Effects of grazing system on production and parasitism of dairy breed heifers and steers grazing wet marginal grasslands

Summary

Production and endoparasitism in first grazing season of Holstein heifers and steers were investigated in two grazing seasons, at low-lying peaty soil. In year 2000, forty animals were included in a 2 x 2 factorial, replicated experiment with two sexes (steers vs. heifers) and two stocking rates (SR): normal vs. low (840 vs. 420 kg live weight per ha at turn out) in a set stocking grazing system. Mean grass height over the entire season were 6.3 ± 4.8 cm (mean ± s.d.) at normal SR and 9.8 ± 6.1 cm at low SR. Mean daily live weight gain during grazing was significantly (P < 0.001) lower at normal SR (256 ± 147 g) compared to low (468 ± 142 g) but sex did not significantly affect the daily gain. Serum-pepsinogen levels, indicating uptake of gastrointestinal nematodes, were higher at normal SR and consistently higher in steers compared to heifers, although not significant. In 2001 the experiment included 80 animals in a 2 x 2 factorial experiment with two sexes (steers vs. heifer), two grazing systems (set stocking and 2-paddock rotation) and four replicates. Pasture quality was low, average DOM 57% and 13.9% crude protein in DM independent of grazing system. Mean daily live weight gain was not significantly affected by grazing system. A tendency (P=0.07) to lower daily gain for the heifers than for steers was observed (427 ± 161 g vs. 474 ± 138 g). Lower levels of pasture contamination with parasites were observed in the paddocks spelled up to mid July but otherwise rotation did not prevent parasite infections.
It is concluded that first grazing season steers and heifers have the same potential for growth when grazing at marginal areas with low pasture quality. Set stocking or the two-paddock rotation scheme did not affect productivity or level of parasite infection at the end of season. Parasite infections can become a problem at high SR. SR is an important factor for both daily live weights gain per animal and total production per ha. However, due to the very heterogeneous structure of marginal areas there is a need for other indicators than kg live weight per ha at turn out in order to defined a clear relationship between stocking rate and production.