There are three critical elements to dry cow management: blood calcium, energy metabolism and immune function. It is important to get all three right to avoid health problems after calving.
Typically, the main focus on managing dry cows has been on maintaining blood calcium around calving and feeding a low-energy, low-potassium, high-fibre diet. But equally important is the health of the cow and the avoidance of immune suppression.
About six years ago a simple experiment was carried out where 26 cows were slightly over-stocked together in the last two weeks of pregnancy on a good dry cow diet. After calving, 65% of the cows calved down and went on to produce the expected amount of milk, while the other 35% stumbled and went down with metritis, followed by mastitis and later problems with fertility. Why did this happen?
The researchers recorded the time the cows spent eating and found the cows that developed metritis were spending less time feeding (see graph). These tended to be the subordinate cows at the bottom of the social order. In fact, for every 10-minute decrease in average daily feeding time, cows were twice as likely to be diagnosed with metritis.
At first, it was thought the metritis was simply caused by low dry matter and low energy intakes pre-calving, but other research since has revealed that something else was going on.
In the run up to calving there is a natural suppression of the cow’s immune system, which sees white blood cell and lymphocyte numbers fall by about 30%. This is thought to be an evolutionary mechanism to stop the cow’s immune system from attacking the developing calf. After calving the immune system normally switches back on, attacks the cotyledons holding the placenta to the uterus and allows the placenta to fall away to give a good clean calving.
When cows are stressed (by moving between groups too close to calving or by over-stocking, for example), extra cortisol and adrenalin are produced. Both are strong immune suppressors, which switch the immune system off even more than normal. So if you have timid cows in a pen (as in the experiment) or new cows that have just moved in late pregnancy into an established pen – or any other stressor – then these cows are going to be fearful. This will increase their cortisol levels, which in turn suppresses the immune system and can reduce white blood and lymphocyte numbers by 60-80%.
With a weaker immune system the pregnant cow is more vulnerable to uterine and mastitis-type infections pre-calving. After calving, it takes longer for the immune system to recover, so the placenta does not break away cleanly and any uterine or mastitis infection is going to have time to multiply and be a much more serious problem.
There are still some unresolved issues and more research is being done to look at the link between stress and dry cow health. High blood NEFAs (non-esterified fatty acids) and low blood calcium and magnesium are also known to cause immune suppression. However, all the research and commercial farm work show the three to four weeks before calving are critical and farmers should try to minimise the number of stressors the cows are exposed to. Some examples of factors which can affect the immune system are:
1 Pen movement pre-calving – cows should not be moved in the last three weeks of pregnancy. Pen moves in the last week before calving have the biggest adverse effect on cow health. If cows need to move into a calving pen, move them at the point of calving when the calf’s legs are showing or no progress is apparent.
2 Social stress – avoid overcrowding. Heifers are particularly badly effected by overcrowding.
3 Stocking density – dry cows in the last three to four weeks ideally need 100 sq ft a cow of straw yard space.
4 Feed barrier – dry cows need 30 inches of feed barrier space and a barrier which provides easy access to a clean, fresh, palatable food.
5 Dry matter intakes in the pre-calvers should be about 12-14 kg/head/day.
6 Fat cows tend to have high NEFAs which will suppress the immune system and increase the risk of fatty liver, ketosis and displacements. Dry cows should calve down with a condition score of 2.5-3.0.
As for the diet, a dry cow should consume 110-120 MJ ME a day on a diet with an energy density of 9-10 MJ/kg DM, protein 13-15%, magnesium 0.45-0.5%, less than 1.3% potassium or sufficient anions to provide a neutral or negative DCAD, with 0.7-1% calcium (depending on the level of DCAD), 0.3 mg/kg DM selenium, 60-100 mg/kg zinc, 2,000-4,000 iu Vitamin E as well as all of the other trace elements and vitamins.