Digestibility of total and phytate phosphorus in young calves

Two experiments were conducted to determine digestibility of total and phytate phosphorus (P) in young calves. In the 1st experiment 14 male calves received a commercial milk replacer (6 l of milk per day) and had free access to a starter concentrate. In the 2nd experiment 21 male calves were divided into 3 groups and fed ad libitum a milk replacer (Group I), milk replacer and starter concentrate (Group II), and milk replacer and silaged maize cobs (Group III). Digestibility measurements were carried out at the age of 10 weeks (1st experiment), and 12 and 16 weeks (2nd experiment). In the 1st experiment phytate P accounted for 27.0% of the total P intake. Phytate P was assayed by capillary isotachophoresis. On average, 27.9% of ingested P, but only 3.0% of phytate P were recovered from the faeces. The proportion of phytate P in total faecal P was 5.8%. In the 2nd experiment phytate P accounted for 8.9, 13.8 and 8.6% of total P in diets of calves of Group I, II and III, respectively. On average, 6.6% of ingested P and 3.6% of phytate P were recovered from the faeces. Dry matter of faeces contained total P, phytate P and phosphate P at 9.74, 0.65 and 4.69 mg/g, respectively. Faecal concentrations of total P significantly correlated with those of calcium (r = 0.71). It can be concluded that young calves utilised phytate P very efficiently as no more than a few % of phytate escaped degradation in the digestive tract.