Cellulases and Their Applications

20 Effect of Urea Supplementation on the Nutritive Value of NaOH-treated Oat Straw E. D O N E F E R , I. O. A . A D E L E Y E , and T. A . O. C. JONES

Downloaded by UNIV OF GUELPH LIBRARY on June 8, 2012 | http://pubs.acs.org Publication Date: June 1, 1969 | doi: 10.1021/ba-1969-0095.ch020

1

Department of Animal Science, Macdonald College (McGill University), Prov. Quebec, Canada

Ground oat straw was treated with a 13.3% NaOH solution (at a rate of 60 liters of solution per 100 kg. straw), neutralized with 16.7 liters of 50% acetic acid, and dried. Untreated or treated straw, each with or without urea (2.5% of ration) and/or sucrose (3.5% of ration) was fed ad libitum to sheep. Alkali treatment resulted in significant increases in energy digestibility, but had no consistent effect on voluntary intake unless urea was also fed. Urea supplementation of treated straw resulted in an average 160% increase in voluntary intake when compared with untreated, unsupplemented controls. Sucrose had no significant effect on either digestibility or voluntary intake. NaOH-treated, urea supplemented straw supplied 220% more digestible energy than the control ration.

*Tphe work of Woodman and Stewart (15) drew attention to the effect of lignification on limiting digestion of plant nutrients by the microorganisms of the rumen. Freudenberg (9) has aptly described lignin as being "comparable with the cement i n reinforced concrete." The action of lignin i n filling the intercellular spaces of the plant accounts for its ability to limit the availability of potential plant nutrients such as holocellulose and protein. Whereas the gross energy of less mature forage plants can be utilized (digested) to the extent of 50-70%, increased lignification with advancing plant maturity can result i n only 20-50% of the potential energy being made available to the animal. Equally or of more importance than the effect of lignification i n decreasing digestibility is the marked reduction i n voluntary intake b y the ruminant of plant 1

Present address: Njala University College, Freetown, Sierra Leone. 328

In Cellulases and Their Applications; Hajny, G., et al.; Advances in Chemistry; American Chemical Society: Washington, DC, 1969.

20.

DONEFER E T A L .

Urea Supplementation

329


material of advanced maturity. As a result of both these effects the ruminant animal is unable in many cases to obtain its maintenance energy requirements when fed highly lignified forage plants. The utilization of low-quality forages takes on special importance because of present attempts and the clear necessity to increase world food supplies. A major factor limiting production of high-quality proteins through development of animal agriculture is the shortage of suitable feedstuffs for these animals. This problem is particularly severe i n tropical areas as the climate encourages rapid plant growth and subsequent over-maturity from a nutritional point of view. In many areas, particularly in developing countries, highly lignified plant by-products such as straws, grain hulls, and sugar-cane bagasse, although available in large supply, are not efficiently utilized and in many cases are completely wasted. The use of chemical procedures to effect delignification have been elaborated particularly through efforts of the pulp and paper industry. Efforts to increase the nutritive value of low-quality forages such as straw date back to the beginning of this century and were highlighted by the procedure reported by Beckmann in 1921 (3) in which treatment of straw with 1.5% N a O H solution effected a twofold increase i n the amount of crude fiber utilized by ruminant animals. W h i l e the Beckmann process has proved popular in small-scale farm operations, wide-scale use has been limited owing to the large volume of dilute N a O H solutions required, the tedious washing operation to remove residual alkali, and the losses of soluble nutrients caused by washing. Recent work i n Finland (13) and Canada (14) have been directed towards modification of the chemical delignification procedures with a view to their wider applicability in low-quality forage improvement schemes. The newer modifications which tend to overcome use of excess chemicals and water have been demonstrated to be as effective in increasing digestibility as the older procedures. In order to reduce chemical costs and to increase labor efficiency, delignification procedures might best be adapted to large-scale operations taking advantage of bulk chemical prices and utilization of grinding, mixing, and perhaps pelleting equipment. The present experiments were undertaken to investigate modified NaOH-treatment procedures and to determine the effect of nitrogen supplementation on both the digestibility and voluntary intake of untreated and treated straw.

Experiment I.

The Effect of NaOH Level and Dilution on the In Vitro Digestion of Oat Straw Cellulose

Methods. The effect of various N a O H levels and dilutions on cellulose digestion was determined by use of an in vitro rumen fermentation



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CELLULASES A N D THEIR APPLICATIONS

procedure (7) with bacterial inoculum (phosphate buffer extract) prepared from rumen contents obtained from a fistulated steer (11). The ground oat straw (Avena sativa) was treated i n 50-gram batches i n a 1000-ml. beaker. The appropriate N a O H solution was mixed with the straw and allowed to react for 24 hours, having observed in preliminary trials that a longer reaction period (five days) resulted in only slight increases in cellulose digested in vitro. Levels of N a O H used varied from 4 to 32 grams expressed per 100 grams of straw, with each N a O H level tested at three different dilutions, 30, 60, and 120 m l . of solution per 100 grams of straw. Actual solution concentrations thus varied from 3.3% (4 grams N a O H per 12 ml.) to 53.3% (32 grams N a O H per 60 m l . ) . After treatment the straws were dried and weighed into fermentation tubes with in vitro cellulose digestion determined after a 24-hour fermentation period. Prior to the introduction of the bacterial inoculum, acetic acid was added to each tube to adjust the p H of the NaOH-treated straw to neutrality. Results and Discussion. The effect of the different N a O H levels and dilutions on in vitro cellulose digestion are illustrated in Figure 1.

I

i

i

i

4

8

16

Figure 1.

I

I

32

NaOH LEVEL (g/IOOgstraw) The effect of NaOH level and dilution on in vitro cellulose digestion Ml. solution • 120 m 60 A 30

The effect of N a O H level was to increase cellulose digestion from the 25% observed for the untreated straw to a maximum of 8 1 % as obtained with 16 grams N a O H in 120 m l . solution. A t each treatment


20.

DONEFER E T A L .


331


level, with the exception of 32 grams N a O H , the effect of the higher water dilution was to cause slight increases in cellulose digested, most possibly because of better mixing of the N a O H and straw and a more complete reaction at the higher moisture levels. A t the 32 gram N a O H level, the levelling-off with 60 m l . of solution and the depression observed at the 120 m l . solution level is interpreted as due to an anti-microbial effect of the high salt levels contained i n the substrate, as unreacted N a O H was not removed by washing although its effect on p H was neutralized by the acetic acid additions. As the purpose of this in vitro experiment was to establish treatment guide-lines for subsequent animal feeding trials, the practicality of the various N a O H levels and dilutions was stressed. Ideally, both the amount of N a O H and water should be minimized in large-scale treatment procedures. Excess alkali either must be removed by washing as i n the classical Beckmann procedure or alternatively, if neutralized by acid, the resultant sodium levels must not overload the animal's ability to maintain acid-base equihbriurn (assuming acetate w i l l be metabolized in the rumen). Use of large amounts of water should also be avoided as the final treated material would have to be dried prior to storage. The combination of N a O H solutions and straw as used i n this in vitro study resulted in mixtures varying in moisture content from 30 to 60% with no unabsorbed liquid present. In contrast, the Beckmann procedure (3) called for steepage of chopped straw in eight times its weight of 1.5% N a O H solution, with the treated material to be washed free of alkali and fed wet or dried. Although the strength of the N a O H solution used by Beckmann was low, the amount of N a O H used per 100 grams of straw was relatively high (12 grams) owing to the large amount of solution used. Lampila (13) proposed the use of 300 m l . of 2 % N a O H solution per 100 grams straw, which is 6 grams N a O H per 100 grams straw or half the amount used in the Beckmann procedure. Lampila reported the in vivo digestibilities for crude fiber of his treated straw were similar to those obtained by Beckmann. Wilson and Pigden (14) reported the effect of N a O H levels up to 15 grams per 100 grams straw on the in vitro dry matter digestion of wheat straw. Their solutions which were all used at a level of 30 m l . per 100 grams straw, and thus quite concentrated, resulted in a maximum of 82% dry matter digested at their highest N a O H level. As a result of the work cited and the in vitro trial herein reported, it was decided to prepare straw for in vivo trials by treating with 8 grams N a O H and 60 m l . of solution per 100 grams of straw. These levels although not resulting in the highest cellulose digestion in the in vitro experiment, minimized the quantity of alkali and water used with an


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CELLULASES A N D THEIR APPLICATIONS

anticipated marked improvement in the nutritive value of the straw (to approximately 60% cellulose digestibility).


Experiment II.

The Effect of NaOH Treatment and Pelleting on the Nutritive Value of Oat Straw

Methods. T R E A T M E N T OF S T R A W . Baled oat straw harvested i n 1965 was prepared for treatment by grinding in a hammer mill (Davis CR-2) ( H . C . Davis and Sons Manufacturing Co., Bonner Springs, Kansas) to pass successively a 3 cm. and 0.35 cm. diameter mesh screen. The ground straw (100 kg.) was placed i n a horizontal batch mixer (Davis S-20) and 60 liters of a 13.3 N a O H % solution (8 kg. N a O H per 100 kg. straw) was added to the straw while the mixer blades were turning. The N a O H solution was contained i n two large polyethylene carboys placed on top of the mixer, with the solution slowly dispensed onto the straw from a spigot fitted on each container. The solution was administered over a 15-minute period with a total mixing time of one hour. The resultant mixture was left in the mixer for 24 hours, after which time 16.7 liters of 50% acetic acid was added and the contents mixed for one hour. The final mixture had a p H of 6 and a dry matter content of 60%. The treated straw was dried by spreading i n a 5-10 cm. layer on a floor, using fans to increase air circulation. Preparation of rations. In this experiment, straw was fed as the sole feedstuff with the animals having free access to water and salt ( N a C l ) containing cobalt and iodine. Treated and untreated (control) straw was fed in either the ground or pelleted form. Pellets were prepared by passing slightly moistened ground straw through the 7/16-inch (1.1 cm.) die of a pellet mill (Templewood Junior Provender Press, Distributed by Superior Processing Equipment, Hopkins, M i n n . ) . The pellets, averaging 2 cm. i n length, were air dried prior to feeding. Animals. Eight female Cheviot lambs (initially 8-10 months old) were confined to individual digestion cages, designed to enable total collection of feces. Each feeding period was of 21-day duration, the first 14 days allowing for adjustment to the ration, with voluntary intake and digestibility measured over the last seven days. Voluntary intake was measured by feeding daily an amount of ration to insure an excess of at least 10% over expected intake, and detennining actual intake by daily weighing of refused feed. A total collection of feces was made daily over the seven-day period with aliquot samples dried and retained for analysis. Four sheep were fed each o f the rations. Analysis and Calculation. Feed and fecal samples were analyzed for gross energy (Parr Oxygen Calorimeter), cellulose (7), dry matter, and crude protein ( I ) . Apparent digestion of dry matter, cellulose, and energy was calculated as the difference between nutrient intake and fecal excretion, expressed as a percent of nutrient intake. Relative Intake (%) was calculated as an expression of voluntary intake per unit animal metabolic size (gram dry matter/ sheep weight^ - ) expressed relative to a "standard" high quality forage assumed to have a voluntary intake of 80 grams dry matter/weight °- , according, to the 0

kg

75


75

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DONEFER E T A L .


333

method of Crampton e t a l (5). Nutritive value indices ( N V I ) were calculated as the product of relative intake and percent digestibility of energy (5) and represent a relative score of digestible energy ( D E ) intake which was also converted to absolute D E intake ( D E i / weight^ ) by multiplying each N V I by the feed gross energy content (kcal./grams) divided by 1.25 (6). k c a

0 75


Statistical significance between treatment means was determined by Duncans Multiple Range Test (8). Results and Discussion. Experiment II results are summarized in Table I. N a O H treatment of the ground unpelleted straw resulted i n significant increases (P < 0.5) i n digestion in all cases except for cellulose, which approached significance. The depression i n digestion because of pelleting largely counteracted the effect of the N a O H treatment. N a O H treatment had no effect on relative intake, which was significantly increased in each case because of pelleting. The decreased digestibility and increased relative intake because of pelleting resulted in almost identical nutritive value indices and digestible energy intakes for all ration combinations. Although digestion of the treated ground straw was significantly increased, a significant (P < .05) but unexplained depression i n voluntary intake of this ration annulled any of the effect of the improved digestibility in terms of increasing energy intake. In this experiment the total ration was restricted to straw in order to study the effect of chemical and physical treatment on the microbial degradation of the forage uncomplicated by interactions with other nutrients. The results suggested nutrient deficiencies in the straw other than supply of energy were inhibiting rumen microbial action. Table I.

The Effect of N a O H Treatment and Pelleting on the Nutritive Value of Oat Straw (Experiment II) m

Treatment: Criteria:

Form:

Untreated

NaOH-treated

Ground

Pelleted

Ground

Pelleted

Digestion Coefficients: (%) Cellulose Dry Matter Gross Energy

43.9°' 36.4° 33.7°

38.2* 31.8 28.4°

57.6 54.4 49.0

34.6 41.0° 34.3°

Relative Intake (% )

44.3

57.7

32.5°

49.4

Nutritive Value Index

15.0"

16.4

16.4"

16.9°

Digestible Energy Intake (kcal./Wt ™)

53.1°

57.3"

53.7

55.5"

kg

6

6

a

c

a

6

b

6

a

a

6

0

Means on the same line having different superscript letters differ significantly (P


Cellulases and Their Applications

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