By September, pre-mating heat recording is underway on many spring-calving dairy farms. While the immediate focus is on cows that have not been seen in heat, the pattern across the herd can also show how many cows have resumed cycling after calving.
When fewer cows than expected are coming into heat, energy balance and body condition are usually the first things we look at. Cows that calve down in less-than-optimal condition will often take longer to cycle, especially when feed intake doesn’t keep up with milk production.
Minerals can’t correct an energy deficit, as feed intake still drives energy balance. But they do play a role in the metabolic, immune and reproductive processes cows rely on during recovery from calving and through early lactation.
Micro minerals such as zinc, copper, manganese, selenium, cobalt, iodine, boron and chromium are used in energy metabolism, immune function, tissue repair and antioxidant systems. The demand for these increases after calving, when we’re asking cows to increase their milk production as they recover from birth. This often forces them to draw on body reserves.
Research has found differences in how cows respond to trace mineral supplementation during this period. In one study of 273 dairy cows, older cows receiving chelated (organic) trace minerals had higher dry matter intake after calving than those receiving inorganic sources.
A related study found fewer cows with higher non-esterified fatty acids, or NEFA, in the group supplemented with organic trace minerals. High NEFA levels indicate greater mobilisation of body fat to meet energy demand. The same study also recorded fewer cows in the treatment group suffering metabolic disorders after calving.
While minerals don’t prevent negative energy balance, poor mineral status can make it harder for cows to manage the metabolic demands that come with it.
Minerals and the return to cycling
The weeks after calving heavily influence what happens at mating.
A cow that has had a harder recovery may eat less, lose more condition and take longer to resume cycling. Trace minerals contribute to several of the systems involved in that recovery.
Zinc and copper are involved in immune function and tissue repair. Copper, zinc, manganese and selenium are also used in antioxidant systems that help protect cells from oxidative stress.
Liver function is particularly critical at this time. Natural metabolic processes must break down stored body fat in order to meet rapid energy demand. If the liver is not well supported with all the minerals and proteins required, this process cannot work efficiently.
Research has also linked trace mineral nutrition with the timing of reproductive activity. One study followed 573 dairy cows under different trace mineral supplementation programmes and found differences in the time from calving to first cycle, along with some later reproductive measures.
New Zealand research points in the same direction. A South Island study involving 555 intensively grazed Friesian cows compared cows receiving supplementary zinc, manganese, copper and cobalt with cows receiving no supplementary trace minerals. More cows in the unsupplemented group required hormonal treatment in order to initiate estrous (or “cycling”).
This clearly points to mineral nutrition being important in the pre-mating discussion. Cows still need enough energy and dry matter intake, but mineral status can affect the systems that are key to metabolising energy that allows recovery from calving, and initiation of early cycling.
Mineral availability
Supplying the right amount of minerals does not guarantee the cow is absorbing enough of those minerals. For instance, copper availability can be reduced by high molybdenum and sulphur intakes, so while on paper the diet contains enough copper, the cow is still receiving less than expected. Not just the range and level is important, but the form of mineral being dosed is important in order to ensure maximum absorption.
Pasture composition and supplementary feeding also change through spring, so mineral intake and availability can change during the same period cows are moving from early lactation towards mating.
If fewer cows are cycling than expected, look back over the weeks since calving. Feed intake, body condition, post-calving health and mineral status can all influence how quickly cows return to normal reproductive activity.
By the time weak or missing heats show up on the pre-mating records, the contributing factors may have been present for several weeks. Reviewing mineral nutrition alongside feed intake and post-calving health can help identify why some cows are taking longer to cycle.
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