Post-weaning diarrhea (PWD) is a major common disease in piglets. Some studies have shown that weaning will reduce the growth performance of piglets and impair their immune function (
Cao et al., 2022). The digestive system of weaned piglets is not yet fully developed and intestinal dysfunction often occurs at this time, which can affect the body’s nutrient absorption (
Pluske, 2013 and
Modina et al., 2019). In addition, weaned piglets face a substantial change in food and living environment, often appear stress reaction, resulting in reduced feed intake, which is very detrimental to the growth and development of weaned piglets (
Uddin et al., 2021). Feeding a low protein diet was effective in reducing the incidence of PWD (
Heo et al., 2009). Weaned piglets are susceptible to a variety of pathogens when exposed to different environments
(Pluske, 2013) and weaning may lead to reduced protein digestibility in piglets (
Hedemann et al., 2003), excessive undigested protein in the intestine will create opportunities for the colonization of pathogenic bacteria, which will increase the incidence of PWD. Thus increasing the protein metabolism of weaned piglets may be able to reduce the incidence of PWD and promote growth of weaned piglets.
Laminaria japonica polysaccharide (LJP) is a kind of natural biomolecule existing inside the kelp cells that reduces the levels of inflammatory factors and has anti-inflammatory effects (
Gao et al., 2022). LJP is also a natural antioxidant, capable of realizing antioxidant damage by scavenging free radicals and has some potential to slow down aging (
Li et al., 2022). In addition to anti-inflammatory and anti-injury effects, LJP also inhibits apoptosis and has strong antiviral activity (
Yue et al., 2017), it also inhibits macrophage foaming and stimulates macrophages to promote body immunity (
Li et al., 2020 and
Fang et al., 2015). LJP has been extensively studied as a feed additive.
Heim et al., (2015) showed that LAM supplementation to sows not only improved piglet growth performance, but also gut health as well as immune status of piglets.
Brugger et al., (2020) also showed that Laminaria japonica enhanced the performance of weaned piglets. It has been observed that the addition of LJP to the feed was effective in improving intestinal morphology, regulating intestinal flora, reducing intestinal dysfunction and may improve production performance in weaned piglets (
Rattigan et al., 2020). LJP also improved the growth performance of weaned piglets under high temperature conditions (
Wang et al., 2021). These studies have shown that LJP not ony promotes health but also improves growth performance of weaned piglets. Protein metabolism plays an important role in the growth of the organism. However, there is limited information concerning the effects of LJP on the protein metabolism of weaned piglets.
In the present study, we hypothesized that the addition of LJP to the diet would regulate protein metabolism and improve growth performance in weaned piglets. The serum physiological and biochemical index is an important indicator to visually evaluate the level of substance metabolism and changes in the internal environment in animals, the objective of present study was to evaluate the effects of LJP on normal physiological functions, protein metabolism and serum biochemical indices in weaned piglets.
This experiment was conducted at the Shanxia pig farm in Shicheng County, Ganzhou City, Jiangxi Province, China in 2023.
Animals and experimental design
A total of 120 healthy crossbred piglets (Berkshire × Licha Black) of similar weight (6.13±0.21 kg) and age (21±1 day) were randomized into four treatment groups with five replicates and each replicate had six piglets that were housed in pens. All piglets were kept in the same feeding conditions for 21 days and each group was offered a basic ration with different levels of LJP (0, 100, 200 and 400 mg/kg) added to the basic ration. The basic diets for piglets were formulated based on the National Research Council (2012) and detailed in Table 1.
Sample collection
At the end of the experiment, one piglet was randomly selected from each pen (24 piglets in total). Blood was taken from the jugular vein of each piglet and centrifuged for 10 min (3000r/min) after standing and the upper layer after centrifugation was the serum. Finally, the serum obtained was stored at -20°C.
Determination of serum biochemical indicators
The commercial test kits for the determination of serum total protein (TP), albumin (ALB), globulin (GLB), albumin-globulin ratio (A/G), uric acid (UA), creatinine (CREA), alanine aminotransferase (ALT) and aspartate aminotran sferase (AST) levels were purchased from the Nanjing jiancheng Bioengineering Institute. The level of TP was determined using the BCA method and optical density (OD) value was recorded at 562 nm. The content of GLB was determined using bromphenol green method and the OD value at 630 nm was recorded. The content of UA was measured using enzyme colorimetric method and the OD value was recorded at 510 nm. CREA concentration was determined by the sarcosine oxidase method recording OD value at 546 nm. The level of ALT was measured by Lai shi method recording OD value at 510 nm. The level of AST was measured by micro plate method reading OD value at 510 nm.
Statistical analysis
SPSS27 software was used to analyze the data. Using each piglets as an experimental unit and multiple tests were performed using the Tukey’s honest significant difference test and differences were considered statistically significant at p<0.05.
The effect of dietary LJP on serum biochemical parameters of weaned piglets is shown in Table 2. Protein is the material basis of all life, which constitutes a variety of physiologically active substances in the body, such as a variety of digestive juices, enzymes, hormones and so on. Low protein metabolism will lead to growth restriction of pigs. The results of this experiment showed that the addition of 200 and 400 mg/kg LJP significantly increased TP activity (p
<0.05) in piglets compared to the control group and the addition of 400 mg/kg LJP significantly increased ALB activity in piglets compared to the control group (p<0.05). Both TP and ALB play important roles in protein metabolism
in vivo and can reflect the nutritional metabolic status of protein in the body (
Zhou et al., 2015 and
Liu et al., 2015). An increase in the content of both can indicate that protein metabolism is vigorous, protein absorption and utilization enhances and growth performance of the animal improves (
Zou et al., 2019).
Li et al., (2022) reported that LJP can promote alanine, aspartate and glutamate metabolism, which is similar to the results of the present experiment. Protein metabolism is actually the metabolism of amino acids. Protein synthesis and catabolism require the action of a variety of transaminases. ALT and AST are two intracellular enzymes that catalyze the conversion of amino acids to ketoacids and their activities reflect the strength of amino acid metabolism (
Vijayavel et al., 2006). However, in this experiment, ALT and AST levels were not significantly different from the control group, which might be due to the fact that the enzyme secretion function of weaned piglets is not still fully developed and the metabolism of amino acids is subject to change, there is a certain effect on protein synthesis and tissue deposition (Montagne
et al., 2007). Weaned piglets have a fragile intestinal tract, kelp extract has the potential to modulate intestinal health (
Yang et al., 2019) and
Rattigan et al., (2020) showed that the addition of LJP to diets modulates the intestinal flora of weaned piglets (
Rattigan et al., 2020) and that normal intestinal flora stimulates material metabolism and immune responses in the body. Consequently, the improved effect of LJP on protein metabolic function in weaned piglets might be related to the modulation of intestinal flora and the improvement of intestinal function. In addition, there were no significant differences in other indicators of liver and kidney functions compared with the control group, which indicated that LJP had no effect on the liver and kidney function of weaned piglets.
