Carnitine is a vitamin-like compound involved in the transport of fatty acids into the mitochondria to produce energy. Carnitine is synthesized from lysine and methionine and derived from the diet (Fischer et al., 2009). Only the L-isomer of carnitine is active for swine. Dietary addition of carnitine is most often targeted to grow-finish pigs and sows.
Addition of carnitine in grow-finish diets has been shown to improve growth performance and carcass leanness (Owen et al., 2001a; James et al., 2013a; Ying et al., 2013). The effects of carnitine in grow-finish pigs have been attributed to an enhancement in the ability to efficiently use fat for energy and to synthesize amino acids and proteins (Owen et al., 2001b). To the pig, this translates into improved growth rate and efficiency, decreased lipid deposition, and increased protein accretion (Heo et al., 2000). However, the effects of carnitine in grow-finish pigs have been inconsistent (Owen et al., 2001a,b; Pietruszka et al., 2009; James et al., 2013b). It’s been suggested that factors that affect energy intake, such as stocking density, health status, and environmental temperature, as well as the amino acid levels in the diet could influence the effects of carnitine in grow-finish pigs (Ying et al., 2013).
Addition of carnitine to diets for sows has been shown to increase birth weight and weaning weight of piglets and litters (Musser et al., 1999; Ramanau et al., 2004; Ramanau et al., 2008; Wei et al., 2018). Carnitine has also been shown to improve litter size and reduce the number of stillborn or non-viable piglets (Musser et al., 1999; Eder et al., 2001; Ramanau et al., 2004; Zhang et al., 2018), although less consistently. There are many mechanisms by which carnitine acts to increase birth weight, but are mainly involved with improvement of nutrient supply and muscle development of fetus via increased concentration of insulin-like growth factors (IGF-1 and IGF-2), enhanced placental development, and improved supply of glucose via placenta (Doberenz et al., 2006; Woodworth et al., 2007; Brown et al., 2008; Eder, 2009; Zhang et al., 2018). In addition, there are other mechanisms by which carnitine acts to increase weaning weight, which are mainly involved with improvement in milk production, milk composition, and suckling behavior (Ramanau et al., 2004; Birkenfeld et al., 2006; Zhang et al., 2018). Recently, carnitine has been associated with enhancement of the antioxidant status of sows and piglets (Wei et al., 2018).
Additive effects of supplementation of sow diets with carnitine and chromium have been found on reproductive performance (Real et al., 2008). Both carnitine and chromium influence energy metabolism of sows but through different mechanisms that seem to act synergistically (Woodworth et al., 2007). The supplementation of sow diets with carnitine and chromium has been shown to additively improve farrowing rate and thus number of piglets born alive (Real et al., 2008).