Grass silage as a dietary mineral source

Dairy farmers shouldn’t underestimate grass silage as a dietary mineral source, as Jeremy Hunt found out at a recent forage mineral day



Dairy farmers need to be fully aware of the precise mineral status of their silages – grass, maize or wholecrop – and the potential impact forage-based minerals can have on herd health and fertility, vet Bill May told farmers in Cheshire.


“Although the nutritional quality of silages is paramount to every dairy farmer, without question it’s essential to know the mineral status of the forages being fed. Being aware of the level of minerals going into the cows through these forages provides essential dietary information that can give a head start when tackling health issues,” said Mr May, of vet practice Lambert, Leonard and May.


Farmers attending the event – held at Richard Fair’s Brookside Farm, Poulton, near Chester, to discuss the effects of forage-based minerals on dairy herd health – were told preventative measures could be taken to avoid health issues where there was a risk the minerals being delivered in the silage could trigger problems.


“It’s a classic case of being forewarned is being forearmed. For instance, where the mineral status of the forage is heightening the risk of milk fever, it may be worth considering administering a long-acting calcium bolus. Even though a farmer may not see any clinical signs of milk fever, being aware it’s an underlying risk – and can be countered – is a valuable preventative treatment.


“Based on sales of milk fever treatments, it’s estimated 5% of the national herd contracts clinical milk fever but about 50% of cows suffer from sub-clinical symptoms. These cows might not always go down, but they are high-risk cows that no dairy farmer wants.


“So often there are health problems that can be traced back to mineral imbalances – problems that might have been avoided or identified earlier if there had been an awareness of the silage’s mineral status,” said Mr May.


While there was still uncertainty about the effect the mineral status of silage eaten during lactation may have on a cow’s predisposition to succumb to milk fever at calving, there was no doubt calcium and magnesium intakes during the transition period – three weeks either side of calving – were critical.


Consultant Mark Tripney of Matrix Ag – which jointly organised the event with Dairy Co and Lambert, Leonard and May – said dairy herd management had become too “cow-centric” and needed to focus more on the soil that produced the forages that fed the cows rather than simply on the cows themselves.


“There are basic management checks that can make a big difference to helping avoid mineral imbalances and their impact on cow health. High-yielding herds achieving more than 9000 litres need to be aware of what’s coming out of the back-end of their cows. They’re pushing out high levels of protein and it’s leading to a big lift in N in the manures.


“And a comparison of the soil analyses of fields will all too often show that fields close to the farm have widely differing mineral profiles compared with those away from the farm.


“Fields near to the buildings can have higher levels of phosphate and magnesium because not only is slurry being applied but these fields are being grazed.


“Silage ground away from the farm is having all the grass taken off and the mineral status reflects that. So it’s no surprise why cow health issues are often associated with animals grazing fields close to the farm itself,” said Mr Tripney.


He told farmers that levels of soil pH also had a direct impact on minerals that were available to cows through silages.


“Once you start to get a pH above 6.6, nutritional issues come into play. Get up to pH 7, and molybdenum becomes more available and there’s a direct effect on fertility.


“Ensuring nutrients are in the right place on the farm is essential to cow health as well as the economics of the farm business.”


Dairy farmers were advised not to underestimate grass silage as a dietary mineral source for cows.


“On many farms, the potash levels are massively over the top, while others have molybdenum issues contributing to fertility problems. High levels of iron can also trigger the availability of copper with subsequent health risks,” said Mr Tripney.


While dairy farmers were able to condition score their cows, Mr Tripney suggested it was time for farmers to condition score their fields.


“Every field on the farm should have a condition check every year. Fields should be looked at in the autumn and problems addressed at the time rather than being left.


“Soil compaction caused by machinery after maize harvesting should be dealt with as a priority and there should be a hit-list of work planned for each field in the spring to help the soil do its job as well as it can.”


Mr Tripney said there was a direct link between soil, forage and cows and the three must be managed together.


“Problems with cow yield or fertility invariably prompt a visit from the vet and the nutritionist and it’s possible that a mineral imbalance may be part of the diagnosis.


“But we’re forgetting how important the soil is in what it provides for the cows. It’s an integrated system. The soil feeds the crop but it’s the fertilisers and manures that feed the soil.”