EFFECTS OF AGE AT PHOTOSTIMULATION ON REPRODUCTIVE EFFICIENCY AND CARCASS CHARACTERISTICS .2. EGG-TYPE HENS

Increasing day length is the primary cue for the timing of sexual matu ration in poultry. Typically, Single Comb White Leghorn (SCWL) pullets are reared under conditions of short days (8L:16D) until 18 wk of age . In this study, the effects of varying the age at photostimulation fr om 16, 18 or 20 wk of age were studied in terms of carcass composition at photostimulation and at sexual maturity, as well as reproductive p erformance. A flock of 1600 SCWL pullets (Shaver 288 strain) were hous ed in floor pens in light-tight facilities (8L:16D). All birds were pr ovided with ad-libitum access to both feed and water. At 16 wk, 18 wk and 20 wk, 50 birds per treatment were moved to laying cages and provi ded to a photoperiod of 14L:10D. An additional 288 birds per treatment were housed two birds per cage, and group egg production and feed con sumption data were collected to 64 wk of age. At photostimulation (n = 20 birds per treatment) and on the day following the first ovipositio n, (n = 20 birds per treatment) birds were killed by cervical dislocat ion. All surviving hens were killed at 64 wk of age. All carcasses wer e studied in terms of selected organ weights and reproductive organ mo rphology. Birds killed at photostimulation and at sexual maturity were further studied for whole body carcass composition. Significant diffe rences were found in dry matter, water, lipid and ash content among tr eatment groups at the age of photostimulation. As age at photostimulat ion increased, absolute weight of carcass fat, protein and ash increas ed. The percent carcass lipid content increased for all groups between photostimulation and sexual maturity with the 16 wk treatment group s howing the largest increase. The time required to reach sexual maturit y from the age of photostimulation decreased as the age at photostimul ation increased. No significant differences were found in total egg pr oduction. The 16 wk group laid significantly smaller eggs. Delaying se xual maturity until 20 wk of age resulted in an increased prime sequen ce length and fewer pause days to produce approximate ly the same numb er of eggs as birds that were photostimulated at 16 wk of age.