Science based paper on the impact of restricting feed in broiler chickens.(Extensive footnotes)
[ed. - this paper was written in support of a petition filed in British courts over the lack of regulations protecting the welfare of chickens. See Petition ]
Broilers are the chickens reared for their meat. Through genetic selection, breeding companies have dramatically increased the growth rate of broilers over recent decades. Continued genetic selection is undertaken within the pedigree flock and these birds form the basis from which future commercial broilers (the ordinary broilers reared for their meat) are produced. Changes in the pedigree flock are passed through several generations of breeding flocks (Fig. 1), taking 4-5 years to reach the commercial broiler stage.
Pedigree (Elite) stock
Fig. 1: The structure of broiler breeding flocks in the UK. (original shows arrows pointing down to the next category)
The parent stock in the UK are usually reared from day-old to 18 weeks and then transferred to laying farms where they begin breeding at around 24 weeks. At any one time there are approximately 6 million broiler breeder hens in the UK producing fertile eggs to supply chicks for commercial broiler production. Up to about 60 weeks of age each of these hens will produce some 120 broiler chicks (FAWC, 1998).
Why is feed restriction practised?
As a result of the genetic selection of broilers for increased growth rate and lower (more efficient) feed conversion ratio it has become necessary to severely restrict the feed intake of the broilers intended for breeding to enable them to survive into adulthood and reproduce successfully.
If the breeding flocks were fed ad libitum they would become obese and suffer thermal discomfort, a high incidence of lameness, and high mortality due to skeletal disorders and heart failure (Katanbaf et al , 1989; Savory et al , 1993). Excessive body weight is also associated with reduced disease resistance (Han and Smyth, 1972; Hocking et al , 1996); increased incidence of multiple ovulations in females, resulting in lowered production of hatching eggs (Hocking et al , 1987; Hocking et al , 1989); poor egg shell quality (Robinson et al, 1993); and reduced fertility in males (Hocking and Duff, 1989).
Compassion in World Farming (CIWF) believes that the proper approach to avoid the health problems that affect broiler breeders is not to restrict their feed, but to end the use of fast-growing genotypes. Instead, slower-growing genotypes should be used as these would not be vulnerable to a high incidence of leg and heart problems arising from fast growth rates, and so feed restriction would not be needed.
How severe is the feed restriction?
The Farm Animal Welfare Network reported in 1996 that a female broiler breeder receives 52g of feed daily at 7 weeks of age, while a commercial broiler (intended for slaughter at around 6-7 weeks) will consume 182g of feed daily. The impact of this restriction can be seen in the fact that at 7 weeks of age a female breeder weighs 780g, while a female commercial broiler weighs around 2440g. Similarly, a male breeder receives 78g of feed daily at 7 weeks of age and weighs just 1100g, compared with a male commercial broiler of the same age that will consume 205g of feed and weigh around 2897g (FAWN, 1996).
In the UK, broiler breeders are generally fed on restricted rations from the age of 15 days (FAWC, 1998). Feed allowances during the rearing period are typically 60-80% less than the birds would consume ad libitum , and may be 25-50% less during the laying period (Yu et al , 1992; Savory et al , 1993). This results in a reduction in adult body weight to approximately 45-50% that of ad libitum fed birds (Katanbaf et al , 1989).
The feed is usually supplied in a single daily feed, which is generally consumed in less than 10 minutes (Savory et al , 1993).
The pedigree flock are subjected to particularly extreme feed restriction. In order to be able to identify those birds that have the most desirable traits for increased production in future generations, they are reared to their maximum potential growth rate up to at least 6 weeks of age, at which point selection takes place. This creates birds that are very heavy and they are then severely feed restricted to ensure they are not overweight for the laying period.
Evidence that feed restriction seriously compromises welfare
Fowls would naturally spend a considerable portion of their day engaged in activities associated with foraging, and when given the choice prefer to work for at least part of their daily feed intake rather than eating it all from a free supply (Duncan and Hughes, 1972). Feed restricted broiler breeders, however, consume their feed in a very short space of time and are chronically hungry. This is demonstrated by the fact that they are strongly motivated to consume feed at all times. Indeed, their level of feeding motivation is 3.6 times greater than that of ad libitum fed birds subjected to 72 hours of feed deprivation, and is just as high one hour after their daily meal as it is one hour beforehand (Savory et al , 1993).
Feed restricted birds are hyperactive, and they show increased pacing before the expected feeding time and increased drinking and pecking at non-food objects afterwards, compared with ad libitum fed birds (Kostal et al , 1992; Savory et al , 1992). The expression of these activities is often stereotyped in nature, is characteristic of frustration of feeding motivation (Duncan and Wood-Gush, 1972), and is positively correlated with the level of feed restriction imposed (Savory and Maros, 1993). Also, feed restricted males are more aggressive than ad libitum fed males (Mench, 1988). In their 1993 paper, Savory et al concluded that restricted fed broiler breeders are “chronically hungry, frustrated and stressed” and that the first of the ‘Five Freedoms’ is being contravened (Savory et al , 1993). The Five Freedoms are a widely recognised approach to assessing animal welfare; the first freedom is freedom from hunger and thirst.
There is also evidence that physiological indices of stress, such as herophil/lymphocyte ratio, basophil and monocyte frequencies, and plasma corticosterone concentration, are higher in feed restricted than in ad libitum fed birds (Maxwell et al , 1990, 1992; Hocking et al , 1993), and are positively correlated with the level of feed restriction imposed (Hocking et al , 1996). According to a recent review “broiler breeders show evidence of physiological stress as well as an increased incidence of abnormal behaviours, and are also chronically hungry” (Mench, 2002).
It has been suggested that qualitative feed restriction, such as dietary dilution to allow the birds to consume large amounts of feed without increasing their energy intake, could alleviate hunger. However, recent research demonstrates that broiler breeder welfare is not improved by using qualitative rather than quantitative feed restriction methods (Savory et al , 1996; Savory et al , 2000).
CIWF believes that the severe feed restriction necessary to maintain health and fertility of broiler breeders results in unacceptable health and welfare problems, and that the need for feed restriction should be removed by ending the use of fast-growing genotypes. This view is supported by the conclusions of the Farm Animal Welfare Council that “the problem of hunger in broiler breeders is not easy to solve with present strains of birds and is likely to get worse if selection for fast growth continues. A long-term solution is to change the genetic strains but, in any case, breeders must avoid exacerbating the problem and reduce their demand for ever increasing growth rates” (FAWC, 1998).
The March 2000 report by the European Commission’s Scientific Committee on Animal Health and Animal Welfare (SCAHAW) states that the “chronic quantitative food restriction” to which broiler breeders are routinely subjected leads to them being “very hungry”. The SCAHAW condemned this practice stating that “the severe feed restriction…results in unacceptable welfare problems” and they insisted that “the welfare of breeding birds must be improved” (SCAHAW, 2000).
Duncan, I. J. H. and Hughes, B. O. (1972) Free and operant feeding in domestic fowls. Animal Behaviour 20 , 775-777.
Duncan, I. J. H. and Wood-Gush, D. (1972) Thwarting of feeding behaviour in the domestic fowl. Animal Behaviour 20 , 444-451.
FAWC (1998) Report on the welfare of broiler breeders. Ministry of Agriculture, Fisheries and Food, August 1998.
FAWN (1996) Broiler breeders. A Farm Animal Welfare Network factsheet, March 1996.
Han, P. F. S. and Smyth, J. R. (1972) The influence of restricted feed intake on the response of chickens to marek’s disease. Poultry Science 51 , 986-990.
Hocking, P. M., Gilbert, A. B., Walker, M. and Waddington, D. (1987) Ovarian follicular structure of white leghorns fed ad libitum and dwarf and normal breeders fed ad libitum or restricted until point of lay. British Poultry Science 28 , 493-506.
Hocking, P. M. and Duff, S. R. I. (1989) Musculo-skeletal lesions in adult male broiler breeder fowls and their relationship with body weight and fertility at 60 weeks of age. British Poultry Science 30 , 777-784.
Hocking, P. M., Waddington, D., Walker, M. A. and Gilbert, A. B. (1989) Control of the ovarian follicular hierarchy in broiler breeder pullets by food restriction during rearing. British Poultry Science 30 , 161-174.
Hocking, P. M., Maxwell, M. H. and Mitchell, M. A. (1993) Welfare assessment of broiler breeder and layer females subjected to food restriction during rearing. British Poultry Science 28 , 493-506.
Hocking, P. M., Maxwell, M. H. and Mitchell, M. A. (1996) Relationships between the degree of food restriction and welfare indices in broiler breeder females. British Poultry Science 37 , 263-278.
Katanbaf, M. N., Dunnington, E. A. and Siegel, P. B. (1989) Restricted feeding in early and late-feathering chickens 1: Growth and physiological responses. Poultry Science 68 , 344-351.
Kostal, L., Savory, C. J. and Hughes, B. O. (1992) Diurnal and individual variation in behaviour of restricted-fed broiler breeders. Applied Animal Behaviour Science 32 , 361-374.
Maxwell, M. H., Robertson, G. W., Spence, S. and McCorquodale (1990) Comparison of haematological values in restricted- and ad libitum -fed domestic fowls: white blood cells and thrombocytes. British Poultry Science 31 , 399-405.
Maxwell, M. H., Hocking, P. M. and Robertson, G. W. (1992) Differential leucocyte responses to various degrees of food restriction in broilers, turkeys and ducks. British Poultry Science 33 , 177-187.
Mench, J. A. (1988) The development of aggressive behaviour in male broiler chicks: A comparison with laying-type males and the effects of feed restriction. Applied Animal Behaviour Science 21 , 233-242.
Mench, J. A. (2002) Broiler breeders: Feed restriction and welfare. World’s Poultry Science Journal 58 , 23-29.
Robinson, F. E., Wilson, M. W., Yu, G. M., Fasenko, G. M. and Hardin, R. T. (1993) The relationship between body weight and reproductive efficiency in meat-type chickens. Poultry Science 72 , 912-922.
Savory, C. J., Seawright, E. and Watson, A. (1992) Stereotyped behaviour in broiler breeders in relation to husbandry and opioid receptor blockade. Applied Animal Behaviour Science 32 , 349-360.
Savory, C. J. and Maros, K. (1993) Influence of the degree of food restriction, age and time of day on behaviour of broiler breeder chickens. Behavioural Proceedings 29 , 179-190.
Savory, C. J., Maros, K. and Rutter, S. M. (1993) Assessment of hunger in growing broiler breeders in relation to a commercial restricted feeding programme. Animal Welfare 2 , 131-152.
Savory, C. J., Hocking, P. M., Mann, J. S. and Maxwell, M. H. (1996) Is broiler breeder welfare improved by using qualitative rather than quantitative food restriction to limit growth rate? Animal Welfare 5 , 105-127.
Savory, C. J. and Lariviere, J. M. (2000) Effects of qualitative and quantitative food restriction treatments on feeding motivational state and general activity level of growing broiler breeders. Applied Animal Behaviour Science 69 , 135-147.
SCAHAW (2000) The welfare of chickens kept for meat production (broilers). Report of the Scientific Committee on Animal Health and Animal Welfare, adopted 21 March 2000.
Yu, M. W., Robinson, F. E. and Roblee, A. R. (1992) Effect of feed allowance during rearing and breeding on female broiler breeders 2: Ovarian morphology and production. Poultry Science 71 , 1750-1761.