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Mineral nutrition in late lactation

With autumn upon us, most dairy farmers will be starting to make decisions about when to start drying off, with body condition at front of mind. Thanks to considerable research both within New Zealand and internationally, it is clear that body condition score at calving plays a significant role in ensuring a productive lactation, including influencing the incidence of metabolic disease, milk production and reproductive success.

Yet while our focus over the next few months is on managing cow body weight and condition, we tend to forget that the mineral status of the cow from drying off through to calving will also play an important role in determining the success of the subsequent lactation, as well as the health and wellbeing of the next generation of cows.

In a similar manner to cows drawing on body condition in early lactation to provide much needed energy for milk production, American researchers (Ellenberger et al., 1931) estimated that cows in early lactation lose as much as 800 to 1,300g of calcium from their bones to support milk production in a process known as lactational osteoperosis. If the cow is to be able to repeat this in subsequent lactations, then bone calcium reserves need to be replenished during the last 20 to 30 weeks of lactation and over the dry period – with cows estimated to require as much as an additional 8g per day of absorbed calcium during this period over and above her requirements for maintenance and milk production. Because calcium and phosphorus are both required in precise amounts to form bone, ensuring adequate phosphorus intakes over this period is equally important, as a phosphorus deficiency may prevent normal bone mineralisation. Unfortunately, feeding too much phosphorus can also present problems and phosphorus intakes over the transition period in particular should be carefully managed.

Many of the feeds that have been introduced into the New Zealand dairy production system over the last few years have wildly different macro (calcium, phosphorus, magnesium, sodium and potassium) and trace mineral composition when compared to pasture. Some feeds, such as maize silage, are particularly low in minerals. Other feeds such as palm kernel and maize DDGS are low in calcium but relatively high in phosphorus, and feeds such as fodder beet are well known for being low in phosphorus content. The introduction of these new feeds, combined with changes in pasture species and production, environmental factors and the increased MS production that we now require from our cows, it is more important than ever to ensure that the mineral requirements of cows are being met throughout lactation.

Trace minerals including cobalt, copper, iodine, selenium and zinc are required in very small amounts but play an important role in many physiological functions, such as enzyme reactions, modulation of the hormonal and nervous systems and in supporting health and immune function. While it might be tempting to reduce trace mineral supplementation for cows over the next few months because the stress of early lactation and mating is behind us, the last third of lactation provides an opportunity to replenish trace mineral reserves before drying off and before foetal demand increases in the last 60 days of gestation.

Taking some time now to review your mineral supplementation programme and ensure that cows are receiving an adequate and balanced amount of essential macro and trace minerals will help to reduce the risk of animal health issues at calving and in early lactation next season.

Talk to your local Nutrition Specialist to design an effective mineral supplementation programme for your herd.

Ellenberger, H., Newlander, J., and Jones, C. H. 1931. Calcium and phosphorus requirements of dairy cows: Weekly balances through lactation and gestation periods. Vermont Agricultural Experiment Station Bulletin 10:245-260.

Article supplied by Natalie Chrystal, Nutritionist, NRM.