Improving nursery pig growth performance
Mitigating the adverse effects of early life transport stress by providing supplemented Trp
By Lauren Brizgys and John S. Radcliffe
At weaning, pigs are often transported significant distances, and the combination of weaning and transport represents a significant early life stressor. Weaning and transportation impose social, environmental, nutritional and immune stress on the pig and have been well documented as the most significant stress event in production resulting in reduced growth performance (Martínez-Miró et al., 2016) and feed efficiency (Y. Bin Shen et al., 2012), impaired intestinal function (Olsen et al., 2005), and increased susceptibility to disease (Adeola and Ball, 1992a).
Impact of early life stress on immune functionThe effect of ELS on immune function is bidirectional and largely dependent on the duration and intensity of the stress (Niu et al., 2022). Long-term, or chronic stress, results in immunosuppression in pigs (Dhabhar, 2014), compromising the immune response to pathogen exposure, increasing glucocorticoid production, reducing blood lymphocyte counts and inhibiting cytokine production (Moeser et al., 2017).
Humoral and intestinal immunity are impacted through reduced serum IgG and lysozyme activity (Li et al., 2015), induced lymphocyte apoptosis in intestinal Peyer’s patches, and reduced intestinal IgA-secreting cells resulting in reduced IgA secretion and decreased intestinal immune barrier functionality (Zhu et al., 2013). Disruption of the gastrointestinal immune barrier allows for increased translocation of luminal bacteria, toxins and antigens triggering mucosal inflammation and upregulation of proinflammatory cytokines (Blikslager et al., 2007).
Stress induced immune activation causes increased release of inflammatory cytokines and chemokines by peripheral immune cells. Upregulation of proinflammatory cytokines mediates small intestine damage and decreases ADFI due to the destruction of intestinal wall integrity (Jiang et al., 2009).
The energetic demands of stress and concurrent immune responses results in a redistribution of nutrients from protein synthesis and growth to maintenance of the immune system, resulting in reduced growth and feed efficiency (Chung et al., 2020).
Tryptophan’s role in stress attenuation Amino acids serve as limiting constituents of key gut barrier proteins, potential energy substrates for maintenance of the intestinal mucosa and are responsible for immune regulatory responses (Wu, 2013).
The essential amino acid Tryptophan (Trp), is an antioxidant precursor of a wide array of bioactive compounds including melatonin, kynurenine, NAD and is the rate-limiting substrate for serotonin (Mao et al., 2014) synthesis. These substrates regulate neurologic function, gastrointestinal motility and secretion, appetite, hemodynamics and whole-body homeostasis (Wang et al., 2015).
Tryptophan affects the brain and nervous system through serotonergic neurotransmission and is the precursor for serotonin synthesis (Adeola and Ball, 1992b). The brain serotonergic system reacts to stressors (Ruis et al., 2000) by increasing serotonin turnover in the brain (Lepage et al., 2005) improving the organisms adaptability to stress (Deakin and Graeff, 1991) by reducing salivary and plasma cortisol concentrations (Y.B. Shen et al., 2012) and increasing stress pathway recovery time (Koopmans et al., 2006).
Increased concentrations of Trp have been reported to increase villus height (Koopmans et al., 2006), and tight junction protein abundance in the small intestine (Liang et al., 2018), promote protein synthesis in epithelial cells (Wang et al., 2015), and activate immunocytes in response to pathogen exposure (Gao et al., 2018).
Approximately 120 million pigs are transported to slaughter annually. Animal loss from down or dead pigs cost the U.S. swine industry ~$52 million annually. (Hao et al., 2021). What is less clear are the costs associated with reduced pig performance, feed efficiency and increased costs for therapeutic treatments following weaning and transportation.
Therefore, the objective of this study was to mitigate the adverse effects of early life transport stress on subsequent vaccine-induced immune challenges in pigs by providing supplemented L-Trp above NRC (2012) recommendations during a 35d nursery period.
MethodsAt weaning, 384 pigs underwent an eight-hour transport. Following transportation, pigs were randomly assigned treatment groups in a 2x2 factorial design of immune challenge (Vaccine challenged vs. Unvaccinated) and dietary treatment (Supplemented Trp vs. Non-supplemented Trp). Nursery diets were fed in four phases over the 35-day period.
Dietary Trp inclusion was either the NRC (2012) recommendation (1X) or twice the current recommendation (2X). Pigs and feeders were weighed weekly to determine body weight and feed intake.
On weeks 2-4 of the nursery phase, half of the pigs on each diet underwent a three-week vaccine induced immune challenge consisting of Mycoplasma (Respisure-One), Influenza (Flusure XP), and Ileitis (Porcilis). At the end of the nursery period, pigs were moved into a grow-finish facility and fed a common diet.
Prior to market, pigs were weighed and backfat and total loin depth were measured via ultrasound at the tenth rib. Carcass data was collected from Indiana Packers Corporation and analyzed using SAS 9.4 statistical software package.
Nursery growth performance Overall, pigs that were provided Trp at 2X the NRC (2012) recommendation were heavier than pigs fed diets with 1X Trp (P<0.005), averaging approximately 1 kg heavier at the culmination of a 35d nursery period (Figure 1).
The heavier body weight in 2X Trp supplemented pigs was the result of overall improvements in ADG (P=0.014) (Figure 2). There was also a tendency for an effect of vaccine challenge on ADG (P=0.057) where 1X Trp supplemented pigs had reduced ADG while 2X Trp supplemented pigs tended to maintain ADG following a vaccine-induced immune challenge (Figure 2).
Market weights and carcass qualitySupplementing Trp during the nursery phase increased carcass weight approximately 4 kg in unvaccinated pigs (P=0.046). There was a two-way interaction of dietary treatment and vaccine challenge (P=0.025) where vaccinated pigs maintained a heavier carcass weight compared to the unvaccinated, non-supplemented pigs (Table 2).
Finally, there was a two-way interaction of dietary treatment and vaccine challenge (P=0.019) on fat deposition (in) where Trp supplemented, unvaccinated pigs had more fat at market compared to non-supplemented pigs (Table 2).
The results of this study indicate supplementing Tryptophan above current NRC (2012) recommendations may have added value in maintaining growth performance in immune challenged pigs.
Overall, increasing dietary Trp in nursery diets to 2X the NRC (2012) recommendation improves ADG in nursery pigs, maintains feed efficiency during a vaccine-induced immune challenge, and increases carcass weight at market.
References available upon request.
Brizgys is a Ph.D. candidate in swine nutrition and endocrinology and Radcliffe is an Extension specialist in nutrition and management, both in the Department of Animal Sciences at Purdue University.
