Recent Advances in Animal Nutrition

225 Pages·1987·3.858 MB·English

by  W. Haresign, D.J.A. Cole,, D.J.A. Cole, W. Haresign and W. Henrichsmeyer (Auth.)

STUDIES in the AGRICULTURAL and FOOD SCIENCES
A series of high-level monographs which review recent research in various areas of
agriculture and food science
Consultant Editors:
DJ.A. Cole University of Nottingham
W. Haresign University of Nottingham
W. Henrichsmeyer Director, Institut für Agrarpolitik, University of Bonn
J.P. Hudson formerly Director, Long Ashton Research Station, University of
Bristol
G. Kimber Professor of Agronomy, University of Missouri-Columbia
J.L. Krider Professor of Animal Sciences, Purdue University
D.E. Tribe Director, Australian Universities' International Development
Program, Canberra
V.R. Young Professor of Nutritional Biochemistry,
Massachusetts Institute of Technology
Titles in stock:
Recent Advances in Animal Recent Advances in Animal
Nutrition—1978 Nutrition—1986
Edited by W. Haresign and D. Lewis Edited by W. Haresign and D.J.A. Cole
Recent Advances in Animal Plant Breeding for Pest and Disease
Nutrition—1979 Resistance
Edited by W. Haresign and D. Lewis G.E. Russell
Recent Advances in Animal The Calf— Fourth edition
Nutrition—1980 J.H.B. Roy
Edited by W. Haresign
Energy Metabolism
Recent Advances in Animal Edited by Lawrence E. Mount
Nutrition—1981
Growth in Animals
Edited by W. Haresign
Edited by T.L.J. Lawrence
Recent Advances in Animal
Mineral Nutrition of Animals
Nutrition—1982
V.l. Georgievskii, B.N. Annenkov and
Edited by W. Haresign
V.T. Samokhin
Recent Advances in Animal
Protein Contribution of Feedstuff s for
Nutrition—1983
Ruminants
Edited by W. Haresign
Edited by E.L. Miller and LH. Pike
Recent Advances in Animal in association with A.J.M. van Es
Nutrition—1984
Advances in Agricultural Microbiology
Edited by W. Haresign and D.J.A. Cole
Edited by N.S. Subba Rao
Recent Advances in Animal
Antimicrobials and Agriculture
Nutrition—1985
Edited by M. Woodbine
Edited by W. Haresign and D.J. A. Cole
STUDIES IN AGRICULTURAL
AND FOOD SCIENCES
Recent Advances in Animal
Nutrition—1987
W. Haresign,PhD
D.J.A. Cole, PhD
University of Nottingham School of Agriculture
BUTTERWORTHS
London Boston Durban Singapore Sydney Toronto Wellington
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First published, 1987
© The several contributors named in the list of contents,
1987
British Library Cataloguing in Publication Data
Recent advances in animal nutrition.—(Studies in the
agriculture and food sciences).—1987
1. Animal nutrition
I. Series
636.08'52 SF95
ISBN 0-407-01163-3
Typeset by Katerprint Typesetting Services, Oxford
Printed and bound in Great Britain by Anchor Brendon
Ltd, Tiptree, Essex
PREFACE
This, the proceedings of the Twenty-first Annual Feed Manufacturers Conference,
contains chapters on a wide range of topics relating to animal nutrition.
The first two chapters relate to the compulsory declaration of the energy value of
poultry feeds, the first of them giving the background to and methods for estimating
it while the second considers the impact that this is likely to have on both the farmer
and compounder. These are followed by a chapter on the extent and nature of
diarrhoea and wet litter in meat poultry. The final two poultry chapters consider
laying birds; one provides a re-evaluation of the dietary phosphorus requirements
with particular emphasis on the various types of supplementary phosphorus, and
the other provides information on the use of naturally occurring products for egg
yolk pigmentation.
The next series of chapters relates to more general aspects of animal nutrition.
Consideration is given to the role that supplementary enzymes can play in im-
proving the utilization of pig and poultry diets. The nutrition of goats is currently a
subject containing much myth; the chapter on the nutrition of goats attempts to
dispel this and put the nutrient requirements of goats onto a more scientific footing.
A further chapter deals with methods for determining the amino acid requirements
of pigs and their consequences for pig nutrition. The final chapter in this section
discusses consumer attitudes to meat quality, how these are changing and the
possible ways in which the animal production industry can respond.
The final section of chapters concentrates on various aspects of ruminant
nutrition. The first two of these consider the nutrition of beef cattle set against the
background of the new AFRC system for protein, one dealing with the nutrient
requirements of the intensively fed beef animal, the other discussing how to meet
the nutrient requirements of beef cattle in forage-based systems of production.
These are followed by considerations of the energy and protein requirements of the
ewe at different stages of the breeding cycle. The final chapter discusses the
complex topic of factors affecting substitution rates in dairy cows on silage-based
rations.
The organizers and the University of Nottingham are grateful to BP Nutrition
(UK) Ltd for the support they gave in the organization of this conference.
W. Haresign
D.J.A. Cole
1
TECHNIQUES FOR DETERMINING THE METABOLIZABLE
ENERGY (ME) CONTENT OF POULTRY FEEDS
C. FISHER AND J.M. McNAB
Institute for Grassland and Animal Production, Poultry Division, Roslin,
Midlothian, UK
Introduction
Apart from the economic importance of energy in feed formulation the present
sustained level of interest in metabolizable energy (ME) determination stems from
two main events. The first was the introduction of rapid bioassays for ME in the
mid-1970s and in particular the work of Dr LR. Sibbald in Canada. The second was
the adoption of energy declarations, and the associated chemical control equation,
into the feed trade in Europe. This latter development has focused attention on the
accuracy, repeatability and suitability of different methods of measuring ME.
The subject has been widely reviewed, both here and elsewhere. Sibbald (1979)
described the development of his methods and in 1982 produced a further very
detailed review. Attention is also drawn to the review by Farrell (1981). Sibbald
(1986) provided an up-to-date description of his bioassay and a complete list of
references, although this was not a review. The development and application of
prediction equations for ME of poultry feeds was discussed by Fisher (1983) and
the derivation of the EEC equation has been described (Fisher, 1986). Since 1975 a
huge literature has developed on the topic; Sibbald (1986) lists 561 references
concerned directly or indirectly with this field and only five of these predate 1975.
Many of these papers are concerned with methodology but the present review is
concerned mainly with those which have appeared since Sibbald's substantive work
in 1982.
Recent developments have tended to highlight the questions of reproducibility in
ME bioassays, across laboratories and across time, and of variation in ME data.
The introduction of energy declarations and of a control equation does this,
because it is presumed that the whole system is based on a defined and reproducible
biological characteristic — the ME of a feed. Attempts to test or verify equations
obviously founder if this cannot be observed consistently. Further development of
ME values for feed ingredients also requires prediction equations to be established
relating ME to chemical composition or to other quality control factors. Progress in
this field is facilitated if results from different laboratories can be combined and
again variations in technique are brought into focus, especially if they lead to
different biasses. It might have been hoped that the introduction of effective rapid
assays would help to achieve the laudable aim of standardization of technique but,
in fact, this has not happened, apparently for two main reasons. First, the rapid
3
4 ME content of poultry feeds
assays require the use of starved birds which has proved controversial; second, it is
clear that the adoption of published techniques led to problems in some laborator-
ies and a whole series of minor and major variations have been introduced. Thus,
we now have a plethora of 'methods' for ME determination described in the
literature and standardization is probably further away now than it was ten years
ago.
TERMINOLOGY AND DEFINITIONS
These topics are relatively free from disagreement and a widely used convention is
followed here, mainly in agreement with Sibbald (1982, 1986). The term ME is
used in a general sense rather than bioavailable energy (BE) as proposed by
Sibbald (1982 and elsewhere). We also continue to use the term endogenous energy
loss (EEL) even though it is usually defined, not as a biological entity, but in
empirical experimental terms, e.g. energy loss from a starved bird. This is conve-
nient and not necessarily confusing. The convention of ignoring energy lost as gases
produced in fermentation is also followed. Pesti and Edwards (1983) propose that
the nomenclature used in this field should be completely changed to reflect the
methods used in experiments but we find this unhelpful. A preferable approach is
to modify the methodology until it measures and reflects well defined biological
entities. The point made by Pesti and Edwards however, that more care is needed
in relating experimental observations to supposedly well defined biological ele-
ments, cannot be repeated too often.
Finally, in the introduction to this chapter it is relevant to comment critically on
the standard of reporting work in this field in journals. ME values are not observed
or measured but are derived by calculation from a whole series of measurements
and far too little basic information is normally reported. Thus it is frequently
impossible to make critical comparisons between different experiments. Further-
more, as the background of the topic develops, far more use could be made of
existing data, and the results from different studies could be combined, if more
detailed tabulation of results was introduced.
Methods for determining the ME of feeds and ingredients
Metabolizable energy is erroneously considered to be a characteristic of a feed; it is
really a characteristic of an animal to whom the feed is given. ME measurement
relates to the complete feed given and values for feed components or ingredients
must, in most cases, be obtained by comparing the results for two or more suitable
feeds (substitution methods). In a few cases (e.g. cereals) this distinction between
feed and ingredients can be eliminated. In either case the assumption of additivity
of ME values amongst feedstuffs is essential and very little progress can be made if
this is not upheld. Energy is of course a useful currency for describing mass
conversion of food elements in the bird. There is a set of problems, analogous to
those discussed here for ME, in determining the 'metabolizability' of any nutrient;
lipid, protein, carbohydrate. For many purposes, and especially for prediction, it
would be preferable if both ME values and digestibility coefficients for the main
components were measured concurrently, but this is rarely done.
C. Fisher and J. M. McNab 5
McNab and Fisher (1981) suggested that the observations required for an ME
bioassay were threefold: (i) a knowledge of energy balance (EB) at (ii) a known
food intake (FI) and (iii) an appropriate measure of EEL. For correction to zero Ir-
retention (NR ) then N-balance (NB) must also be measured. It is useful when
0
discussing methods to bear in mind the relationships shown in Figure 1.1, which, in
particular, have been discussed by Wolynetz and Sibbald (1984).
(b)
/
Slope = b
e = D sl
/ °P '
Food eneryg input
Figure 1.1 (a) Regression of excreta energy on food energy input, (b) Relationship
between ΑΜΕ, TME and food intake as derived from (a), assuming that EEL Φ 0
Figure 1.1a shows the regression of excreta energy (EXE or EXE„ if corrected
for Ν loss) and food (gross) energy input (GEI). The intercept on the y axis
provides an operational definition of EEL (or EEL„); that is, energy excretion at
zero energy input, and the slope of the line yields the true metabolizable energy
(TME or TME„) of the feed as TME = GE(1 - b) where GE is the gross energy of
the feed. Estimates of apparent metabolizable energy (ΑΜΕ or AME„) correspond
in a similar way to the slope of lines joining a given energy balance with the origin
of the graph; thus for the example in Figure Lia, AME = GE(l-b'). The
derivation of Figure 1.1b is obvious if a range of intakes is envisaged. Notice also
that if the intercept is zero then AME = TME and ΑΜΕ is independent of intake.
Negative intercepts suggest an artefact of measurement.
Three general types of energy balance experiment can be identified. (Squibb
(1971) and others have suggested that ME could be assessed by growth but this is
not pursued here.) The three types are as follows:
(1) Traditional assays which involve preliminary feeding periods to establish 'equi-
librium' conditions. Differences in carryover in the digestive tract between the
beginning and end of the assay period ('end-effects') are controlled by trying to
ensure that they are the same. Complete diets must be used in most cases and
substitution methods used for ingredients.
(2) Rapid assays, using starvation before and after giving a known aliquot of test
feed to control 'end-effects' but which permit the birds free access to the feed.
Again, complete diets and substitution methods must be used in most cases.
(3) Rapid assays, as above, but using tube-feeding (or force-feeding or precision
feeding) to place the test feed directly in the bird's crop. These methods usually
avoid the need to substitute feed ingredients into a basal diet.
6 ME content of poultry feeds
Whilst many variations are found in these general groups, this classification
provides a convenient framework within which the many details of procedure can
be discussed. This is done here under a number of headings although this arbitrary
separation of techniques tends to hide many interacting arguments.
BALANCE EXPERIMENT METHODOLOGY
Feed presentation and the measurement of energy intake are amongst the most
difficult aspects of balance experiments. If birds are given free access to the feed, a
technique which still seems to have the widest acceptance, great care is required to
avoid food loss, to recover lost food including that in the drinker, to avoid
separation of food components, to monitor dry-matter changes and to take
samples. In total these are difficult to control in a consistent way but specially
designed systems have been described and used with apparent success (e.g. Terp-
stra and Janssen, 1975).
Such free-feeding methods are used in type (1) assays which form the greater part
of the literature on ME determination for poultry. Farrell (1978) proposed that the
advantages of a rapid, type (2), assay could be obtained by training birds to
consume satisfactory intakes in 1 h after a 23 h fast. In this assay equal quantities of
basal feed and test ingredient were combined, although pelletting of the feed was
recommended to maintain intakes across a range of feeds. Several groups have
reported difficulties in maintaining satisfactory intakes (Mutzar and Slinger, 1980;
Jonsson and McNab, 1983; Parsons, Potter and Bliss, 1984; Kussaibati and Lec-
lercq, 1985) but, notwithstanding this, several assays based on this method of feed
presentation have been described with minor variations in starvation and feeding
times (Chami, Vohra and Kratzer, 1980; Vohra, Chami and Oyawoye, 1982;
Parsons, Potter and Bliss, 1984). Kussaibati and Leclercq (1985) propose an
original assay which fits roughly into the same category but which has not, appar-
ently, been tested elsewhere. Adult cockerels were starved for 24 h, fed ad libitum
for 24 h and then starved for 24 h. Excreta were collected for the final 48 h of this
72 h assay.
Whilst assays of the type proposed by Farrell (1978) can obviously be successful it
is clear that variations in food intake will occur with some feedstuffs. Extensions of
the basic principle could include the use of different, but pre-determined, intakes
(du Preez, Minnaar and Duckitt, 1984) or, if EEL is known, correction of the data
to take account of different intakes. This latter route was followed by Jonsson and
McNab (1983) but these modifications have not been adopted routinely.
The presentation of feed by tube in type (3) assays permits very accurate feeding
and offers the opportunity for controlling some problems such as variations in dry
matter content of the feed. Since dose size is reduced, problems of sampling
become more important. The only real disadvantages of the technique are the limit
on dose size and attitudes towards the acceptability of a procedure which is
frequently called 'force-feeding'. Our experience is that, with practice, the tech-
nique is extremely rapid (15-30 s/bird with most feeds) and that there is little
evidence of more stress beyond that involved in handling. Experience and skill
must be attained, although this is easily done with practice by most operators.
Wehner and Harrold (1982) raised the issue of stress and suggested the use of slurry
feeding to reduce it. However they quoted feeding times of 8 to 12 min with dry
feeds which would be very stressful, but which are unnecessary (Fraser and
C. Fisher and J. M. McNab 7
Sibbald, 1983). Finely divided, hygroscopic or very bulky ingredients may present
problems to inexperienced feeding teams but again these can be overcome with
practice. In this laboratory, glucose monohydrate is routinely fed; this is a problem
material and granulation is used to reduce the difficulties. Alternatives to intuba-
tion of dry feeds include use of slurries (Wehner and Harrold, 1982; Teeter et al.,
1984) or gelatin capsules (Bilgili, Arscott and Kellems, 1982).
Balance experiments with ducks and geese present many problems (Ostrowski-
Meissner, 1984). His assay for ducks involves training birds to consume a normal
intake in 1 h per day but then administering a test dose by tube, so as to avoid
losses in the drinking water. It is suggested that training reduced the 'stress' of tube-
feeding and allowed intakes to be increased from 30 to 70 g. Slurry feeding was
used with ducks by Mohamed et al. (1984) who did not report any problems. Storey
and Allen (1982) fed dry feed to geese by tube but did comment on some
difficulties.
Excreta collection is another simple task which is difficult to do well in routine
experiments. When done with trays under cages the problems include adherence to
feathers, physical losses, contamination with food, feathers and scurf, fermentation
and losses in collection and transfer. Sibbald (1986) lists useful precautions to be
taken; frequent collection e.g. 12-hourly as in Dale et al. (1985), and continuous
mechanical blowing to remove scurf are the sort of devices which might be judged
beneficial.
The only alternative to collection trays is to attach a bag to the bird for collection
and methods for doing this have been described. Sibbald (1983) proposed the use of
adhesives to fasten the bags but preliminary experience in this laboratory was not
encouraging so far as routine programmes were concerned. The use of a harness to
hold the bag (Sibbald, 1986; Almeida and Baptista, 1984) has also been associated
with problems in this laboratory and elsewhere (P.J. Gallimore, personal commu-
nication). In the only direct comparison of methods (Sibbald and Wolynetz, 1986)
there was evidence of increased excreta output on trays as compared with bags.
This led to lower estimates of TME„, by about 0.5 MJ/kg across four feeds, when a
conventional assay was used with zero intake plus one level of feeding. Other
studies showed that the slope of the line relating excreta energy to input was
independent of collection method so TME estimates in multilevel trials were not
affected by collection method. It is not clear whether the use of trays leads to an
overestimate or the use of bags to an underestimate of true excreta loss. Excreta in
bags remains moist for up to 48 h and may be subject to fermentation loss.
Addition of acid to the bags gave results similar to trays which suggests the second
cause, but the acid caused further problems and accumulation of some non-excreta
material on trays seems inevitable. Sibbald and Wolynetz (1986) also found a high
level of data loss with bags which in these studies were fastened to the birds by
adhesive.
For routine use it is difficult to see how trays can be avoided without considerable
increase in cost although this may be justified for work on amino acid availability
where feather and scurf contamination can lead to large, systematic errors.
USE OF DIGESTION MARKERS OR INDICATORS
Accurate feeding and excreta collection in ME assays create a lot of menial,
repetitive and relatively unpleasant tasks but require impeccable standards to be
8 ME content of poultry feeds
maintained. The use of digestion markers or indicators may reduce these problems
and also facilitate balance studies in less-than-ideal animal caging. The proposed
requirement for food intake data is not met but this can be recorded with sufficient
accuracy for correcting AME data without incurring the exacting demands of total
collection. New problems and sources of variation are introduced with markers but
the routine tasks are moved to the more congenial laboratory atmosphere and may
be amenable to automation. Problems due to excreta contamination are not
avoided by markers.
Marker methods were reviewed by Sibbald (1982) in relation to the present
topic. Since that time the use of titanium dioxide (Peddie et al., 1982) and
magnesium ferrite (Neumark, Bielorai and Iosif, 1982) have been proposed for
studies with poultry. Titanium dioxide was adopted as a routine marker in our
laboratory because of safety restrictions on the use of chromium. All markers must
be insoluble and are therefore difficult to analyse by chemical methods. Magnesium
ferrite is determined by physical methods and polythene by gravimetric methods
which do not require the markers to be brought into solution.
At the present time chromium sesquioxide (subject to very variable views on its
safety to humans), acid insoluble ash (Vogtmann, Pfirter and Prabucki, 1975),
'fibre' fractions (Bolton 1954; Almquist and Halloran, 1971), titanium dioxide
(Peddie et al., 1982) and perhaps polyethylene (Roudybush, Anthony and Vohra,
1974) or magnesium ferrite (Neumark, Bielorai and Iosif, 1982) are candidates for
use in routine, practical poultry studies depending on local circumstances. The use
of radioactive markers, 51Cr, 91Y and 4Cfe (Sklan et al., 1975) is attractive if
suitable equipment for their detection is available. It is not possible to draw a
general conclusion about markers. They are not a substitute for meticulous and
carefully controlled work but do have a contribution to make. The simultaneous
use of two or more markers would provide a continuous and very exacting check on
procedures (Dr V. Petersen, personal communication) and such work would have a
considerably enhanced value. In many ways the rapid assays remove the need for
markers, especially in type (3) assays, because the problem of feeding and excreta
collection are greatly simplified. With low dose levels in type (3) assays retention or
loss of marker would be a very critical issue.
SAMPLE PREPARATION AND ANALYSIS
Grinding of feeds prior to evaluation is another unresolved technical issue. In type
(3) assays grain fed whole will appear in the excreta and fineness of grinding may be
a variable in relation to the ME value of some ingredients. In reports of slurry
feeding considerable emphasis seems to be given to fine grinding.
Each of the measurements used to calculate an ME value is subject to potential
bias or imprecision and this is not revealed in the ME data themselves except as
poor repeatability. Again, the small intakes in type (3) assays make these more
sensitive issues. It is surprising that a detailed evaluation of the potential errors in
ME studies has not been reported so that particular attention could be devoted to
the most important steps. It is generally agreed, for example, that more replication
should be used to determine the combustion value of a feed than of excreta, but
such issues are rarely reported. It is probably not too harsh a judgement to say that
too little attention is paid to both the accuracy and precision of the various chemical
analyses used in ME determinations. When ring tests are undertaken the results are