Research Bite One: The effect of exercise on first lactation lameness

A trial undertaken by Massey University in New Zealand has attempted to reduce levels of lameness experienced by dairy heifers using exercise during the rearing period. The hypothesis that exercise would improve the functional anatomy of the foot was first conceived through a USA study published in 2015 by Gard et al. James Wilson, Foot Health Consultant, explains more.

In the randomised controlled trial (RCT) that the USA study implemented, they identified that weaned male dairy calves exercised over rough terrain for four months (n = 10) had a larger digital cushion than control animals exposed to normal farm conditions (n = 10), see Figure 1. This was taken as a measure at the end of the trial, when the calves were six months old, using MRI scanners. From that work, the hypothesis arose that exercising young dairy heifers over rough terrain may aid in the development of a robust digital cushion.

This hadn’t been tested until the recent RCT published by Mason et al. (2022) in New Zealand (NZ). Within that study, 790 mature in-calf heifers from six dairy units were enrolled. Half were exercised for five weeks pre-calving by walking 1 km along the farm race, being held standing for an hour and then returning along the 1 km race to their respective paddock. Control heifers were managed solely at pasture. Just before calving, both groups were brought back together and managed as one group for the remainder of the study. The authors investigated the time to first lameness event using a fortnightly mobility score and farmer-detected lameness. The primary outcome measure was recorded for 30 weeks (15 scoring sessions) from the first heifer calving into the study.

A cox-proportional hazards model effectively allowed the authors to look at the 'time to lameness’ or 'survival to lameness’ while accounting for animals leaving the study or the study ending. They identified no difference in the time to first lameness between the two groups. This effectively meant that exercise and standing had no effect on an animal’s likelihood of experiencing lameness at any time during the monitored period (Figure 2).

Figure 1. A reconstruction of the digital cushion as captured using CT and MRI scans as described by Gard el al. (2015). The exercise group had a significantly larger digital cushion than the control group

Figure 2. A plot showing the cox proportional hazards model as described my Mason et al. (2022). No significant effect was observed between the two treatment groups. Both groups performed equally in relation to ‘survival’ to first lameness event

Of all heifers, 102 lameness events were identified (13% incidence). There was no significant difference between the treatment group (exercised) or the control group in the risk of becoming lame in the first six months after calving. Although this seems like a conclusive finding that exercise is not protective for foot health, there were a range of hypotheses the authors postulated to explain their findings:

• The animals utilised in this study were at pasture already. This means the degree of exercise the control group received may have imparted the same benefits described by Gard et al. (2015) and that the exercise provided no additional benefit to that already gained from the heifer rearing system in place across the units.
• The intervention was much later in life in comparison to that implemented by Gard et al. (2015), meaning that a large proportion of digital cushion and anatomic development may have already occurred.
• The only lameness outcome utilised was a visual mobility score. In other words, no lesion data was recorded, which may have provided more understanding on mild severity lameness (which is difficult).
• The first author reported that challenges to hoof health were well managed on the dairy units recruited. They proposed that the intervention may have a greater impact where lameness challenges are greater.

Overall, before applying this research to UK dairy farms we need further data to either refute or support the hypothesis that exercise during the rearing period reduces the risk of lameness in the first lactation. We have many more dairy heifers housed than the NZ system and have different challenges presenting in partly or completely housed units when compared with NZ’s entirely grazing system.

Editor’s note: while slightly different than exposure to exercise, there is evidence that exposure of heifers to concrete floors pre-calving is beneficial in reducing subsequent lameness, if they are to be exposed to concrete floors after calving (Bergsten, et al 2015). Furthermore, Randall et al (2016) found that heifers that had mild sole lesions in the pre-calving period were associated with a reduced risk of premature culling. One hypothesis for this result is that a mild insult may result in adaptive changes to the foot, leading to greater biomechanical resilience and so, increased longevity. While we await further research, it would be wise to encourage farmers to acclimatise heifers prior to calving to the type of housing, cubicles and floor environment they will be exposed to after calving. (Owen Atkinson)