Detection and genetic characterization of porcine pegivirus in pigs in the United States.

Using next-generation sequencing on vesicular swab and serum from swine from the USA exhibiting lameness and vesicles, porcine pegivirus (PPgV) was first identified and genetically characterized in the United States. Further screening using RT-PCR revealed that 24 of 159 (15.1%) serum samples were positive for PPgV. Future studies are needed to understand clinical impacts of the virus.

Effect of pelleting on survival of porcine epidemic diarrhea virus-contaminated feed.

Porcine epidemic diarrhea virus (PEDV) is a heat-sensitive virus that has devastated the U.S. swine industry. Because of its heat sensitivity, we hypothesized that a steam conditioner and pellet mill mimicking traditional commercial thermal processing may mitigate PEDV infectivity. Pelleting, a common feed processing method, includes the use of steam and shear forces, resulting in increased temperature of the processed feed. Two thermal processing experiments were designed to determine if different pellet mill conditioner retention times and temperatures would impact PEDV quantity and infectivity by analysis of quantitative reverse transcription PCR and bioassay. In Exp. 1, a 3 × 3 × 2 factorial design was used with 3 pelleting temperatures (68.3, 79.4, and 90.6°C), 3 conditioning times (45, 90, or 180 s), and 2 doses of viral inoculation (low, 1 × 10 tissue culture infectious dose (the concentration used to see cytopathic effect in 50% of the cells)/g, or high, 1 × 10 tissue culture infectious dose/g). Noninoculated and PEDV-inoculated unprocessed mash were used as controls. The low-dose PEDV-infected mash had 6.8 ± 1.8 cycle threshold (Ct) greater ( < 0.05) PEDV than the high-dose mash. Regardless of time or temperature, pelleting reduced ( < 0.05) the quantity of detectable viral PEDV RNA compared with the PEDV-inoculated unprocessed mash. Fecal swabs from pigs inoculated with the PEDV-positive unprocessed mash, regardless of dose, were clinically PEDV positive from 2 to 7 d (end of the trial) after inoculation. However, if either PEDV dose of inoculated feed was pelleted at any of the 9 tested conditioning time × temperature combinations, no PEDV RNA was detected in fecal swabs or cecum content. Based on Exp. 1 results, a second experiment was developed to determine the impact of lower processing temperatures on PEDV quantity and infectivity. In Exp. 2, PEDV-inoculated feed was pelleted at 1 of 5 conditioning temperatures (37.8, 46.1, 54.4, 62.8, and 71.1°C) for 30 s. The 5 increasing processing temperatures led to feed with respective mean Ct values of 32.5, 34.6, 37.0, 36.5, and 36.7, respectively. All samples had detectable PEDV RNA. However, infectivity was detected by bioassay only in pigs from the 37.8 and 46.1°C conditioning temperatures. Experiment 2 results suggest conditioning and pelleting temperatures above 54.4°C could be effective in reducing the quantity and infectivity of PEDV in swine feed. However, additional research is needed to prevent subsequent recontamination after pelleting as it is a point-in-time mitigation step.

Pathogenesis of porcine epidemic diarrhea virus isolate (US/Iowa/18984/2013) in 3-week-old weaned pigs.

Porcine epidemic diarrhea virus (PEDV) is associated with clinical diarrhea in naïve swine of all ages. This report describes timing of antibody generation and disease progression following infection with a US PEDV isolate by assessing fecal viral shedding, morphometric analysis of intestinal lesions, and magnitude of immunohistochemical staining. Sixty-three, 3-week-old pigs were randomly allocated into control (n=27) and challenged (n=36) groups. Challenged pigs were administered 1 mL of 1 × 10(3) PFU/mL of US/Iowa/18984/2013 PEDV isolate by oro-gastric gavage. Three control and four challenged pigs were necropsied on days post-inoculation (dpi) 1, 2, 3, 4, 7, and weekly thereafter, until study termination on dpi 35. Clinical disease, fecal shedding, body weight, and temperature were monitored during the study period. Diarrhea was observed in challenged pigs beginning for some on dpi 2, affecting a majority of pigs by dpi 6 and subsiding by dpi 10. Average daily gain was significantly lower (P<0.001) for one week post-infection in challenged pigs. PEDV was detected in feces by PCR on dpi 1 and continued in a subset of pigs until dpi 24. PEDV-specific antigen was detected in villous enterocytes of challenged pigs by immunohistochemistry (IHC) on dpi 1, 2, 3, 4, 7, and 14. Microscopic lesions included severe diffuse atrophic enteritis with significantly reduced (P<0.001) villous length observed on dpi 3, 4, and 7. Under the conditions of this study, fecal shedding of PEDV and IHC staining can precede and continue beyond the observation of clinical signs, thus increasing the risk of viral transmission.

Poor weaning transition average daily gain in pigs is not correlated with pathological or immunological markers of enteric disease during a porcine reproductive and respiratory syndrome virus outbreak.

Previous research suggests that enteric disease and poor gut health interact to decrease pig performance. Our objective was to determine if light birth weight pigs or those from the bottom 10th percentile of transition ADG (tADG) have a higher incidence of pathogen presence or enteric lesions than heavier or faster-growing contemporaries. A total of 1,500 pigs were weighed at birth and divided into 5 birth weight (BRW) categories: <1, 1 to 1.25, 1.26 to 1.5, 1.51 to 1.75, and >1.76 kg. At weaning, 1,054 random pigs were moved to a commercial wean-to-finish barn. Pigs were weighed individually at 0 and 3 wk postweaning. Transition ADG was calculated as the ADG between wk 0 and 3 postweaning. One pig from each of the 10th, 30th, and 70th percentiles of tADG was used to create 1 set of 3 pigs with the same litter size and from the same parity sow. Forty pigs from each of the 3 tADG percentiles were matched for sex, litter size, and sow parity but not BRW to create 20 matched sets of 60 pigs. This allowed for the main effects of BRW and tADG to be studied as a 5 × 3 factorial design. At 3 and 22 wk postweaning, pigs were euthanized for organ system tissue evaluation. Lung, lymph node, and digesta were analyzed for presence of pathogens and for severity of microscopic lesions (0 = not present, 1 = present, with slight erosion, 2 = present, with moderate erosion, and 3 = present and severe erosion). Data were analyzed using PROC GENMOD and GLIMMIX, where pig served as the experimental unit. The fixed effects were BRW and tADG and the random effects were pen and set. There were no BRW × tADG interactions (P = 0.16). There was no correlation (P = 0.12) between tADG and pathogen presence at either 3 or 22 wk postweaning. Incidence and severity of microscopic lesions in the large intestine at 3 wk postweaning decreased linearly with increasing tADG (P = 0.01). Lesion incidence and severity were also affected (P < 0.04) by tADG at 22 wk postweaning, with greater stomach incidence in the 10th percentile. Birth weight affected (P = 0.02) haemolytic Escherichia coli and Salmonella spp. B (includes Salmonella typhimurium) isolation at 3 wk postweaning as well as Brachyspira spp. isolation at 22 wk postweaning (P = 0.05) but in mixed directions. There were no effects (P = 0.21) of BRW or tADG on serum or ileum mucosa immune markers. In summary, it is apparent from this research that neither BRW nor tADG are likely causes of pathogen or lesion incidence.

Characterizing growth and carcass composition differences in pigs with varying weaning weights and postweaning performance.

The unprecedented increase in litter size over the last decade has led to a perceived increase in the number of fallback pigs (Sus scrofa). However, there is little peer-reviewed data available regarding the biological differences between fallback pigs and their normal cohorts. Therefore, the objective of this experiment was to identify differences in the biology and physiology, and thus the growth and metabolism, between pigs with varying weaning weights (WW) and postweaning performance. To accomplish this objective, a total of 120 barrows (PIC C22/C29 × 337) were used in growth and comparative slaughter experiments. Pigs were selected from a population of 960 weanling pigs to represent the 10% lightest, median, and heaviest pigs at weaning (n = 40 pigs per WW category). Eight pigs from each WW category were harvested on d 5 postweaning as the initial slaughter group (ISG). The remaining 96 barrows were housed in individual crates, fed ad libitum quantities of a common diet during a 27-d growth study, and were harvested on d 33 or 34 postweaning. After the completion of the live animal component of the experiment, pigs within each WW category were further stratified into the slowest, median, or fastest 33% ADG categories. This resulted in a total of 9 treatments in a nested design. Fallback pigs were designated as those belonging to the slowest ADG category from either the lightest or median WW categories. Data were analyzed using the GLIMMIX procedure of SAS with the fixed effects of WW category and WW(ADG). Although feed intake was maximized (P < 0.0001) by WW(ADG) category, feed efficiency was not different (P = 0.30). When equalized per unit of BW, WW(ADG) category greatly affected (P < 0.02) eviscerated carcass, organ, and metabolic BW, but not (P = 0.28) empty BW. There were no differences (P > 0.12) in tissue nutrient concentrations, ratios, or energy content among pigs in the growth experiment. All tissue deposition rates, which were calculated as the difference between tissue nutrient concentrations of the growth experiment and initial slaughter groups, were maximized (P < 0.0002) by WW(ADG), even when equalized per unit of BW. In conclusion, WW and ADG affect tissue accretion rates, but not feed efficiency or carcass composition in nursery pigs.

Determining an optimum lysine:calorie ratio for barrows and gilts in a commercial finishing facility.

Our objective was to determine an optimum Lys:calorie ratio (g of total dietary Lys/Mcal of ME) for 35- to 120-kg barrows and gilts (Pig Improvement Company, L337 x C22) in a commercial finishing environment. Seven (3 barrow and 4 gilt) trials were conducted using randomized complete block designs (42 pens per trial, a total of 7,801 pigs). Six treatments with increasing Lys:calorie ratio were used in each study. Diets were corn-soybean meal-based with 6% choice white grease. Lysine:calorie ratios were attained by adjusting the amount of corn and soybean meal. No crystalline Lys was used. In barrow trial 1 (43 to 70 kg), increasing the Lys:calorie ratio (2.21, 2.55, 2.89, 3.23, 3.57, and 3.91) increased (quadratic, P < 0.01) ADG, G:F, income over feed costs (IOMFC), and feed cost per kilogram of gain, and decreased (linear, P < 0.01) backfat. In barrow trial 2 (69 to 93 kg), increasing the Lys:calorie ratio (1.53, 1.78, 2.03, 2.28, 2.53, and 2.78) improved (linear, P < 0.01) ADG, G:F, and IOMFC, and decreased (quadratic, P < 0.01) backfat. In barrow trial 3 (102 to 120 kg), increasing the Lys:calorie ratio (1.40, 1.60, 1.80, 2.00, 2.20, and 2.40) increased (linear, P < 0.03) ADG and G:F, and numerically improved (linear, P = 0.12) IOMFC. In gilt trials 1 (35 to 60 kg), 2 (60 to 85 kg), and 3 (78 to 103 kg), increasing the Lys:calorie ratio (2.55, 2.89, 3.23, 3.57, 3.91, and 4.25; 1.96, 2.24, 2.52, 2.80, 3.08, and 3.36; and 1.53, 1.78, 2.03, 2.28, 2.53, and 2.78, respectively) improved (quadratic, P < 0.04) ADG, G:F, IOMFC, and feed cost per kilogram of gain, and decreased (linear, P < 0.01) backfat. In gilt trial 4 (100 to 120 kg), increasing the Lys:calorie ratio (1.40, 1.60, 1.80, 2.00, 2.20, and 2.40) improved (linear, P < 0.02) ADG, G:F, LM depth, IOMFC, and (quadratic, P < 0.06) feed cost per kilogram of gain. These studies suggest that feed cost per kilogram of gain decreases, and reductions in biological performance and IOMFC are rather modest when feeding marginally Lys-deficient diets early (35 to 70 kg) in the grower-finishing period compared with the more severe penalties in growth and economic performance of feeding marginally deficient diets in the late finishing period (70 kg to slaughter). The equations (Lys:calorie ratio = -0.0133 x BW, kg, + 3.6944 and = -0.0164 x BW, kg, + 4.004, for barrows and gilts, respectively) best describe our interpretation of the Lys:calorie ratio that met biological requirements and optimized IOMFC on these pigs (PIC, L337 x C22; 35 to 120 kg) in this commercial finishing environment.

Effect of sow parity and weight at service on target maternal weight and energy for gain in gestation.

The objective of this study was to evaluate targeted maternal weight gains in sows by parity group during gestation. Weight and backfat gains during gestation by parity, weight, and backfat groups also were analyzed. The data evaluated were a subset (374 sows) of a larger experiment that compared three methods of feeding sows during gestation on weight and backfat gains and subsequent reproductive performance. Feed allowances were based on modeled calculations of energy and nutrient requirements to achieve target sow maternal weight and backfat gains. Actual backfat gain for gilts and sows was regressed on maternal weight gain and estimated energy available for gain. The regression equations were then used to predict maternal weight gains for target backfat gains for three parity groups (gilts, Parity 1 and 2 sows, and Parity 3 and older sows). For gilts and Parity 1 and 2 sows, much greater target maternal weight gains are required to achieve 6 and 9 mm of backfat gain, whereas Parity 3 and older sows require maternal weight gains similar to those targeted to achieve the desired backfat gain. Given similar energy intake levels above maintenance, gilts gained more weight than multiparous sows, as gain was based more on protein and less on fat and thus was more efficient. Gilts required more maternal weight gain than sows to achieve similar backfat gains due to the higher protein and low fat contents of gain in younger, lighter sows compared with older parity sows. Low-backfat sows that needed to gain large amounts of backfat failed to achieve these large gains. We speculate this failure may be due to lower tissue insulation levels with the low backfat levels and higher activity levels of these sows compared with high-backfat sows. It seems that both parity and weight are individually important factors that influence energy and nutrient requirements for gestation in the modern sow.

Comparison of three methods of feeding sows in gestation and the subsequent effects on lactation performance.

A total of 684 sows from breeding groups over 6 wk was used to compare three methods of feeding during gestation on gestation and lactation performance. Control gilts and sows were fed according to body condition based on a scale of 1 to 5 (1 = thin, 5 = fat). Sows were visually assessed for body condition at breeding and were assigned a daily feed allowance to achieve a BCS of 3 at farrowing. Treatment 2 used feeding levels based on backfat thickness (measured between d 0 and 5 after breeding) and weight at weaning for sows or service for gilts. Feed allowance was calculated to achieve a target backfat of 19 mm at farrowing, and remained constant from d 0 to 101 of gestation. Feed allowances were based on modeled calculations of energy and nutrient requirements to achieve target sow maternal weight and backfat gains. Treatment 3 was identical to Treatment 2, except that feeding pattern was altered for thin sows and gilts (<15 mm at service) in an attempt to reach 19 mm by d 36 of gestation. Sows were weighed at the previous weaning, and gilts were weighed at service, with both weighed again between d 112 and 114 of gestation. Backfat was measured between d 0 and 5, and again between d 108 and 113 of gestation. At farrowing, sows on Treatments 2 and 3 had 19 and 19.1 mm of backfat, respectively, whereas control sows tended to have greater (P < 0.07) backfat (20 mm). On average, sows targeted to gain 6 to 9 mm of backfat failed to reach target gains regardless of feeding method. Feeding sows in gestation based on backfat (Treatments 2 and 3) resulted in a numerically higher proportion of sows in the target backfat range of 17 to 21 mm (40.2, 53.3, and 52.6% for control and Treatments 2 and 3, respectively) at farrowing and a numerically lower percentage of fat sows (>21 mm), but no difference in the percentage of thin sows (<17 mm) compared with feeding based on body condition. In conjunction with this observation, sows fed based on BCS were fed higher (P < 0.05) feeding levels in gestation than were sows fed based on backfat depth. Gestation feeding method had no effect on performance during lactation. Feed intake in lactation was lower (P < 0.05) for high backfat sows (>21 mm) at farrowing compared with sows with <21 mm. The high proportion of sows in the optimal backfat category demonstrates that feeding based on backfat and BW has potential for facilitating more precise feeding during gestation.

Increasing weaning age improves pig performance in a multisite production system.

Two trials were conducted to determine the effects of weaning age on pig performance in a multisite production system. The second trial also evaluated the effects of modifying the nursery feeding program according to weaning age. In Trial 1 (2,272 pigs), treatments included weaning litters at 12, 15, 18, or 21 d of age. In Trial 2 (3,456 pigs), litters were weaned at 15, 16, 18, 19, 21, or 22 d of age and categorized into three treatments (15.5, 18.5, or 21.5 d of age). In Trial 2, pigs in each age group were fed one of two nursery feeding programs. Nursery feeding programs varied in both diet formulation and in the quantity of diets fed containing increased levels of whey and spray-dried animal plasma. Each trial was conducted as a randomized complete block design with four blocks of nursery and finishing sites. All weaning-age treatments were weaned from a 7,300-sow farm on the same day into the same nursery. Each block remained intact as pigs moved from nursery to finishing site. Increasing weaning age (12, 15, 18, or 21 d in Trials 1; and 15.5, 18.5, or 21.5 d in Trial 2) increased (linear, P < 0.001) ADG (299, 368, 409, 474 +/- 7 g/d; 435, 482, 525 +/- 13 g/d) and tended to decrease (linear, P < 0.09) mortality (5.25, 2.82, 2.11, 0.54 +/- 0.76%; 2.17, 1.56, 1.30 +/- 0.36%) in the initial 42 d after weaning. Finishing ADG (722, 728, 736, 768 +/- 11 g/d; 783, 790, 805 +/- 11 g/d) also improved (linear, P < 0.01) with increasing weaning age. Overall, increasing weaning age increased (linear, P < 0.001) wean-to-finish ADG (580, 616, 637, 687 +/- 8 g/d; 676, 697, 722 +/- 6 g/d), weight sold per pig weaned (94.1, 100.5, 104.4, 113.1 +/- 1.3 kg; 107.6, 111.6, 116.2 +/- 1.1 kg), and decreased (linear, P < 0.03) mortality rate (9.4, 7.9, 6.8, 3.6 +/- 0.95%; 3.9, 3.4, 2.5 +/- 0.5%). Altering the nursery feeding program did not affect wean-to-finish growth performance. In this multisite production system, increasing weaning age from 12 to 21.5 d of age increased weight sold per pig weaned by 1.80 +/- 0.12 kg for each day increase in weaning age. These studies suggest increasing weaning age up to 21.5 d can be an effective management strategy to improve wean-to-finish growth performance in multisite pig production.