Determination of nutritive value of forages in south Texas using an in vitro gas production technique
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The objectives of this study were to use the in vitro gas production (IVGP) technique to evaluate the pattern and parameters of anaerobic fermentation of forages from south Texas pastures throughout the year to (i) obtain empirical relationships between the IVGP technique fermentation parameters and chemical composition of the forages and (ii) develop equations to compute total digestible nutrients (TDN). During four consecutive years (2006-2009), forage samples were collected monthly (n=39) at the King Ranch, TX, and chemical analyses and IVGP were obtained. For 2006, 2007, 2008 and 2009, the average lag times, h, were 647054, 775065, 749201 and 544146, and the average ratio of millilitre of gas per milligram of dry matter was 041011, 034009, 034007 and 026010 respectively. There was a moderate negative correlation (r=-053) between lignin and neutral detergent fibre (NDF) and a moderate positive correlation (r=058) between crude protein and NDF digestibility. The predicted fractional passage rate (kp) by the large ruminant nutrition system model using the level 2 solution was on average 00366 h-1. The average computed TDN assuming a kp of 004h-1 was 559%. We concluded the IVGP technique may be used to predict TDN values of warm-season forages. 2011 Blackwell Publishing Ltd.