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He was a speaker at the National Rural Health Conference in Auckland this month.
Dr Bryan said he talked about animals' roles in human and environmental health, and touched on anti-microbial resistance.
''I talked about the positive and the negative aspects.''
''Research has shown that one of the positives we see for people who are exposed to animals when they are young, is they are likely to have less asthma and other allergies,'' he said.
''There is also research around people living longer because they own cats and dogs [than those who don't].
''We see changes in the microbiome - if people live with dogs, they will have a different microbiome to people who don't, and I suggest that is a benefit, as opposed to people living in an animal-free environment.''
He said infections which spread to humans were fairly rare, although there could be issues with children in calf sheds.
''Kids tend to help with calves so are at a greater risk of diseases like campylobacter, salmonella, E. coli and leptospirosis.
''There is nothing wrong with kids playing with calves but as they tend to put their fingers in their mouths ... so there is a need for good hygiene practices.''
He said there tended to be a view the rural animal health sector was not as serious about human health and that antibiotic resistance and antibiotic use in animal treatment was a lot higher than in other countries.
However, studies had shown New Zealand was the third lowest user of antibiotics for animal treatment in the world, and the third highest for prescribed antibiotics for humans.
Research showed animals, companion or production, tended to have a positive effect on owners' mental wellbeing.
-By Yvonne O'Hara