Agalaxia contagiosa y calidad de la leche en la raza caprina majorera

Abstract

SUMMARY For this doctoral thesis it has been assessed the impact of contagious agalactia (CA) on quality and production of goat milk in the island of Lanzarote, in the Canary Islands. As specific objectives, experience 1 it has been studied the presence of agents involved in CA in goat herds of Majorera breed of Lanzarote island. In experience 2A, it has been evaluated the effect of the presence of Mycoplasma spp. chronical infections on bulk tank milk's quality of infected herds. In experience 2B, the effect of a clinical CA outbreak on the volume of milk produced by the herd was evaluated. As materials and methods for experience 1, a microbiological study has been performed in 31 herds with the aim to identify the mycoplasma species associated to the chronic infection, mainly analysing individual samples of milk. Our results indicated that, contrary to what it was observed in the Iberian Peninsula, Mycoplasma mycoides subsp. capri is the most frequently isolated species, (57%), followed by Mycoplasma capricolum subsp. capricolum (26%) and Mycoplasma agalactiae (10%), which should be taken into account when applying control and prevention strategies, such as antimicrobial therapy or vaccine prophylaxis. The conclusion of this experience is the confirmation of the emergent role of caprine CA in the appearance of subclinical mastitis in Lanzarote island. For experience 2 it was studied the effect of CA on physical-chemical quality of milk produced in herds from this island, which were chronically infected but asymptomatic. The methodology employed was based in the evaluation of several parameters such as fat percentage, total protein, lactose, total solids, standard plate count (SPC) and presence of Staphylococcus aureus, were evaluated in 13 infected herds and 13 herds considered as no infected by Mycoplasma spp. according to the results of the first experience. For this purpose, between 9 and 12 bulk tank milk samples from these herds were analysed monthly. The results concluded that the existence of CA did not have a significant effect on the quality of milk from bulk-tank for these herds and conditions. They were neither observed significant differences in bacterial counts or herds status for Staphylococcus aureus that could be attributed to mycoplasma infection. These findings invalidate the indirect use of these parameters, frequently analysed in the official milk tests for the detection of chronically infected herds, and suggest that the existence of asymptomatically infected herds would be underestimated. Furthermore, in experience 2B, it was also evaluated the effect of a clinical outbreak of CA on the volume of milk produced by a herd during previous and subsequent years to the clinical episode. With the basis of the methods employed for experience 2B, it was monitored a herd affected by a double clinical outbreak caused by Mycoplasma putrefaciens and Mycoplasma capricolum subsp. capricolum. The results obtained concluded that an acute outbreak of caprine CA causes significant milk production losses, between 8,52 % and 43,59 % of the milk average volumen per animal, what supposes a considerable economical impact of this disease in a herd suffering clinical episodes.These findings make clear the need of controlling the disease in Lanzarote island, increasing movement controls of animals with an unknown status regarding CA.