Nine Friesian calves, averaged 140 kg live body weight aged 5 months, were
randomly allocated into three equal groups. The first group was supplemented with
12 g Niacin (NA) /day per calve for 60 days, the second group was supplemented
with 100 mg/kg body weight Nigel/a sativa seeds (NS) while the last group served as
a control with no supplemented niacin or Nigel/a sativa seeds. Animals were housed
indoors (semi-open shed) during the period of the experiment. Mean maximum air
temperatures; arid ~eJati.\te humidity were 39.9 °C and 67.4%, respectively for the
experimental perice. Rectal temperature, skin temperature and respiration rate were
r.ecofide,d at different intervals 0800 h, 1200 h, 1600 hand 2000 h. Although, the
thermat responses were taken at 1000 h pre exposure and at 1300 h (after 3 h
exposure). The thermal responses were affected by treatments. Comparison of. rectal
temperature for control calves and calves fed NS and NA showed higher temperature
(39.3 vs 39.1 and 38.9 °C at 0800 h; 40.0vs.39.5 and 39.0oGat 1400 h) and skin
temperature (38.1 vs 38.0 and 37.8 °C at 0800 h; 39.3 VS 38.6 and 38'.0 °C at 1400 h,
respectively) and respiration rate (35 vs 33 and 26 respiration per minute (rpm) at
0800; 49 vs 38 and 31 rpm at 1400 h). Meanwhile, exposure to heat stress for 3 h
caused a significant increase of thermal responses in calves fed control diet in
comparison with calves fed NS and NA. Calves fed Niacin (NA) showed a decrease of
respiration rate, rectal and skin temperatures in comparison to other groups which
indicated a possible positive effect of NA supplementation on calves, exposed to hot
summer conditions,
Calves fed diets. supplemented with NA tended to gain less body weight than
did calves fed NS or tine control diet.
Niacin treatment resulted in metabolic changes that was reflected' by an
insignifiCant increase in t glucose in comparison with calves fed NS or lWmt(1(J11 group.
The results indicated a positive effect of niacin supplementation on Friesian
calves exposed to hot summer conditions especially under Upper Egypt conditions
with severe heat stress.