To properly feed a dry cow we need to appreciate that there are big differences between the requirements of the early dry period and the late dry period. How you define these two periods will depend on factors such as breed type, yield, condition score, total length of the dry period and practicalities of managing the two groups. In a high yielding Holstein herd with an eight week dry period and appropriate condition scores, the groups should be about 5-6 weeks early dry and 2-3 weeks late dry period.
Early Dry Period
Once the cow stops milking, her energy requirements fall dramatically. In order to maintain a target body condition score of 2.5 to 3.0 throughout the dry period and avoid putting on excess weight, the cow must adjust in one of two ways:
- Eat less of an energy dense "lactation-type" diet (i.e. Dry Matter Intake, DMI, decreases).
- Eat more of a lower energy/higher fibre diet (i.e. DMI is maintained)
If she maintains her DMI of an energy dense diet (i.e. grass) she will put on condition herself and be more prone to metabolic disease and calving difficulties later on. Note that the weight of the cow is different to her body condition ("fat" or "thin"). e.g. a cow bearing twins can weigh a lot due to the calves and the foetal fluids, but still be in very poor condition (i.e. thin).
The aims of the early dry period are:-
- To maintain total dry matter intake (DMI)
- To restrict gain of body condition
- To keep the cow properly mineralised
To achieve these aims, the cow should be fed on a fibrous, low energy diet (e.g. straw and silage) with appropriate dry cow minerals to balance. She should not be allowed to lose weight as this will lead to fatty liver disease and ketosis, so straw only diets are to be avoided, whatever her body condition score.
Late Dry Period
During the 2-3 weeks leading up to calving the requirements of the dry cow start to change dramatically. Because of the enlarging uterus, her DMI begins to fall. This is combined with an increase in her requirements for energy and digestible undegradable protein (DUP), both for the growing calf and for preparation of the udder for colostrum and milk production. The rumen microbes need about 3-4 weeks to adapt to any change in diet (known as acclimatisation) and therefore this process must begin before the cow calves, otherwise optimal fermentation will not be achieved in the critical first few weeks of lactation. In other words, ideally cows require exposure to the lactating ration before they actually calve.
Therefore the aims of the late dry period are:-
- To start to increase the energy density of the diet
- To allow the rumen to acclimatise to the milking ration
- To achieve 1. and 2. without inducing milk fever
During this late dry period the cow should be offered the same forage as she will eat after calving plus 1-2 kg of parlour cake, or the milking TMR for out of parlour fed herds. Depending on the undegradable protein content of this ration, an additional benefit may be seen by offering small quantities of a digestible undegradable protein (DUP) source. DUP can also be used to pull weight off cows in the early dry period, but speak to one of us before doing this.
Minerals and Milk Fever
When cows used to be 'steamed up' in the dry period, milk fever was a big problem. This was due to cows being over fat at calving together with an oversupply of calcium to the cow before calving via the parlour cake. At the feeding rates described above, steaming up is not a problem, particularly when they have been straw fed early on. Properly formulated dry cow minerals are normally high in magnesium, which helps to increase calcium utilisation around the time of calving. Using magnesium chloride in drinking water can therefore help in the prevention of milk fever, as can the addition of anionic salts, a practice which is currently popular.
Trace elements such as iodine, copper and selenium are also essential to the dry cow for subsequent lactation and fertility, as well as for quality colostrum and calf health. It is worth blood testing some close-up dry cows to be sure that they are properly mineralised.
Every late summer/autumn, we see an upsurge in milk fever cases. This is because grass is a bad feed for dry cows as it is high in potassium, which messes up the mineral balance of the diet (the so called "Dietary Cationic Anionic Balance", or "DCAB"), predisposing to milk fever. In addition, unless they are very tightly stocked (8-12 cows per hectare) on bare pasture, grass tends to cause dry cows to gain in body condition, again predisposing to milk fever. Worse in some ways is sub-clinical milk fever, where blood levels of calcium are low but the cow doesn't show the typical signs of milk fever. This can prevent proper function of the gut and the uterus and may lead to an increased incidence of uterine infections later on, as well as lower yields and displaced abomasums.
The main current area of interest in the control of milk fever, and reducing problems in fresh calved cows is the acidity of the dry cow ration - the 'DCAB' - the Dietary Cation Anion Balance as it is known. It is essentially and in simple terms aiming to get the dry cow ration to produce acid conditions in the body. This acidity helps keep the calcium balance in the body active and ready for action when the cow calves. It means that increased levels of calcium can be fed in the dry period without the risk of milk fever. This increased calcium is thought to be beneficial in preventing many other diseases in the fresh calved cow. The acidity of the diet can be deduced from a knowledge of the ingredients in it but a very simple and worthwhile check is to look at the pH of the urine in some dry cows. Urine pH is an accurate indicator of the body's pH so using simple test papers you can see if the dry cow ration is actually doing what it is supposed to do. A urine pH of less than 7.0 indicates that there is a metabolic acidosis in the cow but it really needs to be around 6.0 to 6.5 to produce the best protection against milk fever. Remember milk fever is only the start of the problem. A lot of other diseases take their cue from milk fever - endometritis, displaced abomasums, ketosis and so on are all diseases which carry an increased risk after milk fever - so try and aim to prevent it at all costs.
A key to getting nutrition right in the dry period is to have cows in the correct body condition in late lactation, at drying off, throughout the dry period and at calving. Body condition scoring is an extremely useful skill to develop and is relatively easy to master. The general recommendation is to have cows at condition score 2.5-3.0 at drying off and then maintain this throughout the dry period, neither gaining nor losing any significant condition. The time to get cow condition right is in late lactation as this is when it is easiest to manipulate the diet composition for individual cows. The aim is to have a consistent group of dry cows all with a similar body condition score. If you would like to learn to condition score your cows, please ask one of us to help. We have a scoring chart handout and will be happy to compare our estimations with your own when on farm, for example at routine fertility visits.