Date Published: May 18, 2011
Publisher: BioMed Central
Author(s): Ditte B Rasmussen, Katrine Fogsgaard, Christine M Røntved, Ilka C Klaas, Mette S Herskin.
Mastitis is a high incidence disease in dairy cows. The acute stage is considered painful and inflammation can lead to hyperalgesia and thereby contribute to decreased welfare. The aim of this study was to examine changes in nociceptive responses toward cutaneous nociceptive laser stimulation (NLS) in dairy cows with experimentally induced Escherichia coli mastitis, and correlate behavioral changes in nociceptive responses to clinical and paraclinical variables.
Seven Danish Holstein-Friesian cows were kept in tie-stalls, where the E. coli associated mastitis was induced and laser stimulations were conducted. Measurements of rectal temperature, somatic cell counts, white blood cell counts and E. coli counts were conducted. Furthermore, scores were given for anorexia, local udder inflammation and milk appearance to quantify the local and systemic disease response. In order to quantify the nociceptive threshold, behavioral responses toward cutaneous NLS applied to six skin areas at the tarsus/metatarsus and udder hind quarters were registered at evening milking on day 0 (control) and days 1, 2, 3, 6 and 10 after experimental induction of mastitis.
All clinical and paraclinical variables were affected by the induced mastitis. All cows were clinically ill on days 1 and 2. The cows responded behaviorally toward the NLS. For hind leg stimulation, the proportion of cows responding by stepping was higher on day 0 than days 3 and 6, and the frequency of leg movements after laser stimulation tended to decrease on day 1 compared to the other days. After udder stimulation, the proportion of cows responding by stepping was higher on day 1 than on all other days of testing. Significant correlations between the clinical and paraclinical variables of disease and the behavioral responses toward nociceptive stimulation were found.
Changes in behavioral responses coincide with peaks in local and systemic signs of E. coli mastitis. During the acute stage of E. coli mastitis nociceptive thermal stimulation on hind leg and mammary glands results in decreased behavioral responses toward nociceptive stimulation, which might be interpreted as hypoalgesia.
Mastitis is a frequent production-associated disease in dairy cows, and is considered painful in the acute stage [1-4]. The severity of mastitis depends on the pathogen, host and environmental factors [5-7]. Escherichia coli provoke acute clinical mastitis characterized by marked increase in local inflammatory mediators accompanied by a strong systemic acute phase response. Cows are more sensitive to bacterial infection in early lactation, where local and systemic inflammatory signs are stronger than in mid or late lactation [7,8].
Bacteriological and clinical examinations confirmed E. coli mastitis in 7 cows (Figure 2 and 3). Rectal temperature (F5,41 = 14.7, P < 0.001), SCC (F5,40 = 12.2, P < 0.001), WBC (F5,41 = 6.1, P < 0.001), milk (χ2 = 24.3 with 5 df, P < 0.001) and udder appearance (F5,41 = 14.4, P < 0.001), anorexia (χ2 = 22.8 with 5 df, P < 0.001) and E. coli count (χ2 = 29.2 with 5 df, P < 0.001) all changed after inoculation of E. coli. This is the first report to present behavioral responses of mastitic dairy cows toward NLS directed at hind legs and caudal udder. The study shows that the cows responded behaviorally toward NLS directed at the udder, as shown by avoidance movements of the hind legs. One day after the inoculation of E. coli into the mammary gland, the cows developed acute local and systemic clinical signs of mastitis, classified as mild to moderate [8,17]. At this time, an increased proportion of behavioral responses with the least forceful leg movement - stepping - was observed. Furthermore, leg movements during the 30 sec period after the NLS tended to be decreasing. These changes suggest that the cows experienced hypoalgesia associated with the acute clinical mastitis. The findings are quite unexpected as the release of inflammatory mediators in the udder at a high level is expected to increase the risk of hyperalgesia . Furthermore, the results are in contradiction with findings by Fitzpatrick et al.  who showed evidence of a period of hyperalgesia in dairy cows after spontaneous mastitis. However, the present data confirm our previous findings of increased nociceptive threshold in mastitic dairy cows . Unfortunately, neither the present study nor our previous study  included stimulation with a non-painful stimulus thus limiting the possibility to conclude whether the decreased responses were due to hypoalgesia or a generalized decreased reactivity. Changes in behavioral responses toward NLS directed at hind legs and caudal udder of mastitic dairy cows coincided with peaks in local and systemic signs of E. coli mastitis. During the acute stage of E. coli mastitis, NLS on hind legs and mammary glands led to decreased behavioral responses, which may be interpreted as hypoalgesia. The authors declare that they have no competing interests. DBR participated in the design of the study, carried out the pilot study and the tests of pain sensitivity, the clinical registrations as well as drafted the first version of the manuscript. MSH enabled lending of the laser equipment, participated in the design of the study, pilot study and performed the statistical analysis. KF has drafted major parts of final manuscript, the graphical figures and contributed to the statistical analysis. CMR was responsible for the experimental induction of mastitis, paraclinical measurements and for the overall experimental plan. ICK contributed to draft the manuscript. All authors read and approved the final manuscript. Source: http://doi.org/10.1186/1751-0147-53-32