The quality of pasture forage under rotational and continual grazing of heifers

The present study was carried out to investigate the effect of different grazing management systems on quality of pasture forage. The experiment was carried out from 1993 to 1996 at an experimental pasture in the Jizerske hory mountains (lat. 51 degrees 20' N, long. 15 degrees 02' W; the altitude is 420 m; the average annual precipitation is 803 mm; the mean annual temperature is 7.2 degrees C). The dominant species are couch grass [Elytrigia repens (L.) Desv.], ryegrass (Lolium;perenne L.), rough bluegrass (Poa trivialis L.), Kentucky bluegrass (Poa pratensis L.), bentgrass (Agrostis capillaris L,), white clover (Trifolium repens L.) and dandelion (Taraxacum officinale Web.). No fertilizers have been applied since 1992. There were two treatments: rotational grazing (R) and continuous grazing (K), both of them on 1.0 ha. The areas were grazed by five young Czech Pied I heifers in 1993 and by six young Friesian x Czech Pied heifers in 1994, 1995 and 1996 (the average initial weights of the heifers ranged from 135 to 180 kg). The area of (R) was divided into six paddocks, each measuring about 0.166 ha, and heifers were grazed from one paddock to another. The sward at (K) was maintained at a height of 5 to 7.5 cm by varying the grazing area available for treatment and by reducing the number of heifers in late summer. Each week, samples of herbage were taken to simulate herbage grazed by the heifers and were subsequently dried and analysed for nutrients and minerals. The mean contents of nutrients and minerals are given in Tabs I and Il. A surplus of crude protein (CP) and K was found in forage at rotational and continuous grazing, however, there was a shortage of energy, crude fibre (CF) and Ne. These results are typical for pasture forage in our climatic conditions. Significant differences in the content of CP (P < 0.01) and CF (P < 0.001) were found between both grazing systems, where at continuous grazing the content of CP was about 10% higher and the content of CF about 10% lower than at rotational grazing. This seemed to be due to greater CP and lower CF content in younger lower award at continuous grazing with a higher rate of white clover (Trifolium repens L.) in sward (Fig. 1). Also the tendency of a higher total minerals content at continual grazing can be connected with the different rate of white clover. Especially higher content of Ca and Mg (P < 0.05) at continual grazing was probably caused by white clover, that has a generally higher content of Ca and Mg than grasses. The higher rate of Na in pasture forage at continual grazing greatly decreased (P < 0.01) the ratio of K/Na. The ratio of K/Ca+Mg in meg. was at both variants always lower than the limit value 2.2. The differences in quality of pasture forage did not strongly affect the average daily liveweight gain of heifers.