Dairy cow productivity is usually focused on daily milk yields, however, reproduction is an important aspect when it comes to performance longevity. Cows that get in-calf quickly and stay in-calf are far more productive than those that don’t. One often overlooked factor is mineral supplementation to support reproductive health. New Zealand soil is naturally deficient in some key minerals, meaning addressing mineral balance can be the difference between a successful mating season and high empty rates. When we take a proactive and consistent approach to mineral nutrition, we see first-round in-calf rates improve and increased reproductive resilience in our dairy herds.
Trace elements in ovulation
Trace elements such as selenium, copper, and zinc are essential for supporting the cow’s reproductive cycle. Selenium is well known for its role in reducing retained foetal membranes and improving overall fertility. However, this goes beyond just a post-calving solution and influences ovarian function, reducing the time to first cycle.
Copper deficiency, another common issue in New Zealand pastures, can result in delayed or irregular cycling. Research shows a balanced copper supplementation program can significantly reduce the incidence of silent heats, where cows fail to show clear signs of ovulation. Without adequate copper levels, cows may be ovulating less predictably, leading to fewer successful inseminations during the first mating round.
Zinc is often associated with hoof health and immune function, but it’s equally important for reproduction. Zinc is essential for hormone regulation, especially in maintaining the luteinising hormone (LH) levels that trigger ovulation. Data suggests that herds receiving consistent zinc supplementation experience more regular cycles, contributing to higher conception rates [1].
Mineral deficiency and empty rates
Research shows mineral imbalances or deficiencies are directly related to higher empty rates. Phosphorus, for instance, is crucial for energy metabolism. Phosphorus deficiency can result in anovulation, meaning cows fail to ovulate and therefore cannot conceive. Studies have shown phosphorus-deficient heifers require 2.8 – 3.7 services per conception, which reduced to 1.3 with phosphorus supplementation [2]. Given the cost of carrying late-conceiving and non-productive animals, phosphorus supplementation is a major factor in keeping cull rates low.
Magnesium also affects reproductive health. Low levels can interfere with calcium metabolism, leading to poor uterine contractions, both at calving and during the post-calving recovery period. Poor post-calving recovery often results in cows that are not physically ready for mating, thereby reducing first-round in-calf rates. Magnesium also stimulates the release of hormones required in re-building depleted bone calcium reserves during lactation. We recommend regular magnesium supplementation throughout lactation to support both calving and reproductive health.
Calcium’s role in conception and retention
Calcium is widely known for its role in milk production, but its impact on reproduction is equally important. Farmers are good at identifying post-calving calcium deficiency that causes clinical milk fever, but less so subclinical hypocalcaemia (low calcium without obvious symptoms) leading to reduced uterine muscle tone and complications around calving and post-calving recovery. Cows with poor recovery are less likely to conceive during the first round of insemination. Studies show cows receiving targeted calcium supplementation were more likely to conceive during the first mating round, and retention rates were higher due to better overall reproductive health.
Ensuring calcium levels remain balanced not only boosts conception rates but also reduces the risk of early embryo loss. Maintaining the delicate balance of calcium, phosphorus, and magnesium contributes to a cow remaining in-calf. By maintaining optimal calcium levels, farmers can improve the chances that cows will stay pregnant through to term, thus improving retention rates across the herd.
Preparing the herd for mating season
One key element of successful mineral supplementation is preparation. Farmers should start considering mineral balance well before the mating season begins. In New Zealand, seasonal changes can significantly affect pasture mineral content, particularly as spring growth starts. Supplementing cows with magnesium and phosphorus before the start of mating ensures they have adequate reserves to support both ovulation and early pregnancy.
Early supplementation is particularly important for cows coming off a demanding peak-milk season. These cows are likely to have depleted mineral reserves, which could delay their return to oestrus. Ensuring adequate mineral levels through targeted supplementation helps these cows return to a productive reproductive cycle faster, giving them a better chance of conceiving during the first insemination period.
Long-term resilience through mineral nutrition
While short-term improvements in in-calf rates are beneficial, we want to build long-term reproductive resilience. Proactive mineral supplementation reduces the risk of fertility-related culling, which has both financial and operational implications for dairy farmers.
A resilient reproductive strategy requires consistent mineral monitoring and adjustments based on soil conditions, pasture growth, and herd health. A comprehensive mineral supplementation programme can improve not just first-round in-calf rates, but also the overall health and longevity of their herd.
First published in Dairy News, October 2024