Vitamin D 3 level effect 159

Corroborating the observation of Lauridsen et al. (2010), there was difference between dietary vitamin D3 levels with regards to sow body condition score,

back-fat depth or feed intake in the current study. In the present study, dietary vitamin D3 level did not influence litter size or numbers born alive or dead.

Contrary to this, Lauridsen et al. (2010) reported a reduction in the number stillborn with increased doses of vitamin D3 (1400 IU and 2000 IU). Although

there is no clear mechanism for reduced number stillborn, in human studies, placental tissues were found to be key sites for the vitamin D receptor (VDR) and the production of 1, 25- dihydroxyvitamin D3 (1, 25(OH)2D3); the active

form of vitamin D3 (Zehnder et al., 2002, Vigano et al., 2003). This may

influence placental development and subsequent foetal growth (Murthi et al., 2016). With regards to the present study, it was found that 2000 IU vitamin D3

in sow gestation diets increased piglet birth and day 1 weight. It has been reported that litter and piglet birth weights increased with 25(OH)D3 supplementation compared to 2000 IU vitamin D3 (Weber et al., 2014), which

may be a result of enhance skeletal growth potential (Hines et al., 2013). Discrepancies between the current study and Weber et al. (2014) may be explained by maternal 25(OH)D3 plasma levels as sows offered a diet with high level of vitamin D3 (2755 IU/kg) in the current study and that of 25(OH)D3

supplemented sows in Weber et al. (2014) are comparable.

Lauridsen et al. (2010) observed a dose response to vitamin D3 on

piglet ADG in the second week of lactation, with 800 IU resulting in greater piglet body weight gain than their 200 IU dose. In the present study, progeny from sows offered the diet with a low vitamin D3 level (1195 IU/kg) had greater

ADG from day 14 to weaning than progeny from sows offered the diet containing a high vitamin D3 level (2755 IU/kg) and as a result piglets were

heavier at weaning. It is well documented that vitamin D3 is important for

muscle development and function (Ceglia, 2008), as vitamin D receptor (VDR) knockout mice suffer reduced body size and weight (Burne et al., 2005). Considering the results of Lauridsen et al. (2010) and this study it suggests that diets with lower vitamin D3 (800- 1100 IU/kg) are adequate to maximise

the body gain of progeny. However, the importance of vitamin D3 in

maintaining piglet weight increases as lactation progresses as calcium mediated transport mechanisms become activated (Weber et al., 2014). Therefore, differences in piglet growth could also be influenced by milk production. Nevertheless, as milk production was not measured in this study further investigation is needed.

Vitamin D3 is hydroxylated to 25(OH)D3 in the liver and as the major

circulating form of vitamin D3 it is an indication of vitamin D status (Zhu and

DeLuca, 2012). Increasing the vitamin D3 level in sow gestation diets

increased sow plasma 25(OH)D3 levels to 34.4 ng/ml, which is still within the normal range (15-60 ng/ml 25(OH)D3) (Lauridsen and Jensen, 2013). However, sow plasma 25(OH)D3 was lower on day 107 of gestation compared to day 28, even when sows were offered the diet with a high level of vitamin D3. Previous studies in dairy cows found that as plasma calcium levels

decrease, 25(OH)D3 is activated to form 1,25(OH)2D3, which enhances

intestinal calcium absorption (Horst et al., 1994). Therefore, the decrease in sow plasma 25(OH)D3 at day 107 may be a result of increased calcium metabolism for impending milk production.

In the current study, as hypothesised colostrum vitamin D3 and

25(OH)D3 levels were significantly increased for sows offered the diet with a high level of vitamin D3. This agrees with previous research that increasing

maternal vitamin D3 increases vitamin D3 in colostrum (Flohr et al., 2014). On

the contrary Weber et al. (2014) found that dietary vitamin D3 level did not

influence colostrum 25(OH)D3 of multiparous sow. In the present study milk vitamin D3 and 25(OH)D3 was not affected by dietary vitamin D3 levels. This

was to be expected as a common lactation diet containing 2000 IU vitamin D was fed to all sows. In agreement with Lauridsen et al. (2010), the present study observed that plasma 25(OH)D3 in piglet serum collected at birth was below detection limits. Thus, increasing maternal dietary vitamin D3 does not

improve the circulating vitamin D3 status of the piglet. However previous

research demonstrated that vitamin D readily crosses the placental barrier (Clements and Fraser, 1988, Goff et al., 1984) and may influence piglet vitamin D stores (Rortvedt and Crenshaw, 2012). Indeed, this supported in the present study where liver vitamin D3 and 25(OH)D3 was increased in progeny born to

sows fed 2000 IU during gestation.

Vitamin D3 also plays an important role in both the innate and adaptive

immune systems (O’Brien and Jackson, 2012). B cells are directly targeted by 1,25(OH)2D3, which inhibits cell proliferation, differentiation and

immunoglobulin secretion (Baeke et al., 2010). Interestingly, in the present study, increasing the vitamin D3 level in sow gestation diets increased

colostrum IgG concentration. Indeed, regardless of vitamin D3 treatment, IgG

concentration of colostrum, in the present study, was found to be greater than previous research findings (Hurley, 2015). However, Bourne and Curtis (1973)

demonstrated that all colostrum IgG is derived from the serum of sows, while in milk, 70 % of IgG is produced locally in mammary tissues. Sow serum IgG was not analysed in the present study.

Vitamin D3 plays an important role in calcium and phosphorous

metabolism and is therefore crucial for sow bone strength and integrity (Lauridsen et al., 2010). Progeny bone measures are also influenced by maternal dietary vitamin D3 level (Rortvedt and Crenshaw, 2012), with vitamin

D3 levels below 2000 IU found to negatively impact piglet bone health at

weaning (35 days old) (Witschi et al., 2011). In disagreement with the hypothesis, piglet femur bone measures were not affected by maternal dietary vitamin D3 level in the current study. Indeed, the overall lack of treatment effect

on bone measures may be a factor of age as piglet bones were collected at birth.

Overall increasing maternal dietary vitamin D3 improved the vitamin D3

status of both the sow and piglets, increased piglet birth and day 1 weight and colostrum IgG concentration, however no subsequent effect on piglet growth to weaning was found.