The results of this study show a clear effect of using rubber mats in combination with zinc ointment for sows with shoulder lesions compared to antibiotic spray. The effect of treatment was statistical significant for lean sows both when the size of the ulcer on day 14 and day 21 were used as responses. For fat sows, the effect was significant when the size of the lesion on day 21 was used as the response, but not when the size of the lesion on day 14 was used. There was no statistical significant effect of parity on the size of the ulcer on day 14, nor on the effect of treatment. There was an effect of parity on the size of the ulcer on day 21, but this effect was correlated with body condition, and therefore the model including treatment and body condition was preferred. There was a minor difference between herds regarding the size of the ulcer both on day 14 and day 21, but herd did not impact on the effect of treatment on the size of the ulcer. This should not be confused with an effect of the risk of a sow developing a shoulder ulcer. The larger the ulcer was on day 1, the larger it was on day 14 and day 21. This implies how important it is to prevent further development at the first signs of an ulcer. Furthermore, farmers must understand that although an old sow has a higher probability of developing a shoulder ulcer, the young sow with a shoulder ulcer will still benefit from a rubber mat. Mats are therefore recommended as a means to reduce the number of sows that need to be euthanised, culled and weaned too early due to this type of lesion. It is also reasonable to expect that mats could be used preventively for sows at risk.
There is only little documentation of how soft a mat must be before a therapeutic effect can be seen. A single study has found that rubber mat with a foam core had preventive effect against shoulder ulcers in one out of two herds, compared with a solid floor of concrete and solid rubber mats
. In the present study, the farmers had no difficulty in keeping the pens clean and dry when using these mats. The mats were fixed to the floor using a special lock system, which held the mats adequately in place and was relatively easy to handle. Therefore, the farmers were generally satisfied with the system.
In Denmark, all use of antibiotic treatment is on prescription only and is monitored in the Vetstat Database
. Danish farmers therefore use various non-antibiotic alternatives for wound healing. One such common treatment is zinc ointment, and farmers have reported positive results from this for treatment of shoulder ulcers. In human medicine, zinc ointment is sometimes used prophylactically to protect the skin against moisture and urine, though decompression is considered to be the main therapy for patients with pressure sores
. However, there is little documentation on the effect of zinc ointment.
In our study, sows in group A had to be treated due to animal welfare considerations. Although the effect of antibiotic spray treatment on chronic lesions has not been well documented, it should be a reasonable choice for topical treatment. Therefore, it was decided to compare current practice (rubber mats and zinc ointment) with antibiotic spray treatment. It may be open to discussion whether it is at all necessary to use local treatment on shoulder ulcers. It is, nevertheless, a limitation that the study is unable to estimate the effect of rubber mats and zinc treatment separately, although we believe that the observed effect is mainly related to the use of rubber mats. At least the study shows that antibiotics for topical use are inadequate if shoulder lesions are to be prevented from getting worse.
The effect of the treatment on shoulder ulcers was only documented for sows on fully slatted floors which are a very common type of flooring used in intensive pig production world-wide. It is assumed that a fully slatted floor puts more pressure on the shoulder than other types of floors, because the surface area on which the sow lies is smaller. Zubrigg
 has shown that shoulder ulcers in sows standing on rubber mats healed significantly faster than ulcers in sows standing on steel sheets or a fully slatted floor. It is therefore likely that mats have an effect in pens with other types of flooring. The type of floor must be considered as part of a multi-factorial complex, and several measures need to be taken to prevent sows from developing shoulder ulcers.
Field trials are complicated and expensive to conduct. They usually result in only a limited number of observations being included in the final study, which might reduce the ability to identify important statistical associations. The allocation into treatment groups was performed at random (and matched according to lesion severity represented by grade of ulcer), without taking any covariates into consideration. This randomisation does not guarantee that all covariates will be equally distributed in group M. Therefore, analytical control of potential confounding variables such as parity and body condition was performed. This approach is recommended for use in large field trials (N>100) with relatively homogenous experimental units, as seen in our field trial
The study was primarily conducted during the coldest period of the year. Unfortunately, this made it impossible to estimate any seasonal variation.