSCC.
Section snippets
Materials and methods
A cross-sectional study was carried out during the natural lactation period of goat herds (November–June). In total, 1068 bulk-tank milk samples were obtained to determine the presence of mycoplasmas and SCC. Samples were collected by the dairy company at the time of milk collection. Each milk tank was also sampled for fat and protein determinations, by which prices are fixed. Samples from the bulk-tanks were preservative-free, transported and refrigerated to the laboratory. Once at the
Results
Of the 1068 bulk-tank milk samples tested, 84 (7.9%) were positive for the presence of Mycoplasma species. Most of the species isolated were M. agalactiae (82%), which was detected in 69 bulk-tank milk samples; MmmLC was detected in 14 bulk-tank milk samples (17%) and, in one bulk-tank milk sample, both Mycoplasma species appeared together. The geometric mean of the BTMSCC for the 1068 samples was 896,000 cells/ml. Our ANOVA revealed a higher SCC in bulk-tank samples containing mycoplasmas than
Discussion
Monitoring bulk-tank milk for contagious pathogens, such as Mycoplasma spp., is a good diagnostic tool and the first step in the diagnosis of mycoplasma-related mastitis in dairy cow herds (Gonzalez et al., 1992, Fox et al., 2003, Olde Riekerink et al., 2006). However, little information is available on mycoplasma detection in the bulk-tank milk for goat herds. In the present report, the presence of mycoplasma was demonstrated in around 8% of the goat bulk-tank milk samples examined, but this
Conclusion
The presence of Mycoplasma spp. in bulk-tank goat milk increases the risk of being above the thresholds for milk payment. Therefore its presence increases the clinical effects with more economic consequences in endemic areas and it is a further incentive to encourage the implementation of specific programs for disease control.
Acknowledgements
This work was financed by the Spanish Ministry of Education and Science Project AGL2006-03105/GAN (Plan Nacional de I+D. Ministerio de Educación y Ciencia). The authors also thank Dr. José B. Poveda (Veterinary School, ULPGC, Arucas, Gran Canaria, Spain) and Dr. Dominique Bergonier (Veterinary School, U. de Toulouse, France) for confirmation of our Mycoplasma spp. identifications.
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