Use of DNA based methods such as real-time Polymerase Chain Reaction (PCR) have increased sensitivity and shortened time for bacteria identification, compared to traditional bacteriology; however, results should be interpreted carefully because a positive PCR result does not necessarily means that there is an infection. One-hundred and eight lactating dairy ewes (Manchega, 56; Lacaune, 52) and 24 Murciano-Granadina dairy goats, were used for identifying the main bacteria causing intramammary infections (IMI) using traditional bacterial culturing and real-time PCR and their effects on milk performances. Udder half milk samples were taken for bacterial culturing and somatic cell count (SCC) three times throughout lactation. IMI was assessed based on bacteria isolated in ≥2 samplings accompanied by increased SCC. Prevalence of subclinical IMI was 42.9% in Manchega, 50.0% Lacaune and 41.7% in goats, estimated milk yield loss being 13.1%, 17.9% and 18.0%, respectively. According to bacteriology results, 87% of the identified single bacteria specie (with more than 3 colonies/plate) or culture-negative growth were identical throughout samplings, which agreed 98.9% with the PCR results. Nevertheless, the study emphasized that one sampling may not be sufficient to determine IMI and therefore, other inflammatory responses such as increased SCC should be monitored to identify true infections. Moreover, when PCR methodology is used, aseptic and precise milk sampling procedure is the key for avoiding false positive amplifications. In conclusion, both PCR and bacterial culture methods proved to have similar accuracy for identifying infective bacteria in sheep and goats. Final choice will depend on their response time and cost analysis, according to the requirements and farm management strategy.

Journal of Dairy Science (Impact Factor: 2.57). 05/2014

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