Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: 3/11/2016
Publication Date: 3/15/2016
Citation: Buhr, R.J. 2016. The chicken alimentary tract and factors that influence feed passage. Meeting Proceedings. p.5-6.
Interpretive Summary: none
Technical Abstract: The chicken alimentary track differs in several ways from most other domestic food production animals. Chickens are considered monogastric omnivores although their stomach consists of two adjacent segments; the chemical proventriculus followed by the mechanical ventriculus (gizzard). The names used for the segments of the chicken small and large intestines are not consistently used in the literature and the boundary landmarks between adjacent segments varies or are not provided. The small intestine consists of three segments (duodenum, jejunum, and ileum) but the demarcation between the jejunum and ileum is frequently arbitrary and not based on morphology or function. The large intestine consists of the paired long cecum and a short colon, and the absence of a rectum (that portion of the colon within the pelvic canal) due to non-fusion of the pubic bones and the termination of the tract into the cloaca in the chicken. Chickens can only swallow their feed whole with no chewing since they have no teeth, but an adult can quickly swallow a whole mouse or discarded sparkplug. The chicken's alimentary tract is short in length and the ingested feed also has a short passage time compared to other domestic animals. The frequent occurrence of antiperistaltic contractions (ingesta reflux) moves the ingesta back-and-forth among several alimentary tract segments (duodenum to crop, gizzard to mouth, and cloaca to ceca) providing repeated opportunity for further digestion and adsorption of nutrients. The anatomical placement of the pancreatic and bile ducts entrances into the distal duodenum, just before transitioning to the jejunum, utilizes these antiperistaltic waves to neutralize the ingesta pH from 2 as it leaves the gizzard to a near neutral pH of 6 within the duodenum. A clear understanding of the relationship between small intestine luminal villi morphology and function is, to a large extent, lacking for poultry. It is frequently stated and assumed that an increased small intestine villus height is an indication of improved absorptive function. However, experiments by Yamauchi et al. (2010) where they resected the proximal jejunum (50% removal), clearly demonstrated that ileal villi lengthening was a consequence of the dysfunctional resected jejunum. The small intestines of the chicken appear to have compensating ability to modify luminal morphology among segments to meet the physiological demand for absorptive surface area and maintain growth performance. Chickens are provided precisely formulated feeds designed specifically to optimize growth in broilers or egg production in laying hens. Pelleting of broiler feed (compared to feed in mash form) can increase feed consumption in broilers by 10 to 20% resulting in an elevated ventriculus-gizzard pH and shorter feed passage times. Broilers reared under continuous light will eat every 20 to 30 minutes, those raised on less than 8 hours light will eat every 20 to 30 minutes in both the light and dark periods, and those subjected to 20 hours light and 4 hours dark daily will fill their crop to capacity within the last hour that proceeds the onset of the dark period.