04-Lancaster Farming, Saturday, September 20, 1997 WHAT ARE THE EFFECTS OF VARYING DAY LENGTH ON GROWTH OF BROILERS? R. MICHAEL HULET Associate Prof. Dept. Poultry Science Many investigates have looked at various day lengths to determine what is optimum foi broiler growah and meat produc tion Continuous daylight, in creasing day lengths, intermittent lighting, and short and long day lengths have been compared The data indicate that the most rapid growth lot modem broileis occurs when birds are grown under continuous 23- or 24-hour day lengths Continuous daylight al lows buds access to teed and water at all times, especially during the coolest portion of the day during hot weather Continuous day length allows broilers to reach their genetic potential for growth and meal production However, genetic selection tor increased broiler growth has re sulted in chickens developing some metabolic lesions it not cor rectly managed Rapidly growing birds have a higher incidence of I) Sudden Death Syndrome (SDS), 2) leg abnormalities such as tibial dyschondroplasia (TD), rotated and twisted tibia or femurs, or rickets type slipped tendons, and 3) asci lics, which is also called “water belly" All these lesions have been linked with the rapid rate of growth of broilers Some investigators have advo cated dilterenl management re gimes to prevent or reduce the de velopment ol the symptoms of metabolic diseases among rapidly glowing birds Investigators from Canada (Classen and Riddel, 1989; Classen ct al, 1991, Blair et al, 1991) have shown that short day lengths al early ages can decrease skeletal disorders and incidences of Egg Age to Haugh Unit Relationship Haugh unit 6 10 1C 20 2C 30 3S 40 48 Age (days) R square = 0 0269, P = 0.001, 0 = 67.5 Haugh units Egg Age to Weight Relationship Egg 61 Wt(g) 6 10 18 20 2C 30 , 36 40 48 R square = 0.0124, P = 0.01,0 = 60.3 g SDS Alabama rcseaichers (Rendcn et al, 1991 and 1992) also showed fewer leg abnormalities and im proved carcass yield with a light ing program that provided de creased day length early in the production cycle However, all ol these experi ments resulted in significantly lower body weights Most oi the decreased day-length programs re duced the day length to 6 hours of light at 3 to 5 days of age causing a reduction in feed consumption and bird growth during this critical period Other researchers have merely reduced feed provided to the birds for an 11 - to 14 day period early in life to reduce growth and hopefully reduce the other meta bolic side effects This strategy has also been successful in reduc ing metabolic lesions but still at the expense of reduced body weight at market age In 1997, a study was reported from Penn State University at poultry science meetings in Geor gia, where light was reduced to 16 hours a day from 3 to 28 days of age and then increased gradually as the birds approached market age. This lighting regime was tested against a conventional 23-hour per day lighting treatment on three different strain crosses of birds. Although there were some strain differences in body growth, it was found that the birds on the experimental lighting treatments had two percent less mortality at seven weeks and actually an in crease in body weight over those raised on the control (23 hr) light ing system." The lowered percent age mortality and enhanced growth was consistent for the three differ ent strain crosses of broilers. Increased activity was noted for the broilers on the experimen tal lighting treatment and may have contributed to the improved health and growth of the broilers. 1 all eggs (771 doz) all eggs (771 dozen) Age (days) Therefore, reduced lighting treat ments starting at three days of age was shown to be an effective management tool for reducing metabolic lesions and mortality while promoting growth of broil ers. ■ BUY. SELL.! 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