Abstract

Principles of supplementation are discussed in respect of both, their positive and negative effects

on roughage digestion and utilization by ruminants. It is pointed out that negative effects mainly

occur when excessively processed concentrate is given in large quantities two times per day. This

lowers rumen pH which in turn depresses cellulose digestion and intake of cellulosic feeds, leading

to problems of acidosis and secondary ketosis due to off-feed conditions. To a large extent, such

problems can be overcome by limited processing and feeding the concentrate mixed with the

roughage.

Supplements can also have positive effects by alleviating deficiencies such as nitrogen or by

providing easily fermentable fiber to increase microbes for attachment to roughages. Supplements

can increase microbial protein production and undegraded protein supply. It is emphasized that

proper use and management of supplements can make the difference between profit and loss for

small farmers. # 1999 Elsevier Science B.V. All rights reserved.

1. Introduction

Most dairy cows, while receiving basal feeds of cellulosic roughages, are given

supplements of a higher quality and nutrient density. Such supplements can have both

positive and negative effects on the digestion of the basal feed. Some of these aspects will

be discussed in more detail, as well as management methods that give the optimal

utilization of feed and healthy animals.

2. Interference with basal digestion of roughage

In order to achieve optimal conditions for digestion of roughages or, more precisely,

cellulosic roughages, the rumen pH must be above 6.2 or thereabouts (Mould and érskov,

1984). At a pH below 6.2, the growth rate of cellulosic bacteria and fungi is inhibited and

ceases altogether at about pH 5.8. It is of paramount importance to avoid inhibition or

cessation of cellulose digestion as this not only reduces digestibility of the cellulosic

roughages, but also reduces intake. This in turn can lead to a higher than expected

proportion of propionic acid in the rumen and lead to reduced milk fat.

In most small holder dairy farms in developing countries, the management strategy for

feeding high quality supplements is to feed it in two discrete feedings, one in the morning

and one in the evening. Mostly it is given in the dry form, but in Indonesia for instance, it

is always suspended in water, which ensures that it is consumed even more rapidly. It is

this twice daily feeding of significant amounts of highly fermentable feeds that often

causes problems of roughage utilization. In severe instances the low pH, which occurs 2

to 3 h after feeding, causes acidosis resulting in the animals going off-feed altogether. For

high producing cattle this in turn leads to ketosis or acetonaemia. Acidosis followed by

ketosis, and low intake and digestion of roughages, leads to other problems such as

laminitis, retained placenta, and infertility. The management of concentrate feeding can

thus determine profit or loss for many small farmers. There are three major routes by

which these conditions can be circumvented.

3. Type of concentrate

Apart from level of concentrate which obviously affects the pH depression following

feeding, the type of concentrate is very important. Obviously 1 or 2 kg/day for dairy cows

will have relatively little effect regardless of type. The most important factor determining

speed of digestion of concentrate is its water solubility and, in the case of starch, the

surfaces that are exposed to microbes. Thus, molasses diets or any product containing a

large proportion of soluble sugar will ferment rapidly and, since it is consumed rapidly,

there is little saliva secreted to buffer the volatile acids formed. This aspect of concentrate

feeding receives little or no attention by feed compounders who generally look at cost and

digestibility only. Concentrate containing a large proportion of easily fermentable fiber

and pectin rather than soluble sugars and starch are degraded much more slowly and by

cellulolytic bacteria (Silva et al., 1989). Thus, cereal brans, sugar beet pulp, dried citrus

pulp, leaf meal, etc. are much more suitable for high level concentrate feeding to dairy

cows. As mentioned earlier, small amounts create no problem but when concentrate

constitutes 30% or more of the total diets these problems will be very important and

effect of type processing, feeding management, and quantity fed will increase.

4. Effect of processing

It is clear that for soluble sugars contained in the feed, processing will have little or no

effect. However for starch based diets, the degree of processing can have serious

180 E.R. érskov / Preventive Veterinary Medicine 38 (1999) 179±185

consequences. This was shown by érskov and Fraser (1975) who looked at the effect of

feeding whole versus processed grain to sheep. Here, it was shown that not only was

digestion of roughage depressed with feeding of processed grain, but intake was also

depressed. The processing caused serious reductions in digestibility and utilization of

roughages, while the digestibility of the grain itself was similar whether it was processed

or not (érskov, 1987). In cattle, however, diets with whole grain were less digestible than

with processed grain, particularly when fed along with roughages. The chewing capacity

of cattle was not as efficient as the chewing capacity of small ruminants. While removal

or disruption of the seed coat is important to give access to rumen bacteria, it is

recognized that any processing in excess of that necessary for access by rumen bacteria

will result in problems such as low rumen pH and negative interaction with roughage

utilization.

In a search for a method which, with minimum processing, still ensured an acceptable

digestibility it was shown that rolling, crimping, pelleting, grinding, and kibbling all were

excessive, but one treatment accomplished all we needed: spraying grain with a solution

of caustic soda at levels of 2.5 to 4.0% depending on the grain (érskov et al., 1981;

érskov et al., 1980). After _24 h, the sodium hydroxide on the grain is converted to

sodium carbonate. On exposure to water or rumen fluid, the fibrous seedcoat falls off and

gives a slow but nearly complete digestion of the starch, thus reducing any adverse effect

on roughage digestion. This process is used on many dairy farms in the UK when either

wheat, barley, maize, or oats is fed. This method resulted in all the advantages achieved

on feeding whole grain to small ruminants, and for very fibrous grains like oats,

digestibility is greater than any form of physical processing.

Feed compounders should be instructed on how to process grain only to the extent

necessary to ensure an acceptable digestibility. Excessive processing causes many

problems in feeding of dairy cows and the problem increases with increasing quantity fed.

Excessive feeding of ground or pelleted starchy concentrate on a dairy farm is almost

always accompanied by problems such as acidosis, ketosis, and laminitis if it is given in

twice daily discrete feeds.

5. Method of feeding of concentrate

Although for some starch concentrates it is possible to manipulate processing to avoid

large fluctuations in rumen pH, this is not the case for concentrate containing soluble

sugar and fine starch particles like tapioca. Systems on large dairy farms which use

completely mixed diets are often used, where mixer wagons mix concentrate and

roughage simultaneously. In order to do this the roughage (e.g. straw, hay or silage) is

normally chopped to make mixing possible. This system effectively prevents cattle from

eating the concentrate too rapidly as it will be eaten together with the roughage.

It is of course also possible to feed the concentrate in four-to-six portions per day rather

than twice daily, which will reduce fluctuations in rumen pH. While for the small farmer

mechanical mixing of roughage and concentrate is not possible, there are many

possibilities in which the concentrate can be mixed with roughages at feeding times and

help to ensure both better feed utilization and better health of dairy cattle. This is a

E.R. érskov / Preventive Veterinary Medicine 38 (1999) 179±185 181

challenge for researchers and extension workers concerned with small scale dairy

production; this effect of management of concentrate feeding increases as level of feeding

increases, which in turn is affected by milk production level. Feeding management which

is acceptable for low level feeding for low production cannot be used for high level

feeding to support high level of production.

6. Benefits of supplementation to digestion

When large amounts of starchy concentrate are fed, especially soluble sugars, the

supplements will seldom if ever benefit the digestion of roughage. Methods of reducing

such interference have been discussed above. Supplements should on the whole be chosen

to complement any nutritional deficiencies in basal feeds as well as to supplementing

energy. This positive interaction can be of different forms. Thus, if there is a deficiency in

the basal feed of, for example, nitrogen, it is advisable and cost effective to choose a

supplement which contains an excess of nitrogen relative to fermentable energy.

However, the rumen environment and thus utilization of the basal feed can also

sometimes be improved by other characteristics of the supplements. In some instances, a

supply of easily digestible fiber can result in a greater number of bacteria in solution, so

that new substrate entering the rumen is invaded more rapidly. This, in turn, reduces the

lag phase, increases the degradation rate, and thus increases rumen turnover. This was

clearly demonstrated by Silva and érskov (1988) who showed that untreated straw

fermented faster in the rumens of animals receiving ammonia-treated straw than when

incubated in the rumens of animals receiving untreated straw and urea. This is shown in

Table 1. Here, it can be seen that at 48 h incubation, 45.3% had disappeared when

incubated in the rumens of sheep given untreated straw, and 53.1% disappeared in the

rumen of animals given ammoniated straw. This led Silva et al. (1989) to find that

supplements could improve the rumen environment of the animals receiving untreated

straw.

Sugar beet pulp was found to contain easily fermentable fiber which increases the

degradation rate of untreated straw (Table 2). Rumen pH and ammonia concentration was

not limiting, but the rumen environment was improved by supplementation with sugar

beet pulp. It can be seen that untreated straw intake and digestibility increased when the

rumen environment was improved with sugarbeet pulp. With ammonia-treated straw the

beet pulp supplement did not improve digestibility or intake since the rumen environment

was already optimal.

Table 1

Effect of feeding untreated or ammoniated straw to sheep on degradation of untreated straw incubated in nylon

bags at similar equal rumen ammonia concentration and rumen. From Silva and érskov, 1988

Diet Rumen NH3 (mg/l) Rumen pH Disappearance (%)

24 h 48 h

Untreated straw . urea 268 6.9 26.5 45.3

Ammoniated straw 244 6.8 38.7 53.1

182 E.R. érskov / Preventive Veterinary Medicine 38 (1999) 179±185

As for the work shown in Table 1, the rumen ammonia concentration was similar or not

limiting as urea was added to the untreated straw. In another trial (Table 3) reported by

Pathirana and érskov (1995), an interesting comparison was made using glyricidia leaves

as a supplement to rice straw. Here, it can be seen that intake of straw was increased both

when glyricidia was added to untreated and urea supplemented straw, but the increase was

significantly greater when it was added to unsupplemented straw.

This suggests that for the unsupplemented straw glyricidia may have both corrected a

nitrogen deficiency and added easily digestible fiber as a source of energy. When

glyricidia was added to urea supplemented straw, the increase in intake appears to have

been due only to easily fermentable fiber. At higher levels of supplementation of the

leguminous forage, intake of straw decreased.

Table 2

Effect of sugar beet supplement on intake and digestibility of straw supplement with urea or of ammonia treated

straw. From Silva et al., 1989

Diet Intake of straw Dry matter digestibility of straw (%)

Untreated straw 414 49

Untreated straw . 15% sugar beet pulp 505 54

Ammonia treated straw 729 57

Ammonia treated straw . 15% sugarbeet pulp 717 56

Table 3

The effect of supplementing untreated or urea supplemented rice straw with glyricidia leaves to sheep. From

Pathirana and érskov, 1995

Urea supplements

(%)

Glyricidia (g/kg)

dry matter

Intake of rice straw

dry matter (g/day)

Total intake dry

matter (g/day)

0 0 574 574

0 50 673 708

0 150 848 998

0 300 721 1030

2 0 690 690

2 50 729 765

2 150 880 1035

2 300 715 1021

Table 4

Effect of supplementing untreated straw with ammonia treated straw Manyuchi et al., 1992

Treatment Intake of untreated

straw (g/day)

Total intake

(g/day)

Untreated straw 641 641

Untreated straw . 200 g ammonia straw 816 1003

Untreated straw . 400 g ammonia straw 667 1019

Ammonia treated straw alone Ð 1152

E.R. érskov / Preventive Veterinary Medicine 38 (1999) 179±185 183

Finally, we can think of making ammonia treated straw into a supplement. This would

be of interest in places where crop residues are grazed. In a small trial Manyuchi et al.

(1992) showed that an addition of 200 g/day of ammonia-treated straw to the diet of

sheep increased intake of untreated straw. At higher levels of supplementation, intake of

untreated straw decreased, obviously due to substitution (see Table 4).

7. Conclusions

The aim of strategic supplementation is to ensure that the rumen environment for

cellulose digestion is optimal. As discussed, supplements can both inhibit and improve

digestion of cellulosis materials. Methods to avoid interference have been discussed as

well as how best to ensure a positive effect. It is also necessary to point out that studies

concerning effects of supplements on the rumen environment can only be done in the

environment where the animals are and with the cellulosic feeds and supplements locally

available. There are no text books to give the answer, only text books on how to best

study these important aspects of ruminant nutrition in order to ensure maximal feed

resource utilization as well as the adequate health of animals.

Supplementation strategies are complex but, where properly understood, can make the

difference between profit and loss for small farmers reliant on cellulosic forages as the

basal diet for ruminant livestock.

1. Supplements can decrease utilization and intake of basal feeds. This can be largely

avoided by attention to processing, feeding management, and by selecting the type of

concentrate.

2. Supplements can alleviate deficiencies in basal feeds and increase intake and

digestion.

3. Supplements can add a source of easily fermentable fiber which may increase

degradation rate and intake of basal feeds.

4. Supplements can increase microbial protein production.

5. Supplements can supply undegraded dietary protein.

6. Supplements constitute an energy source in their own right.

Sometimes supplements relieve more than one nutritional constraint at a time, so large

responses can be achieved with small amounts. Understanding supplementation strategies

can have a great influence on the economy of feeding ruminant livestock. It is a challenge

for nutritionists to explore how best to use locally available supplements to maximum

advantage for small farmers.

Gelen Aramalar:

barley straw treated with sodium hydroxide for feeding sheep