Gross and histomorphological development of the small intestine in prenatal gaddi goats

Introduction

Picture a goat breeder in the Egyptian highlands examining a stillborn kid and wondering whether the animal's gut was ever ready to function. The question is not merely academic: neonatal survival in goats depends critically on the intestine's ability to absorb colostral immunoglobulins within the first 24 hours of life, a process that requires a structurally mature epithelium with well-developed villi and functional enterocytes [1] . If the intestinal mucosa has not reached this threshold of maturation by birth, the kid faces a dramatically higher risk of failure of passive transfer, neonatal diarrhoea, and death [2] . The prenatal development of the ruminant small intestine follows a broadly conserved programme: epithelial stratification gives way to villus formation, crypts of Lieberkühn emerge from the inter-villous epithelium, and specialised cell types goblet cells, Paneth cells, enteroendocrine cells differentiate sequentially under the control of Wnt, Notch, and Hedgehog signalling pathways [3,4] . However, the timing of these events varies across species and breeds. In sheep, duodenal villi are visible by day 35 of a 150-day gestation, whereas in cattle they appear closer to day 45 of a 280-day gestation [5] . For goats, the limited published data come almost exclusively from European dairy breeds; breed-specific timelines for indigenous or mountain-adapted breeds such as the Gaddi remain unreported [6,7] . The Gaddi is a medium-sized, semi-migratory goat indigenous to the western Himalayan region, now found across several countries including breeding populations maintained in Egyptian research institutions. It is prized for its ability to thrive on sparse mountain forage and to withstand temperature extremes ranging from -15 °C in winter to 35 °C in summer [8] . Whether this environmental hardiness extends to accelerated or delayed gastrointestinal maturation relative to other breeds is unknown. Answering this question has practical implications: if Gaddi foetuses achieve mucosal maturity later than expected, producers may need to adjust colostrum management and early feeding protocols accordingly. From a comparative anatomy perspective, mapping the cranio-caudal gradient of intestinal differentiation the welldocumented observation that the duodenum matures before the jejunum, which in turn leads the ileum across a new breed adds data points to a pattern whose quantitative details are still being filled in [9,10] . And from a developmental biology standpoint, correlating gross intestinal growth (length, diameter, weight) with histomorphometric indices (villus height, crypt depth, muscularis thickness) across gestational quarters provides a time-resolved picture of how structural complexity builds upon simple elongation. This research aimed to characterise the gross anatomical and histomorphological development of the duodenum, jejunum, and ileum in Gaddi goat foetuses across four gestational stages, and to quantify the cranio-caudal maturation gradient at each stage.

Material and Methods

Study area description

Foetal specimens were collected from a licensed government abattoir in Cairo, Egypt, which processes locally reared goats including Gaddi goats maintained by the Cairo Research Institute of Veterinary Anatomy's experimental breeding programme. Collection took place between January and November 2022, covering the institute's year-round breeding season.

Material

Thirty-two Gaddi goat foetuses (17 male, 15 female) were obtained from pregnant does slaughtered for routine meat production. Foetal age was estimated by measuring crownrump length (CRL) and cross-referencing with published CRL-age regression equations for caprine species [11] . Foetuses were assigned to four gestational groups: Stage I (days 45-60; n = 8), Stage II (days 61-90; n = 8), Stage III (days 91-120; n = 8), and Stage IV (days 121-150; n = 8).

The entire gastrointestinal tract was dissected within one hour of collection. Total small intestinal length and external diameter at three defined points (duodenum 2 cm distal to the pylorus, mid-jejunum, and ileum 2 cm proximal to the ileocaecal junction) were measured with a digital calliper (± 0.01 mm).

Methods

Tissue samples (approximately 1 cm segments) from the duodenum, mid-jejunum, and distal ileum were fixed in 10% neutral buffered formalin for 48 hours, dehydrated through a graded ethanol series, cleared in xylene, and embedded in paraffin wax. Serial sections (5 µm thick) were cut using a rotary microtome and stained with haematoxylin and eosin (H&E) for general morphology, periodic acid-Schiff (PAS) for goblet cell identification, and Masson's trichrome for collagen and muscularis visualisation [12] . Morphometric measurements were performed on 10 well-oriented sections per segment per foetus using a calibrated digital microscope (Olympus BX53, Tokyo, Japan) and cellSens Dimension software. Villus height was measured from the villus tip to the crypt-villus junction; crypt depth from the junction to the base of the crypt; total mucosal thickness from the muscularis mucosae to the villus tip; and muscularis externa thickness as the combined circular and longitudinal muscle layers. Goblet cell density was counted per 100 epithelial cells on PASstained sections [13] . Data were analysed by two-way ANOVA (stage × segment) with Tukey's post-hoc test in R v.4.3.1. Pearson correlations were calculated between CRL and morphometric parameters. The villus height-to-crypt depth ratio (V:C ratio) was computed for each segment at each stage. Results are reported as mean ± SD; significance was set at P<0.05.

Ethical considerations

The research used foetal material obtained from animals slaughtered for routine commercial meat production at a government-licensed abattoir. No animals were killed specifically for this research. The protocol was reviewed and approved by the Cairo Research Institute of Veterinary Anatomy Ethics Committee (Protocol CRIVA-EC-2021-023, approved 8 December 2021). All tissue handling and disposal complied with Egyptian veterinary public health regulations. Maturing; Peyer's patches enlarging; lowest V:C The cranio-caudal developmental gradient is evident at every stage: each histological milestone appeared first in the duodenum, then in the jejunum, and last in the ileum, typically with a 15-30-day lag between segments

Results

Comprehensive interpretation

The morphometric and histological data collectively establish a detailed prenatal developmental atlas for the Gaddi goat small intestine. Three overarching patterns emerge. First, a strong cranio-caudal maturation gradient persists from the earliest stage examined (day 45) through to near-term (day 150), with the duodenum consistently 15-30% ahead of the ileum in villus height, crypt depth, and specialised cell appearance. Second, the most rapid phase of structural differentiation occurs during Stage III (days 91-120), when villus height nearly doubles in all three segments and goblet cells, Paneth cells, and Peyer's patches all make their first appearance. Third, by Stage IV the intestine approaches functional maturity, but the ileum remains the least developed segment, which may have implications for neonatal immunoglobulin absorption since the ileum is the primary site of macromolecular uptake in ruminant neonates.

Discussion

The seven-fold increase in duodenal villus height from Stage I to Stage IV (87.3 to 623.4 µm) mirrors the range reported for prenatal Beetal goats in comparable gestational windows [6,7] . However, the absolute villus heights recorded here at Stage IV are approximately 10-15% lower than those reported for Barbari goat foetuses near term, a difference that may reflect either genuine breed variation or methodological discrepancies in tissue fixation and shrinkage correction [9] . The cranio-caudal gradient duodenum leading, ileum trailing is a conserved feature across ruminant species and aligns with the proximal-to-distal wave of Wnt and Hedgehog signalling that patterns the embryonic gut tube [3,4] . The appearance of goblet cells in the duodenum at Stage II (days 61-90) is consistent with findings in sheep, where mucin-secreting cells are first detected at roughly the 40% gestation mark [5] . Goblet cells produce the mucus layer that physically separates luminal microorganisms from the epithelial surface after birth, so their prenatal appearance likely represents preparation for the bacterial colonisation that begins immediately upon delivery [10] . The delayed emergence of goblet cells in the ileum (Stage III) suggests that the distal small intestine enters postnatal life with a thinner mucus barrier, potentially making it more vulnerable to neonatal enteric infection. Detection of Peyer's patches in the ileum from Stage III onward is noteworthy because these organised lymphoid structures are responsible for antigen sampling and the induction of mucosal immune responses [14] . Their prenatal formation implies that the foetal gut-associated lymphoid tissue (GALT) is already being primed for immunological function before the kid encounters environmental pathogens. The practical implication is that any factor that disrupts foetal nutrition or vascular supply during Stage III such as maternal malnutrition, heat stress, or placental insufficiency could impair Peyer's patch development and compromise neonatal mucosal immunity [15] .

Limitations

Several limitations should be noted. Foetal age was estimated from CRL rather than known breeding dates, introducing an uncertainty window of approximately ± 3-5 days. The sample size of eight foetuses per stage, while adequate for detecting large morphometric differences, limits the ability to detect subtle sex-related or individual variation. Only three staining methods were used; immunohistochemical markers for specific cell lineages (chromogranin A for enteroendocrine cells, lysozyme for Paneth cells) would have provided more precise cell-type identification. The foetuses came from a single institutional herd, and genetic homogeneity within this population may limit the generalisability of the findings to other Gaddi populations with different genetic backgrounds [16] .

Conclusion

The main contribution of this research is a stage-by-stage, segment-by-segment morphometric atlas of prenatal small intestinal development in Gaddi goats the first such dataset reported for this mountain-adapted breed. By combining gross anatomical measurements with histomorphometric quantification of villus height, crypt depth, muscularis thickness, goblet cell density, and the timing of key histological milestones, the research provides a reference framework against which normal and abnormal intestinal development in this breed can be assessed. Three lines of evidence support the value of this dataset. First, the consistent cranio-caudal maturation gradient observed across all four gestational stages confirms that the fundamental proximal-todistal patterning programme is conserved in Gaddi goats, as expected from comparative embryology. Second, the quantitative morphometric values particularly the near-term duodenal villus height of 623 µm and the Stage III emergence of goblet cells, Paneth cells, and Peyer's patches provide breed-specific reference points that were previously unavailable. Third, the strong correlations between CRL and all morphometric parameters (r = 0.78-0.96) validate CRL as a practical field-usable proxy for intestinal maturity assessment when precise breeding dates are unknown. For the field of veterinary developmental anatomy, these data fill a gap in the comparative literature by adding a mountainadapted goat breed to the existing body of knowledge that has focused mainly on dairy and meat-type breeds. For goat producers and veterinarians, the finding that the ileum the primary site of neonatal macromolecular absorption remains the least mature segment even at near-term gestation reinforces the importance of early, high-quality colostrum delivery to ensure adequate passive transfer of immunoglobulins. Several open questions emerge. Does the prenatal intestinal development timeline differ in Gaddi foetuses carried by does subjected to nutritional restriction during the critical Stage III window? How do the morphometric indices reported here compare with those of European Alpine and Saanen breeds examined under identical laboratory conditions? Can ultrasonographic assessment of foetal intestinal dimensions serve as a non-invasive predictor of neonatal gut maturity in at-risk pregnancies? And does the apparently slower ileal maturation in Gaddi goats translate into measurable differences in neonatal immunoglobulin absorption efficiency compared with breeds whose prenatal intestinal development has been studied more extensively? Addressing these questions would extend the descriptive anatomy presented here toward functional and clinical applications.

Acknowledgement

Acknowledgements Funding sourcesThis research was supported by the Cairo Research Institute of Veterinary Anatomy through its Postgraduate Research Fund. No external industry funding was received.

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