Ruminal protein degradability of a range of tropical pastures

Abstract

Abstract. The rumen degradability parameters of the diet selected by two to four oesophageal-fistulated Brahman steers grazing a range of tropical pastures were determined by incubation of extrusa in nylon bags suspended in the rumen of rumen-fistulated (RF) Brahman steers. The effective protein degradability (Edg) was determined by measuring the rate of disappearance of neutral detergent insoluble nitrogen (NDIN) less acid detergent insoluble nitrogen (ADIN) in the incubated extrusa. Six to eight RF steers also grazed each of the pastures along with the oesophageal-fistulated steers, to allow determination of key rumen parameters and rumen particulate matter fractional outflow rates (FOR). The seven pastures studied included: native tropical grass (C 4 ) pasture (major species Heteropogon contortus and Bothriochloa bladhii), studied in the early wet (NPEW), the wet/dry transition (NPT) and the dry (NPD) seasons; introduced tropical grass (C 4 ) pasture (Bothriochloa insculpta), studied in the mid wet season (BB); the introduced tropical legumes (C 3 ), Lablab purpureus (LL) and Clitoria ternatea (BP); and the temperate grass (C 3 ) pasture, ryegrass (Lolium multiflorum, RG). Using the measured particle FOR values in calculations, the Edg estimates were very high for both C 4 and C 3 species: 0.82--0.91 and 0.95--0.98 g/g crude protein (CP), respectively. Substitution of an assumed FOR (k p = 0.02/h) for the measured values for each pasture type did not markedly affect estimates of Edg. However, C 4 tropical grasses had much lower effective rumen degradable protein (ERDP) fractions (23--66 g/kg DM) than the C 3 pasture species RG and LL (356 and 243 g/kg DM, respectively). This was associated with a lower potential degradability and degradation rate of organic matter (OM) in sacco, lower in vitro organic matter digestibility (IVOMD) and CP concentrations in the extrusa, and lower ammonia-N and branched-chain fatty acid concentrations in rumen fluid for the tropical grasses. As tropical grass pastures senesced, there was a decline in Edg, the ERDP and rumen undegradable protein (UDP) fractions, the potential degradability and degradation rate of OM and the IVOMD. These results provide useful data for estimating protein supply to cattle grazing tropical pastures.

Citrus pulp-based supplement reduces the detrimental effects of high grazing pressure on the performance of beef cattle under a rotational system of Urochloa brizantha

“…The CP content found in pastures in the current study was relatively high, reflecting the plant growth stage and the use of N fertilizer. Assuming a ruminal degradability of protein of 800 g/kgCP (Bowen et al, 2008),it would result in rumen degradable protein (RDP)/digestible organic matter (DOM) ratios of 195 and 197 g RDP/kg DOM for both grazing intensities, values that are in excess of the RDP requirements for microbial protein synthesis in the rumen (CSIRO, 2007). The lower ADG observed in the high grazing pressure is primarily a result of the lower FM allowance used for that pasture management, but could also be linked to harvesting constraints and/or lower availability of leaves in the lower strata, as suggested by the differences found in morphological composition between the post-grazing FM in both treatments.…”

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

“…Values of effective rumen degradable protein (ERDP) give an estimate of N supply to microbes for grazing ruminants (Bowen et al, 2008). Higher and lower supplies of ERDP were obtained for NF-DH2 (222.8 g kg −1 DM) and NNF-DH2 (114.9 g kg −1 DM), respectively.…”

In vitro ruminal degradation of neutral detergent fiber insoluble protein from tropical pastures fertilized with nitrogen

“…Although Ogden (5) showed that in C4-grasses the rate of digestion of the NDIP fraction is faster than its own NDF fraction (11.0 vs 7.8 %/h). In Australian tropical grasses measuring NDIP rates of digestion found a range between 4.7 and 7.9 %/h (6) . However, Singh (2) for tropical grasses in India consider the Sniffen digestion rate of fiber-bound protein of less than 1.5 %/h (7) .…”

“…Also, in Brazilian grasses (8) reported digestion rates between 0.08 and 1.3 %/h for the PB3 fraction. At a given passage rate of 2.5 %/h Ogden (5) or a range between 2.0-4.4 %/h Bowen (6) it is critical to know if the NDIP digestion rate exceeds or not the passage rate. Because grasses frequently make up the only source of protein for many ruminants, information on the NDIP fraction of grasses is a prerequisite to modeling the N economy of ruminants.…”

“…Between 16 % (A. gayanus) and 50 % (B. brizantha) of the NDIP remained after 96 h. Following the calculations of Anderson (27) and using a fixed passage rate of 5 %/h, the NDIP escaping ruminal digestion ranged from 0.32 to 1.32 % of DM. Bowen (6) found a range from 0.50 to 1.0 % of DM of rumen undegradable protein fraction actually measuring passage rate in C4 grasses. The escape value was highest for A. gayanus and lowest for B. brizantha.…”