Effects of deficiency and surplus dietary threonine on reproductive performance of primiparous pregnant gilts
Threonine is an essential amino acid that cannot be synthesized by pigs (NRC, 2012) and is the second limiting amino acid in corn–soybean‐based diets for sows (Soltwedel, Easter, & Pettigrew, 2006). Currently, a dietary standardized ileal digestible threonine‐to‐lysine ratio is 0.71 for gestating gilts as suggested by the NRC (2012). Dietary threonine imbalance is known to impair reproductive performances of gestating sows (Dourmad & Etienne, 2002), but the underlying mechanisms are largely unknown. Either a deficiency or an excess of dietary threonine decreases protein synthesis in rapidly growing tissues of young pigs decreases the total amount of mucin and changes the mucin subtypes, compared with piglets fed the optimal level of dietary threonine (Wang, Zeng, Mao, Wu, & Qiao, 2010). Additionally, diet supplemented with threonine increased serum level of immunoglobulin G in first‐litter gilts (Cuaron, Chapple, & Easter, 1984; Li, Yin, Li, Woo Kim, & Wu, 2007). With high incorporation of threonine into the mucosal proteins (28%–35%) (Munasinghe, Robinson, Harding, Brunton, & Bertolo, 2017; Sr et al., 2002; Stoll et al., 1998), digestive enzymes (5%–11%) (Block, Weiss, & Cornett, 1966), as well as the immunoglobulins (7.4%–10.3%) (Smith & Greene, 1947), threonine is particularly important during periods that are characterized by growth and development of mucosal tissues and the immune system (i.e., gestation).
In late gestation, there is rapid growth of foetal tissue and a shift away from maternal body protein deposition to mucosal membranes (i.e., intestinal and mammary tissue) expansion (Trottier & Johnston, 2001). Therefore, provision of optimal dietary threonine will play an important role for the optimal foetal and mammary gland development (Specian & Oliver, 1991). We hypothesized that deficiency or ST threonine intake in gestation may alter reproductive performance in primiparous sows due to alteration in metabolic state. Therefore, the effects of a DT, an AT and a ST dietary threonine concentration during gestation on gilt body condition, litter performance, blood metabolites and metabolic hormones (serum threonine, IGF‐I, insulin, glucose and urea nitrogen), reproductive hormones and colostrum composition of primiparous pregnant gilts were investigated in this study to address this question.