All dairy farmers could benefit from regularly testing transition cow diets for macro-minerals and monitoring fresh cow blood calcium levels as part of their milk fever prevention strategy, a recent study shows.
Clinical milk fever can occur at calving when a cow is unable to mobilise enough calcium to meet increased demand for milk production. This can result in ‘downer cows’ that may struggle to recover.
Sub-clinical disease also causes immunosuppression and can lead to increased risk of ‘whites’ and displaced abomasums post-calving.
Vet consultant James Husband from EBVC, who carried out the three-year study on 15 farms, says there is no way to tell if cattle are experiencing sub-clinical effects of the disease without testing.
“Sub-clinical milk fever is highly prevalent and the only way to know if it’s occurring is to blood sample fresh calved cows. If blood calcium levels are below 2mmol/litre in the first 24 hours after calving, then sub-clinical milk fever is occurring. Usually at 1mmol/litre, clinical milk fever will occur,” he says.
Blood testing strategies will vary from farm to farm, but subsequent results should be used to discuss appropriate management changes with a vet and nutritionist, advises Mr Husband.
Blood calcium testing: herd-by-herd advice
- High yielding systems – testing all animals immediately after calving is justifiable, especially in the face of a clinical problem
- Mid-yielding, all-year-round (AYR) calving systems, with occasional issues with whites or DAs – test a batch of cows once a month as insurance.
- Block calving herds – test a proportion of cows at the start of the block.
- Farmers can be trained by vet to take samples themselves.
- Samples can be put in fridge and sent off in batches of six to 10.
- Cost – £5/test.
- Over 50% of cows (excluding heifers) should have a blood calcium of over 2mmol/litre in the first 24 hours post calving. A more practical target (as shown in the trial work) could be 75% of cows with a blood calcium of over 1.8mmol/litre.
He says the forages used in dry cow diets represent a significant contributory factor to sub-clinical milk fever.
He recommends regularly testing forages and the transition cow TMR to assess macro-mineral levels, because high levels of calcium, and potassium, in particular can predispose cows to milk fever.
“Potassium blocks magnesium absorption and affects important hormonal mechanisms, which affects how well a cow mobilises calcium after calving.
As a result, feeding low-potassium diets of under 1.4%DM of potassium is crucial to prevent milk fever, unless using a calcium binder.”
To address this, farmers should consider producing a low-potassium haylage on ground that has little or no slurry applied.
Incorporating wholecrop in the diet is also a more attractive way of providing a low potassium, palatable forage compared with chopped straw, which can be difficult to process sufficiently and has reduced palatability.
This can lead to sorting, which can mean potassium intakes are higher than expected, he adds.
After ration macro-mineral testing has been carried out, an appropriate feeding strategy can then be developed with a nutritionist.
This could involve using calcium binders or opting for a DCAB (dietary cation-anion balance) diet where the ration is acidified (see case study below).
Testing dry cow forages and TMRs: herd-by-herd advice
- AYR calving systems – test transition diets when changes are made.
- If just the silage clamp is changing, just test the silage for macro-minerals.
- Block calving herds – test TMR at the start of block to set ration up.
- Transition cow diets should be under 1.4%DM potassium.
- The calcium content will dictate whether calcium binding or the DCAB route is more appropriate.
- Cost – about £30 a sample for TMR.
Robert Mallett, Northleaze Farm, Wiltshire
At Northleaze Farm, regularly monitoring transition cow diets, urine pH and fresh cow blood calcium levels is part of the farm’s routine.
Having experienced ‘major issues’ with milk fever, Robert Mallet started working with vet James Husband to identify a control strategy.
Ration analysis showed the milking ration being fed to transition cows was delivering more than the recommended level of potassium thanks to its grass silage base.
As a result, a dedicated ration was formulated and grass silage was replaced with wholecrop, which is low in potassium.
The background calcium content of the diet was also higher than expected, making a low DCAB (dietary cation-anion balance) route appropriate.
Cows were put on a low DCAB ration, which works by making the cow metabolically acidotic, primarily by using anionic salts.
This helps mobilise calcium from the gut and bones after calving to prevent milk fever. Mr Mallet says the results were almost instant.
“It’s horrible when every cow calving falls over with milk fever, but the diet changes more or less fixed the problem overnight,” says Mr Mallet, who was one of the 15 farms that took part in the recent EBVC study.
The 220-cow herd yields 10,500 litres a cow a year and calves outside from August to March. To avoid milk fever issues, due to high potassium levels in grass, grazed grass intakes are limited.
While at grass, cows less than 21 days from calving are also provided with access to a TMR in the shed.
This transition diet includes 15kg forage rye wholecrop (which helps achieve high intakes), 6kg maize, 1kg soya hulls, 1.25kg rape meal, 0.75kg hypro soya, 120g minerals, 120g magnesium chloride and 90g ammonium chloride.
At the start of the calving period, forages and the TMR will be tested for macro-minerals, which will influence how the ration is balanced.
Blood and urine sampling
Mr Mallett has also been vet trained to take blood samples, which he does on a batch of cows at the start of calving to assess how the ration is working. Last year, nine samples averaged 2.1mmol/litre of calcium.
Due to the fact the farm is managing a DCAB system, herdswoman Sophie Malt will also take urine samples once a week from four transition cows. On a conventional system, urine testing may only be required as part of troubleshooting.
“We do a pH urine dipstick there and then, and if they’re all under pH6, we’re confident there will be no milk fever problems. If they’re all over pH7, we’ll ring James and ask him to acidify the ration further. It’s about prevention and being one step ahead,” explains Mr Mallett, who farms with his wife Maria and son David.
The benefits have been marked, with just two cases of clinical milk fever last year. “Cows also get eating quicker after calving and fertility is better thanks to better health,” comments Mr Mallett.