SỬ DỤNG cây KHOAI mì (sắn) để PHÁT TRIỂN CHĂN NUÔI dê ở AN GIANG, VIỆT NAM

Livestock Research for Rural Development 31 (6) 2019 Guide for preparation of LRRD Newsletter papers Citation of this paper Effect on nutritive value of cassava (Manihot esculenta Crantz) stems of ensiling them with urea Le Thi Thuy Hang and T R Preston Department of Animal Sciences and Veterinary Medicine, Agricultural and Natural Resources Faculty, An Giang University, Vietnam thuyhang.agu@gmail.com Centro para la Investigación en Sistemas Sostenibles de Producción Agropecuaria (CIPAV), Carrera 25 No 6-62 Cali, Colombia Abstract Cassava stems are used partly as plant material for the next crop, but the greater part is discarded after root harvest The ready availability of this waste product has led to experiments in our laboratory to utilize them as the basal diet for goats The stems contain about 33% DM but only 5.5% crude protein (CP) in the DM It was therefore hypothesized that there could be a double benefit from ensiling the cassava stems with urea: (i) to provide the ammonia needed by rumen organisms; and (ii) to improve the digestibility of the stem DM as has been widely proven in the urea-ensiling of low-protein, fibrous feeds such as rice straw The treatments in a random block 5*5 factorial design were: (a) five levels of urea (0, 1, 2, and 4%, DM basis) added to freshly chopped cassava stems; and (b) five storage times (0, 2, 4, and weeks) Each treatment combination was replicated times The positive effects of storing (ensiling) the cassava stem with addition of urea were the reduction in HCN levels and the possible synthesis of protein from the ammonia derived from the urea and the fermentation of part of the carbohydrate in the cassava stems On the negative side was the considerable loss of biomass (about 24%) resulting from the fermentation of part of the cassava stem carbohydrate stimulated by the availability of ammonia from the added urea Key words: ammonia, fermentation, HCN, protein, tannins Introduction Cassava (Manihot esculenta Crantz) is a perennial woody shrub of the family Euphorbiaceae It originated in the Caribbean and South America and is extensively cultivated as an annual crop in the tropics and sub-tropics for the dual purpose of tuberous roots for human consumption and roots and foliage as a feed for animals Cassava foliage is recognized as a source of bypass protein with a high content of digestible nutrients for both non-ruminants and ruminants (Wanapat 1997) The foliage can be used as a supplement for animals in either fresh or wilted form or as hay (Phengvichith and Ledin,2007; Wanapat et al 1997) At root harvest, to 10 months after planting, the foliage production can be about tonnes dry matter (DM)/ha (Mui 1994) It is estimated that more than 2.5 milion tonnes of cassava foliage are produced in Vietnam, of which about 15,000 tonnes in An Giang, Cassava foliage is usually thrown away after harvesting the root, because of its content of cyanogenic glucoside, mainly linamarin and lotaustralin (Alan and John 1993) Hydrolysis of these cyanogenic glucosides liberates hydrogen cyanide (HCN) (Poulton 1988) and causes of toxicity symptoms in animals when the tolerated dose is exceeded Cassava foliage consists of the leaves, petioles and small branches which attach to the highly lignified stem Observations at the Rabbit and Goat Center in Bavi, North Vietnam indicated that the stem was well appreciated by goats and this led to the experiment reported by Thanh et al (2013) in which chopped cassava stems supplemented with fresh cassava foliage supported live weight gains in growing goats of 57 g/day, 100% higher than when Guinea grass was used to supplement the cassava stems According to Thanh et al (2013), cassava stems contain 33% DM but only 5.5% crude protein (CP) in the DM It was therefore hypothesized that there could be a double benefit from ensiling the cassava stems with urea: (i) to provide the ammonia needed by rumen organisms; and (ii) to improve the digestibility of the stem DM as has been widely proven in the urea-ensiling of low-protein, fibrous feeds such as rice straw (Trach et al 1998) The specific objectives were to determine if the addition of urea to cassava stems would facilitate the storage of this feed resource and at the same time improve its digestibility Material and methods The experiment was carried out at An Giang University in An Giang Province in the South of Vietnam from March to June 2015 Treatments and experimental design The treatments in a random block 5*5 factorial design were: (a) five levels of urea (0, 1, 2, and 4%, DM basis) added to freshly chopped cassava stems; and (b) five storage times (0, 2, 4, and weeks) Each treatment combination was replicated times Cassava stems were collected from farmers’ fields directly after root harvesting and chopped by hand Representative amounts were analyzed for DM by infra-red radiation (Undersander et al 1993) prior to hand mixing 20 kg quantities with the indicated amounts of crystalline urea followed by storage in polyethylene bags which were then sealed After the appropriate storage times, samples of the treated stems were taken for measurement of pH (ORION model 420 A) and proximate composition The DM, ash and HCN content were determined according to the standard methods of AOAC (2016) Nitrogen was determined by the Kjeldahl procedure NDF and ADF were analysed according to the procedure of Van Soest et al(1991) Total tannin content was determined according to the method (955.35) of AOAC (2016) Statistical analysis The data were subjected to an analysis of variance (ANOVA) using the General Linear Model (GLM) procedure of Minitab 16 Sources of variation were levels of urea, storage time, the interaction urea levels*storage time and random error Results and discussion There were major effects of urea level and storage time on chemical attributes of the urea- of ensiled cassava stems (Tables 1, and 3; Figures – 8) Table Mean values for effects of urea level on composition of the ensiled cassava stems Urea % SEM p Tannin % 1.24 1.09 1.10 1.02 1.05 0.025