RELATIONSHIPS BETWEEN THE DEGREE OF FOOD RESTRICTION AND WELFARE INDEXES IN BROILER BREEDER FEMALES

1. Broiler breeder females were fed ad libitum, or according to a comm ercial food restriction programme or to gain 0.85, 0.70, 0.55, 0.40 or 0.25 of the body weight of ad libitum-fed birds. Several indices of t he welfare of the birds were assessed at 3-weekly intervals to 18 week s of age and related to body weight by regression analysis. Results fo r 6, 12 and 18 weeks of age are presented in detail. 2. Water intake w as consistently higher in the 0.25, 0.40 and commercial restriction tr eatments. 3. There was a negative curvilinear relationship at each age between body weight and the heterophil-lymphocyte ratio and plasma co rticosterone concentration. 4. There was a positive relationship betwe en the plasma concentration of creatine kinase and body weight at 12 a nd 18 weeks of age. The relationships between body weight and the plas ma activity of alkaline phosphatase and aspartate transaminase changed with age and there were no differences between treatments for lactate dehydrogenase. 5. The time spent resting increased with body weight a t each age. The relationship between time spent preening and body weig ht changed with age whereas that for oral activities was similar among restricted birds at 6, and among all treatments at 12 weeks of age. A t 18 weeks there was an increase in oral activities with decreasing bo dy weight. 6. Fearfulness was positively related to body weight. The r esponse of the comb to phytohaemagglutinin injection was similar in al l treatments and the antibody titre to injections of sheep red blood c ells was curvilinear. 7. A principal components analysis of all measur ed traits at 6, 12 and 18 weeks of age was conducted. Most of the vari ables were redundant but at least one from each of the different class es of welfare indices was retained at 6 and 12 weeks of age. 8. It was concluded that a body weight during rearing in the range of 0.5 to 0. 85 of ad libitum might provide for optimum welfare of broiler breeder females.