Effect of dietary fat level on feed intake, growth, plasma metabolites and hormones of calves fed dry or liquid diets

Abstract

To study the role of fat in adaptation to ruminating function and growth, 24 male Holstein calves were assigned at 3 d of age to conventional or veal feeding regimes. At 6 weeks of age, conventionally-fed calves were weaned to dry diets containing 3 or 10% fat, whereas veal calves were maintained on liquid diets with 10 or 18% fat. There was a significant interaction of fat level and feeding system on average daily gain (ADG); higher dietary fat content lowered ADG of ruminating calves and increased ADG of liquid-fed calves. Calves fed the higher fat dry diet adapted slowly to weaning with frequent bloating; dry matter (DM) intake and ADG were lower at 42–48 d, and total days to 160 kg was greater, but did not increase total DM intake to 160 kg compared to calves fed the lower fat dry diet. Calves fed low fat liquid diets required more days to reach 160 kg than did those fed high fat liquid diets, resulting in higher total DM (but not energy) intake. Overall ADG of calves fed either low fat diet were not different; this was caused by higher gain after 84 d by calves fed the solid diet. Calves fed liquid diets had decreased hematocrit ( P < 0.0002) and increased plasma content of glucose and insulin ( P < 0.0001), cholesterol ( P < 0.025), and T 3 and T 4 ( P < 0.072), as compared to calves fed dry diets. High fat diets increased cholesterol ( P < 0.0046), and total ( P < 0.0027) and neutral ( P < 0.0047) lipid in plasma, as compared to low fat. High fat increased hematocrit in liquid-fed calves (feeding × fat, P < 0.082). All plasma measures were strongly influenced by age; however, no measures explained different abilities of ruminating and liquid-fed calves to utilize high fat diets. Ability of liquid-fed calves to utilize high fat diets may be related to high insulin associated with high lactose intake and plasma glucose concentration.