The impact of sheep pasturing on the energy and organic nutrients levels in the steppe vegetation of the Mohelno Serpentine Steppe National Natural Reserve

Abstract

The aim of this research was to assess the implications of sheep grazing for the nutritional value of the vegetation in the Mohelno Serpentine Steppe National Nature Reserve (NNR). A free pasture controlled by an electric fence was practised from 1997 to 1998. The German Merino sheep were grazing on an area of 4.25 and 6 ha with a pasture load of 6.8–9.4 sheep per 1 ha in 1997 and 6.7–8.7 sheep per 1 ha in 1998. The steppe vegetation samples were collected from five different sites reflecting the phytocenological composition typical of the individual steppe areas. The vegetation samples were collected on an area of 3×1 m2 during the growing season at two-week intervals. The collected samples were tested for the amount of dry matter, fibre, nitrogenous substances, fat, ash, nitrogen-free extractive substances (NFES), gross energy (GE), metabolic energy (ME), lactation net energy (LNE), fattening net energy (FNE), PDIN and PDIE (PDI – referring to the factually digestible nitrogenous substances in the small intestine of the ruminants). During pasture there was a decrease in the dry matter levels but its average levels remained high (35.45–46.78%). The effect on the nitrogenous levels became apparent (P < 0.05) mainly in the second year of grazing (10.00–10.94% compared to 11.64–19.35% in the vege­tation dry matter). However, in comparison with the pasture vegetation the effect remained less significant. A similar situation was observed in relation to the fluctuation of PDIN and PDIE (64.60–70.71 compared to 75.18–124.98 g/kg of the dry matter and 79.03–82.71 compared to 89.41–29.27 g/kg of the dry matter respectively). The fat levels (3.80–4.02%) were not affected by the site (P < 0.05) but the specific utilization. The grazing brought about a marked increase in the fat levels (P < 0.001). The amount of the fibre during the first year was affected only in terms of its decreased site variability (29.60–31.31%). The conclusive evidence (P < 0.05) of the decrease did not appear until the second year of grazing (21.76–27.88%). In the course of the pasture the ash levels identified in the dry matter were fluctuating between 8.74–10.19% depending on the site conditions and the form of utilization. Conside­rably high levels (P < 0.05) were recorded on more intensely grazed areas. NFES levels in the step areas (45.16–47.26%) were steady both in terms of the site conditions and the form of utilization. The energy levels did not reflect the site variability. The ME, LNE and FNE levels (9.39–9.79; 5.52–5.80 and 5.34–5.69 MJ per kg of the dry matter respectively) were affected by the form of utilization. During the pasture the site variability of the energy levels decreased. There was also a substantial increase in the amount of energy established in the dry matter, which rose to the levels usual for pasture vegetation.

Keywords

• sheep pasture
• protected areas
• nutritional value