In situ digestibility evaluation

F.A.R.M.E. Institute is one of only a handful of commercial facilities providing in situ evaluation of forages, grains, and byproduct feeds. A broad range of services is offered to meet the needs of the individual dairy farmer, the farm consultant, and the plant breeder. F.A.R.M.E. Institute personnel have years of experience in evaluating forage digestibility, testing forage preservatives, predicting bypass proteins and amino acids, and implementing results for ration balancing.

The in situ evaluations are conducted in high producing (>70 lbs. milk daily), ruminally fistulated dairy cows. The cows are fed a TMR consisting of corn silage, mixed haycrop silage, grains and various byproducts (including animal protein and fat supplements) formulated to support 90 lbs. of milk.

The in situ technique involves incubating test materials for 6 different time periods. Test materials are incubated in situ in the form in which they would be fed. In the case of forages and large particle size feedstuffs, chewing is simulated to provide more accurate results. After in situ incubation, the samples are frozen to detach bacterial contaminants, rinsed thoroughly and dried. After weighing and chemical analysis of the incubation residues, a disappearance curve is generated.

A statistical model allows the disappearance curve to be separated into distinct pools with associated rates of digestion. The pools for each nutrient (NDF, NSC, and CP) and their rates of digestion are presented in two formats.

The first is output suitable for use in either the Cornell or University of Pennsylvania net carbohydrate and protein system models. For the Univ. Penn. version, simply enter appropriate pools sizes and rates of digestion into the feeds worksheet. For the Cornell version, only rates of digestion may be entered directly. The pool sizes for NSC are adjusted by providing a value for percent of NSC represented by starch. Pool size for digestible NDF is entered indirectly through the lignin value provided in the printout. This lignin value is a mathematical manipulation to cause the CNCPS program to calculate the appropriate pool size for digestible NDF; it is not a chemically analyzed value. Also, due to this manipulation the Cornell version cannot use the crude protein digestion kinetics which have been generated.

The second set of output is provided for customers without direct access to the net carbohydrate protein systems or for quick evaluation of forages. This output allows more digestion pools than are available for the net carbohydrate and protein systems. In some cases, the increased number of pools allows the disappearance data to be described more accurately. The pools and their rates of digestion are combined with standard disappearance rates to estimate ruminal digestion of NDF and NSC and protein bypass values. For samples which have been evaluated for NDF, NSC, and crude protein disappearance, an estimate of TDN and NEl which is based on digestibility of nutrients rather than chemical composition is also provided.

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