Evaluation of somatic cell count thresholds to detect subclinical mastitis in Gyr cows.

The objectives of this study were (1) to determine the sensitivity (Se) and specificity (Sp) of somatic cell count (SCC) thresholds to identify subclinical mastitis in Gyr cows caused by major and minor pathogens; (2) to study the effects of month of sampling, rear or front mammary quarters, herd, intramammary infection (IMI), and bacterial species on SCC at quarter level; and (3) to describe the prevalence of IMI in Gyr cows in commercial dairy herds. In total, 221 lactating Gyr cows from 3 commercial dairy farms were selected. Milk samples were collected from individual quarters once a month for 1 yr from all lactating cows for SCC and bacteriological analysis. Mammary quarters were considered the experimental units and the SCC results were log(10)-transformed. Four SCC thresholds (100, 200, 300 and 400 × 10(3) cells/mL) were used to determine Se and Sp to identify infected mammary quarters. The overall prevalence of IMI in quarter milk samples of Gyr cows was 49.8%, and the prevalence of minor pathogens was higher (31.9%) than that of major pathogens (17.8%). Quarter samples with microbial isolation presented higher SCC compared with negative samples. Sensitivity and Sp of selected SCC thresholds varied according to the group of pathogen (major and minor) involved in the IMI definition. Sensitivity increased and Sp decreased when mammary quarters with only major pathogens isolation were considered positive. The use of a single SCC analysis to classify quarters as uninfected or infected in Gyr cows may not be a useful test for this breed because Se and Sp of SCC at the studied thresholds were low. The occurrence of IMI and the bacterial species are the main factors responsible for SCC variation in mammary quarters of Gyr cows. Milk samples with major pathogens isolation elicited higher SCC than those with minor pathogens.

dos Reis CB ，Barreiro JR ，Moreno JF ，Porcionato MA ，Santos MV ... -  《-》

Dynamics of somatic cell counts and intramammary infections across the dry period.

Pantoja JC ，Hulland C ，Ruegg PL 《-》

Effect of coagulase-negative staphylococci on somatic cell count in Dutch dairy herds.

Sampimon O ，van den Borne BH ，Santman-Berends I ，Barkema HW ，Lam T ... -  《-》

Effect of somatic cell count and mastitis pathogens on milk composition in Gyr cows.

Malek dos Reis CB ，Barreiro JR ，Mestieri L ，Porcionato MA ，dos Santos MV ... -  《BMC Veterinary Research》

Diagnosing intramammary infections: evaluation of composite milk samples to detect intramammary infections.

Composite milk samples, in which milk from all 4 bovine quarters is collected in a single vial, are widely used in many developed dairy industries for detection of intramammary infections (IMI). These samples are more economical for use in culturing protocols than individual quarter samples, and may be useful when considering management options at the cow and herd level. The dilution effect may be problematic, however, resulting in lower sensitivity (Se) in IMI detection on composite samples. Relative Se and specificity (Sp) in composite samples have previously been described for some major pathogens, but because the causative organism for IMI is initially unknown, it is beneficial to investigate the reliability of composite samples for detection of all types of mastitis-causing bacteria. The Canadian Bovine Mastitis Research Network has a large data collection platform-the National Cohort of Dairy Farms-containing a vast amount of data on mastitis in Canada. These data have been used to further investigate the Se and Sp of composite samples in detecting IMI caused by specific mastitis pathogens. Milk samplings of selected cows before dry-off, after calving, and during lactation (n=48,835 samples) were employed to this end. Composite samples showed moderately high Se for Staphylococcus aureus (77.1%, 95% CI=73.3-80.5) and Streptococcus dysgalactiae (73.4%, 95% CI=60.9-83.7), with moderate Se for Streptococcus uberis (62.1%, 95% CI=49.3-73.8) and coagulase-negative staphylococci (59.8%, 95% CI=58.4-61.2). Sensitivities always increased as the number of affected quarters increased. Composite samples also showed high Sp (>97%) for most organisms. Factors such as lactation number and stage of lactation were evaluated for their influence on the Se and Sp of composite sampling, but were only found to be significant for coagulase-negative staphylococci. Predictive values using the herd prevalences found across Canada were calculated and can be useful in field scenarios when composite sampling is employed to assist mastitis management. When used to detect newly occurring IMI in pairs of samples taken before dry-off, post-calving, and also prior to and subsequent to the dry period, composite samples were shown to have lower Se but similar Sp for all pathogens investigated. Composite samples can be used to detect IMI and new IMI in dairy cows, but the Se and Sp of the procedure should be taken into account.

Reyher KK ，Dohoo IR 《-》