Milk Fever

Also know as

Parturient paresis

Description

This metabolic problem occurs mainly in dairy cows just before or after calving. It tends to affect high producing cows more commonly (and mature cows rather than first calf heifers), but occasionally occurs in beef cows as well. Just because a cow does not produce a large amount of milk does not mean she will never get milk fever.

Signs of milk fever come on swiftly--over a period of 2 to 24 hours--starting with loss of appetite and slowdown of the digestive tract. The cow may stop chewing her cud and may not pass much manure. Her gait becomes stiff and awkward, and then she goes down and is unable to get up. After a few hours she slips into a coma and dies.

Sometimes a cow is short on both calcium and magnesium. This is why treatment is often aimed at replenishing both of these important elements. In some instances a case of milk fever will also be complicated by ketosis, a metabolic disorder that occurs in cattle when energy demands (such as high milk production) exceed energy intake and result in a negative energy balance.

Ketotic cows often have low blood glucose (blood sugar). If this if the case, the cow will respond to the calcium therapy by standing up, but continue to show signs of ketosis--which may include nervousness and circling.

Signs

• Down cow—immediately or soon after calving,
• Lethargy
• Cold extremities
• Lack of muscle tone in the rumen

Cause

Sudden loss of calcium in the body may cause a cow to collapse at calving time. More calcium is being pulled from her body tissues (for milk production) than can be immediately replaced from the digestive tract (from feed) and from bones.

Most of the time, bones serve as a storage area for extra calcium; the body can pull a little calcium from these reserves during times of shortage. But in a cow that suddenly creates a large amount of milk, these reserves are not enough.

serious shortage has severe effects on body function--since calcium is necessary for proper working of nerves and muscles.

Calcium level in blood is controlled by many factors including the interrelationship of calcium and phosphorus (the ratio of these two important minerals in the feed), the amount of phosphorus in the bloodstream, vitamin D levels in the body, and proper working of the thyroid and parathyroid glands--which play a major role in the cow’s metabolism.

Calcium levels in blood may drop dramatically when the cow begins lactation, but if everything else in the body is normal, the lost calcium is generally replaced within a few hours. The parathyroid gland in the brain sends signals via certain hormones (aided by vitamin D) to release calcium stores in the bones.  

If the parathyroid gland is inactive, however, this signal is not sent. Stored calcium isn’t mobilized into the blood to make up the shortage. Activity of the parathyroid can be influenced by the rate of calcium intake from feed.

Cows on a high calcium diet (such as alfalfa or other legumes) during their dry period (before calving again) are often more susceptible to milk fever because the body is getting an excess of this mineral and the parathyroid gland has become somewhat inactive.

The body is lulled into a false sense of plenty. Calcium absorption from the gut alone has been adequate to maintain blood levels of calcium while the cow is dry. There is very little exchange of calcium between blood and bone during that time, and the parathyroid gland has become dormant.  

Age plays a role in whether a cow develops milk fever, since younger animals can mobilize calcium reserves more readily from the bones. As she gets older, the calcium is bound up more solidly in bones; it’s less free to be drawn upon in times of shortage.

As a cow ages, her ability to absorb calcium from the gut also decreases compared with a younger animal. Another predisposing factor is that mature cows tend to produce more milk (hitting their peak for milk production by their third and fourth calves) and are hence more at risk for sudden calcium depletion than are first-time calvers.

Prevention

For normal working of the parathyroid gland, calcium and phosphorus intake should be in proper ratio. A dry cow on good grass pasture (or a mix of alfalfa and grass hay) will have a more normal calcium/phosphorus ratio and be less prone to develop milk fever when she suddenly starts lactating at calving time.

Effective nutritional management during the dry period and early lactation has decreased clinical cases of milk fever to lower than 1% in most dairies, but subclinical cases (without obvious signs) have been reported to affect as many as 73% of animals after their third and later calves.

These subclinical cases may result in decreased milk production, decreased immune function, increased risk of ketosis, decreased reproductive performance, and increased risk of early removal from the herd, so it is very important to try to prevent this condition.

Make sure dry cows have lower levels of calcium in their diet during late pregnancy. Requirements for calcium do not increase until after they calve and are lactating. If you overfeed calcium (using feeds like alfalfa that are high in calcium) in late gestation, cows become too fat and also more prone to milk fever.

The body gets used to a high level and can’t adjust quickly enough when the cow’s needs are suddenly higher after she calves. Cows do better if given feeds that are lower in calcium and higher in phosphorus, until after calving.

Feeding low potassium forages during the pre-fresh period can also help, resulting in an acid-forming response in dairy cows. This response is essential to improve the cow’s ability to mobilize calcium from the bones and to absorb dietary calcium from the small intestines.

Other methods to prevent milk fever include adding ammonium chloride salts to the feed during the weeks before calving or giving every cow an oral dose of calcium chloride gel (or a bolus) at calving, followed by a diet high in calcium.

When using oral calcium chloride, best results are obtained if you give the first dose about 12 hours before calving (if you detect she’s in early labor), another dose immediately after calving, again 12 hours after calving, and a final dose 24 hours after calving.

Significantly increasing calcium content of the diet starting the day she calves can also greatly reduce the risk for milk fever. If you have very many instances of milk fever in your herd, discuss the problem with your veterinarian for more advice on prevention and treatment.

The changes resulting from use of low potassium diets and forages may not be enough to lower blood pH. The use of anionic salts is recommended to further decrease the blood pH in order to improve calcium metabolism.

These adaptations help support the cow’s elevated calcium demands for colostrum and milk production at calving. The use of low potassium diets in association with mineral anionic supplement during the pre-fresh period has effectively contributed to the decrease in milk fever instances in dairy farms.

When feeding anionic salts during the pre-fresh period, it is important to monitor the effectiveness of the mineral supplements. The easiest method is to measuring urine pH in pre-partum dairy cows that have been consuming anionic salts for at least two days. Urine pH of cows consuming these diets should be within the 6.0 to 6.5 range of pH.

Treatment

A cow with milk fever needs an IV injection of a soluble calcium salt. Usual treatment is 400 to 800 ml of a 25% solution of calcium gluconate. A large cow may need 1000 ml.

Milk fever cases are often treated with 500 milliliters of 23% calcium gluconate given by IV, followed by administration of two oral calcium bolus given 12 hours apart. The oral calcium bolus should not be administered if cows do not respond to the calcium IV treatment.

Under-dosing increases the risk of incomplete response (inability of the cow to get up) or a relapse, but giving too much too quickly into the vein can produce toxic effects. In those instances the heart rate increases dramatically (up to 160 beats per minute), the cow has trouble breathing, and may die within a few minutes.

Heart rate should always be monitored while the IV is given; the rate of administration should be slowed or stopped temporarily if the heart rate rises rapidly. It's always wise to allow at least 10 minutes for giving the usual dose of IV solution.

Even though giving it intravenously is the preferred route because recovery is more rapid, some veterinarians split the dose and give half intravenously and the other half under the skin, to reduce risk for toxicity.

Subcutaneous administration of calcium solution is often effective if you are treating the cow yourself at the first hint of trouble, before she goes down. The dose can be put into two sites under the skin, and the area massaged to help increase the rate of absorption.

The cow can also be given an oral gel containing calcium chloride, to help increase her chance for recovery and to prevent a relapse.

Best response occurs if a cow is treated as soon as signs are observed, before she goes down. Even if treatment is given soon after a cow goes down, she responds rapidly. 

Within minutes she’ll have muscle tremors and begin to show signs that her digestive tract is working again; she will be burping and defecating (passing firm balls of feces covered with mucus). Heart rate improves, and she will be able to stand (and usually urinates after she stands up).

A cow often begins eating and drinking soon after she stands up.

The longer she’s been down, the greater the risk for muscle damage and complications, especially if she’s been down 4 hours or more. If she is lying out flat before you find her (no longer resting on her breastbone with her head up), prop her up until she can be treated--to reduce the risk of choking and drawing fluid into her lungs if she regurgitates.

In milk fever cows, failing to rise after treatment with IV calcium is a signal that normal muscular function has not been reestablished. Cows may choke on the calcium bolus if treatment is given while they are still down.

A veterinarian should be consulted and further treatment should be evaluated when milk fever cows do not respond to IV administration of calcium.

If you suspect a subclinical case, giving two oral calcium bolus (first bolus immediately after calving and second bolus 12 hours later) to high producing cows (two or more lactations) can minimize the risk of developing milk fever.