IS CARNITINE REALLY A VITAMIN?
Vitamins are organic compounds that are essential to the animals and are required in small quantities in the diet because they cannot be synthesized by the body. So technically, Carnitine does not fall into that category as it can be synthetized by animals in the presence of Vitamin C, Vitamin B and iron. But in modern farming, that synthesis covers only 25% of the daily requirement and therefore, the remaining 75% needs to be brought by the diets. That is why we call it a vitamin-like nutrient.
L-Carnitine can be partly found in animal by-products like whey powder (at 500ppm), animal and fish meal (at 100ppm) but its level is very low or almost absent in grains and plants (<5ppm). For strategies limiting the portion of animal by-products, the addition of synthetic L-Carnitine become a requirement to maintain feed efficiency both for Swine, Poultry and Aquaculture. Diets currently found on the market in Asia contains around 10ppm of L-carnitine where it should at least be at 60ppm.
L-Carnitine is indeed essential for utilization of fat. Once the fatty acids are in the cytoplasm of target cells as heart or skeletal muscles, L-Carnitine will be used as carrier to pass the barrier of the mitochondrion before fatty acids can be converted into ATP for energy. Once the fatty acids are delivered into the mitochondria, the L-Carnitine will be released back to the cytoplasm to capture another fatty acid. This cycle can explain why a small dosage of 50ppm of L-Carnitine in the feed is sufficient to fuel the mechanisms. Nevertheless, it seems that the higher is the fat content in the feed and the more critical is the supplementation of L-carnitine to support the functions of mitochondria.
During their first week of age, piglets are not equipped for producing L-Carnitine and they therefore rely on the colostrum and the milk (highly concentrated in L-Carnitine) from their mother to help them to process milk fat into energy. It is possible to measure the level of carnitine in the milk to ensure a proper supply to piglets. The table below is summarizing all the benefits of L-carnitine supplementations for Swine, Poultry, Fish and Shrimp nutrition.
Studies in Swine (Woodworth et al. -2003) demonstrated that L-carnitine-fed sows had greater circulating leptin concentrations at day 28 of gestation. Leptin that is secreted by adipose tissue and acting as a satiety signal, plays a role in regulation of energy metabolism. The balance between Carnitine / Leptin / Energy balance is highly influencing the reproductive cycles. When the energy balance is negative (loss of weight), the ovarian cycle is stopping and oestrus is delayed.
One of the most interesting study made on carnitine consisted in measuring the impact of L-carnitine supplementation on the multiplication of muscle fibres. Instead, foetus cells get specialized from 80 days of gestation. After that day, the number of muscles fibres is fixed for all the life of the future pig. To improve the future pig carcass conformity, one strategy is to stimulate the multiplication of the number of muscle fibres in the foetus before the 80thday of gestation. Musser et al. (2001) reported two studies where piglets from sows fed L-carnitine during gestation had 27.8 and 6.5% more muscle fibers compared to piglets from control sows.
In an earlier study, Musser et al. (2000) found that L-carnitine enhanced muscle fiber development of the offspring and observed that the benefit was maintained at slaughter. Pigs from sows fed diets with L-carnitine during gestation had greater (P < 0.05) loin depth (59.4 versus 57.0 mm) and lean percent (55.1 versus 54.5%). L-carnitine is actually considered as a vitamin-like nutrient as it still need to be supplied through the diet essentially through synthetic L-carnitine. With the development of the genetic potential of animals, that nutrient will become more and more limiting and I forecast L-carnitine to become a must for Swine, Poultry and even Aquaculture nutritionists in the coming years. We will probably need more researches to understand precisely the interactions between L-carnitine and other nutrients (fat content in the diet, lysin, Vitamin C, iron, chromium) or farm situation (age, level of production, stress, immunity) to ensure to bring consistent results to farmers.