Nutritional assessment of three baled rice straw varieties intended for use as ruminant feed in Namibia

Abstract

This study determined and compared the proximate and chemical composition of Angola, IRGA 418 and SUPA rice straw varieties harvested and baled in 2016 and 2017. In both 2016 and 2017, SUPA straw had the highest dry matter (DM) content (960.7 ± 0.50 g/kg and 939.4 ± 0.10 g/kg), neutral detergent fibre (NDF) (575.2 ± 9.90 g/kg and 594.7 ± 9.00 g/kg), acid detergent fibre (ADF) levels (374.7 ± 6.30 g/kg and 379.9 ± 9.90 g/kg) and cellulose (CL) content. Angola straw had the highest crude protein (CP) content (39.1 ± 2.00 g/kg, p < 0.05; 60.7 ± 2.70 g/kg) and acid detergent lignin (ADL) concentration (p < 0.05) in both years. Organic matter (OM), hemicellulose (HC), ash, fat and mineral content varied with year in all rice straw varieties. Angola straw had the lowest metabolisable energy (ME) of the three straw varieties. All straw varieties were deficient in at least one or more essential nutrient components. Nutritional and chemical composition varied with rice straw variety, year of cultivation and baling. Therefore, pre-treatment to improve digestibility and supplementation of deficient nutrients is recommended for effective use as ruminant feed. IRGA 418 straw was recommended as the best choice for ruminant feeding based on higher digestibility (IVOMD) and ME values.