NCDC212: Metric Definition of the Physical Component of Dairy Diets
Statement of Issues and JustificationThe objective of this committee would be to define the metric for measuring the physical component of dairy diets. Once a consistent metric is adopted, experiments to define requirements would follow, but the primary purpose of this group would be to generate a critical mass of researchers using the same metric so that it becomes the standard. It is important that the metric be theoretically and practically reasonable, but it is also clear that there is a range of metrics that could be set, and the requirements would reflect that metric. So no one metric is absolutely right, but it is important to set a standard even though it will be at least partly arbitrary.
Everyone understands that long particles (presumably those containing insoluble fiber) are essential in some amount in the diet of a ruminant for 'normal' or 'optimum' rumen function. Any one who has tried to model rumen fill has found that at least two particle size 'pools' are required. The problem is there is no agreement or consistency in what size and sieving technique should be done to divide these. Not only that, but multiple different empirical models and recommendations exist that use different sizes, or worse yet, the same nominal size done by different techniques (which are in fact different values). On top of that this physical part interacts with the total amount of fiber and other aspects of carbohydrate digestibility in the rumen, and a useful system has to take that into account. There is clearly a lot of old and recent data that could be integrated, and I think it will take a core of people measuring the same thing and using the same terms to move this forward. My thinking is that we would basically formulate the bones of a system that would be in the next dairy NCR publication and do our best to populate the structure with data and set some standards so that others can contribute useful data to it.
This area of information is very important to the dairy industry nationally. Quantifying the critical physical characteristics of fiber in the dairy diet and understanding its relationship and interactions in the rumen processes will be extremely useful in diet formulation. Such information will be useful not only to the scientists working to understand the rumen processes, but should provide practical guidelines to dairyman and dairy practitioners who rely on NRC recommendations to formulate diets for our dairy herds.
The 2001 NRC recommendations say that particle size is important and that their recommendations are for forage of adequate particle size. This is obviously very qualitative and is so because there was not an organized cohesive data set for them to draw on to make quantitative recommendations which is the ultimate goal of this kind of publication. In terms of interest to stakeholders - most commercial ration balancing programs incorporate some sort of estimate for this, not because there are good estimates but because people want to balance for it. So I think the commercial programs show the need in the industry and the desire to adopt this, and the NRC shows that the scientific status of what we have is not very good. In the mid 1990's we organized a seminar on this at ADSA and it drew a huge crowd composed of both scientists and industry nutrition consultants (farmers per se do not attend that meeting in significant numbers). The topic has also been a large draw at the major regional dairy conferences.
The impact will be on improved animal health (fine diets cause digestive disturbances) and economic. Fine diets can result in lost revenue due to fat test depression on one hand, yet relying on forages as the only dietary source of fiber can raise diets costs, and excessively long forages can reduce intake and productivity. It is clearly a case where better optimization data is needed.
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