Macrocarpa - when to keep the cows & deer away...

It seems everybody has their own theory about what happens to stock when they eat trees. So much so, that some farmers keep all stock, especially pregnant cows, hinds and ewes, away from them.

As for the confusion, well it is not surprising. Even the experts err on the side of caution when giving their advice on what is harmful and what is not.

While it is commonly accepted that in-calf cows should be kept away from macrocarpa, anecdotal evidence suggests there is a bit more to it than that.

Farmnews was told recently about one dairy farmer, new to the province, who took out a line of pine trees in the confusion. However, it turns out he may not have acted too hastily as overseas research, and evidence here in NZ, suggests that pine trees can in fact cause problems too.

The common problem is abortion in cows, most of which have been reported in the later stages of pregnancy. To complicate matters further, cows usually retain membranes and it is often at this time, unless appropriate treatment is given, that cows can become severely ill and die.

The biggest problem with tree toxicity is that the evidence is very much circumstantial and anecdotal with no hard facts or recent research to back up any theories. Certainly an old research paper states “many veterinarians in this country view sceptically the evidence for macrocarpa abortion and would prefer more exhaustive feeding trials than those carried out to date.”

This view is still held by many as one vet spoken to by Farmnews described the area as a “joke” when it comes to getting good information on the subject.

So what do we know:

Trees: The bark and foliage of macrocarpa is shown to cause problems, but so to have other members of the Cypress family including leylandii.

The pine needles of Pinus radiata has been linked to abortion problems, as have other members of the Pinus family.

When, why, how: In a farm situation, animals suffering from boredom or hunger may eat from these trees but the biggest risk appears to be from hedge trimmings or prunings which have been left to wilt.

Gail Wylie, of Dairy Management Ltd, suggested this is because the sugars concentrate in the wilted leaves and become palatable to the animals. Most of the reported abortion problems from trees have been associated with the eating of prunings.

Livestock: In-calf cows are especially at risk as they get closer to term. There is also evidence to suggest cows with access to Pinus prunings during mating may fail to get in-calf. Pinus has also been associated with underweight calves born alive.

As far as Farmnews has been able to establish no research has been carried out on deer in this area. The general consensus from vets spoken to is that deer probably are effected but there is no clear evidence to confirm this.

Certainly many deer farmers err on the side of caution when planting shelter trees next to fences. Paul Langford, of Northern Southland Vet Services, said he has never seen real evidence of abortion in deer but sometimes an unexplained large loss from scanning to fawning can suggest a problem like this may have occurred.

Justin Muschamp, of Vet Co. Edendale, also said while there is no evidence to confirm deer are effected, he would imagine they could be effected similarly to cattle.

It is believed sheep are not affected and the suggestion is this may be because the rumen function of sheep varies considerably from cattle and deer. Extensive research work has not been carried out to confirm this belief.

Cows, especially those within two months of calving, seem the most susceptible to abortion. Evidence of when abortion occurrence varies.

Gary Clark, of LabNet Invermay, reported of 10 abortions from a herd of 400 cows two days after having access to leylandii. He suggests abortions can occur two to three days after grazing but experimental evidence suggests they can occur up to 10 days after.

Other symptoms including severe depression prior to abortion and in some cases animals will die if severely ill.

Following abortion, cows will often retain membranes and fail to “bag-up” and so don’t come into production afterwards.

Gail Wylie said farmers shouldn’t be put off trees because of their concerns but rather be slightly more generous when fencing shelter. This way any prunings fall within the fence line. The benefits of managed shelter far outweigh no shelter at all in terms of animal welfare and pasture production, she said.

Also, following a storm, farmers might want to consider picking up any branches thrown down from the larger macrocarpa or pine trees on their property - particularly if they fall within range of deer or cattle.

Other than this, ensuring animals are not hungry or bored when they have access to trees is very important.

Since writing this article Farmnews has been able to find out more on the subject.

Kathy Parton, of Massey University, confirmed that the dangerous time for cattle eating macrocarpa was in the animal’s third trimester of pregnancy. She also pointed out that it did not matter if the macrocarpa was alive, fallen down or had been trimmed as it was toxic in each case.

At this stage she said there is no “real evidence that sheep are affected. They have done some work ... but have not found any indications that they are effected.”

Cattle which consume macrocarpa may abort and can die (depending on how much they eat).

The component in macrocarpa which is believed to cause the abortions is Isocupressic acid. In a joint study which involved Dr Parton, Dr Dale Gardner and Dr NB Williamson in 1996 it was found that macrocarpa collected from the Palmerston North area contained 0.8% and 1.24% isocupressic acid, compared to 1.70% which has been found in Ponderosa Pine needles in the US.

This compares with a Leyland Cypress sample which contained 1.4% isocupressic acid. Further to this study it was found by Dr Gardner that an oral dose of about 100mg/kg of isocupressic acid fed twice daily for several days was required to induce an abortion. Therefore a pregnant cow averaging 430kg would need to ingest 7-8kg of macrocarpa containing 1.24% isocupressic acid daily to cause an abortion.

Dr Parton said the few radiata pine samples which had been tested at Massey had also revealed concentrations of isocupressic acid. She also pointed out that Golden Cypress and many other trees do contain the acid to a degree.

Abortions from eating macrocarpa often result in weak or dead calves, dystocia, retained foetal membranes and secondary complications such as peritonitis or toxaemia (and then death).

Meanwhile, Colin Mackintosh, of AgResearch Invermay, said he suspected that Pinus was relatively safe for deer but that Cupressus were a risk.

Note: Dr Gardner said there is no evidence that people could be effected - at least not causing abortions.