The effect of particle size and indigestible NDF on growing lamb performance

The NDF has been proposed as a reliable predictor of voluntary DMI under certain conditions. However, as formulating a diet to a specific level of NDF without reference to the iNDF could markedly affect the resulting intake, digestibility, and metabolizable energy content of the diet, therefore, adjusting the amount of iNDF in the diet of high production animals is very useful. On the other hand, Feed particles are retained selectively in the rumen that can explain the variable digestibility of rations with similar chemical characteristics. Therefore, the objectives of this experiment were to combination of Particle Size and iNDF of rations for its relation to lamb performance.
For this experiment, 20 lambs used with an average weight of 25.15±2.82 kg and similar age (8 month) in a completely randomized design with 4 treatments in 5 replications. The NDF content of rations in experimental treatments were similar and including: 1) alfalfa with medium particle size and low iNDF, 2) alfalfa with fine particle size and low iNDF, 3) alfalfa with medium particle size and high iNDF and 4) alfalfa with fine particle size and high iNDF. For determination of iNDF, using ruminal fistulated ewes and samples incubated in the rumen for 288h; and peNDF was determined by dry sieving technique. Animals were housed in individual cages and after adaptation on environment and ration, offered treatments for ad libitum intake over 80 days. Weight in 15 days and daily feed consumption was determined. Apparent and real digestibility of dry matter and organic matter of ration, ruminal parameters, and feed conversion were determined.
The Results of this experiment showed that the effect of dietary iNDF on dry matter intake, chemical characteristics of rations and nutrients digestibility was significant but this effect on peNDF was not significant. Rations for higher iNDF had higher feed intake and lower dry matter digestibility, But really digestibility were similar between treatments. The effect of iNDF and physical characteristics of fiber (P The Results from this experiment showed that different levels of particle size and iNDF could effect on some animal parameters but their effect on Production performance and animal growth was not significant. the results showed that using iNDF as a fibrous index is more sensitive than NDF in fiber regulation of ruminant rations.