Chromium is an essential trace mineral primarily involved in the metabolism of glucose. Chromium potentiates the action of insulin by facilitating the binding of insulin to receptors and thus improving glucose utilization (NRC, 2012). Feed ingredients commonly used in swine diets contain a significant amount of chromium, ranging from 1,000 to 3,000 ppb, but bioavailability is typically low. Organic sources of chromium, such as chromium picolinate, chromium nicotinate, chromium propionate, and chromium yeast, are more bioavailable and more utilized in swine diets than inorganic sources, such as chromium chloride. The use of chromium sources is legally allowed in swine diets up to 200 ppb according to a letter of non-objection from the Food and Drug Administration. Dietary addition of chromium is most often targeted to finishing pigs and sows.
Addition of chromium to diets for finishing pigs has been related to improvements in growth performance and carcass leanness, with no impact on characteristics related to pork quality (Lindemann et al., 1995; Lien et al., 2001; Sales and Jančík, 2011; Gebhardt et al., 2018b). The mechanism of chromium to improve lean deposition is not clear, but it could be due to the stimulation of protein deposition and lipid degradation as a response to insulin activity (Lien et al., 2001). However, the effects of chromium on grow-finish pigs have been modest (Gebhardt et al., 2018b) and not consistent (Mooney and Cromwell, 1999; Shelton et al., 2003; Matthews et al., 2005; Kim et al., 2009). The variation in chromium status of the pig, amount of available chromium in the diet, and environmental conditions could contribute to inconsistency. Due to this variability and inconsistency in performance, there is currently no estimate for chromium requirements for swine (NRC, 2012).
Addition of chromium to diets for sows has been related to an increase in litter size (Lindemann et al., 1995; Lindemann et al., 2004; Wang et al., 2013). The ability of chromium to increase litter size is primarily associated to the influence of insulin and glucose on nutritional status and reproductive hormones of sows before breeding (Cox et al., 1987; Whitley et al., 2002; Woodworth et al., 2007). The magnitude of the effect of chromium on litter size is dependent on dose and feeding duration, but the improvement on sow prolificacy is generally consistent.
Additive effects of supplementation of sow diets with chromium and carnitine have been found on reproductive performance (Real et al., 2008). Both chromium and carnitine influence energy metabolism of sows but through different mechanisms that seem to act synergistically (Woodworth et al., 2007). The supplementation of sow diets with chromium and carnitine has been shown to additively improve farrowing rate and thus number of piglets born alive (Real et al., 2008).