Effects Of Feeding Frequency On The Growth Performance,Nutrient Digestion And Absorption Of Growing Pigs

Feeding frequency is one of the key factors that affect the growth performance of pigs besides dietary nutrition level and environmental hygiene.There have been many studies on the effect of feeding frequency on the growth performance of pigs at home and abroad.Some studies have shown that the increase of feeding frequency can improve the growth performance of pigs,but some studies have found that the change of feeding frequency does not affect the growth performance of pigs,which may be related to the differences of feeding modes and experimental animals in different studies.As an important digestive organ,intestine is responsible for the digestion and absorption of nutrients,which is very important for the growth and development of animals.It is not clear whether feeding frequency can regulate the growth performance of the body by affecting the intestinal function.Therefore,this paper aims to study the effects of different feeding frequency on growth performance and intestinal nutrient digestion and absorption of growing pigs under the same feeding conditions,and further explore the effects of feeding frequency on intestinal function combined with intestinal transcriptome,so as to provide a theoretical reference for the feeding mode of efficient growth of pigs.The research of this paper mainly includes the following three parts:1.Effects of different feeding frequency on the growth performance and nutrient digestibility of growing pigsThis part aims to compare the effects of different feeding frequencies on the growth performance,organ weight and organ index and nutrient digestibility of growing pigs.Twenty-four 47-d Duroc×Landrance×Yorkshire growing pigs with a similar body weight of 15.64±0.69 kg were selected,and randomly divided them into 3 groups,each with 8replicates,and 1 pig in each replicate.The M1 group was fed once a day at 7:00;the M3group was fed three times a day at 7:00,12:00 and 17:00;the M5 group was fed at 7:00 and9:30,12:00,14:30 and 17:00 five times.The total daily feeding amount of each pig was the same.According to the nutritional needs of the National Scientific Research Council（NRC,2012）,the daily feeding amount was adjusted with the age of growing pigs.The experiment lasted for one month.On the 21st day of the experiment,0.3%chromium trioxide（Cr2O3）was added to the diet as an indicator.The transition period was four days.Then feed samples and fecal samples were collected for three consecutive days for the determination of digestibility.During the experiment,all growing pigs were allowed to drink freely,and the feed intake of growing pigs was recorded.At the end of the experiment,the final weight of growing pigs was weighed and recorded,and then slaughtered and sampled.The stomach,liver,pancreas,spleen,kidney,large intestine and small intestine were separated and collected for weighing and recording.The results showed that the average daily gain and final body weight of growing pigs which fed three times and five times a day,were significantly increased（P<0.05）,while the feed to gain ratio was significantly decreased（P<0.05）compared with those fed once a day.The weight and organ index of kidney,spleen,stomach,small intestine and large intestine were not affected by feeding frequency among the three groups（P>0.1）,but the weight of liver and pancreas and organ index of liver were increased in the three feeding groups compared with the one feeding group and five feeding groups（0.05<P<0.1）.The results of total intestinal apparent digestibility showed that the total intestinal apparent digestibility of crude protein in the three times a day group was significantly higher than that in the one time a day group（P<0.05）,but there was no significant difference between the three times a day group and the five times a day group（P>0.05）.The results showed that compared with once a day,three and five times a day significantly improved the growth performance of growing pigs.In addition,compared with feeding once a day,feeding three times a day significantly improved the digestibility of crude protein.2.Effects of different feeding frequency on the digestive enzymes and gastrointestinal hormones of growing pigsThis part aims to compare the effects of different feeding frequencies on the digestive enzyme activity and gastrointestinal hormone concentration of growing pigs.The design of the experiment was the same as the first experiment.Pancreatic tissue,gastrointestinal chyme and other tissues were collected.The activity of digestive enzyme and the concentration of gastrointestinal hormone were determined.The results showed that the activities of trypsin and chymotrypsin were significantly increased in the three and five times a day groups compared with the one time a day group（P<0.05）.In duodenum,compared with the group fed once a day,the sucrase activity of the groups fed three times a day and five times a day was significantly lower（P<0.05）,and the maltase activity of the group fed five times a day was significantly lower（P<0.05）.At the same time,compared with the groups fed once a day and three times a day,the lipase activity of the group fed five times a day also increased significantly（P<0.05）.In ileum,the amylase activity of three times a day group was significantly higher than that of five times a day group（P<0.05）,while the lipase activity of three times a day and five times a day were was significantly higher than that of the one time a day group（P<0.05）.Feeding frequency had no significant effect on the concentrations of cholecystokinin（CCK）,gastric inhibitory peptide（GIP）,peptide tyrosine（PYY）and glucagon like peptide-1（GLP-1）in duodenum and ileum.The results showed that feeding frequency affected the activities of enzymes related to carbohydrate,lipid and protein digestion,but had no significant effect on gastrointestinal hormones.3.Effects of feeding frequency on transcriptional expression profile of jejunum mucosa and the expression of genes related to intestinal digestion and absorption of growing pigsThis part aims to study the effects of different feeding frequencies on the transcriptional expression profile of the jejunal mucosa and the expression of genes related to intestinal digestion and absorption of growing pigs.The design of the experiment was the same as the first experiment.Intestinal tissues and mucosa were collected for transcriptome sequencing analysis and determination of gene expression related to intestinal digestion and absorption.The results showed that 191 differentially expressed genes（P<0.05;FC≥1.5 or≤0.67）,including 86 down regulated genes and 105 up-regulated genes,were screened in the three times a day group compared with the one time a day group.KEGG enrichment analysis showed that most of these genes were enriched in glucose and lipid metabolism and amino acid metabolism pathways,includingα-linolenic acid metabolism,citric acid cycle,primary bile acid biosynthesis,fructose and mannose metabolism,steroid biosynthesis,fatty acid metabolism,fatty acid prolongation,vitamin digestion and absorption,and arginine biosynthesis.Compared with the group fed once a day,78 differentially expressed genes were screened（P<0.05;FC≥1.5 or≤0.67）,including 45 down regulated genes and 33 up-regulated genes.KEGG enrichment analysis showed that most of these genes were enriched in bile secretion,fat digestion and absorption,and ATP transporter metabolism pathway;compared with three times a day group,234 differentially expressed genes（P<0.05;FC≥1.5 or≤0.67）were screened in the five times a day group,including 146 down regulated genes and 88 up-regulated genes.KEGG enrichment analysis showed that the pathways of KEGG enrichment were primary bile acid synthesis,galactose metabolism and ATP transporter metabolism.The results of gene expression related to intestinal digestion and absorption showed that the relative m RNA expression levels of EAAT3 and ATB^0,+in duodenum of rats fed five times a day were significantly higher than those of rats fed once a day（P<0.05）.Compared with the once-a-day group,the relative expression of Pep T1m RNA was significantly increased in the three and five times-a-day groups（P<0.05）,and the relative expression of GLUT2 gene was significantly increased in the three times-a-day group（P<0.05）.In the anterior segment of ileum,the relative m RNA expression levels of amino acid transporter B0AT1,y⁺LAT1 and b^0,+AT and fatty acid transporter FATP4 were significantly lower in the three and five times a day groups than those in the one time a day group（P<0.05）,and the relative m RNA expression levels of receptor T1R1 and T1R3 were also significantly lower in the three times a day group and five times a day group（P<0.05）.The results showed that the metabolic pathways of carbohydrate,amino acid and fatty acid were affected by different feeding frequency under the same daily feeding amount.In addition,feeding frequency changed the expression of some amino acids,small peptide transporters and fatty acid transporters.To sum up,this study shows that feeding frequency can affect the digestive enzyme activity of gastrointestinal tract and nutrient digestion and absorption of jejunum of growing pigs,and regulate the growth performance of growing pigs under the same daily feeding amount.