ARS | Publication request: Determination of nutritive value of forages in south Texas using an in vitro gas production technique

Submitted to: Grass and Forage Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 26, 2011
Publication Date: March 26, 2012
Citation: Aguiar, A.D., Tedeschi, L.O., Roquette, F.M., Mccuistion, K., Ortega-Santos, J.A., Anderson, R.C., Delaney, D., Moore, S. 2012. Determination of nutritive value of forages in south Texas using an in vitro gas production technique. Grass and Forage Science. 66:526-540.

Interpretive Summary: Diets consumed by grazing cattle, sheep, and goats can vary greatly depending on production systems, geographical location, and season but little is known about how different types of forage and their stage of maturity can affect the ability of these animals to resist being colonized by foodborne pathogens such as Escherichia coli O157:H7, Salmonella, and Campylobacter. The objective of this study was to evaluate the use of a specialized laboratory technique called the in vitro gas production technique for studying the digestion of south Texas forages throughout several years and seasons. We found that the specialized technique was able to reliably estimate the digestibility of forages differing in maturity and conclude that this technique can help us study how the digestion of different diets may affect the gastrointestinal availability of nutrients used for growth of foodborne pathogens. Ultimately, these findings can help livestock producers to more effectively manage their livestock feeding systems to minimize risks of pathogen colonization for continued production of safe and wholesome meat and milk for the American consumer.

Technical Abstract: The objective of this study was 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 obtain empirical relationships between the IVGP technique fermentation parameters and chemical composition of the forages and develop equations to compute total digestible nutrients (TDN). During 4 consecutive years (2006 to 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 6.47±0.54, 7.75±0.65, 7.49±2.01, and 5.44±1.46, and the average ratio of ml of gas per mg of dry matter was 0.41±0.11, 0.34±0.09, 0.34±0.07, and 0.26±0.10, respectively. There was a moderate negative correlation (r = -0.53) between lignin and NDF, and a moderate positive correlation (r = 0.58) between CP and NDF digestibility. The predicted fractional passage rate (kp) by the Large Ruminant Nutrition System model using the level 2 solution was on average 3.66%/h. The average computed TDN assuming a kp of 0.04 h-1 was 55.9%. We concluded the IVGP technique may be used to predict TDN values of warm-season forages.