FROM THE FARM REPORT: SHOULD WE UPDATE MINERAL REQUIREMENTS DURING PREGNANCY IN DAIRY COWS?
- Marcos Marcondes
- Jul 21
- 2 min read
A recent study published in the Journal of Dairy Science suggests that it might be time to rethink how we feed minerals to dry cows. For years, nutrition guidelines have assumed that cows only need extra minerals late in pregnancy, but this new research shows that cows start needing more minerals much earlier — sometimes as soon as 30 to 40 days after conception. That means many cows could be underfed important nutrients like calcium, phosphorus, magnesium, and sulfur during much of their pregnancy.
The study followed over 60 pregnant and nonpregnant cows to measure how minerals like calcium, potassium, and phosphorus are stored in the body throughout gestation. The results showed that the demand for minerals increases steadily — not just in the last two months. For example, by mid-pregnancy, sulfur needs were already six times higher than they were earlier in gestation. This steady increase suggests that waiting until the final trimester to boost mineral levels might be too late to support healthy calf development and set cows up for success after calving.
One of the key takeaways from the research is that fetal growth isn’t the only factor driving mineral demand. The mammary gland, placenta, and uterus also begin accumulating minerals well before the last trimester. The study introduced a new way to measure how efficiently these tissues use minerals as pregnancy progresses, showing that cows become better at retaining minerals over time — but only if their diets provide enough to begin with.
Compared to traditional systems like NRC (2001) and NASEM (2021), this new model predicts slightly higher mineral needs in mid- to late gestation — especially for calcium, magnesium, and sulfur. Importantly, these levels still fall within safe feeding guidelines and don’t pose a risk of overfeeding. The goal is not to increase mineral intake across the board, but rather to match supply more accurately with the cow’s changing needs during pregnancy.
It’s important to note that this model still requires validation in other herds and conditions. However, it offers new insights into how mineral needs evolve during pregnancy and raises important questions about whether our current feeding strategies are truly meeting those needs. These findings deserve close attention from both nutritionists and dairy producers aiming to optimize cow and calf health.
For farmers and nutritionists, the practical message is clear: Don’t wait until the dry cow is two months from calving to start thinking about minerals. Earlier adjustments could improve fetal growth, reduce metabolic stress, and support better health and production after calving. It also opens the door to more precise and cost-effective mineral supplementation throughout gestation.
Bottom line: If we want to support the full genetic and productive potential of modern dairy cows, it's time to bring our mineral nutrition models into the 21st century. Nutritionists and producers should begin to consider gestation stage-specific mineral needs — not just in the last trimester, but across the entire pregnancy.
— Marcos I. Marcondes
