Effects of Including Ruminally-Inert Fat in the Diet of Heat Stressed Lambs on Dry Matter and Water Intake and Physiological Parameters

The effect of three ruminally-inert fat supplements in the diet of crossbred lambs on dry matter intake (DMI), water intake (WI), and physiological parameters associated with heat stress under tropical conditions (28-30°C, 75% relative humidity) was determined. Twelve lambs (25.83 kg average initial weight) were fed to meet or exceed current NRC recommendations with a basal diet providing 17% CP and consisting of 50% alfalfa hay, 36.24 cracked corn, 12.01% soybean meal, and supplemented or not with 1.75% of ruminally-inert fat provided as free fatty acids (FFA) or two experimental fat products from palm oil (E1 and E2). The lambs were assigned to one of 3 latin squares. Treatments were: no additive (NA), or diets containing FFA, E1 and E2. Feed was offered daily at 4% of lamb BW (DM basis). Experimental periods were 21 d, consisting of 14 d of adaptation to the diet followed by 7 d of data collection. Data collected included: DMI (g/d), WI (L/d), percentage WI in relation to animal body weight, and the ratio DMI/WI was determined. Physiological parameters associated with heat stress included: respiration rate (RR), heart rate, (HR), and rectal temperature (RT). Data were analyzed according to a 4 x 4 Latin Square experimental design replicated 3 times. Tukey-test was used for mean comparison. There were no differences (P>0.05) in DMI or WI among experimental treatments averaging 1190 g/d and 4.48 L/d. Percentage WI in relation to animal body weight and the ratio DMI/WI were also similar for all experimental treatments (averaging 21.93% and 3.76, respectively). Inclusion of ruminally-inert fat did not affect HR, RR and RT and averaged 109 breaths/min, 73.24 beats/min, and 102.9°C. In summary, the inclusion of 1.75% ruminally-inert fat in the diet of crossbred lambs did not affect DMI, WI and physiological parameters associated with heat stress under tropical conditions.