Hypocalcaemia is the most important nutritional disorder affecting dairy cows and can be controlled by good transition cow management and nutrition.
However, clinical milk fever is reported to affect 4-9% of UK dairy cows and this is only the tip of the iceberg1. Studies show the subclinical form could affect as many as 39% of dairy cows2.
Factors which put a cow at risk of milk fever include:
■ Being older/had several calvings
■ High yields
■ Previous milk fever
■ Inadequate/no dietary acidification
■ Body condition score above 3.5.
A case of milk fever could cost more than £200. However, this does not take into account losses attributable to subclinical disease or the knock-on effects, including retained cleansings, metritis and negative impacts on fertility.
Calcium is the most abundant mineral in the body, and is the key structural component in bone. Only 1% of calcium lies outside the animal’s skeleton and this ionised calcium is essential for physiological functions, including nerve conduction, muscle contraction and relaxation, some enzyme activation and blood clotting.
Preventing hypocalcaemia will save time, effort and money in the long run, and can be aided by reducing the risk of milk fever.
The calcium bolus Bovikalc is a routine option for cows that have calved three times or more or those with a history of milk fever. The bolus contains calcium chloride and calcium sulphate, and helps reduce milk fever because:
■ The bolus dissolves rapidly in the rumen and the calcium chloride released provides an immediate source of calcium.
■ The calcium sulphate is broken down by rumen bugs and provides a slower calcium supply.
■ The calcium chloride helps to reduce the pH of the cow’s urine, which assists mobilisation of her own calcium reserves.
In a clinical case of milk fever, a cow should be treated initially with an intravenous solution of calcium, which can be followed up with calcium boluses to help reduce the risk of recurrence.
When a cow calves, her calcium requirement increases by around 70-80 grams a day (mostly due to colostrum production).
A bottle of 40% calcium solution will provide 12g of calcium, while a Bovikalc bolus provides 42g. The bolus is easier to administer and reduces the associated risk from using a contaminated needle.
Ignoring the risk of milk fever and having no prevention plan can affect herd performance. Several studies have looked at the impact of clinical and subclinical hypocalcaemia. These include:
■ Increased incidence of calving difficulties – lowered muscle tone results in reduced uterine contractility, leading to delayed calvings and even stillbirths.
■ Retained foetal membranes (RFM) – the incidence in dairy cattle is estimated to be around 4% and milk fever may predispose an animal to RFM.
■ Metritis and endometritis(whites) often follow a difficult calving or RFM, and have a significant impact on subsequent fertility.
■ Inadequate adaptation from dry to milking cow ration, left displaced abomasum (LDA) etc all result from a reduction in dry matter intake prior to, and around, the time of calving.
Cows treated for clinical milk fever have been found to increase the number of serves per conception and have longer calving-toconception intervals. The reasons for this are not fully understood, but may be because:
■ Cows with hypocalcaemia have fewer and smaller follicles at first ovulation and a longer luteal phase, which may be associated with a longer calving to conception interval.
■ Uterine involution and the process the uterus undergoes post-calving to prepare for the next cycle are dependent upon rhythmical uterine contraction. Milk fever reduces the uterus’ ability to contract, making the process less efficient. The reduced contractility following milk fever increases the risk of endometritis. Affected cows have a reduced ability to become pregnant and are more likely to be culled for reproductive failure.
■ Decreased immune function due to a reduction in white blood cell function means it is more likely cows succumb to infections such as metritis, endometritis and mastitis.
There has been much talk about DCAD (dietary cation anion difference) diets and a reduction in milk fever incidence can be achieved by feeding a low DCAD diet. This can be a full or partialDCAD ration, but both aim to decrease urine pH, and increase calcium flux, with increased urine calcium excretion.
It allows the in-calf cow to respond to sudden increased calcium demand by switching calcium from urine to milk.
However, DCAD diets tend to suppress dry matter intake (DMI), especially if blood pH is reduced. This is detrimental at a time when dry matter intake is critical. DCAD rations are not ideal for heifers as their skeleton is still immature and hence calcium reserves are not as available.
The best advice, in most cases, is to discuss preventing milk fever with your vet. References: 1. Husband (2005): In Practice 27, 88-92. 2. Sampson et al (2009): Veterinary Therapeutics 10 (3) 131 – 139.