Characterization of feed efficiency in young Holstein bulls

Agronomic and livestock sectors are recognized among the major contributors of greenhouse gases (GHG) emissions. Methane is strongly associated with global warming and is the major GHG produced by ruminants. The characterisation of feed efficiency with the selection of the most efficient animals is an important step towards the reduction of GHG emission in the dairy sector. Therefore, the aim of this study was to characterise the feed efficiency in young Holstein bulls, candidates to artificial insemination. Data were collected between May 2018 and July 2020 in the genetic centre of the Associazione Nazionale Allevatori della Razza Frisona e Jersey Italiana (ANAFIJ, Cremona, Italy) on 111 young Holstein bulls. The 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 one pen was equipped with the Automated HeadChamber System (AHCS; GreenFeed C‐Lock Inc., Rapid City, SD, USA) to record CH4 emissions (g/d). Average daily gain (ADG) was estimated as the regression of body weight (BW) on days of test. Feed efficiency was expressed as feed conversion ratio (FCR), i.e. the ratio between DMI and ADG. Means of age, BW, ADG, DMI and CH4 emissions were 276±42 d, 298±63 kg, 1.12±0.29 kg/d, 8.24±2.20 kg/d and 220±41 g/d, respectively. Average FCR was 7.55±2.48, with the lowest values indicating more efficient animals. Moderate to low positive Pearson correlations were assessed between BW and DMI (0.49; p < .001) and between BW and CH4 emissions (0.24; p < .01). Methane production was weakly positively correlated with DMI (r=0.23; p < .01). Regarding FCR, a low positive favourable correlation with CH4 (0.20; p < .01) was estimated, meaning that improving (i.e. reducing) FCR would lead to less CH4 emitted in the atmosphere. Also, a moderate positive correlation between FCR and BW (0.46; p < .001) was observed. Large variability for FCR among individuals has been observed, suggesting that there is potential to improve (and therefore to reduce in terms of absolute values) FCR in Italian Holstein population