Effects of dietary β‐(1,3)(1,6)‐D‐glucan supplementation on growth performance,intestinal morphology and haemato‐immunological profile of mirror carp (Cyprinus carpio L.)

In recent years, aquaculture research has focused on probiotics, prebiotics, and β‐glucans, in order to improve health status and growth performance. Information regarding the effects of β‐glucan on growth performance and intestinal immunity of mirror carp (Cyprinus carpio L.) is scarce. An experiment was therefore conducted to investigate the effects of a yeast β‐glucan preparation (MacroGard^®) on growth performance, intestinal morphology and haemato‐immunological indices of mirror carp. Carp (initial weight 11.1 ± 0.0 g) were fed highly purified diets supplemented with 0% (control), 0.1%, 1% or 2% MacroGard^® for 8 weeks. Fish fed diets containing 1% and 2% MacroGard^® showed significant improvements in weight gain, specific growth rate and feed conversion ratio compared to fish fed both the control and the 0.1% MacroGard^® containing diet. Histological appraisal of the intestine showed a significantly higher infiltration of leucocytes into the epithelial layer of fish fed diets supplemented with 1% and 2% MacroGard^® in the anterior intestine compared to fish fed the control and 0.1% MacroGard^® diet. This effect was not observed in the posterior intestine. There were no significant differences in the intestinal absorptive surface area and number of goblet cells in either intestinal region. At the end of the experiment, the haematological status of the fish was examined. Compared to control fed fish, the haematocrit value was significantly elevated in fish fed the 2% MacroGard^® diet. Furthermore, the blood monocyte fraction was significantly higher in fish fed the 1% and 2% MacroGard^® diets. No significant changes were observed in the other blood parameters assessed. The present study shows that high dietary β‐glucan inclusion increases growth performance without detrimental effects on the health indicators assessed. Increased intraepithelial leucocytes in the anterior intestine may indicate a localized immune response; no detrimental effects on intestinal morphology were observed.     

Use of a Mini-Transposon to Study Chondroitinase Activity Associated with Edwardsiella ictaluri

Abstract

Edwardsiella ictaluri, the etiological agent of enteric septicemia of catfish (ESC), is the leading cause of bacterial disease in commercially raised channel catfish Ictalurus punctatus. Little work has been conducted at a genotypic level to determine potential virulence characteristics, but the production of chondroitin sulfatase is a suspected virulence factor. Using transpositional mutagenesis, we created stable E. ictaluri mutants that are deficient in chondroitinase activity. Channel catfish were challenged by injection with E. ictaluri transposon mutant MI15. None of the catfish challenged with the mutant died or showed signs of ESC. These fish were held for 2 weeks and then challenged by injection with the known virulent parent strain of E. ictaluri. The challenged naive control fish showed clinical signs of and a mortality rate consistent with ESC, whereas catfish that had been injected with MI15 prior to challenge with the parent strain were resistant to disease. This work represents a preliminary study to suggest a possible role of chondroitin sulfatase activity in the virulence of E. ictaluri.     

Oral Vaccination of Channel Catfish against Enteric Septicemia of Catfish Using a Live Attenuated Edwardsiella ictaluri Isolate

Enteric septicemia of catfish (ESC), caused by Edwardsiella ictaluri, is the most problematic bacterial disease affecting catfish aquaculture in the southeastern United States. Efforts to develop an effective ESC vaccine have had limited industrial success. In commercial settings, ESC vaccines are typically administered by immersion when fry are transferred from the hatchery to rearing ponds. While this approach is a practical method of mass delivery, this strategy administers vaccines to very young fish, which lack a fully developed immune system. To circumvent this limitation, an oral vaccination strategy was evaluated as a means of immunizing catfish at the fingerling stage of production, when fish possess a more complete immune arsenal. A virulent E. ictaluri isolate (S97-773) was attenuated by successive passage on media containing increasing concentrations of rifamycin. In laboratory trials, cultured vaccine was diluted and mixed with feed (100 mL diluted vaccine/454 g feed). This mixture was then fed to Channel Catfish Ictalurus punctatus fingerlings. Two separate dilutions of cultured vaccine (1:10 and 1:100) were used to create the vaccine–feed mixture, equating to estimated doses of 5 × 10⁷ and 5 × 10⁶ CFU/g of feed, respectively. After 30 d, catfish were exposed by immersion (1 × 10⁶ CFU/mL) to the virulent parental strain of E. ictaluri. The target dose (1:100 dilution, ～5 × 10⁶ CFU/g of feed) offered exceptional protection (relative percent survival = 82.6–100%). In addition, negligible deaths occurred in fish vaccinated at 10 times the target dose (1:10 dilution, ～5 × 10⁷ CFU/g of feed). In pond trials, antibody production increased 18-fold in orally vaccinated fish. When compared with nonvaccinated controls, vaccination significantly improved survival, feed fed, feed conversion, biomass produced, and total harvest. This research demonstrates Channel Catfish can be successfully immunized in a commercial setting against E. ictaluri with a single dose of an orally delivered, live attenuated, E. ictaluri vaccine.

Received July 31, 2014; accepted March 2, 2015     

Transmission of Edwardsiella ictaluri from Infected,Dead to Noninfected Channel Catfish

Abstract

Enteric septicemia of catfish (ESC) was transmitted horizontally from channel catfish Icialurus punctatus that had died from Edwardsiella ictaluri infection to contact channel catfish during 2 d of habitation in a tank. The contact channel catfish became positive for E. ictaluri antibody, became infected with this bacterium, and had signs of ESC and died within 12 d postexposure. Edwardsiella ictaluri was recovered from 24 of the 30 contact channel catfish that died from ESC, as well as from 9 of the 25 tested contact survivors. The cannibalizing of E. ictaluri-infected fish, or the shedding of E. ictaluri from dead fish, or both, were shown to be mechanisms of horizontal transmission of ESC among channel catfish.     

Cool Weather Feeding Influences Responses of Channel Catfish to Edwardsiella ictaluri Challenge

Abstract

A pond study was conducted from November 1 through April 30 with young (age-0; average size, 43 g) and market-size (age-2; average size, 660 g) channel catfish Ictalurus punctatus to compare three management regimens: No feeding, partial feeding (no feeding in December, January, and February), and continuous feeding according to fish size and water temperature. Weight change, feed conversion ratio, and responses to experimental challenge with Edwardsiella ictaluri were evaluated. No significant difference in weight gain occurred between partially fed and continuously fed fish in either age-group; average weight increase for fed age-0 fish was 99% and for fed age-2 fish was 38%. The nonfed age-0 fish lost 12.3% and the nonfed age-2 fish lost 7% of their initial weight. Feed conversion ratios were significantly lower in partially fed fish than in continuously fed fish in both age-groups. Mortality from E. ictaluri challenge among age-0 fish was significantly higher in the nonfed fish, but among the age-2 fish, mortality was significantly lower in the nonfed fish. No difference in mortality rate occurred between partially fed and continuously fed fish in either age-group. Starvation induced lower antibody production against E. ictaluri antigen in the age-0 fish but higher antibody production in the age-2 fish. Phagocytic index was lower in nonfed fish than in fed fish from both age-groups. This study indicates no benefit from feeding age-0 and age-2 channel catfish during December, January, or February if feeding is reintroduced in March and continued through April. Although starvation was immunosuppressive in small channel catfish, it enhanced resistance to bacterial infection in larger fish. However, more research information is needed before reduced feeding can be recommended to enhance resistance of channel catfish to E. ictaluri.     

Olfactory Organ of Channel Catfish as a Site of Experimental Edwardsiella ictaluri Infection

Abstract

Edwardsiella ictaluri, the causative agent of enteric septicemia of catfish (ESC), is one of the most important pathogens to infect channel catfish Ictalurus punctatus. Although the full pathogenesis of E. ictaluri is unclear, the olfactory organ is thought to be a site of entry. We have examined the effects of applying E. ictaluri directly into the olfactory capsule of channel catfish. Olfactory organs of 30 experimental fish were exposed to E. ictaluri for 1 h (1 mL, 1 × 10⁶ colony-forming units/mL). Live fish were sampled at 1, 24, 48, and 72 h, and days 5 and 14 postinfection, and their olfactory organs were examined by light and electron microscopy. Damage, including loss of sensory cilia and microvilli from the olfactory mucosal surface, was observed at 1 h postinfection. Degeneration of olfactory receptors and supporting cells was evident by 24 h postinfection. The nonsensory region also showed signs of degeneration, such as columnar cells lacking cilia. Electron microscopic immunocytochemistry confirmed the presence of E. ictaluri on the mucosal surface and within the epithelium. Host leukocytes responded to bacteria by migrating through the olfactory epithelium into the interlamellar lumen and phagocytosing organisms, but phagocytosed E. ictaluri did not appear to be destroyed. Our results indicate that during initial stages of infection channel catfish olfactory epithelium is vulnerable, and E. ictaluri can enter the host through the olfactory organ. It is also possible that host phagocytic cells serve as a vehicle for the systemic dissemination of E. ictaluri     

Distribution of Edwardsiella ictaluri in California

Abstract

Wild and domestic populations of channel catfish Ictalurus punctatus were examined to determine the distribution of the disease called enteric septicemia of catfish (ESC) in California. The causative agent of ESC, Edwardsiella ictaluri, was isolated from five separate sites in California. Two of these isolations were from rectal swabs of asymptomatic fish, confirming that a carrier state may exist. Normal-appearing fish with serum antibody titer to E. ictaluri were commonly found in domestic channel catfish populations, suggesting that many fish become infected but recover. Wild channel catfish with antibody to E. ictaluri were also found in major reservoirs and water distribution canals. Edwardsiella ictaluri appears to be widely distributed within California.     

Immune Response and Resistance of Channel Catfish to Edwardsiella ictaluri Challenge when Fed Various Dietary Levels of Zinc Methionine and Zinc Sulfate

Abstract

The effects of dietary levels of zinc from zinc methionine (ZnM) and zinc sulfate ZnSO₄ on nonspecific immune responses and disease resistance of juvenile channel catfish Ictalurus punctatus (mean initial weight of 3.3 g) were determined. Fish in triplicate aquaria were fed to satiation twice daily for 16 weeks with an egg white basal diet without zinc supplementation or supplemented with 5, 20, and 60 mg zinc/kg as ZnM or 20 and 60 mg zinc/kg as ZnSO₄. Relative percentages of peripheral blood lymphocytes, thrombocytes, and macrophages were not affected by dietary zinc. The relative percentages of neutrophils significantly increased in fish fed 20 and 60 mg Zn/kg as ZnM. Chemotactic responses of macrophages were significantly higher for fish fed the three ZnM-supplemented diets and the 60-mg ZnSO₄. Dietary zinc, however, had no influence on the phagocytic activity of macrophages for Edwardsiella ictaluri. Likewise, neither the source nor the level of dietary zinc provided protection to channel catfish against E. ictaluri. The severity of E. ictaluri infection (number of colony-forming units/g trunk kidney) and the percentage offish that were culture negative for E. ictaluri (15 d postchallenge) were also unaffected by dietary zinc.     

Effects of Feeding Spirulina on Specific and Nonspecific Immune Responses of Channel Catfish

Abstract

Administration of various immunostimulants to fish has resulted in enhanced immune responses. The purpose of this study was to determine if feeding Spirulina, a processed form of the blue-green alga Spirulina platensis, enhanced specific and nonspecific immunity and resistance against Edwardsiella ictaluri infection in channel catfish Ictalurus punctatus. Peritoneal phagocytes from fish fed Spirulina showed enhanced phagocytosis to zymosan and increased chemotaxis to E. ictaluri exoantigen. No significant difference in mortality due to E. ictaluri existed between fish fed Spirulina and fish fed a basal diet. No significant difference in antibody titer or in the percentage of fish positive for E. ictaluri antibody was found between the groups after immunization with formalin-killed E. ictaluri. Spirulina-fed fish had significantly higher antibody titers to key hole limpet hemocyanin (KLH) on day 22, and a greater percentage of these fish were positive for KLH antibody on days 15 and 36. Feeding Spirulina enhanced nonspecific cellular immune responses such as chemotaxis and phagocytosis but did not provide protection against infection with E. ictaluri. The use of Spirulina in feed resulted in enhanced antibody responses to KLH, a thymus-dependent antigen, but not to E. ictaluri, a thymus-independent antigen. These results indicate that stimulation of the nonspecific immune system of channel catfish does not provide enhanced protection from E. ictaluri.     

Rearing conditions affected responses of weaned pigs to organic acids showing a positive effect on digestibility,microflora and immunity

Three experiments were conducted to assess the response of weaned pigs to organic acid SF3, which contains 34% calcium formate, 16% calcium lactate, 7% citric acid and 13% medium chain fatty acids. Dietary treatments had no effect on growth performance of piglets (21‐day weaning) fed the commercial prestart diet for 1 week before receiving the experimental diets supplemented with SF3 at 0, 3 or 5 g/kg diet (Exp. 1), whereas diarrhea frequency averaged across a week was decreased by SF3 supplementation (5 g/kg diet) in piglets fed the experimental diets immediately after weaning (Exp. 2). In Exp. 3, piglets (28‐day weaning) were fed the control (containing pure colistin sulfate and enramycin, respectively, at 20 mg/kg diet) for 1 week and then were fed the control or SF3‐supplemented (5 g/kg diet) diet for 2 weeks. The SF3‐fed piglets had greater apparent ileal digestibility of calcium and dry matter, while also demonstrating greater overall gross energy, up‐regulated jejunal expression of sodium‐glucose cotransporter‐1 and transforming growth factor‐β, down‐regulated jejunal expression of tumor necrosis factor (TNF)‐α, higher ileal Lactobacillus, with lower total bacteria content, lower plasma TNF‐α but higher IgG levels than the control‐fed piglets. Collectively, SF3 consumption improved diarrhea resistance of weaned pigs by improving nutrient digestibility, piglet immunity and intestinal bacteria profile. © 2016 Japanese Society of Animal Science     

Survival and Antibody Response of Channel Catfish,Blue Catfish,and Channel Catfish Female × Blue Catfish Male Hybrids after Exposure to Edwardsiella ictaluri

Abstract

Juvenile Norris strain channel catfish Ictalurus punctatus, blue catfish I. furcatus, and Norris strain channel catfish female × blue catfish male hybrids were challenged with Edwardsiella ictaluri by bath immersion or intraperitoneal injection (high or low dose) in aquaria. Survival (%) after bath immersion was highest for blue catfish (89.5 ± 2.8), intermediate for hybrids (73.8 ± 6.7), and lowest for channel catfish (62.0 ± 4.2). Prechallenge antibody levels to E. ictaluri, measured by enzyme-linked immunosorbent assay, were negative (mean ± SE optical density [OD] = 0.010 ± 0.003). Postchallenge antibody response for blue catfish (OD = 0.132 ± 0.045) was significantly lower than that of channel catfish (OD = 0.350 ± 0.045), whereas the response of the channel × blue catfish F₁ hybrids (OD = 0.263 ± 0.051) was intermediate and not significantly different from either parental species. Intraperitoneal injections of E. ictaluri resulted in significant mortality only in channel catfish (88.3 ± 2.6% survival) and were sublethal to hybrid catfish and blue catfish with 100.0% and 99.3 ± 0.4% survival, respectively. Antibody responses after the injection challenge were significantly different among catfish groups and injection dose with no group × dose interaction. Antibody responses after the injection challenge were consistent with the immersion challenge, and means of high and low challenge doses were lowest in blue catfish (OD = 0.061 ± 0.014), intermediate in hybrids (OD = 0.187 ± 0.014), and highest in channel catfish (OD = 0.272 ± 0.014). For all fish groups combined, the high injection challenge dose resulted in higher antibody levels (OD = 0.206 ± 0.011) than low injection challenge dose (OD = 0.140 ± 0.012). Overall results indicate greater resistance to E. ictaluri and lower antibody response in blue catfish, and show the potential to identify molecular markers linked with disease resistance and introgression of resistance genes from blue catfish into channel catfish.     

Evidence that Enteric Septicemia of Catfish (ESC) was Present in Arkansas by the Late 1960s: New Insights into the Epidemiology of ESC

Abstract

Enteric septicemia of catfish (ESC), a disease of channel catfish Ictalurus punctatus, was first reported in 1979 based on isolates obtained from 1976 through 1978. Channel catfish that had been preserved in 1970, labeled “nutritional cranial spot,” and stored at the Stuttgart National Aquaculture Research Center were tested with Gram stains, histology, and immunohistochemistry to demonstrate that the specimens were actually infected by Edwardsiella ictaluri (the causative agent of ESC). A reexamination of catfish disease case records has indicated that ESC might have been present in Arkansas in 1969. Investigation of these old records and specimens has led to insights on the discovery and epidemiology of the disease.     

Effect of Vitamin E on the Immune Response of Channel Catfish to Edwardsiella ictaluri

Abstract

Three-month-old fingerling channel catfish Ictalurus punctatus were fed purified diets supplemented with ∝-tocopherol acetate to provide 0, 60, and 2,500 mg vitamin E/kg for 180 d. A 30-s immersion bath and an oral booster were used to deliver a bacterin of formalin-killed Edwardsiella ictaluri to half of the fish from each dietary treatment. Resistance of red blood cells to peroxidation was used as an index of antioxidant status. The susceptibility of red blood cells to oxidative hemolysis decreased with increasing levels of dietary vitamin E. Vaccinated and nonvaccinated fish were evaluated for agglutinating antibody titers and macrophage activity. Humoral antibody titers in response to E. ictaluri were significantly (P ≤ 0.05) higher in vaccinated fish than in nonvaccinated fish; however, no such differences in agglutinating antibody titers were detected among any of the dietary treatment groups. Both vaccination and vitamin E significantly enhanced the ability of macrophages to phagocytize virulent E. ictaluri. Results of this study indicate that elevated levels of dietary vitamin E may affect the ability of channel catfish to respond immunologically to bacterial pathogens.     

Effect of Mediterranean saltbush (Atriplex halimus) ensilaging with two developed enzyme cocktails on feed intake,nutrient digestibility and ruminal fermentation in sheep

The aim of this study was to assess the effects of feeding Atriplex halimus (AH) silage treated with two developed enzyme cocktails to sheep on feed intake, nutrient digestibility and ruminal fermentation. The AH silage was treated without or with 2 L of ZAD1^® or ZAD2^®/1000 kg with 5% molasses and ensiled for 30 days. Barley grain (300 g/head/day) was fed as an energy supplement once daily at 10.00 hours and AH silage with or without enzyme treatment was offered ad libitum to animals twice daily at 09.00 and 16.00 hours. Sheep were fed on four experimental forage diets comprised of AH silage and barley (D1), AH silage treated with ZAD1^® and barley (D2), AH silage treated with ZAD2^® and barley (D3) and AH silage treated with a combination of ZAD1^® and ZAD2^® (1:1) and barley (D4). Ensiling AH with enzymes reduced its contents of neutral detergent fiber and acid detergent fiber. The dry matter intake of AH of D2, D3 and D4 decreased (P < 0.001) as compared to D1. However, enzyme‐treated diets had greater total digestible nutrients intake (P < 0.001) as compared to D1. The nutrients digestibility for D2, D3 and D4 were higher than those for D1 (P < 0.001), and were higher for D3 as compared to both D2 and D4. Sheep fed on D3 had highest (P < 0.001) ruminal total volatile fatty acids concentration, ammonia nitrogen concentration and microbial protein yield. It could be concluded that AH silage treated with ZAD1^® or ZAD2^® improved digestibility and rumen fermentation in sheep.     

Evaluation of Zebrafish Danio rerio as a Model for Enteric Septicemia of Catfish (ESC)

Abstract

Zebrafish (also known as zebra danio) Danio rerio were injected intramuscularly with Edwardsiella ictaluri at doses of 6 × 10³, 6 × 10⁴, or 6 × 10⁵ colony-forming units per gram (CFU/g) or sterile phosphate-buffered saline (sham) or were not injected. Mortality occurred from 2 to 5 d postinjection (dpi) at rates of 0, 76.6, and 81.3% for the low, medium, and high doses, respectively, and E. ictaluri was isolated from dead fish. Survivors were sampled at 10 dpi and E. ictaluri was not isolated. Sham-injected and noninjected controls did not suffer mortality. Histopathology trials were performed in which zebrafish were injected with 1 × 10⁴ CFU/g or sham-injected and sampled at 12, 24, 48, 72, and 96 h postinjection for histological interpretation. Collectively, these zebrafish demonstrated increasing severity of splenic, hepatic, cardiac, and renal interstitial necrosis over time. To evaluate the progression of chronic infection, zebrafish were injected with 1 × 10² CFU/g and held for 1 month postinjection. Beginning at 12 dpi and continuing for an additional 2 weeks, zebrafish demonstrated abnormal spiraling and circling swimming behaviors. Histopathology demonstrated necrotizing encephalitis. In immersion trials, zebrafish were exposed to low, medium, and high doses (averaging 1.16 × 10⁵, 1.16 × 10⁶, and 1.16 × 10⁷ CFU/mL of tank water) of E. ictaluri for 2 h. Mortality occurred from 5 to 9 d postexposure at rates of 0, 3.3, and 13.3% for the low, medium, and high doses, respectively; E. ictaluri was isolated from dead fish. Channel catfish Ictalurus punctatus exposed to the medium doses suffered 100% mortality, and E. ictaluri was isolated from these fish. This study demonstrates the potential use of zebrafish as a model for E. ictaluri pathogenesis.     

Dietary bovine lactoferrin induces changes in immunity level and disease resistance in Asian catfish Clarias batrachus

The effects of including bovine lactoferrin (Lf) in the diet of the Asian catfish (Clarias batrachus) on specific and non-specific immunity as well as disease resistance were investigated. The catfish were fed four different diets for 2 weeks: a commercial diet as control and the same diet supplemented with 50, 100 and 200mg bovine Lf/kg feed. After 1 and 2 weeks, serum bacterial agglutination titre against Aeromonas hydrophila as a measure of specific immunity; natural serum haemolysin titre, lysozyme activity and oxidative radical production by neutrophils as a measure of non-specific immunity as well as disease resistance against A. hydrophila challenge to vaccinated and non-vaccinated animals were evaluated. The results showed that Lf supplements, particularly at 100mg level, significantly (P<0.05) enhanced serum lysozyme level, oxidative radical production and level of protection against A. hydrophila challenge in non-vaccinated animals irrespective of length of exposure. The specific immunity was not influenced by Lf feeding as evidenced from the bacterial agglutination titre and level of protection in vaccinated animals. As Lf feeding at 100mg/kg for 1 week is able to enhance the non-specific immunity and disease resistance of catfish efficiently, these results support the possible use of Lf as an immunostimulant for farmed catfish.     

Risk Factors Associated with Enteric Septicemia of Catfish on Mississippi Commercial Catfish Farms

Abstract

A gram-negative bacterium, Edwardsiella ictaluri, is the cause of enteric septicemia of catfish (ESC), which is one of the most prevalent bacterial diseases in farm-raised catfish. The objective of this study was to identify risk factors associated with ESC mortalities and are reported by farm personnel. To identify risk factors a catfish management database was developed. The odds ratios (OR) of the final multivariable logistic regression model were: (1) volume of the pond (OR, 0.56), (2) interval from harvest until a mortality event (OR, 1.49), (3) interval from stocking until a mortality event (OR, 0.52), (4) nitrite measured within 14 d of a mortality (OR, 3.49), (5) total ammonia measured within 14 d of a mortality (OR, 20.48), and (6) sum of feed fed for 14 d prior to the disease outbreak (OR, 1.02), all of which were significantly (P ≤ 0.05) associated with ESC occurrence. This study showed that some commonly recorded production variables were associated with ESC outbreaks and if monitored could help identify “at risk” ponds prior to disease outbreaks.

Received September 18, 2013; accepted December 17, 2013     

Effect of dietary nucleotide supplementation on performance and development of the gastrointestinal tract of broilers

1. Two experiments were conducted to determine the effects of dietary nucleotide supplementation on broiler performance, and physical and morphological development of the gastrointestinal tract.

2. Experiment 1: A total of 180 one-d-old male chicks were placed in battery brooders in 3?×?6 replicate pens containing 10 chicks each. Chicks were randomly assigned to one of the three dietary treatments; a maize-soyabean meal based diet supplemented with 0, 0·25, and 0·50% Torula yeast RNA (as a source of nucleotides) from 0 to 16?d of age.

3. Experiment 2: A total of 1344 one-d-old male chicks were placed in floor pens and reared on recycled wood shavings (two flocks) under a high stocking density (0·068?m²/bird). Chicks were randomly assigned to one of the 4 dietary treatments (0, 0·25% Torula yeast RNA, 2% and 6% Nupro®) for the starter period (0 to 14?d of age) with 6 replicate pens containing 56 chicks each. All the birds were fed on the same common grower diet with no supplementation of nucleotides from 15 to 32?d of age.

4. Experiment 1: Supplementing the diets with up to 0·50% Torula yeast RNA did not affect broiler performance, or relative intestinal tract weight and length of broilers at any periods measured.

5. Experiment 2: From 0 to 14?d of age, broilers fed on the diets supplemented with 0·25% Torula yeast RNA and 2 and 6% Nupro® were significantly heavier and had improved feed conversion (feed:gain) ratios as compared with the birds fed on the control diet. Supplementing the starter diet only with 2% Nupro® supplementation significantly improved body weight (BW) gain as compared with the control diet over the entire experiment (0 to 32?d of age). Broilers fed on the diets supplemented with 2 and 6% Nupro® from 0 to 14?d of age had better feed conversion (feed:gain) ratios over the entire experiment (0 to 32?d of age) as compared with the birds fed on the control diet, even though the birds were only fed on the diets supplemented with Nupro® from 0 to 14?d of age. The broilers fed on the diets supplemented with 0·25% Torula yeast RNA and 2% Nupro® had higher villus height and an improved villus height-to-crypt depth ratio as compared with birds fed on the control or 6% Nupro® diet at 14?d of age.

6. It is generally assumed that nucleotides are not an essential nutrient; thus there is no need to supplement the diets of broilers reared under normal conditions. However, dietary nucleotide supplementation may be important to maintain maximum growth performance when birds are exposed to stress conditions, such as high stocking density combined with dirty litter.     

An Elevated Dietary Level of Ascorbic Acid Fails to Influence the Response of Anterior Kidney Neutrophils to Edwardsiella ictaluri in Channel Catfish

Abstract

Channel catfish Ictalurus punctatus (weight, 320–420 g) were fed diets with 100 or 1,000 mg ascorbic acid/kg of diet for 7 weeks in ponds. Anterior kidney neutrophil function was assessed by incubating the neutrophils with Edwardsiella ictaluri. Percent phagocytosis, phagocytic index (the mean number of bacteria phagocytized per cell by all neutrophils, including nonphagocytic ones), and bactericidal capabilities of the anterior kidney neutrophils were measured at 0, 90, 180, 270, and 360 min. Serum cortisol was also measured. No significant difference was observed between the two diets with respect to anterior kidney neutrophil function or serum cortisol levels. However, serum cortisol levels did affect mean phagocytic index of anterior kidney neutrophils. Catfish that had serum cortisol levels greater than 10 μg/dL displayed a significant decrease in the phagocytic index when compared with catfish that had cortisol levels less than 5 μg/dL.     

Effect of experimental feed additives on aflatoxin in milk of dairy cows fed aflatoxin‐contaminated diets

Three studies were conducted to determine the potential of experimental feed additives (EFAs), clays or non‐digestible yeast oligosaccharides, to reduce milk aflatoxin (AFM₁) concentrations in lactating Holstein cows consuming aflatoxin‐contaminated diets. All studies included a pre‐treatment period and a 2‐week experimental period in a randomized block design. During the pre‐treatment period, cows received a total mixed ration (TMR) with no aflatoxin contamination. During both experimental weeks, all cows were fed a TMR containing aflatoxin‐contaminated corn. During experimental week 1, cows received no EFA’s in the TMR, but EFA’s were included in the TMR for the second experimental week. In studies 1 and 2, the experimental period consisted of 2 weeks each lasting 7 days with 12 cows per treatment. Aflatoxin M₁ concentrations were analysed by HPLC for milk samples collected on days 5–7 and days 11–14. In various experiments, treatments included control (no EFA), 100 g/cow daily of experimental Lallemand^® product, 10 g/cow daily of MTB‐100^®‐2004, (Alltech, Inc.), 10 g/cow daily of MTB‐100^®‐2006, (Alltech, Inc.), 10 g/cow daily of experimental Alltech^® product (Alltech, Inc.) and 227 g/cow daily of Astra‐Ben 20^® (AB‐20^®; Prince Agri Products, Inc.). In study 3, the experimental period of 2 weeks each lasting 8 days and milk samples were collected from day 4 to 8 and day 11 to 16. Milk samples from study 3 were analysed for AFM₁ concentrations by ELISA. For all experiments, changes in AFM₁ concentrations because of the addition of EFA’s were calculated. Four of the five EFAs tested in this study had no significant effect on AFM₁ concentrations. However, the addition of AB‐20^® resulted in a significant decrease in AFM₁ concentrations (60.4%). In summary, the addition of AB‐20^® to the diet of cattle appears to be effective for significantly reducing AFM₁ concentrations in the milk of cows fed an aflatoxin‐contaminated diet.