The effect of fine particle removal from ground forage samples on In Saccro dry matter and neutral detergent fiber disappearance values

[摘要] ENGLISH ABSTRACT: In vitro and in situ methods using the in sacco technique have a wide application in ruminantnutrition as they allow the degradability and quality of forages and ruminant diets to bedetermined quicker and at a lower cost than in vivo methods. These trials make use of artificialfibre bags, made of polyester (dacron) or nylon which are available in variable pore sizes.Results from such degradability trials are of great value to feed formulation programs such asAMTS.cattle and CPM Dairy and the more accurate the results are obtained from such trials themore accurate feed formulation models are enabling the ruminant nutritionist to formulate thebest diet possible to reach the genetic potential of ruminants. The accepted method for in saccotrials (NRC, 2001) requires that the feed samples are ground through a 2 mm screen. Thisusually results in a variety of particle sizes, including a significant amount of extremely fineparticles. Research has, however, shown that these fine particles can potentially be washed outof the dacron bags that are used in in sacco degradability trials. This would result in an overestimationof the soluble and rapidly fermentable nutrient fractions. The objective of this studywas to determine the effect of fine particle removal from ground forage samples on the chemicalcomposition and in vitro dry matter (DM) and neutral detergent fibre (NDF) degradability offorages. Lucerne hay, oat hay and wheat straw samples were sourced from seven differentlocations in the Western Cape. Samples were milled through a 2 mm screen and then sievedthrough either 150 μm, 125 μm or 106 μm. All fractions were analysed for DM, crude protein(CP), NDF, fat and ash. Based on the NDF content of the original samples, four samples fromeach forage type were selected for in vitro trials to determine DM and NDF disappearance overtime. Samples were incubated for 0, 6, 24 and 48 hours in an ANKOM Daisy II incubator.Significant variation occurred within forage types in terms of chemical composition. Fine particle removal had no effect on the NDF content of lucerne hay and wheat straw, but sieved oat hayfractions had a higher NDF content than the un-sieved samples. The NDF content was onaverage 635.9 for the sieved OH fractions, whereas the NDF content of the un-sieved sampleswas 606.8. The CP content of sieved oat hay (61.4 on average) and wheat straw fractions (47.7on average) were lower than the un-sieved fractions (65.7 for OH and 55.4 for WS), whereas forlucerne hay, sieving had no effect on CP content.Dry matter and NDF disappearances were significantly higher for the un-sieved samples thanfor the sieved fractions for all three forage types at all incubation times, which indicates an overestimationof the soluble and readily digestible forage fractions. Compared to sieved samples,DMD values at 0 hours (washing only) of the un-sieved samples were, on average, 13.8%higher for lucerne hay, 27.3% for oat hay and 44.7% for wheat straw. At 48 h, the overestimationof lucerne DMD for the un-sieved samples was between 4.0% (compared to 106 μmsieve) and 7.3% (compared to 150 μm sieve). This over-estimation in the un-sieved sampleswas carried over to all four time points. No significant differences between the fractions (150,125 and 106) were found within a forage type at all incubation times. The estimated degradationrates and the predicted digested proportions were also significantly higher for the un-sievedfractions compared to the sieved fractions. It was concluded that fine particle removal fromforage samples would result in more accurate estimations of in sacco nutrient degradability.

[发布机构] Stellenbosch University