Intramammary infection in heifers: the application of infrared thermography as an early diagnostic tool

[摘要] Mastitis is mainly caused by intramammary infection (IMI) with bacteria. Heifer IMI in early lactation impacts negatively on welfare, milk production and longevity in the herd. Prevention of subclinical and clinical mastitis caused by IMI with major pathogens, such as Streptococcus uberis and Staphylococcus aureus, could be improved if more information about the origin of heifer IMI were available. The challenges of establishing when in the pre- or peri-partum period the infection occurs make targeting of preventive management difficult. It usually requires the collection of mammary secretion prior to calving through invasive techniques, which can in itself contribute to an increased risk of infection. Non-invasive techniques, such as infrared thermography (IRT) have been applied and validated as a method for diagnosing mastitis in adult cows in controlled environmental conditions, but not in heifers under field conditions. Therefore, this study aimed to evaluate the usefulness of IRT for early detection of IMI in primigravid dairy heifers in the last trimester of gestation. The study was conducted on a commercial dairy farm with approximately 700 lactating cows. One hundred and twenty Holstein-Friesian heifers in the last trimester of gestation were enrolled in the study. IRT images of the udders were collected before calving (the first set two months prior to estimated calving date and the second set two weeks prior to estimated calving date), using a FLIR E300 infrared camera. Each set of IRT images included two projections of the udder, one caudocranial and one ventrodorsal, whereby the caudocranial projection is commonly used in lactating cow studies but the ventrodorsal projection data is easier to collect. IRT images were analysed using the geometric analysis tool of ThermaCAM Research 2.10 Pro software to obtain descriptive parameters. At calving, colostrum samples were collected aseptically from individual quarters for standard aerobic bacteriological culture and somatic cell count measurement by flow cytometry. IMI was defined as the presence of ≥10 colony-forming unit (cfu) per culture plate. Udder temperature gradients were used for the statistical analysis. Synchronization of IRT image collection with farm routines allowed for easy, fast and non-invasive collection of udder surface temperature data. IMI prevalence measured by bacterial culture of colostrum from all quarters was 20% with the majority of bacteria isolated belonging to the group of coagulase negative staphylococci (CNS; 89.7%). SCC geometric means at calving were 336, 365 and 867 (x1000 cells/ml) for mammary quarters that were culture-negative, culture-positive with <10 cfu/plate and IMI positive, respectively. Ventrodorsal projection of the udder could replace caudocranial projection for assessment of udder surface temperature, based on the strong correlation between temperature data from both projections (e.g. r = 0.91 and r = 0.97 for dT’max’ two months prior to calving and 2 weeks prior to calving, respectively). In addition, the ventrodorsal projection allowed for the detection of a lower maximum temperature in quarters with likely worst outcome (IMI, major pathogen and higher SCC). Nevertheless, IRT was unreliable as predictor of IMI with minor pathogens or elevated SCC (p > 0.05; binomial logistic regression and ordinal logistic regression, respectively). The method had very limited accuracy for discrimination between infected and not infected quarters (area under the receiver operating characteristic curve close to 0.5). Thus, although the collection of IRT data is a practical and non-invasive method that can easily be incorporated into the heifer management routine on a large dairy farm, it cannot be recommended as a screening tool for early and non-invasive detection of heifer IMI before calving.

[发布机构] University:University of Glasgow;Department:School of Veterinary Medicine

[关键词] SF600 Veterinary Medicine