Abstract The objective of this study was to examine factors contributing variation in serum 25-hydroxyvitamin D3 (25-OH-D3) levels in replacement gilts. In a randomized complete block design, 432 Duroc × Whiteline (Landrace and Large White composite) gilts housed 9 per pen were randomly allocated to be fed one of four diets from 100 to 172 days of age for 12 replicate pens per treatment. The corn-soybean meal diets consisted of two levels of 25-OH-D3 supplementation (50 μg (2,000 IU) 25-OH-D3/kg as HyD®, DSM Nutritional Products or no HyD®) and two calcium-to-phosphorus (Ca/P) ratios (1.5 STTD Ca/STTD P or 2.4 STTD Ca/STTD P). All diets contained 800 IU/kg vitamin D3, 0.28% STTD P, and no phytase. Gilts were housed in a curtain-sided, naturally ventilated barn on slatted concrete flooring and had ad libitum access to feed and water. The barn contained four rows of pens, and the gilts selected for blood 25-OH-D3 analysis were housed in the two middle rows to minimize their exposure to sunlight. At 172 days of age, blood was collected from a subset of gilts (n = 60), composed of littermates across dietary treatments, and analyzed for serum 25-OH-D3 levels. Other factors evaluated included piglet birth weight (μ = 1558 g), average daily gain (ADG) from birth to weaning (μ = 302 g), ADG from weaning to 100 days of age (μ = 724 g), ADG from 100 to 172 days of age (μ = 1059 g), and ADG from birth to 172 days of age (μ = 805 g). Data were analyzed as a 2 × 2 factorial with Ca/P and HyD® as fixed effects. The level of HyD® supplementation explained 78% of the variation in gilt serum 25-OH-D3 (P 0.01); gilts fed HyD® had greater serum 25-OH-D3 levels than females not fed HyD® (87.5 vs. 45.1 ng/mL). However, the calcium-to-phosphorus ratio did not affect gilt serum 25-OH-D3 (P 0.05). Litter explained 11% of the variation in serum 25-OH-D3 (P 0.05). Growth rate from weaning to 100 days of age explained 1% of the variation (P 0.05), where an increase of 1 g in ADG reduced serum 25-OH-D3 by 0.056 ng/mL. In summary, 90% of the variation in gilt serum 25-OH-D3 was explained by diet, litter, and ADG from weaning to 100 days of age. These results showed that while diet explained the majority of the variation in serum 25-OH-D3 at 172 days of age, maternal influence is another factor to consider when maximizing gilt serum 25-OH-D3 levels.
Knauer et al. (Wed,) studied this question.