Abstract
Aim of study: To evaluate the impact of Cistus ladanifer L. (rockrose) tannins on ruminal degradability and fermentation characteristics and the use of polyethylene glycol (PEG), as feed additive, to mitigate the anti-nutritional effects of rockrose tannins.Material and methods: Aerial parts of rockrose plants were harvested in March, freeze dried and divided in 4 subsamples which were treated with 0, 25, 50 and 75 g of PEG/kg of dry matter (DM). The mixtures were analysed for chemical composition including total phenolics, total tannins and condensed tannins. In situ rumen organic matter (OM) and N rumen degradability was evaluated using three rumen-cannulated rams and ruminal fermentation pattern (volatile fatty acids (VFA), gas production) was evaluated in vitro using a Rumen Simulation Technique (RUSITEC) apparatus.Main results: In situ experiment indicated that the effective degradability of the OM and N increased linearly (p<0.05) with PEG inclusion due to an increase of the degradation rate (p<0.05). RUSITEC data indicated that substrate disappearance and gas and VFA production increased linearly (p<0.05) with PEG inclusion. Research highlights: Inclusion of PEG to C. ladanifer feed was effective to prevent the anti-nutritive effects of tannins. Thus, the use of PEG as feed additive can promote a better utilization of this shrub by ruminants.
Highlights
In the south of Portugal, during the summer and fall/early winter, pastures are almost non-existent or with low productivity and poor nutritional value
The crude protein (CP) concentration of the aerial part of rockrose was close to the recommendation of the NRC (1985) for maintenance sheep diets (70 vs 80 g/kg of dry matter (DM))
Fibre concentration was moderate and much less than most of grass hays used in ruminant nutrition (i.e. 300 g neutral detergent fibre (NDF)/kg DM vs 500 to 600 g NDF/kg in many hays)
Summary
In the south of Portugal, during the summer and fall/early winter, pastures are almost non-existent or with low productivity and poor nutritional value. The dominant vegetation during those periods is trees and shrubs, evergreen plants less sensitive to variations in temperature and rainfall This type of vegetation has always been an important source of primary nutrients for grazing animals. In relation to other feed sources, shrubs have lower nutritive value because they usually contain high levels of parietal compounds and anti-nutritional compounds, tannins. Despite their poor nutritional quality, the inclusion of shrubby species in ruminant diets assumes a high importance in the Mediterranean area in order to control the combustible vegetation as fire prevention and to maintain animals reducing feeding costs mainly during the periods when the feed deficits require expensive supplementation. Due to land abandonment and recurrent fire events, the area
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