DEVELOPING strategies to increase the amount of saleable product while reducing dietary inputs is a priority for many animal, dairy and poultry scientists.
University of Illinois researchers have been looking at how dietary components affect gut health and disease resistance in chickens.
"An important nutritional outcome is how well an animal is able to digest and metabolize its diet," Ryan Dilger, an assistant professor in the University of Illinois department of animal sciences, said.
Poultry and swine nutritionists are concerned about dietary fiber in alternative feed ingredients, particularly the byproducts of biofuel production. Fiber concentrations are very high in these ingredients because the starch content is removed during processing.
Dilger and master's degree student Emma Wils-Plotz looked at how purified fiber fed to young chicks affects their dietary threonine requirements, intestinal morphology and ability to resist a disease challenge. Threonine is an essential amino acid that accounts for as much as 11% of mucin, an important component of the mucus layer covering the intestine's absorptive surface that promotes gut health by protecting the body against bacteria and digestive enzymes, an announcement said.
Previous research has suggested that mucin dynamics may be sensitive to threonine availability. Dilger and Wils-Plotz hypothesized that dietary threonine requirements would increase in the presence of two purified fiber sources, cellulose and pectin, which are natural components of many feed ingredients.
They fed diets containing purified cellulose, pectin or silica sand (control) to chicks and found that bodyweight gain and feed efficiency were reduced when 7% supplemental pectin was added to the diet. Pectin created a viscous environment in the gut that interfered with the birds' ability to access dietary nutrients, thus reducing growth performance. Feeding 7% purified cellulose did not provide any nutritional benefit, the researchers said.
In a second experiment, Wils-Plotz and Dilger quantified the dietary threonine requirement in the presence and absence of purified fiber sources. Chicks were fed one of the three fiber-containing diets. Within each diet, chicks were subdivided into seven groups, each fed a different level of threonine supplementation ranging from 0.0 to 9.6 g/kg.
Contrary to the researchers' expectations, birds fed the diet with pectin had the lowest threonine requirements at 5.6 g/kg; birds fed the control diet had the highest, estimated to be 6.8 g/kg, and cellulose-fed birds required 5.8 g/kg, the announcement said.
Wils-Plotz and Dilger collected ileal tissue from chicks that was then examined for physical changes in the villi, crypts and goblet cells, which produce and secrete mucin.
Chicks fed cellulose or pectin had deeper crypts than chicks fed the control diet; crypts were deepest for birds fed cellulose and adequate threonine levels, and their outer intestinal muscle layer (serosa) was thicker, the researchers said. Chicks fed diets containing fiber had higher goblet cell counts than the birds fed the control diet, with the highest levels in birds fed the pectin diet with adequate or high threonine levels.
The findings suggest that dietary threonine concentration and fiber source affect growth performance, intestinal morphology and mucin secretion in young chicks, the announcement said. The results also established optimal dietary threonine levels.
Having determined these levels, the researchers wanted to see if fiber and threonine in the diet could affect how chicks respond to a coccidiosis challenge.
"Right now, there are few advancements in coccidiosis vaccine development, so we tried to develop dietary approaches to assist the bird through a coccidiosis challenge," Dilger said. "Our hypothesis was that by providing adequate threonine, the bird would have better immune defenses through improved gut function and immunity."
Chicks received either a diet supplemented with pectin or a threonine-deficient control diet and either 75% or 125% of the previously determined optimal threonine supplement of 6.8 g/kg. Within each dietary treatment, one group of chicks was inoculated with Eimeria maxima; the other was not.
"The goal was to determine the interaction between dietary fiber and dietary threonine, knowing that pectin was going to negatively affect digestion and that threonine was going to positively affect intestinal health," Dilger explained.
Growth and feed efficiency were monitored for 16 days; then, ileal tissue, mucosal scrapings and the ceca were collected. The researchers looked at growth performance, morphological changes in the intestine, changes in the cecal environment and gene expression in the ceca and mucosa.
"The most important part of the story was the cytokine response to the acute coccidiosis infection," Dilger said.
Cytokines regulate how the immune system communicates with the rest of the body and adjust the immune response, he explained. Interleukin-12 expression in the ceca was increased in birds fed the control diet with high threonine. Interleukin-1 beta expression increased with infection, but only in birds fed the low-threonine diet.
Expression of interferon gamma, a protein made and released in response to the presence of pathogens, increased in the ileal mucosa of birds fed the high threonine level and was highest in the uninfected chicks. It increased with infection, but only in control-fed birds.
The researchers concluded that, while pectin had some protective effects against coccidiosis infection, threonine supplementation had an even greater influence on the intestinal immune response and helped to maintain growth of chicks infected with coccidiosis, the announcement said.
The research is described in more detail in "Effect of Fiber & Threonine on Chick Growth" by Wils-Plotz and Dilger and "Modulation of the Intestinal Environment, Innate Immune Response & Barrier Function by Dietary Threonine & Purified Fiber During a Coccidiosis Challenge in Broiler Chicks" by Wils-Plotz, M.C. Jenkins and Dilger, which both appear in the March 1 issue of Poultry Science.
At the recent International Poultry Science Forum in Atlanta, Ga., University of Georgia researchers Mathew Abraham, Larry McDougald and Robert Beckstead discussed the potential for reduced nitarsone sensitivity of Histomonas meleagridis, a flagellated protozoan parasite that is the causative agent of blackhead disease in gallinaceous birds (abstract M3).
Nitarsone (4-nitrophenylarsonic acid) is currently the only approved anti-histomonal drug available in the U.S., Abraham et al. explained.
In the present study, they tested the sensitivity of nitarsone in both in vitro and in vivo conditions. For the in vitro study, three different strains collected from outbreaks in North Carolina (Strain MNC), Michigan (Strain ZM) and Georgia (strain BG) were treated with purified nitarsone at 0, 100 or 400 micrograms/mL in three replicate cultures. Strain ZM and Strain BG at both 100 and 400 micrograms/mL showed a diminished growth compared to their respective control groups, the researchers said. However, strain MNC treated with nitarsone at 100 micrograms/mL did not show any effect, and their growth pattern was almost similar to that of the control group.
In the in vivo study, Abraham et al. said, two-week-old turkey poults were divided into nine groups: three groups were inoculated cloacally with Strain MNC, three groups were infected with histomonas and fed nitarsone from the first day of life and three groups remained uninfected.
A commercial nitarsone premix was used to mix the turkey starter ration at 0.0187% (187 parts per million). At 10 days post-infection, birds were weighed, euthanized and necropsied, and cecal and liver lesions were scored.
According to the researchers, the nitarsone-treated group did not show any significant improvement in average weight gain compared to the infected control group. Average weight gains of the uninfected control, infected control and infected nitarsone-treated groups were 191.97 g, 117.71 g and 83.91 g, respectively.
Abraham et al. reported that there were no significant differences in the liver and cecal lesions of infected control and infected nitarsone-treated groups, but both showed a significant difference from the untreated control group (P < 0.0001).
Abraham et al. concluded that development of nitarsone resistance by certain strains of histomonas is strengthening the need for alternative chemotherapeutics or immunoprophylaxis against blackhead disease.