FEED DIGESTIBILITY AND MICROBIAL NITROGEN PRODUCTION IN PAIR-FED LAMBS AT 20°C AND 50°/42°C WHEN WATER INTAKE WAS RESTRICTED AT THE HIGHER TEMPERATURE

Abstract

This experiment was conducted to investigate the effect of high temperature on
feed digestibility and microbial nitrogen production (MNP) in lambs when feed
intake (FI) and water intake (WI) were both controlled so as to be similar to those at
thermo neutrality. Eight lambs were allocated into a pair feeding experiment. They
were fed oaten chaff (1.67% N) and watered at similar levels, irrespective of
temperature. Two ambient temperature treatments were applied (20°C constant, or
50°C during the day and 42°C at night). Lambs at 20°C were given ‘a restricted feed
allocation that was determined by the unrestricted Fl of their pair-mates at 50°/42°C
on the previous day, and water ad libitum, while lambs at 50°/42°C were watered at
the minimum level (2.8 lld) that allowed dry matter (Db/1) intake to be maintained at 20°C levels. DM and N digestibility at 20°C (66.9 and 67.7 % respectively) were
higher than at 50°/42°C (62.9 and 64.2 % respectively), but temperature did not
afiect MNP and efliciency of MNP (EMNP), means of 4.8 g/d and 12.5 g/kg
digestible organic matter intake respectively. Both respiration rate (RR) and rectal
temperature (RT) at 50°/42°C (126 breaths/min and 4O.2°C, respectively) were
higher than at 20°C (40 breaths/min and 38.6°C, respectively). It was concluded that in lambs at 50°/42°C, which had the same DM intake and a higher WI than at 20°C, DM digestibility was increased while MN? and EMNP were not influenced.