Avian Anatomy and Digestion
photo credit: a) Klasing 1999 – General avian digestion, b) Dickson 1992 – Chicken GIT
The rate of passage of food through the GIT differs depending on external temperature,reproductive status, and age. Egg laying hens experience faster food passage than non laying hens by approximately one hour. Food passage is also more rapid in young hens than in old hens by approximately one and half hours.
Turkeys have evolved digestive systems that correlate with their food sources. Species who share similar food sources and ecological pressures tend to evolve similar morphometric similarities in their digestive anatomy through convergent evolution. The digestive anatomy and physiology is adapted in a way that promotes flight . For example, the weight of the GIT is situated centrally as to not interfere with the ability of the bird to fly.
In general, the avian digestive tract is a continuous tube open at either end.
The general pathway for food for birds:
The rate of passage of food through the GIT differs depending on external temperature,reproductive status, and age. Egg laying hens experience faster food passage than non laying hens by approximately one hour. Food passage is also more rapid in young hens than in old hens by approximately one and half hours.
Turkeys have evolved digestive systems that correlate with their food sources. Species who share similar food sources and ecological pressures tend to evolve similar morphometric similarities in their digestive anatomy through convergent evolution. The digestive anatomy and physiology is adapted in a way that promotes flight . For example, the weight of the GIT is situated centrally as to not interfere with the ability of the bird to fly.
In general, the avian digestive tract is a continuous tube open at either end.
The general pathway for food for birds:
Beak
The beak functions in grasping and mechanical processing (sorting, hulling,tearing, crushing) of foods, and morphologically differs among species as a result of different requirements for obtaining and processing different food sources. Turkeys and GuineaFowl tend to have short, stout beaks with prominent ridges reflecting their need for cracking seeds. Birds tend to have a weak sense of taste due to their low abundance of taste receptors, low levels of saliva, and lack of mastication. However, birds tend to have many touch receptors on the beak, tongue, and within the oral cavity.
Esophagus
Acts as a connector for food passage between the mouth and the stomach.
Crop
Wild turkeys and Guinea fowl have a crop, while birds that do not have a crop tend to have an extensible esophageal pouch. The crop serves as a storage site for food when the proventriculus and gizzard are filled to capacity allowing birds to forage for large amounts of food. Stored food within the crop also serves as an energy source that can be utilized during sleep.
Proventriculus:
The proventriculus and the gizzard (or ventriculus) comprise the stomach. Digestion is initiated at the proventriculus with the release of mucus, hydrochloric acid, and pepsin. In both Turkeys and Guineafowl, the proventriculus is elongated and relatively small compared to the gizzard.
Ventriculus / Gizzard
Gizzards are more pronounced in birds that eat harder to digest materials such as seeds, as send in both Turkeys and Guinea fowl.
This organ is large, and muscular, and functions in mechanical mixing and grinding of food. The cuticle of the gizzard and acts as a protective barrier for the underlying mucosa from digestive enzymes and acid. In turkeys and guineafowl, this layer is particularly thick. The gizzard changes seasonally with changes in diet. It tends to be large, muscular, and gritty with a hard cuticle in the winter when food sources are mainly seeds, and tends to weight much less is summer when easily digested foods are being eaten and there is less need for its extra mechanical action.
Intestine
The small intestine is less variable between species. It mainly functions in absorption.
Ceca
The ceca is found within the intestinal wall at the junction between the small intestine and the rectum and functions in the vegetative digestion and water balance. It is very large in turkeys and Guinea fowl.
Cloaca.
The end products of the GIT and the urogenital ducts empty into the cloaca. This large chamber is compartmentalized to avoid contamination between waste products and reproductive gametes which pass through upon their release.
Food is not passed through in one direct motion throughout the GIT. It is passed back and forth between organs for greater digestive and absorptive efficiency. This mechanism is called retrograde movement and occurs between the proventriculus and the gizzard, the small intestine and the gizzard, the rectum and the small intestine, and the cloaca and rectum.
The beak functions in grasping and mechanical processing (sorting, hulling,tearing, crushing) of foods, and morphologically differs among species as a result of different requirements for obtaining and processing different food sources. Turkeys and GuineaFowl tend to have short, stout beaks with prominent ridges reflecting their need for cracking seeds. Birds tend to have a weak sense of taste due to their low abundance of taste receptors, low levels of saliva, and lack of mastication. However, birds tend to have many touch receptors on the beak, tongue, and within the oral cavity.
Esophagus
Acts as a connector for food passage between the mouth and the stomach.
Crop
Wild turkeys and Guinea fowl have a crop, while birds that do not have a crop tend to have an extensible esophageal pouch. The crop serves as a storage site for food when the proventriculus and gizzard are filled to capacity allowing birds to forage for large amounts of food. Stored food within the crop also serves as an energy source that can be utilized during sleep.
Proventriculus:
The proventriculus and the gizzard (or ventriculus) comprise the stomach. Digestion is initiated at the proventriculus with the release of mucus, hydrochloric acid, and pepsin. In both Turkeys and Guineafowl, the proventriculus is elongated and relatively small compared to the gizzard.
Ventriculus / Gizzard
Gizzards are more pronounced in birds that eat harder to digest materials such as seeds, as send in both Turkeys and Guinea fowl.
This organ is large, and muscular, and functions in mechanical mixing and grinding of food. The cuticle of the gizzard and acts as a protective barrier for the underlying mucosa from digestive enzymes and acid. In turkeys and guineafowl, this layer is particularly thick. The gizzard changes seasonally with changes in diet. It tends to be large, muscular, and gritty with a hard cuticle in the winter when food sources are mainly seeds, and tends to weight much less is summer when easily digested foods are being eaten and there is less need for its extra mechanical action.
Intestine
The small intestine is less variable between species. It mainly functions in absorption.
Ceca
The ceca is found within the intestinal wall at the junction between the small intestine and the rectum and functions in the vegetative digestion and water balance. It is very large in turkeys and Guinea fowl.
Cloaca.
The end products of the GIT and the urogenital ducts empty into the cloaca. This large chamber is compartmentalized to avoid contamination between waste products and reproductive gametes which pass through upon their release.
Food is not passed through in one direct motion throughout the GIT. It is passed back and forth between organs for greater digestive and absorptive efficiency. This mechanism is called retrograde movement and occurs between the proventriculus and the gizzard, the small intestine and the gizzard, the rectum and the small intestine, and the cloaca and rectum.
Nutrition and Metabolic Requirements
(Photo credit: Bill Marchel)
Wild Turkeys and GuineaFowls are homeothermic animals, so they need to maintain a relatively constant body temperature and do so through thermoregulation. The body temperature of these birds is affected by many different factors including:
- Age, Sex, Size, Breed
- Activity
- Types of food
- Diurnal rhythm
- Ambient temperature
- Season
- Molting
- Plumage
- Nesting habits
The basal metabolic rate (BMR) is defined as the minimal amount of energy required by a homeothermic organism while at rest.
Wild turkey
Winter is the most stressful time of year for wild turkeys in terms of satisfying energy requirements, as food becomes unobtainable due to snow cover leading to starvation and higher mortality rates. Reproduction in late winter and spring may be affected if wild turkey hens cannot obtain enough food to reach the necessary weight for breeding.
Standard metabolic rates for females have been found to be similar across seasons and averaged 0.461 ml O2/g/hr. SMR tends to be greater for females than males during summer and autumn seasons.
The daily energy expenditure (DEE) for wild turkeys was found to be 189.3 M^0.61. The following is a table of the average weight of the various subspecies of Wild Turkey:
(Dickson 1992)
An example of the amount of a common food, such as a red oak acorn ( 5.04 kcal/g), needed to satisfy the energetics of the Eastern Turkey using the observed DEE of 189.3 M ^0.61 would be:
189.3 x (9.6 kg )^0.61 = 752 kcal/ day * kg, meaning 149206 red oak acorns would need to be consumed to maintain maintenance, thermoregulation and basic activity levels.
A fair amount of studies have been done on the energetics of wild turkeys, but the results are inconclusive based on comparisons with captive turkeys. The BMR of a Wild turkey does not differ between sexes per gram mass, but does differ between age classes. Juveniles have a higher BMR during winter, while adults have a higher BMR in the summer. Females have a higher cost for thermoregulation than do males, probably due to size differences between males and females (males > females).The thermal temperature limit is lower in winter than in summer which may be a result of acclimatization or from better insulation and fat storage. Increased lipid reserves may provide the turkey with insulation allowing for a lower BMR.
The availability and nutritional content of food is important in reproducing turkeys. Wild turkeys whom obtain more protein rich foods like snails are able to have higher egg production. Egg laying hens have been observed to eat more snails and snail shells (source of calcium) than non egg laying hens. Percentages of snails eaten include 10.9% , 3.0%, and 0.8% for egg layers, pre-egg layers and post egg layers respectively.
The optimum intake of phosphorus for wild turkeys is approximately 0.7 %. Inadequate intake of phosphorus has been shown to alter the timing and progression of egg laying.
189.3 x (9.6 kg )^0.61 = 752 kcal/ day * kg, meaning 149206 red oak acorns would need to be consumed to maintain maintenance, thermoregulation and basic activity levels.
A fair amount of studies have been done on the energetics of wild turkeys, but the results are inconclusive based on comparisons with captive turkeys. The BMR of a Wild turkey does not differ between sexes per gram mass, but does differ between age classes. Juveniles have a higher BMR during winter, while adults have a higher BMR in the summer. Females have a higher cost for thermoregulation than do males, probably due to size differences between males and females (males > females).The thermal temperature limit is lower in winter than in summer which may be a result of acclimatization or from better insulation and fat storage. Increased lipid reserves may provide the turkey with insulation allowing for a lower BMR.
The availability and nutritional content of food is important in reproducing turkeys. Wild turkeys whom obtain more protein rich foods like snails are able to have higher egg production. Egg laying hens have been observed to eat more snails and snail shells (source of calcium) than non egg laying hens. Percentages of snails eaten include 10.9% , 3.0%, and 0.8% for egg layers, pre-egg layers and post egg layers respectively.
The optimum intake of phosphorus for wild turkeys is approximately 0.7 %. Inadequate intake of phosphorus has been shown to alter the timing and progression of egg laying.
Nutritional Value and Digestibility of 8 common Wild Turkey food sources in Mississippi (Fall and Winter)
(Billingsley 1970)
These above food sources are common for the Wild turkey during fall and winter.
The order of decreasing nutrient content and utilization was Crude fat, crude protein, and nitrogen free extract. No difference in the ability to utilize the nutrients in these foods was found between juveniles and adults.
These 8 food sources ranked in order of nutritive value: Spicebush, chuff, grape, water oak, dogwood, pecan, sugar berry, and greenbrier.
These above food sources are common for the Wild turkey during fall and winter.
The order of decreasing nutrient content and utilization was Crude fat, crude protein, and nitrogen free extract. No difference in the ability to utilize the nutrients in these foods was found between juveniles and adults.
These 8 food sources ranked in order of nutritive value: Spicebush, chuff, grape, water oak, dogwood, pecan, sugar berry, and greenbrier.
Nutritional Evaluation of Wild Turkey Food sources in Northern Regions
![Picture](/uploads/4/6/5/1/46519323/2971351.png?407)
Digestibility of of the nutrients represented in table 2, was equal/greater to 50%. Digestibility for fat, protein and fibre was 88%, 71%, and 62% respectively. These results are similar to the results from the study of Mississippi foods (shown above).
(Decker 1991)
Food Sources of the Helmeted Guinea Fowl
When the contents of guinea fowl crops were analyzed, their percentages were 35% grass seeds, 21.6% insects, 17.4% Cyperus bulbs, 11.3% fruits of dicotyledons, 9.9% leaves and other vegetable matter, 1.9% pebbles, and 3% water. The mineral contents of the crops varies seasonally and are shown in the following table.
(Ayeni 1983)
Natural sources of graminaceous and herbaceous foods are abundant during the rainy season. During rainy periods, guinea fowl feed on insects and plant material in large quantities. Below is a list of the species of insects found inside the crops of guinea fowl. Calcium is an important mineral necessary for efficient reproduction as it is the main constituent of eggshells.. The dietary requirement for guinea fowl is found to be 2.75%. The amount of plasma calcium has been related to the amount of eggs that can be produced. Plasma phosphorus levels were not significantly correlated with differences in reproductive success as is seen in wild turkeys.
Natural sources of graminaceous and herbaceous foods are abundant during the rainy season. During rainy periods, guinea fowl feed on insects and plant material in large quantities. Below is a list of the species of insects found inside the crops of guinea fowl. Calcium is an important mineral necessary for efficient reproduction as it is the main constituent of eggshells.. The dietary requirement for guinea fowl is found to be 2.75%. The amount of plasma calcium has been related to the amount of eggs that can be produced. Plasma phosphorus levels were not significantly correlated with differences in reproductive success as is seen in wild turkeys.
(Ayeni 1983)
References
- Dickson, J.G. (1992). The wild turkey: biology and management. Stackpole Books: Mechaniesburg, PA.
- Ayeni, J.S.O. (1983). The biology and utilization of helmeted guinea-fowl (Numida meleagris galeata Pallas) in Nigeria. II. food of helmeted guinea-fowl in Kainji lake basin area of Nigeria. Afr. J. Ecol. 21: 1-10.
- Billingsley, B.B. and Arner, D.H. (1970). The nutritive value and digestibility of some winter foods of the eastern wild turkey. J. Wildlife Management. 34 (1) : 176- 182.
- Decker, S.R, Pekins, P.J. and Mautz,W.W. (1991). Nutritional evaluation of winter foods of wild turkeys. Can. J. Zool. 69: 2128 - 2132.
- Klasing, K.C. (1999). Avian gastrointestinal anatomy and physiology. Seminars in Avian and Exotic Pet Medicine. 8(2) : 42-50.
- Healy, W.M. and Powell S.M.(2000). Wild turkey harvest management: biology, strategies, and techniques. Sheperdstown, WV.
- Nguyen, L., Hamr, J. and Parker, G.H. (2004). Wild turkey, Meleagris gallopavo silvestris, behavior in central ontario during winter. Canadian Field - Naturalist. 188 (2) : 251- 255.
- Oberlag, D.F., Pekins, P.J. and Mautz, W.W. (1990). Influence of seasonal temperatures on wild turkey metabolism. J. Wildlife Management. 54 (4) : 663 - 667.
- IUCN. 2012. IUCN Red List of Threatened Species (ver. 2012.1). Available at:http://www.iucnredlist.org.