Dairy cattle feed intake system
In order to feed dairy cattle well, especially high-producing dairy cattle, the livestock farmer must know how much feed his cattle will eat. This can be estimated using a Feed Intake Model. A model such as this calculates, on the one hand, the feed intake capacity and, on the other hand, the various feeds are compared to one another with respect to their satiety value. For variable feed materials such as raw feeds (fresh grass, grass silage and maize silage), the satiety value is calculated per batch using the data from the results form of a laboratory.
In 2002, the CVB first introduced a Feed Intake Model. It was a system which was developed by the Research Institute for Animal Husbandry in Lelystad. The outcome of an evaluation of this model was sufficient to work on an improvement of this.
During the development of the ‘Dairy Cattle Feed Intake Model 2007' only use was made of recent feeding trials. This means that results were used from cattle as they are currently living at the dairy cattle farms. At the start of the lactation the new model predicts a somewhat higher feed intake than the old model. This removes a major criticism of the old model. The new model also provides a more accurate estimate of the feed intake. This is achieved by, among other things, taking account in the prediction of the feed intake capacity of the current milk yield and milk composition as well as the weight of the animals.
The new model was ‘validated' by predicting the feed intake for a number of independent feeding trials using the new model and then comparing these predictions with the actual (measured) feed intake. The results were so satisfactory that the new model was introduced with every confidence. Nevertheless, practical experience still has to be gained with the new model.
Dairy cattle protein system
If you want to feed dairy cattle properly then you have to take account of the rumen. A large proportion of the feed components are broken down in the rumen by the micro-organisms living in it. This breakdown is referred to as ‘rumen fermentation'. The feed fraction which is broken down in the rumen is called ‘rumen non-bypass'. The part escaping rumen breakdown is called ‘bypass'. Of the rumen bypass fraction of a feed component, a part (and sometimes all) is digested in the reticulum and the small and large intestines of the cow.
During the breakdown of feed protein in the rumen by the microflora, nitrogen is released mostly in the form of ammonia. This nitrogen is vital for the growth of the micro-organisms. Carbohydrates which are fermented in the rumen provide, on the one hand, ‘volatile fatty acids' which are extremely useful for the animal and, on the other hand, the energy essential for the growth of the micro-organisms. The growth of micro-organisms means an increase in ‘bacterial mass' and especially in the microbial proteins which are important for the cow. The microbial protein, like the by-pass feed protein, is digested when it flows out of the rumen to the reticulum and the small and large intestines. During the digestion of microbial protein amino acids which are necessary for milk protein synthesis, are released in a relative proportions which often better match the amino acid pattern of milk protein than that which applies for by-pass feed proteins.
In order to provide high-production dairy cattle with the necessary nutrients it is very important that there is proper control of the ration composition as far as the intake of rumen bypass or non-bypass nutrients is concerned.
In order to achieve this we have to know what happens in the rumen for all the feed constituents which can be fed to cattle. This knowledge will be gained by filling a number of dragon bags with a certain quantity of a feed material, ‘putting' this in the rumen and analysing how much of the feed components has disappeared from the bag after a longer or shorter period of incubation time as a result of being broken down by rumen flora.
The first CVB system in which specific attention was paid to rumen processes was the DVE/OEB system which was introduced in 1991. DVE stands in Dutch for ‘intestinal digestible protein' and is a measure of the amount of protein which is made available to the dairy cow from the feed. OEB is the Dutch abbreviation for ‘rumen degradable protein balance' and provides information on the quantity of microbial protein which can be produced on the basis of, on the one hand, the quantity of nitrogen available to the rumen and, on the other hand, the quantity of energy available to the rumen. In the event of a positive OEB there is a surplus of nitrogen available to the rumen microflora and in the event of a negative OEB there is a shortage.
In the new ‘DVE/OEB 2007 system', compared to the system of 1991, a much more detailed description is given of what exactly happens in the rumen. This applies to the protein fraction present in the feed and, to a greater extent, the carbohydrate fraction. This latter fraction is now split into starch, sugars, cell wall carbohydrates (NDF) and ‘residual non starch polysaccharides'. In the old system account was only taken of the starch breakdown.
In addition an estimate is also made for both protein and the individual carbohydrates of what fraction is ‘dissolved' in the rumen liquid, which fraction is present in very small particles which are easily transported with the fluids flow in the rumen, and which fraction is present in somewhat ‘larger particles'.
The question arises of why there must be such a precise examination of what happens with all kinds of components in the rumen. The answer is that only then can we properly estimate how much microbial protein (in addition to bypass feed protein) and how much volatile fatty acids (in addition to rumen bypass carbohydrates) are available to the cow for the production of milk. To put it simply: if you do not know what is happening in the rumen then you can not provide the current high-production dairy cattle with the best possible nutrients.
Firstly, the amount of energy which is released during rumen breakdown varies per carbohydrate fraction. The degree to which this energy is used for the synthesis of microbial protein is then dependent on the way in which a carbohydrate is present in the rumen: whether it is dissolved or is present as very small particles in the rumen liquid or whether it is present in somewhat larger particles which are broken down ‘step for step'.
Account is taken in the new system of all these aspects in the calculation of the quantity of rumen fermentable organic matter and with which degree of efficiency the released energy is used by the micro-organisms for their growth.
Another important point in the new system is that there it provides much more insight into the dynamics of the breakdown of the nutrients in the rumen. This enables a much better balancing of the nitrogen supply and the energy supply to the micro-organisms. The new system also provides a good insight into the speed of a ration. These aspects were missing in the old system.
The concept of the DVE/OEB 2007 system is therefore much more complicated than the 1991 system. The system is not, however, completely new. Various systems from abroad and also the company systems of various major (compound) feed companies were already based to a greater or lesser extent on this concept. On the other hand, this concept has been revitalised in the new CVB protein system such that it can safely be said that it competes well with all the other systems which exist.
As stated above, the new system is highly complex and detailed. This is because rumen physiology is so complex. This is unavoidable because of the high demands made on dairy cattle nowadays.
Although the system is complex and complicated, a dairy cattle farmer will see fairly little of this. Terms such as DVE, OEB and FOS are calculated in another way but have the same meaning as in the old system. In the future we shall, however, use the term ‘FOSp' to indicate that we are really talking about the ‘fermentable organic matter in the rumen'. There are three new key figures which give information on the dynamics and speed of rumen fermentation. These are: OEB-2, FOSp-2 and the ratio figure FOSp-2 / FOS. OEB-2 shows the balance between the nitrogen and the energy supply at rumen level during the first two hours after feeding. FOSp-2 indicates how much organic matter is degraded in these first two hours. The ratio figure FOSp-2 / FOSp describes the speed of a ration: the higher the ratio, the quicker the ration is degraded.
Just as in the old system it is advisable, but now in both the short and the longer term, to ensure that the OEB value is not negative. In order to prevent the waste of nitrogen at rumen level, the OEB should be as close to nil as possible.
At the time when the DVE/OEB 2007 system was presented, the validation was not yet completed. The first results were such that there at that time was no reasons to modify the standards with respect to the quantity of DVE which is required for milk protein production. A final answer can only be given when this validation is completed. This will be the case in mid-2007. For this reason and for other reasons (such as a more precise evaluation of a number of feed materials on the basis of research to be carried out soon), it was decided that the system would officially replace the old system not in March 2007 but from October 2007 onwards. The necessary experience can be gained with the new system in the interim period.
Both new CVB systems are described in so-called documentation rapports:
• S. Tamminga et al.: Protein evaluation for ruminants: the DVE./OEB 2007 system; CVB documentation report nr. 53, March 2007.
• M.C. Blok et al.:"Voeropnamemodel Melkvee, versie 2007; CVB-documentatierapport nr. 51, maart 2007 (in Dutch).
For more information please send an E-mail to: cvb@pdv.nl.
