Effect of diurnally fluctuating high ambient temperatures on performance and feeding behaviour of multiparous lactating sows

Forty-two multiparous Large While sows were used to investigate the effect of diurnally fluctuating temperature (T) on lactation performance and feedi ng behaviour. The animals were allocated to one of the four thermic treatme nts: constant T at 25 degreesC (25C) and 29 degreesC (29C) or equal-mean di urnal cyclic T varying from 21 to 29 degreesC (25V) and from 25 to 33 degre esC (29V). Photoperiod was fixed to 14 h of light. The sows were given food ad libitum between the 7th and the 19th day post partum. Lactation perform ance was measured for all sows whereas the feeding behaviour was recorded o nly on 28 sows. The ad libitum food intake was comparable at 25C and 25V (6 .31 kg/day) as were milk production and body reserves mobilization. In cont rast, food intake at 29V was higher than at 24C (4.53 v. 3.48 kg/day) with no difference in milk production between the two treatments. The increased daily food intake at 29V resulted from higher intakes over the coolest peri ods of the day and especially during the dark period. Neither meal size nor daily number of meals were significantly affected by T. Feeding behaviour was mainly diurnal but with differences between treatments: 0.90 of total f ood intake at 29C v. 0.78 at the other three T. It appears that the effects of diurnally fluctuating T on lactation performance of sows depend on the mean level of T.