A total of 69 sows (DNA Line 200 × 400) and their progeny were used to determine if feeding a combination of vitamin D₃ and 25(OH)D₃ influences neonatal and sow vitamin D status, muscle fiber morphometrics at birth and weaning, and subsequent growth performance. Within 3 d of breeding, sows were allotted to one of three dietary treatments fortified with 1,500 IU/kg vitamin D₃ (CON), 500 IU/kg vitamin D₃ + 25 μg/kg 25(OH)D₃ (DL), or 1,500 IU/kg vitamin D₃ + 50 μg/kg 25(OH)D₃ (DH). When pigs were sacrificed at birth, there were no treatment effects for all fiber morphometric measures (P > 0.170), except primary fiber number and the ratio of secondary to primary muscle fibers (P < 0.016). Pigs from CON fed sows had fewer primary fibers than pigs from sows fed the DH treatment (P = 0.014), with pigs from sows fed DL treatment not differing from either (P > 0.104). Pigs from CON and DL fed sows had a greater secondary to primary muscle fiber ratio compared to pigs from DH sows (P < 0.022) but did not differ from each other (P = 0.994). There were treatment × time interactions for all sow and pig serum metabolites (P < 0.001). Therefore, treatment means were compared within the time period. At all time periods, sow serum 25(OH)D₃ concentrations differed for all treatments with the magnitude of difference largest at weaning (P < 0.011), where serum 25(OH)D₃ concentration was always the greatest when sows were fed the DH diet. At birth, piglets from DH fed sows had greater serum 25(OH)D₃ concentrations than piglets from sows fed the DL treatment (P = 0.003), with piglets from sows fed CON treatment not differing from either (P > 0.061). At weaning, serum concentrations of 25(OH)D₃ in piglets from all sow treatments were different (P < 0.001), with the greatest concentration in piglets from DH sows, followed by CON, and followed by DL. There were no treatment × time interactions for any of the metabolites measured in milk and no treatment or time main effects for 24,25(OH)₂D₃ concentration (P > 0.068). Colostrum collected within 12 h of parturition contained less (P = 0.001) 25(OH)D₃ than milk collected on day 21 of lactation. Regardless of time, concentrations of 25(OH)D₃ in milk were different (P < 0.030), with the largest 25(OH)D₃ concentration from DH fed sows, followed by DL, and then CON. In conclusion, combining vitamin D₃ and 25(OH)D₃ in the maternal diet improves the vitamin D status of the dam and progeny and it increases primary muscle fiber number at birth.

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