Effect of light regimen under various ambient temperatures on sow and litter performance.

Primiparous Large White females were exposed to one of two light regimens characterized by an increase (from 12 to 16 h/d, LONG treatment) or a decrease (from 12 to 8 h/d, SHORT treatment) in photoperiod during gestation. Two successive replicates were conducted, and farrowings occurred in January and July. During the last month of gestation, during lactation and after weaning, ambient temperatures varied between 18 and 25 degrees C and between 25 and 38 degrees C for the first and second replicates, respectively. Weaning occurred at 3 wk postpartum. Percentage of sows in estrus within 10 d after weaning was higher (P < .05) in the SHORT than in the LONG group for both replicates and when farrowing occurred in January compared with July for both photoperiod groups (SHORT-January: 92%, LONG-January: 53%, SHORT-July: 32%, LONG-July: 14%). Loss of live weight in sows during lactation was higher in July than in January and higher in the SHORT than in the LONG photoperiod (P < .05). Live weight of pigs at birth was higher in July than in January, whereas growth rate of pigs until weaning was higher in January (P < .05). Temperature may have a greater influence on sow and litter performance than photoperiod.