29 DECEMBER 2015
A cows lactation may begin with the act of calving, but the performance of that lactation can be traced right the way back through her transition period, her dry period and even back to the end of her previous lactation. The dry and transition periods of a cow have a huge impact on the incidence of metabolic disorders such as milk fever, retained foetal membrane and ketosis. Those periods are also directly related to egg quality and therefore to fertility into lactation.
The big question is: What are the options for managing dry cows to maximise lactation performance?
LOW CALCIUM OR 0% CALCIUM
The ideal dry cow diet is one that provides little or no calcium (30g per day). unfortunately, this is almost completely unachievable, especially on our predominantly grass silage based diets where the forage alone could be providing in excess of double that. where alternative forages are available that can help, but the use of a calcium binder can simulate the same effect on any.
Just like a mycotoxin binder carries mycotoxins safely through the cow, a calcium binder prevents the cow from absorbing calcium, whilst ensuring there is still an adequate supply in the bloodstream, by stimulating the cows’ own calcium mobilising systems. This creates a perfect balance of calcium in the cow around the time of calving, which greatly reduces the risk of milk fever, held cleansings, ketosis and twisted stomachs.
DCAB & Partial DCAB Systems DCAB stands for Dietary Cation Anion Balance and measures the balance of positive and negative ions within the cows’ diet. The ions that are measured come from Potassium (K) and Sodium (Na) on the positive side, and from Chloride (Cl) and Sulphur (S) on the negative side.
A highly positive DCAB score, promotes intakes and milk yield and is easily sustained by the generally high levels of positive ions (cations) that we find in most of our feedstuffs and particularly in grass silages. Unfortunately, a high DCAB score adversely affects dry cows. In particular, these very high positive scores are closely linked to milk fever and, as a result, can also have an impact on retained foetal membranes, displaced abomasums and other performance related problems right through lactation.
To minimise these effects, we can feed specific ingredients to bring the overall DCAB score down. Products such as Magnesium Chloride or Ammonium Chloride are required to pull down the DCAB value of a diet and can be supplied as a straight ingredient, through the water supply, or as part of a dry cow concentrate.
In a ‘full’ DCAB system, the DCAB score is made significantly negative. At these low levels, cows become very sensitive to changes in the DCAB value and as a result it is necessary to regularly check the pH of their urine. Typically urine pH would be around 8.0, but on the full DCAB system could drop as low as 6.0. Reducing DCAB by this much drives the cow into a metabolic acidosis. Just like with rumen acidosis, this additional acid loading has to be buffered. The cows own response to this is to mobilise calcium to buffer the acid. It is this mobilisation of calcium that significantly reduces her risk of milk fever.
A ‘partial’ DCAB system, aims to pull the DCAB value of the diet down to around 0 meq/kg. Typically, a partial DCAB diet will have a DCAB range of -50 to +50 meq/kg. At this level, there is no need to check urine pH making it significantly easier to manage and administer than the full system.
In principle the two systems work exactly the same, however with the partial system being less extreme, it is also slightly less effective. When used correctly though, it will still do a great job of reducing the incidence of milk fever. The downside of both of these, is that the DCAB score will be constantly moving as a result of dietary changes. Even simply moving back through a silage clamp, the DCAB scores from different fields will have a range of values. As a result, forages need to be tested regularly for their mineral content to make sure that the correct levels of negative anions can be provided.
With a typical forage mineral analysis taking up to 10 days, it can be difficult to keep up with changes to the diet, as well as proving potentially expensive. If DCAB values move up out of the optimum range, milk fevers will start to occur; whilst too negative a DCAB score can actually cause milk fevers if there isn’t enough calcium in the diet.
Keeping dry cows in one group is not without its problems, but is a very practical system, particularly in smaller herds where grouping cattle in low numbers really isn’t feasible. The principle of this is that cows are dried off as normal at around 8 weeks pre-calving. They can then be fed on just one diet, right the way through until they reach the point of calving. This means that there are fewer changes of diet, giving the rumen a much better chance of remaining stable.
The issues surrounding a one group system are those of intakes and energy. There will be a big variation in the requirements of cows that are spread throughout the dry period. In the early part of the dry period, cows will eat quite a lot, but actually have a fairly low energy requirement. In the second half of the dry period, the calf is starting to develop and grow very rapidly. This creates a situation where she wants to eat less, but her requirement for energy is constantly on the rise.
This is where the problem of a one group system can really become apparent. As a result of these cows being together, there will always need to be a compromise of either over feeding cows that are further away from calving, to ensure the cows that are closer to calving are adequately provided for, or under feeding cows that are closer to calving to avoid those further away from calving getting too fat.
Neither of these is ideal for effective dry cow management; picking the lesser of two evils, is still choosing an option that is essentially incorrect. That being said, it is not always possible to do anything different to this in some situations. Regular body condition and rumen fill scoring of dry cows in a single group is absolutely vital to keep an eye on these problems. In conjunction with issues around calving, such as milk fever or retained cleansings, scoring a dry cows’ body condition and rumen fill is really the only way to check their performance through this period. Her body condition score should ideally be between 3.0 – 3.5, with a rumen fill score of around 4.0. The most important factor with body condition score however is that it doesn’t change, with cows losing weight being particularly problematic.
Where possible and practical, managing dry cows in 2 groups has many benefits. The biggest benefit is the flexibility that a 2 group system can offer. In essence, the 2 group system consist of a group of dry cows, usually referred to as the ‘Far Off’ group, that contains cows from the day they are dried off through to around 3 weeks pre-calving. For the last 3 weeks of the dry period, cows are moved into what is often known as a ‘Close To’ group, but also sometimes called the ‘Transition’ or ‘Pre-Fresh’ group.
Cows in the far off group are fed on a maintenance diet. The target with these cows is to maximise their intakes and make sure that the rumen stays nice and big, whilst also ensuring that they neither gain nor lose weight. In order to achieve this, the far off group should be fed on a bulky, low energy density diet, probably containing some chopped straw. This means that cows need to consume a lot of the mix to achieve their energy requirements.
In the close-to group, the cows’ intakes will begin to fall away. At the same time, her energy requirement will be rapidly rising as her calf goes into the final stages of development. This means that the energy density of the diet needs to be higher to satisfy her changing requirements. Her requirement for high quality protein is also greater at this stage. Feeding a high quality dry cow concentrate is the ideal way to achieve this, as it is very energy dense. This concentrate should also provide the high quality protein, and an appropriate level of mineral supplementation too.
Feeding high quality (bypass) protein, helps to provide protein to the calf, as well as improving the quality of the colostrums that the cow produces, by replenishing her ‘protein pool’. Replenishment of this pool also helps her to prepare for her next lactation. As with the 1 group system, regular body condition and rumen fill scoring should be undertaken to ensure that the diet is giving the correct balance of intake and energy.
IN WITH THE MILKERS
Keeping dry cows in with the milkers is a more traditional approach to managing them, and is still popular in quite a few herds. This system does work quite well, up to a point. It gives the opportunity to look at the dry cows when they come through the parlour twice a day, and ensures that the rumen population remains stable with no changes in diet. On the down side though, leaving dry cows with lactating cows means that the stimulus to milk is never removed and it can be difficult to get cows to fully dry off.
Nutritionally the milking cow diet is probably higher in energy and too low in fibre to be ideal for dry cows, which could potentially compromise cows going into lactation, limiting intakes and maybe leaving cows at more risk of ketosis. The other issue with the nutrition in milking cows is mineral status. Dry cows have a higher requirement for certain vitamins and minerals than lactating cows, and the biggest difference between milking and dry cow diets will be the calcium status. Milking cow diets are always high in calcium, due to the high amount of calcium found in milk. Unfortunately, these types of diets leave dry cows at significant risk of milk fever.
Finally, the other risks associated to this system of dry cow management are purely management based. With dry cows in with the main herd, there is always a chance that one of the cows may be inadvertently milked and leave antibiotics in the milk tank. The other issue, is the risk that a cow may end up calving in the cubicles with the main herd. This creates problems for the calf in particular, and leaves it at significant risk from pathogens during the first few hours when it has no immunity.
High straw levels are a great addition to a dry cow diet, to help to create a higher volume, lower energy density base mix. This system really helps when forage quality is good and the diet would otherwise be too high in energy and not bulky enough. The important thing with a high straw diet is the chop length of the straw. If the chop length is too long, cows will be able to sort the ration and a lot of the straw will be wasted. Ideally, the straw should be shorter than the width of a cows’ muzzle. As part of a fully managed dry cow diet, chopped straw can be the ideal ingredient to manipulate energy and protein levels to the appropriate levels.
It’s generally believed that a heifer calving for the first time is at no risk of milk fever; that’s a disease for older cows. Whilst this is partially correct, in that only around 2% of heifers will get a clinical milk fever, it is now understood that as many as 35% of heifers could get a sub-clinical milk fever. These are the heifers that appear to be fine around calving, but never quite hit the peak yields that others do, or that have more days to first service and conception; heifers that just don’t quite do what you believe they should. In calf heifers should be managed as dry cows for the last 8 – 10 weeks pre calving to give them the same regime as the older cattle would be get. Whilst there can be problems with heifers bagging up too early, if this can be managed the benefits to heifers in the long term could be huge; in terms of milk production, fertility, health and the viability and growth rate of her calf too.