Dietary linseed and starch supplementation decreases methane production of fattening bulls
Résumé
The objective was to determine CH(4) production from bulls fed a feedlot diet rich in either fibre (F)or starch and lipid (SL) over the fattening period. Fifty six Charolais bulls (259 +/- 9.4 d of age and 339 +/- 8.2 kg live weight (LW)) were allocated randomly to one of two diets and blocked with 4 replicate pens/diet based on LW and age, and fattened for up to 18 months. Both treatments included barley straw with the appropriate concentrate mixture rich in fibre or starch and fat. The concentrate mixture and barley straw were available ad libitum, and the intake ratio (870:130: dry matter (DM)basis) for the concentrate mixture and barley straw was similar for both diets. Methane production was determined for each bull for 5 d using the sulfur hexafluoride tracer gas method at the beginning (24 d on diet +/- 3.4), middle (120 d +/- 8.2), and end (228 d +/- 11.1) of the fattening period. Feed intake was measured daily and bulls were weighed every 15 d. Ruminal fluid samples were collected on the last day of each CH(4) measurement period by rumenocentesis and measured for pH and concentrations of volatile fatty acids (VFA). Bulls fed SL had lower DM, organic matter and gross energy intake (P<0.05) than bulls fed F. Bulls fed SL had lower CH(4) production (L/d and L/kg LW gain) than bulls fed F (-20% and -24%, respectively, P<0.01). Bulls fed SL had higher CH4 (g/kg DM intake) than bulls fed F (+20%, P<0.05) at the end of fattening. Bulls fed SL had lower ruminal VFA and a lower acetate relative proportion than bulls fed F (-13% and -11%, P<0.001, respectively), but diet had no effect on ruminal pH. Body LW gain was 1.49 versus 1.58 kg/d (P=0.05) for bulls fed F and SL, respectively, during the first 200 d of fattening. There was no relationship between CH(4) production as L/d or L/kg LW gain and residual feed intake. Supplementation with extruded linseed lipids combined with starch in feedlot diet decreased enteric CH(4) emissions, as L/d, L/kg LW and L/kg LW gain, from fattening bulls, mainly due to lower DM intake, with reduced CH(4) emissions as L/d, L/kg LW and L/kg LW gain persisting throughout the fattening period.