Effects of age and state of incisor dentition on faecal output of dry matter and on faecal and urinary output of nitrogen and minerals, of sheep grazing hill pastures

Abstract

SUMMARYExcretion of D.M., N, Ca, P and Mg in faeces, and N, P and Mg in urine were measured at intervals over 12 months in breeding Scottish Blackface sheep grazing hill pastures. These values were used with data on reproductive performance and body compositional changes, to calculate the energy, nitrogen and mineral balances. The sheep were: 11 6½-year-old with sound mouths (SM), 16 6½-year-old with broken mouths (BM), 16 5½-year-old with all permanent incisors clipped to gum level (CM) and 16 2½-year-old (Y). An energy supplement was given at the end of gestation and during early lactation. All faeces were collected and creatinine was used as an internal marker to estimate urine volume.Faecal D.M. output ranged from 443 to 662 g/day, with highest values in November and lowest in May. Average values for the BM sheep were lower than those for the other groups but when output was expressed as a power function of body weight, the values for the Y sheep were 15% higher than those for the other groups. Faecal excretions of Ca and P in January and February were very low and the values for P were half the expected endogenous faecal loss.Urinary output ofN ranged from 6·0 g/day in February to 22·2 g/day in August and the corresponding urinary urea N: total N ratios were 0·24 and 0·69. Urinary Mg output was highest in late summer and early winter but urinary P showed no consistent trends.The estimated daily intakes of DOM (g) were 936 in November 1969, 599 in January, 414 in February, 1075 in May, 1150 in August and 946 in November 1970.The loss of energy from the body between mating (November) and mid-lactation (June) ranged from 9·5 to 16·8% of the total calculated ME requirements in the Y and BM sheep, respectively. Maintenance requirements averaged 204 kJ/kg body weight/day and the value for the Y sheep was 12% higher than the mean for the older sheep.Nitrogen and mineral balances were calculated for February, May, August and November. The sheep were protein-deficient in winter, not from a shortage of crude protein in the diet but because of its low digestibility (34%). Intakes of Ca and P in winter were low and a real possibility of a P deficiency exists. Estimates of the concentrations of N and of minerals in the herbage consumed by the sheep were made and compared with those obtained for cut herbage from the same pastures. It would appear that the sheep selected herbage of a higher protein content than that of the cut herbage. Herbage selection was greatest in November.