Abstract
The aim of this study was to evaluate the effect of ammoniation by urea on the nutritional value of elephant grass hay harvested after flowering. A completely randomized design, in double factorial designs with an additional treatment: 4 urea doses (2, 4, 6 and 8%) x 2 treatment periods (30 and 45 days) + 1 (Control) with four replicates each, was employed. Dry matter, ash, ether extract, neutral detergent fiber, acid detergent fiber, cellulose, lignin, neutral detergent fiber corrected for the ash and the protein, total nitrogen, acid detergent insoluble nitrogen, neutral detergent insoluble nitrogen, non-protein nitrogen, in vitro gas production and carbohydrates fractionation were analyzed. The treatments influenced the contents of DM, EE, NDF, ADF, lignin, cellulose, NDFap, fraction A + B1, fraction B2, fraction C, TN, NPN, ADIN, NDIN, L and Vf2. There was a positive linear effect of urea dose for NDF, ADIN, NDIN and L, positive linear effect on fraction A + B1, NT and NPN, and positive quadratic effect for Vf2, with absolute maximum point of 4.5%. Elephant grass hay harvested after flowering has its nutritional value improved, with a minimum dose of 4.5% urea on a dry matter basis.
Highlights
In Brazil, the elephant grass (Pennisetum purpureum Schum.) is a forage plant of important use in livestock feeding, both for its great dry mass production and for its longevity and nutritive value (DIEHL et al, 2013)
Like most tropical forages, it has low nutritional value when harvested at an advanced stage of maturity, and as forage is the main component of ruminant diets in Brazil, the low-quality forage might result in low animal productivity (DÍAZ et al, 2015)
The maturity of the forage plant is an indicator of its fiber content, considering there is an increase of neutral detergent fiber (NDF) and acid detergent fiber (ADF) as the plant gets older (LU; KAWAS; MAHGOUB, 2005), and the NDF has a close relationship with the nutritional value of the forage, acting as a predictor of digestibility (DANIEL et al, 2014)
Summary
In Brazil, the elephant grass (Pennisetum purpureum Schum.) is a forage plant of important use in livestock feeding, both for its great dry mass production and for its longevity and nutritive value (DIEHL et al, 2013). Elephant grass is mainly grown in the form of spare forage areas, which are designated for cutting and provided chopped in the trough as pasture supplementation over the dry season. It is usually harvested at an advanced stage of maturity, when it presents greater forage mass production per area, but low nutritional value (GUEDES et al, 2006). An alternative to optimize the use of low quality forages for ruminants is through techniques of treatment, which may be chemical, physical and biological, all with the principle of making them more digestible for ruminants, especially by acting on the fiber portion. The ammoniation promotes higher degradation of cellulose and hemicellulose, due to the expansion of its molecules with rupture of hydrogen bonds and increased fiber hydration (MORAIS et al, 2017), this technique leads to an increase in the crude protein content of the roughage, promoted by the addition of non-protein nitrogen derived from the urea hydrolysis (NISA et al, 2007), and increased digestibility (GARCÍA-MARTÍNEZ et al, 2009)
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