Effects Of Calcium Propionate Supplementation On Growth Performance And The Mechanism Of Rumen Development In Dairy Calves

The present study was conducted to investigate the effects of calcium propionate supplementation on growth performance and the mechanism of rumen development in dairy calves. Through different period feeding and slaughter trials, the effect of adding calcium propionate on growth performance, internal organs and the gastrointestinal development of dairy calves were investigated. By determinantion of rumen fermentation, blood parameters and mRNA gene expression of rumen epithelium, the mechanism for regulation of rumen epithlium by propionate was expounded through endocrine system and G protein coupled receptor pathways. Finally, differentially expressed genes of rumen epithelium were screened based on the transcriptome technology, providing comprehensive theoretical framework for regulating rumen development of dairy calves.Exp.1. The effects of dietary CaP supplementation on growth performance, the development of the internal organs, and the gastrointestinal tract development of calves in different feeding stages were investigated. Male Jersey dairy calves (n= 54, age= 7 ± Id, BW= 23.1 ± 1.2kg) were divided into 3 treatments:1) control without CaP supplementation (CON),2) 5%CaP supplementation (DM basis), and 3) 10%CaP supplementation (DM basis). The 160-d feeding experiment and was divided into 3 feeding stages:Stage 1 (0 d to 30 d), Stage 2 (30 d to 90 d), and Stage 3 (90 d to 160 d). At the end of each stage, six calves were randomly selected and slaughtered from each treatment. Adding CaP increased BW of calves after 90d compared to the CON group (P= 0.013,0.018, and 0.006). The ADG of 5%CaP was greater than the CON group at 120-160d (P= 0.046). The 10%CaP group improved ADG of calves at 30-60d,60-90d, and 120-160d compared with the CON (P= 0.013,0.080,0.044).10%CaP supplementation exhibited the greatest spleen weight among the treatments at the end of the experiment (P= 0.010). The liver weight of 5%CaP and 10% CaP group were greater than that of the CON group (P =0.003) at 90d. Liver weight of 10%CaP at 160d was greater than CON group (P= 0.037). Adding CaP increased the rumen weight after 90d of calves (P= 0.006,0.010). The morphological measurements of intestines showed that adding CaP improved the development of intestine. In summary, CaP supplementation increased growth performance, liver and spleen development of in internal organs and the gastrointestinal tract development in calves. The results of the present study indicated that it is better to add 10% CaP before feeding 90 d and 5% CaP supplementation during the period from feeding 90-160d.Exp.2. The effects of CaP supplementation on rumen fermentation and development of the rumen epithelium were investigated in the present study. The animals, treatments and feeding regimes are all the same as the Expt 1. Supplementation of calcium propionate increased TVFAs (P=0.0370) and had a tendency to. increase rumen fermentation parameters of acetic acid (P= 0.0632), isobutyric acid and propionic acid (P= 0.0903) (P= 0.0591) of dairy calves for 30-d feeding. Addition of 10% calcium propionate reduced the amount of ammonia nitrogen in the rumen of calves feeding 90d (P= 0.0013). Addition of 5% CaP had greater content of propionate (P= 0.0029) and valeric acid (P= 0.0133) of calves feeding 160d. Adding CaP increased the thickness of rumen walls at feeding 30d (P= 0.0085) and 90 d (P= 0.0126) in dairy calves. CaP supplementation improved rumen papillae length and had positive correlation with the level of CaP supplementations, but no significant effect on the papillae width (P= 0.2754) of calves feeding 30d. For calves feeding 90d, dietary addition of CaP improved rumen papillae length compared to the CON group (P= 0.0016) and adding 10% CaP increased the papillae width (P= 0.0293). Adding 5% CaP increased rumen papillae length, and adding 10% CaP increased the papillae width of calves feeding 160d. The results in the present study indicated that adding calcium propionate promoted the rumen fermentation, improved the rumen propionate content and the development of rumen epithelium. In terms of the level of CaP supplementation, adding 10% CaP had a good response for calves feeding less than 90d, whereas adding 5% CaP showed a great response in rumen fermentation and the development of rumen epithelium of calves for feeding 90d to 160d.Exp.3. This study aimed to elucidate the mechanism of rumen epithelial development by measurement of blood parameters of dairy calves in differ ent feeding stages and mRNA expression of rumen epithelia. The animals, treatments and feeding regimes are all the same as the Expt 1. Before one day of each stage, six calves were randomly selected to sample blood from jugular vein. In addition, the rumen epithelium were sampled from 3 calves which were randomly selected from the control group and 5%CaP group at feeding 160 d to determine the mRNA expression. The results showed that addition of calcium propionate raised blood glucose levels, which increased with the levels of calcium propionate supplementation and addition of 10% calcium propionate significantly increased blood glucose levels of calves feeding 30 days (P< 0.05). The effects of calcium propionate supplementation on insulin concentration were similar to glucose. Addition of calcium propionate increased IGF-1 concentration of calves and 5%CaP had the highest IGF-1 concentration of calves feeding 160 days. Addition of 5% calcium propionate increased CDK4, IGF-1R and INSR gene expression, and significant increased CCND1 and GPCR43 of rumen epithelia of calves feeding 160d. The results indicated that the mechanism of rumen epithelial development mediated by propionate could be explained into two pathways:on one hand, propionate increased blood glucose, insulin, and IGF-1, leading to the higher INSR and IGF-1 mRNA expression of rumen epithelium to improve the rumen epithelium development; on the other hand, propionate increases GPCR43 mRNA expression to improve the rumen epithelial development as a signal molecule.Exp.4. This study investigated the differences of calcium propionate supplementation on gene expressions of rumen epithelia of 160 calves through RNA sequence (RNA-Seq). The aim of the present study was to explore the mechanism of rumen epithelial development and to provide a basic foundation of nutritional regulation of rumen development. Three 160-d fed calves were selected from each of 5%CaP or CON group, and slaughtered. Rumen epithelia were sampled. After a series of procedures for total RNA extraction and transcriptome library establishment, the HiSeq 2500 platform was used to sequence. A total of 18084 genes were mapped in Bos taurus, in which the gene expressed only from 5%CaP group was 718, followed by 696 only from the CON group, and 16670 expressed from both of groups. There were 369 genes significantly different expressed between the two treatments, including 216 higher and 153 lower expression of 5%CaP compared to the CON group. GO enrichment analysis indicated that improved rumen epithelial growth due to adding calcium propionate was probably related to increased expressions of TGM3, TGM1, OVOL1, DSP, IVL, SPINK5, CLDN4, CNFN and KRT36 genes. Pathway analysis showed that genetic variations mainly presented on metabolism, signal transduction, and endocrine systems. A series of genes related to rumen epithelial development were successfully screened, providing a theoretical basis and more research targets about rumen epithelial development in dairy calves.