Factors affecting the voluntary intake of food by sheep. 4. The effect of additives representing the primary tastes on sham intakes by oesophageal-fistulated sheep.

1. Sheep with oesophageal fistulas were sham-fed on pelleted lucerne (Medicago sativa) hay to assess the palatability of added chemicals representing the tastes of sweet (sucrose), sour (hydrochloric acid), salt (sodium chloride), bitter (urea) and umami (monosodium glutamate; MSG). 2. Plain pellets and four concentrations of each chemical were sham-fed for 30 min after 5.5 h deprivation in 5 x 5 Latin-square experiments following a period of adaptation feeding. 3. Sucrose, at concentrations of 15-120 g/kg air-dried pellets, depressed intakes with a linear relation between intake (I; g) and concentration (C; g/kg): I = 1001-3.42C. 4. HCl at 6.25-25.0 g/kg pellets had no effect on sham intakes but at 50 g/kg reduced them by 50% of control (P less than 0.05). 5. NaCl at 50 200 g/kg increased sham intakes by 26% (P less than 0.01) with no evidence of a dose-related effect. 6. Urea at 10-80 g/kg decreased sham intakes by 26.9% (P less than 0.01) with no evidence of a dose-related effect. 7. MSG at 5-40 g/kg in two experiments increased sham intakes by 16.1 and 40.8% (P less than 0.05). In another experiment at 1-8 g/kg there was no significant effect. 8. When palatability and post-ingestive effects are separated by sham-feeding, the effect of added chemicals on intake may be completely different from when they are ingested normally (e.g. NaCl and sucrose). This newly developed technique enables the palatability effect of feed additives to be tested critically and economically.