Livestock farmers are being urged to test their feed this winter after new analysis reveals alarming declines in key trace elements, raising new concerns about cow health, fertility and calf development.
Data from 1,500 silage samples shows that while dry matter levels are increasing overall in 2025, essential mineral concentrations continue to decline for the third consecutive year.
Copper decreased from 8 mg/kg DM in 2023 to just 6 mg/kg in 2025, and zinc levels decreased from 32 mg/kg to 27 mg/kg over the same period. This summer’s drought also contributed to lower cobalt and iron levels.
Nettex commercial and technical manager Nia Williams said the trend posed particular risks to pregnant cows in year-round dairy systems, as well as spring calving beef and dairy herds that rely primarily on forage.
She noted that mineral deficiencies during pregnancy can have negative effects on both mother and fetus, increasing the likelihood of calving complications and weakening the calf’s immunity.
“Significant deficiencies can cause serious metabolic diseases such as milk fever and grass stagger, as well as reproductive, immune and fetal development problems,” she says. “These can have long-term effects on cow health, ability to return to calf and longevity within the herd.”
Industry nutritionists say mineral profiles often vary widely between fields and silage cuts, so forage analysis is widely recommended at this point in the season, regardless of year-to-year trends.
Mr Williams stressed that mineral levels are affected by soil type, weather patterns and land management, so the only reliable way to avoid deficiencies is to analyze the feed.
“Knowing what’s in your feed allows you to balance it correctly,” she says, adding that taking multiple samples in the field and between cuts provides the most accurate information.
To support herds with identified deficiencies, farmers often use controlled-release supplementation strategies such as bolus administration. Williams said targeted supplements can help maintain trace element balance and support fertility, immunity and postpartum performance.
He also warned that fluctuations in feed quality this year could affect colostrum. Dairy farmers should aim for a Brix value of 22% or higher, she said. If colostrum is poor or insufficient, she advised using frozen colostrum from another dam or a high-quality colostrum supplement.
Energy and protein levels must also be carefully managed. Williams pointed to a recent veterinary newsletter highlighting the risks of underfeeding cows in late pregnancy, including weakened calf immunity and reduced nutrient transfer across the placenta.
“By understanding the mineral profile of feed and using appropriate supplementation strategies, farmers can take a proactive approach to managing deficiencies and improving overall herd performance,” she said.
While winter feeding is underway, livestock advisors say early testing and balanced rations remain the most effective way to protect cow health and calf viability.
