Remaining productive with fewer animals had "probably been the normal course of events for New Zealand farming," O'Connor said.
Therefore, the recommendation wouldn't present much of a problem for the primary sector.
"That 15 per cent may be no real interference or challenge for the industry. It may be part of the ongoing evolution of what we have in terms of livestock protein production."
New Zealand had also pledged to slash emissions by 30 per cent below 2005 levels, and 11 per cent below 1990 levels, by 2030.
Mackay pointed out that the country had fewer stock units than in 1990, and research showed that sheep and beef farmers were close to being carbon neutral.
He asked O'Connor if he was being tough on farmers.
"We've made some great progress, but we're all in one country here," O'Connor said.
"We have done a great job across agriculture and that's been acknowledged, and it's made it easier for all of us as we go forward."
"So it's not just one sector against the other – it's how we co-operate."
As New Zealand's contribution to global emissions was minimal, Mackay asked if we were a "climate change martyr," while India, China and the US were "sitting on their hands."
O'Connor said it was better to be at the leading edge of climate change than to be playing catch up.
Listen below:
"Other countries are more desperately having to change what they're doing. You watch China – when they make a decision to move down this lower emissions path – and they're starting to indicate that already – there will be massive change in the country."
"We don't want to see the kind of change that might have to occur quickly - we want to see evolution into a low carbon economy, and I think it's quite possible."
As a result of this, O'Connor believed farmers shouldn't fear the Climate Change Commission's report.
"That shouldn't spook agriculture or the primary sectors at all. It should actually endorse what we've done and encourage us to move on."
Also in today's interview: O'Connor discussed his diplomacy advice to Australia on dealing with China and the UK's interest in joining the CPTPP.