Longitudinal investigations of anatomical and morphological development of the gastrointestinal tract in goats from colostrum to postweaning

Recent nutritional strategies and feed additives to stimulate proper rumen development in young goats

Domestic goats (Capra aegagrus hircus) are important producers of milk, meat, and hair. The early weaned goats may face fundamental issues related to the incomplete rumen development to deal with the transition from liquid feeds into solid feeds. Therefore, the present review focuses on the nutritional strategies and feeding methods to enhance the proper rumen morphological development, fermentation efficiency and microbiota structure in young goats. The enhanced rumen development caused by these nutritional strategies can have lasting positive effects on their overall growth performance and health status, leading to decreasing mortality rates and susceptibility to disease after weaning. A wide range of areas was summarized including liquid feed management in preweaning goats (colostrum, milk, and milk replacer), solid feed management (concentrate and roughages), endogenous and exogenous volatile fatty acids and ketones, plant extracts, prebiotics and probiotics as well as rumen microbial contents that can be incorporated into the kids as an alternative to antibiotics to avoid pathogens and enhance the proper establishment of microbial community. Such nutritional strategies and current breeding recommendations can be used for the development of young goats' production systems to enhance the long-term digestive function efficiency in goats.

Early Weaning Impairs the Growth Performance of Hu Lambs Through Damaging Intestinal Morphology and Disrupting Serum Metabolite Homeostasis

This study aimed to evaluate the effect of early weaning (EW) on the growth performance, gastrointestinal development, serum parameters, and metabolomics of Hu sheep lambs. Twenty-four male Hu lambs were initially ewe-reared. A total of 12 lambs were weaned at 30 d of age (D30) as the EW group, and the remaining 12 lambs were weaned at 45 d of age (D45) as the control (CON) group. Serum samples were collected from six lambs per treatment on D30, D33, D36, and D45, and the lambs were slaughtered on D45 to collect the rumen and small intestine. The results showed that, compared with the CON group, the average daily gain (ADG), final body weight (p < 0.001), as well as average daily feed intake (ADFI) of lambs in the EW group significantly decreased in the first (p = 0.004) and second (p = 0.013) 5 days of treatment. Additionally, EW increased the ruminal weight and papillae length but reduced the duodenal villus height on D45 (p < 0.05). As for the serum parameters, the concentrations of glucose on D33, D36, and D45 (p < 0.001), and the IL-6 content on D45 (p = 0.018) were observed to be lower, while the levels of immunoglobulin A (IgA) (p = 0.027), IgG (p = 0.035), and IgM (p = 0.002) on the four ages were all higher in the EW group than those in CON group. Additionally, both treatment and age interactively affected the levels of GLU (p = 0.001), TP (p = 0.041), and IL-6 (p = 0.016). Additionally, the serum metabolomics analysis on D45 showed that the contents of 5-HT and arachidonic acid were increased, while L-phenylalanine, L-tyrosine, and L-glutamic acid were reduced in the EW group (p < 0.05). These differential metabolites were enriched in the Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways, including inflammatory mediator regulation, protein digestion and absorption, and phenylalanine and tyrosine biosynthesis. The current results identify that EW at D30 decreased the growth performance (ADG and ADFI) of Hu lambs within two weeks post-weaning, which might be associated with impaired duodenal morphology and glucose metabolism. The serum metabolomics analysis revealed that EW altered the concentrations of 5-HT, phenylalanine, tyrosine, and arachidonic acid, which could serve as potential regulatory targets for modulating the health of EW Hu lambs.

Butyrate metabolism in rumen epithelium affected by host and diet regime through regulating microbiota in a goat model

The rumen is an important organ that enables ruminants to digest nutrients. However, the biological mechanism by which the microbiota and its derived fatty acids regulate rumen development is still unclear. In this study, 18 female Haimen goats were selected and slaughtered at d 30, 60, and 90 of age. Multi-omics analyses (rumen microbial sequencing, host transcriptome sequencing, and rumen epithelial metabolomics) were performed to investigate host-microbe interactions from preweaning to postweaning in a goat model. With increasing age, and after the introduction of solid feed, the increased abundances of Prevotella and Roseburia showed positive correlations with volatile fatty acid (VFA) levels and morphological parameters (P < 0.05). Epithelial transcriptomic analysis showed that the expression levels of hub genes, including 3-hydroxy-3-methylglutaryl-CoA synthase isoform 2 (HMGCS2), enoyl-CoA hydratase, short chain 1 (ECHS1), and peroxisome proliferator activated receptor gamma (PPARG), were positively associated with animal phenotype (P < 0.05). These hub genes were mainly correlated to VFA metabolism, oxidative phosphorylation, and the mammalian target of rapamycin (mTOR) and peroxisome proliferator activated receptor (PPAR) signaling pathways (P < 0.05). Moreover, the primary metabolites in the epithelium changed from glucose preweaning to (R)-3-hydroxybutyric acid (BHBA) and acetoacetic acid (ACAC) postweaning (P < 0.05). Diet and butyrate were the major factors shaping epithelial metabolomics in young ruminants (P < 0.05). Multi-omics analysis showed that the rumen microbiota and VFA were mainly associated with the epithelial transcriptome, and that alterations in gene expression influenced host metabolism. The "butanoate metabolism" pathway, which transcriptomic and metabolomic analyses identified as being upregulated with age, produces ketones that regulate the "oxidative phosphorylation" pathway, which could provide energy for the development of rumen papillae. Our findings reveal the changes that occur in the rumen microbiota, host transcriptome, and metabolome with age, and validate the role of microbiota-derived VFA in manipulating host gene expression and subsequent metabolism. This study provides insight into the molecular mechanisms of host-microbe interactions in goats and supplies a theoretical basis and guidance for precise nutritional regulation during the critical time window for rumen development of young ruminants.

Physical, Metabolic, and Microbial Rumen Development in Goat Kids: A Review on the Challenges and Strategies of Early Weaning

The digestive system of newborn ruminant functions is similar to monogastric animals, and therefore milk flows into the abomasum instead of rumen for digestion. The rumen undergoes tremendous changes over time in terms of structure, function, and microbiome. These changes contribute to the smooth transition from the dependence on liquid diets to solid diets. Goat kids are usually separated at early ages from their dams in commercial intensive systems. The separation from dams minimizes the transfer of microbiota from dams to newborns. In this review, understanding how weaning times and methodologies could affect the normal development and growth of newborn goats may facilitate the development of new feeding strategies to control stress in further studies.

Early Solid Diet Supplementation Influences the Proteomics of Rumen Epithelium in Goat Kids

It is well known that solid diet supplementation in early life can significantly promote rumen development and metabolic function in young ruminants. However, the changes in the expressed proteome and related metabolism in rumen epithelium in response to a supplemented solid diet remain unclear. In this study, rumen epithelial tissue from goats in three diet regimes including milk replacer only (MRO), milk replacer supplemented concentrate (MRC), and milk replacer supplemented concentrate plus alfalfa pellets (MCA) were collected for measurement of the expression of epithelial proteins using proteomic technology (six per group). The results showed that solid diet significantly improved the growth performance of goats, enhanced the ability of rumen fermentation, and promoted the development of epithelial papilla (p < 0.05). Proteome analysis revealed the distinct difference in the expressed protein in the MRC and MCA group compared with the MRO group (42 upregulated proteins and 79 downregulated proteins in MRC; 38 upregulated proteins and 73 downregulated proteins in MCA). Functional analysis showed that solid diet supplementation activated a variety of molecular functions in the epithelium, including protein binding, ATP binding, structural constituent of muscle, etc., in the MRC and MCA groups. Meanwhile, the expression of proteins related to fatty acid metabolism, the PPAR signaling pathway, valine, leucine, and isoleucine degradation, and butanoate metabolism were upregulated, being stimulated by solid feed. In contrast, the proteins associated with carbohydrate digestion and absorption and glycosaminoglycan degradation were downregulated. In addition, the protein expression of enzymes involved in ketone body synthesis in the rumen was generally activated, which was caused by solid feed. In summary, solid feed promoted the development of rumen epithelium by changing the expression of proteins related to fatty acid metabolism, energy synthesis, and signal transduction. The ketone body synthesis pathway might be the most important activated pathway, and provides energy for rumen development.

Effect of Supplementing Different Levels of L-Glutamine on Holstein Calves during Weaning

Weaning stress affects the health and performance of calves. L-glutamine (L-Gln) is commonly used as a functional antioxidant and energy supplement in the body. However, dietary L-Gln supplementation improving weaning stress of calves is unclear. Thus, we aimed to explore the effects of L-Gln (provided by rumen-protected L-Gln) on calves during weaning. Seventy-five Holstein calves (54.0 ± 2.68 kg; 42 ± 2.1 d of age) were assigned to five groups: no supplementation and L-Gln with 1%, 2%, 3%, and 4% dry matter daily intake (DMI) supplementation groups, respectively. The experiment lasted for 28 days (42–70 d of age of calves), and the calves were weaned at 15 d of experiment. DMI and body weekly weight of all calves were recorded. Blood samples of nine healthy calves with similar body weight were collected from each group at 0, 7, 14, 16, 18, 21, and 28 d of experiment for detecting serum L-Gln, glucose, insulin, urea nitrogen, D-lactate, cortisol, haptoglobin, interleukin-8, immunoglobulin (Ig) G, IgA, IgM, total antioxidant capacity, superoxide dismutase, glutathione peroxidase, catalase, and malondialdehyde. At the end of the experiment, six healthy calves with similar body weight from each group were selected for slaughter and morphological analysis of small intestine tissue. The results showed that the L-Gln supplementation in the diets improved the negative effects of sudden weaning in calves. Furthermore, compared to the higher-level L-Gln supple-mentation (3 and 4% of DMI) groups, the dietary lower-level L-Gln supplementation (1 and 2% of DMI) had higher average daily gain, glutathione peroxidase and IgG concentration, and villus height/crypt depth of the duodenum and jejunum, as well as lower cortisol, haptoglobin, and interleukin-8 concentration of weaned calves. These results provided effective reference for relieving the negative effects of calves during weaning.