The dry period extends from the end of lactation until the cow calves again. It enables the milk-producing tissue in the udder to regenerate and the rumen to recover. A dry period that is too long or too short will affect milk production. Studies have shown that a dry period of less than 45 days will significantly reduce milk yield in the next lactation because more time is needed for the udder to recover and revert to its normal size. This process is called involution.
In a dry period of more than 60 days, such as might occur after an abortion, a cow can easily become too fat, leading to metabolic problems and low milk yield after calving.
Calculating the drying-up date
Gestation in a cow lasts for nine months. In the eight weeks before calving, the foetus grows exceptionally fast; about 60% of the increase in the birth mass of the calf takes place during this period. The nutrition supplied to the cow during the dry period must at least ensure that foetal growth takes place. To calculate the drying-up date, you need to know the expected calving date. This is calculated from the servicing date, once it has been confirmed that the cow is pregnant.
The average gestation period of cows varies from 275 to 283 days. To determine the drying-up date, subtract 60 days from the expected calving date.
If you stop milking a cow, it will dry up. A cow with a high milk production of 20kg or more must be milked once a day during the last two to three days before drying up. The cow may also be fed straw to reduce her milk production. At the final milking, administer a long-lasting dry cow antibiotic in each of the four quarters to prevent the udder from infection by mastitis-causing bacteria during the dry period.
When an udder is not drained, the milk is slowly re-absorbed, and this process suppresses milk production. Eventually the cow dries up and can be moved to the dry cow group.
Dry period feeding
During the two to three weeks before calving, a cow undergoes a significant hormonal change. She usually loses her appetite, especially in the days just before calving. If you ignore this, it may result in ketosis (using up stored fat in the body), a fat liver, a displaced abomasum or a retained placenta after calving.
A cow that is a poor feeder before calving will often feed poorly after calving. The production of such a cow will be below average, and she will tend to have more physical problems. It is important that cows be in a good condition when dried up. Lean cows do not have enough energy reserves to maintain high production during early lactation, as their energy needs exceed their energy intake. Cows that are too fat can also be a problem: they eat less and often have reproductive problems.
The correct nutrition
Feed coarse, good quality, rough-textured fodder during the first four to six weeks of the dry period. This may include maize silage, grass hay or small grain hay or silage. Grass or grass and clover pasture may also be used. Do not feed too much maize as the cows will grow too fat. Supply a suitable lick with the coarse fodder to ensure that the cow gets enough minerals and trace elements.
Feed concentrates in the last three weeks of the dry period. Start at 1kg/ cow/ day and increase this steadily to about 3kg/ day just before calving.
Only coarse fodder
with a low potassium content (maize silage and small grain hay or silage) should be supplied during this period. Avoid coarse fodder with a high potassium level, such as kikuyu, rye-grass and clover. This can cause problems such as milk fever and a retained placenta.
The cow should have the correct balance of trace elements at this stage to prevent a retained placenta and mastitis infections after calving. Administer vitamins A and E with zinc and selenium to milkers 14 days before calving.
Sources: Elsenburg infopak by CJC Muller; ‘Care and feeding of the dry and post-parturient cow’ by PG Stewart, Cedara Agricultural Development Institute; ‘Managing your dry cows’, by Dr Rich Vanderwal and Dr Mary Lou Swift, Abbotsford Veterinary Clinic, British Columbia, Canada.