In the wake of preliminary analysis of an in-depth farmer survey, DairyNZ’s Southland/South Otago regional leader Richard Kyte says farmers have been advised of its key findings including that cow ill-health increased last season as the proportion of swedes fed as part of the total diet increased. Feeding swedes on the milking platform (farm) in spring when cows approached calving and early lactation also increased the incidence of ill-health.
“We also found that in spring 2014, there was a higher incidence of ill-health for Herbicide Tolerant (HT) swedes compared with other varieties of swedes. However the reason for the increased incidence of disease is still unknown. Nevertheless farmers should apply caution regardless of the swede variety being fed.
“The survey has additionally identified a departure from the ten year climate average in 2014. The warmer air temperatures and fewer frost days may have enhanced both leaf growth and maturity,” he says.
DairyNZ carried out the survey between November 2014 and February 2015 to help understand the factors that caused some cows in Southland/South Otago to die or become ill. In total 134 affected and unaffected farmers and 34 graziers were interviewed as part of the survey.
“The survey has thrown some light on a shift in farming management practices in Southland and South Otago in the last 10 years as a contributing factor.
“Many farmers have moved to feeding cows swedes at two points in the season - when they are wintering cows off farm and again when they bring their cows back to the milking platform/farm to calve and milk.
“We still haven’t got all the answers to the reasons why we saw an increase in ill-health last year. We may know more when the plant analyses are complete,” he says.
“We think the increased incidence of ill-health in spring relates to the farming trend whereby cows come home from grazing off-farm to feed onto more mature and higher risk crops planted on the milking platform (farm). All swedes carry a risk of adverse health effects when cows graze crops that are bolting - getting mature, growing longer stems and flowering,” says Richard.
“Both crops are planted at the same time - but are, therefore, fed at different stages of maturity and growth. As the swedes mature and reach the reproductive state they are known to have a higher concentration of glucosinolates (GSLs). These are the naturally-occurring compounds that have been associated with the issue.”
Richard says the chemistry of glucosinolates for swedes and other brassicas is complex. It changes with swede variety, growing conditions and crop maturity. Further complexity is added when the glucosinolates are changed during eating and digestion.
“The results of our survey confirm that all varieties of swedes can present a risk to animals depending on how and when they are fed and used as part of the farming system. If farmers plant swedes, and many have this season, then they need to manage how and when they feed it to their cows.”
Richard says the next update for farmers will be when plant analysis results are available. “This update is expected to be available to farmers in late July and that will be an important piece in the puzzle. We can then focus on pulling together our final consolidated report on all the elements of the work we have done on the issue.”
DairyNZ has already set in train a number of steps for helping farmers this season.
“While we are continuing the plant analysis, unfortunately there are no quick tests for swede plants that will provide an early warning signal for farmers,” he says.
“However, DairyNZ is working with farmers this season to identify early signs of ill-health in animals by monitoring a small selection of cows. We are compiling blood samples from cows and want to record incidences of ill-effects throughout this season. This kind of work is the first step in assessing how we can develop a baseline system for detecting early signs of ill-health in cows. This work, along with our final report will help us know what’s important and useful to study going forward,” says Richard.
Farmer advice: Go to www.dairynz.co.nz/swedes for further information and the full advice that has just been sent to Southland farmers including photos to assist farmers with monitoring their crops.
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