Digestion kinetics of leaf, stem and inflorescence from five species of mature grasses

Abstract

The objective of this study was to measure the digestion kinetics for mature (green and nonsenescent) components of five grass species using in sacco and in vitro incubations to define rates of degradation and nutrient release. Mature perennial ryegrass, tall fescue, Yorkshire fog, phalaris and paspalum were hand separated into leaf blade, stem and inflorescence (flower head) for incubations. Concentrations of neutral detergent fibre (NDF) in fractions were in the ranges 492-677 (leaf), 626-718 (stem) and 501-677 (inflorescence) g kg −1 dry matter (DM). Crude protein concentrations in the DM of the respective fractions were 70-236 (leaf blade), 35-77 (stem) and 75-120 (inflorescence) g kg −1 DM. Soluble DM (% of the total) determined after mincing accounted for 31-54% of leaf, 26-56% of stem and 20-49% of inflorescence and fractional degradation of the insoluble DM was very slow, in the ranges 0.04-0.11 (leaf), 0.03-0.05 (stem) and 0.03-0.08 (inflorescence) h −1 . After 24 h of in vitro incubation, plant nitrogen content became limiting for fermentation in most instances, especially with tall fescue and paspalum. Volatile fatty acid (VFA) production appeared to be similar for leaf, stem and flower fractions, but the proportion of plant DM released as VFA after 48 h was only 7-12%, with a higher value (19%) for tall fescue. Nitrogen concentration in forage DM was not directly related to VFA yield in vitro. In conclusion, the in sacco kinetics suggested slow colonisation of all components, but especially stem, which will limit the rate of nutrient production. Effective degradability was highest for leaf but rates in vivo will depend on the speed and extent of particle size reduction by chewing during eating and ruminating.

In situ rumen degradation kinetics as affected by type of pasture and date of harvest

“…Using a slower passage rate (0.02 instead of 0.05) increased the degradation of NDF by 140-300 g kg -1 NDF. Such increase has been already reported by Chaves et al (2006a) and occurs as a consequence of a longer residence in the rumen.…”

“…On the other hand, Sun et al (2010) predicted similar fractional degradation rates of NDF in perennial ryegrass for early spring (0.099 -0.183 h −1 ) and Hoffman et al (1993) for autumn samples (0.09 h −1 ). Degradation rates for DH3 were similar to those predicted by Chaves et al (2006a) for perennial ryegrass leaves. However, values obtained for DH1 and DH2 were higher, probably because of the differences in the stage of maturity between our (vegetative stage) and their (reproductive stage) samples.…”

“…Faster fractional degradation rates of DM were found for early spring than late spring and autumn. This might be related to a lower leaf:stem ratio, as stems degrade slower than leaves (Chaves et al, 2006a).…”

“…Protein escaping from the rumen was higher in autumn than in early and mid spring for NNF, RGWC and MIXED, whereas for NF it was higher during mid spring and autumn than early spring. The higher UDP might be related to an increase in the N that is linked to the cell walls, which usually occurs as the growing season progresses and plants mature, resulting in a lower leaf:stem ratio (Chaves et al, 2006a). According to NRC (2001), ERDP estimates satisfy the requirements of a 500 kg LW Holstein Friesian lactating dairy cow (Milk production: 20 l day −1 , Fat: 4.4 %, milk crude protein: 3.5 %, without body weight change) i.e.…”

Effects of cinnamon leaf, oregano and sweet orange essential oils on fermentation and aerobic stability of barley silage

“…18 To begin the incubation, 20 mL of rumen fluid inoculum was dispensed into each vial. Each vial was immediately sealed and placed on a rotary shaker platform (90 rpm; Lab-Line Instruments Inc., Melrose Park, IL, USA), then placed in a temperature-controlled (39 ± 0.5…”