Presenting a webinar on managing scours in the breeding season, Dr Gunn said while the occurrence of calf scours within production systems varied from season to season, farmers could have a problem this year.
"Some areas of Australia have been blessed with really good rain ... this might mean more diseases are around that like wetter weather (including calf scours)," she said.
During the herd rebuild, people have bought in animals from other herds which means they have brought in new pathogens.
Scours is most problematic in calves less than six weeks of age, with northern NSW seeing it in calves from ages four to 12 weeks.
A number of pathogens can cause calf scours and often more than one pathogen is involved.
"Pathogens are shed by calving cows and older calves," she said.
"Shedding increases at calving ... as you go through calving, more and more bugs are built up in a paddock and towards the end of calving you normally see a problem."
Younger calves require a smaller dose of pathogen to cause disease.
To prevent calf scours it is important to protect those less than six weeks old including newborns, those from heifers, and calves with low immunity which are generally calves that have not received enough colostrum.
Reduce contact with calving cows, sick calves or calves greater than four weeks of age
Do not leave calving cows in one paddock for more than three weeks, and if wet and boggy move more frequently.
Selecting calving and nursing paddocks in advance is crucial. Do not use paddocks in which scours have occurred in the previous 12 months.
Spell paddocks for at least three months before calving, or graze with low risk stock which may be calves greater than six months old, yearlings, dry cows or sheep.
Options for calving cow management includes; drifting cows with calves off, drifting cows yet to calve out, group into mobs where the calf age range is less than two weeks, pregnancy test early and late, synchronise or spread cows out at a low stocking density.
Don't mix mobs until all calves are greater than four weeks old.