Influence of dietary l-carnitine on growth, biological traits and meat quality in Tilapia

This study was designed to determine whether l -carnitine supplementation is necessary in a tilapia diet containing low-fish meal and a high lipid level, which is beneficial economically and for the environment. The effects of dietary l -carnitine on the growth, body composition, blood traits and post-thaw drip from muscle in hybrid tilapia were investigated. Five isonitrogenous and isocaloric diets were fed to the fish with a mean body weight of 141.7 g for 168 days. The control diet contained fish meal as the major protein source with 7% lipid. Other diets contained 7% or 12% lipid, in which fish meal was largely replaced by plant proteins, and supplemented with l -carnitine or not. Results showed that supplemental dietary l -carnitine did not affect the growth performance, feed efficiency or protein efficiency ratio, while the supplementation significantly reduced the mesenteric fat ratio. Whole body and muscle proximate compositions were unaltered by any dietary treatment. The total plasma lipid, triacylglycerol and cholesterol values of tilapia fed diets with alternative plant proteins were significantly lower than those of the control fish, whereas increasing the dietary lipid content increased the aforementioned blood traits. A decrease in plasma ammonia and an increase in urea were observed in dietary l -carnitine-supplemented fish. Post-thaw drip from muscle was reduced in fish fed supplemental dietary l -carnitine. The observations of this study revealed that neither the growth performance nor the feed utilization of hybrid tilapia was improved by a dietary l -carnitine treatment, but that it did lead to a reduced mesenteric fat ratio, altered nitrogen metabolism and improved meat quality.     

Effect of dietary l-carnitine supplementation and energy level on oxidant/antioxidant balance in laying hens subjected to high stocking density

This study aimed to investigate the effect of l -carnitine and energy level and on oxidant/antioxidant balance in laying hens subjected to high stocking density. A total of 176, 32-week-old laying hens were assigned to eight groups with four replicates and hens in four groups were placed at the normal stocking densities of 500 cm²/hen (four hens per cage) and in the remaining four groups were placed at the high stocking densities of 287.5 cm²/hen (seven hens per cage). Hens received diets of high (2,850 kcal/kg ME) or normal (2,650 kcal/kg ME) energy which are supplemented with 0 or 200 mg/kg l -carnitine for 70 days. Results showed that exposure to high stocking density increased (p < .05) plasma malondialdehyde (MDA) and nitric oxide (NO) levels and decreased (p < .05) erythrocyte superoxide dismutase (SOD), catalase (CAT) and superoxide dismutase (GPx) activities. l -carnitine supplementation increased (p < .05) erythrocyte SOD, CAT and GPx activities, and decreased (p <.05) MDA and NO level in high stocking densities. The oxidan/antioxidan balance of birds was not influenced by increasing dietary energy level. The results of the present study indicate that the supplementation of l -carnitine to the birds subjected to high stocking density could effectively reverse the negative effects of high stocking density by improving oxidant/antioxidant balance. Therefore, l -carnitine supplementation at level of 200 mg/kg to diet may be as a favourable alternative to deal with oxidative stress caused by high stocking density in laying hens.     

The effect of dietary l-carnitine supplementation on pulmonary hypertension syndrome mortality in broilers exposed to low temperatures

Oxidative stress is involved in the development of pulmonary hypertension syndrome (PHS) in broilers. l-Carnitine has an antiperoxidative effect and supplemental l-carnitine has been revealed to increase broiler heart weight. The present study was conducted to evaluate the effect of an addition of 100 mg/kg l-carnitine to the basal diets on PHS mortality in cold-exposed broilers. Two-hundred and forty mixed-sex broilers were equally assigned to three groups. The control group was reared in normal temperatures throughout the experiment. Starting on day 14 continuing until the end of the experiment, the other two groups were subjected to a step-down temperature programme (by lowering the temperature 1-2 degrees C per day down to 12-14 degrees C) with or without l-carnitine added to the basal diets. Cold exposure increased the right/total ventricle ratio (RV/TV) and plasma malondialdehyde (MDA), reduced superoxide dismutase (SOD) and led to pulmonary vascular remodelling in birds without feeding additional l-carnitine. Supplemental l-carnitine reduced plasma MDA, increased SOD, inhibited remodelling and postponed the occurrence of PHS for 1 week in cold-exposed broilers; nevertheless, it did not significantly influence the cumulative PHS mortality (p > 0.05). On days 24 and 32, birds fed supplemental l-carnitine had lower RV/TV and higher total ventricle/body weight (p < 0.05) but unchanged right ventricle/body weight ratios (p > 0.05) compared to their cold-exposed counterparts, indicating an increase in left ventricle weight. However, from day 39 on, their RV/TV ratios were suddenly increased (p < 0.05). It was suggested that the l-carnitine-induced increase in left heart weight might partially account for the postponed occurrence of pulmonary hypertension in the early stage by elevating cardiac output, which might, in turn, lead to the resulting increase in pulmonary pressure. In view of its complex effects on cardiopulmonary haemodynamics, l-carnitine supplementation may be impractical for reducing PHS.     

Effects of feeding l-carnitine to gilts through day 70 of gestation on litter traits and the expression of insulin-like growth factor system components and l-carnitine concentration in foetal tissues

We investigated the influence of supplemental l -carnitine on foetal blood metabolites, litter characteristics, l -carnitine concentration in skeletal muscle and insulin-like growth factor (IGF) axis components in foetal hepatic and skeletal muscle tissues at day 40, 55 and 70 of gestating gilts. A total of 59 gilts (body weight = 137.7 kg) received a constant feed allowance of 1.75 kg/day and a top-dress containing either 0 or 50 ppm of l -carnitine starting on the first day of breeding through the allotted gestation length. Foetuses from the gilts fed diets with l -carnitine tended to be heavier (p = 0.06) and the circulating IGF-II tended to be lower (p = 0.09) at day 70, compared with the foetuses from the control gilts. Insulin-like growth factor-I messenger RNA (mRNA) was lower (p = 0.05) in hepatic tissue in the foetuses collected from gilts fed l -carnitine. Free and total carnitine concentration increased (p < 0.05) in the skeletal muscle from the foetuses collected from gilts fed supplemental l -carnitine. This study showed that l -carnitine had beneficial effects on the average foetal weight at day 70 of gestation, associated with changes in the foetal IGF system.