Introduction
Iron (Fe) is a vital micronutrient and associated with many metabolic processes in the body, such as binding oxygen, as a cofactor in many enzymes, energy metabolism, and gene synthesis (Frazer and Anderson, 2005; Youdim et al., 2009; Antonides et al., 2015). For the gestating mammal, Fe deficiency can cause some adverse impacts on their reproductive performance, such as reduced fertility, increased risk of premature birth and stillbirth (Buffler et al., 2017; Wan et al., 2018). Similarly, iron deficiency also affects young animals, leading to anemia, reduced activity of the iron enzyme, reduction in defense capabilities, and growth retardation (Haas and Brownlie, 2001; Tang et al., 2015). Moreover, several studies have identified the probability of early Fe deficiency in nursery piglets was higher than in other growth stages (Mateo et al., 2006; Chen et al., 2008a). Supplementation additives have been suggested for improving the health status of sows or nursery piglets (Val-Laillet et al., 2018; Palade et al., 2019).
The δ-aminolevulinic acid (ALA) is a non-protein amino acid, which plays a role in regulating heme biosynthesis and metabolism (Kang et al., 2012). The heme is the prosthetic group of hemoglobin (Hb), myoglobin, and other substances, and affects physiological functions in the animal body (Ogun and Valentine, 2019). ALA has been reported to improve animal health and production performance (Kommera et al., 2006; Sonhom et al., 2012; Phour et al., 2018). Min et al. (2004) reported that dietary supplementation of ALA improved the concentration of Fe, Hb, and the total Fe binding capacity in weaned pigs. Chen et al. (2008a) observed that Fe and Hb levels were increased with supplementation of ALA while that of plasma tumor necrosis factor-α was reduced under the inflammatory challenge. Similarly, Mateo et al. (2006) reported that sow diets containing 0.05% ALA increased the RBC counts in nursery pigs. Wang and Kim (2012) also indicated that first-party sows that fed ALA during the gestation and lactation period not only increased the concentration of Fe in the plasma and milk but also increased the birth weight and weaning weight of piglets. Moreover, ALA supplementation in the diet improved Fe concentration and immune function in broilers and egg quality in laying hens as reported by Wang et al. (2011) and Yan et al. (2010).
The findings from the above-mentioned studies indicated that dietary supplementation of ALA can affect the health condition and the production performance of swine and poultry. We hypothesized that the supplementation of ALA to sows might reduce the probability of Fe-deficiency anemia in piglets by improving Fe status in sows and promoting the reproductive performance and growth performance in sows and piglets, respectively. However, in previous studies, ALA was generally added to the diet in combination with other additives. Therefore, the objective of this study was to investigate the effect of dietary ALA on sows on the performance and Fe status in sows and suckling piglets.
Materials and Methods
The experiment was conducted at the swine experimental unit of Dankook University. The protocols used in the current experiment were approved by the Animal Care and Use Committee of Dankook University, South Korea.
Experimental design and diet
A total of 16 multiparous sows (average 2.6 parities; Yorkshire × Landrace) were allocated to two treatments based on parity, body weight (BW), and backfat thickness (BFT). The experimental treatments were the basal diet group (CON; piglets were injected with iron dextran (50 mg·pig-1) subcutaneously within 24 h postpartum) and the basal diet containing 0.1% ALA group (piglets were not injected with iron dextran). The ALA was supplemented in the diet from day 100 of gestation until day 28 of lactation and was produced by recombinant Escherichia coli which contains the Rhodobacter capsulatus hemA gene (Easy Bio System Inc., Seoul, Korea). The experimental diets were formulated to meet and exceed the nutritional requirement recommended by NRC (2012). Sows were fed a gestation diet and were restricted to feed (approximately 2.5 kg·day-1) during late gestation and then allowed ad libitum access to the lactation diet after 4 days of farrowing (Table 1). On day 107 of gestation, all sows were moved into farrowing crates (2.50 × 1.80 m2) with space on both sides of the crates (2.5 × 0.5 m2) for the neonatal pigs, also it can provide free access to drinking water for sows and piglets in the overall period. The temperature in the farrowing house was maintained at a minimum of 20℃ and supplemental heat was provided for nursing piglets using heat lamps.
Performance measurement
The BW and BFT of sows were measured on day 100 of gestation, farrowing (24 h postpartum), and on day 28 of lactation (weaning day). The BFT was measured at the P2 position (both sides of the last rib and 65 mm from the backbone) using Ultrasound (Piglog105, Frontmatec, Kolding, Demark) referring to the method of Hoque et al. (2021). According to dietary treatments, the piglets were cross-fostered to balance the number of suckling piglets within 3 days. However, we just collected the growth performance data of cross-fostered pigs and did not collect blood parameters. The individual weight of piglet was measured at birth (within 24 h postpartum) and on day 14 and day 28 of lactation. During the lactation period, the daily feed intake of sows was recorded.
Sample collection and chemical analyses
At farrowing and on day 14 and 28 of lactation, blood samples were collected from 8 sows in each treatment (5 mL) and 30 suckling piglets of each treatment (2 piglets each litter) via anterior vena cava (2 mL) into a 5 mL tube (with K3EDTA as an anticoagulant). Each anticoagulant blood sample was divided into 2 portions. The first portion was used to determine red blood cells (RBC) using an automatic blood analyzer (Nihon Kohden, Celltac Alpha, Tokyo, Japan). The second portion was centrifuged at 3,000 × g for 15 min at 4℃ (Eppendorf centrifuge 5810R, Hamburg, Germany) to obtain plasma. Fe concentration was determined using the colorimetric method with the commercial kit (Olympus Diagnostics, Hamburg, Germany).
Statistical analysis
All data were analyzed by t-test procedure of SAS (SAS Inst. Inc., Cary, NC, USA) with each sow being the experimental unit. Data variability was expressed as the standard error of means (SEM). The p-value of ≤ 0.05 was considered significant, and p ≤ 0.1 was considered a trend.
Results
Reproductive performance of sows
The effects of supplementation of ALA in the sow’s diet on the reproductive performance of sows are shown in Table 2. During the lactation period, supplementation of ALA significantly increased the average daily feed intake (ADFI) (p < 0.05) of sows during lactation, whereas there was no difference (p > 0.05) in BW, BFT gain and loss, or litter size of sows between the control and ALA groups.
Growth performance of piglets
The birth weight of piglets was increased (p < 0.05) by supplementation of ALA in the sows’ diet (Table 3). No differences were observed in BW, average daily gain (ADG), or survival of piglets during the lactation period (p > 0.05).
Blood profiles of sows and piglets
Before farrowing, RBC counts were increased (p < 0.05) in sows, when ALA was supplemented in the diet, however, the concentration of Fe was not affected during the experiment (p > 0.05) (Table 4). Additionally, the number of RBC on day 28 were observed in weaning piglets born to sows that received 0.1% ALA in the lactation diet (p < 0.05) (Table 5). Although Fe concentration in the piglets showed a trend in increment on day 28 (p = 0.09). However, from day 0 to day 14, differences were not observed in treatment groups.
Discussion
Growth performance of sows and piglets
Recently, ALA is widely used as a feed additive in animal feed, because of its beneficial effects on growth performance, nutrient digestibility, immunity, and blood Fe status (Sato et al., 2012; Pedrosa-Gerasmio et al., 2019; Chen et al., 2020). In the present study, dietary supplementation with ALA improved the ADFI of sows during lactation, the result was consistent with the previous study, which observed that the ADFI and BFT loss was improved by feeding ALA to lactation sows (Wang et al., 2009). Moreover, some previous studies also indicated that the ALA had positive effects on improving the growth performance of sows (Cho and Kim, 2011; Wang and Kim, 2012). Because ALA is closely associated with the synthesis of heme which is the main stable structure of the hemoglobin molecule, subsequently it plays the same role in oxygen and carbon dioxide transport. Supplementation of ALA was effective to enhance the blood oxygen contents, activate cell functions, and accelerate intracellular redox reactions (Fujii et al., 2017; Chernova and Smith, 2020). In the present study, supplementation of ALA to lactating sows was conducive to the recovery of self-metabolism of postpartum sows as it improved feed intake of sows. However, Wang and Kim (2012) demonstrated that the sows fed diets containing 90 mg·kg-1 ALA had no effect on feed intake during the lactation period of sows. Similarly, Yan and Kim (2011) and Chen et al. (2008a) reported that supplementation of ALA with different levels (3 mg·kg-1 and 0, 5, 10, and 15 mg·kg-1, respectively) in weaning pig diets had no effects on feed intake. The discrepancies in results might be due to different growth phases, additive doses, and environmental conditions during the experiment.
Blood profiles of sows and suckling piglets
Additionally, the birth weight of suckling piglets was higher when sows fed with ALA, which indicated dietary supplementation with ALA had a positive effect on the growth performance of their offspring. Similarly, Lee et al. (2016) reported that supplementation with different levels of ALA in lactation sows’ diets significantly improved BW and ADG of suckling pigs. In line with our findings, Wang and Kim (2012) also reported that supplementation of 90 mg·kg-1 ALA to sows’ diet increased the BW of suckling piglets on day 7 and 21 of postpartum and enhanced the ADG of suckling piglets during 0 to 7 days. Hossain et al. (2016) demonstrated that when post-weaning piglets fed with 0.5 or 1 g·kg-1 ALA increased their growth performance (BW, ADG, and body weight gain/feed intake) as compared to the piglets fed on the control diet. In addition, Chen et al. (2008a) reported that diet supplemented with ALA (15 mg·kg-1) improved the ADG of weaned piglets challenged by Escherichia coli lipopolysaccharide. On the contrary, no significant differences were observed in response to the supplementation of ALA in weaning pigs (Mateo et al., 2006) and broilers (Chen et al., 2008b). The inconsistent results of the above studies might be due to the different ages of animals, the feeding form of additive, and different species.
Some studies indicated that ALA as a vital precursor for biosynthesis tetrapyrrole played an important role in controlling heme synthesis (Xiong et al., 2018). Also, heme has a unique property, namely a Fe molecule can be combined within a tetrapyrrole (Battersby, 2000; Terry and Smith, 2013), which allows heme to exert activity both as an electron carrier and a catalyst for redox reactions (Ajioka et al., 2006). Hence, heme was the major functional form of Fe (iron-heme) (Smith and Wilks, 2012). Adding ALA to the diet may increase the concentrations of heme and iron-heme, thereby improving the utilization of Fe (Anderson, 2001). In the current study, the addition of ALA in sows' diet increased the RBC counts in sows before farrowing and maintained the counts of RBC in sows’ blood closer to initial values. This was similar to the findings of Wang et al. (2009) and Mateo et al. (2006). Moreover, the RBC concentration of piglets also increased in response to the treatment effect of ALA on day 28, which agreed with Hossain et al. (2016) who reported that supplementation of ALA in weaning piglets’ diet improved plasma RBC concentration of weaning pigs. Similarly, Yan and Kim (2011) demonstrated that dietary ALA supplementation increased RBC counts in weaning pigs. It has been revealed that feeding ALA to animals had positive effects on the synthesis of blood cells and RBC (Chen et al., 2008a; Hossain et al., 2016).
Besides, the RBC count is an important indicator for assessing Fe concentration in the blood (Tang et al., 2015). With regards to serum concentrations of Fe, no significant effect was observed in this study. Nevertheless, the concentration of Fe in suckling piglets showed trends in increment until weaning, which is in line with the previous report from Lee et al. (2016), who reported that dietary supplementation with ALA to lactation sows increased Fe concentration in the blood of suckling pigs. The finding of the present study corroborated with previous studies which demonstrated that the Fe concentration was increased when weaning pigs were fed diet containing ALA (Chen et al., 2008a; Wang et al., 2009). Wang and Kim (2012) reported similar results that dietary treatments with ALA enhanced the plasma Fe concentrations of piglets. Although in the present study, the Fe concentration was not improved significantly between the two treatment groups, however, the increasing trend of Fe status may reduce the incidence rate of Fe-deficiency anemia and improve the growth performance of piglets.
Conclusion
The results of this study revealed that the supplementation of ALA in sows' diet from day 100 of gestation to lactation improved the ADFI during the lactation and improved the RBC counts of sows. Meanwhile, the supplementation of ALA to the sows' diet had positive effects on suckling piglets on birth weight and blood RBC levels. However, the iron status of piglets in the two treatment groups was similar.
