Use of animal performance and gas flux for estimating dry matter intake in growing steers.

Dry matter intake (DMI) estimation in ruminants is important for providing a balanced diet, increasing animal performance, and reducing nutrient excretion. Gas flux (CO ₂ and CH ₄ production) is related to DMI; however, there is limited information regarding the use of gas flux production when estimating DMI in growing steers. This study aimed to 1) determine the relationship of animal growth performance and gas flux variables with DMI of growing steers fed a backgrounding diet, and 2) evaluate the DMI accuracy of eight equations to predict DMI from growing steers fed a forage-based diet. The relationship between DMI, animal growth performance, and gas flux variables was evaluated in 130 backgrounding steers, and two equations were generated to predict DMI. Then, six retrieved equations from the literature and the two new equations were used to determine the prediction accuracy using an independent dataset. Models were compared based on the mean square prediction error (MSPE), the decomposition of the root MSPE (RMSPE), and the concordance correlation coefficient (CCC). In backgrounding steers, DMI had a positive and significant relationship (P < 0.01) with shrunk body weight (SBW), average daily gain, and CO₂ and CH₄ production. The production of CO₂ and CH₄ independently explained 48.1% and 40.9% of the observed DMI in growing steers, respectively. One equation retrieved from the literature had an excellent agreement with the observed DMI, with a CCC value of 0.93 and an RMSPE of 0.19 kg/d, representing 2.5% of the average DMI. That equation used SBW and dietary energy concentration. The use of CO₂ production had adequate agreement with the observed DMI, with a CCC value of 0.73 and an RMSPE of 0.45 kg/d, representing 6% of the average DMI. Other equations had null to moderate agreement with the observed DMI, with CCC values ranging from 0.00 to 0.47 and an RMSPE from 0.51 to 4.40 kg/d. In conclusion, there is a positive relationship between DMI, animal growth performance, and gas flux in growing steers fed a backgrounding diet. In addition, CO₂ production has the potential to be used to predict DMI in growing steers fed a forage-based diet. Future research is required to evaluate the relationship between CO₂ production and DMI, especially under grazing conditions.