Research Bite: an induction model for sole ulcers failed on repeated attempts

Research conducted at Minnesota University tested an induction model for sole ulcers, predominantly built around enforced standing and poor foot angle. Frustratingly perhaps, the results seem to provide more questions than answers. Nick Bell looks at what can we learn from this study.

Study design

Induction model studies are important for establishing causal relationships. Cramer et al (2023) used a series of three iterative experiments (phases) to search for an induction model for sole ulcers.

Previous studies have highlighted several possible risk factors for sole ulcers but none have tested these experimentally.

The challenges applied in this study were: hoof blocks fitted to exert pressure to the flexor tuberosity; lying time restriction; feed restriction and systemic lipopolysaccharide (LPS) (table 1).

Tables describing the phases of the induction model, and the challenges applied:

Phase 1:

Challenge name	Duration of Challenge	Hoof Block	Lying time restriction	Feed restriction	LPS	Follow-up
P1BL	14 days either side of calving	Plastic wedge	2 x 2.5hr daily	No	No	70 Days
Control	None	None	None	None	No	70 days

Phase 2:

Challenge name	Duration of challenge	Hoof block	Lying time restriction	Feed restriction	LPS	Follow-up
P2BL	42d from 126 days in milk	Plastic wedge with extra thin block	18hr for 2d/wk	None	No	58 days
P2B	42d from 126 days in milk	Plastic wedge with extra thin block	None	None	No	58 days

Phase 3:

Challenge name	Duration of challenge	Hoof block	Lying time restriction	Feed restriction	LPS	Follow-up
P3BLF	14d prepartum to 28 postpartum	Wooden non-wedged block with extra thin block	6hr, 2 consecutive days/wk	70% DIM restriction 2d/wk	No	55 days
P3BLF + LPS	14d prepartum to 28 postpartum	Wooden non-wedged block with extra thin block	6hr, 2 consecutive days/wk	70% DIM restriction 2d/wk	1d/wk for 3wks postpartum	55 days
Control	None	None	None	None	No

Heifers were used throughout the study with a challenge period spanning first calving for Phases 1 and 3, and primiparous heifers used for Phase 2. Heifers were assessed for lesion score; lameness score; withdrawal on hoof tester if sole haemorrhage observed; thermographic temperature; lying times and metabolic markers.

The results

Despite those challenges, none of the Phases were successful in inducing sole ulcers! However, the authors noted:

A higher number of new sole haemorrhages in both Phase 2 groups: P2BL and P2B
2 out of 4 cows went lame in P2B
3 out of 4 cows went lame in P2BL
3 out of 4 cows went lame in P3BLF
2 out of 4 cows went lame in P3BLF+LPS
Most lame cows then recovered in the post-challenge period
The lateral hoof was 5.5ºC and 6.3ºC warmer than medial for P3BLF+LPS and P3BLF respectively
Lying times were reduced by around 1 hour, most notably in the Phase 2 groups

What difference might these findings make in the field?

Whilst these results don’t conclusively confirm or disprove any existing theories on sole ulcers development, they provide some indication that the duration and magnitude of challenges need to be significant.

For example, the lying time restrictions were perhaps not as extreme as we encounter in field situations. It is not uncommon to observe heifers with lying times as low as 6 hours a day when rejecting cubicles, displaced from feed barriers and having to compete with cows for lying space in overstocked sheds. Similarly, lying time restriction can be much greater than those applied in the study for herds experiencing long pen times when milking three times a day, or for herds with poor cubicle comfort.

Challenge periods were 28-42 days. Perhaps this wasn’t long enough? Most sole ulcers would be encountered longer after calving, following perhaps 80-120 days of challenge under farm conditions.

Interestingly, Phase 2 did not involve a calving event and yet this group encountered some sole haemorrhage and lameness, unlike heifers with a calving event, studied during Phase 1. This might be an indication that calving events are less important than the challenge caused by focal pressure on the flexor tuberosity, restricted resting time and feed restriction.

While the blocking was designed to exert pressure under the flexor process of PIII, perhaps the pressure created by a poorer foot angle was not the same as the focal pressure created by sole overgrowth. Perhaps we should question the importance of foot angle and moderate lying time restriction, as used in Phase 1?

Could the challenges have induced changes in the feet that were not detected? The researchers only applied hoof testers when sole haemorrhage was visibly present, but acknowledged they may have missed deeper bruising with this approach.

Finally, while feed restriction leading to body condition score loss may be a risk factor, previous research has suggested that low body condition score per se appears more important. Would repeating the study with thin heifers have led to more success?

None-the-less, some effects were induced. Lameness, raised skin temperature and sole haemorrhage were induced by Phases 2 and 3, and the authors concluded the abaxial-axial rotation used in Phases 2 and 3 that would have increased pressure on the axial aspect of the flexor tuberosity looked most effective for inducing sole haemorrhage and lameness. Needless-to-say, further induction studies are required!

Reference

Cramer G, Shepley E, Knauer W, Crooker BA, Wagner S and Caixeta LS, 2003: An iterative approach to the development of a sole ulcer induction model in Holstein cows. Journal of Dairy Science, 106:7, pp 4932–4948.