Directory UMM :Data Elmu:jurnal:A:Animal Feed Science and Technology:Vol85.Issue1-2.May2000:
Animal Feed Science and Technology
85 (2000) 23±32
Review article
Alternative home-grown protein sources for
ruminants in the United Kingdom
R.J. Wilkinsa,*, R. Jonesb
b
a
Institute of Grassland and Environmental Research, North Wyke, Okehampton, Devon EX20 2SB, UK
Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK
Received 1 February 2000; accepted 6 March 2000
Abstract
Improved sources of home-grown protein are required to substitute for animal proteins and
soyabean meal in ruminant feeds. The present dominance of grassland feeds for protein supply in
Britain is highlighted and possibilities for increasing microbial protein (MP) supply on grass-based
diets are considered. There are particular opportunities for improving MP supply and animal
performance from the use of grasses with increased content of water-soluble carbohydrates (WSC)
and by the prevention of WSC and protein breakdown during ensiling through the use of bacterial
inocula or chemical additives to restrict fermentation.
Potential contributions from legumes and kale as alternative forages are reviewed. Whilst white
clover and lucerne may give higher levels of MP than grass, this arises largely from high herbage
protein concentration and high levels of feed intake, with large quantities of N being lost in excreta.
There is evidence of natural protection of protein in red clover from polyphenol oxidase and in lotus
and sainfoin by condensed tannins. These attributes may result in improved protein supply to the
animal, but further research is required, particularly with silages.
The grain legumes, peas and beans are not ideal protein supplements for grass silage because of
their rapid degradation in the rumen, but are more suited as supplements to maize silage with low
content of protein and good supply of readily available energy. Progress in plant breeding has
opened up the possibility of increased use in Britain of lupins, which have much lower rates of
degradation in the rumen than peas and beans and should form an effective complement to grass
silage. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Protein; Ruminants; Grasses; Legumes; Silage
*
Corresponding author. Tel.: 44-1837-82558; fax: 44-1837-82998.
E-mail address: [email protected] (R.J. Wilkins)
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 1 4 0 - 1
24
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
1. Introduction
There has been much recent focus on protein in ruminant feeding because of
restrictions to the use of animal proteins, efforts to reduce costs of ruminant production
and concerns arising from the low recovery of N in production systems and loss of N
compounds to the environment.
In the UK, prohibition in the use of animal proteins subsequent to the BSE crisis
produced a gap in the supply of protein to ruminants. At the same time it was increasingly
realised that there were large losses of N to the environment, because only 5±20% of the
N consumed by ruminants was being recovered in meat or milk. Jarvis et al. (1996)
calculated that the nitrate-N content in water draining from a typical dairy farm was
above the EU limit for most of the winter. They also drew attention to high losses to the
atmosphere of ammonia and nitrous oxide, with potentially adverse environmental
effects. Clearly, approaches to facilitate reduced inputs of N and improve the economy of
production may restrict environmental losses.
Table 1 indicates that more than 70% of the crude protein (CP) consumed by ruminants
in Britain is from grassland feeds, with some 14% from cereals, 10% from oilseeds and
only a trivial quantity from peas (Pisum sativa) and beans (Vicia faba). This
predominance of grassland as a source of CP applies throughout the more maritime
areas of Europe. We contend that whilst production of CP could be readily increased at
low cost, this would not solve the problem of protein supply, because of inef®cient
utilisation of N by the animal. For instance, increasing N fertiliser application to
grassland from the current average level of 120 kg N/ha to 300 kg N/ha would double CP
production from grassland (calculated from Morrison et al., 1980) through increased
yields of dry matter (DM) and increased CP concentration in the DM. This extra CP could
not, however, completely replace all of the other feed sources of N, because of limitations to
feed intake and inef®cient utilisation of CP in grassland feeds, as discussed later. The extra CP
from grassland would lead to poor production response and increased environmental losses.
This paper will discuss (a) possibilities for improving the ef®ciency of utilisation of CP
in grassland feeds, (b) the potential for use of alternative forages, generally to complement grassland feeds, and (c) the potential use of home-grown concentrate supplements.
2. Improving ef®ciency of utilisation from grassland feeds
The concentrations of CP in grazed grass, silage and grass hay are normally in the
range 150±220, 100±160 and 80±120 g/kg DM, respectively, varying seasonally, with N
Table 1
Supply of crude protein to ruminants in Britain in 1995 (kt) (from Entec, 1997 and personal calculations)
Beans and peas
Animal and ®sh
Maize gluten
Oilseeds
Cereals
Grassland feeds
21
40
175
567
800
4150
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
25
fertiliser rate, stage of maturity and the magnitude of losses during conservation. For
grassland feeds with high CP contents this CP is broken down rapidly in the rumen,
leading to high concentrations of rumen ammonia and low levels of undegraded dietary
protein (UDP). Low supply of energy to the rumen often limits microbial protein (MP)
synthesis, again restricting the supply of amino acids to grass-fed animals. These effects
may be exacerbated in silages, because of the breakdown of true protein (TP) to free
amino acids, peptides and ammonia which has already occurred in the silo and the
removal during the silage fermentation of most of the readily available energy in WSC.
Beever et al. (2000) noted that the yield of MP with silages varied from 13 to 28 g
microbial N/kg organic matter apparently digested in the rumen for silages, compared
with values of 33±58 for fresh forages.
There is more scope for increasing the ef®ciency of utilisation of CP in grass feeds by
increasing MP rather than UDP. MP could be increased by improving the supply of
readily available energy in feed and or by improving the synchrony in the supply of N and
energy to rumen microbes. In temperate grasses the major source of readily available
energy is from WSC with concentrations in fresh grasses varying from 50 to 350 g/kg
DM. There are characteristic differences in WSC seasonally (low in autumn), with stage
of growth (high during stem development) and between species (higher in ryegrass,
particularly Italian ryegrass (Lolium multi¯orum), than in other sown species).
Humphreys (1989) demonstrated that WSC content is heritable and varieties of perennial
ryegrass (Lolium perenne) have been bred with markedly enhanced WSC content. This
would be expected to increase MP yield and improve animal performance. Miller et al.
(1999) reported that milk yields were 3 kg/day higher for cows stall fed the high sugar
ryegrass (Aberdove) (200 g WSC/kg DM) than normal ryegrass (AberElan) (130 g WSC/
kg DM), but there were also differences between the varieties in DM intake and
digestibility.
The addition of readily available energy in sugar or starch to grass silages has had
marked bene®cial effects on MP supply and N retention by ruminants (Chamberlain et al.,
1985; Huhtanen, 1998). Likewise the use of additives to restrict fermentation during
ensiling and thus to retain WSC in the silage has resulted in an ef®ciency of MP synthesis
slightly higher than that of barn-dried hay made from the same crop (Jaakkola and
Huhtanen, 1993). High retention of TP in the silage may also have contributed to ef®cient
protein utilisation.
An alternative approach to improve N utilisation is to reduce the rate of protein
breakdown and thus ammonia release in the rumen and achieve better synchrony in
supply of N and energy to rumen microbes. For fresh grasses attention has centred on the
possible use of grass with the `green gene' mutation in which some of the normal
senescence processes are inhibited. Such grasses may retain higher CP contents as they
mature and Thomas (1987) demonstrated that the light harvesting chlorophyll protein
content was maintained in the grass for 6 days after cutting, whereas there was a four-fold
decline with normal grasses. It is, however, not clear whether these changes in protein structure result in improvements in protein utilisation in vivo with either fresh grasses or silages.
With silages, there are possibilities to change the composition of the CP through the
use of additives. Bacterial inocula have been demonstrated to produce silages with higher
proportions of TP than silages made without additive (Merry et al., 2000). This apparently
26
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
Table 2
Nitrogen utilisation from grass and maize silage (g/day) (Valk, 1994)
Grass
Grassmaize silage
N consumed
726
534
N in:
Urine
Faeces
Milk
N in milk as proportion of N consumed
437
157
132
0.18
216
174
144
0.27
arises from the inocula promoting rapid pH fall in the early stages of ensiling and thus
reducing protease activity in the silo. Many studies, reviewed by Merry et al. (2000), have
demonstrated improvements in animal performance with silages made with inoculant and
Sharp et al. (1994) reported an improvement of 33% in the ef®ciency of microbial protein
synthesis when silages made with inocula were compared with well preserved untreated
silage. Additives containing formaldehyde or tannins can have profound effects on N in
grasses, as discussed by Beever (1980), resulting in reductions in protein breakdown and
ammonia release in the rumen. However, responses depend on the application rate used,
and there is a substantial risk of `over-protection' of protein with reduced in vivo
digestibility and enhanced faecal loss.
High temperature dehydration of grasses reduces rumen ammonia concentrations
compared with fresh or frozen grasses (Beever, 1980). This is associated with N solubility
being reduced by high temperatures during drying. Beever (1980) noted substantial
overall bene®ts from dehydration on N supply to the animal and attributed two-thirds of
the increase to extra dietary protein escaping rumen degradation and one-third to
improved MP production. This form of grass conservation is, however, unlikely to be
widely adopted, because of high energy and capital costs.
There is potential to increase the ef®ciency of utilisation of N in grassland feeds by
appropriate supplementation. Reference has already been made to responses to additional
readily-available carbohydrate. In a recent experiment with cows grazing ryegrass
swards, the provision of 8 kg/day of a starch-rich supplement with 135 g CP/kg DM
compared with a supplement containing 210 g CP/kg DM was calculated to increase the
ef®ciency of conversion of feed N to milk N from 0.12 to 0.20 (Gibb, M.J., personal
communication). Valk (1994) has shown that the supplementation of grazed grass with
maize silage improved milk protein output and halved the loss of N in urine (Table 2).
Positive milk production responses have resulted from the supplementation of grass
silage with concentrates of increased CP content which result in higher intakes of grass
silage (Aston et al., 1998). Whilst such an approach may be economically attractive, it results
in substantial increase in CP intake and increased losses of N to the environment (Table 3).
2.1. Alternative forages
In the UK we see possible contributions from the forage legumes Ð white clover
(Trifolium repens), red clover (Trifolium pratense), lucerne (Medicago sativa), lotus
27
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
Table 3
Effect of increasing crude protein proportion in concentrate feed with ad libitum grass silage (from Aston et al.,
1998)
Crude protein in concentrate
N consumed
0.16
388
0.26
473
N in:
Urine and faeces
Milk
N in milk as proportion of N consumed
292
96
0.25
367
106
0.22
(Lotus spp.) and sainfoin (Onobrychis vicifolia) Ð and from kale (Brassica oleracea var.
acephala). They may be particularly useful in association with grass silage, because most
production systems in the UK are likely to continue to include a substantial proportion of
grass silage, made from herbage excess to grazing requirements.
All of these forages are capable of giving relatively high yields of DM and of CP as
indicated in Table 4. These forages are characterised by high levels of feed intake (Fraser
et al., 1999a, b; Beever et al., 2000). Table 5, from Dewhurst et al. (2000), demonstrates
higher intakes and milk yields for silages made from white clover, red clover and lucerne
than from grass silage and that levels of intake and production were intermediate when
cows were fed mixtures of legume silages and grass silages. Moorby et al. (1998) found
higher levels of performance and milk production from cows fed on kale-barley
(Hordeum distichon) silage and mixtures of this silage with grass silage than with grass
silage alone.
In relation to protein composition and utilisation there are major differences between
these forages. White clover and lucerne may have many of the disadvantages of grass
silage with low concentrations of WSC and extensive proteolysis during ensiling resulting
in silages with low levels of TP and high concentrations of free amino acids, illustrated
here for lucerne and red clover in Fig. 1 (Winters et al., 1999). Free amino acids were
reduced by use of inoculum, but were still markedly higher in lucerne than in red clover.
Davies et al. (1999) using in-vitro rumen simulation technology, concluded that ef®ciency
Table 4
Protein production from forage crops in the UK (adapted from Entec, 1997)
CP g/kg DM
White clover
Lucerne
Sainfoin
Red clover
Lotus
Kale
Grass
220
200
200
180
180
160
140
Yield (t/ha)
DM
CP
6
10
7
9
7
6
11
1.3
2.0
1.4
1.6
1.3
1.0
1.5
28
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
Table 5
Effect of legume silages on feed intake and milk production with cows fed 8 kg/day of concentrates (from
Dewhurst et al., 2000)
Grass
White clover
Red clover
Lucerne
Grass: white clovera
Grass: red clovera
S.E.D.
Dry matter intake (kg/day)
Silage
Milk yield (kg/day)
11.1
12.1
13.5
13.6
11.9
11.0
0.80
24.9
31.5
28.1
27.7
27.9
28.6
1.81
a
Cows fed 1:1 mixtures of silages on DM basis.
of microbial-N synthesis was 34% higher in untreated red clover silage compared to
untreated lucerne silage, furthermore, when the red clover silage was treated with a
biological inoculant this difference was even greater. Beever and Thorp (1996) concluded
that MP yields were higher for silages made from white clover and lucerne than for grass
silages, but this arose largely from high CP contents and high levels of feed intake.
With silages made from red clover, lotus and sainfoin, contents of TP may be high and
of free amino acids low. The high contents of TP in red clover silages were ®rst noted by
Albrecht and Muck (1991) and Jones (1993) and has been attributed to the high content of
polyphenol oxidase in red clover.
Lotus and sainfoin contain tannins which may restrict protein breakdown in the silo
and in the rumen. This would be expected to increase UDP supply with these forages.
Waghorn and Shelton (1997) have provided clear evidence that tannins in Lotus
corniculatus grown in New Zealand improve protein utilisation, with reductions in rumen
ammonia concentrations by 27% and increased absorption of essential amino acids from
the small intestine of 50%. This resulted mainly through increased UDP. Thomson et al.
(1971) demonstrated improved utilisation of protein in dehydrated sainfoin than in
dehydrated lucerne and associated this with the condensed tannins in the sainfoin.
Fig. 1. Free amino acids (mol/kg N) in silages made from lucerne and red clover either untreated or treated with
a biological inoculant (adapted from Winters et al., 1999).
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
29
Nutritional responses are related to the content and structure of condensed tannins.
There are, however, marked effects of forage species and conditions of growth on both the
composition and content of tannins. Thus, nutritional responses, even for particular
species, may be inconsistent, as discussed by Waghorn and Shelton (1997). They
concluded, however, that net bene®t was more likely to occur with Lotus corniculatus
than with L. uliginosus.
There is a need for much more information on the ensiling of these legumes and impact
on the nitrogenous fraction and responses in vivo. Relevant information is being obtained
in current programmes in IGER and in the EU project LEGSIL (Wilkins et al., 1998;
Pahlow et al., 2000).
The performance of lotus and sainfoin in Britain is rather varied, with some problems
both in establishment and persistency. However, the nutritional attractions encourage
further research in order to identify approaches to give more reliable and sustained
performance.
There is a greater possibility in the short term for increased use of red clover. The crop
is widely adapted to the soils and climates of northern and western Europe and in a recent
experiment DM yields were higher for red clover than grass with 200 kg N fertiliser/ha at
seven out of nine sites in UK, Germany, Sweden and Finland (Halling et al., 2000). The
species has limited persistence, but is particularly suited to mixed and organic farming
systems. Although of high moisture content and low WSC content, recent research has
demonstrated successful ensilage through combination of wilting and use of either
biological or chemical additives (Winters et al., 1999; Pahlow et al., 2000). Current
breeding programmes promise to produce red clovers with markedly enhanced
persistence, capable of sustaining yields for at least 3 years.
Kale can be used in autumn and winter either as fresh material or as silage. With
substantial contents of both CP and WSC and high digestibility (Young et al., 1997), the
MP synthesis and overall protein utilisation with fresh kale is likely to be high. On
ensiling, however, most of the WSC is fermented to organic acids. Kale silage, with low
contents of WSC and TP, is unlikely to be a good complement for grass silage, although,
as noted earlier, there is evidence of high DM intakes with mixtures including kale silage
and grass silage.
Table 6 gives a pro®le of alternative forages as sources of protein for ruminants. When
used as supplements for grass silages with moderate to high CP content. characteristics
increasing ef®ciency of MP and UDP supply are particularly important. On the other
hand, the contribution to CP concentration in the diet will be of increased consequence
when forages are used to supplement a protein-de®cient basal diet such as maize (Zea
mais).
2.2. Alternative concentrate feeds
Concentrates may either increase MP from the whole ration or increase UDP supply.
As noted earlier, with basal-diets containing grass silage of reasonable CP content, it is
particularly important to consider the characteristics of the concentrate in relation to
those of the grass silage. In many cases, large responses may be obtained with
carbohydrate-rich rather than protein-rich concentrates. The situation is different with
30
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
Table 6
Pro®le of alternative forages as sources of protein for ruminants
Yield of DM
Grass
White clover
Red clover
Lucerne
Lotus
Sainfoin
Kale
a
***
**
***
***
**
**
**
CP concentration
**
***
***
***
**
***
**
Contribution to:
Microbial protein
Undegraded dietary protein
*
*(*)
**
*(*)
**
**
**
*
*
*
*
***
***
*
a
More asterisks indicate increase of merit. For all forages contribution to microbial protein will be higher for
fresh materials than for silages.
maize-based diets where the basal diet may contain
85 (2000) 23±32
Review article
Alternative home-grown protein sources for
ruminants in the United Kingdom
R.J. Wilkinsa,*, R. Jonesb
b
a
Institute of Grassland and Environmental Research, North Wyke, Okehampton, Devon EX20 2SB, UK
Institute of Grassland and Environmental Research, Plas Gogerddan, Aberystwyth, Ceredigion SY23 3EB, UK
Received 1 February 2000; accepted 6 March 2000
Abstract
Improved sources of home-grown protein are required to substitute for animal proteins and
soyabean meal in ruminant feeds. The present dominance of grassland feeds for protein supply in
Britain is highlighted and possibilities for increasing microbial protein (MP) supply on grass-based
diets are considered. There are particular opportunities for improving MP supply and animal
performance from the use of grasses with increased content of water-soluble carbohydrates (WSC)
and by the prevention of WSC and protein breakdown during ensiling through the use of bacterial
inocula or chemical additives to restrict fermentation.
Potential contributions from legumes and kale as alternative forages are reviewed. Whilst white
clover and lucerne may give higher levels of MP than grass, this arises largely from high herbage
protein concentration and high levels of feed intake, with large quantities of N being lost in excreta.
There is evidence of natural protection of protein in red clover from polyphenol oxidase and in lotus
and sainfoin by condensed tannins. These attributes may result in improved protein supply to the
animal, but further research is required, particularly with silages.
The grain legumes, peas and beans are not ideal protein supplements for grass silage because of
their rapid degradation in the rumen, but are more suited as supplements to maize silage with low
content of protein and good supply of readily available energy. Progress in plant breeding has
opened up the possibility of increased use in Britain of lupins, which have much lower rates of
degradation in the rumen than peas and beans and should form an effective complement to grass
silage. # 2000 Elsevier Science B.V. All rights reserved.
Keywords: Protein; Ruminants; Grasses; Legumes; Silage
*
Corresponding author. Tel.: 44-1837-82558; fax: 44-1837-82998.
E-mail address: [email protected] (R.J. Wilkins)
0377-8401/00/$ ± see front matter # 2000 Elsevier Science B.V. All rights reserved.
PII: S 0 3 7 7 - 8 4 0 1 ( 0 0 ) 0 0 1 4 0 - 1
24
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
1. Introduction
There has been much recent focus on protein in ruminant feeding because of
restrictions to the use of animal proteins, efforts to reduce costs of ruminant production
and concerns arising from the low recovery of N in production systems and loss of N
compounds to the environment.
In the UK, prohibition in the use of animal proteins subsequent to the BSE crisis
produced a gap in the supply of protein to ruminants. At the same time it was increasingly
realised that there were large losses of N to the environment, because only 5±20% of the
N consumed by ruminants was being recovered in meat or milk. Jarvis et al. (1996)
calculated that the nitrate-N content in water draining from a typical dairy farm was
above the EU limit for most of the winter. They also drew attention to high losses to the
atmosphere of ammonia and nitrous oxide, with potentially adverse environmental
effects. Clearly, approaches to facilitate reduced inputs of N and improve the economy of
production may restrict environmental losses.
Table 1 indicates that more than 70% of the crude protein (CP) consumed by ruminants
in Britain is from grassland feeds, with some 14% from cereals, 10% from oilseeds and
only a trivial quantity from peas (Pisum sativa) and beans (Vicia faba). This
predominance of grassland as a source of CP applies throughout the more maritime
areas of Europe. We contend that whilst production of CP could be readily increased at
low cost, this would not solve the problem of protein supply, because of inef®cient
utilisation of N by the animal. For instance, increasing N fertiliser application to
grassland from the current average level of 120 kg N/ha to 300 kg N/ha would double CP
production from grassland (calculated from Morrison et al., 1980) through increased
yields of dry matter (DM) and increased CP concentration in the DM. This extra CP could
not, however, completely replace all of the other feed sources of N, because of limitations to
feed intake and inef®cient utilisation of CP in grassland feeds, as discussed later. The extra CP
from grassland would lead to poor production response and increased environmental losses.
This paper will discuss (a) possibilities for improving the ef®ciency of utilisation of CP
in grassland feeds, (b) the potential for use of alternative forages, generally to complement grassland feeds, and (c) the potential use of home-grown concentrate supplements.
2. Improving ef®ciency of utilisation from grassland feeds
The concentrations of CP in grazed grass, silage and grass hay are normally in the
range 150±220, 100±160 and 80±120 g/kg DM, respectively, varying seasonally, with N
Table 1
Supply of crude protein to ruminants in Britain in 1995 (kt) (from Entec, 1997 and personal calculations)
Beans and peas
Animal and ®sh
Maize gluten
Oilseeds
Cereals
Grassland feeds
21
40
175
567
800
4150
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
25
fertiliser rate, stage of maturity and the magnitude of losses during conservation. For
grassland feeds with high CP contents this CP is broken down rapidly in the rumen,
leading to high concentrations of rumen ammonia and low levels of undegraded dietary
protein (UDP). Low supply of energy to the rumen often limits microbial protein (MP)
synthesis, again restricting the supply of amino acids to grass-fed animals. These effects
may be exacerbated in silages, because of the breakdown of true protein (TP) to free
amino acids, peptides and ammonia which has already occurred in the silo and the
removal during the silage fermentation of most of the readily available energy in WSC.
Beever et al. (2000) noted that the yield of MP with silages varied from 13 to 28 g
microbial N/kg organic matter apparently digested in the rumen for silages, compared
with values of 33±58 for fresh forages.
There is more scope for increasing the ef®ciency of utilisation of CP in grass feeds by
increasing MP rather than UDP. MP could be increased by improving the supply of
readily available energy in feed and or by improving the synchrony in the supply of N and
energy to rumen microbes. In temperate grasses the major source of readily available
energy is from WSC with concentrations in fresh grasses varying from 50 to 350 g/kg
DM. There are characteristic differences in WSC seasonally (low in autumn), with stage
of growth (high during stem development) and between species (higher in ryegrass,
particularly Italian ryegrass (Lolium multi¯orum), than in other sown species).
Humphreys (1989) demonstrated that WSC content is heritable and varieties of perennial
ryegrass (Lolium perenne) have been bred with markedly enhanced WSC content. This
would be expected to increase MP yield and improve animal performance. Miller et al.
(1999) reported that milk yields were 3 kg/day higher for cows stall fed the high sugar
ryegrass (Aberdove) (200 g WSC/kg DM) than normal ryegrass (AberElan) (130 g WSC/
kg DM), but there were also differences between the varieties in DM intake and
digestibility.
The addition of readily available energy in sugar or starch to grass silages has had
marked bene®cial effects on MP supply and N retention by ruminants (Chamberlain et al.,
1985; Huhtanen, 1998). Likewise the use of additives to restrict fermentation during
ensiling and thus to retain WSC in the silage has resulted in an ef®ciency of MP synthesis
slightly higher than that of barn-dried hay made from the same crop (Jaakkola and
Huhtanen, 1993). High retention of TP in the silage may also have contributed to ef®cient
protein utilisation.
An alternative approach to improve N utilisation is to reduce the rate of protein
breakdown and thus ammonia release in the rumen and achieve better synchrony in
supply of N and energy to rumen microbes. For fresh grasses attention has centred on the
possible use of grass with the `green gene' mutation in which some of the normal
senescence processes are inhibited. Such grasses may retain higher CP contents as they
mature and Thomas (1987) demonstrated that the light harvesting chlorophyll protein
content was maintained in the grass for 6 days after cutting, whereas there was a four-fold
decline with normal grasses. It is, however, not clear whether these changes in protein structure result in improvements in protein utilisation in vivo with either fresh grasses or silages.
With silages, there are possibilities to change the composition of the CP through the
use of additives. Bacterial inocula have been demonstrated to produce silages with higher
proportions of TP than silages made without additive (Merry et al., 2000). This apparently
26
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
Table 2
Nitrogen utilisation from grass and maize silage (g/day) (Valk, 1994)
Grass
Grassmaize silage
N consumed
726
534
N in:
Urine
Faeces
Milk
N in milk as proportion of N consumed
437
157
132
0.18
216
174
144
0.27
arises from the inocula promoting rapid pH fall in the early stages of ensiling and thus
reducing protease activity in the silo. Many studies, reviewed by Merry et al. (2000), have
demonstrated improvements in animal performance with silages made with inoculant and
Sharp et al. (1994) reported an improvement of 33% in the ef®ciency of microbial protein
synthesis when silages made with inocula were compared with well preserved untreated
silage. Additives containing formaldehyde or tannins can have profound effects on N in
grasses, as discussed by Beever (1980), resulting in reductions in protein breakdown and
ammonia release in the rumen. However, responses depend on the application rate used,
and there is a substantial risk of `over-protection' of protein with reduced in vivo
digestibility and enhanced faecal loss.
High temperature dehydration of grasses reduces rumen ammonia concentrations
compared with fresh or frozen grasses (Beever, 1980). This is associated with N solubility
being reduced by high temperatures during drying. Beever (1980) noted substantial
overall bene®ts from dehydration on N supply to the animal and attributed two-thirds of
the increase to extra dietary protein escaping rumen degradation and one-third to
improved MP production. This form of grass conservation is, however, unlikely to be
widely adopted, because of high energy and capital costs.
There is potential to increase the ef®ciency of utilisation of N in grassland feeds by
appropriate supplementation. Reference has already been made to responses to additional
readily-available carbohydrate. In a recent experiment with cows grazing ryegrass
swards, the provision of 8 kg/day of a starch-rich supplement with 135 g CP/kg DM
compared with a supplement containing 210 g CP/kg DM was calculated to increase the
ef®ciency of conversion of feed N to milk N from 0.12 to 0.20 (Gibb, M.J., personal
communication). Valk (1994) has shown that the supplementation of grazed grass with
maize silage improved milk protein output and halved the loss of N in urine (Table 2).
Positive milk production responses have resulted from the supplementation of grass
silage with concentrates of increased CP content which result in higher intakes of grass
silage (Aston et al., 1998). Whilst such an approach may be economically attractive, it results
in substantial increase in CP intake and increased losses of N to the environment (Table 3).
2.1. Alternative forages
In the UK we see possible contributions from the forage legumes Ð white clover
(Trifolium repens), red clover (Trifolium pratense), lucerne (Medicago sativa), lotus
27
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
Table 3
Effect of increasing crude protein proportion in concentrate feed with ad libitum grass silage (from Aston et al.,
1998)
Crude protein in concentrate
N consumed
0.16
388
0.26
473
N in:
Urine and faeces
Milk
N in milk as proportion of N consumed
292
96
0.25
367
106
0.22
(Lotus spp.) and sainfoin (Onobrychis vicifolia) Ð and from kale (Brassica oleracea var.
acephala). They may be particularly useful in association with grass silage, because most
production systems in the UK are likely to continue to include a substantial proportion of
grass silage, made from herbage excess to grazing requirements.
All of these forages are capable of giving relatively high yields of DM and of CP as
indicated in Table 4. These forages are characterised by high levels of feed intake (Fraser
et al., 1999a, b; Beever et al., 2000). Table 5, from Dewhurst et al. (2000), demonstrates
higher intakes and milk yields for silages made from white clover, red clover and lucerne
than from grass silage and that levels of intake and production were intermediate when
cows were fed mixtures of legume silages and grass silages. Moorby et al. (1998) found
higher levels of performance and milk production from cows fed on kale-barley
(Hordeum distichon) silage and mixtures of this silage with grass silage than with grass
silage alone.
In relation to protein composition and utilisation there are major differences between
these forages. White clover and lucerne may have many of the disadvantages of grass
silage with low concentrations of WSC and extensive proteolysis during ensiling resulting
in silages with low levels of TP and high concentrations of free amino acids, illustrated
here for lucerne and red clover in Fig. 1 (Winters et al., 1999). Free amino acids were
reduced by use of inoculum, but were still markedly higher in lucerne than in red clover.
Davies et al. (1999) using in-vitro rumen simulation technology, concluded that ef®ciency
Table 4
Protein production from forage crops in the UK (adapted from Entec, 1997)
CP g/kg DM
White clover
Lucerne
Sainfoin
Red clover
Lotus
Kale
Grass
220
200
200
180
180
160
140
Yield (t/ha)
DM
CP
6
10
7
9
7
6
11
1.3
2.0
1.4
1.6
1.3
1.0
1.5
28
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
Table 5
Effect of legume silages on feed intake and milk production with cows fed 8 kg/day of concentrates (from
Dewhurst et al., 2000)
Grass
White clover
Red clover
Lucerne
Grass: white clovera
Grass: red clovera
S.E.D.
Dry matter intake (kg/day)
Silage
Milk yield (kg/day)
11.1
12.1
13.5
13.6
11.9
11.0
0.80
24.9
31.5
28.1
27.7
27.9
28.6
1.81
a
Cows fed 1:1 mixtures of silages on DM basis.
of microbial-N synthesis was 34% higher in untreated red clover silage compared to
untreated lucerne silage, furthermore, when the red clover silage was treated with a
biological inoculant this difference was even greater. Beever and Thorp (1996) concluded
that MP yields were higher for silages made from white clover and lucerne than for grass
silages, but this arose largely from high CP contents and high levels of feed intake.
With silages made from red clover, lotus and sainfoin, contents of TP may be high and
of free amino acids low. The high contents of TP in red clover silages were ®rst noted by
Albrecht and Muck (1991) and Jones (1993) and has been attributed to the high content of
polyphenol oxidase in red clover.
Lotus and sainfoin contain tannins which may restrict protein breakdown in the silo
and in the rumen. This would be expected to increase UDP supply with these forages.
Waghorn and Shelton (1997) have provided clear evidence that tannins in Lotus
corniculatus grown in New Zealand improve protein utilisation, with reductions in rumen
ammonia concentrations by 27% and increased absorption of essential amino acids from
the small intestine of 50%. This resulted mainly through increased UDP. Thomson et al.
(1971) demonstrated improved utilisation of protein in dehydrated sainfoin than in
dehydrated lucerne and associated this with the condensed tannins in the sainfoin.
Fig. 1. Free amino acids (mol/kg N) in silages made from lucerne and red clover either untreated or treated with
a biological inoculant (adapted from Winters et al., 1999).
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
29
Nutritional responses are related to the content and structure of condensed tannins.
There are, however, marked effects of forage species and conditions of growth on both the
composition and content of tannins. Thus, nutritional responses, even for particular
species, may be inconsistent, as discussed by Waghorn and Shelton (1997). They
concluded, however, that net bene®t was more likely to occur with Lotus corniculatus
than with L. uliginosus.
There is a need for much more information on the ensiling of these legumes and impact
on the nitrogenous fraction and responses in vivo. Relevant information is being obtained
in current programmes in IGER and in the EU project LEGSIL (Wilkins et al., 1998;
Pahlow et al., 2000).
The performance of lotus and sainfoin in Britain is rather varied, with some problems
both in establishment and persistency. However, the nutritional attractions encourage
further research in order to identify approaches to give more reliable and sustained
performance.
There is a greater possibility in the short term for increased use of red clover. The crop
is widely adapted to the soils and climates of northern and western Europe and in a recent
experiment DM yields were higher for red clover than grass with 200 kg N fertiliser/ha at
seven out of nine sites in UK, Germany, Sweden and Finland (Halling et al., 2000). The
species has limited persistence, but is particularly suited to mixed and organic farming
systems. Although of high moisture content and low WSC content, recent research has
demonstrated successful ensilage through combination of wilting and use of either
biological or chemical additives (Winters et al., 1999; Pahlow et al., 2000). Current
breeding programmes promise to produce red clovers with markedly enhanced
persistence, capable of sustaining yields for at least 3 years.
Kale can be used in autumn and winter either as fresh material or as silage. With
substantial contents of both CP and WSC and high digestibility (Young et al., 1997), the
MP synthesis and overall protein utilisation with fresh kale is likely to be high. On
ensiling, however, most of the WSC is fermented to organic acids. Kale silage, with low
contents of WSC and TP, is unlikely to be a good complement for grass silage, although,
as noted earlier, there is evidence of high DM intakes with mixtures including kale silage
and grass silage.
Table 6 gives a pro®le of alternative forages as sources of protein for ruminants. When
used as supplements for grass silages with moderate to high CP content. characteristics
increasing ef®ciency of MP and UDP supply are particularly important. On the other
hand, the contribution to CP concentration in the diet will be of increased consequence
when forages are used to supplement a protein-de®cient basal diet such as maize (Zea
mais).
2.2. Alternative concentrate feeds
Concentrates may either increase MP from the whole ration or increase UDP supply.
As noted earlier, with basal-diets containing grass silage of reasonable CP content, it is
particularly important to consider the characteristics of the concentrate in relation to
those of the grass silage. In many cases, large responses may be obtained with
carbohydrate-rich rather than protein-rich concentrates. The situation is different with
30
R.J. Wilkins, R. Jones / Animal Feed Science and Technology 85 (2000) 23±32
Table 6
Pro®le of alternative forages as sources of protein for ruminants
Yield of DM
Grass
White clover
Red clover
Lucerne
Lotus
Sainfoin
Kale
a
***
**
***
***
**
**
**
CP concentration
**
***
***
***
**
***
**
Contribution to:
Microbial protein
Undegraded dietary protein
*
*(*)
**
*(*)
**
**
**
*
*
*
*
***
***
*
a
More asterisks indicate increase of merit. For all forages contribution to microbial protein will be higher for
fresh materials than for silages.
maize-based diets where the basal diet may contain