Pregnancy toxaemia in cows
Over-fat pregnant cows provided with insufficient food during the last two months of pregnancy can develop the disease which is similar to pregnancy toxaemia (twin lamb disease) of sheep. Deprivation of feed in fat beef cattle causes the movement of large amounts of fat from body stores to the liver.
Fat pregnant cows, particularly those with poor teeth or carrying twin calves, are very susceptible to pregnancy toxaemia. The disease is more common in first calf heifers than in older cows, and occurs in cows that are in the last two months of pregnancy or that have just calved.
Changing the diet of pregnant beef cows from a good quality, to a poor quality diet in an attempt to reduce body weight and enhance ease of calving results in pregnancy toxaemia.
Starvation is the cause of death
Although there are a number of causes of death in pregnant cows, closer investigation of affected herds will show that very little, or only poor quality feed was provided for cows in the last two months of pregnancy, just as the developing calves were demanding most nutrients. These cows starve to death, even though they are in good condition.
In a pregnant cow there is a large demand for glucose by the developing calf in the last few weeks before birth. There is even greater demand on a cow carrying twins. The developing calf may press on the rumen, reducing its volume, especially if the cow is very fat.
If only low-quality fibrous diets, such as straw and stubble are available, the cow is unable to meet this demand for glucose. Although body fats can be mobilised in huge quantities, they cannot be used if there is insufficient glucose.
In these cases the fat accumulates in the liver, the liver becomes enlarged, pale yellow and fatty. Chemicals called ketone bodies are also produced. These and other chemicals produced in starved fat cows can eventually lead to their death.
All pregnant cows are at risk
Two-year-old heifers and aged cows have died with pregnancy toxaemia so cattle of all ages are at risk. Cows that have lost teeth or have poor jaw conformation are particularly susceptible because they cannot graze well.
The number of cows that die varies widely between properties and between years. Some owners usually seek veterinary advice when more than one cow dies. However, losses as high as ten per cent of the breeding herd have been reported.
Pregnant beef cows which are in thin body condition on poor pasture can become extremely emaciated and eventually recumbent and die of starvation, but they do not develop pregnancy toxaemia.
Preventing Pregnancy toxaemia
Pregnancy toxaemia can be prevented by ensuring that beef cows are not starved or undernourished in the eight weeks before calving.
Even after one or two cows are affected, further cases can be prevented by providing high quality supplementary feed.
Management of the food supply to the herd is the most important factor that determines whether cows will be affected by pregnancy toxaemia. On properties where the disease occurs, there is usually no supplementary feed provided for autumn calving cows in late summer and autumn when pastures are dry and there is little growth. Provision of good quality hay to pregnant cows during this period will prevent pregnancy toxaemia.
Cows should not be over-fat during pregnancy. Over-fat cows seem to be more susceptible to pregnancy toxaemia if they are starved for short periods; for example, if held in yards for several hours.
If pregnancy toxaemia occurs, remaining cows should be sorted into groups corresponding to body condition and fed accordingly.
The water supply to cows should also be checked during summer and autumn. Many cows have died on properties where a dam has dried up during this period.
Detecting early Pregnancy toxaemia
In herds where there is no regular observation of stock, cows may simply be found dead.
The first signs are easily overlooked. Cows in the early stages stop eating and appear dull and depressed. They often isolate themselves from the rest of the herd and do not forage for feed. They become weak and cannot stand.
Some cows, particularly those closer to calving, are unsteady on their feet, maybe aggressive, restless and reluctant to enter yards or a crush. Some will even charge at moving objects. These cows usually go down, and usually die.
At post mortem the liver is enlarged, pale yellow and greasy.
Treating pregnancy toxaemia
In general, cows which continue to eat will recover if given some supportive treatment and good quality feed. Cows which stop eating for three days or more will eventually die.
- intravenous glucose electrolyte solutions
- propylene glycol by mouth
- anabolic steroids
- water and balanced electrolytes given intra-ruminally
- glucose, calcium and magnesium salts given intravenously or under the skin
The longer treatment is delayed, the less effective it will be.
Veterinary treatment is aimed at restoring the metabolic balances in the cow and removing the calf to reduce the energy drain on the cow.
Cows that have been down for more than a day usually die.