Tropentag, September 18 - 20, 2019 in Kassel "Filling gaps and removing traps for sustainable resources development"

Estimating Rumen Undegradable Protein from Proximate Nutrient, Fiber Fractions, and in vitro Fermentation of Tropical Feedstuffs

University of Hohenheim, Animal Nutrition and Rangeland Management in the Tropics and Subtropics, Germany

Abstract

Estimates of rumen undegradable crude protein (RUP) are a prerequisite in feed evaluation and nutrient recommendation systems. The in situ method is the reference method used for RUP determination. However, this method is expensive, time-consuming, and requires fistulated animals. Therefore, this study aims to predict the RUP of tropical feedstuffs from proximate nutrients, fiber fractions, and rumen in vitro feed fermentation characteristics.

A total of 46 tropical feedstuffs, namely, 6 concentrates and by-products, 17 forage legumes, and 23 forage grasses, were used to develop RUP prediction equations. With use of the software Minitab (2018), stepwise linear regression was performed and the determination coefficient (R²) was calculated for identified RUP equations at rumen passage rates of 2, 5, and 8%/h.
The dataset included information on (arithmetic mean±standard deviation): concentrations (per kg of dry matter [DM]) of organic matter (OM; 902±38.9 g), crude protein (CP; 160±87.3 g), neutral detergent fiber (490±132.1 g), acid detergent fiber (287±86.3 g), acid detergent lignin (48±28.8 g), digested OM (0.6±0.1 g kg^-1 OM), and metabolisable energy (10±1.9 MJ kg^-1 DM), as well as cumulative gas production (GP) during 24 h of in vitro incubation (32±8.3 ml/200 mg DM) and in situ RUP proportion (per kg CP) at rumen passage rates of 2%/h (228±90.8 g), 5%/h (299±104.0 g), and 8%/h (342±110.6 g).

The CP concentration and GP were good predictors of the proportion of RUP across all feedstuffs. The CP concentration accounted for 60, 72, and 77% and the GP for 14, 7, and 4% of the variability in the RUP proportion at rumen passage rates of 2, 5, and 8%/h, respectively. The following models were developed (coefficient±mean standard error):
RUP 2%/h = (40.9±8.5 + 0.3±0.1 × CP – 1.5±0.3 × GP) × 1000/CP (R²=0.74; p<0.01),
RUP 5%/h = (34.1±10.6 + 0.4±0.1 × CP – 1.4±0.4 × GP) × 1000/CP (R²=0.80; p<0.01), and
RUP 8%/h = (25.2±12.5 + 0.4±0.1 × CP – 1.3±0.4 × GP) × 1000/CP (R²=0.81; p<0.01), where RUP is in g kg^-1 CP, CP is in g kg^-1 DM, and GP is in ml/200 mg DM.
In conclusion, the RUP proportions of tropical ruminant feedstuffs can be predicted from CP concentration and GP.

Keywords: In-vitro fermentation, tropical feedstuffs, undegradable crude protein

Contact Address: Khaterine Salazar-Cubillas, University of Hohenheim, Animal Nutrition and Rangeland Management in the Tropics and Subtropics, Fruwirthstrasse 31, 70599 Stuttgart, Germany, e-mail: khaterine.salazar-cubillasuni-hohenheim.de