To control digital dermatitis (DD), M2-stage lesions need to be treated as soon as possible after they are detected. Waiting more than a few days for the next time the trimmer is scheduled to visit will never get DD under control.
Dr. Dörte Döpfer has proposed ‘pen walks’ for detecting DD—heels are inspected while cows are confined in head locks. But, depending on barn lighting and alley cleanliness, clearly seeing and classifying lesions from a crouching position can be a real challenge. An alternative for parlour-milked herds is to inspect hind feet during milking.
Several studies have examined the accuracy of DD detection in the milking parlour compared with lifting feet in a trim chute. Although only hind feet can be examined by this method, hind foot lesions typically account for about 95% of DD cases.
Researchers at the University of Bristol (Stokes et al., 2012) used the borescope illustrated on the right to inspect hind feet in the parlours of 3 farms. Parlour screening was as accurate as the inspection of lifted feet in determining the presence of 86 DD lesions on 160 hind feet (99% agreement).
French researchers (Relun et al., 2011) inspected the cleaned hind feet of cows in the milking parlours of 4 farms using a swivelling mirror and headlamp immediately followed by inspection of lifted feet in a trim chute. Parlour inspection correctly identified 90% of the DD lesions detected in the trim chute (sensitivity = 90%); the method incorrectly diagnosed lesions on 20% of the feet where no visible lesions were observed in the trim chute (specificity = 80%).
In a Danish study (Thomsen et al., 2008), cleaned hind feet were examined directly (without using a mirror) in 3 different milking parlour configurations—herringbone, parallel and carousel. Accuracy estimates are summarized in the table below.
A recently-completed trial by Laura Solano and her colleagues at the University of Calgary’s Faculty of Veterinary Medicine has demonstrated that routine DD detection in the parlour is a viable alternative to both pen walks and detection at trimming. A total of 6,991 cleaned hind feet were inspected in the milking parlours of 9 Alberta dairy farms using a 7.5 cm square cosmetic mirror glued to an egg spatula with a head lamp providing extra illumination (shown in left photo). Results were compared with evaluation of feet lifted at trimming within 5 days of parlour inspection.
Sensitivity of the parlour inspection method was 92%, meaning that 92% of the DD lesions identified at trimming were also detected in the parlour. A specificity of 88% indicated that 88% of the hooves that were DD-free at trimming were also DD-free in the parlour.
Classification of specific M-stages in the DD infection cycle was less accurate. The highest sensitivity was found for the detection of M4 (81.3%) and M2 (59.9%) lesions; the lowest for detecting M3 (0.0%) and M1 (5.9%) lesions.
The researchers concluded that inspection of rear feet in the milking parlour was a reliable, economic and simple method to detect the presence of DD lesions although it was not accurate enough to replace definitive identification of M-stages in the trimming chute. Treatment of M2-stage lesions immediately after detection could result in a significant reduction in acute DD cases.