Improving forage nutritive value and botanical composition in a natural grassland using different grazing methods and herbage allowances

Abstract

The present study aimed to define the most appropriate management for a natural grassland during winter so as to improve its botanical composition and forage nutritive value during the subsequent spring. The experiment was conducted in an 8.4-ha Pampa biome natural-grassland area and divided into 12 0.7-ha paddocks for 196 days. During the first 84 days (winter), two grazing methods (GM), namely continuous (CS) and rotational grazing (RS), and two herbage allowances (HA), namely 12 and 18 kg DM/100 kg bodyweight, were imposed on the ewes in early pregnancy, which resulted in the following four treatments: C18, C12, R18 and R12. From Day 85 onward (final third of pregnancy), all paddocks were managed with C18 so as to avoid intake restrictions. The sward was characterised by herbage mass (HM), green leaf mass (GLM), stem mass, senescent material, legume mass, forage growth (FG), canopy height, canopy density and weeds mass (other than grass and not preferred species). The qualitative characteristics were shown as neutral detergent fibre (NDF), acid detergent fibre (ADF), lignin, crude protein (CP) content and ingested crude protein. Although GLM was higher when RS was applied, HM did not differ between GM and HA when management factors were applied during winter. In spring, increased HM was observed in paddocks managed with 18% HA. Weeds mass presented GM × HA interaction, with the lowest participation in Treatment C12. The NDF and ADF levels differed between HA, in addition to being higher in 12% HA and during winter periods. In spring, the lowest NDF levels were found in paddocks under 12% HA and ADF changed only along the periods. The GM and HA applied during winter did not change the lignin content. The CP in winter differed only over the periods. Treatment C12 was applied in the winter and resulted in 8.1% more CP than did C18, R12 and R18 in the spring. There was a GM × HA × Period interaction in ingested CP, revealing that the treatments during winter influenced the quality of the ingested herbage during spring. Ewes in C12 ingested herbage with more CP than did the animals in the other treatments. Variations in grazing methods combined with HA during winter influenced the chemical and structural characteristics of the sward. High stocking rate with continuous stocking presented better chemical characteristics than did the other treatments and the use of high stocking rate in continuous grazing may have an important effect on spring pasture quality due to changes in sward structural characteristics.