Increasing productivity in goats grazing Mediterranean woodland and scrubland by supplementation of polyethylene glycol

Abstract

A single daily oral dose of polyethylene glycol (PEG) — a tannin-binding agent — has been shown to substantially improve feed intake and efficiency of utilization by sheep and goats consuming tannin-rich forage. The aim of this study was to quantify the effect of supplementing 10 g/day of PEG on the performance of does grazing on Mediterranean woodland and scrubland. The experiments were carried out in production systems based on Mamber goats raised only for the production of slaughter kids (Experiment 1), dual-purpose Mamber goats raised for slaughter kids and milk (Experiment 2) or Damascus×Anglo-Nubian goats raised mainly for milk (Experiment 3). In Mamber goats, PEG supplementation was associated with higher body weight (BW) gain during pregnancy ( p<0.01), higher kid birth-weight ( p<0.05) and daily BW gain until weaning ( p<0.10 and p<0.05 in Experiments 1 and 2, respectively), and no difference in milk yield. In contrast, the response of Damascus×Anglo-Nubian goats to PEG was a 43% increase in milk yield ( p<0.001) but no response in kid weight at birth. These responses are consistent with previous findings that show the resilience of Mamber goats to practices aimed at increasing their milk production while these goats respond well to practices that improve the probability of successful reproduction in harsh environments. In contrast, Damascus×Anglo-Nubians respond to increased available nutrients by increasing their milk production. Supplementation with PEG has the potential to improve the profitability of systems in which liberally supplemented and high-yielding dairy goats feed on Mediterranean browse. However, its contribution to production systems exploiting well adapted but low-yielding local goats is limited.