Standing fracture repair in racehorses

New research shows lower limb fractures in racehorses repaired under standing sedation have a similar outcome to those repaired under general anaesthetic, but with the advantages of less time, cost and risk.

The study, conducted by Richard Payne and Polly Compston at Rossdales Equine Hospital, Newmarket, has been published recently in the Equine Veterinary Journal.

The report includes details of racehorses with lower limb fractures that were repaired by Rossdales Equine Hospital up to June 2011. Thirty four racehorses were included in the report - thirty Thoroughbreds and four Arabs.

After premedication with acepromazine, sedation was maintained with i.v. boluses of detomidine and butorphanol. Local analgesia (high 4- (or 6-) point block) together with a ring block was performed by the operating surgeon.

Non-displaced fractures included in the study were: incomplete sagittal fracture of the proximal phalanx (14/34 ); lateral condylar fracture of the third metacarpus (12/34); medial condylar fracture of the third metacarpus (7/34 ) and 1 lateral condylar fracture of the third metatarsus. Repair was achieved by the insertion of one or more lag screws.

Hospital records, owner and trainer telephone questionnaires and website research were used to evaluate follow-up. The short and long-term results achieved were comparable with those for similar procedures carried out by the same surgeon under a general anaesthetic. Twenty of the horses returned to racing within an average of 226 days.

On average, the time from completion of the repair to the horse returning to racing was actually shorter when carried out under sedation, than similar cases repaired under general anaesthesia. However, the authors point out that horses selected for standing repair were those with non-displaced fractures which would be expected to require less time to heal than those with displaced fractures that required repair under general anaesthesia.

The authors stressed the need for a competent and experienced hospital team to ensure that health and safety concerns did not become an issue.

“Over the past few years we have been developing an increasing number of techniques, which allow us to perform a variety of surgical procedures in the standing horse. This negates the risks associated with general anaesthesia in our equine patients, which are especially relevant for horses with broken legs, because of their risk of re-injury to the site of fracture repair when the horse stands up again after recovery from anaesthesia” said Richard Payne. “Polly’s study showed that the outcome for racehorses that have a standing fracture repair is every bit as good as for those where the fracture is repaired under a general anaesthetic.”

 

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Seasonal variation in metabolic rate in ponies

Shetland ponies can drop their body temperature to save energy when food is scarce, according to a study carried out in Germany.

Warmblooded animals can keep functioning in cold conditions, but to do so they expend much energy maintaining their body temperature. Some primitive species seemed able to allow their temperature to fall to conserve energy. It was thought that animals lost this ability as a consequence of domestication. But recent studies have shown that the Przewalski horse, the primitive relative of the modern day horse, seems to have retained the ability to control its body temperature according to the environmental conditions.

Lea Brinkmann and colleagues at the University of Göttingen, Germany, wanted to see if this characteristic was still present in domesticated animals.

They conducted a study to see if Shetland ponies, one of the earliest domesticated breeds, retained the ability to drop their body temperature when food is scarce.

The research team studied a group of ten Shetland ponies throughout the year, monitoring subcutaneous and rectal temperatures, heart rate, general body condition and activity levels.

They noticed that, during the summer, the animals’ subcutaneous temperatures dropped over night, being lowest around dawn, and rose to a peak around mid-day. “This is consistent with a daily shallow hypometabolism,” the team says.

Then at the onset of winter, the researchers divided the ponies into two groups. One group received full rations; the other ponies were fed a restricted diet providing only 30% that of the control group.

The feed-restricted group had significantly lower daily subcutaneous temperatures compared with the control group on cold winter days, when the ambient temperature fell below 0°C. Mean heart rate and locomotor activity closely followed the ambient temperature.

Feed-restricted ponies showed a significant drop in average heart rate (from 52.8 beats per minute in summer) to 29bpm in winter. This response differed significantly from that of the ponies on full rations, suggesting that the feed restricted ponies had a lower metabolic rate.

Ponies were significantly less active in the winter than in the summer.

“Our results show that Shetland ponies exhibit signs of a winter hypometabolism indicated by reduced heart rate and subcutaneous temperature” the team conclude. “Thus, domesticated horses seem to have maintained the capacity for seasonal adaptation to environmental conditions by seasonal fluctuations in their metabolic rate.”

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