IntroductIonThe most common form of dietary vitamin D supplemented in livestock diets is cholecalciferol (vi-

Abstract Several studies have suggested there is a critical relationship between piglet birth weight and preweaning mortality. Thus, the objective of the current work was to identify a birth weight threshold value for preweaning mortality. Birth weight and survival data from two studies involving a combined total of 4,068 piglets from 394 litters on four commercial farms (three European, one U.S.) were compiled for a pooled, multistudy analysis. Overall preweaning mortality across the two studies was 12.2%. Key variables used in the analysis were piglet birth weight (measured within 24 h of birth) and corresponding survival outcome (dead or live) by weaning at 3–4 wk of age. A mixed effects logistic regression model was fit to estimate the relationship between preweaning mortality and birth weight. A random effect of study was included to account for overall differences in mortality between the two studies. A piecewise linear predictor was selected to best represent the drastic decrease in preweaning mortality found as birth weight increased in the range of 0.5–1.0 kg and the less extreme change in weight above 1.0 kg. The change point of the birth weight and preweaning mortality model was determined by comparing model fit based on maximizing the likelihood over the interval ranging from 0.5 to 2.3 kg birth weight. Results from the analysis showed a curvilinear relationship between birth weight and preweaning mortality where the birth weight change point value or threshold value was 1.11 kg. In the combined data set, 15.2% of pigs had birth weights ≤1.11 kg. This subpopulation of pigs had a 34.4% preweaning mortality rate and represented 43% of total preweaning mortalities. These findings imply interventions targeted at reducing the incidence of piglets with birth weights ≤1.11 kg have potential to improve piglet survivability. Additional research is needed to validate 1.11 kg as the birth weight threshold for increased risk of preweaning mortality.

Three experiments were conducted to study the effects of extrusion processing on growth performance of weanling pigs. In Exp. 1, 350 weanling pigs (initially 4.4 +/- 1.0 kg BW and 10 +/- 2 d of age) were used to study the effects of various carbohydrate sources (corn, cornstarch, broken rice, wheat flour, and grain sorghum), with or without moist extrusion processing, on growth performance in a 5 x 2 factorial arrangement of treatments. No carbohydrate source x extrusion processing interactions were observed (P > .10). Growth performance was not affected by extrusion processing; however, pigs fed corn had poorer growth performance (P < .05) than those fed other carbohydrate sources. In Exp. 2, 360 weanling pigs (initially 5.0 +/- .5 kg BW and 10 +/- 2 d of age) were used to determine the interactive effects of ingredient processing and diet complexity on growth performance. Three processing combinations were used with either a simple or complex diet formulation in a 3 x 2 factorial arrangement of treatments. The three processing conditions were 1) pelleted only (control); 2) corn that was moist-extruded and then the complete diet was pelleted (extruded); or 3) the complete diet was expanded and then pelleted (expanded). Pigs fed extruded diets had a greater improvement in ADG as diet complexity increased than those fed other diets (processing x diet complexity interaction, P < .10). Pigs fed moist-extruded corn had the best growth performance (P < .01). In Exp. 3, 210 weanling pigs (initially 6.8 +/- 1.5 kg BW and 21 +/- 2 d of age) were fed pelleted diets containing nonextruded corn (14.5% gelatinization; control) or corn extruded to provide 38.7, 52.7, 64.4, or 89.3% gelatinization. Average daily gain and ADFI decreased and then increased (P < .05), but apparent digestibility of DM, CP, and energy (P < .01) increased and then decreased with increasing gelatinization. These results indicate that moist extrusion processing of carbohydrate sources has variable effects on growth performance of early-weaned pigs and that the degree of gelatinization does not seem to be a major factor in explaining this variation.

Abstract 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 &gt; 0.170), except primary fiber number and the ratio of secondary to primary muscle fibers (P &lt; 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 &gt; 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 &lt; 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 &lt; 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 &lt; 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 &gt; 0.061). At weaning, serum concentrations of 25(OH)D3 in piglets from all sow treatments were different (P &lt; 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 &gt; 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 &lt; 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.

Two studies were conducted to evaluate the growth performance and percentage bone ash of nursery pigs fed various combinations of Ca and P provided by inorganic sources or phytase. In Exp. 1, pens of pigs (n = 720, initially 6.1 ± 0.98 kg) were blocked by initial BW. Within blocks, pens were randomly assigned to one of six treatments (12 pens per treatment) in a three-phase diet regimen. Treatments were arranged in a 2 × 3 factorial with main effects of Ca (0.58% vs. 1.03%) and standardized total tract digestible (STTD) P (0.33% and 0.45% without phytase, and 0.45% with 0.12% of the P released by phytase). During treatment period, Ca × P interactions were observed for all growth criteria (P < 0.05). When diets had low Ca, pigs fed 0.45% STTD P with phytase had greater (P < 0.01) ADG and ADFI than those fed 0.33% or 0.45% STTD P without phytase. When high Ca was fed, ADG and ADFI were similar among pigs fed 0.45% STTD P with or without phytase and were greater than those fed 0.33% STTD P. Gain:feed was reduced (P < 0.01) when high Ca and low STTD P were fed relative to other treatments. On d 21, radiuses were collected from 1 pig per pen for bone ash analysis. Pigs fed 0.33% STTD P had decreased (P < 0.05) percentage bone ash than those fed 0.45% STTD P with or without phytase when high Ca was fed, but this P effect was not observed for low Ca diets (Ca × P interaction, P = 0.007). In Exp. 2, 36 pens (10 pigs per pen, initially 6.0 ± 1.08 kg) were used in a completely randomized design. Treatments were arranged in a 2 × 3 factorial with the main effects of STTD P (at or above NRC [NRC. 2012. Nutrient Requirements of Swine. 11th rev. ed. Washington (DC): National Academic Press.] requirement estimates) and total Ca (0.65, 0.90, and 1.20%). Experimental diets were fed during phases 1 and 2, followed by a common phase 3 diet. Diets at NRC (2012) P level contained 0.45% and 0.40% STTD P, compared with 0.56% and 0.52% for diets greater than the NRC (2012) estimates, in phase 1 and 2, respectively. During treatment period, increasing Ca decreased (linear, P = 0.006) ADG, but increasing STTD P marginally increased (P = 0.084) ADG, with no Ca × P interaction. When diets contained NRC (2012) P levels, pigs fed 1.20% Ca had decreased (P < 0.05) G:F than those fed 0.65% or 0.90% Ca; however, when high STTD P were fed, G:F was not affected by Ca (Ca × P interaction, P = 0.018). In conclusion, excess Ca decreased pig growth and percentage bone ash when diets were at or below NRC (2012) requirement for STTD P, but these negative effects were alleviated by adding monocalcium P or phytase to the diet.