Feeding Values of Indigenous Browse Species and Forage Legumes for the Feeding of Ruminants in Ethiopia: A Meta-Analysis

Abstract

The foliage of browse species and forage legumes has good nutritional value and can be utilized as a protein source in ruminant diets. However, its efficient utilization requires the establishment of a comprehensive database of feeding values. Two databases, i.e., forage nutritive value (92 studies) and in vivo animal performance (62 feeding experiments), were built to assess the feeding value of the foliage of browse species and cultivated forage legumes in Ethiopia. The forage nutritive value data (chemical composition and in vitro digestibility) were summarized as descriptive statistics. The analysis of in vivo data was conducted using a mixed model procedure with fixed (forage supplement) and random (studies) factors. Forage categories had crude protein (CP) ranging from 17.6 ± 5.2% (indigenous browse species) to 22.4 ± 4.5% (multipurpose fodder tree/shrub species), respectively. Variations were observed in CP values between the vegetative and blooming stage harvesting of herbaceous forages (22.7 ± 4.1% versus 19.8 ± 3.5%). The leaves contained more CP than the twigs in multipurpose fodder tree/shrubs (22.8 ± 3.2% versus 18.8 ± 0.6%) and the pods in indigenous browse species (18.0 ± 5.0% versus 15.3 ± 2.3%). However, the greatest mean in vitro organic matter digestibility (IVOMD) of 70.1 ± 10.8% was observed in the foliage of indigenous browse species. The variation in IVOMD was small among the forage categories (61.2 ± 11.2%–63.5 ± 10.8%). Twigs of the multipurpose fodder tree/shrub species had the lowest IVOMD of 53.0 ± 6.9%. Herbaceous forage legumes tended to have higher NDF and ADF values than the other forage categories. In terms of nutrient concentration and digestibility, large variations were observed within the same forage categories and species. The supplementation of forage, on average at 277.5 ± 101.4 g/day (±SD), to a low-quality basal diet resulted in a significant (p < 0.05) improvement in the apparent digestibility of DM, CP, and NDF as well as the daily intake of DM, CP, and metabolizable energy (ME). The application of sole forage supplementation was determined to have comparable effects on DM intake (p = 0.2347) with dietary supplements based on concentrate feedstuffs. However, CP intake (p = 0.0733) tended to be lower for forage over the concentrate treatment. The averaged daily gain (ADG) of the animals was significantly increased (p < 0.05) by 71.2% due to the forage supplement compared to unsupplemented treatment (11.6 ± 5.47 g/d (±SE) vs. 40.3 ± 4.99 g/d (±SE)). Overall, the nutrient utilization and production performance of animals fed with low-quality basal diets could be improved when an appropriate amount of forage is included as supplement. The large variation recorded in the nutritional composition of browse species and forage legumes could provide an opportunity to screen for species and varieties with superior nutritional quality.