The energy and protein needs of scavenging laying hens

D J Farrell 

School of Land and Food Sciences, The University of Queensland,
Brisbane, Qld 4072, Australia.
d.farrell@mailbox.uq.edu.au

Abstract

The daily energy and protein requirements of a 1.2 kg scavenging hen, laying a 38 g egg at a rate of 20% production, are calculated. The hen produces 4 batches of chicks each year and raises them to 6 weeks. She travels 2.25 km/day and in doing so climbs 100 m. Apparent metabolisable energy for the hen is 689 kJ and her dietary protein requirements are 6 g/day. A typical scavenging feed resource base of 250 kg/household per year will support 12.5 scavenging hens for energy and 13 hens for their protein needs. 

Keywords: Scavenging hens, energy and protein needs

 
Introduction

There are large numbers of unmanaged, scavenging village chickens, particularly in Asia, Africa and Latin America.  These provide meat and eggs at little or no cost to their owners. These chickens rely on worms, insects, larvae, and snails but mainly on household scraps for food. Occasionally they are given grain. Use of published equations to predict the apparent metabolisable energy (AME) and protein needs of scavenging hens are inappropriate because they are based on caged, high-producing, improved breeds. This paper uses an approach based on first principles to calculate the energy and protein needs of scavenging chickens.

Assumptions and Calculations

Village hens vary greatly in live weight (W), but they are generally light-bodied and low-producing. They may travel a substantial distance each day and may gain a small amount of weight during a production cycle. When sitting on eggs and brooding their chicks, they travel only a short distance each day. Temperature will also influence energy needs in particular.

The normal scenario of scavenging hens is that they will brood four batches of chicks per year. Thus they will be incubating eggs for 12 weeks and rearing their chicks for 24 weeks. So for about half of the year their activity will be curtailed. On average they will lay about 70 small eggs each year; the majority of these they will incubate.

The typical scavenging hen will weigh 1.2 kg, lay a 38 g egg at a rate of 20% production; she will travel each day 1.5km for 26 weeks of the year and 3 km for the remainder of the year. The average distance traveled is therefore 2.25 km/day; some of this will be climbing, and it is assumed the hen climbs 100 m each day when scavenging.

The basis of several of the energy costs used in the calculations is given by Farrell (1986). It is generally accepted that the maintenance energy needs of mature hens is 370 kJ/kg W (Johnson 1983).

Results and Discussion

The maintenance requirements of the mature hen will be 1.2 W x 370 kJ AME =  444 kJ per day. The efficiency of utilisation of energy for maintenance (k_m.) is 0.80, giving 555 AME kJ/day. The daily egg mass will be 7.6 g x 6.7 kJ, thus the energy content of the egg is 51 kJ. If the hen travels 2.25 km/day at a cost of 3 kJ per km/kg W, or 3.6 kJ for the 1.2 kg hen, this amounts to 6.75 kJ/day. The 100 m vertical climb will cost an additional 3 kJ, giving a total of 9.75 kJ/day. Since the latter two figures are net energy, they must be converted to AME using efficiency factor (k_e) of 0.70 for egg formation and 0.35 for activity. The ME will therefore be 73 kJ and 29 kJ, respectively.

It is assumed that the hen is in a thermo-neutral environment so there is no energy cost of thermo-regulation. The hen may gain 0.5 g/day; this will contain 11 kJ and the efficiency factor will be 0.75, giving a AME requirement of 15 kJ/day. The energy cost of eating has been measured and was found to be 3% of the hen’s daily maintenance heat production (Van Kampen 1976). This will be:

0.03 x 555 or 17 kJ AME/day. 

The total energy requirement of this scavenging hen will be 689 kJ/day. The costs are summarised in Table 1.  

For protein requirements, there will be a maintenance component and an amount for that deposited in the egg. The former is usually calculated from endogenous and metabolic nitrogen (TN) loss in excreta (mg/day) using the equation:

TN = 283 W^0.73 (Brody 1945)

Thus the 1.2 kg hen will need 323 mg of nitrogen or about 2 g of protein (N*6.25) for maintenance. The daily egg mass of 7.6 g will contain 1 g of protein. These are net protein figures and must be adjusted for protein digestibility and utilization of the protein. This will be only about 0.5 because of the composition of the food. Hence the dietary protein needs are 6 g/day. Similar calculations can be made for daily needs of calcium and phosphorus, which will be about 500 and 100 mg, respectively.

Roberts (1992) introduced the concept of the scavenging feed resource base (SFRB) and calculated this to vary from 200 to 400 kg for each household per year. Roberts (1992) calculated this to contain about 12.5 MJ AME/kg and 112 g of crude protein/kg. Using an average SFRB of 250 kg per household per year, the total energy will in theory support 12.5 scavenging hens. The crude protein is sufficient for 13 hens, and both are therefore equally limiting. Roberts (1992) did not provide analyses for Ca and P and these are also likely to be limiting if egg production is to be increased.

 
References

Brody S 1945 Bioenergetics and Growth. Reinhold Publishing Corporation.

Farrell D J 1986 Energy expenditure of laying ducks: confined and herded. In: Duck Production Science and World Practice (Editors. D I Farrell and P Stapleton), pp. 70-82. The University of New England, Armidale, NSW.

Johnson  R I 1983 Energy metabolism of poultry. Proceedings Australian Nutrition Society. 8: 72-82.

Roberts  J A  1992 The scavenging feed resource base in assessments of productivity of scavenging village chickens. Australian Centre for International Agricultural Research.  Proceedings No. 39.

Van Kampen M 1976 Activity and energy expenditure of hens. 3. The energy cost of eating and posture. Journal of  Agricultural Science (Cambridge) 87:  85-88.

 Received 30 October 2000

Back to top