Investigating the impact of mastitis on dairy cows
The animal article of the month for December is entitled ‘Impact of subclinical and clinical mastitis on sensitivity to pain of dairy cows’
Concern about dairy cows welfare is not a new issue, but there is a huge variation among farm producers and veterinarians about their perception of pain in domestic animals.
Although severe clinical mastitis is usually considered painful and high scores of pain were acknowledged by farmers and veterinarians, subclinical mastitis is not usually considered painful or a source of distress to the animals. Mastitis may elicit higher pain sensitivity as the resulting inflammatory process induces alterations in the nociceptive pain information processing and may provoke hyperalgesia and exaggerate answer to painful stimuli.
In the present study, ninety Jersey cows were selected from commercial dairy herds, and they were evaluated for mammary gland health condition, somatic cells count (SCC) in the milk, and pain sensitivity was evaluated as the thermal nociceptive threshold. Thermal nociceptive threshold was measured applying a thermal stimulus at the dorsal region of the middle phalanges of both rear legs, just above the hoof and observing the foot-lift response.
Cows were considered healthy when they present low SCC (less than 200 000 cells/ml and no visual alterations in milk and/or udder), with mild or moderate subclinical mastitis when they do not show visual alterations in milk and/or udder but present intermediary level of SCC (more than 200 000 or 500 000 cells/ml) and with clinical mastitis when visual alterations in milk and/or udder were detected, as heat, swelling and discoloration of the udder, abnormal secretion.
In the present research, we show that moderate subclinical mastitis tended to decrease thermal nociceptive threshold despite non noticeable alterations in the udder or milk, and suggest that this might be related to higher concentrations of chemical mediators which could enhance vasodilatation and pain sensitivity. We also found that log10SCC above 6.4 sharply decreased thermal nociceptive threshold values probably meaning increased sensitivity to pain.
Changes in the behavior of animals has been studied as a tool for early diagnosis of diseases or physiological or metabolic disturbances before the onset of clinical symptoms. Interestingly, animals can exhibit changes in behavior and / or sensitivity to pain before the onset of clinical symptoms. On the other hand, the trend of increased sensitivity to pain of cows with subclinical mastitis might warn farmers and technicians to improve or adopt animal care procedures before the onset of clinical symptoms as apparently cows might be distressed even without visual alterations in the udder or milk.
The full article is freely available for one month via journals.cambridge.org/anm/dec15
Authors: M. D. P. Peters, I. D. B. Silveira and V. Fischer
The animal Article of the Month is selected by the Editor-in-Chief and is freely available for one month