**Background:** The reproductive performance of sows is a key economic factor in swine production. Primiparous sows often have lighter progeny and reduced passive immunity. Colostrum provides essential immunoglobulins (mainly IgG) to piglets, who are born immunologically naïve. Oxidized beta-carotene (OxC-Beta) has been proposed to modulate immune function and improve health. This study aimed to evaluate whether supplementing OxC-Beta to gestating and lactating sows could improve piglet birth weight, immune status, and reduce preweaning mortality.
**Methods:** A total of 194 sows (Topigs Norsvin TN20, TN70, Z-line) in two groups were assigned to a control diet (CON; N=99) or a test diet (OxBC; N=95) supplemented with 80 ppm oxidized beta-carotene (Avivagen, Ottawa, ON, Canada). Sows were blocked by parity: gilts (P0, N=47), first parity (P1, N=38), and second parity and older (P2+, N=109). Diets were corn-soybean meal based, formulated to meet or exceed NRC (2012) requirements. Treatments began at approximately day 60 of gestation and continued through lactation. A subset of 112 sows was randomly selected for intensive sampling. Sow weight was estimated via heart girth tape at start, farrowing, and weaning. Litter weights were recorded within 24 h of farrowing. Cross-fostering within treatment occurred within 24 h. Twelve presuckle piglets per diet were euthanized at birth and at weaning for tissue collection. Blood was collected from the hepatic vein, and liver samples were taken for flow cytometry (phagocytic activity of Kupffer cells, CD4, CD8 alpha, CD335 cell populations) and vitamin A analysis. Sow plasma immunoglobulins (IgG, IgM) were measured via ELISA at gestation, farrowing, and weaning. Colostrum and milk samples were analyzed for IgG, IgA, and composition (fat, lactose, total solids, true protein, urea). Sow reproductive performance (litter size, piglet weights, stillbirths, mummies, wean-to-estrus interval) and subsequent litter data were recorded. Piglets from the second group were followed into the nursery (common diet) for growth. Statistical analysis used the MIXED procedure in SAS 9.4 with fixed effects of treatment, parity, farrowing room, and random effect of sow. P ≤ 0.05 was significant; 0.05 < P ≤ 0.10 was a tendency.
**Key Results:** No significant differences were observed between dietary treatments for piglet immune parameters: phagocytic activity in Kupffer cells (P=0.84), CD4 (P=0.68), CD8 alpha (P=0.79), or CD335 (P=0.54). However, time effects were significant: phagocytic activity tended to be higher at birth (2.85% of cells) than weaning (0.33%, P=0.05); CD4 was higher at birth (14.25%) than weaning (8.62%, P<0.01); CD8 alpha was higher at weaning (44.38%) than birth (5.83%, P<0.0001); CD335 was higher at weaning (10.02%) than birth (3.92%, P<0.0001). Sow plasma IgG tended to be lower in OxBC sows (89.74 vs. 125.52 ng/mL, P<0.10), and IgM was significantly lower (20.27 vs. 29.58 ng/mL, P<0.01). Colostrum and milk antibodies (IgG, IgA) did not differ between treatments (P≥0.18), but significant treatment-by-parity interactions were noted (P≤0.04). Colostrum and milk composition (fat, lactose, total solids, true protein, urea) did not differ by treatment (P≥0.22). Sow reproductive performance (litter size, piglet birth weight, weaning weight, stillbirths, mummies, wean-to-estrus interval) showed no significant treatment effects (P>0.15). Subsequent litter performance also did not differ (P>0.36). Plasma vitamin A in sows and piglets did not differ by treatment (P>0.05), but time and parity effects were significant. Piglet liver vitamin A was not different between treatments (P=0.56), but increased from birth (5.5 ppm) to weaning (23.9 ppm, P<0.0001). Nursery data were not statistically analyzed due to limited replication (N=1 per treatment).
**Clinical Implications:** This study found that supplementing oxidized beta-carotene at 80 ppm from day 60 of gestation through lactation did not improve sow reproductive performance, piglet growth, or piglet immune status under the conditions tested. The observed decrease in sow plasma IgM and tendency for decreased IgG suggest a potential immunomodulatory effect, but this did not translate into measurable benefits for piglet health or performance. The lack of effect on vitamin A status confirms that OxC-Beta does not act as a vitamin A precursor. These results contrast with some previous studies that reported immunological benefits, possibly due to differences in sample size, herd genetics, management, or the specific immune parameters measured. The study highlights the need for further research with larger sample sizes and assessment of additional innate immune components (e.g., neutrophils, lymphocytes) to clarify the role of oxidized beta-carotene in swine nutrition. For practitioners, these findings suggest that under commercial conditions similar to this study, OxC-Beta supplementation may not reliably enhance sow or piglet outcomes.