Comparing genetic indexes for reducing lameness in dairy cows

WE wish to follow up on our recent study1 where we aimed to evaluate the lameness advantage genetic index by quantifying its association with claw horn lesions and lameness in 2352 Holstein cows. A secondary objective was to screen all genetic indexes (other than lameness advantage) for an association with the same outcomes, which showed that both feet and legs and locomotion (assessed in type classification) were associated with lameness, but not with claw horn lesions. This suggests that selecting on these indexes would result in fewer lame cows, but not fewer claw horn lesions. As mobility scoring has a limited sensitivity to detect foot lesions, likely due in part to an evolutionary advantage of cattle masking signs of pain, it is important not to exacerbate this problem with genetic selection. Lameness advantage is associated with both sole lesions and lameness, as well as infectious lesions;2 we believe this is the best option for those aiming to improve foot health through selective breeding.In recent discussions with farmers and others, it has been useful to not only compare genetic indexes by the presence/absence of an association with foot health, but also by the strength of that association. Unfortunately, our analysis was not designed for the latter purpose because we analysed each index in its original units. That means, for example, the effect of the profitable lifetime index (£PLI) appeared very small but related to a £1 change in an index that ranged from about –£400 to +£600 in our data; whereas lameness advantage ranged from about –3 to +4.5, with each unit representing a larger change within the spread of values. We have reanalysed our data after scaling each genetic index so a single unit represents an equivalent shift in the distribution for all indexes.3 This allows the strength of the association between genetic indexes and claw horn lesions and lameness to be directly compared, which we think is useful when deciding on a breeding strategy. Without room to discuss these additional results in full, we would like to highlight that lameness advantage has the strongest association with the likelihood of cows developing sole haemorrhage or sole ulcers, as well as one of the strongest associations with lameness. Increasing the average value of the lameness advantage genetic index in dairy herds can complement management and environmental strategies, such as the AHDB ‘Healthy Feet Programme’,4 to reduce lameness in dairy cows