Chemical composition and in vitro ruminal fermentation of selected grasses in the semiarid savannas of Swaziland

African Journal of Range and Forage Science (Impact Factor: 0.43). 01/2009; 26(1):9-17. DOI: 10.2989/AJRFS.2009.

ABSTRACT Little is known about the grass species type, composition and nutritive value in the semiarid savannas that sustain most of Swaziland's cattle population through the seven-month-long dry season. This study was conducted to investigate the nutritional characteristics of grasses collected from two grazing areas (Big Bend and Simunye), which differed mainly in soil types. Mature grass species were harvested and evaluated for chemical composition (organic matter, neutral detergent fibre [NDF], acid detergent fibre [ADF], crude protein [CP] and minerals) and in vitro ruminal fermentation (in vitro gas production, in vitro organic matter degradability and partitioning factors). The most common grass species in the Big Bend grazing area were Bothriochloa insculpta, Cenchrus ciliaris and Urochloa mosambicensis. In the Simunye grazing area the most common species were B. insculpta, U. mosambicensis, Heteropogon contortus, Panicum deustum and P. maximum. For grasses harvested from Simunye, the most (P < 0.05) degradable (532 mg g−1 dry matter) was B. insculpta, which also had the least fibre (597 g kg−1 NDF and 351 g kg−1 ADF) and the highest CP content (79.8 g kg−1). The most common grass species harvested from the Big Bend area did not differ (P > 0.05) in their Mg, P, Cu, Fe, Zn, CP and NDF content. However, U. mosambicensis had the highest (P < 0.05) ADF content. The least fermentation efficiency (partitioning factor = 2.2 mg degradable organic matter [DOM] ml−1 gas) was observed for U. mosambicensis as a result of low DOM coupled with high cumulative gas production. It was concluded that all the grasses investigated in this study show a deficit for Ca, P and protein. Therefore, supplementation is needed to ensure maximum forage utilisation and to satisfy nutrient requirements of ruminant livestock.

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    ABSTRACT: Four tropical grasses (Cynodon dactylon, Cd, C. plectostachyus, Cp, Brachiaria humidicola, Bh and Pennisetum purpureum, Pp) harvested in Central Brazil during the dry season at 100-day age were compared in terms of chemical composition and in vitro gas production pattern in order to select the most promising species for feeding ruminants during the dry season. Because of its lower proportion of neutral detergent fibre (NDF, 709g/kg dry matter, DM) and lignin (44g/kg), and its higher nitrogen (N) content (15.3g/kg), Pp appears to have the higher nutritive value in such conditions. In contrast, Cp showed a high NDF (843g/kg) and lignin (115g/kg) contents, and low N content (8.7g/kg). Microbial fermentation, estimated by the gas production pattern agreed well with chemical composition of the studied species, and ranked them as follows: Pp>Cd≥Bh>Cp. The metabolic energy content of grasses was estimated from the volume of gas produced at 24h and their crude protein content, and were (in MJ/kg DM): Cd, 5.76; Cp, 5.15; Bh, 5.91; Pp, 9.12. In another experiment, Cp, Bh and Pp were chosen to study the bacterial adhesion (estimated by 15N as microbial marker) and polysaccharidase and ß-glucosidase enzymatic activities after in vitro incubation of grasses for 4, 8, 12, 24 and 32h. The pattern of microbial adhesion and total enzymatic activities agreed well with the chemical composition and gas production results. Although P. purpureum promoted a higher adhesion and total cellulolytic activity, bacterial enzymatic activity (per unit of adhered bacteria) showed that populations associated with the grasses do not differ qualitatively in their cellulolytic capability.
    Animal Feed Science and Technology - ANIM FEED SCI TECH. 01/2000; 83(2):145-157.
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    ABSTRACT: Feed value is the potential of the feed to supply the nutrients required by an animal both quantitatively and qualitatively in order to support a desired type of production. Where chemical composition and digestibility of a given feed is known it is possible to calculate its energy content by using appropriate regression equations. Eleven tropical grass species and mixed grass hay, seven legumes and browse trees, and six concentrates were evaluated in terms of chemical composition (CP, EE, OM, CHO and NDF), digestibility (in vitro organic matter digestibility -IVOMD and enzyme solubility of organic matter- EZOM) and calculated energy values. The grass species were: Andropogon timorensis (Kunth), Rev. Gram., Brachiaria brizantha, (A.Rich) Stapf, Bothriochloa radicans (Lehm) A. camus, Chloris guyana Kunth, Cynodon dactylon (L.) Pers, Hyparrhenia rufa (Nees) Stapf, Panicum maximum (Jacq.), Pannisetum purpureum (Schumacher), Setaria sphacelata Stapf & C. E. Hubb, and Tripsacum fasciculatum Trin. ex Aschers. Most of the grasses were cut at an advanced stage of growth. The legumes and browses included Acacia catechu (L. f.) Willd., Gliricidia sepium (Jacq.) Kunth ex Walp, Leucaena leucocephala (Lam.) de Wit, Lannea grandis Lannea grandis Engl., Macroptilium atropurpureum (DC.) Urban, Sesbania grandiflora (L.) Poir and Zyziphus Mauritania (Lam.). The concentrates were: cotton seed cake, fishmeal, maize bran, soybean meal and sunflower cake. Mean CP and EE content (g/kg DM) were highest with the concentrates (310 and 97, respectively), followed by the legumes and browse trees (183 and 33, respectively) and lowest in the grasses (65 and 15, respectively). The OM and the CHO content varied least between the feed types. Mean NDF content (g/kg DM) was lower in the legumes/browse trees (378) and concentrates (314) compared to the grasses (698). The metabolic energy (ME) content (MJ/kg DM) in the feeds was highest with concentrate (11.9) and nearly of the same order in the grasses and legumes/browse trees (7.0). The organic matter digestibility using the conventional Tilley and Terry method and the enzymatic methods varied greatly among the feeds. The enzymatic method showed overall higher OM solubility values with some feeds compared to the in vitro organic matter digestibility method (overall mean of 63.4 Vs 53.2%). However, there was good agreement between the two methods with grasses (r2 = 0.80) compared to legumes/browse trees (r2= 0.34) and concentrates (r2=0.22). It is concluded that with increasing modernisation of ruminant livestock production in the tropics, there is a need to evaluate locally available feed resources and place the data in feedstuff tables in order that producers can select the feeds for optimal productivity.
    Veterinary Archives (; Vol.76 No.1.