Seasonal changes in circadian grazing patterns of Kerry cows (Bos taurus) in semi-feral conditions in Killarney National Park, Co. Kerry, Ireland

Domestic cattle generally graze during the day although some night-rime gra zing also occurs. However, questions remain as to the effect of management on circadian grazing patterns. This study provides for the first time a qua ntification of seasonal, circadian and animal variation in grazing behaviou r and grazing time in cattle in semi-wild conditions. The objectives of the study were to examine how daily grazing times and the temporal distribution of grazing activity changed with season and to exami ne the extent to which grazing patterns were influenced by day-length. A gr oup of 12 heifers of the Kerry breed continuously grazed a lowland field of 4.7 ha. The old permanent pasture sward was dominated by Holcus spp. and A grostis spp. Feed availability was never limiting. Length and periodicity o f grazing were recorded using vibracorders attached to the necks of seven a nimals. Results showed that daily grazing times remained constant over most of the grazing season (circa 10-11 h per day), however, some variation occurred la te in the season. The temporal distribution of grazing activity changed as the season advanced so that by October grazing patterns became significantl y different to those of July. The time interval between grazing bouts at da wn and dusk decreased with decreasing day-length. nn increased percentage o f night-time grazing occurred at shorter day-lengths. It is concluded that there is a significant seasonal effect of day-length o n temporal distribution of grazing activity with night-time grazing featuri ng more as day-length decreases. The maintenance of similar total daily gra zing times in the face of changing day-length (with the exception of late i n the season) suggests that daily grazing times are a function of the attai nment of a relatively constant nutritional requirement by the animal. (C) 2 001 Elsevier Science B.V. All rights reserved.