Effect of the level and frequency of PEG supply on intake, digestion, biochemical and clinical parameters by goats given kermes oak (Quercus coccifera L.)-based diets

Polyethylene glycol (PEG; molecular weight: 4000) was used to deactivate tannins in kermes oak (Quercus coccifera L.) foliage. Five groups of four Alpine×Local breed male goats were each given Q. coccifera ad libitum and 300 g of ground barley grains. Ten and 20 g of PEG were mixed with barley and distributed daily to groups 2 and 3, respectively. Groups 4 and 5 received 10 and 20 g PEG, respectively, at 2-day intervals. Group 1 did not receive PEG and served as a control. Animals were housed in individual pens for 21 days to adapt to dietary treatments and then acclimatised to metabolic cages for 3 days before starting the total faecal and urine collection period (6 consecutive days). Feed intake, apparent diet digestibility, nitrogen balance, urinary excretion of allantoin and blood metabolite profiles were determined. A clinical examination of the goats was performed 1 day prior to the start of the experiment and then again of day 24. Q. coccifera foliage was high in acid detergent lignin (207 g/kg dry matter) and condensed tannins (58.5 g leucocyanidin eq./kg dry matter) and medium in crude protein (CP; 80 g/kg dry matter). PEG level and frequency had no effect on Q. coccifera intake, or on the digestibility of DM, organic matter or neutral detergent fibre in the diets (P>0.05). However, the apparent digestibility of CP and urinary excretion of allantoin were increased with PEG, the increase being highest when 10 g PEG was administered daily (P<0.05). Provision of 20 g PEG daily did not lead to a further increase. The positive effect was maintained in goats receiving 20 g PEG at 2-day intervals. Nitrogen retention and daily gain tended to increase with the daily administration of PEG, but without significance (P>0.05). Goats in groups 1, 2, 3, 4 and 5 grew at a rate of 61.4, 77.3, 82.9, 67.0 and 64.8 g/day, respectively. Overall, concentrations of glucose, urea, creatinine, albumin, phosphorus and magnesium in serum were within the normal ranges for local goats. Nutrient deficiency, mainly proteins and calcium, was considered the main reason for the slight hypoproteinaemia and hypocalcaemia. Except for urea, the level and the frequency of PEG supply had no effect on the above metabolites and calcium, total proteins and Gamma-GT. The significant increase of the level of urea in the serum was ascribed to an increase in the nitrogen level of the diet caused by the disruption of tannin-protein complexes due to PEG and probably by a decrease in the rate of urea excretion by the kidney. The apparent sate of health of goats was acceptable. Respiratory and rumen contraction frequencies did not vary among dietary treatments. It is worth noting that compared to values found 1 day prior to the start of this experiment, there was a decrease of the cardiac frequency for all goats noted on day 24. It was concluded that supplementing goats with appropriate level of barley, i.e. 300 g/day as in this experiment, matched maintenance and growth requirements of animals. The slight increase in the nitrogen value of Q. coccifera-based diets with PEG supply did not a priori justify the use of this costly reagent. Moreover, despite growth rates in excess of 60 g/day, sub-clinical intoxication was suspected. These findings highlight the importance of monitoring pathologic aspects in evaluation of tanniniferous browse species for livestock feeding.