Scours — calf diarrhoea — is the number-one cause of death in pre-weaned calves worldwide. The calf rarely dies of the infection itself; it dies of dehydration. Understanding that one fact changes how you treat it: the priority is fluids, fast, every time.
What causes it Scours has several culprits, often overlapping, and they cluster by age: - First few days: often E. coli (and poor colostrum leaving the calf defenceless). - ~5–14 days: rotavirus, coronavirus, cryptosporidium — the common viral/protozoal scours. - 2–4 weeks: coccidiosis, Salmonella. You usually can't tell which from looking; a vet can test a faecal sample if scours is a recurring herd problem. But the *treatment of the dehydration* is the same regardless of cause.
Treatment: fluids first, fluids most - Oral rehydration salts (electrolytes) are the mainstay. Mix as directed and feed *in addition to* milk, not instead of it — the old advice to "rest the gut" by withholding milk is outdated; the calf needs the energy from milk to fight and recover. Space milk and electrolyte feeds a couple of hours apart. - Keep feeding milk unless your vet says otherwise. A scouring calf is burning energy and starving. - Assess dehydration: sunken eyes, skin that stays "tented" when pinched, weakness, cold mouth, inability to stand = severe. A calf that can't stand or won't suckle needs IV fluids from a vet — oral won't be absorbed fast enough. - Keep it warm and dry. A sick, dehydrated calf chills easily; a calf jacket and deep dry bedding help it spend energy on recovery, not on staying warm. - Antibiotics are not routine. Most scours is viral or protozoal — antibiotics do nothing for those and breed resistance. Use them only for specific bacterial cases on vet advice (e.g. a calf that's also septic/feverish).
Prevention — where the real wins are Scours is overwhelmingly a management disease: - Colostrum, colostrum, colostrum. Calves that get enough good colostrum quickly are dramatically more resistant. This is your single biggest lever (see "How much colostrum does a newborn calf need?"). - A clean, dry calving area — calves pick up bugs in the first minutes of life. - Clean, individual calf housing for the first weeks; don't group young calves with older ones. - Scrupulous feeding hygiene — buckets, teats, and mixers cleaned every feed. Dirty equipment seeds the next outbreak. - All-in/all-out and don't overcrowd — pathogen pressure builds when pens are crowded and never rested. - Vaccinate the dam (rotavirus/coronavirus/E. coli scour vaccines, given pre-calving) so her colostrum carries protection — especially valuable on farms with a recurring scours problem.
The mindset Treat the dehydration immediately and aggressively; investigate the cause if it's recurring; and put your energy into prevention, because a scours outbreak is far cheaper to avoid than to treat.
Sources University of Wisconsin — Calf Scours: Causes and Treatment. AHDB Dairy — Calf Diarrhoea Management. Merck Veterinary Manual — Diarrhea in Neonatal Calves.