The feeding value for ruminants of straw and wholecrop barley and oats treated with anhydrous or aqueous ammonia or urea

Animal Feed Science and Technology, 8 (1983) 247--257 Elsevier Science Publishers B.V., Amsterdam - - P r i n t e d in The Netherlands

247

THE FEEDING VALUE FOR RUMINANTS OF STRAW AND WHOLECROP BARLEY AND OATS TREATED WITH ANHYDROUS OR AQUEOUS AMMONIA OR UREA

E.R. 0RSKOV, G.W. REID, S.M. HOLLAND, C.A.G. TAIT and N.H. LEE* The R o w e t t Research Institute, Bucksburn, Aberdeen A B 2 9SB (Gt. Britain) (Received 5 April 1 9 8 2 ; a c c e p t e d for publication 9 November 1982)

ABSTRACT 0rsk0v, E.R., Reid, G.W., Holland, S.M., Tait, C.A.G. and Lee, N.H., 1983. The feeding value for ruminants of straw and whole-crop barley and oats treated with anhydrous or aqueous ammonia or urea. Anita. Feed Sci. Technol., 8: 247--257, Ammonia-treated or untreated barley straw supplemented with urea was given as the only f e e d to two groups of Friesian heifers weighing approximately 550 kg. The digestibility of dry matter (DM) was 58.8 and 49.9%, daily feed intake was 5.88 and 3.87 kg and daily liveweigh t change was +324 and - 4 4 7 g for the ammonia-treated and control barley straw diets~ respectively. Anhydrous or aqueous ammonia (NH3) was injected into large round straw bales covered with plastic. The rates o f degradation o f barley straw in nylon bags and digestibility in vivo were the same for both ammonia treatments. The distribution of N in the bales was also similar and uniform with both treatments. No differences were recorded in the rate of degradation in nylon bags if the plastic was removed 2 or 8 weeks after treatment. Anhydrous or aqueous ammonia or isonitrogenous amounts of urea were injected into large round bags containing whole-crop barley or oats collected with a forage harvester. The digestibility of starch b y steers was about 92% for ammonia-treated samples and 78% for the urea'treated samples" Urea and a m m ° n i a efficiently preserved the w h ° l e ' c r ° p materials but untreated control samples and samples treated with NaOH deteriorated during storage.

INTRODUCTION The effect on digestion in the rumen of treating straw with ammonia h a s b e e n e x t e n s i v e l y s t u d i e d ( s e e S u n d s t 0 1 e t al., 1 9 7 7 ) a n d t h e t e c h n i q u e is b e i n g u s e d o n f a r m s in s e v e r a l c o u n t r i e s . T h e a d v a n t a g e o f u s i n g a n i t r o g e n o u s a l k a l i in c o m p a r i s o n w i t h . s o d i u m h y d r o x i d e is m a i n l y t h a t t h e inc r e a s e in t h e m i c r o b i a l r e q u i r e m e n t f o r n i t r o g e n w h e n t h e p o t e n t i a l d i g e s t i b i l i t y is i n c r e a s e d is s u p p l i e d b y a m m o n i a w h i c h is a b s o r b e d b y t h e s t r a w . *Present address: South Korea Institute of Science and Technology, Seoul, S. Korea.

0377-8401/83/$03.00

© 1983 Elsevier Science Publishers B.V.

248 Another practical advantage is t h a t no mechanical processing of the straw is required before treatment. Further, an excess of ammonia in the ~rine m a y be a useful N fertilizer whereas an excess of sodium may, in the long-term, prove harmful to soft structure. Few experiments have investigated ammonia-treated straw given a s the only feed. In the first experiment reported here a comparison was made between ammonia- and urea-treated straw as the only feed for dairy heifers. This was followed by a comparison between anhydrous and aqueous ammonia for treatment of straw and finally a comparison was made between anhydrous and aqueous ammonia as a m e t h o d for treating whole-crop cereals. Laksesvela and Slagsvold (1980)have demonstrated that lambs digest ammonia-treated whole barley better t h a n untreated whole or ground grain. Srivastava and Mowat (1980) have demonstrated t h a t ammonia increases the digestibility of moist whole grains. The objective of the t r e a t m e n t of whole-crop material was to determine if the grain was fully digested and whether the improved value of the straw could give a feed adequate to sustain high levels of production. MATERIALS AND METHODS

Experiment 1 Objective The objective of Experiment 1 was to compare the use of ammoniatreated straw with untreated straw as the sole diet for Friesian heifers.

Animals Eight Friesian heifers approximately 2 years old and weighing on average 440 + 14 kg liveweight were used. They were allocated at random to receive, to appetite, diets of ammonia-treated or urea-treated barley straw. After 7 weeks the treatments were switched and feed intake was recorded for a further 7 weeks. After estimation o f feed intake the heifers were placed in metabolism crates and the faeces collected for 7 days to determine the digestibility of DM, organic matter (OM) and acid detergent fibre (ADF) in the diets (see q)rskov et al., 1980).

Preparation of diets Quantities of 4 t of barley straw containing 9 g N/kg DM were either left uncovered in a stack or sealed between polythene sheets (1000 gauge). Anhydrous ammonia was injected into the sealed stack at the rate of 30 kg/t air-dry straw. The stack was left covered for 2 m o n t h s after which the polythene was removed and the stack aerated for 2 days before the straw was given to the heifers. The untreated straw was sprayed at feeding times with a solution of urea (50 : 50 w/v) to give the same N content (16 g/kg DM) as t h a t in the ammonia-treated straw. Both straws were also sprayed with a solution o f Na2SO4 at 2 g/kg air-dry straw plus trace minerals and vitamins to provide per kg feed: 150 mg ZnSO,-7H20; 80 mg MnSO4" 4H20;

\

249 200 mg MgO; 5 g COSO4" 7H~O; and I mg KIO3. The vitamins,were included to supply 5000 iu vitamin A , 1000 iu vitamin D and 20 iu vitamin E per kg. The Na2SO4 was added to give a calculated 10 : 1 ratio of N to S.

Management The heifers were offered fresh straw twice daffy but straw was always available. The straw w a s not chopped before feeding. The heifers were weighed twice weekly. Average liveweight gain was calculated as the mean o f the first three weighings and the last three weighings of each period.

Experiment 2 Objective The objective of Experiment 2 was to compare the use of anhydrous and aqueous ammonia in efficacy for improvement of nutritive value of straw and to determine the m i n i m u m time necessary for sealing the straw stack.

Preparation of straw samples Eight round bales (1.3-m diameter) of between 150 and 200 kg of barley straw were used. The bales contained on average 830 g DM kg -1 and 6 g N/kg DM. The bales were enclosed in plastic bags for 2 or 8 weeks, but before t h e y were sealed holes were drilled in the centre and around the periphery of the bales and straw samples placed in the holes. The samples were tied with string so t h a t t h e y could be withdrawn without removal of the plastic cover.

Treatments The treatments used were a 2 X 2 × 2 factorial arrangement with two application rates of ammonia to supply 25 or 35 g NH3 per kg, two sources of NH3 (aqueous or anhydrous) and cover removal at either 2 or 8 weeks. The anhydrous ammonia was injected through a metal pipe extending for about 50 cm into the bales, while the aqueous ammonia (35% w/w) was applied through a funnel onto the top of the bale.

Measurement of temperature The temperature in each bale was measured at 2-h intervals during the first 24 h and subsequently once daily for a period of 26 days, using a Jenway Auto Ranger (Scientific Industrial International) digital thermometer. The temperature was recorded at a depth of about 50 cm. The plastic cover was pierced and sealed immediately after withdrawal of the measuring rod.

Determination of the distribution of nitrogen and degradation of dry matter Samples were withdrawn at weekly intervals for N determination. Before

250 analysis t h e y were allowed to stand for 24 h to eliminate volatile NH3. The samples obtained from the periphery were subsequently ground through a 2.5-mm screen in a laboratory hammer mill and incubated in nylon bags in the rumens o f sheep. Four sheep fitted with large rumen cannulae (40 mm) and maintained on dried grass were used for the estimation o f degradability. Except for the first period, during which incubation intervals of 7, 12, 24 and 48 h were used, a sequence of 12, 24, 48 and 72 h was used to ensure an adequate description of t h e a s y m p t o t e of the equation p = a + b ( 1 - e -ct) (Orskov and McDonald, 1979). This equation describes the course of digestion from nylon bags where a is the intercept value, b is the quantity which will degrade in time t, thus (a + b ) is equal to the a s y m p t o t e value of the potential digestibility; c is the rate constant for degradation of the b fraction; and p is the proportion degraded at time t. Each sample was tested with two sheep, and to reduce possible errors due to differences b e t w e e n sheep, t h e y were changed for e a c h weekly sample. The residues in the nylon bags were dried for 48 h at 60°C. Digestibility in vivo At the end of the trial, the four bales which had covers removed at 8 weeks were tested for digestibility in vivo with four 6-month-old sheep, of average liveweight 40 kg. The design used was a 4 X 4 latin square with 18day periods. Faeces were collected during the last 8 days of each period. The straw from each bale was passed through a mesh bale grinder with a 40-mm screen and given ad libitum to the sheep; trace minerals and sodium sulphate were given as in Experiment 1. Experiment 3 Objective The objective of Experiment 3 was to investigate whether ammonia or urea treatment of whole-crop cereals could improve the digestibility of b o t h the straw and the grain. Preliminary Several trials have shown that ammonia treatment of dry grain, unlike NaOH treatment of barley and oats (Orskov et al., 1980), has little or no effect on the digestibility of grain. In a preliminary experiment a sample of barley was prepared and a 35% solution of NH3 was added to give 30 g kg -1 and additional water to give 50 g DM kg -1 . After 4 weeks the grain was given ad libitum to steers and digestibility determined. The mean digestibility of the starch was 81.2% , indicating that adequate digestion of starch might be possible with moist grain. This observation led to an examination of whole-crop cereals treated with anhydrous or aqueous NH3 or urea, since it might be possible to produce a high-quality feed of grain and straw witho u t the need to separate them.

251

Preparation of samples Various whole-crop materials were cut b y a conventional m o w e r and then collected b y a precision chop--forage harvester. The DM content of the whole crop was 455 g kg -1. From analysis of the starch the grain/straw ratio was calculated to be 1 : 1.6 for b o t h barley and oats. All samples were enclosed in large bale bags as used in Experiment 2. Both barley and oats were harvested at a b o u t 7 days before estimated ripeness. The following samples were prepared: (1) whole-crop barley untreated; (2) whole-crop barley treated with anhydrous NH3 at 30 g/kg DM injected into the plastic bag; (3) whole-crop barley treated with aqueous NH3 (35%) to give 30 g NH3/ kg DM; (4) whole-crop barley with a urea solution added at the rate of 60 g/kg DM to give N levels similar to the NH3-treated materials. The urea solution was added to the chopped whole-crop materials in a feed mixer trailer; (5) whole-crop barley mixed with NaOH ( 3 0 % ) to give NaOH at 60 g/kg DM. The NaOH solution was added to the crop material in a feed mixer trailer; (6) whole-crop oats untreated; (7) whole-crop oats with anhydrous NH3 at 30 g/kg DM injected into the bale bag; and (8) whole-crop oats treated with NaOH at 60 g/kg DM. The NaOH was a d d e d while the material was mixed in a feed mixer trailer as for samples 4 a n d 5. After a period of 8 weeks the plastic covers were removed. Samples 1, 5 and 6 deteriorated during storage, and no further observations were made on them.

Microbial examination The three bales which were discarded were not considered safe for feeding, b u t fungi and bacterial counts were made on the others according to Livingstone et al. (1971).

Digestibility measurements Eight 16-month-old Hereford × Friesian steers were used for determination of digestibility of DM and starch. Each material was given ad libitum to four cattle for a period of 18 days, during the last 8 days of which the faeces were collected. Samples of faeces were dried to constant weight at 100 ° C. Starch in feeds and faeces was determined b y the m e t h o d o f Thivend et al. (1965). The results were analysed b y analysis o f variance.

252 RESULTS

Experiment 1 Except for one heifer during Period 2 which lost excessive weight and was removed from the experiment, all heifers appeared healthy during the trial. The feed intakes and liveweight gains and the digestibility coefficients are shown in Table I. Feed intake increased by more t h a n 50% (P < 0.001), daily liveweight gain increased by 770 g (P < 0.001) and the digestibility of DM, OM and ADF increased by about 10 percentage units (P < 0.001). TABLE I Experiment 1 : the effect of ammonia treatment of barley straw on daily intake of dry matter, liveweight gain and digestibility by Friesian heifers Treatment

DM intake (kg day -1)

Ammonia-treated straw 5.88 Untreated straw 3.87 SE of treatment differences 0.31

Liveweight gain (g day -1)

Digestibility (%) DM

OM

ADF

324 -447 78

58.8 49.9 1.8

56.9 47.0 2.0

63.7 52.3 1.4

Experiment 2 Temperature The temperature within each bale increased within 2--4 h after injection of NH3 to about 30°C after which it slowly decreased to ambient temperature at about Day 16. With the anhydrous NH3, during the first day, the temperature in parts of the stack reached as low as - 4 0 ° , owing to heat loss caused b y evaporation of the liquid NH3. Pockets of low temperature were n o t noted after Day 3 and were never recorded in the bales treated with aqueous NH3.

Nitrogen content. The initial N c o n t e n t of the straw was 6 g/kg DM. Estimation of N in central and peripheral samples was carried out during e a c h period. Treatm e n t had no consistent effect on N content. The overall mean ~N content for central samples was 16.1 and for peripheral samples 16.9 g/kg DM. There was no difference in N content between central and peripheral samples due to t r e a t m e n t with aqueous or anhydrous NH3, thus values of central and peripheral samples were combined. The N c o n t e n t o f straw with the aqueous and anhydrous NH3 given at the two rates of application is given in Table II; values with both times of cover removal have been combined. After the first 2 weeks there was no

253 consistent increase or decrease in N c o n t e n t . The N c o n t e n t at the higher rate o f application was a b o u t 2 g kg -1 greater t han for t h e lower rate o f NH3 application. Th e m e t h o d o f NH3 application appears to have no consistent effect on N c o n t e n t . Th e effect o f cover removal at 2 or 8 weeks is given in Table III. The effect o f early cover removal decreased the N c o n t e n t by an average o f a b o u t 2 g/kg straw DM. TABLE n E x p e r i m e n t 2: t h e e f f e c t o f t i m e after application on N c o n t e n t of NH~-treated straw (untreated straw c o n t a i n e d 6 g N/kg DM) F o r m of NH s

Anhydrous Aqu eous Anhydrous Aqueous

TABLE

Rate of application (g NHs]kg straw)

N c o n t e n t (g]kg DM) in w e e k : 1

2

3

4

5

6

8

25 25 35 35

13.0 12.6 14.2 15.2

14.9 15.2 16.6 17.0

15.6 15.1 18.1 16.7

14.9 17.1 16.5 17.3

18.0 17.5 18.8 19.2

18.4 15.3 15.1 16.6

17.3 15.8 17.4 17.7

III

Experiment 2 : the effect of cover removal at 8 or 2 weeks on N content of bales treated w i t h a q u e o u s o r a n h y d r o u s NH3 F o r m o f NH3

Aqueous Aqueous Anhydrous Anhydrous

Cover removal (weeks)

8 2 8 3

N content (g/kg DM) in week: 3

4

5

6

8

18.2 15.0 16.9 15.2

18.0 15.5 17.0 15.1

18.3 17.9 19.5 17.6

16.2 14.1 18.3 16.7

16.2 16.9 18.4 16.6

E f f e c t o f a m m o n i a t r e a t m e n t o n degradation Th e effect on rate o f degradation o f DM is given in Table IV. Here, the fitted value f o r 48-h incubation is given, calculated f r o m t he equation p = a + b ( 1 - e - C t ) , where p is degradability (%) and t is t i m e (h). This value was chosen because it c or r e s ponded m os t closely to the digestibility in vivo. The values obt ai ned for Week 1 were clearly lower than t he remainder. However, after Week 1 t h e r e appeared to be no consistent increases in degradation rate at 48 h nor were t her e differences bet w een these samples when the plastic cover was r e m oved at 2 or 8 weeks. The digestibility in vivo o f DM and OM is given in Table V, t o g e t h e r with th e feed intakes during t he trial. T here was no significant difference in digestibility bet w e e n rates o f application or bet w een m e t h o d s o f N H 3 application.

254 TABLE IV Experiment 2: the effect of time of cover removal (2 o~c 8 weeks), form of ammonia and level of application of ammonia on DM disappearance from nylon bags incubated in the tureen for 48 h Cover removal (week)

F o r m of NH 3

8 8 8 8 2 2 2 2

Anhydrous Aqueous Anhydrous Aqueous Anhydrous Aqueous Anhydrous Aqueous

Rate of application (g/kg straw)

Degradation at 48 h (%) in week: 1

2

3

4

5

6

8

25 25 35 35 25 25 35 35

44.9 39,0 49,4 45.0 40,8 44,6 45,8 41.9

55.0 52.1 51.4 53.5 56.1 45.6 57.3 53.9

52.0 61.3 47.9 53.9 52.3 51.9 45.8 53.6

58.0 64.1 57.8 53.7 55.8 48.9 59.4 55.7

54.8 57.0 58.7 51.0 52.6 .49.5 56.1 54.7

56.0 55.3 49,3 51.6 51.1 53.1 50.4 49.2

49.6 53.8 58.5 50.7 53.8 55.4 50.7 55.0

53.6 -+ 0.6 SE for 2 r 8 weeks Values fitted from the equation p = a + b(1--e-Ct). The mean value for untreated straw after 48-h incubation was 37.3%.

TABLE V E x p e r i m e n t 2 : t h e e f f e c t o f f o r m o f a m m o n i a a n d level o f a p p l i c a t i o n o n i n t a k e a n d digestibility of NH3-treated straw by sheep

Form of NH3

Anhydrous Aqueous Anhydrous Aqueous SE o f d i f f e r e n c e

Quantity injected (g kg -~)

Feed intake (g D M d a y -I )

Feed intake (g D M / k g W ° ' 7 5 / d a y )

25 25 35 35

762 767 754 817 46

50.8 48.3 48,8 52.2 1.4

Digestibility (%) Dry matter

Organic matter

50.5 49.4 51.8 51.8 1.4

51.6 50.5 52.9 52.4 1.4

Experiment 3 Data on aspects of preservation are given in Table VI. The bacteria were mainly gram-positive cocci and gram-negative thin rods. T h e s e samples were well preserved and their counts compare with values of about 109 g-1 for bacteria and 108 g-1 for fungal propagules in deteriorated moist grain (~ rskov et al., 1979). The N content of the different samples is also given. Since control samples of oats and barley deteriorated during storage, the increase in N c o n t e n t cannot be clearly assessed although for oats the NaOHtreated sample is likely to be similar to the untreated control. In Table VII the effect of treatment on digestibility of DM and starch is given. Starch from the urea-treated whole-crop barley was less digestible (P < 0.05) than t h a t from the NH3 treatments. However, feed intake was lower (P < 0.01) with the NH3- than with urea-treated whole-crop barley or NaOH-treated whole-crop oats.

255 TABLE VI Experiment 3: the effect o f different methods o f treating whole-crop cereals on counts of bacteria and fungal propagules Treatment

Bacterial count/ g fresh material

Fungal propagules/ g fresh material

N content (g/kg dry matter)

Whole-crop barley with urea Whole-crop barley with aqueous NH 3 Whole-crop barley with anhydrous NH 3 Whole-crop oats with NaOH Whole-crop oats with anhydrous NH3

2.6 X 107 2.1 X 107

2.1 x 10 ~ 6.5 x 104

28 30

2.4 x 107

1.6 x l 0 s

30

6.8 x 107 1.2 x 106

1,5 x 104 9.0 X 104

21 33

TABLE VII Experiment 3: the effect o f different treatments of whole-crop cereals on feed intake and digestibility of DM and starch b y steers (means _+ SEM) Treatment

Whole-crop barley with urea Whole-crop barley with aqueous NH 3 Whole-crop barley with anhydrous NH 3 Whole-crop oats with NaOH Whole-crop oats with anhydrous NH~

Feed intake (kg DM day -1)

Digestibility (%) Dry matter

Starch

5.01 + 0,40

54.2 +_ 3.8

78.0 -+ 4.1

3.11 -+ 0.57

56.9 + 3.8

88.0 -+ 4.7

2.79 -+ 0.81 7.61 -+ 0.47

58.8 _+ 2.9 64.1 _+4.0

92.8 -+ 2.3 87.3 -+ 4.5

3.91 -+ 1.90

63.6 _+ 3.0

95.4 _+ 4.5

DISCUSSION T h e r e s u l t s o f E x p e r i m e n t 1 c l e a r l y d e m o n s t r a t e a n i m p r o v e m e n t in t h e v a l u e o f s t r a w as a r e s u l t o f N H 3 t r e a t m e n t . T h e y a l s o d e m o n s t r a t e t h a t u r e a a d d e d a t f e e d i n g t i m e s d i d n o t h a v e a s i m i l a r e f f e c t . F r o m t h e i n c r e a s e in digestibility, the NH3 treatment increased the nutritive value by about 20% W h e n t h e s t r a w w a s g i v e n a d l i b i t u m t h e i n c r e a s e in d i g e s t i b i l i t y e n a b l e d the heifers to increase their DM intake by 52% and their intake of digestible DM by 80%, and changed a daffy liveweight loss of 440 g to a liveweight gain o f 3 3 0 g. T h e s i m i l a r i t y o f r e s u l t s w i t h a q u e o u s a n d a n h y d r o u s NH3 w a s n o t u n e x p e c t e d as o t h e r a u t h o r s ( S u n d s t ¢ l e t a l . , 1 9 7 9 ) h a v e n o t e d s i m i l a r r e s u l t s w i t h l a b o r a t o r y e x p e r i m e n t s . Sundstqtl e t a l . ( 1 9 7 9 ) s u g g e s t e d t h a t i f t h e

256 straw had a moisture content of less than 120 g kg -1 the use of aqueous NH3 may be preferred. It is quite possible that with higher moisture contents anhydrous NH3 may become distributed more evenly throughout the bale than would aqueous NH3 as we have generally noticed a poor distribution of NH3 in very moist materials (E.R. Orskov and G.W. Reid, unpublished results). The lack of difference in degradation at 48 h between stacks uncovered after 2 or 8 weeks suggests that even at temperatures normally prevailing in Britain there would be no benefit from treating straw bales for longer than 2--3 weeks. The average external temperature during the period of treatment was about 4 ° C, the experiment being carried out during the m o n t h of January. The effect of NH3 treatment on whole crops requires further study as to possible reasons w h y the food intakes were low. The intakes were lower than those achieved b y Greenhalgh and Pirie (1979) and Petchey et al. (1980) using NaOH treatment of whole cereal crops and, indeed, the NaOH-treated oats gave better intakes than the corresponding ammonia treatments. The use of urea as a m e t h o d of applying NH3 relies on its immediate and extensive hydrolysis to NH3. The optimal temperature for the hydrolysis of urea b y the urease enzyme is about 60 °, and hydrolysis is slower at temperatures lower than 2 0 ° (l~.J. Wallace, personal communication, 1982). Urea is quite effective as a source of ammonia in tropical regions (SaaduUah et al., 1981). Compared with anhydrous or aqueous NH3, urea's safer handling properties make it an attractive alternative in the tropics. On the other hand the intake of whole-crop barley treated with urea was excellent and also the preservation of the whole-crop material with urea was excellent; this was in agreement with previous findings concerning the preservation of moist cereal grains (©rskov et al., 1979). Any practical interest in the treatment of whole crops with NH3 must in the long term await trials to demonstrate whether intakes can be as high as or higher than for treatments involving the combination of treated straw with processed cereals. These effects are n o w under investigation and appear to be related to the uneven distribution of ammonia when applied to moist materials. ACKNOWLEDGEMENTS The authors wish to thank members of the Duthie Experimental Farm, particularly Mr. S.W. Beattie for helpful co-operation, and Dr. D. Flemming of the Commonwealth Agricultural Bureau for editing the manuscript. We also wish to thank Dr. C.S. Stewart for microbial examination of the wholecrop samples.

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