INTRODUCTION
Vitamin D has not been a major issue in the swine industry for several decades but in the past few years, attention on vitamin D and its status in pigs has risen with the increasing occurrence of metabolic bone diseases in some production settings (
Madson et al., 2012). Recently, seemingly low concentrations of plasma vitamin D have been identified in periweaning failure to thrive syndrome (PFTS), noted by veterinarians and researchers since 2008 (
Huang et al., 2011). Consequently, products are available in the US as a means to specifically modify the plasma vitamin D levels in an attempt to prevent pigs from developing metabolic bone diseases and the mortality associated with PFTS. Some of the products contain only vitamin D while other products are a combination of fat-soluble vitamins.
Several recent studies have been conducted to investigate vitamin D requirements and/or supplementation/administration to sows and piglets (
Lauridsen et al., 2010;
Witschi et al., 2011;
Rortvedt et al., 2012;
Flohr et al., 2014a). The supplementation of vitamin D to gestation and lactation diets at concentrations above
NRC (1998) requirement was demonstrated to increase serum vitamin D concentration of sows (
Lauridsen et al., 2010) and their progeny (
Witschi et al., 2011). Regarding vitamin D supplementation to piglets, when newborn pigs were supplemented with vitamin D
3 via oral administration at 40,000 or 80,000 IU of vitamin D
3, higher serum 25-hydroxycholecalciferol (25-OH D
3) concentration was detected at weaning compared with pigs without vitamin D
3 administration (
Flohr et al., 2014a). On the other hand,
Goff et al. (1984) suggested that the parenteral vitamin D
3 treatment to sows at d 20 prepartum by i.m. injection of vitamin D
3 was an effective method for enhancing vitamin D status of newborn piglets because the vitamin D status of sows was closely correlated to that of the fetus and neonatal piglets. Based on these limited results, an increased serum vitamin D concentration of piglets seems to be possible via several methods such as oral administration to piglets, supplementation to maternal feed and injection to sows. However, the relationship of that increased serum concentration to increased performance or bone measure is not always present. Regarding other fat soluble vitamins, vitamin E injection of 300 IU to neonatal pigs has been demonstrated to increase plasma α-tocopherol levels on 1 d after injection (
Hill et al., 1999), and
Håkansson et al. (2001) reported that plasma retinol concentration of suckling piglets were influenced by the vitamin A status of sows and colostrum. However, limited information is available for a direct comparison of fat-soluble vitamin administration to newborn pigs by different administration routes. Therefore, the objective of the current research was to evaluate the effects of a variety of supplemental fat-soluble vitamin products administered by different administration routes to young pigs as well as the efficacy of vitamin D
3 injection to sows prepartum.
RESULTS
The effect of vitamin D
3 supplementation with vitamins A and E to newborn pigs in Exp. 1 on plasma 25-OH D
3, retinol, and α-tocopherol concentrations is shown in
Table 1. At 10 d after administration all groups treated with a vitamin D
3 product had higher plasma 25-OH D
3 concentration than the control group (p<0.05). Additionally, when the pigs received the injectable product, the plasma 25-OH D
3 concentration was the highest among treatments (p<0.05). At weaning, plasma values for injection and oral treatments declined from 10 d after administration but plasma values for the injection treatment remained elevated relative to plasma values for the other pigs (p<0.05). With regard to plasma retinol and α-tocopherol concentrations, there were no differences except at 10 d after administration when plasma α-tocopherol concentrations of pigs in the injection group were the highest among all treatments (p<0.05) and tended to be maintained until weaning (p = 0.09).
In Exp. 2 (
Table 2), the effect of vitamin D
3 and variable vitamin A and E administration to newborn pigs on plasma 25-OH D
3 concentrations demonstrates again that the plasma concentrations at 10 d after administration can be increased by either oral or injectable administration (p<0.05), that values decline from 10 d after administration to weaning regardless of treatment, and that values at weaning can remain higher than those of control pigs in which no treatment was administered (p<0.05). The injectable product resulted in the highest plasma values and the results were higher than the oral administration treatments at weaning (p<0.05). In the case of α-tocopherol, the vitamin E injection to piglets was also more effective to increase plasma α-tocopherol concentration at 10 d after administration compared with the oral administration (p<0.05). However, at weaning the highest numerical value was actually from one of the oral products that contained vitamin E and it, as well as the injectable product, was higher than that of the control pigs (p<0.05). Plasma 25-OH D
3 levels of sows were higher at weaning than farrowing in both Exp. 1 and 2 (p<0.05).
The effects of the treatments on BW and growth in Exp. 1 and 2 are provided in
Table 3 and
4. No differences among treatments were detected on BW and average daily gain (ADG) of pigs during suckling periods in either experiment.
The effect of vitamins D
3 and E supplementation via drinking water to nursery pigs in Exp. 3 is presented in
Table 5. The control and injection treatments from the nursing phase in Exp. 2 were used as the main treatment effects in the statistical analysis of
Table 5. When pigs then received vitamins D
3 and E via drinking water in the nursery, the pigs had higher plasma 25-OH D
3 and α-tocopherol concentrations at d 14 postweaning (p<0.01). Additionally, the change of plasma 25-OH D
3 concentration from weaning to d 14 postweaning in pigs supplemented with vitamins via drinking water was also higher than pigs without water vitamin supplementation (p<0.01). In contrast, plasma retinol concentration was adversely affected at d 14 postweaning by high levels of vitamins D
3 and E in drinking water (p<0.05). Even though there was no difference on plasma 25-OH D
3 concentration at d 14 postweaning between the lactation treatments (control and injection), a lower change of plasma value was observed in the injection treatment that had higher plasma values at weaning compared with the control treatment (p<0.01). In the case of plasma α-tocopherol concentration, higher plasma values were observed in the injection treatment than the control treatment at weaning (p<0.01) and a trend at d 14 postweaning (p = 0.07). The plasma values declined from weaning to d 14 postweaning and a greater reduction was detected in the injection treatment (p<0.05).
In Exp. 4 (
Table 6), a vitamin D
3/A/E injection to gestating sows increased absolute serum 25-OH D
3 concentration at farrowing and its change from pre-administration values (p<0.01). Piglets from sows that received the prepartum vitamin D
3 injection had higher serum 25-OH D
3 concentrations than those in the control group at birth (p<0.01) and this improvement was maintained until weaning (p<0.05) but vitamin D
3 injection to sows did not affect the change of serum 25-OH D
3 concentration of piglets during suckling period.
DISCUSSION
This is the first study to investigate the plasma fat-soluble vitamin profiles of nursing piglets administered with fat-soluble vitamins by different administration routes. In both Exp. 1 and 2, the results, collectively, demonstrate that the vitamin D
3 status of pigs at weaning can be improved by administration of vitamin D
3 by a variety of methods and the results agree with those of recent studies (
Rortvedt et al., 2012;
Flohr et al., 2014a). However, plasma 25-OH D
3 and α-tocopherol concentrations declined from 10 d after administration to weaning in pigs from the injection and oral treatments, which agrees with
Flohr et al. (2014a). This result suggests that plasma values are presumably diluted with the increase in blood volume associated with the rapid growth of the pigs as well as utilized by, or deposited in, various tissues. In contrast to Exp. 2, there was no decline in plasma 25-OH D
3 level of control pigs in Exp. 1. Because of no vitamin administration to the control pigs, the control pigs illustrate the normal physiological response in the suckling period but the reason for the discrepancy between experiments is unclear. Therefore, further study is needed to verify these responses.
Plasma 25-OH D
3 levels in sows increased from farrowing to weaning in both studies which may result from the feed intake change from the restricted feeding in gestation to
ad libitum in lactation.
Flohr et al. (2014b) reported sows fed gestation and lactation diets containing vitamin D
3 had increased 25-OH D
3 levels in plasma and milk by increasing supplementation levels from 1,500 to 6,000 IU per kg diet at farrowing, 10 d of lactation and weaning but there were no day effect and interaction between treatment and day of lactation in milk 25-OH D
3 levels. Therefore, this result indicates that, while plasma 25-OH D
3 levels in sows can be increased from farrowing to weaning by absolute higher vitamin D
3 intake in lactation than gestation, milk 25-OH D
3 levels for the suckling piglet may be more difficult to increase. However, it should be noted from the current study that plasma values for control pigs were higher at 10 d after administration than at birth which demonstrates that milk clearly contributes to the vitamin D status of the pig.
Comparing the results between oral and injectable methods in the present experiments, it was demonstrated that the i.m. injection of vitamin D
3, and E was able to enhance those statuses more than the oral administration. There have been few studies to compare the efficacy of different vitamin administration routes to pigs. In the case of sheep, ewes that received vitamin D
3 by i.m. injection had higher plasma 25-OH D
3 concentration and more lasting effects than those treated by oral administration (
Hidiroglou et al., 1984). The parenteral administration of vitamin D
3 does not require the process of intestinal absorption that oral administration of vitamin D
3 requires. It has been documented that only 50% of orally administered vitamin D is absorbed (
McDowell, 2000). Therefore, the process of intestinal absorption of vitamins probably affected the difference of plasma 25-OH D
3 and α-tocopherol concentration in this study. Regarding vitamin A status, there was no effect on plasma retinol concentration of piglets by vitamin A administration. When dogs were administered 10,000 IU of retinyl palmitate per kg BW orally, plasma retinol concentration increased slightly to be maximized at 6 h, and then declined to the baseline at 48 h (
Raila et al., 2002). These results suggest that each fat-soluble vitamin may have different biological responses and effectiveness to enhance plasma vitamin profiles by types and administration routes.
There were no differences among treatments on BW and ADG of pigs during the suckling period in either experiment. These results again agree with some recent research (
Flohr et al., 2014a).
Rortvedt et al. (2012) also reported no improvement of ADG for 35 d after weaning in pigs administered a single oral mega-dose of vitamin D
3 (40,000 IU) at birth (0.38 kg/d) compared with control pigs (0.41 kg/d). In contrast,
Tousignant et al. (2013) reported that in field conditions, pigs administered vitamin D
3 (40,000 IU) orally at 2 d of age were heavier at weaning and d 7 postweaning than control pigs without vitamin D
3 administration but that the difference vanished at d 26 postweaning. The results of the current study indicated that there was no improvement in piglet growth by vitamin administration even though plasma levels of vitamins were clearly increased. This would seem to indicate that although some individuals may categorize normal plasma levels as “low”, the levels are adequate for normal growth in an environment such as existed for the current research.
In Exp. 3, the water supplementation of vitamin D
3 and E increased plasma 25-OH D
3 and α-tocopherol concentrations which mean supplementation of vitamins via drinking water to nursery pigs is an effective method to enhance plasma status of vitamins. This result agreed with a previous study which reported the water supplementation of vitamin D
3 to nursery pigs from weaning for 10 d elevated serum 25-OH D
3 concentration on d 10 postweaning (
Flohr et al., 2014a). For vitamin E status,
Wilburn et al. (2008) reported the water vitamin E supplementation increased plasma α-tocopherol concentration of weanling pigs.
With regard to the changes of plasma 25-OH D
3 concentrations, the pigs in the lactation injection group that had higher plasma values at weaning had smaller increases of plasma 25-OH D
3 concentrations at d 14 in response to the water supplementation compared with those in the control group that had lower values at weaning, resulting in no difference in absolute plasma values between the lactation treatments at d 14 postweaning.
Trang et al. (1998) reported there is an inverse linear correlation between basal 25-OH D
3 and the increase in 25-OH D
3 for vitamin D
3-treated humans. This result means that improvements from vitamin treatment at birth could vanish after weaning when pigs are switched from milk to feed. In the case of plasma α-tocopherol concentration, the values declined after weaning regardless of treatment which is in line with the results from previous studies (
Bonnette et al., 1990;
Moreira and Mahan, 2002;
Wilburn et al., 2008). On the other hand, even though a greater reduction of plasma values was observed in pigs from the injection group that had higher plasma values at weaning than those in the control group that had lower values, the pigs in the injection group still maintained higher plasma α-tocopherol levels than those in the control group. In previous studies, plasma α-tocopherol concentration declined steadily over 21 d after weaning when pigs were not supplemented with vitamin E (
Moreira and Mahan, 2002;
Wilburn et al., 2008). Plasma α-tocopherol concentration in the current study was measured only at d 14 postweaning which does not allow determination if that decline would continue; thus, the effect of injection at birth seems to remain. However, because of limited data available in this study and lack of previous research, further study is needed to explain the changes in plasma α-tocopherol concentration from weaning when pigs have different plasma levels at weaning.
In Exp. 4, a vitamin D
3 injection to gestating sows increased serum 25-OH D
3 levels of sows at farrowing and of their offspring at birth. This result means the maternal vitamin D status affects the status of offspring at birth and it may result from the placental transportation which agrees with the observations of
Goff et al. (1984) who reported that when sows received vitamin D
3 by i.m. injection at d 20 prepartum, vitamin D status of their progeny was improved. Even though the difference in the serum 25-OH D
3 levels of piglets between treatments was maintained until weaning there was no difference in the magnitude of that treatment difference (or the change from birth to weaning) of 25-OH D
3 concentration in serum of piglets which means the improvement of vitamin D
3 status of gestating sows probably did not influence sow milk content. It may be noted that dietary vitamin D level was approximately 3 times higher in Exp. 4 than in Exp. 1 and 2, that the serum values of control sows at farrowing in Exp. 4 were approximately 2 times higher than those in Exp. 1 and 2, and that weaning serum values of control piglets in Exp. 4 were double that of the values at birth and 55% to 93% higher than the weaning values for control pigs in Exp. 1 and 2. Therefore, while milk may not be one of the best means of supplying vitamin D
3, it either is adequate to increase serum values of piglets if sows are supplemented at levels above
NRC (1998) recommendation or else the colostrum D
3 concentration is elevated sufficiently from the sow dietary concentrations to allow the piglet serum values at weaning to be maintained at a higher level.