The flow of calcium and phosphorus to the proximal duodenum was measured over 22 24-hr periods in sheep fitted with re-entrant duodenal cannulae. The sheep were offered one of six diets in a ground and pelleted form supplying 1.4–30 g of nitrogen per day from three different protein sources. The estimated metabolizable energy content of the diets was 1.9 or 1.3 Mcal/kg. The diets supplied 2.0–5.8 g of calcium per day and 2.2–3.3 g of phosphorus per day. Between 49.9% and 61.2% of the dietary calcium intake appeared at the duodenum in the sheep given all diets except the one supplying 1.4 g of nitrogen per day, where the value was 98.5%. There were highly significant correlations between the daily calcium intake and the flow of calcium to the duodenum, the excretion of calcium in the faeces, the retention of calcium and the calcium content of the rumen. Between 85.0 and 119.1% of the daily phosphorus intake appeared at the duodenum in the sheep given all six diets. The flow of phosphorus was correlated with the dietary phosphorus intake. There were significant correlations between the flow of calcium and phosphorus to the duodenum and, also, their retention.
Effects of Dietary Phosphorus Level on the Expression of Calcium and Phosphorus Transporters in Laying Hens
