Polyethylene glycol influences feeding behaviour of dairy goats browsing on bushland with different herbage cover

The effects of supplemental polyethylene glycol (PEG) on feeding behaviour, diet composition, intake and milk production were studied in late lactating Sarda goats browsing on a lentisk-based bushland with different herbage cover. The goats were allotted to two groups that browsed 7 h daily on 2 plots characterised by different cover proportions of woody and herbaceous species. These proportions were 90% woody vs. 10% herbaceous species in one plot (W -- woody, close bushland with low herbage cover) and 70% woody vs. 30% herbaceous species in the other plot (H -- herbaceous, open bushland with high herbage cover). Each group was divided into two sub-groups: one fed with 50 g day⁻¹ of PEG 4000 MW (PEG⁺) and the other receiving no PEG supplementation (PEG⁻). The feeding behaviour was different between groups; goats in herbaceous plot (H-goats), had a longer grazing time, expressed as percentage of total observation time than the counterparts (64% vs. 58%, P <0.05). The intake was not affected by the treatments. The percentage of the species eaten by the goats was different in the two groups: H-goats ate more herbaceous and less woody species than goats in woody plot (W-goats). In each group the PEG tended to affect the botanical composition of the diet. PEG dosed goats ate more tanniferous species than control counterparts (P =0.12). The average daily milk production was 473, 591, 541 and 589 ml, respectively in W-PEG⁻, W-PEG⁺, H-PEG⁻ and H-PEG⁺ sub-groups with significant effect of herbage coverxPEG dose interaction (P <0.05). The milk urea was affected by herbage cover (P <0.001) and PEG supplementation (P <0.001). In conclusion, the effect of PEG is strictly dependent on pasture composition. In open bushland, featured by moderate woody cover, the effect of PEG is more intense on diet selection, due to its marked post-ingestive effects. In close bushland, characterised by high proportion of tanniferous species prevails the efficacy of PEG as a performance booster.