Milk fever is a disorder mainly of dairy cows close to calving. It is a metabolic disease caused by a low blood calcium level (hypocalcaemia) It is a common metabolic disorder in dairy cattle that generally affects older,high producing cows.
At the beginning of lactation high yielding cows experience a sudden rise in demand for calcium to replace the large amount lost through milk. This may result in great decrease in blood calcium if the cow is not able to replenish the calcium fast enough, causing a disease called milk fever. The majority of milk fever cases occur within 48 to 72 hours of calving when demand for calcium for milk production exceeds the body’s ability to mobilize calcium reserves. Fever is a misnomer as body temperature is usually below normal. Low blood calcium interferes with muscle function throughout the body causing general weakness, loss of appetite and eventually heart failure. Losses are due to deaths (about one in 20 affected cows dies), a reduction in the productive lifespan of each affected cow of about three years, and reduction in milk production following each milk fever episode, as well as costs of prevention and treatment.
You can diagnose milk fever in three distinct phases:
Cows are hypersensitive, restless, and may have body tremors. They shift body weight and have unbalanced gait, especially in the hind legs. This phase is tricky because you have only one hour window to detect and treat the cow. If you do not treat the cow at this stage, it progresses to phase 2
This stage lasts a bit longer, ranging from one hour to half a day (12 hours). The cow has a clearly observable difficulty while moving around and is generally dull. Body temperature drops and the muzzle dries up. Heart rate increases to more than 100bpm. The strength of the heartbeat (tarchycardia) falls and may not be easily noticeable.
The cow loses ability to stand on her feet and lies down sternally. You may observe constipation and the cow will have difficulty defecating or urinating since the smooth muscles will have paralysis. The cow tucks the head in the flanks.
You still have a better chance of saving the cow. However, if you do not treat the cow, the condition will progress to phase 3.
The cow has lost all the ability to stand, body temperature has dropped drastically and the heart rate has increased to over 120bpm. Cow exhibits lateral recumbency (lies on the side) and does not respond to stimuli. Tarchycardia is very weak and if you do not introduce an intravenous injection, the cow will slip into a coma and die after a few hours.
In typical cases cows show some initial excitement or agitation and a tremor in muscles of the head and limbs. Then they stagger and go down to a “sitting” position, often with a ‘kink’ in her neck, and finally lie flat on their side before circulatory collapse, coma and death. A dry muzzle, staring eyes, cold legs and ears, constipation and drowsiness are seen after going down. The heart beat becomes weaker and faster. The body temperature falls below normal, especially in cold, wet, windy weather. These signs are due mainly to lowered blood calcium levels. Sometimes there are additional signs due to complicating factors. Bloat is common in cows unable to “sit up” because the gas in the rumen is unable to escape. Pneumonia and exposure may affect cows left out in bad weather.
About 80% of cases occur within one day of calving because milk and colostrum production drain calcium (and other substances) from the blood, and some cows are unable to replace the calcium quickly enough. High producers are more susceptible because the fall in their blood calcium level is greater. Selecting cows for high production may, therefore increase the problem with milk fever. Some individual cow families or breeds (for example, Jerseys) are more susceptible than others.
Age is important. Heifers are rarely affected. Old cows increase in susceptibility up to the fifth or six calving because they produce more milk and are less able to replace blood calcium quickly.
The feeding management of dry cows in the 2 weeks before calving is very important, because it affects both the amount of calcium available to replace blood calcium and the efficiency with which the available calcium can be used.
When the amount of calcium in the diet is greater than is needed, the efficiency of absorbing calcium from the intestine and the efficiency of transferring calcium from the skeleton both become very sluggish and the chance of milk fever is greatly increased.
Also, grazing pastures in Southern Australia winter and spring results in alkaline blood which creates conditions unfavorable for the availability of calcium in the body and predisposes the cow to milk fever. Feeding hay prior to calving and restricting access to green feed results in acidic blood which favours calcium mobilization from bone and improves calcium absorption from the intestines, both of which are important factors in preventing the occurrence of milk fever.
Fat cows are at a greater risk than thin cows. This is partly because their feed and calcium intake has been higher and partly because fat cows produce more milk at calving time.
Some cows get milk fever several days or even weeks before or after calving. This is usually due to the feed, especially the dietary calcium, being insufficient to meet the heavy demand due to the rapidly growing foetus or milk production in early lactation.
In early lactation, cows should receive as much calcium as possible, and clover-dominant pasture are therefore desirable. They will help to prevent grass tetany as well as milk fever.
How to treat milk fever
Treat the affected cow as soon as possible because death is certain if you don’t. Collect the animal’s blood sample for further clinical analysis before you administer any treatment.
Depending on the stage of the condition, you may choose one of the three options available for administering the treatment.
Oral treatment : For animals that are still in the early stages of the condition, oral treatment is a viable option. The advantage of this option is that the calcium gets absorbed in the intestines. However, some people may be reluctant to use this option because calcium gels ulcerate the oral cavity or the cow’s intestines. Furthermore, the unpalatability of these gels will lead to reduced feed intake. On the other hand, administering a liquid calcium solution increases the risk of pulmonary aspiration since the solution is very caustic. You can use 300 ml, or more, of a 40% solution of calcium gluconate. Since a myriad of other minerals such as magnesium, phosphorus and glucose (for energy) may be in short supply at the same time, you can use a combined mineral solution that contains these minerals.
Subcutaneous administration : You inject calcium solution in the peripheral parts. Since the animal has a low pulse and an inefficient circulation, you should split the dose and administer it in different parts. This will facilitate a speedy uptake of the treatment into the system. One problem with this method is that, there is a likelihood of the drug causing necrosis at the injection site. This is attributed to the poor circulation of blood in the peripheral tissues.
Intravenous injection : Administer 500 milliliters of 23 percent calcium gluconate intravenously. It will boost the blood calcium level, which is not only necessary but also critical in an emergency situation. IV injection provides a rapid increase in blood calcium and provides the desired result almost instantly. Take caution while administering an IV treatment so that you do not end up killing the cow with a heart attack. Administer the dose slowly to boost the blood calcium levels slowly. Take note that blood calcium will drop again after four hours, taking the cow back to a hypocalcaemic state. Administering large IV doses will not benefit a cow with milk fever much. Once the cow has regained strength, add oral treatment to reinforce the IV.
Preventing milk fever episodes
Feeding plays a key role in preventing the occurrence of milk fever. Keep cows on low calcium diets to stimulate their body systems to mobilize calcium from the bones. This will help in maintaining a level concentration of calcium in the blood. It is easier for the cow to mobilize calcium from the bones than from the feeds.
Conduct mineral test for the feeds and check for availability of calcium, phosphorus, magnesium, potassium, sodium, sulfur, and chloride. Consult an animal nutritionist to help you develop an effective feeding plan that will take care of your cow’s mineral needs and prevent incidences of milk fever.
Identify the animals that are at risk of developing milk fever and put them on dry matter feed for about three weeks before calving. Limit the amount of grass and green pasture feeding to reduce the risk of grass tetany. Ensure that the feed has no mold or traces of mycotoxins (e.g. afflatoxin) in it.
Administer high energy low calcium feeds to improve productivity. Cereals have high energy and phosphorus as an added advantage. You can add about 100 grams of ammonium chloride to the feed if the cow’s rumen has a high pH (test urine pH). Begin administering this ration to the cow two days before parturition and continue until two days after parturition.
Physical monitoring : When the cows are about to calve down, keep a closer watch over them to allow you detect milk fever early should such an incidence occur. After parturition, gradually introduce calcium rich feeds and do not restrict the cow’s feeding. You can even use calcium feed supplements.
Vitamin supplementation : If you cannot find proper dietary management programs readily, you can inject the cow with vitamin D intravenously (co-factor for calcium absorption). Administer this before parturition (usually between two to seven days before calving). If the cow does not calve down withing the projected window and the seven-day window elapses, repeat the treatment after 10 days (as necessary). Supplement vitamin D intake for all the lactating animals. Peg the supplementation to 50,000 units per head per day for all the cows. This will help the cows to utilize calcium much better.
Mineral supplementation : Some farmers prefer to take the precaution and inject the cow with calcium gluconate just before or after calving. This method is quite a success in preventing milk fever since the boost builds up calcium reservoir in the blood to make it readily available for making milk. There should be a caveat here. IV administration of calcium will boost calcium level in the blood but the effect is likely to wear off after some time if the cow’s biological calcium regulation system has not taken effect. You can drench the cow with a calcium solution for two days before parturition. Since magnesium deficiency is almost always associated with milk fever, you can add magnesium into the drenching solution. Drenching after injecting the cow will prevent relapse of milk fever.
N/B): Recovered cows should not be milked for 24 hours; then the amount of milk taken should be gradually increased over the next 2-3 days.