Methods and consequences of including reduction in greenhouse gas emission in beef cattle multiple-trait selection

Table 3 Method of assessing effects of selection on GHG emissions from the beef cattle production system

Performance measure	Performance level^a
After selection
Young animal pasture feed (PF_A), MJ	PF_B + Σ(∆PF_i)
Young animal feedlot feed (FF_A), MJ	FF_B + Σ(∆FF_i)
Young animal total feed, MJ	PF_A + FF_A
Cow pasture feed (CF_A), MJ	CF_B + Σ(∆CF_i)
Total feed (TF_A), MJ	PF_A + FF_A + CF_A
Young animal GHG emission at pasture (PG_A), g	PG_B + Σ(∆PG_i)
Young animal GHG emission in the feedlot (FG_A), g	FG_B + Σ(∆FG_i)
Young animal total GHG emission, g	PG_A + FG_A
Cow GHG emission at pasture (CG_A), g	CG_B + Σ(∆CG_i)
Total GHG emission (TG_A), g	PG_A + FG_A + CG_A

Effects of selection	Before selection (X_B)	After selection (X_A)	% Change
Total product^b, kg	KG_B	KG_A	(X_A/X_B × 100) − 100
Total feed, MJ	TF_B	TF_A
Total GHG emissions, g	TG_B	TG_A
$ net return^c,d,e	DNR_B	DNR_B + Σ(VTC_i)
Product per unit of feed^e, kg/MJ	KG_B/TF_B	KG_A/TF_A
GHG per unit of product, g/kg	TG_B/KG_B	TG_A/KG_A
GHG per unit of feed, g/MJ	TG_B/TF_B	TG_A/TF_A
$ net return per unit of feed^e, $/MJ	DNR_B/TF_B	[DNR_B + Σ(VTC_i)]/TF_A
$ net return per unit of GHG^e, $/g	DNR_B/TG_B	[DNR_B + Σ(VTC_i)]/TG_A

^aIncludes level of performance of the production system before selection (per cow): young animal pasture feed (PF_B), young animal feedlot feed (FF_B), total young animal feed (PF_B + FF_B), cow pasture feed (CF_B), total feed (TF_B), young animal GHG emission at pasture (PG_B), young animal GHG emission in the feedlot (FG_B), cow GHG emission (CG_B), total GHG emission (TG_B), total product (KG_B), $ net return (DNR_B)
^bExpressed as equivalent steer beef, before (KG_B) and after (KG_A) selection
^cFeed price before selection is based on a land value of $400/DSE (feed required by a 50 kg dry sheep (9.7 MJ/head/d) [20]), leased at 7% p.a. [21]
^dTotal value of trait change, Σ(VTC_i) = Σ(∆T_i from selection x economic value of T_i); ∆T_i assumes that selection intensity, i is equal to1
^eUses total feed, before and after selection, assessed over the limited feed period

ISSN: 1297-9686