Simple SummaryCaecotrophy in small herbivores, including rabbits, is the instinctive behavior of eating soft feces. Little is known about the impact of caecotrophy on growth and metabolism. In the present study, we used an Elizabeth circle to prevent rabbits from eating soft feces and measured changes in feed intake, body weight, internal organ weight, serum biochemical indices and liver lipid droplet accumulation. Liver tissue was also used for transcriptome sequencing. Results indicated that fasting caecotrophy decreased rabbit growth and lipid synthesis in the liver.AbstractIn order to investigate the effects of fasting caecotrophy on hepatic lipid metabolism in rabbits, 12 weaned female New Zealand white rabbits were randomly divided into (n = 6/group) a control and fasting caecotrophy group. Rabbits in the experimental group were treated with an Elizabeth circle to prevent them from eating their own soft feces for a 60-day period. Growth and blood biochemical indices, transcriptome sequencing and histology analysis of the liver were performed. Compared with the control group, final weight, weight gain, liver weight, growth rate and feed conversion ratio, all decreased in the experimental group (p < 0.05). RNA sequencing (RNA-seq) analysis revealed a total of 301.2 million raw reads (approximately 45.06 Gb of high-quality clean data) that were mapped to the rabbit genome. After a five-step filtering process, 14,964 genes were identified, including 444 differentially expressed genes (p < 0.05, foldchange ≥ 1). A number of differently expressed genes linked to lipid metabolism were further analyzed including CYP7A1, SREBP, ABCA1, GPAM, CYP3A1, RBP4 and RDH5. The KEGG (Kyoto Encyclopedia of Genes and Genomes) annotation of the differentially expressed genes indicated that main pathways affected were pentose and glucuronide interactions, starch and sucrose metabolism, retinol metabolism and PPAR signaling. Overall, the present study revealed that preventing caecotrophy reduced growth and altered lipid metabolism, both of which will help guide the development of new approaches for rabbits’ feeding and production. These data also provide a reference for studying the effects of soft feces in other small herbivores.

Cecotrophy is a special behaviour of rabbits. Eating soft faeces can improve feed efficiency and maintain gut flora in rabbits. In our previous study, we found that fasting from soft faeces significantly reduced growth rate and total cholesterol (TC) in New Zealand white rabbits (NZW rabbits), thereby resulting in lower values for body weight and fat deposition in the soft faeces fasting group than in the control group. However, it has not been demonstrated whether cecotrophy by NZW rabbits can regulate lipid metabolism by changing the diversity of caecal microorganisms. In this study, thirty‐six 28‐day‐old weaned NZW female rabbits were randomly divided into two groups (the soft faeces fasting group and the control group) and fed to 90 days. Rabbits in the experimental group were treated with an Elizabeth circle to prevent them from eating their soft faeces. Then, the caecal contents of three rabbits from the soft faeces fasting group and three rabbits from the control group were collected for metagenomic sequencing. We found that the abundance of Bacteroides increased, while Ruminococcus decreased, compared with the control group after fasting from soft faeces. Relative abundance was depressed for genes related to metabolic pathways such as ascorbate and aldarate metabolism, riboflavin metabolism and bile secretion. Moreover, there was a general correlation between variation in microbial diversity and fat deposition. Bacteroides affects body weight and TC by participating in the riboflavin metabolism pathway. By investigating the effect of cecotrophy on caecal microorganisms of rabbits, we identified the key microorganisms that regulate the rapid growth performance of NZW rabbits, which may provide useful reference for the future research and development of microecological preparations for NZW rabbits.

Background: Rabbit produce two kinds of feces: hard and soft feces, and they have a preference for consuming the latter. Although this habit of rabbits has been reported for many years, little is known on whether this behavior will impact growth performance and metabolism. The RNA-Seq technology is an effective means of analyzing transcript groups to clarify molecular mechanisms. The aim of the present study was to investigate the effects of fasting caecotrophy on growth performance and lipid metabolism in rabbits. Results:Our results indicated that, compared with the control group, the final body weight, weight gain, liver weight, specific growth rate and feed conversion ratio were all decreased in the experimental group (P<0.05). Oil red staining of the liver tissue indicated that fasting caecotrophy resulted in decrease of lipid droplet accumulation. RNA sequencing (RNA-seq) analysis revealed a total of 301.2 million raw reads approximately 45.06 Gb of high-quality clean data. The data were mapped to the rabbit genome (http://www.ensembl.org/Oryctolagus_cuniculus). After a five step filtering process, 14964 genes were identified, including 444 differentially expressed genes (P<0.05, foldchange≥1). Especially for remarkable changes of genes related to lipid metabolism, RT-PCR further validated the remarkable decrease of these genes in fasting caecotrophy group, including CYP7A1, PPARG, ABCA1, ABCB1, ABCG1, GPAM, SREBP, etc. KEGG annotation of the differentially expressed genes indicated that the main pathways affected were retinol metabolism, pentose and glucuronide interactions, starch and sucrose metabolism, fatty acid degradation, steroid hormone biosynthesis. Conclusion:In conclusion, the present study revealed that banning caecotrophy reduced growth rate and altered lipid metabolism, our results laid instructive basis for rabbit feeding and production. These data also provides a reference for studying the effects of soft feces on other small herbivores. Introduction 2 Many small herbivores have a natural instinct of caecotrophy[1]. Because of the 3 small body shape and their digestive tract volume is limited, the average residence 4 time of food in the digestive tract is relatively short [2, 3]. In order to meet their 5 nutrition needs, small herbivores need to obtain adequate high-quality food[4]. Small 6 herbivores mainly rely on low-quality, high-fiber plant stems and leaves as food 7 sources, with cellulose from symbiotic microorganisms in the hind-gut aiding in 8 digestion[5, 6]. Because microbial fermentation takes longer time than the average 9 residence time of food in the digestive tract, increasing digestibility by ingesting 10 incompletely-digested nutrients is an important nutritional strategy for small 11 herbivores [7-9]. 12 There are two types of feces excreted by rabbits: hard feces (nutrient-poor) and 13 soft feces (consist of protein, vitamins, and inorganic salts) [10-12]. Soft feces also 14 contain a large number of microorganisms, which are important for microbial 15 fermentation in he...

Simple SummaryBy histological sectioning and staining of rumen tissues from calves fed with a high or low ratio of non-fibrous carbohydrate/neutral detergent fiber diet, we found that the length and width of papillae were significantly affected by the ratio. From microRNA expression analysis we found cell proliferation, differentiation, physical and nutrient stimuli processes participate in the development of the rumen. In addition, bta-miR-128 was found to affect rumen development by negatively regulating PPARG and SLC16A1. Our findings provided an important resource for the continuing study of rumen development and absorption.AbstractRumen development in calves is affected by many factors, including dietary composition. MicroRNAs (miRNAs) are known to function in the development of the rumen in cattle, what is not known is how these miRNAs function in rumen development of calves fed with high and low ratios of non-fibrous carbohydrate (NFC)/neutral detergent fiber (NDF). A total of six healthy Charolais hybrids bull calves of similar weight were divided into two groups; three calves were fed a mixed diet with NFC/NDF = 1.35 (H group), and three were fed a mixed diet with NFC/NDF = 0.80 (L group). After 105 days on the diet, calves were sacrificed and rumen tissues were collected. Tissues were subjected to histological observation and miRNA expression analysis. Functional enrichment analysis was conducted on the target genes of the miRNAs. Targeting and regulatory relationships were verified by luciferase reporter assay and quantitative PCR (qPCR). We found that the length of rumen papilla in the L group was significantly greater than that in the H group, while the width of rumen papilla in H group was significantly greater than that that in L group. We identified 896 miRNAs; 540 known miRNAs, and 356 novel predicted miRNAs. After statistical testing, we identified 24 differentially expressed miRNAs (DEmiRNAs). miRNA-mRNA-cluster network analysis and literature reviews revealed that cell proliferation, differentiation, physical and nutrient stimuli processes participate in rumen development under different NFC/NDF levels. The regulatory relationships between three DEmiRNAs and five target genes were verified by examining the levels of expression. The binding sites on bta-miR-128 for the peroxisome proliferator activated receptor gamma (PPARG) and solute carrier family 16 member 1 (SLC16A1) genes were investigated using a dual luciferase assay. The results of this study provide insight into the role of miRNAs in rumen development in calves under different NFC/NDF levels.

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