Recommendations from nutritionists, genetic suppliers, and academia offer a range of vitamin inclusion levels for each production phase. The most recently published vitamin requirement estimates from the National Research Council (NRC)¹ are below the current recommendations of genetic companies and standard inclusion levels observed in commercial industry diets.^1-4 Vitamins are included above requirement levels to provide a margin of error against losses in vitamin efficacy during storage and feed manufacturing and provide an insurance factor for ingredient variability and diet mixing imprecision. However, even after accounting for a liberal 15% safety margin,⁵ current industry supplementation recommendations for fat-soluble vitamins (A, D, E, and K) are commonly 1.3 to 7.6 times greater than the current sow NRC requirements. The historical approach to vitamin research was to establish requirements based on levels required to alleviate or prevent symptoms of deficiency rather than establish requirements for optimal performance.⁶ Therefore, the objective of this research is to evaluate the bodily vitamin concentrations and performance of sow and progeny fed current industry standard vitamin inclusion levels in sow and nursery diets. The hypothesis is commercial industry levels improve sow and progeny performance and vitamin status compared to reduced vitamin supplementation with added fat-soluble vitamins at NRC requirements.

Animal care and use

All experimental procedures were reviewed and approved by the Animal Care and Use Committee of United Animal Health, Inc.

Materials and methods

Animals, housing, and management

A total of 244 sows (PIC 1050, Pig Improvement Company) with mean body weight (BW) of 250.9 kg (range, 166.9-317.1 kg) and mean parity of 2.5 (range, 0-7) were used. The trial was set up as a randomized complete block design (RCBD) with two treatments (industry vs reduced vitamin supplementation level). The industry vitamin supplementation treatment levels were within ranges reported in commercial production surveys.^2,7 The reduced vitamin supplementation treatment contained vitamins A, D, E, and K added at NRC requirements¹ for gestation and water-soluble vitamins supplemented at approximately half the inclusion rate of the industry treatment. Gestating sows from three breeding groups within a batch farrow system were individually housed and received a common diet with industry standard vitamin levels prior to study enrolment. Due to the arrangement of the facility feeding system and pig flow, the two vitamin supplementation levels were fed for the entire lactation period as well as a portion of gestation immediately preceding lactation: group one was fed for 39 days of gestation, group two for 70 days, and group three for 81 days. Sows were sorted by vitamin supplementation level into separate gestation feed rows with equal representation of parity groupings per row to facilitate feeding of the two diets. Upon entry into farrowing, sows (n = 122/treatment) were randomly allotted to trial in replicate blocks based on parity and BW; blocks were contained within farrowing rooms. Each lactation stall was equipped with a box feeder and individual hopper. When necessary, suckling litter sizes were standardized within 24 hours of birth according to farm standard procedure by transferring piglets among sows on the same treatment; sows that received piglets from a different treatment were removed from the trial. Piglets that were cross fostered were ineligible for serum vitamin analysis.

At weaning, a subsample (765 piglets; PIC 337 × PIC 1050, mean [SD] initial BW: 6.38 [1.09] kg) representative of all 96 litters of group three were allotted to pens (mean [SD]: 12.75 [0.44] pigs/pen) with .26 m²/pig, round bar flooring, stainless-steel 2-hole feeders, and stainless-steel cup waterers. The trial was set up as a RCBD with blocking factors of sow parity and weaned piglet BW; litters were balanced across pens. There were 15 replicate pens for each of 4 treatments arranged in a 2 × 2 factorial design with two sow vitamin inclusion levels (industry vs reduced) and two nursery vitamin inclusion levels (industry vs reduced supplementation level for all vitamins and vitamins A, D, E, and K added at NRC requirement). The supplemented water-soluble vitamin levels of the reduced treatment were decreased proportionately to the reduction of the vitamin D level in the reduced treatment compared to the industry treatment. Porcine reproductive and respiratory syndrome and Mycoplasma hyopneumoniae were endemic in the herd but no clinical symptoms were present during the trial.

Experimental diets and feeding

All experimental diets were formulated to be adequate in all macronutrients according to NRC¹ and utilized up-to-date loading values for commodity grain ingredients. Sows were offered separate gestation and lactation diets (Table 1). In gestation, sows were fed once daily using a drop box set to deliver 1.8 to 2.7 kg feed in meal-form fed to maintain a target body condition score of 3 across all groups and treatments. Sows received experimental gestation diets for at least 6 weeks prior to being transferred to lactation. During lactation, sows were fed experimental lactation diets ad libitum and litters were not provided creep feed. At weaning, nursery diets were budgeted by weight until 6 weeks post weaning (Table 2). Within each production phase, diets were formulated to provide the same macronutrient and trace mineral nutrition with only the level of vitamin supplementation differing between treatments. Diets that were formulated to contain reduced levels of vitamins were manufactured and delivered to feeders before diets with industry levels of vitamins.

Performance measurements, sample collection, and analysis

Individual sow weights were recorded as sows were moved to farrowing (entry weight) 5 to 7 days prior to expected farrowing date, and at weaning. Sow weight post farrowing was calculated via a linear regression model (adjusted r² = 0.93):

Post-farrow sow weight = 29.31485 + (entry weight × 0.89191) + (parity × 1.30677) – (total born × 0.28966) – (native litter weight × 0.79842)  

where entry weight is used to represent gravid sow weight at the conclusion of pregnancy and native litter weight indicates combined total weight of piglets born alive, stillborns, and mummified fetuses. Lactation feed intake was recorded. Litter performance was measured by recording native litter weight, standardized litter weight (standardization of litter size completed within first 24 hours post farrowing), number of pigs in standardized litters, piglet count at processing, litter wean weight, number of pigs weaned, and mortality. Litter average daily gain (ADG) was calculated as:

Litter ADG = (litter wean weight + mortality post-standardization weight – standardized litter weight) ÷ (piglet days of live pigs at weaning + piglet days of post-standardization mortality)

Piglet days represents the product of the number of piglets and their days of living for respective subsets ie, pigs alive at weaning, pigs that died post standardization, etc. Litter gain to feed ratio (G:F) was calculated as:

Litter G:F = (litter wean weight + mortality post-standardization weight – standardized litter weight) ÷ sow    feed intake  

Analysis of fat-soluble vitamin A (ultra-high performance liquid chromatography [UHPLC]), vitamin D (25-hydroxyvitamin D₂ and 25-hydroxyvitamin D₃; liquid chromatography with tandem mass spectrometry [LC/MS/MS]), and vitamin E (UHPLC) in blood serum and liver samples (wet-tissue basis) were performed through the Iowa State University Veterinary Diagnostic Laboratory. Sows from the third group (n = 96) were bled within 24 hours of farrowing (d 0) and 1 day prior to weaning. From the same group of sows, one average-sized pig per litter was tagged and bled on day 5 post farrowing. One day prior to weaning (d 19), pigs bled and tagged on day 5 post farrowing and two additional pigs per litter were bled (total n = 288). Simultaneously, pigs tagged on day 5 were euthanized and liver samples collected. At weaning, all sows from the third group were shipped to a packing plant and liver samples collected.

At 40 days post weaning, 2 pigs/sow of the third sow group from whom blood samples had been collected at weaning were reidentified (n = 192) and bled. One average-sized pig per pen, for a total of 15 pigs/treatment, was euthanized and liver sample collected.

Statistical analysis

Normality of distribution and identification of outliers were determined for all metrics using the UNIVARIATE procedure of SAS Enterprise Guide 7.1 (SAS Institute Inc). An observation more or less than 3 standard deviations from the mean for each metric was deemed an outlier and not included in the dataset. A linear mixed model (MIXED procedure of SAS) was used to analyse sow and litter performance data using sow as the experimental unit, dietary treatment as the fixed effect, and random effects of group and block nested within group. A linear mixed model was also used to analyse nursery performance metrics (experimental unit of pen) as a RCBD with fixed effects of sow diet, nursery diet, and the interaction, and random effect of nursery block. Physiological vitamin concentrations measured in sow progeny were averaged within litter at each timepoint (birth, weaning, nursery exit) and similarly analysed with block included as a random effect. Morbidity, mortality, and other health-related metrics were analysed using (negative) binomial distributions for count data with small means via proc GLIMMIX. The REG procedure of SAS was used to generate the prediction equation for post-farrowing weight. Sow entry weight was used as a covariate for post-farrowing and exit weights; sow entry weight was insignificant (P ≥ .28) as a covariate for lactation feed intake, number of pigs at weaning, weaning weight, litter ADG, and litter G:F and therefore not included in the model for those metrics. Standardized litter size, birthweight, and nursery start weight were used as covariates for the analyses of number of pigs at weaning, litter wean weight, and nursery growth performance metrics, respectively. Results were considered statistically significant at P ≤ .05; results with P values > .05 and ≤ .10 were considered a trend.

Results

Sow and litter performance

Sow weight at entry into lactation was significantly heavier (P = .05) for sows fed the reduced vitamin supplementation treatment than for sows fed the industry vitamin levels treatment. After accounting for entry weight, there was no evidence for difference in sow weights post farrowing (P = .43) or at the end of lactation (P = .26; Table 3). There was a 5% reduction (P = .02) in lactation average daily feed intake (ADFI) of sows fed reduced vitamin supplementation levels compared with sows fed industry vitamin levels. There was no evidence for differences in native litter or standardized litter performance with the exception that sows fed industry levels of vitamins tended to improve (P = .08; Table 4) litter G:F.

There was no evidence for differences in sow serum vitamin A concentrations on day 0 (P = .96; Figure 1) or day 19 (P = .98) of lactation regardless of vitamin supplementation level. However, vitamin A supplementation at NRC requirement for gestation reduced (P = .001) vitamin A concentrations in the liver by 15.67% compared with sows fed industry vitamin level. Serum vitamin A in piglets did not differ (P = .15) between sow vitamin supplementation levels at day 5, but on day 19 serum vitamin A was 18.81% greater (P = .003) in piglets from sows receiving NRC level compared to piglets from sows fed industry level. On day 19, numerically lower (P = .27) hepatic vitamin A concentration was observed among offspring of sows receiving NRC level compared to offspring of sows fed industry level.

For sows fed NRC recommended level compared with industry vitamin level, serum vitamin D was decreased (P < .001; Figure 2) by 24.52% and 31.24% on days 0 and 19, respectively. In piglets from sows fed NRC recommended level, serum vitamin D was less (P < .001) on both day 5 (49.13% less) and day 19 (37.03% less) compared to piglets from sows fed industry vitamin level.

Serum vitamin E on day 0 was reduced (P = .01; Figure 3) in sows fed NRC recommended level compared with industry vitamin level, but no evidence of difference (P = .92) was observed on day 19. No evidence for a difference (P = .91) in sow liver vitamin E concentration was observed between treatments. Maternal vitamin supplementation level did not affect (P = .29) piglet serum vitamin E at day 5 but by day 19 serum vitamin E was 16.42% less (P < .001) in offspring from sows fed NRC recommended level compared to offspring of sows fed industry level. Moreover, vitamin E liver concentration was reduced (P < .001) over 25% in piglets from sows fed NRC recommended level compared to sows fed industry level.

Nursery performance

Across treatments, nursery mortality, removals, and medication rates were low (Table 5). No interactions (P ≥ .26) between sow vitamin supplementation and nursery pig supplementation levels were observed for nursery growth performance. Pigs fed industry levels in nursery had increased ADG (P < .001), ADFI (P < .001), G:F (P = .002), and BW (P < .001) at the end of the nursery period compared to pigs fed reduced levels in the nursery, regardless of vitamin level fed to the sow (Table 6). Pigs weaned from sows fed industry vitamin levels tended to be heavier (P = .09) at 40 days post weaning than pigs weaned from sows fed reduced vitamin levels.

Nursery pig vitamin levels

Downstream impact of maternal supplementation level on piglet serum vitamin levels at 40 days post weaning reduced serum vitamin A (P = .02) concentration among offspring whose dams were fed NRC recommended compared to industry levels (Table 5 and Figure 4). An interaction was observed (sow × nursery, P = .02) between sow and nursery vitamin supplementation level for serum vitamin E due to the NRC level fed to the sow (P = .02) or nursery pig (P < .001) reducing nursery pig serum vitamin E, although the reduction observed among nursery pigs fed NRC recommended levels and whose dams were fed industry levels was not as severe as the reduction observed in pigs fed NRC levels and whose dams also were fed NRC levels. Regardless of vitamin levels fed to their dam, hepatic stores of vitamin E were also less (P = .03) at 40 days post weaning in pigs fed NRC levels compared to pigs fed industry vitamin levels. Nursery vitamin supplementation at NRC levels compared to industry levels also reduced piglet serum concentrations of vitamin A (P < .001) and vitamin D (P < .001) after 40 days, regardless of sow vitamin supplementation. An interactive effect (sow × nursery, P = .01) of sow and nursery vitamin supplementation on hepatic vitamin A stores at the end of nursery was observed because industry supplementation level in the nursery improved (P < .001) stores compared to NRC level supplementation, but the improvement was less pronounced in offspring of sows which had been fed industry vitamin levels compared to offspring of sows which had been fed NRC vitamin levels.

Discussion

When provided in excess, fat-soluble vitamins accumulate within the animal. One limitation of this study is that initial body stores of vitamins were not controlled for, nor was the study designed to measure the impact of the duration of reduced vitamin supplementation during gestation. Since NRC vitamin requirements do not change throughout gestation, further research is needed to understand how stage of gestation might influence vitamin requirements and depletion of maternal reserves.

Apart from vitamin supplementation level impacting pig physiology and performance in this study, measured physiological concentrations of vitamins A and D were low compared to longstanding reference values⁸ used as the basis for veterinary diagnostics (Scott L. Radke, DVM, email communication, September 2019). Serum vitamin A levels measured in both sows and piglets were well below the minimum thresholds of reference ranges (0.25-0.40 mg/kg for sows; 0.40-0.50 mg/kg for neonates) as were piglet liver concentrations (36-57 mg/kg for weaned pigs; 57-114 mg/kg for grow-finish pigs). Serum vitamin D levels measured in NRC-level fed sows of this study were below historic “normal” reference ranges (35-100 ng/mL for sows) and regardless of maternal feeding level, both neonates and especially weaning-age piglets had levels below or well-below the “normal” reference ranges (5-15 ng/mL for neonates; 25-30 ng/mL for weaned piglets; 30-35 ng/mL for grow-finish pigs). Although sow vitamin E concentrations fell just below or aligned with historic reference values for serum and liver depending on sampling timepoint, notably suckling piglet levels were well above historic reference values (1.5-2.5 mg/kg serum; 3.0-5.0 mg/kg liver). However, post weaning piglet serum vitamin E concentrations were lower than “normal” range (2.0-2.5 mg/kg serum).

Serum and tissue levels are not positioned for use as sole diagnostic criterion for establishing deficiencies since immunological and physiological anomalies can impact the dynamic levels measured; clinical or pathological signs of deficiency should be used to support diagnoses of vitamin deficiencies.⁸ Expected tissue levels as reported by Puls⁸ are based on literature and case studies from 1981-1993 (vitamin A) or dating back even farther to 1969 (vitamin E) and 1964 (vitamin D). While management and rearing conditions from that era would be hardly recognizable today, documented changes in pig physiology include greater reproductive prolificacy, faster growth, more efficient nutrient utilization, later maturation, and altered tissue deposition of chemical components accompanying high lean-gain genotypes.^9-11 These changes not only could be responsible for shifting nutrient requirements and highlight the need for updated vitamin supplementation recommendations, but could also impact vitamin accumulation in tissues. Caution should be exercised in interpreting tissue vitamin levels against traditional “normal” ranges until research validates expected tissue levels in healthy pigs of modern genotypes reared in commercial environments.

The results of the current study suggest there is an industry wide need to re-evaluate vitamin supplementation levels. The vitamin A requirement for optimal reproductive performance is age dependent and likely greater in younger sows.¹² Gilts that received adequate dietary vitamin A through nine months of age completed two reproductive cycles without vitamin A supplementation without developing deficiency symptoms, suggesting adequate vitamin A stores in the liver.^13,14 Moreover, mature sows without vitamin A supplementation required 4 parities before deficiency symptoms became evident.¹⁵ Thus, it is important that females receive adequate vitamin supplementation during gilt development for long-term reproductive success and might explain why vitamin supplementation level in gestation and lactation diets had no direct impact on sow or litter performance over the single reproductive cycle measured in this study. Nonetheless, serum and liver concentrations in this study suggest NRC-level fed sows deplete liver vitamin A stores to sustain circulating levels and offspring serum levels at birth via placental transfer. Since vitamin transfer from sow to offspring is a dynamic process, the serum concentration at birth provides minimal information on how fetal and neonatal hepatic vitamin A stores were established then modulated during lactation and could be responsible for the elevated serum vitamin A observed in offspring of NRC-level fed sows by the time of weaning.

Supplementation of vitamin D at current industry levels compared to NRC levels consistently increased serum vitamin D concentrations in both sows and piglets from birth to weaning. Current NRC requirements for vitamin D may be inadequate not only due to genetic advances in reproductive output, but a majority of vitamin D trials that established requirements were conducted when pigs had access to sunlight thus facilitating endogenous synthesis of vitamin D.^6,11 Placental transfer of vitamin D from sow to progeny is low and since piglets are born with low serum concentrations of 25-hydroxycholecalciferol [25(OH)D₃], a biomarker for vitamin D status, pigs are susceptible to vitamin D deficiency.^16-18 Nonetheless, providing supplemental 25(OH)D₃ to the dam can improve both sow and fetal vitamin D status.¹⁹ Vitamin D supplementation can also improve the vitamin D status of young pigs without influencing growth performance or bone mineralization.²⁰ In a different study, litter weight gain from sows fed a diet with vitamin D at 2000 IU/kg was greater than that of litters from sows fed a diet with vitamin D at 200 IU/kg.²¹ Larger doses of vitamin D (1400 and 2000 IU/kg) decreased the number of stillborn piglets compared with smaller doses in the diet (200 and 800 IU/kg).¹⁷ In the present study, dietary vitamin D level failed to impact stillborn numbers possibly due to insufficient power to detect a statistical difference, or due to differences in farrowing management practices and limited ability to detect response patterns with just two treatment levels (800 and 2000 IU/kg).

It is curious that sow vitamin E serum concentration was less among NRC-level fed sows compared to industry-level fed sows at the beginning of lactation yet sows of both treatments had similar concentrations in both serum and liver by the end of lactation. The inability to control for initial sow hepatic vitamin E concentration between treatments limits fully understanding the effects of vitamin supplementation on maternal vitamin E status. Moreover, since gestational intake of vitamin E was around 126 to 170 IU/day (median NRC and industry treatment intakes, respectively) but lactation mean intake was > 300 IU/day for both treatments (305 IU/day for NRC level, 462 IU/day for industry level) with ad libitum feed intake, the higher total vitamin E intake during lactation may have been satisfactory to maintain maternal homeostatic levels while simultaneously deprioritizing lactational transfer to offspring.

Unsurprisingly, no difference in neonate vitamin E concentration between treatments was observed at birth since transfer of vitamin E from dam to offspring occurs primarily postnatally via milk.²² Yet reductions in circulating and stored vitamin E concentrations of NRC-level fed sows’ offspring were apparent by the end of the suckling period despite sow vitamin E status not showing a response to treatment. Piglet vitamin E status is important to combat oxidative stresses, especially those incurred early in life such as iron injection²² and establish hepatic vitamin E reserves to support performance in subsequent production phases. Improved immune response can be elicited with high doses of supplemental vitamin E; additional vitamin E in sow diets increased serum IgG in sows at farrowing and in pigs on days 1 and 28 post partum.²³ In the same study, vitamin E supplementation increased number of pigs born per litter and improved weaning weights.

In agreement with the present study, gestation vitamin supplementation levels had limited impact on farrowing and litter performance.²⁴ However, increasing gestation vitamin supplementation from NRC levels to approximately twice the industry treatment levels of the current study has been shown to increase body condition and suppress lactational feed intake of a common diet fed ad libitum. Stressful conditions increase vitamin requirements; moreover, B-vitamin (niacin, thiamine, pantothenic acid, and vitamin B₆) deficiencies can suppress appetite while deficiencies in vitamins A and E lessen immunocompetence and antioxidative capacity which could impact subclinical health status and indirectly affect appetence.¹ The greater lactational feed intake of the industry-level fed sows in the present study tended to reduce litter gain efficiency since the higher caloric intake did not convert to heavier weaning weights. Although the greater feed consumption also did not prevent BW loss, body composition was not measured. Thus, it is possible that body condition of the industry-level fed sows increased with potential benefit to subsequent reproductive performance.

Despite limited growth benefits, the downstream impact of maternal supplementation on weaned pig vitamin status was clearly demonstrated. The feeding of both dam and offspring fat-soluble vitamins at NRC levels compounded to yield even lower serum vitamin E and hepatic vitamin A concentrations than supplementing either production phase alone at NRC levels yielded. Therefore, vitamin supplementation decisions should consider lifecycle supplementation risks and opportunities.

The magnitude of improved growth (10%-12%) observed due to the industry supplementation level is notable considering expected improvement in weight gain due to feed-grade antibiotics is generally only 3% to 9%²⁵ yet extensive resources are allocated to identifying antibiotic-alternative growth promoters. Similar magnitude improvements in ADG, ADFI, and feed efficiency due to similar vitamin supplementation strategies over NRC levels have been reported by others.^26,27 However, which specific vitamins are responsible for growth improvements has yet to be established. Supplementation of B vitamins at levels similar to the industry concentrations fed in the present study do not always elicit improvements relative to NRC feeding levels,²⁸ but high-lean growth potential pigs have greater demand for B vitamins to support optimum growth efficiency²⁹; indeed, the pigs of the present study had 4% less ADFI yet 6.5% greater ADG than those which failed to respond to B-vitamin supplementation.²⁸ To identify optimal vitamin supplementation beyond NRC levels, further research is needed to determine the impact of specific vitamins for pigs of varying growth potential and possible interactions between vitamins.

Implications

Under the conditions of this study:

• Reduced vitamins suppress sow ADFI and potentially impact future performance.
• Vitamin supplementation above NRC levels benefits nursery pigs.
• Physiological vitamin levels are “deficient” by historic reference values.

Acknowledgments

The authors would like to acknowledge the Iowa State University Veterinary Diagnostic Laboratory for their support in performing the vitamin analyses.

Conflict of interest

None reported.

Disclaimer

Scientific manuscripts published in the Journal of Swine Health and Production are peer reviewed. However, information on medications, feed, and management techniques may be specific to the research or commercial situation presented in the manuscript. It is the responsibility of the reader to use information responsibly and in accordance with the rules and regulations governing research or the practice of veterinary medicine in their country or region.

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