Effect of photoperiod before and after birth on puberty in ewe lambs

Previous studies have shown that exposure to long days followed by short days after 12 wk of age advances the onset of puberty in ewe lambs. The aim of this experiment was to determine whether or not puberty would be advanced by exposure of lambs to such a photoperiodic regime when the long days were given before birth and the short days immediately after birth. Ewes kept in natural photoperiod (NP) were housed on January 15 and allocated at random to one of four treatments: 1) NP/NP, natural photoperiod before and after parturition (n = 26); 2) SD/SD, short days (SD; 9L:15D) before and after parturition (n = 27); 3) LD/NP, long days (LD; 18L:6D) before parturition and NP after parturition (n = 27); and 4) LD/SD, LD before parturition and SD after parturition (n = 26). Mean (+/- SEM) birth date for all lambs was March 20 +/- 1 day, and the number of days of exposure to long and short days prior to parturition was 64 +/- 2 and 67 +/- 2 days, respectively. From ewes on the four treatments, 24, 20, 14, and 16 female lambs, respectively, were reared. Lambs were weighed at birth and at weekly intervals after weaning. Reproductive activity in ewe lambs was assessed from serum progesterone concentrations in blood samples collected twice weekly from August 1 until puberty was reached or the experiment terminated on November 17 (34 wk after birth). Time of puberty in lambs exposed to NP both before and after birth (24 of 24 lambs reached puberty on October 15 +/- 4.0 days mean +/- SEM); 30 wk of age) was not different (p 0.05) from that in lambs given LD before birth and NP after birth (14 of 14 lambs reached puberty on October 23 +/- 3.3 days; 31 wk of age) Puberty had not occurred at the end of the experiment (p 0.0001) in most lambs given SD after birth regardless of whether they were given SD or LD before birth (SD/SD, 5 of 20 lambs reached puberty with a mean puberty onset of October 27 +/- 3.0 days [31.5 wk of age]