Some might even have experienced difficult conversations with staff about stock handling and welfare regarding the possible cause of the fractured leg.
Spontaneous humeral fractures in first-lactation New Zealand dairy heifers were first reported in 2008 on a dairy farm in Manawatu and have since been seen all over the country. On many properties multiple animals have been affected in the same year and some farms have been affected in successive years. Although two-year-olds are more commonly affected, three-year-olds can also be affected and the condition is usually encountered up to two months after calving. The onset is sudden and there is no humane treatment available other than slaughter.
Anecdotally, the condition has become more prevalent in recent years and could be linked to droughts.
At post-mortem examination the fractures are horrific, spiralling up the shaft of the humerus as seen in the picture, which contrasts a normal bone with a fractured one.
A telephone survey of 500 dairy farmers in 2015 showed the condition was more common than anyone had realised. It is likely that in the 2014-15 season about one in eight NZ dairy herds experienced humeral fractures, with each affected farm losing on average 2-3% of their heifers. However, as is the case with all diseases, there have been some badly hit farms, losing as many as a quarter of their heifers. Based on those figures the estimated loss to the NZ dairy industry is about 5000 young dairy cows a year. The dollar value is about $10 million but the welfare cost is certainly far greater.
At the same time humeral fractures first appeared, another previously unrecognised condition known as “sciatic palsy” or “dropped hock syndrome” was described in NZ. In “dropped hock syndrome” the cow gradually loses the use of its hind legs, adopting an odd gait in which the hocks progressively drop lower and lower until the cow becomes recumbent. Again there is no effective treatment and most severely affected animals are eventually destroyed. There are potential similarities between the two conditions, in that they both may be related to defective collagen formation.
Some veterinarians have speculated that both conditions share a common cause and interestingly there have been a number of farms which have suffered from both conditions.
Some of the earlier NZ investigations into humeral fractures focused on copper deficiency, and although some affected cattle were deficient in copper not all were. Copper deficiency in NZ is not a new problem, but humeral fractures are.
Based on preliminary results we believe that during periods of under-nutrition, less bone is formed and laid down, making the bone brittle. After calving the bone is further weakened when bone tissue is mobilised to supply calcium for milk production, eventually resulting in spontaneous fracture. It can’t be coincidental that the fractures occur at or around peak yield and the onset of mating.
With the aid of a generous grant from the C Alma Baker Trust a research team at Massey University – Jenny Weston, Keren Dittmer, Chris Rogers and Kevin Lawrence – is to begin investigating possible causes for this problem. The objective is to gather information that could provide a starting point for further investigation into this syndrome in cattle. The team will start by surveying farmers who have had fractured humeri and compare their answers to similar farms that haven’t had the problem.
Then, based on the results of the survey, they will approach farms that have had this condition and follow groups of heifers for two years, sampling and imaging the front legs at regular points.
Since this condition appears to be unique to NZ, there’s no overseas research to piggyback on. Instead the team will have to do the hard yards themselves. It does, however, raise the question – what has significantly changed in the NZ dairy industry in the past 10 years to allow this condition to develop?
If you would like to be involved in this project go to www.surveymonkey.com/r/HumeralFractureSurvey and enter your name and details, and the details of your veterinarian.
Kevin Lawrence BVetMed, MVS, Massey University
