Residual feed intake of genomic tested young Holstein bulls

The Intergovernmental Panel on Climate Change has reported that anthropogenic greenhouse gases (GHG) have been responsible for most of the observed temperature increase since the middle of the twentieth century. Agriculture and livestock are major contributors to the rise in global temperature due to GHG emissions. Methane (CH4) is associated with global warming, therefore the mitigation of emissions has become a hot research topic. The objective of this study was to calculate the residual feed intake (RFI) of young genomic tested Holstein bulls. The RFI is an indicator of feed efficiency which can indirectly quantify the reduction of GHG emissions. Data were collected on 111 young Holstein bulls between May 2018 and July 2020 at the genetic centre of the Associazione Nazionale Allevatori della Razza Frisona e Jersey Italiana (ANAFIJ, Cremona, Italy). Pens of the genetic centre were equipped with Roughage Intake Control system (RIC; Hokofarm Group, Voorsterweg, The Netherlands) to record dry matter intake (DMI, kg/d), and with the Automated System (GreenFeed C-Lock Inc., Rapid City, SD, USA) to record CH4 emissions (g/d). Average daily gain was estimated as the regression of body weight on test days. Expected DMI was obtained from a linear regression of DMI on metabolic body weight (BW0.75) and average daily gain (ADG). Residual feed intake was calculated as the difference between measured DMI and expected DMI. Age, body weight, BW0.75, ADG, actual DMI, expected DMI, CH4 emissions and RFI averaged 276±42 d, 298±63 kg, 71.91±11.71 kg, 1.12±0.29 kg/d, 8.24±2.20 kg/d, 8.10±1.47 kg/d, 220±41 g/d and 0.07±1.56, respectively. Pearson correlations between RFI and CH4 was weak (0.16; P<0.05). Negative RFI values identify animals with lower feed intake and greater efficiency. Improving individual feed efficiency using RFI would lead to a reduction of GHG emissions in the long-term.