Intake and digestive kinetics of leaf and stem fractions

Abstract

ResumenRuminally fistulated steers were used in a 4 x 4 Latin square to test effects of immature (vegetative) and mature (post reproductive) leaf and stem fractions from subirrigated meadow hay on organic matter intake (OMI), organic matter digestibility (OMD), and digestive kinetics. Hay was harvested 1 June (immature) and 1 October (mature), chopped into 3-to 5-cm lengths, then separated into leaf and stem fractions using a modified Clipper Cleaner Model Super 69D. Steers were provided ad libitum access to fractions and supplemented with urea so that diets were iso-nitrogenous. Particulate passage was determined usingYb labeled large hay particles [1.7-mm screen] and Er labeled small particles [< 1.7-mm and 0.212-mm screen]. Samples were collected from the rumen, omasum, feces, and un-masticated diets for particle size determination. Particle size was determined using wet sievin techniques. Voluntary OMI of immature fractions (15.4 g kg BW) was greater (P < 0.05) than mature fractions (12.5 g kg'' BW). Within maturity OMI and OMD of leaves and stems were similar. Immature fractions had greater (P < 0.05) OMD (63.2%) than mature fractions (55.7%). Large and small particle passage rates were faster (P < 0.05) for immature fractions [3.2% hour'1 (large) and 4.3% hour'' (small)] than mature [(2.3% hour"' (large) and 2.9% hour'' (small)]. Critical particle size for ruminal escape was 1.18 mm for both leaves and stems regardless of maturity. Differences in OMI and OMD between immature and mature fractions were explained by changes in structural components of the cell wall that made particles more resistant to mechanical and microbial breakdown.Key Words: digestibility, retention, particle size, rumen, feces, omasum Forage maturity influences quality of forages (Streeter et al. 1968, Nichols 1989. A decline in forage quality can be attributed largely to changes in the leaf and stem ratios (Nelson and Moser 1994) and associated decline in stem quality. Forage intake is associated with the proportion of indigestible fiber and the length of time retained in the rumen (Ulyatt et al. 1986). Particle size and passage rate were inversely related (Ehle 1984). Poppi et al. (1985) and Hendricksen et al. (1981) particulas chicas marcadas con Er [malla < 1.7-mm y 0.212-mm). Para determinar el tamano de particula se colectaron muestras del rumen, omaso, heces fecales y dietas sin masticar. El tamano de particula se determino usando la tecnica de cribado humedo. El consumo voluntario de materia organica de fracciones inmaduras (15.4 g kg'' PV) fue mayor (P < 0.05) que el de las fracciones maduras (12.5 g kg'' PV). Dentro de madurez, el consumo de materia organica y la digestibilidad de la materia organica de hojas y tallos fueron similares. Las fracciones inmaduras tuvieron una mayor (P < 0.05) DMO (63.2%) que las fracciones maduras (55.7%). Las tasas de paso fueron mas rapidas (P < 0.05) para las fracciones inmaduras [3.2% hora 1(grandes) y 4.3% hora'' (pequenas)] que para las maduras [(2.3% hora'1 (grandes) y 2.9% h...

Stable isotope‐labelled feed nutrients to assess nutrient‐specific feed passage kinetics in ruminants

“…Potential diet‐related factors can be attributed to the diet composition and quality, including forage type, vegetative forage part (e.g. stem/leaf proportion), concentrate proportion in the diet and various forage and pasture management practices such as stage of maturity, stage of regrowth, harvesting and forage conservation practices and grazing time . Common feed‐processing techniques such as pelleting generally increase FPR.…”