Abstract
Simple SummaryPre-weaning mortality is a significant economic and welfare issue for the Australian pig industry. Tryptophan can increase serotonin and melatonin production. Serotonin can decrease stress and indirectly increase calcium, which may improve sow health. Meanwhile, melatonin may decrease stillbirths and improve piglet viability at birth and, in turn, increase survival to weaning. This study determined whether feeding 0.16%, 0.42% or 0.56% tryptophan (per kg of feed) to sows during late pregnancy until seven days of lactation could improve piglet survival and viability to weaning and increase the levels of calcium and melatonin in sows. Supplementing tryptophan at levels of 0.42 and 0.56% increased piglet survival compared to no supplementation but did not have an effect on piglet viability. Furthermore, tryptophan supplementation did not increase sow melatonin and calcium levels compared to 0.16%. Further research is required to understand how tryptophan may improve piglet survival, particularly through sow maternal behaviour, and if 5-hydroxytryptophan (the form of tryptophan that directly converts to serotonin and melatonin) would further improve piglet survival. Tryptophan indirectly increases plasma calcium levels, which may improve sow health, and melatonin production, which may improve piglet survival when supplemented during late gestation and lactation. It was hypothesised that tryptophan would increase piglet survival and increase sow circulating melatonin and calcium. Seventy-two multiparous (Landrace x Large White) sows were allocated to either control (0.16% tryptophan; n = 24), low tryptophan (0.42%; n = 24) or high tryptophan (0.56%; n = 24). Piglet viability measures consisted of weights, behaviour, meconium staining, rectal temperature, blood glucose and serum immunoglobulin G concentration. Blood samples collected from sows were analysed for melatonin (two daytime and three night-time samples; n = 17) and calcium (two samples pre- and post-farrowing; n = 14). Both tryptophan treatments increased piglet survival compared to the control group (p < 0.001). Tryptophan had no effect on piglet viability (p > 0.05) and no effect on sow plasma melatonin and calcium concentrations compared with the control group (p > 0.05) except at 21:00 when low tryptophan sows had higher melatonin concentration compared with high tryptophan (p = 0.011). Further research to understand the mediating effects of tryptophan (particularly 5-hydroxytryptophan) on piglet survival, including sow behaviour, is warranted.
Highlights
In Australia, approximately 18% of piglets die between the start of parturition and weaning [1], resulting in an annual loss and industry cost of 1.2 million piglets and AUD 60 million, respectively [2,3]
Pre-weaning mortality is a significant economic and welfare issue affecting the pig industry [29]. Both Low and High tryptophan supplementation increased the probability of piglet survival compared with the control group
Two common indicators of colostrum intake, blood glucose and serum immunoglobulin G (IgG) levels [33], were similar in piglets born to control and tryptophan supplemented sows, and piglet rectal temperature was similar for all treatments. These findings indicate that tryptophan supplementation had no effect on piglet viability; it is worth noting that the degree of meconium scoring was low in all piglets, which is indicative of a low level of parturition-induced hypoxia
Summary
In Australia, approximately 18% of piglets die between the start of parturition and weaning [1], resulting in an annual loss and industry cost of 1.2 million piglets and AUD 60 million, respectively [2,3]. Energy reserves and viability are reduced in hypoxic piglets which survive parturition, as well as those with low birth weight. These piglets are more vulnerable to other leading causes of mortality, such as crushing by the sow and starvation within the first three days of life [6]. To improve survival at birth and weaning, a possible solution is to increase oxygen availability and nutrient supply to the fetuses prior to parturition through sow nutrition [7,8]
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