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Effects of lucerne supplementation and defaunation on feed intake, digestibility, N retention and productivity of sheep fed straw based diets
Animal Feed Science and Technology, 45 (1994) 119-129
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Effects of lucerne supplementation and defaunation on feed intake, digestibility, N retention and productivity of sheep fed straw based diets S.H. Bird*, B. Romulo ~, R.A. Leng Department of Biochemistry, Microbiologyand Nutrition, Universityof New England, Armidale, N.S. W., Australia (Received 8 July 1993; accepted 8 July 1993 )
Abstract
The effects of a lucerne supplement and defaunation on feed intake, digestibility and N retention were studied in cannulated wethers given either an ammoniated wheat straw or an untreated wheal straw diet. Supplementation of the wheat straw diets with lucerne chaff ( 150 g day- ~) significantly increased total dry matter (DM) intake from 520 to 715 g day- ~ (untreated wheat straw) and from 615 to 815 g day-l (ammoniated wheat straw ). Intake of wheat straw was not significantly altered by the lucerne supplement. Defaunation of the wethers had no significant effect on feed intake. The rumen digestibility of untreated straw and ammoniated straw were measured using the nylon bag technique. Lucerne supplementation significantly increased the digestibility (% DM disappearance after 24 h incubation) of untreated wheat straw from 26 to 31% and ammoniated wheat straw from 39 to 43%. When defaunation was combined with lucerne supplementation the digestibility of untreated wheat straw increased from 26 to 33% and ammoniated wheat straw increased from 39 to 50%, indicating that the effects of these two treatments were additive. Lucerne supplementation significantly increased N retention in wethers fed either the untreated wheat straw diet or the ammoniated wheat straw diet and defaunation significantly increased N retention in the animals fed the wheat straw diet. In a second study, 64 crossbred lambs (32 faunated and 32 defaunated) were offered one of four dietary treatments. The dietary treatments were either wheat straw or ammoniated wheat straw supplemented with two levels of lucerne (0 and 150 g day- ~). Daily feed intake, liveweight gain and wool production were measured over a 70 day period. Daily liveweight gain was significantly increased by lucerne supplementation (P< 0.01 ) and ammoniation of straw (P < 0.01 ) while the effects of defaunation were not statistically significant. Wool production was significantly increased by defaunation (P < 0.01 ), lucerne supplementation (P < 0.01 ) and ammoniation of straw (P< 0.01 ). A combination of these three treatments increased wool production by 2.51 g clean wool day- 1. *Corresponding author. ~Present address: 12025 Rockridge Drive, Fontana, CA, USA.
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Introduction
Cereal straw, one of the most abundantly produced agro-industrial byproducts (Jackson, 1977), is a major source of feed for livestock in the tropics and subtropics. However, straw can only support low animal productivity when used as a basal diet since it is deficient in available N and has a low digestibility (see Preston and Leng, 1986 ). Approaches which have been used to increase straw utilisation by ruminants include: straw treatment, dietary supplements and manipulation of the rumen ecosystem. Methods of straw treatment including physical, chemical and biological treatments have been demonstrated to increase voluntary feed intake and/or digestibility (see Jackson, 1977; Owen, 1978; Ibrahim, 1983; Sundst~l and Coxworth, 1984). There is general agreement, however, that treatment of cereal straw with ammonia (ammoniation) is the most effective treatment because it enhances both the digestibility and the N content of the straw. Supplementation with leguminous forages has been shown to improve both DM digestibility and intake of high fibre diets and to enhance ruminant production (see Alvarez et al., 1978; Priego et al., 1979; Herrera et al., 1980; Dixon et al., 1981; Moran et al., 1983; Faulkner et al., 1985; Rodriguez et al., 1985). The beneficial effects of these supplements (on straw utilisation by ruminants) have been attributed to the provision of readily fermentable cell wall carbohydrates, N, vitamins, minerals and possibly other essential nutrients for the cellulolytic bacteria in the rumen (Juul-Nielsen, 1981; Ndlovu and Buchanan-Smith, 1985 ). Manipulation of rumen function through the permanent removal of protozoa (defaunation) appears to have considerable potential for improving ruminant productivity. Defaunation has been shown to increase liveweight gain and wool production of lambs (Bird et al., 1979). These beneficial responses have been attributed to an increased availability of protein (microbial and dietary ) in the rumen (see Bird and Leng, 1985 ). These studies were designed to examine the effects of lucerne supplementation and defaunation on intake, digestibility, N retention and productivity of sheep fed either an ammoniated or an untreated straw diet. Materials and methods
Experiments 1 and 2 Twenty-four mature Merino × Border Leicester wethers fitted with permanent rumen fistula (average 36 kg body weight) were randomly allocated to four treatment groups in a 2 × 2 factorial design. The basal diets used in Experiments 1 and 2 were wheat straw (800 g day- ~) and ammoniated wheat straw (800 g day -l ) respectively. The two dietary treatments were lucerne chaff supplementation at two levels (0 and 150 g day-~ ) and the two fauna
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states were faunated and defaunated. All diets were supplemented with urea (14 g day -l ) and minerals (42 g day -1 ) (see Table 1 for composition of mineral mix). Experimental periods lasted 90 days with a transition period of 14 days between experiments.
Experiment 3 Sixty-four mixed sex crossbred lambs (Border Leicester/Merino × Dorset horn) with a mean body weight of 32 kg were allocated to eight treatment groups (diets in a 2 × 2 × 2 factorial design. The diets used were either wheat straw (offered ad libitum) or ammoniated wheat straw (offered ad libitum) supplemented with two levels of lucerne (0 and 150 g day -1 ) and the two fauna states were faunated and defaunated. The untreated straw diet was supplemented with urea ( 14 g day- l ) and all diets were supplemented with 42 g day-1 minerals (see Table 1 ). Daily feed intake, wool production and body weight change were recorded over a 70 day period. In all experiments, animals were offered feed at 09:00 h and the lucerne supplement was placed on top of the straw which was chopped to a length of approximately 3 cm. Thermo-ammoniation was used to treat the straw (see Perdok and Leng, 1987). Ammoniation increased the N content of straw by 36% and decreased the neutral detergent fibre (NDF) content by 6%, while acid detergent fibre (ADF) remained relatively unchanged. The chemical composition of the dietary ingredients is given in Table 1. Animals were defaunated with sodium lauryl diethoxy sulphate (alkanate 3SL3, ICI, Melbourne, Vic. ) administered either via the rumen fistula or orally using a stomach tube (see Bird and Leng, 1984). Each animal was dosed on 3 consecutive days with 120 ml of alkanate solution ( 10% w/v ). Feed was not provided during this period. Animals were sampled regularly for 4 weeks Table 1 Chemical composition of dietary components Composition
Wheat straw
Ammoniated straw
Lucerne
Mineral mixture
Dry matter (g kg -1 ) Feed composition (g kg- 1 DM ) Organic matter Neutral detergent fibre Acid detergent fibre Hemicellulose Soluble protein N in buffer
930
910
890
980
880 730 560 180
900 690 560 130
920 370 31 60
-
-
-
310
-
1Composition of the mineral (g kg -1 ): Ca(H2PO4)2, 125; Na2SO4, 62.5; NaC1, 62.5; premix (Pfizer 422), 62.5; dried molasses, 437.5; urea, 250.
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following the administration of alkanate to determine whether the defaunation treatment had been successful. Additional rumen fluid samples were collected from the defaunated animals to ensure the ciliate-free state was maintained during the experimental periods. Refaunation of the control animals was achieved by drenching the defaunated animals with 50 ml of rumen fluid on 3 consecutive days. The refaunated sheep were allowed 2 weeks to re-establish their protozoal population before measurements commenced. The donor sheep were fed a straw-based diet.
Measurements and analytical methods Daily dry matter ( D M ) intake was estimated from the difference between DM offered and that refused. The in sacco DM digestibility was measured from the disappearance of DM in dacron bags suspended in the rumen of sheep (see Orskov et al., 1980; Setala, 1983). Samples (1 g) of straw and lucerne (ground to 2 ram) and 2-3 g samples of cotton wool cellulose were used for the in sacco studies. The in vivo DM digestibility and N retention were estimated by the total collection method over a period of 7 days. Liveweight changes were calculated from the differences between the means of three consecutive final and initial weighings measured before feeding time. Wool growth was estimated using the dye banding procedures of Chapman and Wheeler (1963). Methods for proximate analyses and total N followed the Association of Official Analytical Chemists (1980) and N D F and ADF determinations followed the procedures of Van Soest ( 1963 ). Protozoa were monitored according to the procedures of Warner (1962). Results
Experiments I and 2 The in sacco digestibilities (24 h) of wheat straw (Experiment 1 ) and ammoniated wheat straw (Experiment 2 ) in faunated and defaunated sheep are presented in Tables 2 and 3. Defaunation significantly increased the in sacco digestibility of untreated wheat straw ( P < 0.05) and ammoniated wheat straw ( P < 0.01 ). Lucerne supplementation significantly increased the in sacco digestibility of untreated wheat straw (P < 0.001 ) and ammoniated wheat straw ( P < 0.01 ). Lucerne supplementation significantly increased N retention in wethers fed either the untreated wheat straw ( P < 0.001 ) or ammoniated wheat straw ( P < 0.05 ) and defaunation significantly increased N retention in animals fed untreated wheat straw ( P < 0.01 ). Supplementation of the basal diet with lucerne chaff significantly increased total DM intake from 520 to 715 g day -~ (Experiment 1 ) and from 615 to 815 g day- 1 (Experiment 2 ). The intake of wheat straw was not significantly
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Table 2 Mean total DM ( T D M I ) and straw DM (SDMI) intake of and the in sacco (24 h) digestibility (%) for wheat straw (WS), cottonwool cellulose (CW) and lucerne (L), the in vivo DM digestibility of the diet (%) and N retention in faunated ( + P ) and defaunated ( - P ) sheep fed straw-based diet with ( + L) or without ( - L) lucerne supplement Protozoa (P)
Lucerne (L)
TDMI (gday -1 )
SDMI (gday -~ )
DM digestibility (%) In sacco
+P +P -P -P SEM
+L -L +L -L
N retention (gday -~ ) In vivo
WS
CW
L
715 520 750 610 36.9
525 465 560 555 36.9
31 26 33 28 1.1
52 b 44 c 57 a 52 b 2.7
73 69 75 73 1.1
45 37 43 45 3.2
4.6 b 2.5 c 6.4 a 2.8 c 0.34
NS ** NS
NS NS NS
* *** NS
* * *
** ** NS
NS NS NS*
** ***
Effect
P L P× L
***P< 0.001; **P< 0.01; *P< 0.05; NS, not significant.
Table 3 Mean total DM ( T D M I ) and straw DM (SDMI) intake of and the in sacco (24 h) digestibility (%) for ammoniated wheat straw (AWS), cottonwool cellulose (CW) and lucerne (L), the in vivo DM digestibility of the diet (%) and N retention in faunated ( + P ) and defaunated ( - P ) sheep fed ammonia treated straw based diet with ( + L) or without ( - L) lucerne supplement Protozoa (P)
Lucerne (L)
TDMI (gday -1 )
SDMI (gday -~ )
DMdigestibility (%) In sacco
+P +P -P -P SEM
+L -L +L -L
Nretention (gday -~ ) In vivo
AWS
CW
L
815 615 800 700 39.3
630 560 615 625 41.2
44 39 50 43 1.6
42 36 53 44 2.8
73 75 74 77 I.I
53 46 56 51 1.3
7.7 3.6 7.6 5.9 0.58
NS *** NS
NS NS NS
** ** NS
** * NS
NS * NS
* NS NS
NS * NS
Effect
P L P×L
***P<0.001; **P<0.01; *P<0.05; NS, not significant.
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Table 4 Mean total D M ( T D M I ) and straw DM (SDMI) intake, mean daily weight change ( D W C ) and mean daily clean wool growth ( C W G ) of faunated ( + P ) and defaunated ( - P ) lambs on either an untreated ( U S W ) basal diet or a wheat straw basal diet with ( + L ) or without ( - L ) lucerne supplement Protozoa
Straw
Lucerne
TDMI (gday -t )
SDMI (gday -1 )
DWC (gday -1 )
CWG (gday -1 )
+P +P +P +P - P -P -P -P SEM
AWS AWS UWS UWS AWS AWS UWS UWS
+L -L +L -L +L -L +L -L
825 755 535 455 840 675 710 510 26.7
650 710 350 390 665 635 520 455 27.3
58 41 -20 -69 72 14 - 1 -62 9.6
3.09 2.50 2.23 1.64 4.15 3.15 3.15 2.27 0.219
Effect P
*
*
NS
***
S
***
***
***
***
L P× S P×L S× L PXS×L
*** ** * NS NS
NS ** * NS NS
*** NS NS NS NS
*** NS NS NS NS
*P< 0.05; **P< 0.01; ***P< 0.001; NS, not significant.
altered by the lucerne supplement. Defaunation of the wethers had no significant effect on feed intake.
Experiment 3 Daily liveweight gain was significantly increased by lucerne supplementation ( P < 0 . 0 1 ) and ammoniation of straw ( P < 0 . 0 1 ) while the effects ofdefaunation were not statistically significant (Table 4). Wool production was significantly increased by defaunation (P<0.01), lucerne supplementation (P< 0.01 ) and ammoniation of straw ( P < 0.01 ). A combination of these three treatments increased wool production from 1.6 to 4.15 g clean wool day- 1. Discussion Cereal straws are characterised by their high content of lignocellulose and low level of nitrogen. Consequently, these materials are poorly digested and can only support a low level of production when they are used as a basal diet for ruminants. In these studies, thermo-ammoniation increased the nitrogen content of the straw from 0.5 to 1.4% and the in sacco DM digestibility of the straw from 26 to 39% (24 h incubation). These values fall within the range
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of values quoted in the literature. Sundstol and Coxsworth (1984) suggest that if the treatment of straw is done correctly, the increase in organic matter (OM) digestibility and N content is 10-12 and 0.8-1.0 percentage units respectively. While the reasons for the change in digestibility have not been clearly defined, it is apparent that both chemical and physical changes in the straw and a larger, more active pool of microorganisms (supported by the additional nitrogen) are contributing factors. With the use of a scanning electron microscope, Harbers et al. (1982) noted structural differences between untreated and ammoniated straw and observed that rumen bacteria and fungi readily invaded tissues damaged by the ammoniation process. In contrast, Streeter and Horn (1982) have suggested that solubilisation of hemicellulose was responsible for most of the increase in DM digestibility associated with ammoniation treatment. The change in the digestibility of straw was probably the major factor contributing to the increase in straw DM intake of the wethers which increased from 465 g day -~ (untreated straw) to 560 g day -~ (ammoniated wheat straw). The higher nitrogen retention in the wethers receiving ammoniated wheat straw was due to a higher intake of N rather than an increase in the efficiency of utilisation. A similar response was observed in the growth study. Ammoniation of the straw increased straw DM intake of the faunated lambs from 390 to 710 g day- ~and the straw DM intake of the defaunated lambs increased from 455 to 635 g day -~ as a result of ammoniation. It has been suggested by Orpin and Bountiff (1978 ) that forage supplements containing significant quantities of soluble nutrients may influence the rate of fibre digestion in the rumen by stimulating colonisation of plant material by rumen microorganisms. In this study, the in sacco digestibility of both untreated and ammoniated straw were significantly increased by the inclusion of 150 g day- ~lucerne in the ration. It is possible that this increase in digestibility was partly due to additional ammonia generated in the rumen from the degradation of the soluble N component of the lucerne supplement. However, in a similar study in which a supplement of 250 g day-~ lucerne was accompanied by an increase in the in sacco digestibility of rice straw, McMeniman et al. (1988 ) concluded that this response could not be attributed to either ammonia or sulphide concentration in the rumen. The lucerne supplement would also have increased the availability of amino acids and readily fermentable carbohydrate which could have enhanced the proliferation of ceUulolytic microbes (Juul-Nielsen, 1981 ), although it has been suggested by Preston and Leng (1986) that the lysis of microbial cells in the rumen should provide an adequate supply of amino acids. In a number of studies where the dietary content of fermentable N was adequate no requirements for soluble proteins have been demonstrated (see Kempton et al., 1979). Despite the increase in the digestibility of wheat straw, voluntary intake of
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straw was not significantly higher for the animals receiving the lucerne supplement. However, both total DM intake and N retention were higher in the wethers receiving the lucerne supplement and in the growth study, body weight gain and wool production were improved by supplementation. The higher N retention in the animals receiving the lucerne supplement was due to higher N intake and a more efficient utilisation of N by the wethers (Table 2 ). The increased efficiency of N utilisation was probably due to a greater yield of microbial protein synthesised in the rumen. The reported changes in rumen function associated with defaunation suggest that the activity of the protozoa results in a depression of the ratio of protein to energy in the end products of rumen fermentation. It is now generally accepted that in the absence of ciliates the efficiency of microbial growth is enhanced and more microbial and dietary protein flows from the rumen (see Bird and Leng, 1985; Veira, 1986 ). In addition, it is often reported that defaunation depresses digestion of feed material in the rumen, although the effects are not consistent and there is no consensus of opinion on the reasons for this change. At one extreme, Coleman ( 1988 ) states that "ciliate protozoa are quantitatively important in the digestion of cellulose in the rumen", while at the other extreme, Hungate (1975) claims that the amount of cellulose digested by the protozoa is small in relation to the bacteria. In contrast to previous work (for a review see Bird and Leng, 1985; Veira, 1986 ) these studies clearly show that defaunation was associated with an increase in the in sacco digestibility of both treated and untreated straw and that compared with faunated animals, the intake of straw tended to be higher in the defaunated animals (wethers and lambs). These results suggest that the digestive activity of the protozoa which is lost upon defaunation has been more than compensated for by an increase in the digestive capacity of the remaining population of bacteria and fungi. This effect could be due to the replacing of an organism with low cellulolytic activity (the protozoa) with organisms of higher cellulolytic activity (bacteria and fungi) or it could be due to the elimination of the predatory activity of the protozoa. The colonisation of ingested plant material requires the transfer of organisms between feed residues and newly ingested food via the rumen fluid. A population of protozoa may reduce this transient population and thereby reduce the rate of colonisation of new feed particles in the rumen. In these studies, defaunated animals were given at least 4 weeks to recover from the defaunation treatment before measurement of rumen function was commenced. The work of Orpin and Letcher (1984) clearly demonstrates that, following the defaunation treatment, the period of time allowed for the rumen microorganisms to recover may be critical in determining the effect of defaunation on rumen function. In the studies of Orpin and Letcher, between 3 and 4 weeks were required for the number of viable bacteria to reach a stable plateau in the defaunated rumen and the organic matter digestibility in
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the rumen of these animals showed a similar trend. In the past, measurements have often been made in defaunated animals within 2-3 weeks of the defaunation treatment and in light of the results of Orpin and I_etcher (1984) it must be questionable whether some of the reported results truly represent the effect of the absence of protozoa on rumen function. Defaunation resulted in a significant improvement in N retention in the wethers and higher wool production in the lambs. Both these responses were achieved without a significant change in N intake indicating that compared with faunated animals the efficiency of N utilisation in the defaunated animals was significantly higher. The improvement in wool production from the defaunated lambs in these studies was in accordance with the earlier defaunation studies of Bird et al. (1979) and Bird and Leng (1984) and was probably due to an increase in the availability of microbial protein from the ciliate-free rumen (see Veira et al., 1984). Surprisingly, in this study defaunation had no significant effect on body weight gain of the defaunated lambs. The defaunated lambs receiving the ammoniated wheat straw diet had a lower growth rate than the faunated lambs but this trend was reversed on the other three diets. The negative response on the treated straw diet was not compatible with the rumen function studies, which indicated that defaunation was associated with an increase in the in sacco digestibility of straw, a slightly higher intake of straw and higher N retention. Further work is required to establish the relationship between body weight gain and defaunation on ammoniated straw diets.
Acknowledgements The authors would like to acknowledge the assistance of R. Woodgate for the maintenance of experimental animals and the collection of experimental data. These studies were supported by funds from the Australian Centre for International Agricultural Research.
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cattle on a diet based on sisal pulp II. Supplementation with Ramon (Brosimumalicastrum) forage and rice polishings. Trop. Anim. Prod., 4: 287-293. Rodriguez, A., Riley, J.A. and Thorpe, W., 1985. Animal performance and physical disturbances in sheep fed diets based on ensiled sisal pulp (Agravefourcroydes). I. The effect of supplementation with protein, forage and minerals. Trop. Anim. Prod., 40:32-38. Setala, J., 1983. The nylon bag technique in the determination of ruminal feed protein degradation. Agric. Soc. Finland, 55:1-7. Streeter, C.L. and Horn, G.W., 1982. Effect of treatment of wheat straw with ammonia and peracetic acid on digestibility in vitro and cell wall composition. Anim. Feed Sci. Technol., 7:325-329. Sundst~l, F. and Coxworth, E.M., 1984. Ammonia treatment. In: F. Sundstol and E.M. Owens (Editors), Straw and Other Fibrous By-products as Feed. Elsevier, Amsterdam, pp. 196249. Van Soest, P.J., 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. J. Assoc. Off. Agric. Chem., 46:829-835. Veira, D.M., 1986. The role of ciliate protozoa in nutrition of the ruminant. J. Anim. Sci., 63:1547-1560. Veira, D.M., Ivan, M. and Jui, Y., 1984. The effect of ciliate protozoa on the flow of amino acids from the stomach of sheep. Can. J. Anim. Sci., 64 (Suppl.): 22-23. Warner, A.G.I., 1962. Enumeration of rumen micro-organisms. J. Gen. Microbiol., 28:119128.
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Effects of lucerne supplementation and defaunation on feed intake, digestibility, N retention and productivity of sheep fed straw based diets S.H. Bird*, B. Romulo ~, R.A. Leng Department of Biochemistry, Microbiologyand Nutrition, Universityof New England, Armidale, N.S. W., Australia (Received 8 July 1993; accepted 8 July 1993 )
Abstract
The effects of a lucerne supplement and defaunation on feed intake, digestibility and N retention were studied in cannulated wethers given either an ammoniated wheat straw or an untreated wheal straw diet. Supplementation of the wheat straw diets with lucerne chaff ( 150 g day- ~) significantly increased total dry matter (DM) intake from 520 to 715 g day- ~ (untreated wheat straw) and from 615 to 815 g day-l (ammoniated wheat straw ). Intake of wheat straw was not significantly altered by the lucerne supplement. Defaunation of the wethers had no significant effect on feed intake. The rumen digestibility of untreated straw and ammoniated straw were measured using the nylon bag technique. Lucerne supplementation significantly increased the digestibility (% DM disappearance after 24 h incubation) of untreated wheat straw from 26 to 31% and ammoniated wheat straw from 39 to 43%. When defaunation was combined with lucerne supplementation the digestibility of untreated wheat straw increased from 26 to 33% and ammoniated wheat straw increased from 39 to 50%, indicating that the effects of these two treatments were additive. Lucerne supplementation significantly increased N retention in wethers fed either the untreated wheat straw diet or the ammoniated wheat straw diet and defaunation significantly increased N retention in the animals fed the wheat straw diet. In a second study, 64 crossbred lambs (32 faunated and 32 defaunated) were offered one of four dietary treatments. The dietary treatments were either wheat straw or ammoniated wheat straw supplemented with two levels of lucerne (0 and 150 g day- ~). Daily feed intake, liveweight gain and wool production were measured over a 70 day period. Daily liveweight gain was significantly increased by lucerne supplementation (P< 0.01 ) and ammoniation of straw (P < 0.01 ) while the effects of defaunation were not statistically significant. Wool production was significantly increased by defaunation (P < 0.01 ), lucerne supplementation (P < 0.01 ) and ammoniation of straw (P< 0.01 ). A combination of these three treatments increased wool production by 2.51 g clean wool day- 1. *Corresponding author. ~Present address: 12025 Rockridge Drive, Fontana, CA, USA.
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Introduction
Cereal straw, one of the most abundantly produced agro-industrial byproducts (Jackson, 1977), is a major source of feed for livestock in the tropics and subtropics. However, straw can only support low animal productivity when used as a basal diet since it is deficient in available N and has a low digestibility (see Preston and Leng, 1986 ). Approaches which have been used to increase straw utilisation by ruminants include: straw treatment, dietary supplements and manipulation of the rumen ecosystem. Methods of straw treatment including physical, chemical and biological treatments have been demonstrated to increase voluntary feed intake and/or digestibility (see Jackson, 1977; Owen, 1978; Ibrahim, 1983; Sundst~l and Coxworth, 1984). There is general agreement, however, that treatment of cereal straw with ammonia (ammoniation) is the most effective treatment because it enhances both the digestibility and the N content of the straw. Supplementation with leguminous forages has been shown to improve both DM digestibility and intake of high fibre diets and to enhance ruminant production (see Alvarez et al., 1978; Priego et al., 1979; Herrera et al., 1980; Dixon et al., 1981; Moran et al., 1983; Faulkner et al., 1985; Rodriguez et al., 1985). The beneficial effects of these supplements (on straw utilisation by ruminants) have been attributed to the provision of readily fermentable cell wall carbohydrates, N, vitamins, minerals and possibly other essential nutrients for the cellulolytic bacteria in the rumen (Juul-Nielsen, 1981; Ndlovu and Buchanan-Smith, 1985 ). Manipulation of rumen function through the permanent removal of protozoa (defaunation) appears to have considerable potential for improving ruminant productivity. Defaunation has been shown to increase liveweight gain and wool production of lambs (Bird et al., 1979). These beneficial responses have been attributed to an increased availability of protein (microbial and dietary ) in the rumen (see Bird and Leng, 1985 ). These studies were designed to examine the effects of lucerne supplementation and defaunation on intake, digestibility, N retention and productivity of sheep fed either an ammoniated or an untreated straw diet. Materials and methods
Experiments 1 and 2 Twenty-four mature Merino × Border Leicester wethers fitted with permanent rumen fistula (average 36 kg body weight) were randomly allocated to four treatment groups in a 2 × 2 factorial design. The basal diets used in Experiments 1 and 2 were wheat straw (800 g day- ~) and ammoniated wheat straw (800 g day -l ) respectively. The two dietary treatments were lucerne chaff supplementation at two levels (0 and 150 g day-~ ) and the two fauna
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states were faunated and defaunated. All diets were supplemented with urea (14 g day -l ) and minerals (42 g day -1 ) (see Table 1 for composition of mineral mix). Experimental periods lasted 90 days with a transition period of 14 days between experiments.
Experiment 3 Sixty-four mixed sex crossbred lambs (Border Leicester/Merino × Dorset horn) with a mean body weight of 32 kg were allocated to eight treatment groups (diets in a 2 × 2 × 2 factorial design. The diets used were either wheat straw (offered ad libitum) or ammoniated wheat straw (offered ad libitum) supplemented with two levels of lucerne (0 and 150 g day -1 ) and the two fauna states were faunated and defaunated. The untreated straw diet was supplemented with urea ( 14 g day- l ) and all diets were supplemented with 42 g day-1 minerals (see Table 1 ). Daily feed intake, wool production and body weight change were recorded over a 70 day period. In all experiments, animals were offered feed at 09:00 h and the lucerne supplement was placed on top of the straw which was chopped to a length of approximately 3 cm. Thermo-ammoniation was used to treat the straw (see Perdok and Leng, 1987). Ammoniation increased the N content of straw by 36% and decreased the neutral detergent fibre (NDF) content by 6%, while acid detergent fibre (ADF) remained relatively unchanged. The chemical composition of the dietary ingredients is given in Table 1. Animals were defaunated with sodium lauryl diethoxy sulphate (alkanate 3SL3, ICI, Melbourne, Vic. ) administered either via the rumen fistula or orally using a stomach tube (see Bird and Leng, 1984). Each animal was dosed on 3 consecutive days with 120 ml of alkanate solution ( 10% w/v ). Feed was not provided during this period. Animals were sampled regularly for 4 weeks Table 1 Chemical composition of dietary components Composition
Wheat straw
Ammoniated straw
Lucerne
Mineral mixture
Dry matter (g kg -1 ) Feed composition (g kg- 1 DM ) Organic matter Neutral detergent fibre Acid detergent fibre Hemicellulose Soluble protein N in buffer
930
910
890
980
880 730 560 180
900 690 560 130
920 370 31 60
-
-
-
310
-
1Composition of the mineral (g kg -1 ): Ca(H2PO4)2, 125; Na2SO4, 62.5; NaC1, 62.5; premix (Pfizer 422), 62.5; dried molasses, 437.5; urea, 250.
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following the administration of alkanate to determine whether the defaunation treatment had been successful. Additional rumen fluid samples were collected from the defaunated animals to ensure the ciliate-free state was maintained during the experimental periods. Refaunation of the control animals was achieved by drenching the defaunated animals with 50 ml of rumen fluid on 3 consecutive days. The refaunated sheep were allowed 2 weeks to re-establish their protozoal population before measurements commenced. The donor sheep were fed a straw-based diet.
Measurements and analytical methods Daily dry matter ( D M ) intake was estimated from the difference between DM offered and that refused. The in sacco DM digestibility was measured from the disappearance of DM in dacron bags suspended in the rumen of sheep (see Orskov et al., 1980; Setala, 1983). Samples (1 g) of straw and lucerne (ground to 2 ram) and 2-3 g samples of cotton wool cellulose were used for the in sacco studies. The in vivo DM digestibility and N retention were estimated by the total collection method over a period of 7 days. Liveweight changes were calculated from the differences between the means of three consecutive final and initial weighings measured before feeding time. Wool growth was estimated using the dye banding procedures of Chapman and Wheeler (1963). Methods for proximate analyses and total N followed the Association of Official Analytical Chemists (1980) and N D F and ADF determinations followed the procedures of Van Soest ( 1963 ). Protozoa were monitored according to the procedures of Warner (1962). Results
Experiments I and 2 The in sacco digestibilities (24 h) of wheat straw (Experiment 1 ) and ammoniated wheat straw (Experiment 2 ) in faunated and defaunated sheep are presented in Tables 2 and 3. Defaunation significantly increased the in sacco digestibility of untreated wheat straw ( P < 0.05) and ammoniated wheat straw ( P < 0.01 ). Lucerne supplementation significantly increased the in sacco digestibility of untreated wheat straw (P < 0.001 ) and ammoniated wheat straw ( P < 0.01 ). Lucerne supplementation significantly increased N retention in wethers fed either the untreated wheat straw ( P < 0.001 ) or ammoniated wheat straw ( P < 0.05 ) and defaunation significantly increased N retention in animals fed untreated wheat straw ( P < 0.01 ). Supplementation of the basal diet with lucerne chaff significantly increased total DM intake from 520 to 715 g day -~ (Experiment 1 ) and from 615 to 815 g day- 1 (Experiment 2 ). The intake of wheat straw was not significantly
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Table 2 Mean total DM ( T D M I ) and straw DM (SDMI) intake of and the in sacco (24 h) digestibility (%) for wheat straw (WS), cottonwool cellulose (CW) and lucerne (L), the in vivo DM digestibility of the diet (%) and N retention in faunated ( + P ) and defaunated ( - P ) sheep fed straw-based diet with ( + L) or without ( - L) lucerne supplement Protozoa (P)
Lucerne (L)
TDMI (gday -1 )
SDMI (gday -~ )
DM digestibility (%) In sacco
+P +P -P -P SEM
+L -L +L -L
N retention (gday -~ ) In vivo
WS
CW
L
715 520 750 610 36.9
525 465 560 555 36.9
31 26 33 28 1.1
52 b 44 c 57 a 52 b 2.7
73 69 75 73 1.1
45 37 43 45 3.2
4.6 b 2.5 c 6.4 a 2.8 c 0.34
NS ** NS
NS NS NS
* *** NS
* * *
** ** NS
NS NS NS*
** ***
Effect
P L P× L
***P< 0.001; **P< 0.01; *P< 0.05; NS, not significant.
Table 3 Mean total DM ( T D M I ) and straw DM (SDMI) intake of and the in sacco (24 h) digestibility (%) for ammoniated wheat straw (AWS), cottonwool cellulose (CW) and lucerne (L), the in vivo DM digestibility of the diet (%) and N retention in faunated ( + P ) and defaunated ( - P ) sheep fed ammonia treated straw based diet with ( + L) or without ( - L) lucerne supplement Protozoa (P)
Lucerne (L)
TDMI (gday -1 )
SDMI (gday -~ )
DMdigestibility (%) In sacco
+P +P -P -P SEM
+L -L +L -L
Nretention (gday -~ ) In vivo
AWS
CW
L
815 615 800 700 39.3
630 560 615 625 41.2
44 39 50 43 1.6
42 36 53 44 2.8
73 75 74 77 I.I
53 46 56 51 1.3
7.7 3.6 7.6 5.9 0.58
NS *** NS
NS NS NS
** ** NS
** * NS
NS * NS
* NS NS
NS * NS
Effect
P L P×L
***P<0.001; **P<0.01; *P<0.05; NS, not significant.
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Table 4 Mean total D M ( T D M I ) and straw DM (SDMI) intake, mean daily weight change ( D W C ) and mean daily clean wool growth ( C W G ) of faunated ( + P ) and defaunated ( - P ) lambs on either an untreated ( U S W ) basal diet or a wheat straw basal diet with ( + L ) or without ( - L ) lucerne supplement Protozoa
Straw
Lucerne
TDMI (gday -t )
SDMI (gday -1 )
DWC (gday -1 )
CWG (gday -1 )
+P +P +P +P - P -P -P -P SEM
AWS AWS UWS UWS AWS AWS UWS UWS
+L -L +L -L +L -L +L -L
825 755 535 455 840 675 710 510 26.7
650 710 350 390 665 635 520 455 27.3
58 41 -20 -69 72 14 - 1 -62 9.6
3.09 2.50 2.23 1.64 4.15 3.15 3.15 2.27 0.219
Effect P
*
*
NS
***
S
***
***
***
***
L P× S P×L S× L PXS×L
*** ** * NS NS
NS ** * NS NS
*** NS NS NS NS
*** NS NS NS NS
*P< 0.05; **P< 0.01; ***P< 0.001; NS, not significant.
altered by the lucerne supplement. Defaunation of the wethers had no significant effect on feed intake.
Experiment 3 Daily liveweight gain was significantly increased by lucerne supplementation ( P < 0 . 0 1 ) and ammoniation of straw ( P < 0 . 0 1 ) while the effects ofdefaunation were not statistically significant (Table 4). Wool production was significantly increased by defaunation (P<0.01), lucerne supplementation (P< 0.01 ) and ammoniation of straw ( P < 0.01 ). A combination of these three treatments increased wool production from 1.6 to 4.15 g clean wool day- 1. Discussion Cereal straws are characterised by their high content of lignocellulose and low level of nitrogen. Consequently, these materials are poorly digested and can only support a low level of production when they are used as a basal diet for ruminants. In these studies, thermo-ammoniation increased the nitrogen content of the straw from 0.5 to 1.4% and the in sacco DM digestibility of the straw from 26 to 39% (24 h incubation). These values fall within the range
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of values quoted in the literature. Sundstol and Coxsworth (1984) suggest that if the treatment of straw is done correctly, the increase in organic matter (OM) digestibility and N content is 10-12 and 0.8-1.0 percentage units respectively. While the reasons for the change in digestibility have not been clearly defined, it is apparent that both chemical and physical changes in the straw and a larger, more active pool of microorganisms (supported by the additional nitrogen) are contributing factors. With the use of a scanning electron microscope, Harbers et al. (1982) noted structural differences between untreated and ammoniated straw and observed that rumen bacteria and fungi readily invaded tissues damaged by the ammoniation process. In contrast, Streeter and Horn (1982) have suggested that solubilisation of hemicellulose was responsible for most of the increase in DM digestibility associated with ammoniation treatment. The change in the digestibility of straw was probably the major factor contributing to the increase in straw DM intake of the wethers which increased from 465 g day -~ (untreated straw) to 560 g day -~ (ammoniated wheat straw). The higher nitrogen retention in the wethers receiving ammoniated wheat straw was due to a higher intake of N rather than an increase in the efficiency of utilisation. A similar response was observed in the growth study. Ammoniation of the straw increased straw DM intake of the faunated lambs from 390 to 710 g day- ~and the straw DM intake of the defaunated lambs increased from 455 to 635 g day -~ as a result of ammoniation. It has been suggested by Orpin and Bountiff (1978 ) that forage supplements containing significant quantities of soluble nutrients may influence the rate of fibre digestion in the rumen by stimulating colonisation of plant material by rumen microorganisms. In this study, the in sacco digestibility of both untreated and ammoniated straw were significantly increased by the inclusion of 150 g day- ~lucerne in the ration. It is possible that this increase in digestibility was partly due to additional ammonia generated in the rumen from the degradation of the soluble N component of the lucerne supplement. However, in a similar study in which a supplement of 250 g day-~ lucerne was accompanied by an increase in the in sacco digestibility of rice straw, McMeniman et al. (1988 ) concluded that this response could not be attributed to either ammonia or sulphide concentration in the rumen. The lucerne supplement would also have increased the availability of amino acids and readily fermentable carbohydrate which could have enhanced the proliferation of ceUulolytic microbes (Juul-Nielsen, 1981 ), although it has been suggested by Preston and Leng (1986) that the lysis of microbial cells in the rumen should provide an adequate supply of amino acids. In a number of studies where the dietary content of fermentable N was adequate no requirements for soluble proteins have been demonstrated (see Kempton et al., 1979). Despite the increase in the digestibility of wheat straw, voluntary intake of
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straw was not significantly higher for the animals receiving the lucerne supplement. However, both total DM intake and N retention were higher in the wethers receiving the lucerne supplement and in the growth study, body weight gain and wool production were improved by supplementation. The higher N retention in the animals receiving the lucerne supplement was due to higher N intake and a more efficient utilisation of N by the wethers (Table 2 ). The increased efficiency of N utilisation was probably due to a greater yield of microbial protein synthesised in the rumen. The reported changes in rumen function associated with defaunation suggest that the activity of the protozoa results in a depression of the ratio of protein to energy in the end products of rumen fermentation. It is now generally accepted that in the absence of ciliates the efficiency of microbial growth is enhanced and more microbial and dietary protein flows from the rumen (see Bird and Leng, 1985; Veira, 1986 ). In addition, it is often reported that defaunation depresses digestion of feed material in the rumen, although the effects are not consistent and there is no consensus of opinion on the reasons for this change. At one extreme, Coleman ( 1988 ) states that "ciliate protozoa are quantitatively important in the digestion of cellulose in the rumen", while at the other extreme, Hungate (1975) claims that the amount of cellulose digested by the protozoa is small in relation to the bacteria. In contrast to previous work (for a review see Bird and Leng, 1985; Veira, 1986 ) these studies clearly show that defaunation was associated with an increase in the in sacco digestibility of both treated and untreated straw and that compared with faunated animals, the intake of straw tended to be higher in the defaunated animals (wethers and lambs). These results suggest that the digestive activity of the protozoa which is lost upon defaunation has been more than compensated for by an increase in the digestive capacity of the remaining population of bacteria and fungi. This effect could be due to the replacing of an organism with low cellulolytic activity (the protozoa) with organisms of higher cellulolytic activity (bacteria and fungi) or it could be due to the elimination of the predatory activity of the protozoa. The colonisation of ingested plant material requires the transfer of organisms between feed residues and newly ingested food via the rumen fluid. A population of protozoa may reduce this transient population and thereby reduce the rate of colonisation of new feed particles in the rumen. In these studies, defaunated animals were given at least 4 weeks to recover from the defaunation treatment before measurement of rumen function was commenced. The work of Orpin and Letcher (1984) clearly demonstrates that, following the defaunation treatment, the period of time allowed for the rumen microorganisms to recover may be critical in determining the effect of defaunation on rumen function. In the studies of Orpin and Letcher, between 3 and 4 weeks were required for the number of viable bacteria to reach a stable plateau in the defaunated rumen and the organic matter digestibility in
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the rumen of these animals showed a similar trend. In the past, measurements have often been made in defaunated animals within 2-3 weeks of the defaunation treatment and in light of the results of Orpin and I_etcher (1984) it must be questionable whether some of the reported results truly represent the effect of the absence of protozoa on rumen function. Defaunation resulted in a significant improvement in N retention in the wethers and higher wool production in the lambs. Both these responses were achieved without a significant change in N intake indicating that compared with faunated animals the efficiency of N utilisation in the defaunated animals was significantly higher. The improvement in wool production from the defaunated lambs in these studies was in accordance with the earlier defaunation studies of Bird et al. (1979) and Bird and Leng (1984) and was probably due to an increase in the availability of microbial protein from the ciliate-free rumen (see Veira et al., 1984). Surprisingly, in this study defaunation had no significant effect on body weight gain of the defaunated lambs. The defaunated lambs receiving the ammoniated wheat straw diet had a lower growth rate than the faunated lambs but this trend was reversed on the other three diets. The negative response on the treated straw diet was not compatible with the rumen function studies, which indicated that defaunation was associated with an increase in the in sacco digestibility of straw, a slightly higher intake of straw and higher N retention. Further work is required to establish the relationship between body weight gain and defaunation on ammoniated straw diets.
Acknowledgements The authors would like to acknowledge the assistance of R. Woodgate for the maintenance of experimental animals and the collection of experimental data. These studies were supported by funds from the Australian Centre for International Agricultural Research.
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cattle on a diet based on sisal pulp II. Supplementation with Ramon (Brosimumalicastrum) forage and rice polishings. Trop. Anim. Prod., 4: 287-293. Rodriguez, A., Riley, J.A. and Thorpe, W., 1985. Animal performance and physical disturbances in sheep fed diets based on ensiled sisal pulp (Agravefourcroydes). I. The effect of supplementation with protein, forage and minerals. Trop. Anim. Prod., 40:32-38. Setala, J., 1983. The nylon bag technique in the determination of ruminal feed protein degradation. Agric. Soc. Finland, 55:1-7. Streeter, C.L. and Horn, G.W., 1982. Effect of treatment of wheat straw with ammonia and peracetic acid on digestibility in vitro and cell wall composition. Anim. Feed Sci. Technol., 7:325-329. Sundst~l, F. and Coxworth, E.M., 1984. Ammonia treatment. In: F. Sundstol and E.M. Owens (Editors), Straw and Other Fibrous By-products as Feed. Elsevier, Amsterdam, pp. 196249. Van Soest, P.J., 1963. Use of detergents in the analysis of fibrous feeds. II. A rapid method for the determination of fibre and lignin. J. Assoc. Off. Agric. Chem., 46:829-835. Veira, D.M., 1986. The role of ciliate protozoa in nutrition of the ruminant. J. Anim. Sci., 63:1547-1560. Veira, D.M., Ivan, M. and Jui, Y., 1984. The effect of ciliate protozoa on the flow of amino acids from the stomach of sheep. Can. J. Anim. Sci., 64 (Suppl.): 22-23. Warner, A.G.I., 1962. Enumeration of rumen micro-organisms. J. Gen. Microbiol., 28:119128.