Studies on Broiler Breeding

Abstract

In this investigation we expected to get some fundamental informations on the pattern of growth of cockerels and of changes of body conformations during their growing period from hatching to eleven weeks of age. Observations were done under natural and experimentally controlled conditions. In the latter case, cockerels were fed on quantitatively restricted diet for one week during early or late stages, to retard their growth. Two hundred and ten newly hatched White Leghorn male chicks were used. Four different feeding treatments were projected; first group was fed ad lib. as control, the second group (Treatment I), was given the restricted feed for a week at one week of age, the third group (Treatment II), was given the restricted feed for a week at two weeks of age, and the fourth group (Treatment III), was given the restricted feed for a week of eight weeks of age. After the period of feed restriction, all the groups were fed ad lib. Random samples of five or six cockerels were dissected and measured to analyse the growth and effects of feed restriction and following recovery in full feeding.1. Recovery from the effect of feed restriction for one week was partly achieved by an abnormally rapid growth. But this rapid growth did not continue for a long time, it disappeared before they could exceed the normal body growth in control at eleven weeks of age. In spite of their high growth rate and good efficiency of compensatory growth, they could not improve any feed efficiency.2. Changes of weight or length of parts of body in final stage or normal growth were expressed as a magnification of their initial values of day-old chicks. Magnifications were 3.0 in the weight of eyeball, 3.5 in the length of metatarsal bone, 14.2 in the weight of the edible visera including the heart, liver and gizzard, 26.0 in the weight of vertebral column, rib and hip bone, 33.3 in the weight of tarsometatarsus, 34.3 in the live weight, 36.7 in the weight of bone on femur-tibiotarsus, 59.3 in the weight of muscle on femur-tibiotarsus and 272 in the weight of pectoralis minor muscle. The lower magnification, the earlier growth completes. Namely, nerves make most rapid growth in the early stage and they followed by the growth of bones and of muscles. Such growth gradients were also found among bones or muscles. For example bones and muscles of femur-tibiotarsus grow earlier than bone of pelvic limb and pectoralis major muscle.3. Differences between the magnifications of length of metatarsal bone and of the weight of it show higher growth rate in length than weight.4. Early developing organs such as nerves and bones have the priority to grow even under restricted feeding. Recovery shows also different pattern between parts of the muscles or of the bones. Late developing organs or the parts of the same organ are affected more severely by the restricted feeding than early developing one, but recoveries of the former are quicker than that of the latter. Muscles and edible visera are likely to be affected but the latter recovered more rapidly.5. As treatmental group I, in which feed was restricted when their growth rate was highest, the effect of restriction was greater and severer than treatmental groups II and III where the restriction was practiced at the stages of lower growth rate. Treatment I was recovered slower compared with treatments II and III.6. Dressing percentages of all treatmental groups were lower immediately after restriction and after a week than control, while percentage of the weight of head and bone of tarso-metatarsus, weight of edible visera to live weight were also higher than control at each period mentioned above. The fact that the visera take priority in growth among the other organs may be concerned with their own metabolic and nutritional functions to support the whole growth of organs.