Too often dry cows are one of the ignored groups on the farm, but a lot of nutrition research demonstrates how important the dry cow period is for the future success of the cow’s lactation. Rose Jackson of Scarsdale Veterinary, Derby, reports.
Most dairy farms now have a “transition” group for two to three weeks prior to calving where the cows are given a palatable, straw-based diet to try to maximise intakes and rumen fill.
Making sure the cows start the dry period in the right condition score is vital for dry period success. Diet changes should only be made in the last third of lactation to aim for body condition score 2.5-3 at drying off.
The aims of nutrition in the dry period are to:
- Prevent negative energy balance and ketosis
- Prevent milk fever
- Optimise immune function
- Achieve a smooth transition on to lactation diet
Ketosis is a common condition of high-yielding dairy cattle. When a cow calves, her feed intake is depressed, but her energy demands increase rapidly at the start of lactation.
This mismatch of energy needs and intakes leads to low circulating glucose levels. As a result the cow starts to mobilise her own body fat, which produces NEFAs (non-esterified fatty acids) and these are then changed into ketones by the liver.
Clinical ketosis (acetonaemia) is the result of these ketones building up in the blood. Clinical ketosis can lead to cows going off their food and performing poorly.
Occasionally, they can develop “nervous ketosis”, which includes symptoms such as aggression, staggering and obsessive licking, as a result of the excessive ketones in the blood affecting brain function. However, as with many diseases these clinical cases represent the tip of the iceberg.
Sub-clinical ketosis is associated with an increased risk of displaced abomasums, metritis, mastitis and other conditions associated with poor immune function. Cows with sub-clinical ketosis will also produce less milk and have poorer fertility levels than normal.
Milk fever is a very common condition usually affecting cows in the 24-hour period around calving when the calcium demands of lactation and milk increase rapidly.
Calcium levels are tightly controlled in cows and when demand suddenly changes, it takes 12-18 hours for the body to adapt and be able to absorb more calcium from the gut and bone. This means the first 12-24 hours after calving is critical for a dairy cow.
Studies estimate that even in the absence of clinical signs of milk fever, up to 40% of all dairy cows are sub-clinically affected, which can lead to held cleansings, dirty cows after calving and poor fertility in the next lactation.
There are various strategies for controlling milk fever:
Calcium restriction: feeding low levels of calcium before calving tricks the cow into mobilising her own stores of calcium. However, this is very difficult to achieve with grazing cows as grass and grass silage contain high levels of calcium.
Magnesium chloride: magnesium is needed for the body to mobilise calcium and so adding this to the ration or water can help keep levels of milk fever under control.
Magnesium chloride tastes awful so care must be taken to make sure intakes are good (12kg dry matter intake a cow a day). If it is put in the water then they should have no access to any other water source and care must be taken to make sure the trough doesn’t run dry, as magnesium can be highly toxic.
Full DCAB (Dietary Cation and Anion Balance): this involves adding DCAB salts to the transition ration in order to slightly acidify the cow, which makes the adaptation to absorb calcium at calving much faster.
As with magnesium chloride, the salts are fairly unpalatable so intakes must be monitored. To ensure the cows have acidified sufficiently, urine pH must be checked regularly, which makes this quite a complex system to use in practice.
Partial DCAB: this is a simpler version of full DCAB where “low DCAB” forages are utilised, often in combination with magnesium chloride – it is not as effective as full DCAB but it’s simpler, needs less monitoring and results in a more palatable diet. To do this accurately you need to have good forage analysis available to calculate the correct DCAB values.
Vet Watch is written by memebers of the XL Vets group. For more information visit www.xlvets.co.uk