Multiple antibiotic resistance in fecal, cecal and colonic coliforms from pigs fed therapeutic and subtherapeutic concentrations of chlortetracycline

Multiple resistance and antibiotic resistance were examined in coliforms isolated at slaughter from the large intestines of two groups of growing pigs that had received antibiotic-free diets since weaning. One group of pigs was from an antibiotic-fed (AB) herd that routinely received chlortetracycline (CTC) in feed, while the other group was from a nonantibiotic-fed (NAB) herd that had not received antibiotics for 8 yr. After a 20-d adjustment period in a common production facility, the mean number of antibiotics in the resistant pattern of isolates from NAB pigs was found to be lower (P less than .05) than that in isolates from AB pigs. The proportions of isolates resistant to ampicillin, kanamycin, neomycin, penicillin, streptomycin and sulfamethizole were lower (P less than .05) in NAB pigs than in AB pigs. Similar herd differences were not observed after pigs from both herds were maintained in a common production facility on an antibiotic-free diet for 105 d. Oral administration of CTC at therapeutic (220 micrograms/g of diet) and at subtherapeutic (27.5 micrograms/g) levels for 14 d increased (P less than .05) the mean numbers of antibiotics in the resistance patterns of isolates from NAB pigs, but did not alter multiple resistance in isolates from AB pigs. After 14 d, subtherapeutic CTC increased the percentage of isolates resistant to ampicillin, kanamycin, penicillin, streptomycin, tetracycline and sulfamethizole, while therapeutic CTC only increased the percentage of isolates from NAB pigs resistant to penicillin, tetracycline and sulfamethizole. Similar antibiotic effects were not seen in isolates from AB pigs after 14 d and were not seen in isolates from either group of pigs at the end of an 85-d feeding trial.     

Antibiotic resistance of fecal coliforms from swine fed subtherapeutic and therapeutic levels of chlortetracycline

The effect of feeding subtherapeutic (27.5 micrograms/g of diet for 85 d) and therapeutic (220 micrograms/g of diet for 14 d, followed by an antibiotic-free diet for 71 d) levels of chlortetracycline (CTC) on the antibiotic resistance of fecal coliforms of pigs from two herds (36 pigs/herd) with different histories of antibiotic exposure when housed in a newly constructed confinement facility was determined. The CTC-resistant coliforms were higher (65 vs 51%) for antibiotic (AB) pigs than for nonantibiotic (NAB) pigs after they had been fed an antibiotic-free diet for 21 d. Percentages of isolates resistant to ampicillin, kanamycin, neomycin and tetracycline and multiple antibiotic resistance were greater (P less than .05) in AB pigs after 21 d. Feeding subtherapeutic CTC resulted in a linear increase in CTC-resistant coliforms with time on experiment (P less than .03, NAB; P less than .06, AB). The CTC-resistant coliforms increased during the 14 d that therapeutic CTC was fed, then they decreased during the 71 d that the antibiotic-free diet was fed, resulting in a quadratic response with time (P less than .03, AB). Feeding subtherapeutic CTC resulted in a greater increase in CTC-resistant coliforms in AB (47%) than in NAB (23%) pigs. The CTC-resistant coliforms decreased after the therapeutic group had been returned to the antibiotic-free diet (P less than .05, NAB). Feeding CTC caused greater changes in the precentages of isolates from NAB pigs that were resistant to selected antibiotics and in multiple antibiotic resistance than in isolates from AB pigs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Differences in antibiotic resistance in Escherichia coli,isolated from East-European swine herds with or without prophylactic use of antibiotics

The aim of the study was to compare the resistance patterns of Escherichia coli isolates from pig herds with or without prophylactic use of anti-microbial substances. The presented pig units received either antibiotics or oregano as preventive feed additives. The trial was performed from April to October 2001, in the large 'country-corner', Hungary-Rumania-Serbia. Thirty of 39 evaluated herds suffered E. coli O139 K88 ac or ad LT STb caused losses, the remaining were negative for E. coli O139. Thirteen of the selected 30 herds produced with oregano feed supplementation (Oregpig Pecs, Hungary) antibiotic-free pigs. These units had no history of prophylactic antibiotic use since 1995. The remaining 17 herds routinely used prophylactic antibiotic feed supplementation. In each herd, pigs of four different age groups (suckling piglets, weaners. fattening swine and breeding sows), showing the clinical symptoms of wasting, were investigated. E. coli O139 K88 ac or ad LT STb were tested for their resistance to antibiotics, available in this region. Oregano-fed herds demonstrated high significantly (P < 0.001) lower MICs (microg/ml) for ampicillin, doxycyclin, enrofloxacin, gentamycin, oxytetracyclin and sulfamethacin compared to herds with prophylactic use of antibiotics. Resistance to ceftiofur revealed significant (P < 0.05) differences between the antibiotic- or oregano-treated units. The present results confirm literature data, that prophylactic use of antibiotics likely plays a role in inducing resistance of E. coli and other intestinal bacteria. Thus, imposing greater restrictions on antibiotic use in animal agriculture is likely to reduce but not eliminate the occurrence of resistant isolates.     

日粮添加罗伊氏乳杆菌LR1对猪常见病毒疫苗免疫效果的影响

试验利用前期筛选的猪源罗伊氏乳杆菌LR1全程替代饲用抗生素,旨在研究其对猪常见病毒疫苗免疫效果的影响。试验选取144头21日龄杜洛克×长白×大白断奶仔猪,随机分为3组,每组8个重复,每个重复6头猪。对照组（CON）饲喂基础日粮,抗生素组（OA）饲喂基础日粮+100 mg/kg喹乙醇+75 mg/kg金霉素（抗生素在第120天停用）,益生菌组（LR1）饲喂基础日粮+5×10¹⁰ CFU/kg罗伊氏乳杆菌LR1,试验周期166 d。试验所有猪根据统一免疫程序进行疫苗免疫,并于试验开始第14、42、120、127、134、166天检测猪血清中猪繁殖与呼吸综合征病毒（PRRSV）、猪瘟病毒（HCV）、猪口蹄疫病毒（FMDV）、伪狂犬病毒（PRV）、细小病毒（PPV）抗体水平以及血清中IgG含量。结果表明：①与对照组和抗生素组相比,益生菌组第14天血清中口蹄疫抗体水平显著提高（P<0.05）;②与对照组相比,益生菌组和抗生素组第120天血清中的细小病毒抗体水平均显著提高（P<0.05）;③益生菌组第166天血清中的猪繁殖与呼吸综合征病毒抗体水平显著高于对照组（P<0.05）,且益生菌组第166天血清中的猪瘟抗体水平显著高于对照组和抗生素组（P<0.05）。综上所述,日粮添加罗伊氏乳杆菌LR1在一定程度上能够提高猪常见病毒疫苗免疫后的抗体水平,提示其不仅可以作为饲用抗生素的潜在替代品,同时在预防和治疗猪病毒性疾病方面具有应用前景。     

The Effect of Chlortetracycline Feed Additive on the Antibiotic Resistance of Fecal Coliforms of Weaned Pigs Subjected to Experimental Salmonella Infection

The effect of chlortetracycline fed at concentrations of 10 or 20 grams per ton on the antibiotic resistance of fecal coliforms from weaned pigs from four different farms was studied. At admission to experimental quarters, coliforms resistant to at least one antibiotic predominated in all groups of animals.

In pigs from three farms, chlortetracycline caused a reduction in the proportion of sensitive coliforms excreted, the extent of reduction depending on feeding practices on the farm of origin. In another experiment using pigs from a fourth farm, almost all coliforms isolated were resistant.

Of all resistant strains isolated, those carrying resistance to a multiplicity of antibiotics predominated, and resistance to tracycline unaccompanied by that to other agents was relatively infrequent.

Special studies of hemolytic coliforms from pigs from one farm identified two particular antibiotic sensitive types. No further isolations of these types were made once chlortetracycline administration began although 21 additional isolates were made from littermates receiving unsupplemented ration.

These findings suggest that the elimination of sensitive strains resulting from chlortetracycline administration was due to a replacement of these strains by different resistant types rather than by acquisition of resistance by previously sensitive strains.

     

Influence of antibiotics used as feed additives on the immune effect of erysipelas live vaccine in swine

To investigate the influence of antibiotics used as feed additives on the immune response to erysipelas live vaccine, the pig inoculation test was applied. Avilamycin, oxytetracycline quaternary salt, enramycin, virginiamycin and tylosin phosphate were selected as test antibiotics. Five experimental feeds containing each antibiotic at the highest concentration permitted for feed additives in Japan, and the basal diet lacking antibiotics were examined. Twenty-nine pigs were divided into six groups. At first all the groups were fed with the antibiotic-free basal diet for 7 days, and then each group received the experimental feeds. On the 14th day after feeding with test feeds all the pigs, except for one control pig in each group, were immunized with the vaccine and all the pigs were then challenge-exposed to a virulent strain of Erysipelothrix rhusiopathiae 14 days after vaccination. The clinical response was observed every day for 14 days. In all the groups, most of the vaccinated pigs did not develop any clinical signs of acute erysipelas after the challenge exposure, whereas non-vaccinated control pigs died or showed severe generalized erythema with profound depression and anorexia. No differences in the protection against the challenge exposure were observed among the groups. Therefore, the present results suggest that these selected antibiotics would not interfere with the immune effect of the vaccine if given at the usual concentrations used for feed additives.     

Use of chlortetracycline for treatment of new feedlot cattle

Two 56-d shipping fever trials of similar design were conducted the same season (fall) at Kansas State University (KSU) and at Purdue University (PU) to compare various levels of chlortetracycline (0 or 350 mg X head-1 X d-1 continuously or 1, 2 or 4 g X head-1 X d-1 for the first 14 d). Weanling crossbred steer calves were utilized (210 head of Angus X Simmental, averaging 197 kg, at KSU; 268 head of Angus X Hereford, averaging 192 kg, at PU). For the first 28 d in the KSU trial (October 13 to December 8), cattle that received 4 g X head-1 X d-1 the first 14 d gained more rapidly (P less than .05) than cattle fed 350 mg X head-1 X d-1 continuously or than the controls that received no chlortetracycline (CTC; 1.05 vs .92 or .93 kg/d, respectively). Cattle that received 4 g CTC X head-1 X d-1 for the first 14 d required less (P less than .05) dry matter per kg gain than steers that received 350 mg X head-1 X d-1 continuously over the 56-d period. In the PU trial (October 6 through December 1), all CTC treatments resulted in increased feed efficiency (P less than .05) over the controls through 28 d, and the 4 g X head-1 d-1 for 14 d and 350 mg X head-1 X d-1 continuously, improved feed efficiency over the other groups for the 56-d period.(ABSTRACT TRUNCATED AT 250 WORDS)     

罗伊氏乳酸杆菌LR1对猪蛋白消化酶基因表达、肌肉抗氧化指标及氨基酸组成的影响

试验旨在研究长期饲喂罗伊氏乳酸杆菌LR1（Lactobacillus reuteri 1）对猪胃及胰腺蛋白消化相关酶的基因表达、肌肉抗氧化指标及冰鲜肉氨基酸谱的影响。选用144头（杜×长×大）21日龄断奶仔猪（平均体重6.49 kg±0.04 kg）,随机分为3组。对照组饲粮为基础饲粮,抗生素组饲粮为添加抗生素的基础饲粮（仔猪阶段添加100 mg/kg喹乙醇和75 mg/kg金霉素,生长肥育猪阶段添加75 mg/kg金霉素）,LR1组饲粮为添加5×10¹⁰ CFU/kg LR1的基础饲粮,试验期175 d。结果表明：与对照组相比,①抗生素组猪胰腺中弹性蛋白酶的表达降低（P<0.05）;LR1组胃窦、胃贲门及胃底黏膜中胃蛋白酶A的表达提高（P<0.05）,同时也高于抗生素组（P<0.05）。②抗生素组猪背最长肌（longissimus dorsis muscle,LDM）总抗氧化能力（total antioxidant capacity,T-AOC）及总超氧化物歧化酶（total superoxide dismutase,T-SOD）活力增加（P<0.05）;LR1不影响LDM中丙二醛（malondialdehyde,MDA）含量,T-AOC、T-SOD及谷胱甘肽过氧化物酶（glutathione peroxidase,GSH-Px）活力（P>0.05）。③饲粮添加抗生素及LR1不影响冰鲜肉水解氨基酸含量及组成（P>0.05）;抗生素组24 h冰鲜肉中甲硫氨酸（苦味氨基酸）含量、甜味氨基酸总量及游离氨基酸总量降低（P<0.05）,而LR1降低24 h冰鲜肉中甲硫氨酸含量（P<0.05）;饲粮中添加抗生素及LR1均降低48 h冰鲜肉中甜味氨基酸、苦味氨基酸、必需氨基酸及总游离氨基酸（P<0.05）,同时,抗生素组48 h冰鲜肉中鲜味氨基酸含量降低（P<0.05）。综上,与对照组相比,长期饲喂LR1可提高猪胃对蛋白质的消化功能,改善24 h冰鲜肉的风味;而长期饲喂抗生素降低猪胰腺的消化功能,提高肌肉抗氧化能力,但降低24及48 h冰鲜肉的风味。     

Effect of feeding chlortetracycline or virginiamycin on shedding of salmonellae from experimentally-infected swine

Swine from a herd routinely fed subtherapeutic levels of chlortetracycline (CTC) were fed a diet containing 55 mg of CTC/kg, a diet containing 55 mg of virginiamycin/kg, or a control diet. All animals were inoculated with Salmonella typhimurium that was susceptible to tetracycline. The quantity, duration and prevalence of shedding of S. typhimurium were determined. The infecting organism was first recovered from the animals fed CTC or the control diet on d 2, from animals fed virginiamycin on d 7 and from animals in a second control group on d 10. The infecting organism was recovered in fewer samples obtained during the initial 7 d postinfection than in those obtained during the last 24 d of the study. Little transfer of resistance to the infecting organism seemed to have occurred from the resident microflora because only two isolates (1%) had resistant patterns that differed from that of the infecting organism. Feeding CTC or virginiamycin to swine did not significantly increase or prolong shedding of an experimentally infected tetracycline-susceptible strain of S. typhimurium. Neither antibiotic affected the drug resistance of the infecting organism.     

Effect of chlortetracycline on the spread of R-100 plasmid-containing Escherichia coli BEL15R from experimentally infected pigs to uninfected pigs and chicks

Swine from two herds with different histories of antibiotic exposure were fed diets containing 0 or 55 mg of chlortetracycline (CTC)/kg. One of five pigs in each herd-diet treatment group was infected orally with Escherichia coli strain BEL15R that was resistant to nalidixic acid (NA), chloramphenicol (C), streptomycin (S), sulfamethizole (TH) and tetracycline (TE). Effects of CTC on the quantity and duration of fecal shedding of E. coli BEL15R and on the transmission of strain BEL15R and its R-100 plasmid from infected pigs to uninfected pigs and chicks were determined. Quantity and duration of shedding were greater in infected antibiotic-herd pigs than in infected nonantibiotic-herd pigs. Feeding on CTC increased the duration of shedding in infected pigs from both herds. Strain BEL15R colonized and was shed in one uninfected antibiotic pig in each treatment group, but it did not colonize in any of the uninfected nonantibiotic-herd pigs or in the uninfected chicks. In vivo transfer of resistance to C, S, TH and TE occurred in the infected antibiotic-herd pigs but not in the infected nonantibiotic-herd pigs. Transfer of the R-100 plasmid occurred from the infected to the uninfected antibiotic-herd pigs and to the uninfected chicks housed near the antibiotic-herd pigs fed CTC, but not to the chicks housed with the antibiotic-herd pigs fed the control diet. No transfer of resistance occurred from the infected nonantibiotic-herd pigs fed either CTC or control diet.     

Effect of potential multimicrobe probiotic product processed by high drying temperature and antibiotic on performance of weanling pigs

In this study, the effect of a potential multimicrobe probiotic subjected to high-temperature drying was investigated. Potential multimicrobe probiotics produced by solid substrate fermentation were dried at low (LT, 40°C for 72 h) or high (HT, 70°C for 36 h) temperature. In Exp. 1, 288 weaned pigs (BW, 6.43 ± 0.68 kg) were allotted to 4 treatments on the basis of BW (4 pens per treatment with 18 pigs in each pen). Dietary treatments were negative control (NC; basal diet without any antimicrobial), positive control (PC; basal diet + 0.1% chlortetracycline), basal diet with 0.3% probiotic LT, and basal diet with 0.3% probiotic HT. Diets were fed in 2 phases, phase I (d 0 to 14) and phase II (d 15 to 28); and growth performance, apparent total tract digestibility (ATTD, d 28), and fecal microflora (d 14 and 28) were evaluated. Over the 28-d trial, pigs fed PC and probiotic diets had greater ADG (P < 0.001), ADFI (P < 0.05), and G:F (P < 0.01) than pigs fed NC diet. The ATTD of DM and GE was greater (P < 0.05) in pigs fed probiotic diets when compared with pigs fed the NC diet. At d 28, fewer Clostridia (P < 0.01) were identified in the feces of pigs fed PC and probiotic diets than pigs fed the NC diet. However, the performance, ATTD of DM and GE, and fecal Clostridia population were similar among pigs fed probiotic LT and HT diets. In Exp. 2, 288 weaned pigs (initial BW, 5.84 ± 0.18 kg) were allotted to 4 treatments in a 2 × 2 factorial arrangement on the basis of BW. The effects of 2 levels of probiotic HT (0.30 or 0.60%), each with or without antibiotic (chlortetracycline, 0 or 0.1%), on performance, ATTD, intestinal morphology, and fecal and intestinal microflora were investigated. Feeding of 0.60% probiotic HT diet improved (P < 0.05) overall ADG, ATTD of DM and GE, and Lactobacillus population in the feces and intestine, and reduced the population of Clostridium and coliforms in feces (d 14) and ileum. Inclusion of antibiotic improved (P < 0.05) the overall ADG, ADFI, and ATTD of DM at d 14 and reduced fecal Clostridium population at d 28. Increased (P < 0.05) villus height at jejunum and ileum, and villus height:crypt depth at the ileum was noticed in pigs fed 0.60% probiotic HT and antibiotic diets. In conclusion, high drying temperature had no effect on the efficacy of potential multimicrobe probiotic product. However, the probiotic product dried at high temperature was more effective at 0.60% inclusion, whereas inclusion of an antibiotic improved pig performance but did not show any interaction with probiotics.     

Effects of tylosin feeding on the antibiotic resistance of selected gram-positive bacteria in pigs

The effect of tylosin on macrolide resistance of gram-positive bacteria of pigs was determined. After an initial base-line period during which the pigs were given antibiotic-free feed, 1 group of 8 pigs was given tylosin feed (100 g/US ton of feed), and a 2nd group of 7 was given antibiotic-free feed. Samples were taken at 2- to 3-week intervals. For each pig, rectal, skin, and nasal swab samples were collected for enumeration of fecal streptococci and skin and nasal staphylococci. Percentages of macrolide resistant organisms of each group were tabulated on the basis of colony counts from antibiotic free and erythromycin-containing plates. After the introduction of tylosin into the feed of 1 group, a clear difference between the 2 groups with respect to the macrolide resistance of their gram-positive microflora was observed. The data indicate that tylosin feeding results in an increase in macrolide resistance of the bacterial flora of pigs.     

Evaluation of site and age of weaning on pig growth performance

Site-segregated early weaning (SSEW) refers to the practice of weaning pigs from the sow at an early age and placing them in a nursery that is physically isolated from the breeding herd. An experiment involving 369 pigs was conducted at the Prairie Swine Center to investigate the impact of SSEW on pig performance when the herd of origin has a high health status and when housing and management conditions are kept as similar as possible across weaning regime. Three treatments were compared: weaning at 21+/-3 d and keeping the pigs on-site in an all-in-all-out nursery room (Control), weaning at 12+/-2 d of age and keeping the pigs on-site in a separate but identical all-in-all-out nursery room (OSEW), or weaning at 12+/-2 d of age and moving the pigs off-site to an all-in-all-out nursery room located 16 km from the Center (SSEW). Ventilation, feed, penning, feeders, and drinkers were kept as similar as possible for all treatments. Off-site weaning improved 56-d body weight (P < .05) by 12.5 and 8.3% compared with OSEW and Control, respectively. The improvement appeared to be the result of improvements primarily in feed intake but also due to enhanced efficiency of nutrient utilization. This experiment confirms that SSEW results in significant improvements in 56-d weights, even when the herd of origin has a relatively high health status.     

Antimicrobial resistance of fecal coliforms from pigs in a herd not exposed to antimicrobial agents for 126 months

Patterns of antimicrobial resistance were determined for lactose-fermenting fecal coliforms obtained during a 20-month period from pigs in a herd without exposure to antimicrobial drugs for 126 months. Mean percent resistance to cephalothin, chloramphenicol, kanamycin, naladixic acid, streptomycin and tetracycline was lower (P less than 0.01) for isolates obtained during the 20-month period (Group 2) than for isolates obtained during the first 13 months (Group 1) after the withdrawal of antibiotics. Mean tetracycline resistance was 40.5% for Group 2 isolates. Approximately 44% of the Group 2 isolates were resistant to the 10 antimicrobial agents compared with 74.9% for the Group 1 isolates (P less than 0.01). Multiple resistance was lower (P less than 0.01) in the Group 2 isolates than in the Group 1 isolates. Four resistance patterns (tetracycline, tetracycline-streptomycin, tetracycline-sulfisoxazole, tetracycline-streptomycin-sulfisoxazole) accounted for 74% of the resistant isolates.     

Differences in Antibiotic Resistance in Escherichia coli,Isolated from East‐European Swine Herds With or Without Prophylactic Use of Antibiotics

The aim of the study was to compare the resistance patterns of Escherichia coli isolates from pig herds with or without prophylactic use of anti‐microbial substances. The presented pig units received either antibiotics or oregano as preventive feed additives. The trial was performed from April to October 2001, in the large ‘country‐corner’, Hungary–Rumania–Serbia. Thirty of 39 evaluated herds suffered E. coli O139 K88 ac or ad LT STb caused losses, the remaining were negative for E. coli O139. Thirteen of the selected 30 herds produced with oregano feed supplementation (Oregpig^® Pecs, Hungary) antibiotic‐free pigs. These units had no history of prophylactic antibiotic use since 1995. The remaining 17 herds routinely used prophylactic antibiotic feed supplementation. In each herd, pigs of four different age groups (suckling piglets, weaners, fattening swine and breeding sows), showing the clinical symptoms of wasting, were investigated. E. coli O139 K88 ac or ad LT STb were tested for their resistance to antibiotics, available in this region. Oregano‐fed herds demonstrated high significantly (P < 0.001) lower MICs (μg/ml) for ampicillin, doxycyclin, enrofloxacin, gentamycin, oxytetracyclin and sulfamethacin compared to herds with prophylactic use of antibiotics. Resistance to ceftiofur revealed significant (P < 0.05) differences between the antibiotic‐ or oregano‐treated units. The present results confirm literature data, that prophylactic use of antibiotics likely plays a role in inducing resistance of E. coli and other intestinal bacteria. Thus, imposing greater restrictions on antibiotic use in animal agriculture is likely to reduce but not eliminate the occurrence of resistant isolates.     

Streptococcal meningitis in pigs: field trial to study the prophylactic effect of trimethoprim/sulphadiazine medication in feed

Half the progeny in a 200-sow herd (2045 pigs) was given feed medicated with 500 g/tonne of a 1:5 trimethoprim/sulphadiazine mixture from three to nine weeks of age. The other half (1989) acted as controls. The trial lasted 12 months. No difference was observed between the two groups in the incidence of streptococcal meningitis and the morbidity and mortality from all disease causes during the growing/fattening periods did not differ significantly. The main diseases encountered were pneumonia (7.24 per cent), streptococcal meningitis (5.12 per cent), leg and foot disorders (3.34 per cent) and the after-effects of vices (1.86 per cent). The resistance of faecal coliforms to trimethoprim was studied during the six-week period of trimethoprim/sulphadiazine feeding. Faecal coliforms in both medicated and non-medicated groups developed almost 100 per cent resistance. However, resistance developed more slowly in the untreated pigs. The medicated pigs showed a small overall improvement in feed conversion rate up to 18 weeks of age mainly because of a marked improvement between three and six weeks.     

Effects of frequent out-of-feed events on growth performance of nursery and grow-finish pigs

Two experiments were conducted to evaluate effects of out-of-feed events on nursery and grow-finish pig performance. An out-of-feed event is a period of time that pigs do not have access to feed as a result of late feed delivery or bridging in bulk bins, feed lines, or feeders. In these studies, we created an out-of-feed event by removing the feeders from pens or preventing access to the feeder. In Exp. 1, 190 pigs (initially 6.4 +/- 1.6 kg and 21 +/- 3 d of age) were used in a 35-d growth study. Treatments involved a 20-h feed withdrawal for 1, 2, or 3 randomly selected times or a control treatment where feeders were never withdrawn. Feeders were withdrawn on d 11 for pigs with 1 out-of-feed event, d 8 and 23 for pigs with 2 out-of-feed events, and d 9, 14, and 20 for pigs with 3 out-of-feed events. There was a treatment (P < 0.06) effect only during weeks in which an out-of-feed event occurred. Growth rate was lower (P < 0.05) for pigs with 1 out-of-feed event (d 11) compared with control in the d 8 to 14 period. During the same period, those pigs with the first of 2 (d 8) or 3 (d 9) out-of-feed events had intermediate ADG. In the d 15 to 21 period, only pigs with the second and third of 3 out-of-feed events (d 15 and 20) had lower growth performance compared with control pigs, whereas growth performance was similar to the control for those with 1 or 2 out-of-feed events. Pigs with 3 out-of-feed events had greater ADG and G:F (P < 0.05) compared with the other 3 treatments for the d 22 to 28 period. For the overall study (d 0 to 35), there were no differences (P > 0.86) in growth performance among pigs with 0, 1, 2, or 3 out-of-feed events. In Exp. 2, 479 pigs (initially 41.6 +/- 4 kg) were used in an 85-d growth study. Treatments involved feed withdrawal (20 h) weekly for the duration of the study; feed withdrawn weekly from d 45 to 85; or a control treatment where pigs had access to feed for the duration of the experiment. Feed withdrawal occurred on a randomly selected day with the exception of Saturday, Sunday, or a day before a weigh day (usually a Thursday every other week). From d 0 to 45, 46 to 85, and the overall d 0 to 85 period, there were no differences (P > 0.12) in ADG, ADFI, G:F, or average final BW among treatments. Results suggest that out-of-feed events of 20 h or less have no long-term detrimental effects on growth performance in nursery or grow-finish pigs.     

Relationship between weaning age and antibiotic usage on pig growth performance and mortality

A total of 2,184 pigs (DNA 600 × PIC L42) were used to evaluate the effects of weaning age and antibiotic (AB) use on pig performance from weaning to marketing in a commercial production system. Experimental treatments were arranged in a 3 × 2 factorial with main effects of weaning age (18.5, 21.5, or 24.5 d of age) and with the use of ABs or an antibiotic-free (NAE) program. At birth, pigs were ear tagged, and the date of birth and sex recorded. Pigs were weaned from a 4,000-sow farm over four consecutive weeks. Four weaning batches (one per week) of 546 pigs were used. Each weaning batch had one-third of pigs of each weaning age. Pigs were placed in pens by weaning age and then randomly assigned to an AB or NAE program. There were 14 replicate pens per treatment and 26 pigs per pen (13 barrows and 13 gilts). Pigs allocated to the AB program were fed a diet containing 441 mg/kg chlortetracycline (CTC) from day 8 to 21 postweaning. They were also administered 22 mg/kg of body weight (BW) of CTC via drinking water for five consecutive days after a porcine respiratory and reproductive syndrome outbreak during week 7 after weaning. In the first 42 d postweaning, increasing weaning age improved (linear, P < 0.001) BW at day 42, average daily gain (ADG), and average daily feed intake (ADFI). From weaning to 197 d of age, increasing weaning age increased (linear, P < 0.001) ADG and ADFI. Pigs on the AB program had greater (P = 0.031) ADG and ADFI compared with NAE pigs. An interaction (linear, P = 0.005) was observed for feed efficiency (G:F). When ABs were provided, increasing weaning age did not result in any change in G:F; however, in the NAE program, increasing weaning age increased G:F. Pigs on the AB program had lower (P < 0.001) total losses (mortality and removals) than those on the NAE program. Increasing weaning age marginally (linear, P = 0.097) decreased total losses. Increasing weaning age decreased (quadratic, P < 0.001) the number of pigs treated with an injectable AB but the AB program did not (P = 0.238). The weight sold (at 197 d of age) per pig weaned was increased (linear, P = 0.050) by increasing weaning age and by using AB in feed and water (P = 0.019). In summary, increasing weaning age linearly improved most of the pig performance criteria and relatively the short-term use of ABs reduced mortality and removals with both factors contributing to increased weight sold per pig weaned.     

Granulated lysozyme as an alternative to antibiotics improves growth performance and small intestinal morphology of 10-day-old pigs

Lysozyme is a 1,4-β-N-acetylmuramidase that has antimicrobial properties. The objective of this experiment was to determine the effect of a purified granulated lysozyme, compared with antibiotics, on growth performance, small intestinal morphology, and Campylobacter shedding in 10-d-old pigs. Forty-eight pigs (n = 16 per treatment), with an initial BW of 4.0 ± 0.1 kg (P > 0.40), were weaned at 10 d of age, blocked by litter and sex, and assigned to pens (8 pigs/pen). Each block was randomly assigned to consume 1 of 3 liquid dietary treatments for 14 d: a control diet, the control diet + lysozyme (100 mg/kg of diet), or the control diet + antibiotics (neomycin and oxytetracycline, 16 mg/kg of diet). Pigs were weighed and blood was sampled on d 0, 7, and 14. Blood was analyzed for plasma urea N and IgA. After 14 d of treatment, pigs were killed and samples of the jejunum and ileum were collected and fixed to measure villus height and crypt depth. Rectal swabs were taken on d 0, 7, and 14 of treatment, and samples of ileal and cecal contents were taken at d 14 of treatment to determine the presence of Campylobacter. Pigs consuming lysozyme and antibiotics gained BW at a faster rate than did control pigs over the course of the study (402 ± 12 and 422 ± 14 g/d, respectively, vs. 364 ± 14 g/d; P < 0.02), resulting in heavier ending BW (9.9 ± 0.3, 9.9 ± 0.3, and 9.0 ± 0.2 kg for pigs in the lysozyme, antibiotic, and control groups, respectively; P < 0.03). Immunoglobulin A decreased and plasma urea N increased over the course of the study (P < 0.1), regardless of dietary treatment (P > 0.6). Crypt depth was increased in pigs fed lysozyme- and antibiotic-treated diets, compared with pigs fed the control diet, in both the jejunum (60.0 ± 2.8 and 62.2 ± 3.0 μm, respectively, vs. 50.7 ± 3.1 μm; P < 0.03) and ileum (76.0 ± 7.5 and 72.2 ± 5.0 μm, respectively, vs. 52.4 ± 3.5 μm; P < 0.02). Villus height did not differ in the jejunum (P > 0.2) but was increased in the ileum of pigs consuming the lysozyme- and antibiotic-treated diets, compared with pigs fed the control diet (312 ± 20 and 314 ± 10 μm, respectively, vs. 263 ± 15 μm; P < 0.4). Small intestinal total mucosa and mucosal protein concentrations, as well as disaccharidase-specific activities, were not altered by lysozyme or antibiotics (P > 0.05). Campylobacter was detected in 27% of control samples but in only 5% of samples from pigs fed antibiotics and 8% of samples from pigs fed lysozyme (P < 0.01). Thus, granulated lysozyme is a suitable alternative to antibiotics for 10-d-old pigs consuming manufactured liquid diets.     

Antibiotic resistant Escherichia coli in southeastern Australian pig herds and implications for surveillance

To investigate public health implications of antibiotics to control post‐weaning scours, we surveyed 22 commercial pig herds in southeastern Australia. Fifty faecal samples per herd were collected from pre‐ and post‐weaned piglets. Presumptive Escherichia coli isolates were confirmed by MALDI‐TOF MS. Isolates (n = 325) were screened for susceptibility to 19 veterinary antibiotics using MIC broth microdilution. All 325 E. coli isolates underwent further testing against 27 antibiotics used in human medicine and were screened for ETEC adhesin and enterotoxin genes (F4 (K88), F5 (K99), F6 (987P), F18, F41, STa, STb, Stx2e and LT) by multiplex PCR. Isolates identified as phenotypically resistant to third‐generation cephalosporin (3GC) and aminoglycoside antibiotics were screened by multiplex PCR/reverse line blot to detect common β‐lactam and aminoglycosides resistance genes, confirmed by sequencing. Twenty (6.1%) of the E. coli isolates were resistant to 3GC antibiotics and 24 (7.4%) to the aminoglycoside antibiotic gentamicin. Genetic analysis revealed six different extended spectrum β‐lactamase (ESBL) genes (blaCTX‐M‐1, ‐14, ‐15, ‐27, blaSHV‐12 and blaCMY‐2‐like genes), four of which have not been previously reported in Australian pigs. Critically, the prevalence of 3GC resistance was higher in non‐pathogenic (non‐ETEC) isolates and those from clinically normal (non‐diarrhoeal) samples. This highlights the importance of non‐ETECE. coli as reservoirs of antimicrobial resistance genes in piglet pens. Antimicrobial resistance surveillance in pig production focused on diagnostic specimens from clinically‐affected animals might be potentially misleading. We recommend that surveillance for emerging antimicrobial resistance such as to 3GC antibiotics should include clinically healthy pigs.