The digestibility and fermentation characteristics of PROLIQ® determined by in vivo digestibility trial and in vitro gas production: A dissertation submitted in partial fulfilment of the requirements for the degree of Bachelor of Science with Honours

Abstract

PROLIQ® is a liquid stock food prepared from by-products of milk processing including mother liquor, dissolved air flotation solids (DAFS), and cheese fines. The organic matter digestibility of PROLIQ® is assumed to be 0.95 but this has never been shown experimentally nor have its fermentation characteristics been determined. PROLIQ® apparent dry matter (DM) and organic matter (OM) digestibility was assessed in an in vivo trial and its fermentation characteristics in an in vitro gas production trial. In experiment 1 the in vivo digestibility of PRO LIQ® was determined by feeding hay or hay plus PROLIQ® to 8 sheep housed in metabolism crates for 31 days. Total collection of faeces and refusals was carried out over the last 7 days of the feeding period. The apparent DM and OM digestibility of the hay was determined directly and the apparent DM and OM digestibility of PROLIQ® was assessed through the difference between the amount of faeces assumed to come from hay and the total amount of faeces. The apparent DM and OM digestibility of hay were 0.617 (SEM 0.016) and 0.644 respectively, hay plus PROLIQ® diet 0.668 (SEM 0.015) and 0.704 and the apparent DM and OM digestibility of PROLIQ® were 0.763 (SEM 0.045) and 0.859 respectively. In experiment 2 the in vitro fermentation characteristics of PROLIQ® were determined by measuring the gas production of mixtures of increasing PROLIQ® concentration combined with a buffer medium and rumen fluid inoculum incubated at 39°C for 96 hours. The treatments were 0%, 25%, 50%, 75% and 100% PROLIQ® and a blank was included. Each treatment was replicated 3 times within one run and there were 3 runs.The amount of gas released from the mixture was measured using a pressure transducer and syringe system where gas was removed from the flask until the transducer registered atmospheric pressure. Cumulative gas production curves were plotted for the total mean and the mean of each run for each treatment, and the lag time, gas pool size and degradation rate (% h⁻¹ ) and fractional degradation rate (μ)were determined. The lag time and degradation rate were determined using the model of (McDonald 1981) Y = A + B [1-e(⁻ct)] where Y is the amount of gas produced at time T, A + B is the potential gas production, c is the degradation rate and t is time. The gas pool size and μ were determined from curves fitted using exponential regression rising to a maximum point and the equation Y= A (1-e⁻bt). The lag time was 0 for all treatments except for 75% and 100% PROLIQ® which had lag times of 0.3 and 0.07 hours respectively. The degradation rates(% substrate disappearance per hour) was highest for 75% PROLIQ® at 12.5 followed by 100%, 50%, 25% and 0% PROLIQ® in that order. The gas pool size was greatest for 100% PROLIQ® at 235 ml and decreased from that point in the order of 25%, 0%, 50% to 194 ml for 75% PROLIQ®. μwas greatest for 50 and 75% PROLIQ® at 13.3 decreasing to 12.5 at 100% and 10.7 and 8.0 at 25% and 0% PROLIQ® respectively. There were significant (p<0.05) positive effects on the rate of gas production when PROLIQ® was added to the hay but a trend toward negative effects on the total gas production and gas pool size when the level of PROLIQ® was greater than 25%.