| Resumo: |
ABSTRACT This study was conducted to calculate the heat requirements of Hy-line W-36 and Hy-line W-98 layer chicks placed on different dates, and to select one of these strains based on heat requirements and egg prices. An environmentally-controlled, mechanically-ventilated, and fan and pad-cooled house with a capacity of 94,500 chicks was designed. Based on the identification of September as the month with the highest egg prices, placement dates were selected (16th of March, 1st of April, 16th of April, 23rd of April and 1st of May) to coincide with economic egg weight in that month. The heat requirements for a rearing period of 35days of both evaluated strains starting on the above-mentioned dates were calculated using heat and moisture balance method commonly used for livestock and poultry houses. Those placement dates corresponded to economic egg weight dates (with 50-52 g eggs) of 15th of August, 1st of September, 16th of September, 23rd of September and 1st of October. Total heat requirements during the 35-day rearing periods of chicks placed on the identified dates were respectively calculated as 640, 601, 413, 401 and 369 kW/h for Hy-line W-36 and respectively as 778, 732, 551, 539 and 497 kW/h for Hy-line W-98 chicks. September had the highest egg prices for both strains (4.73 and 5.06 US cents/egg). The lowest heat requirement was observed when chicks were placed on the23rd of April. Hy-line W-36 chicks presented higher total heat requirement than Hy-line W-98 chicks. Therefore, 23rd of April as the most economic placement date and Hy-line W-36 as the most cost-effective layer strain.
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