Genetics and Animal Welfare - Genetics and the Behavior of Domestic Animals - page 440

Research on chickens shows that birds selected for egg production stop
eating when their metabolic needs are met, but broiler chickens selected
for meat production do not stop eating until their gut is completely full
( Nir et al., 1978 ).
From an appetite standpoint, the welfare of broiler chickens and market
pigs being fattened for slaughter is good. These animals are allowed to eat
until satiated. However, a welfare problem related to increased appetite
occurs in breeder hens and sows of the fast-growing offspring. Breeders have
to be maintained on a calorie-restricted diet ( Close, 1996 ). For example,
broiler breeders on a restricted diet produce more eggs ( Robinson et al.,
1991 ), but if allowed to eat until satiated, they develop reproductive pro-
blems ( Yu et al., 1992a ). Furthermore, if sows are fed all they can eat, they
become over-fat, which can result in leg problems and difficulties farrowing.
Problems occur because breeder animals' appetites far exceed their basic
metabolic needs.
Broiler breeders used for egg production are fed 60 80% less than they

would eat if fed ad lib. to prevent them from becoming overweight
( Karunajeewa 1987; Hocking 1993; Hocking et al., 1993; Yu et al., 1992a,b;
Zuidhoff et al., 1995 ). When hens go into egg production to produce broiler
chicks, they are restricted to 25

50% of what they would eat if they ate until
satisfied. Feed restriction in sows is slightly less extreme compared to broiler
chickens. Gestating sows are fed approximately 60% of their ad lib. intake
of a standard grain concentrate diet ( Lawrence et al., 1989 ). A sow nursing
piglets is allowed to eat all she wants, but during gestation, she is kept on a
calorie-restricted diet to prevent her from becoming too fat.
A review of a number of studies shows that feed restriction in breeding
sows and chickens results in many abnormal behaviors, such as stereotypies
( Lawrence and Terlouw, 1993 ). Appleby and Lawrence (1987) and Tolkcomp
et al. (2005) found that stereotypies developed in sows only when their feed
intake was restricted. In a subsequent experiment, the same research team con-
cluded that the amount of feed sows are fed on commercial farms is not high
enough to satisfy their motivation for feeding ( Lawrence et al., 1989 ). They
further concluded that hunger resulting from a restricted diet may be a major
cause of stress in confined housing systems. Bergeron and Gonyou (1997)
found that stereotypies developed when the diet did not have sufficient energy
to prevent hunger. Similar results have been found in other animals. Savory
et al. (1992) found that feed restriction in broiler breeder hens also results in
stereotypies. It is becoming increasingly clear that feed restriction in animals
selected for increased appetite is a serious welfare concern.

Importance of Roughage Feeds
It is a common practice in the poultry and pork industries to feed highly con-
centrated diets consisting of mostly grain to breeding sows and broiler