Dose- and Time-Dependent Effects of Cobalt Chloride Supplementation on Growth Performance and Intestinal Development in Weaned Piglets

The aim of our study was to evaluate the effect of dietary cobalt chloride (CoCl2) supplementation on diarrhea, growth performance, and intestinal development in post-weaning piglets. Twenty-six piglets weaned at 21 days of age (d 21) with similar body weights were randomly assigned to three treatments: a control group (n = 10), a low-dose CoCl2 group (1 mg/kg of diet; n = 8) and a high dose CoCl2 group (2 mg/kg of diet, n = 8). Piglets were housed individually and fed the experimental diets for 28 days, with a dietary transition at day 15. During the early post-weaning period (d0 to d14), dietary CoCl2 supplementation was associated with favorable trends in growth performance parameters, including ADG (average daily gain: linear, 0.05 < p < 0.1) and gain to feed ratio (linear, p < 0.05), as well as reduced fecal scores (Linear, p < 0.05). However, during the later post-weaning period (d15 to d28), increasing dietary CoCl2 levels were unfavorable trends in feed intake (Linear, p < 0.05) and ADG (Linear, 0.05 < p < 0.1). At the intestinal level, CoCl2 supplementation was associated with dose-related changes in intestinal morphology, epithelial cell differentiation, and luminal pH. Alterations were observed in duodenal crypt depth (CD) and ileal villus height (VH), and duodenal VH/CD (Linear, p < 0.05), without significant effects on ileal epithelial proliferation and apoptosis (p > 0.1). Changes in the numbers of goblet cells in villi (Quadratic, p < 0.05) and crypt (Linear, p < 0.05), and enteroendocrine cells (Quadratic, p < 0.05) in crypt exhibited dose-dependent trends. In addition, with the increase in the CoCl2 concentration, the expressions of genes related to nutrient transporters (DMT1, GLUT2, and SGLT1) and metabolism (HIF-1α, FBP1, and FBP2), as well as those related to the NOTCH signaling pathway (LGR5, ATOH1, HES1, and NOTCH2), showed a linear decrease (Liner, p < 0.05). This was the case except for LDHA and DLL4 (Liner, p < 0.05). The expression of the former was the lowest in the high-dose group, while that of the latter was the lowest in the low-dose group. In vitro, CoCl2 exposure was associated with reduced organoid budding rates (Quadratic, p < 0.01), the budding numbers (Linear, p < 0.05) per organoid, and altered gene expression of SGLT1 and CHGA (Linear, p < 0.05). In summary, dietary supplementation with CoCl2 exhibited dose- and time-dependent trends in weaned piglets. CoCl2 supplementation during the early post-weaning period (two weeks after weaning) was associated with favorable trends in growth performance and diarrhea, whereas prolonged supplementation (4 weeks after weaning) or higher dietary level (2 mg/kg of diet) were associated with unfavorable trends in growth performance and intestinal development. These findings suggest that CoCl2 may have potential as a short-term (two weeks after weaning), low-level (below 2 mg/kg diet) nutritional supplement, while caution is warranted regarding long-term supplementation or higher dietary inclusion levels.