Food intake

While there is a wide variation between the eating habits of different birds in the flock, fowls do tend to eat meals on about 15-minute intervals through the daylight hours and, to some extent, during darkness. They tend to eat larger portions at first light and in the late evening.

Factors that affect food intake include:

  1. Age and live weight
  2. Environmental temperature
  3. Energy content of the food
  4. Level of other key nutrients
  5. Egg production
  6. Water quality and temperature
  7. The health status of the flock

Similar factors affect the rate of movement of the food through the digestive system with a meal of normal food taking approximately 4 hours to pass through in the case of young stock, 8 hours in the case of laying hens and 12 hours for broody hens. Intact, hard grains take longer to digest than the cracked grain and, quite often some whole grain will pass through unchanged.

Enzyme action

After ingestion, the food is mixed with saliva and mucous from the mouth and oesophagus and these secretions thoroughly moisten the food. The enzyme amylase, which is produced by the salivary and oesophageal glands and found in the saliva and mucous, can now commence to breakdown the complex carbohydrates. However, the amount of enzyme action at this stage is minimal and the first major enzyme activity takes place in the proventriculus and in the gizzard.

Hydrochloric acid, pepsin and gastrin

The secretions of the proventriculus or glandular stomach as it is often called, include hydrochloric acid to lower the pH of the system and the food mixture, the enzyme pepsin that acts on protein, and the hormone gastrin that stimulates the production and release of gastric juice in the proventriculus and pancreatic juice from the pancreas.

Breaking the food particles

The gizzard is a very powerful organ with the function of physically breaking the food particles into smaller sizes to make the work of the enzymes easier. At the same time the enzymes previously released into the food with the saliva and by the proventriculus are thoroughly mixed into the food thus improving their opportunity to carry out their work. This breaking and mixing function of the gizzard is enhanced by the presence of insoluble grit such as stones.

The food material enters the duodenum from the gizzard. Enzyme activity in this region is, in the main, a continuation of the breakdown of proteins started in the gizzard. Pancreatic juice and bile from the liver enters via ducts located at the distal end of the duodenum at about the junction of the duodenum and the jejunum if it were differentiated. However, because of back flow of pancreatic juice and bile towards the gizzard, the actions of these secretions start earlier in the digestive process than would be expected by their entry point to the small intestine. One effect is an increase in the pH of the intestinal contents of the latter half of the duodenum from strongly to weakly acid.

  • In addition to enzymes, the pancreas produces insulin and sodium bicarbonate. The insulin is involved in the maintenance of blood sugar levels while the sodium bicarbonate, being strongly alkaline, will increase the pH of the intestinal contents.

Reducing complex food compounds

The small intestine also produces enzymes that play their part in the digestive process of reducing the complex food compounds eaten to the simple compounds or building blocks that can be absorbed across the intestinal wall for transport to the organ or location where either they will be further processed, stored or used. Food materials that escape enzyme action along this tract are subjected to bacterial breakdown in the caeca thus providing a system of at least partial recovery of some nutrients.

Waste (faeces)

The remainder of the material consisting of waste and undigested food are mixed with the urine in the cloaca and eliminated from the body as faeces. The appearance of the faeces varies considerably, but typically is a rounded, brown to grey mass topped with a cap of white uric acid from the kidneys. The contents of the caeca are also discharged periodically as discrete masses of brown, glutinous material.

  • The average daily production of faeces from laying hens is between 100 and 150 grams. These fresh droppings are approximately 75% water and will air dry under favourable conditions to approximately 30% water.

Feed consumption of Brown Egg Laying Hens in relation to Body Weight

Age
(wk)

Body weight
(g)

Feed consumption
(kg/100 birds/d)

Age
(wk)

Body weight
(g)

Feed consumption
(kg/100 birds/d)

1

70

0.07

40

2020

23.97
4

310

0.61

44

2040

27.25
8

670

1.81

48

2050

30.50
12

990

3.31

52

2060

33.72
16

1330

5.09

56

2070

36.92
20

1720

7.50

60

2080

40.11
24

1910

11.44

64

2090

43.31
28

1950

13.95

68

2100

46.50
32

1980

17.31

72

2100

49.69
36

2000

20.67

76

2100

52.88

Cumulative Feed consumption for Male and Female Broilers (g)

Age
(weeks)

Male

Female

0

0

0

1

135

131

2

425

404

3

912

848

4

1616

1490

5

2576

2228

6

3717

3229

7

4998

4310

8

6430

5475

9

8007

6721

Water consumption rates for chickens

Water is an essential nutrient for life. Water consumption can be limited if the water is too hot or is contaminated with excess minerals. Water and food consumption rates are interdependent and so reduced water intake can also lead to reduced food intake. Tables 7 and 8 provide data on typical water consumption levels for layers and broiler, respectively.
Typical Daily Water consumption for Layer (litres per 1000 birds) Birds

 

 

20oC

32oC

Layer pullet

4 weeks

50

75

12 weeks

115

180

18 weeks

140

200
Laying hens

50% production

150

250

90% production

180

300

Typical Daily Water consumption for Broiler (litres per 1000 birds) Birds

Age

20oC

32oC

1 weeks

24

40

3 weeks

100

190

6 weeks

240

500

9 weeks

300

600