The influence of the grape pomace on the ruminal parameters of sheep

To overcome an animal feed shortage in Iran, the effect of replacing alfalfa with grape (Vitis vinifera sp.) by-product plus polyethylene glycol (PEG, MW 6000) on the ruminal parameters and retained nitrogen (Nr) of sheep was assessed. In a change-over design experiment 6 sheep with similar live weight (61.8 kg), were used during 3 periods of 28 days. The three dietary treatments, which were iso-caloric and iso-nitrogenous, were; control (alfalfa hay, barley grain, wheat chaff, wheat straw), GP diet (grape pomace, barley grain, wheat chaff and urea) and GP diet + PEG. PEG was used to deactivate tannins in grape pomace. Animals were held in individual metabolism cages. They were adapted to experimental conditions for 21 days, before the commencement of the measurement periods. In each period, the digestibilities of organic matter (OMD), NDF (NDFD), crude protein (CPD) and ruminal parameters (pH, ammonia, bacteria and protozoa population), microbial protein synthesis using urinary purine derivatives and N metabolism in sheep were measured. The concentration of OMD, NDFD and CPD was decreased using grape pomace and the addition of PEG only, improved CPD. The amount of endogenous fecal nitrogen loss and Nr in GP diet were less than control (P < 0.05), these amounts were increased by the addition of PEG (P < 0.05). GP diet caused reduction in ruminal parameters (pH, ammonia, cellulolytic and proteolytic bacteria population and protozoa number) and microbial protein yield as compared to the control. The addition of PEG increased those parameters (P < 0.05). In conclusion, GP diet had a detrimental effect on the rumen parameters and Nr with positive influences of PEG addition on most of these parameters.