Histidine maintenance requirement and efficiency of its utilization in young pigs

An experiment was conducted in young pigs (initial BW 10.1 kg) to estimate the maintenance requirement for histidine and its efficiency of utilization for protein accretion using a comparative slaughter technique. Three groups of six pigs each were fed a purified diet supplying 0, 14 or 56 mg histidine per kg BW0.75. Following 21 d of feeding, pigs were killed for whole body compositional analysis. A representative group of six pigs was killed at the beginning of the experiment. Retention of histidine and total N were the main criteria of response. Histidine retention (R2 = 0.73) and N retention (R2 = 0.78) were linear functions of histidine intake (p < 0.001). Histidine requirement for zero histidine retention was 15.5 mg/kg BW0.7, whereas histidine required for zero N retention was 4.1 mg/kg BW0.75. At zero histidine retention, the pigs retained daily 82 mg N/kg BW0.75, presumably due to the degradation of histidine-rich compounds such as haemoglobin and/or carnosine. The slope of the regression line relating histidine retention to N retention indicated that 105 mg of histidine was deposited per gram of total N which was considerably less than the estimated histidine concentration in body protein (179 mg/g N). Based on the slopes of regression equations for histidine and N retention, marginal efficiency of histidine utilization was calculated to be 0.94 and 1.34, respectively.