Effect of PEG and olive cake feed blocks supply on feed intake, digestion, and health of goats given kermes oak ( Quercus coccifera L.) foliage

Abstract

Four groups of four Alpine × local male goats (20-month-old), each on kermes oak ( Quercus coccifera L.) foliage were used to investigate nutrient intake and utilisation, blood metabolites and clinical parameters when supplemented with polyethylene-containing and polyethylene-free feed blocks and with polyethylene glycol (PEG, molecular weight 4000). PEG was used to neutralise tannins. The composition (g/kg DM) of feed blocks (B and B PEG, respectively) was: olive cake (367 and 331), cactus fruit (90 and 80), wheat bran (243 and 218), quicklime (154 and 139), urea (73 and 66), salt (73 and 66) and PEG (0 and 100). Group 1 was not supplemented (control) and group 2 was supplemented with feed blocks (B). PEG-containing feed blocks were fed to goats in group 3 (B PEG). The fourth group received feed blocks and PEG separately, i.e. mixed with 5 g processed barley (B+PEG). The amount of PEG distributed to the latter group was calculated so that goats supplemented with B PEG or B+PEG consume the same amount of PEG. Animals were adapted on experimental diets for 21 days before starting a 6-day-faecal collection period. The nutritive value of kermes oak foliage was low due mainly to high levels of phenolic compounds particularly lignin (236 g/kg DM) and tannins (34.8 g equivalent tannic acid/kg DM) and low concentration of crude protein (62 g/kg DM). Accordingly, dry matter intake (34.8 g/kg W 0.75) and apparent digestibility of DM (0.527), CP (0.332) and neutral detergent fibre (NDF, 0.429) were low in goats fed on this shrub species as a sole diet. Although DM intake of feed blocks was low (113 g per day), supplementation of PEG-free blocks almost doubled consumption of kermes oak (61.2 g/kg W 0.75) and intakes of digestible organic matter and CP increased from 17.4 and 1.0 g/W 0.75, respectively, to 46.6 and 33.0 g/W 0.75. Further improvement of these parameters was not observed by incorporation of PEG in block or by PEG supply along with the block (B PEG and B+PEG versus B, P>0.05). Irrespective of dietary treatments, blood metabolites, i.e. glucose, urea, total proteins, albumin, creatinine, gamma-glutamyltranspeptidase, calcium, phosphorus and magnesium were within the normal range for local goats. Feed blocks increased serum urea ( P<0.05), probably as consequence of improved N value of the diet. Biochemical parameters and clinical signs suggested a partial intoxication of goats solely on kermes oak. Supplementation with feed blocks with or without PEG improved cardiac, respiratory and rumen contraction frequencies and raised body temperature to the normal value (37 °C). Olive cake-based feed block enriched with squeezed cactus fruits was found to be a cost effective supplement to substantially improve the nutritive value of kermes oak-based diet and to maintain healthy goats.