Contrasting rearing and finishing regimens on performance and methane emissions of Angus steers.
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Abstract
Beef cattle production contributes to global warming mainly through the emission of methane (CH4) generated during
the normal process of feed digestion. Compensatory growth could provide a means to reduce CH4 emissions, since feed
efficiency improves during refeeding and an increase in feed digestibility could explain this improvement. Steers are
commonly fattened on pasture or feedlot, so the aim of the experiment was to evaluate the effect of dietary restriction
in Angus steers on DM digestibility (DMD) and CH4 emission under two contrasting refeeding diets. Eighty steers
with an average live weight (LW) of 444±39 kg and age of 18±1 months, were blocked, and randomly assigned to 1
of 4 treatments, in a 2×2 factorial arrangement: severity of dietary restriction (moderate vs mild) and fattening system
(pasture vs feedlot). During the 97 days period of dietary restriction target growth rates were 0.3 and 0.6 kg/d, for
moderate and mild groups, respectively. The dietary restriction period was followed by a subsequent fattening period
of 84 days. Methane emissions and DMD were measured at the end of fattening period in 36 and 80 steers, using SF6
and acid insoluble ash technique, respectively. During fattening, previous moderate restricted steers had higher LW
gain compared to mild steers (1.2 vs 1.0 kg/d; P<0.01). Feedlot steers had higher LW gain (1.3 vs 0.9 kg/d; P<0.01)
than pasture steers. Irrespective of previous dietary restriction treatment, methane emission and methane yield were
lower for feedlot steers (P<0.05; 230 vs 313 g CH4/d, and 22.2 vs 25.8 g CH4/kg DMI, respectively). No difference
in DMD was evident between previously restricted steers, whereas feedlot steers achieved higher DMD than pasture
steers (82.1 vs 69.2%; P<0.01). Moderate steers had lower methane intensity than mild steers (246 vs 321 g CH4/LW
gain; P<0.01). In conclusion, for both finishing systems, the lower methane intensity of steers initially subjected to a
moderate dietary restriction is due to their relatively higher performance during fattening, rather than lower methane
emissions or yield per se.