Tuesday, 23 October 2012

Cow health: Metabolic illnesses

Cows today produce much more milk and meat than their ancestors ever did. They are fed optimum diets and kept in maximum production the whole time, regardless of how unnatural that is to an animal. This causes many problems and illnesses to cows and calves. Most common ones are milk fever, ketosis (acetone disease) and grass staggers (grass tetany, hypomagnesemia, winter tetany).

Milk fever

Milk fever can occur in cows and pigs right or soon after calving / parturition. If not treated quickly, severe milk fever can kill the animal in one day.

Cause: Milk fever is caused by low levels of calcium in the blood. After calving the milk production starts on high efficiency, and a lot of calcium is suddenly needed. This calcium is released from the animal's bones. If calcium cannot be released quickly enough, the calcium needed for muscles to function is used instead, causing milk fever. Milk fever can be prevented by keeping the cow in very low-calcium diet during it's dry period, giving the body time to increase it's calcium release mechanism.

Milk fever can occur later in the production period if the amount of calcium in the diet suddenly drops, or absorption of calcium is decreased due to another illness. Heifers and cows with low milk yield rarely suffer from milk fever.

Symptoms: Milk fever is not actually a fever, but paralysis. First the cow stops eating, it's skin feels cool, and it's muscles of the cow may tremble. Soon the large muscles in the legs cannot support the animal's weight anymore, and it falls, unable to stand. The cow may lie on it's side, whereupon it's rumen may fill with gas, suffocating the animal. Rumen movements stop, and within a day the animal dies due to paralysis of the lungs, liver and heart.

(c) www.nadis.org.uk
Treatment: Intravenous infusion of calcium is needed to raise the level of calcium in the blood. This is done by a vet, who must also listen to the animal's heart while infusing the drug (calcium is potentially toxic, and may cause heart failure). Only enough is given for the cow to get up and start eating, so it can fill it's own calcium levels naturally. Sometimes another treatment is needed, if the diet contains too little Ca. This can be given orally by anyone.

The risk for ilk fever can be reduced by ensuring that the dry period diet is low in calcium. The diet can also be tailored to affect the cation-anion balance of the cow's body: by lowering the pH of the body (increasing anion salts) three weeks before calving, the calcium is released from the bones more effectively. This can prevent up to 50 % of the cases of milk fever.

Milk fever in The Merck Veterinary Manual

Ketosis

(c) Valley Veterinary Clinic
Cause: Ketosis is caused when the cow has too little glucose in it's blood. Cows synthetise glucose in their liver, but this creates acidic ketones. Normally rumen microbes can use them as energy. If too much glucose is formed this way (due to lack of it in the blood), the microbes cannot use all of the ketones, and the pH of the animal drops.

Earlier ketosis occurred right before milk production peak, when the cow ate less than it needed to produce milk. Nowadays ketosis occurs commonly for recently calved fat cows, because their body releases more fats for energy than their liver can handle. The liver collects fat, and can no longer produce glucose, leading to ketosis.

Symptoms: Decreased appetite especially for concentrated feeds, eating of strangle substances such as dirty straw, apathy, quietness, loss of weight, dry feces, acidic smell in the animal's breath (not all people can smell ketones). Ketone levels in the milk are elevated. Cows may drop cuds, because they are acidic and thus taste bad.

Prevention and treatment:  More important than treating ketosis is to prevent it altogether. Make sure the cows are in good shape before calving, which also makes the calving easier and reduces the following metabolic stress. Avoid cows with ultra high milk yield, because they are more prone to ketosis. Adjust the diet for each animal so that they get enough precursors for gluconeogenesis even if their appetite is low. If possible, limit milking so the cow needs less glucose for production.

Treatment for ketosis is intravenous infusion of glucose, injection of cortisone, propylene glycol given orally

Ketosis in the The Merck Veterinary Manual

Grass staggers (grass tetany, hypomagnesemia)

Grass staggers is a form of convulsion caused by acute lack of magnesium. Young grass is low on magnesium, so this disease often affects cattle which has just been let to pasture.

Cause: Grass staggers is caused by lack of magnesium. Grass in the pasture can have too little magnesium if the grass is young, or it has been fertilized with too much potassium and nitrogen and too little magnesium. Absorption of magnesium is decreased if the diet has over 20 % of protein, over 3 % of potassium or too little fiber. Appetite also affects to how much the animal eats, and how much it thus gets magnesium.

Symptoms: When the magnesium level in the blood decreases, the animal cannot no longer control it's muscles. First the animal appears overly alert and tense, it is restless and its movements are uncoordinated. Soon it's muscles convulse, and the animal gets a seizure. The cow is sweaty and it's body temperature is high due to constant muscle tension.

Treatment: Magnesium must be injected to the animal as soon as possible, for it may die at any moment. Sometimes cows with grass staggers die just from the needle prick, so even quick treatment may not save the animal. If the injection is given and the cow picks up, magnesium must be given orally for five days. The diet of the whole cattle must be checked! If the cause is low Mg levels of the pasture grass, every animal in the herd may get sick and die.

Hypomagnesemic tetany in The Merck Veterinary Manual




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