A trial was conducted to test the following hypothesis; broiler exposure to coarse insoluble fibre in the diet or litter will result in enhanced gizzard function and performance, improved adaptability to an intermittent feeding program and an increase in the occurrence of reverse peristalsis. Ross 308 broiler chickens were either intermittent or ad libitum fed a basal diet, a basal diet diluted with 15 % coarse hulls (barley and oats) or a basal diet diluted with 15 % finely ground hulls in a 2x3-factorial experiment (n = 17 birds/treatment). From 18 days of age, the birds were transferred to individual cages. Birds on intermittent feeding had restricted access to feed from 11 days of age. From 18 days of age, the restrictive feeding program consisted of four one-hour meals and one two-hour meal per day. AME value and faecal starch digestibility were determined by quantitative collection of excreta. At 31 and 32 days of age, birds were inoculated with CrEDTA via the cloaca. Weights were recorded and digesta samples collected from the gizzard, duodenum, jejunum, and ileum. There was no interaction between diet and feeding regime for any of the parameters measured. The addition of coarse oat and barley hulls resulted in birds with fuller, heavier gizzards (p < 0.001). Intermittently fed birds raised on the coarse hull diet exhibited an improved starch digestibility compared to birds not exposed to hulls (p < 0.001). The presence of chromium in all intestinal tract sections of birds from the six treatment groups, confirms that reflux occurs along the entire length of the gastro intestinal tract, irrespective of insoluble fiber content of the feed or feeding regime.
In commercial broiler production feed is available to birds ad libitum often under continuous or near continuous lighting programs. This approach to husbandry is associated with potential overconsumption (Svihus et al., 2010). Restrictive feeding, by the use of intermittent lighting programs, has been shown to reduce such problems and improve feed efficiency (Decuypere et al., 1994). Intermittent feeding requires the bird to retain ingested feed for greater lengths of time than ad libitum feeding by storing ingesta in the crop and proventriculus/gizzard (Buyse et al., 1993). By stimulating gizzard development with the dietary inclusion of barley and oat hulls, it is possible that the resulting increase in holding capacity, heightened gizzard function and occurrence of reverse peristalsis will enable the broiler to thrive under intermittent feeding.
The purpose of this study was to investigate the effect of a dilution of broiler diets with hulls on bird performance, reverse peristalsis in the digestive tract, and ability to adapt to an intermittent feeding regime.
MATERIALS AND METHODS
Day-old male broiler chickens (Ross 308) were raised on a commercial pelleted starter diet in a multilevel brooder. At 11 days of age the birds were moved to 12 group cages.
Two cages were assigned to each of 6 treatments in a 2-feeding regime × 3-diet experimental design. At 18 days of age, 17 birds were randomly selected from each of the six groups (102 in total) and transferred to individual cages. Temperature was reduced from 31 °C to 28 °C at 7 days of age and to 25 °C at 16 days of age.
Diets were steam-pelleted through a 3 mm die, and consisted of a basal control diet, a basal diet diluted with either 15% unground coarse, or fine ground hulls (equal weights of hulls from oats and barley). Irrespective of feeding regime, ad libitum (AL) or intermittent feeding (IF), birds experienced complete darkness between the hours of 02.00 and 08.00. From 11-18 days of age, the IF groups had access to feed from 08.00 to 09.00, 12.00 to 13.00, 16.30 to 17.30, and from 21.00 until the light went off at 02.00. From 18 days of age, these birds had access to feed from 08.00 to 09.00, 12.00 to 13.00, 16.00 to 17.00, 20.00 to 21.00, and from 24.00 until the light went off at 02.00.
Feed intake and weights for individual birds were recorded twice a week from 18 days of age until the end of the study. Quantitative excreta collection for AME was carried out between 26 and 29 days of age. At 32 and 33 days of age, after one hour off feed, 2 ml of CrEDTA marker was administered into the cloaca of the bird. Birds were then returned to their cages and given access to feed as determined by their normal feeding program for two hours then euthanized and dissected. Weights were recorded for gastrointestinal sections, contents were dried then digested in nitric acid using a closed chamber microwave, then analysed for chromium content using inductively coupled plasma emission spectroscopy (ICP). Excreta samples were frozen, mixed, dried and then analysed for gross energy content and starch along with feed samples. Data was analysed using a 2 × 3 factorial arrangement followed by pair-wise comparisons using the Duncan procedure with P < 0.05 as significance level.
There was no significant interaction between feeding regime and diet for any parameter measured (Table 1). The AL birds tended to consume more feed than IF birds (P = 0.07). Diet affected feed intake (P < 0.05) due to an increased feed intake for diets with coarse hulls added. No significant effect of feeding regime on weight gain was observed. However a reduced (P < 0.01) weight gain for birds consuming the finely ground hull diet was observed. Dilution of the diet with hulls reduced gain:feed (P < 0.001). Feeding regime did not affect AME or starch digestibility. Dilution with hulls, however, improved starch digestibility (P < 0.001). The amount of dry matter in the crop was higher (P < 0.05) in IF groups than in AL groups. Both IF and dilution with hulls reduced (P < 0.001) gizzard pH (Table 1). The addition of hulls to diets resulted in fuller and larger gizzards, with birds exposed to coarse hulls yielding the largest (P < 0.001) gizzards. Chromium at levels considerably higher than the background level was present in all sections of the gastrointestinal tract, with no significant difference between treatments (Table 2). However, chromium levels tended to be higher in the gizzards (P = 0.07) and the jejunum (P= 0.06) of the AL fed birds.
Access to coarse hulls stimulated gizzard development, in agreement with previous studies, highlighting the stimulatory effect of structural material on the gizzard (Svihus et al., 2010). The large particle size and hardness of the coarse hulls explains why birds consuming that diet developed the heaviest gizzards. The coarse hull particles are retained in the gizzard until they are ground to a certain critical size that allows them to pass through the pyloric sphincter (Hetland et al., 2003). This leads to an increase in the volume of the organ´s contents and a muscular adaptation to meet the greater demand for grinding.
Table 1. Performance and digestive characteristics of birds (17- 32/33 days of age)
Table 2. Levels of chromium detected in the digestive tracts of birds
Birds fed the fine hull diet also exhibited heavier gizzards than the control group, although less so than the coarse hull group, suggesting that the fine particles were retained and partly induced the same response. In accordance with previous findings, the increase in volume and weight of gizzards in birds was accompanied by a reduction in pH in the caged bird (Nir et al., 1994). The strong effect of feeding regime on pH in the control birds may be explained by the increase in the dry matter content of the crop and gizzard with IF leading to increased fermentation, resulting in more acidic digesta flowing into the gizzard.
These gains in gizzard function coupled with a longer retention time have been shown to result in improvements in nutrient digestibility and feed utilization (Svihus, 2011). This was confirmed by starch digestibility data from the current experiment, and also by the considerably higher AMEn of the hulls-diluted diets than what would be expected based on calculated energy value of the control diet and the hulls (NRC, 1994). The lack of interaction between feeding system and diet structure indicates that the increase in volume of the gizzard does not influence the bird´s ability to adapt to meal feeding.
The tendency for higher levels of chromium to be present in the gizzards and jejunal contents of AL birds fed the hull diets is contrary to what was expected. Reflux has been characterized as an organized motility response to feed shortage, resulting in temporary reestablishment of normal motility along the digestive tract (Clench and Mathias, 1992). It was assumed that reverse peristalsis, especially the gastroduodenal reflux, would be one method by which the IF birds would improve feed utilization. In view of this, the intermittent feeding system was perhaps not severe enough to induce an anti-peristaltic response. Conversely, reflux could be viewed as characteristic of optimal mixing of the lumen contents of satiated birds. However, Cr-EDTA is a liquid phase marker and retention time in the gizzard is dependent on particle size (Vergara et al., 1989). If digesta was refluxed back into the gizzard, the marker would be the part of the fraction to pass first through the pylorus sphincter. Chromium levels measured in the gizzard may not be wholly representative of the extent of the gastroduodenal reflux and explains why the chromium results do not concur with the pH levels in the gizzard and the large amount of DM present, from birds fed on the hull diets. Previous research has suggested the stimulating effect of coarse fibre on gizzard function, in particular more frequent and powerful contractions and the subsequent intraluminal pressure changes that they induce, will lead to an increase in the occurrence of gastric refluxes (Hetland et al., 2003). In the current study, Cr levels in the gizzard appeared higher in birds with access to the hulls, though this was not significant due to the high degree of variability in results. The aforementioned limitation of the liquid phase marker and increase in gizzard contents in birds exposed to the hull treatments, suggest that further work should be carried out investigating the potential for reflux of solid particles and possible interaction with improvements in nutrient digestibility.
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This paper was presented at the 23rd Annual Australian Poultry Science Symposium, in Sidney, New South Wales from February 19-22, 2012. Engormix.com thanks the organizing committee and the authors for this contribution.