Babies under a year old should not be given cow's milk because it is much too salty for them, nutritionists have warned.
It is almost four times as salty as breast milk, say researchers who have found that those fed cow's milk before 12 months tended to have the highest salt diets.
Dr Pauline Emmett and Vicky Cribb, nutritionists from Bristol University, found that seven in 10 babies had too much salt in their diets.
The study, published in the European Journal of Clinical Nutrition, looked at almost 1,200 eight-month-olds born in 1991 or 1992.
Cow's milk, they noted, contains 55mg of salt per 100ml, almost four times that found in breast milk (15mg / 100ml). Concentrations in formula milk vary from 15 to 30mg / 100ml.
A baby consuming 700ml of cow's milk daily (or 25 fluid ounces) would be getting 385mg of salt from that source alone - almost half the recommended maximum (one gram) for a baby up to a year old. One in eight of the children studied were fed only cow's milk, as opposed to breast or formula.
The researchers warned: "These findings show that salt intakes need to be substantially reduced in children of this age group.
"Infants need foods specifically prepared for them without added salt, so it is important to adapt the family diet.
"This research suggests that clear advice is needed for parents about what foods are suitable for infants.
"This should be given to all parents and carers, and should include the important advice not to use cows' milk as a main drink before 12 months of age."
The researchers also found that those fed cow's milk tended to be given other foodstuffs relatively high in salt, including processed foods like baked beans and tinned spaghetti.
They went on: "Given that three-quarters of salt in the diet comes from processed adult foods, successful salt-reduction strategies can only be achieved with the co-operation of the food industry.
"Manufacturers have a responsibility to reduce the salt content of food products.
"This process has already started in UK but much more needs to be done."
Giving babies too much salt in their diets can encourage a liking for the flavour that lasts a lifetime.
That can lead to health problems. Only last week experts reiterated the dangers of taking in too much salt, which is known to increase blood pressure. More than 4,000 deaths a year could be prevented it British adults reduced their mean daily intake from 8.6g to 6g, they said.
Giving far too much salt to small children can also damage their kidneys.
The Department of Health recommends avoiding giving cow's milk as a drink until a baby is a year old.
The NHS Choices website explains: "This is because it doesn't contain the right balance of nutrients to meet your baby’s needs."