Researchers are stumped as to what is causing the estimated 4500-5000 dairy cows that are breaking their shoulders every year.
Veterinarians and other experts are mystified to explain why an increasing number of dairy cows are ending up with broken shoulders.
Dairy heifers seem to be most prone to the humerus bone injuries during their first lactation, although they occasionally fall to them in the second lactation. Experts believe the broken shoulders are not an issue with beef cattle.
Broken shoulders appeared mostly during peak lactation in September-October, although they also occurred before calving and through to December, Massey University veterinary professor Dave West told farmers at Limestone Downs Station’s annual field day.
West said a soon-to-be-released study from the university showed this was a serious problem in the dairy industry.
“They are spontaneous, there’s no history of trauma. You go out into the paddock and you find them. Farmers have reported cows walking past and you hear a bang and there’s another one with a broken shoulder.”
The issue was first reported in Manawatu in 2008 when a Foxton farm had five cows with broken shoulders. At Limestone Downs, there were 16 cases between August and November last year. All the cows were purchased apart from one which was reared on the farm.
Some of the heifers were second calvers and had been on the farm for more than a year before the problem occurred, West said.
Based on a random phone survey of 500 farmers, researchers determined that about 10 per cent of all dairy farms had this issue.
“It’s usually about 2 per cent of first calvers and 2 per cent of second calvers.
“If you add up the number of heifers in New Zealand, you’re talking 4500-5000 heifers every year in New Zealand are breaking bones,” he said.
The estimated loss at this level was about $9.24 million.
Broken shoulder reports were found across the country including “quite a few” in Waikato.
West said the problem was likely being under reported by farmers.
“It’s not a nice condition, farmers don’t want to admit that they have a problem, sometimes they are put down in the back paddock and they might wait until they have half a dozen and then they might contact the vet.”
This is despite farmers knowing there was little a vet could do.
Testing from pathologists revealed the bones were osteoporotic, meaning they were weaker and not formed properly. A microscopic examination of the affected bone showed it had been present for some time, and the bones were not formed properly during its growth.
Low copper levels were associated with some of the affected cattle, including those at Limestone Downs.
West said he found it difficult to accept it was the only cause as copper deficiencies in cattle had occurred for a long time.
Research showed the damage was during bone development of cattle while they were still young.
“My personal view is that the way we rear calves is the only thing that I can think of that’s changed informally throughout the country so dramatically.”
He believed that lactation drain was obviously a trigger factor.
Whether it was a calcium or protein deficiency among the cattle was unclear.
Modern calf rearing minimised the amount of milk fed to dairy calves whereas beef calves still fed off their mother for a much longer period. He believed this was why it was not so much of an issue in the beef industry.
Genetics may also be a factor as the injuries had been associated with higher producing cows and some cows may be more susceptible than others.
“I personally don’t give them credit for creating such a change in our cattle that they are producing so much milk that their bones give way, but it’s certainly part of it.”
Another contributing factor could be the hangover effect of the drought where post-drought autumn and winter pasture growth was often deficient in minerals.
He urged the industry to undertake larger scale and more in-depth research to determine the cause of the injuries.
Source: Stuff
