Effect of yolk sac removal at hatch on growth and feeding behavior in lines of chickens differing in body weight.

Influence of residual yolk on growth, feeding behavior, and development of certain internal organs during the first week after hatch were measured in lines of chickens that had undergone long-term selection for high (HW) or low (LW) 56-day body weight. At hatch chicks were assigned to one of the following treatments: removal of residual yolk (Y), sham operated (S), or no surgery (I). Body weight gains of HW chicks began on day 1 while LW chicks did not begin to gain weight until several days after hatch. Food intake increased linearly in both lines, but at a higher rate for HW than LW chicks. Seven days after hatch, relative to body weight, shanks were longer and pancreases and small intestines heavier for HW than LW chicks. Among treatments, body weight gains were greater for I and S than for Y chicks in the HW line, but not the LW line, demonstrating a differential response by fast and slow growing chicks to removal of the yolk sac. Feed intake differed on day 3, with Y chicks eating less than S chicks; I chicks were intermediate. Results indicate that presence of residual yolk sac during the first three days after hatch are critical to growth and development of chicks.