The herbage intake, eating behaviour and calf production of beef cows grazing improved pastures on the Northern Tablelands of New South Wales

Abstract

The effects of grazing pressure on herbage intake and grazing performance of Hereford breeding cows were studied during 1974-75 at Glen lnnes on the Northern Tablelands of New South Wales. The objective was to identify a grazing pressure that allowed a high output of weaner liveweight per unit area without deleterious effects on cows or pastures. Grazing pressure was expressed through stocking rate equivalents of 0.93 (L), 1.22 (M) and 1.49 (H) cows ha-1 for two replicated groups, which contained five cows and one oesophageally fistulated heifer. Measurements were taken each month from August to November of the characteristics of the pastures and of the grazing performance of the cows. Overall there was less herbage available to cows in the second year but at the L and M grazing pressure there was no significant difference between cow performance. Cows were lighter (P < 0.01) and weaned lighter calves from the H grazing pressure in both years even though a hay supplement was given during lactation (September-October). Intake of digestible organic matter (DOMI) by pregnant cows decreased from autumn to winter at all grazing pressures. This coincided with a decrease in the availability of pasture dry matter (PDM) in the winter. With the onset of calving in late winter (August), cows increased DOMI by 43% due partly to increased grazing times (28% longer) and partly due to the ability of cows to ingest more of the available herbage (86% more DOM kg-1 PDM). This altered grazing pattern apparently was an attempt by cows to obtain their requirements for lactation from the low PDM in late winter. The mean 200 day weaning weight of calves of 187 kg suggested that cows and calves in L and M were successful in compensating, whereas the 165 kg weaners in H indicated that these cows and calves were less so. The results indicate that under similar conditions to the experiment a stocking rate of 0.93-1.22 cows ha-1 would permit a high output of weaner liveweight per ha without deleterious effects on cows or pastures. However, with these stocking rates it was suggested that calving should be delayed for 2 to 4 weeks to best match cows' energy demands for lactation to the Spring growth of highly digestible herbage.