Effects of diet quality and time lapse after meal termination on rumen load, rate of passage and feeding behaviour.

Abstract

Ruminant utilisation of poor quality feeds is governed by rates of degradation and passage through the rumen. Firstly, the passage rate of feed material determines the degree of bypass nutrients and the efficiency of synthesis of microbial protein in the rumen, making modelling of passage rate important. Secondly, diurnal feeding behaviours are not normally used in predicting feed intake although their influences are vital in understanding the dynamics of intake. Lastly, critical to rumen kinetics studies lies in understanding the dynamics of rumen fill levels post meal termination. The objectives of the study were to: (1) develop digesta passage rate prediction models for climatically, nutritionally and genetically diverse classes of ruminant herbivores; (2) ascertain the effects of diet quality on diurnal feeding behaviour in sheep and goats; and (3) determine the influence of diet quality on passage rates and, the extent and trend of solid digesta disappearance after meal termination. Artificial neural networks were used to develop prediction models for liquid and solid passage rates. Studies that reported fractional passage rates, class and body mass of ruminants were included in the dataset. Factors that affect rates of passage included animal and feed factors. The database was composed of observations of domestic and wild ruminants of variable body mass (1.5 to 1238 kg) from 74 studies and 17 ruminant species from different climatic regions. Observations were randomly divided into 2 data subsets: 75% for training and 25% for validation. Developed models accounted for 66 and 82% of the variation in prediction of passage rates for solid and liquid, respectively. On validation using an independent dataset, these models attained 42 and 64% of precision in predicting passage rates for solid and liquid, respectively. The effects of tropical roughage and diet quality on dry matter intake, duration and number of daytime and night time eating bouts, idling sessions and ruminating activities in small ruminants were investigated. Roughage quality was improved by urea treatment of veld hay, while diet quality was improved by supplementing with lucerne hay, sunflower meal, lespedeza, fish meal and sunflower meal. Day-time (0600-1800 h) and night time (1800-0600 h) feeding behaviour activities of sheep and goats were recorded. Generally, roughage and diet quality, and time of the day had significant effects on time spent ruminating and eating. Intake rates (g/bout and g/min) were not affected by diet and roughage qualities. Generally, goats and sheep fed on roughage alone ruminate at night and eat more during the day but those fed roughage and supplemented with lucerne hay spent more time ruminating than eating. Time spent eating and ruminating had positive correlations to feed intake. Intake rates (g/min and g/bout) had strong positive correlations to intake, which were significant. Improvement of roughage quality increased solid passage rate but did not affect liquid digesta passage rates from the rumen. Roughage quality had no effects on wet and dry digesta load in the foregut and hindgut compartments, except on abomasum dry matter load. Time lapse post feeding had no effects on rumen digesta load in the foregut and hindgut compartments, except on the dry and wet digesta load in the omasum. Proportions of digesta load in the rumen decreased linearly up to 24 h post feeding termination regardless of roughage quality. There is a possibility that this trend shapes into an exponential “decay” curve after 24 h post feeding termination. In conclusion, this study developed more précised prediction models for solid and liquid passage rates for ruminants fed on a variety of diets and/or feeds from different climatic regions. Roughage intake was limited as a result of increased rumination time of low quality roughages. There is a potential of using feeding behaviour to predict passage rates and predict intake. Digesta passage rate prediction models should include all animals, including those in a negative energy balance. The rate of clearance of digesta after meal termination was significantly greater for sheep fed on the improved roughage quality (IRQ) compared to the poor roughage quality (PRQ).