Facial eczema cloud on summer’s horizon

LIC statistics for the 2019/20 season record the average milk production per cow in May was about 60 percent of the peak production in October – which is good for seasonal pasture-based cows. If only the production curve could be lifted from peak yield to the yield at the end of lactation by a straight line, or ideally a convex line, a lot more milk would be produced. That would help meet global demand plus the carbon footprint per kg milk would most likely decrease as more production means less pollution per unit of production.

The average statistics are most likely distorted by drying off lower-producing cows but falling milk production through the summer represents a lost opportunity given that in different circumstances (such as cows fed a total mixed ration) the fall from peak would be more gradual. Lots of factors can hasten the drop in milk production post peak including the quality and quantity of forage available and heat stress. Often farmers opt to feed less supplementary feed and choose cheaper options, which could be a false economy when milk pay-out forecasts are so positive. One insidious problem that could be spreading as temperatures rise is facial eczema. Facial eczema is caused by a common fungus, Pithomyces chartarum, which produces spores containing a toxin called sporidesmin during humid weather conditions typically following a dry spell. If consumed, the spores release sporidesmin into the digestive tract,

Litres per cow

Months

Average litres/cow This line indicates how production would look if the summer slump was lessened.

| Falling milk production through the summer represents a lost opportunity.1

from where they are absorbed into the bloodstream to become concentrated in the bile ducts and severely damage the liver. Initial signs include diarrhoea and sudden milk production drop followed 10-14 days later by restless behaviour as cows seek shade – the condition makes animals sensitive to the sun. By the time symptoms are seen, the liver damage that causes the most economic losses has already occurred; there is no specific treatment for the liver damage so prevention is critical. Advances in breeding for tolerance hold hope but in the meantime prevention by spraying the fungus or delivering high rates of zinc to the animal before and during the risk period is our best response. Alternative summer forage crops can make a difference by filling a quality and quantity deficit and reducing the intake of infected pasture. Although regional spore counts can help identify trends at the start and end of the season, on-farm spore counts are more valuable when making decisions because the microclimate makes a huge difference to the challenge for individual herds. As with most things, attention to detail is worthwhile when calculating zinc dose rates – knowing the weight of your cows can help, as does responding to blood test results to determine if zinc supplement levels are adequate. In practice we find that blends and compound feeds offer a reliable way to manage zinc supplementation at the higher levels required for facial eczema prevention. Introducing zinc early at half rate allows cows to get used to the taste and starts building levels in the blood before spore levels explode.

For further information, contact your Farmlands Technical Field Officer or the friendly team at your local Farmlands store.

Article supplied by Dr Rob Derrick, Farmlands Head of Nutrition and Animal Health 1.New Zealand Dairy Statistics 2019-20. Average production cow by herd size in 2019/20. https://www.lic.co.nz/about/dairy-statistics/.