One of them, John Haigh, QC, wasn't having the minister's comments.
"How can you remove the emotional issue when you're dealing with animals who are confined in this way?" he asked.
And keynote speaker Dr Jonathan Balcombe, an American biologist who lived in New Zealand as a child, and who has written books about the inner lives of animals, stood to tell Mr Carter the science is already clear.
"I would reiterate my phrase, sentience [the capacity to feel, from pleasure and joy to pain] is the bedrock of ethics and the science does show now that animals have rich emotional and cognitive lives and therefore they ought to be accorded the kind of considerations that we accord our own species, and that's what's relevant.
"It's not about how their intelligence compares to ours, it's about how much they can feel pain, suffering, joy and pleasure."
Lawyer Catriona MacLennan pointed out that the law in this country allows hens to be kept in cages with 550sq cm of space each, which is slightly smaller than an A4 piece of paper.
The law is being reviewed and the proposal is that over an unspecified period of time they will get 750sq cm of space each, slightly larger than an A4 page, which she said would still be "completely unacceptable."
Mr Carter, who said that as a farmer a bond with animals came with the territory, would not comment on the welfare code for laying hens but did receive praise for being the minister who saw legislation through Parliament strengthening penalties for animal cruelty.
SPCA stalwart Bob Kerridge, who founded this conference and the Companion Animal Council, said Mr Carter had also called for the coming complete review of the Animal Welfare Act where proposals such as banning intensive farming practices will be put.
While many animals were discussed at the conference, chickens featured large.
Dr Annie Potts, associate professor and co-director of the New Zealand Centre for Human-Animal Studies attached to Canterbury University, took delegates on a journey through the history of the domestic chicken, previously revered in various cultures but downgraded in more recent times to mere food and treated appallingly.
Chickens, she said, display tenderness, deception, altruism and grief and can even suffer from post-traumatic stress.
They endure negative emotions, such as fear, anxiety and boredom - along with intense joy and pleasure.
"They love dust-bathing ... they also love sunbathing and will stretch out their wings to the warmth of the sun's rays."
It was "intensely distressing" that the overwhelming majority of chickens lived in grossly abnormal and unrewarding environments, she said, and urged the conference not to forget about broiler chickens.
These animals are raised solely for meat and in their 12-week life they are forced to put on so much weight their legs often twist and deform. Because artificial lighting is used, they never get to stretch out in the sun.
Dr Balcombe, a vegan, spoke about a range of animals.
Sheep are much more perceptive than people think, he said, citing a study which showed they could recognise faces and remember 50 or so of their original flock two years later.
That showed they have an inner mental life; they have consciousness and awareness.
"They have a life that to them is precious."
The human relationship with animals is a troubled one, he said, but if animals can feel pleasure, denying them their life has a moral weight attached.
We need to think of animals as individuals, he said: "It's not just a gull - it's that gull."
The irony of Western society was that most people abhorred animal cruelty but then funded it at the local supermarket.
But he remains hopeful people will at least cut down on eating animals - saying they have to.
Ethics aside, the human population now stands at seven billion and the world's resources are limited.
It is simply not sustainable to feed so many people on a meat-based diet, said Dr Balcombe.
"Either we get there or it's not going to be a very pretty world."
Hen cages
Now: 550sq cm (slightly smaller than an A4 piece of paper).
In future: 750sq cm (slightly larger than A4).