In carnitine deficiency, fatty acid oxidation is reduced, and fatty acids are diverted into triglyceride synthesis, particularly in the liver. Mitochondrial failure develops in carnitine deficiency when there is insufficient tissue carnitine available to buffer toxic acyl-coenzyme (CoA) metabolites. Toxic amounts of acyl-CoA impair the citrate cycle, gluconeogenesis, the urea cycle and fatty acid oxidation. Carnitine replacement induces excretion of toxic acyl groups in the urine (Stumpf et al., 1985). Skeletal muscles are generally involved, with weakness, lipid myopathy and myoglobinuria often aggravated or precipitated by fasting or exercise. For exercising pigeons, L-carnitine supplementation improved fatty acid oxidation efficiency during heavy exercise (Janssens et al., 1998).
The increases in plasma and hepatic acylcarnitines in broilers fed 0.5% L-carnitine indicated that supplementary carnitine lessens the load of free acyl groups in the liver by eventual oxidation or excretion (Smith et al., 1994). Barker and Sell (1994) found that carnitine intake (0, 50 and 100 mg per kg) (0, 22.7 and 45.5 mg per lb) did not affect body weight, feed conversion efficiency and proximate composition at 21 days in turkeys and at 45 days in broilers. However, more recent research indicates liveweight gains and feed efficiency improved with carnitine supplementation (Iben and Meinhart, 1997; Rabie et al., 1997a, d; Rabie and Szilagyi, 1998). Iben and Meinhart (1997) noted that broilers given L-carnitine with optimum lysine and methionine were 2.47% heavier than controls. Amount and percentage of abdominal fat and ether extract in breast meat of 53-day-old broilers were significantly reduced in response to carnitine supplementation (Rabie et al., 1997a).
Egg quality and hatchability have been improved with supplemental carnitine (Leibetseder, 1995; Rabie et al., 1997b, c). L-carnitine had a beneficial effect on albumen quality and could modify the components of the edible part of the egg during the late laying period (Rabie et al., 1997b). With 50 and 100 mg per kg (22.7 and 45.5 mg per lb) in the feed of layer hens, hatchability increased by 4% and 2.9%, respectively (Leibetseder, 1995).