**Rate of Passage of Digesta in Ruminants; Are Goats Different? Different?**

**Rate of Passage of Digesta in Ruminants; Are Goats** 

DOI: 10.5772/intechopen.69745

Mehluli Moyo and Ignatius V. Nsahlai

Mehluli Moyo and Ignatius V. Nsahlai Additional information is available at the end of the chapter

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/intechopen.69745

#### **Abstract**

Fluid passage rates through the rumen influence digestion of soluble food nutrients, amount of short-chain fatty acids absorbed in the rumen and that pass out of the rumen, the amount of by-pass protein of dietary origin and the amount of microbial protein available to the host as a protein source, making modelling of passage imperative. Current research on passage rate should seek to incorporate various factors that affect rumen fill, and solid and liquid passage rates to develop intake and passage rate prediction models. The aim of this paper was to discuss factors that affect rates of passage of digesta and rumen digesta load. Ambient temperature, animal physiological status and reproductive status, fermentation and diet quality are major factors affecting digesta passage rates. The animal physiology also influences digesta passage rate. Computation of animal production level to account for all the physiological processes that affect passage rate is vital. Discrepancies on how ambient temperature and particle density (buoyancy) affect the passage rate of digesta in the rumen may cause uncertainty in calibration of temperature and buoyancy in prediction models. Corrected for diet properties, goats have similar passage rates to other ruminants.

**Keywords:** diet selection, feeding behaviour, intermediate feeder, prediction model, ruminant

#### **1. Introduction**

Goats have become one of the most important livestock for resource-limited farmers around the world because they can survive in harsh climatic conditions from cold temperate regions (in the Siberia) to hot arid deserts (in the Kalahari). Key to their ability to survive in diverse climatic regions is their ability to walk through tight, narrow places and their capability of efficiently utilising vast plant feed resources. Goats are important as a source of protein (milk and meat) and wealth. Given the increasing importance of goats among resource-limited farmers in tropical

Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2018 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2016 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons

and subtropical regions around the world, research on the physiological aspects of goat nutrition is vital for improved goat production. Feed availability and quality are the major factors affecting yields for and quality of chevon and milk in rural goat production systems. Enhanced milk and chevon productivity is largely dependent on their selective feeding behaviour supported by improved nutritional status through supplementation of poor-quality roughages with feeds of high nutritional value (e.g., protein and energy concentrates). Concentrates are generally expensive for resource-limited farmers in rural communities around the world, especially in Africa and Asia. Hence, cost-effective usage of these feeds is vital. Fundamental to cost-effective concentrate supplementation forimproved productivity of goat farming systems in the tropics relies on accurate and precise prediction of roughage intake. Accurate prediction of roughage intake would enable farmers to calculate precise quantities of concentrates to be fed to achieve a cost-effective level of production of good-quality meat and milk.

flow to a great extent [6]. Maximal rumen load for dry matter is determined by allometric procedures as a function of body weight [1, 2]. However, a ruminant's fill capacity also depends on the volume of digesta that causes rumen distension and on rate of flow of digesta from and rates of degradation of digesta in the rumen [6, 7]. As a result, criticism on determination of rumen fill based on body weight alone has been raised giving better models for rumen load based on body weight, mature body weight and dietary crude protein [1]. This fill capacity may also be determined practically by manually emptying the rumen at a time when full gut capacity is reached and weighing out digesta at that time [8] or slaughtering animals upon meal termination [9]. Rumen fill varies greatly with body weight and feeding habit. Rumen fill is approximated to be about 9 and 13% of body weight for browsers and grazers, respectively [8]. Interestingly, there is no apparent approximation of rumen fill based on body weight for intermediate feeders such as goats, although it may be assumed to fall within the range of 9–13% when grazers and browsers are regarded as extremes.

Rate of Passage of Digesta in Ruminants; Are Goats Different?

http://dx.doi.org/10.5772/intechopen.69745

41

Carrying out rumen evacuations to determine maximal rumen digesta load is not an easy task. It is assumed that the only or best way to know when an animal has reached its maximal gut capacity is when it stops or terminates feeding [10]. This theory is supported by Boudon et al. [11], where termination of short-term feed intake was attributed to signalling from the rumen wall as a result of rumen fill. Taweel et al. [12] and Williams et al. [13] reported scenarios whereby maximal rumen fill was greater after termination of late afternoon feeding bouts just around sunset than bouts from other parts of the day. According to these results, measuring maximal rumen fill after termination of morning feeding maybe misleading. However, Baumont et al. [14] reported rumen fill to reach its first maximum after the main morning meals, with a daily maximal rumen fill being reached after the evening meal. Similar results were obtained by Thomson et al. [15], where maximal rumen fill was observed after termination of first morning meal and late evening meal at 0900 h and 2000 h, respectively, in grazing sheep. Assuming that at meal termination, ruminants would have reached maximal rumen capacity is misleading as well. This assumption is supported by Taweel et al. [12] and Chilibroste et al. [16] who reported findings where maximal rumen capacity had not been reached when grazing dairy cows terminated feeding bouts. Greenhalgh and Reid [17] reported similar results where sheep fed on hay and straw-terminated feed intake way before maximal gut capacity was reached. These and other experimental results therefore suggest the existence of different sets of rumen fill levels which are time dependent, either before or after feeding bouts. These fill levels may be a function of the rate of emptying ofrumen digesta after eating has stopped. At any given time, rumen fill levels are a function of the rate of feed intake, rates of digestion and particle breakdown, and rates of outflow [13]. As such, rumen fill levels or values are dynamic and thus should not be regarded as constants and times

in which rumen capacity is measured should be taken into account as well.

evacuation.

Based on rates of passage and digestion, estimation of rumen capacity using mathematical procedures gives variable but useable results. Estimated rumen pool size based on passage and degradation rates at the point of meal termination gave values which were even twice as large when compared to average observed values obtained from the literature (Nsahlai, unpublished data). Failure of mathematical procedures to achieve tenable outcomes suggests that something uncertain takes place during the period after meal termination before

One of the major challenges in developing sustainable and cost-effective feeding strategies for goats in rural production systems in Africa, Asia, and other parts of the world is the inability to accurately predict roughage intake in goats. This is partly due to limited information on the critical factors that affect intake, passage rates of digesta and rumen fill for goats. Nsahlai and Apaloo [1] examined the appropriateness of model in [2] to predict the intake in ruminants grazing on poor quality roughages in tropical regions and showed that the model, though structurally adequate, underestimated roughage intake, partly due to poor estimates of gut fill and rate of passage. Similarly, the authors [3–5] showed that the model of Illius and Gordon [2] overestimated retention time in browsing ruminants for particle sizes less than 2 mm. Nsahlai and Apaloo [1] pointed out that the model of Illius and Gordon [2] erroneously estimates rumen fill levels and passage rates as a function of body weight alone.

Given the role of fluid passage rates through the rumen in affecting by-pass proteins and fatty acids that are assimilated in the hindgut, passage of fluid would have a significant influence on milk protein and butterfat composition in dairy goats. This makes the study and modelling of digesta passage rate relatively important. Modelling of passage rates would necessitate prediction of roughage intake, microbial protein yield and milk composition in goats. Before any passage rate modelling exercise can be effectively carried out, factors that affect passage rates need to be reviewed and used to predict digesta passage rates.

Given the abundant literature on passage rates for cattle and sheep, and other ruminant feeding types, and limited data on goats, the chapter (i) identifies the major factors that affect passage rates in ruminants, (ii) explains the fundamental mechanisms by which each identified factor possibly affected rates of digesta passage from the rumen, (iii) gives suggestions of the major factors that can be considered as critical input factors for developing passage rate prediction models distinguishing studies on goats and (iv) determines whether goats are different with respect to other ruminants in terms of passage rates.

## **2. Rumen fill, gut capacity and its estimation**

Gut fill is referred to as rumen fill with respect to ruminants based on the facts that the rumen is the only site in the gastrointestinal tract where distension has an effect of restricting digesta flow to a great extent [6]. Maximal rumen load for dry matter is determined by allometric procedures as a function of body weight [1, 2]. However, a ruminant's fill capacity also depends on the volume of digesta that causes rumen distension and on rate of flow of digesta from and rates of degradation of digesta in the rumen [6, 7]. As a result, criticism on determination of rumen fill based on body weight alone has been raised giving better models for rumen load based on body weight, mature body weight and dietary crude protein [1]. This fill capacity may also be determined practically by manually emptying the rumen at a time when full gut capacity is reached and weighing out digesta at that time [8] or slaughtering animals upon meal termination [9]. Rumen fill varies greatly with body weight and feeding habit. Rumen fill is approximated to be about 9 and 13% of body weight for browsers and grazers, respectively [8]. Interestingly, there is no apparent approximation of rumen fill based on body weight for intermediate feeders such as goats, although it may be assumed to fall within the range of 9–13% when grazers and browsers are regarded as extremes.

and subtropical regions around the world, research on the physiological aspects of goat nutrition is vital for improved goat production. Feed availability and quality are the major factors affecting yields for and quality of chevon and milk in rural goat production systems. Enhanced milk and chevon productivity is largely dependent on their selective feeding behaviour supported by improved nutritional status through supplementation of poor-quality roughages with feeds of high nutritional value (e.g., protein and energy concentrates). Concentrates are generally expensive for resource-limited farmers in rural communities around the world, especially in Africa and Asia. Hence, cost-effective usage of these feeds is vital. Fundamental to cost-effective concentrate supplementation forimproved productivity of goat farming systems in the tropics relies on accurate and precise prediction of roughage intake. Accurate prediction of roughage intake would enable farmers to calculate precise quantities of concentrates to be fed to achieve

One of the major challenges in developing sustainable and cost-effective feeding strategies for goats in rural production systems in Africa, Asia, and other parts of the world is the inability to accurately predict roughage intake in goats. This is partly due to limited information on the critical factors that affect intake, passage rates of digesta and rumen fill for goats. Nsahlai and Apaloo [1] examined the appropriateness of model in [2] to predict the intake in ruminants grazing on poor quality roughages in tropical regions and showed that the model, though structurally adequate, underestimated roughage intake, partly due to poor estimates of gut fill and rate of passage. Similarly, the authors [3–5] showed that the model of Illius and Gordon [2] overestimated retention time in browsing ruminants for particle sizes less than 2 mm. Nsahlai and Apaloo [1] pointed out that the model of Illius and Gordon [2] erroneously estimates rumen fill levels and passage rates as a function of body weight alone. Given the role of fluid passage rates through the rumen in affecting by-pass proteins and fatty acids that are assimilated in the hindgut, passage of fluid would have a significant influence on milk protein and butterfat composition in dairy goats. This makes the study and modelling of digesta passage rate relatively important. Modelling of passage rates would necessitate prediction of roughage intake, microbial protein yield and milk composition in goats. Before any passage rate modelling exercise can be effectively carried out, factors that affect passage

Given the abundant literature on passage rates for cattle and sheep, and other ruminant feeding types, and limited data on goats, the chapter (i) identifies the major factors that affect passage rates in ruminants, (ii) explains the fundamental mechanisms by which each identified factor possibly affected rates of digesta passage from the rumen, (iii) gives suggestions of the major factors that can be considered as critical input factors for developing passage rate prediction models distinguishing studies on goats and (iv) determines whether goats are dif-

Gut fill is referred to as rumen fill with respect to ruminants based on the facts that the rumen is the only site in the gastrointestinal tract where distension has an effect of restricting digesta

a cost-effective level of production of good-quality meat and milk.

40 Goat Science

rates need to be reviewed and used to predict digesta passage rates.

ferent with respect to other ruminants in terms of passage rates.

**2. Rumen fill, gut capacity and its estimation**

Carrying out rumen evacuations to determine maximal rumen digesta load is not an easy task. It is assumed that the only or best way to know when an animal has reached its maximal gut capacity is when it stops or terminates feeding [10]. This theory is supported by Boudon et al. [11], where termination of short-term feed intake was attributed to signalling from the rumen wall as a result of rumen fill. Taweel et al. [12] and Williams et al. [13] reported scenarios whereby maximal rumen fill was greater after termination of late afternoon feeding bouts just around sunset than bouts from other parts of the day. According to these results, measuring maximal rumen fill after termination of morning feeding maybe misleading. However, Baumont et al. [14] reported rumen fill to reach its first maximum after the main morning meals, with a daily maximal rumen fill being reached after the evening meal. Similar results were obtained by Thomson et al. [15], where maximal rumen fill was observed after termination of first morning meal and late evening meal at 0900 h and 2000 h, respectively, in grazing sheep. Assuming that at meal termination, ruminants would have reached maximal rumen capacity is misleading as well. This assumption is supported by Taweel et al. [12] and Chilibroste et al. [16] who reported findings where maximal rumen capacity had not been reached when grazing dairy cows terminated feeding bouts. Greenhalgh and Reid [17] reported similar results where sheep fed on hay and straw-terminated feed intake way before maximal gut capacity was reached. These and other experimental results therefore suggest the existence of different sets of rumen fill levels which are time dependent, either before or after feeding bouts. These fill levels may be a function of the rate of emptying ofrumen digesta after eating has stopped. At any given time, rumen fill levels are a function of the rate of feed intake, rates of digestion and particle breakdown, and rates of outflow [13]. As such, rumen fill levels or values are dynamic and thus should not be regarded as constants and times in which rumen capacity is measured should be taken into account as well.

Based on rates of passage and digestion, estimation of rumen capacity using mathematical procedures gives variable but useable results. Estimated rumen pool size based on passage and degradation rates at the point of meal termination gave values which were even twice as large when compared to average observed values obtained from the literature (Nsahlai, unpublished data). Failure of mathematical procedures to achieve tenable outcomes suggests that something uncertain takes place during the period after meal termination before evacuation.
