The endogenous phosphorus excretion of preruminant lambs

Abstract

Twenty-seven preruminant male crossbred lambs, aged 1-2 days at the start of the experiment, were used. Three lambs were sacrificed on day 1 and selected bones taken for analysis. Twenty-four lambs, in groups of three, were bottle-fed on low-phosphorus milk replacers in a 2 x 4 factorial experiment. The sole source of protein in the diets was whole beef blood, supplemented with L-isoleucine and DL-methionine, to supply either 10 or 25% of the total dietary energy as protein. At each protein level the diets were supplemented with CaCO3 to provide four ratios of Ca:P (0.5:1, 1:1, 2:1 and 10:1). The daily intake of gross energy was controlled at 880 kJ-0.73. Faeces and urine were collected separately each day and bulked during the last seven days of the experiment for the estimation of N, Ca and P. Serum Ca and P concentrations were determined at weekly intervals. The lambs were sacrificed at the end of the experimental period of 21 days and selected bones were taken for analysis. The concentrations of bone ash, Ca and P all decreased significantly when compared with values determined at the start of the experiment. The lambs given the high-protein diets showed significantly greater losses of bone ash, Ca and P, and had lower serum P, but higher serum Ca concentrations, than lambs fed on the low-protein milk replacers, irrespective of the dietary Ca:P ratios. Phosphorus excretions during the last seven days of the experiment were as follows: faecal P (day-1); low-protein group (n = 12), 3.1 � 0.5 mg kg-1; high-protein group (n = 11) , 4.1 � 0.5 mg kg-1; all lambs (n = 23), 3.6 � 0.3 mg kg-1. Urinary P (day-1): low-protein group (n = 12), 0.92 � 0.22 mg kg-1; high-protein group (n = 11) , 0.61 � 0.03 mg kg-1; all lambs (n = 23), 0.77 � 0.12 mg kg-1. Faecal and urinary P excretion was unaffected by variation in the dietary Ca:P ratio.