A long-term calcium and phosphorus balance experiment with laying hens is described.
The cumulative balances of calcium and phosphorus over a whole year were seen to be physiologically impossible.
Results from other workers using short term balances could be equally impossible and a similar situation has recently been noted in balance experiments with ruminants.
The techniques employed in the experiment were, therefore, investigated in detail.
Only systematic errors could be responsible and it was found that the most likely source of such errors was (a) the spilling of food on to the floor or into the water bowl, and (b) failure to collect all the droppings.
These errors only become apparent in long-term experiments and are more pronounced when diets containing high levels of calcium and/or phosphorus are fed.