Effects of dietary level of
Leucaena leucocephala
on
performance of Angora and Spanish doelings
A. Yami
a, A.J. Litherland
b, J.J. Davis
b, T. Sahlu
b,*, R. Puchala
b, A.L. Goetsch
b aAlemaya University of Agriculture, Dire Dawa, EthiopiabE (Kika) de la Garza Institute for Goat Research, Langston University, Langston, OK 73050, USA
Received 5 March 1999; accepted 21 January 2000
Abstract
Thirty Angora (162 kg initial body weight) and 20 Spanish doelings (192 kg initial body weight), approximately 8 months of age, were used in an 10 week experiment to evaluate effects of dietary level ofLeucaena leucocephalaon body weight (BW) gain and ®ber growth. The control diet (CS) included 9% dry matter (DM) of formaldehyde-treated casein; other diets consisted of 15, 30, 45 or 60% DM of leucaena leaf meal (0.75% mimosine; 15, 30, 45 and 60 l, respectively). Diets were formulated to be 2.13 Mcal metabolizable energy/kg DM, and ranged in crude protein from 10 to 14% of DM. DM intake was greater (P<0.05) for 45 l than for CS and 15 l (710, 648, 815, 899 and 811 g per day for CS, 15, 30, 45 and 60 l, respectively) and similar (P>0.05) between Angora and Spanish doelings. BW gain was similar (P>0.05) among diets (48, 28, 38, 34 and 26 g per day for CS, 15, 30, 45 and 60 l, respectively) and between breeds. Mohair growth rate was lower (P<0.05) for 60 and 30 l than for CS (1.34, 1.18, 0.94, 1.16 and 0.88 mg cmÿ2per day, and mohair diameter was greatest (P<0.05) for CS and
lowest (P<0.05) for 60 l (27.7, 25.9, 25.1, 25.0 and 23.8mm for CS, 15, 30, 45 and 60 l, respectively). Cashmere growth rate and ®ber diameter for Spanish goats were similar among diets, and primary and secondary follicle activities for both Angora and Spanish goats were not affected by dietary treatments (P>0.05). Diet affected (P<0.05) plasma concentrations of urea, threonine, arginine, valine, phenylalanine, isoleucine, leucine and lysine, with concentrations increasing as dietary level of leucaena increased. In conclusion, diets of moderate to high levels (e.g., 45%) of leucaena with 0.75% mimosine can be fed to goats without adverse effects on BW gain or ®ber growth. However, further study of the composition of leucaena-based diets appears necessary to achieve most ef®cient utilization.#2000 Elsevier Science B.V. All rights reserved.
Keywords:Leucaena; Goat; Growth; Mohair; Cashmere
1. Introduction
Leucaena (Leucaena leucocephala) is a drought-resistant, leguminous tree found throughout the tropics and subtropics (Devendra, 1993). Leucaena leaves are readily consumed and nutritious; however, leucaena contains toxic compounds such as mimosine
(Ham-mond, 1994). Mimosine is a free amino acid partially degraded byruminal microorganismsandplantenzymes to 3,4- or 2,3-dihydroxypyridine (DHP). Some rumi-nants host speci®c ruminal bacteria that can degrade 3,4-or 2,3-dihydroxypyridine (DHP) to nontoxic com-pounds (Jones et al., 1985). But even in goats that do not possess DHP-degrading bacteria, 30 to 40% of the diet of goats can be composed of leucaena without adversely affecting live weight gain (Virk et al., 1991). Fiber growth of Angora goats is very responsive to dietary characteristics such as level and ruminal Small Ruminant Research 38 (2000) 17±27
*Corresponding author. Tel.:1-405-466-3836;
fax:1-405-466-3138.
E-mail address: sahlu@mail.luresext.edu (T. Sahlu)
0921-4488/00/$ ± see front matter#2000 Elsevier Science B.V. All rights reserved.
degradability of protein (Sahlu et al., 1993; Davis et al., 1999). Because 37 to 67% of leucaena protein escapes ruminal microbial degradation (Garcia et al., 1996), it may be a particularly suitable feedstuff for ®ber-producing goats. However, the nutritive value and toxicological effects of leucaena with ®ber-pro-ducing goats have not been extensively studied, par-ticularly at high dietary levels. Furthermore, the rate of mohair growth by Angora goats is much greater than that of cashmere by Spanish goats, suggesting differ-ent nutridiffer-ent needs and production responses to varying diets. Therefore, objectives of this experiment were to evaluate effects on live weight and ®ber growth by Angora and Spanish goats of different dietary levels of leucaena compared with a diet containing a feedstuff high in ruminally undegraded protein.
2. Materials and methods
2.1. Animals and diets
Thirty Angora (162 kg initial body weight) and 20 Spanish doelings (192 kg initial body weight),
approximately 8 months of age and not having pre-viously consumed leucaena, were blocked by breed and allocated to ®ve dietary treatments (Table 1) to achieve similar body weight (BW) and stretched ®ber length. The control diet (designated as CS) included 9% dry matter (DM) of formaldehyde-treated casein (7.8 g formaldehyde per kg crude protein) as a source of ruminally undegraded protein. Casein (Sigma Che-mical Co., St. Louis, MO, USA) was sprayed with 10% (w/v) formaldehyde and stored in sealed, plastic bags for at least 1 week prior to use. Other diets consisted of 15, 30, 45 or 60% DM of leucaena leaf meal (0.75% mimosine; designated as 15, 30, 45 and 60 l, respectively). Diets were formulated to be iso-energetic (2.13 Mcal metabolizalbe energy/kg DM, based on NRC, 1981), ranged in crude protein from 10 to 14% and were pelleted.
Goats were penned individually, and diets were offered once daily for ad libitum consumption during the experimental period (i.e., 10% orts). A 7 day adaptation period began on 9 November, followed by 10 week experimental period. During adaptation, a 1:1 mixture of 45 l pellets and cottonseed hulls was fed, with daily mimosine intake of approximately
Table 1
Composition (% dry matter) of diets consumed by Angora and Spanish goats
Item Dieta
CS 15 l 30 l 45 l 60 l
Ingredient
Leucaena leaf meal 0.0 15.0 30.0 45.0 60.0
Cottonseed hulls 61.0 50.0 42.0 34.0 27.0
Ground corn 19.5 24.0 17.0 10.0 2.0
Formaldehyde-treated casein 9.0 0.0 0.0 0.0 0.0
Urea 0.5 1.0 1.0 1.0 1.0
Molasses 7.0 7.0 7.0 7.0 7.0
Dicalcium phosphate 1.0 1.0 1.0 1.0 1.0
Pellet binder 1.0 1.0 1.0 1.0 1.0
Trace mineral premixb 0.8 0.8 0.8 0.8 0.8
Vitamin premixc 0.2 0.2 0.2 0.2 0.2
Nutrient composition
Dry matter 93 93 93 93 93
Crude protein 14 10 12 13 13
NDF 58 49 59 55 52
ADF 46 39 39 41 39
Mimosine 0.00 0.19 0.41 0.56 0.47
aCS: Formaldehyde-treated casein; 15, 30, 45 and 60 l15, 30, 45 and 60% leucaena leaf meal, respectively.
b95% NaCl and at least 0.2% Mn, 0.16% Fe, 0.033% Cu, 0.1% Zn, 0.007% I and 0.005% Co.
c2200 IU/g Vitamin A, 1200 IU/g Vitamin D and 2.2 IU/g Vitamin E.
68 mg kgÿ1
BW. Feed intake was recorded daily during the experiment, and BW was determined at the beginning and end.
Feed and ort samples were dried at 608C for 3 days, allowed to air-equilibrate, ground in a Wiley mill to pass a 1 mm screen and analyzed for DM, ash (AOAC, 1990), acid detergent ®ber, neutral detergent ®ber (Goering and van Soest, 1970), total nitrogen (Tech-nicon Instrument Co., Tarrytown, NY) and mimosine (Tangendjaja and Wills, 1980).
2.2. Fiber and histology
Fiber regrowth rate was determined with a right mid-side patch by clipping to skin level (Oster blade 40) a measured square (approximately 15 cm15 cm) on Days 47 and 70 of the experiment. Fiber diameter and cashmere yield by weight were determined using an optical ®ber distribution analyzer (OFDA 100, Zellweger Uster, Charlotte, NC). For histological measurement, biopsy punch (8 mm; P250, Acuderm, Ft. Lauderdale, FL) skin sections were collected under local anesthesia (1 ml lidocaine) on Days 0, 52 and 70. Skin samples were ®xed (10% w/v buffered formalin), processed through graded alcohols and embedded in paraf®n wax with the epidermal surface up. Skin was serially sectioned (8mm) in the transverse plane and stained with adapted Sacpic stain; primary and sec-ondary follicle activities were assessed according to staining characteristics of the inner root sheath (Nixon, 1993).
2.3. Blood and ruminal ¯uid
On Day 48 of the experiment, ruminal ¯uid and blood samples were collected at 0 and 3 h after feed-ing. Ruminal ¯uid was sampled via a stomach tube immediately after jugular venipuncture. After mea-surement of pH, ruminal ¯uid was preserved with HCl, frozen at ÿ208C and later assayed for ammonia nitrogen by the phenol-hypochlorite colorimetric pro-cedure of Broderick and Kang (1980). In addition, volatile fatty acids in ruminal ¯uid were analyzed by gas chromatography as described by Lu et al. (1990). Blood samples were collected in two 5 ml tubes containing potassium EDTA or potassium oxalate-sodium ¯uoride (Becton Dickinson Vacutainer Sys-tems, Rutherford, NJ) and placed in ice. Plasma was
harvested after centrifugation (1500g) for 15 min at 48C and then frozen (ÿ208C). Plasma concentrations of urea nitrogen, glucose and total protein were assayed colorimetrically using a Technicon AutoAna-lyzer II System, with methodology described by Sahlu et al. (1993). The concentration of nonesteri®ed fatty acids was determined with a commercial kit using an enzymatic colorimetric procedure (Wako Pure Che-mical Industries, Richmond, VA), also as described by Sahlu et al. (1993). Plasma amino acid concentrations at 3 h post-feeding were determined as outlined by Puchala et al. (1996).
Commercially available kits (ICN Biomedicals, Inc., Costa Mesa, CA) were used for analysis of triiodothyronine (T3; Catalog No. 07-292102), thyr-oxine (T4; Catalog No. 07-290102) and cortisol (Cat-alog No. FI 9303), with procedures previously validated for goats by Puchala et al. (1996). Duplicate samples were analyzed in single runs, with intra-assay coef®cients of variation of 7.4, 7.6 and 10.2% for T3, T4and cortisol, respectively.
2.4. DM digestibility, nitrogen retention and in situ measures
Apparent DM digestibility and nitrogen retention were measured in a separate experiment, with ®ve adult Angora wethers and ®ve adult Spanish wethers. The experiment consisted of two simultaneous 55 Latin squares. The goats were placed in metabolism crates and ®tted with fecal bags. Each period was 14 days in length, with 9 days for adaptation and 5 days for feces and urine collections. During the second week of each period, feed intake was limited to 90% of that in the preceding week during which intake was ad libitum (10% orts). Feces and urine were weighed daily and mixed thoroughly; 10% daily aliquots were composited and stored atÿ208C until analysis. Com-posite feed samples were formed by daily sampling on the last 7 days of each period. Feed samples were analyzed for DM and nitrogen as described earlier. Feces was dried at 558C in a forced-air oven, then analyzed for DM and total nitrogen. Urine was lyo-philized and analyzed for DM and total nitrogen.
and a 4 days sampling period. Samples of leucaena and formaldehyde-treated casein were ground to pass a 2 mm screen, and 0.5 g samples were weighed into duplicate dacron bags (14 cm9 cm; 50mm pore size) on two consecutive days. Four bags per treatment were washed in cold water for 10 min in an automatic washing machine to estimate solubilization and small particle out¯ow through pores. Bags were closed with elastic bands, submerged in cold water for 15 s, attached to a 0.25 m weighted ¯exible rod and sus-pended in the rumen for 2, 4, 8, 12, 16 or 24 h. After removal from the rumen, bags were immediately submerged in cold water, washed for 10 min, dried for 24 h in a 558C forced-air oven and analyzed for total nitrogen. Ruminal disappearance of nitrogen was calculated using the equation of érskov (1982), assuming a ruminal digesta passage or dilution rate of 5% per hour.
2.5. Statistical analyses
Data were analyzed by General Linear Models procedures of SAS (1989). For single measures in the 10 week primary experiment, data were analyzed with a model consisting of diet, breed and dietbreed. The analysis for ®ber characteristics was conducted separately for Angora and Spanish doelings. Differ-ences among means were determined by least signi®-cant difference with a protected F-test (P<0.05). Repeated measures analysis (SAS, 1989) was used for measures made at different times. The simulta-neous latin squares for DM digestibility and nitrogen
retention were analyzed as a split-plot, with a main plot of breed or square and subplot of diet.
3. Results
3.1. Feed intake, BW gain and ®ber
Factors responsible for the lower than expected mimosine concentration in the 60 l diet (Table 1) are unclear. The estimated ruminally undegraded pro-tein concentration for leucaena leaf meal was approxi-mately 50% of total crude protein. DM intake was greater (P<0.05) for 45 l than for CS and 15 l and similar between breeds (P>0.05; Table 2). Crude protein intake ranked (P<0.05) 45>30>15 l, with CP intake for 60 l and CS being similar (P>0.05) to that for 30 l; DM intake was similar between breeds (P>0.05). Mimosine intake ranked (P<0.05) CS<15<30 l and 60<45 l and was greater (P<0.05) for Angora than for Spanish goats. BW gain was similar among diets (P>0.05), although BW gain:DM intake was greater (P<0.05) for CS than for 15, 45 and 60 l. BW gain and BW gain:DM intake were similar between breeds (P>0.05). DM digestibility decreased as the level of leucaena increased, being greater (P<0.05) for CS and 15 l than for 45 and 60 l, and was 5% units lower (P<0.05) for Angora than for Spanish goats. Nitrogen retention was similar among treatments and between breeds (P>0.05).
Alopecia was observed early in the experiment (i.e., 10 days after initiation of the preliminary period) in 16
Table 2
Effects of dietary leucaena level on feed intake, ADG, ADG:DM intake, DM digestibility and N retention in Angora and Spanish goatsa
Item Dietb SEM Breed
CS 15 l 30 l 45 l 60 l Angora Spanish
Daily intake
DM (g) 710 bc 648 c 815 ab 899 a 811 ab 57 800 830
CP (g) 107 ab 70 c 102 b 126 a 105 ab 7 100 104
Mimosine (mg kgÿ1BW0.75) 0 d 143 c 380 b 600 a 437 b 10 166 b 134 a
ADG (g) 48 28 38 34 26 8 31 25
ADG:DM intake (g kgÿ1) 50 a 25 b 35 ab 29 b 14 b 8 37 32
DM digestibility (%)c 59 a 59 a 56 ab 53 bc 51 c 1 53 b 58 a
N retention (%)c 38 25 39 29 32 4 35 30
aWithin a row, means with different letters differ (P<0.05).
bCS: Formaldehyde-treated casein; 15, 30, 45 and 60 l15, 30, 45 and 60% leucaena leaf meal, respectively.
cMeasured in a separate experiment with ®ve adult Angora and ®ve Spanish wethers and two simultaneous 55 Latin squares.
Angora and 9 Spanish goats. Mohair growth rate for Angora doelings was lower (P<0.05) for 30 and 60 l than for CS, with values for 15 and 45 l being similar (P>0.05; Table 3). In accordance, mohair mean ®ber diameter was greatest (P<0.05) among treatments for CS, lower (P<0.05) for 60 l than for 15 and similar (P>0.05) among 15, 30 and 45 l. The percentage of kemp in the ¯eece of Angora doelings was similar among treatments (P>0.05), as was also true for primary and secondary follicle activities. No ®ber measures for Spanish goats were affected by diets (P>0.05).
3.2. Ruminal ¯uid
Ruminal ¯uid pH was affected (P<0.05) by a diet H time interaction (Table 4). Ruminal pH increased as dietary level of leucaena increased and was generally lower for CS than for diets containing leucaena. The ruminal ammonia concentration was similar (P>0.05) among treatments and there tended (P<0.06) to be an interaction between breed and time, being greatest for Angora doelings at 3 h post-feeding. The total volatile fatty acid concentration in ruminal ¯uid was similar among treatments and between breeds (P>0.05). There was an interaction between diet and time
(P<0.05) for the molar percentage of propionate and the acetate:propionate ratio. In general, the acet-ate:propionate ratio was greater for CS versus diets with leucaena at 0 h and lower at 3 h post-feeding.
3.3. Plasma
Plasma urea concentration generally increased (P<0.05) with increasing dietary level of leucaena, and was greater (P<0.05) for Angora versus Spanish doelings (Table 5). Concentrations of protein, glucose, nonesteri®ed fatty acids, cortisol, T3 and T4 were similar between breeds. Urea concentrations for CS were intermediate to those for diets with leucaena. Differences among diets in plasma total protein centration were fairly similar to those in urea con-centration, although the concentration for CS was similar to lowest concentrations for diets with leu-caena. Glucose, nonesteri®ed fatty acids, cortisol and T4concentrations were similar among diets (P>0.05). For T3concentration there was an interaction (P<0.05) between diet and time, being greater for CS than for leucaena diets at 0 h but not at 3 h post-feeding.
Diet and breed affected plasma concentrations at 3 h post-feeding of a number of amino acids (Table 6). For most essential amino acids quanti®ed Table 3
Effects of dietary leucaena level on ®ber characteristics of Angora and Spanish goatsa
Item Dietb SEM
CS 15 l 30 l 45 l 60 l
Angora goats
Mohair
growth rate (mg cmÿ2per day) 1.34 a 1.18 ab 0.94 b 1.16 ab 0.88 b 0.14
Mean fiber diameter (mm) 27.7 a 25.9 b 25.1 bc 25.0 bc 23.8 c 0.6
Kemp (%) 0.12 0.15 0.14 0.18 0.18 0.04
Follicle activity (%)
Primary 48 44 52 50 50 10
Secondary 96 95 92 94 95 4
Spanish goats
Guard hair growth rate (mg cmÿ2per day) 0.27 0.25 0.27 0.28 0.14 0.06
Cashmere
Growth rate (mg cmÿ2per day) 0.06 0.05 0.10 0.08 0.04 0.02
Mean fiber diameter (mm) 17.9 16.4 17.5 17.6 16.7 0.6
Follicle activity (%)
Primary 54 56 22 25 24 12
Secondary 77 86 89 85 78 5
aWithin a row, means with different letters differ (P<0.05).
bCS: Formaldehyde-treated casein; 15, 30, 45 and 60 l15, 30, 45 and 60% leucaena leaf meal, respectively.
Table 4
Effects of dietary leucaena level on ruminal ¯uid pH and ammonia and volatile fatty acid concentrations in Angora and Spanish goats
Item Time after
feeding (h)
Dieta SEM Breed Significance levelb
CS 15 l 30 l 45 l 60 l Angora Spanish Diet Breed Time Diettime
pH 0 6.56 6.56 6.61 6.67 6.72 0.05 6.67 6.58 0.01 NS 0.01 0.01
3 6.01 6.18 6.23 6.48 6.48 6.23 6.31
Ammonia (mg dlÿ1) 0 6 5 5 6 6 2 6 5 NS 0.01 0.01 NS
3 15 17 17 15 17 21 12
Volatile fatty acids mM 0 58 61 57 66 60 8 41 50 NS NS 0.02 NS
3 83 68 60 58 57 60 62
Molar percentage acetate 0 77 73 72 72 73 1 73 74 NS NS 0.01 0.01
3 64 65 69 68 70 67 68
Propionate 0 13.1 14.5 14.8 16.6 14.2 1.2 15 15 0.03 NS 0.01 0.01
3 22.3 22.7 19.5 19.1 16.6 21 19
Butyrate 0 7.6 9.9 9.7 9.2 10.9 0.6 9.3 9.6 0.01 NS NS 0.01
3 11.3 10.9 10.3 10.5 12.0 11.3 10.7
Valerate 0 0.68 0.85 0.74 0.95 0.83 0.09 0.80 0.82 NS NS NS 0.01
3 1.31 1.14 1.13 1.19 1.12 1.13 1.20
Isobutyrate 0 0.50 0.72 2.20 0.59 0.59 0.60 1.29 0.56 NS NS NS NS
3 0.34 0.22 0.15 0.30 0.24 0.17 0.33
Isovalerate 0 0.61 0.53 0.50 0.52 0.47 0.10 0.57 0.48 NS NS 0.01 NS
3 0.42 0.19 0.30 0.30 0.20 0.13 0.44
Acetate:propionate 0 6.0 5.1 4.9 4.5 5.1 0.3 5.1 5.1 0.04 NS 0.01 0.01
3 2.9 3.0 3.6 3.7 4.4 3.4 3.6
aCS: Formaldehyde-treated casein; 15, 30, 45 and 60 l15, 30, 45 and 60% leucaena leaf meal, respectively.
bNS: Nonsigni®cant (P>0.05); treatment H breed and breed H time interactions were nonsigni®cant (P>0.05).
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Table 5
Effects of dietary leucaena level on plasma constituent concentrations in Angora and Spanish goats
Item Time after
feeding (h)
Dieta SEM Breed Significance levelb
CS 15 l 30 l 45 l 60 l Angora Spanish Diet Breed Time Diettime
Urea (mg dlÿ1) 0 14 12 12 16 19 1.5 15 14 0.01 0.02 0.01 NS
3 19 15 17 20 21 21 17
Protein (g lÿ1) 0 43 43 44 43 49 2 44 45 0.02 NS 0.01 NS
3 48 49 49 50 54 51 50
Glucose (mg dlÿ1) 0 58 61 57 66 60 8 58 63 NS NS NS NS
3 83 68 60 58 57 67 59
NEFA (mEq lÿ1) 0 397 436 399 422 328 46 420 380 NS NS 0.01 NS
3 140 172 230 248 191 170 220
Cortisol (ng mlÿ1) 0 1.2 1.4 1.2 1.8 1.6 0.2 1.3 1.6 NS NS 0.01 NS
3 0.6 0.8 0.7 1.2 0.8 0.8 0.9
Triiodothyronine (ng dlÿ1) 0 197 169 151 154 131 15 170 150 NS NS NS 0.04
3 168 139 156 175 180 160 167
Thyroxine (mg mlÿ1) 0 8.9 10.9 9.0 9.5 8.8 1.2 9.2 9.6 NS NS NS NS
3 11.7 10.3 10.2 10.3 8.9 9.4 11.3
aCS: Formaldehyde-treated casein; 15, 30, 45 and 60 l15, 30, 45 and 60% leucaena leaf meal, respectively.
bNS: Nonsigni®cant (P>0.05); treatment H breed and breed H time interactions were nonsigni®cant (P>0.05).
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(i.e., threonine, arginine, valine, phenylalanine, iso-leucine, iso-leucine, lysine), concentrations increased as the dietary level of leucaena increased. For some of these amino acids (i.e., threonine, valine, isoleucine, leucine), the CS concentration was intermediate to levels for diets with leucaena, although for others the concentration for the CS diet was near or below that for 15 l, which was typically lowest among leucaena-containing diets (i.e., arginine, phenylalanine, lysine). Concentrations of ®ve of the essential amino acids measured (i.e., arginine, valine, methionine, isoleu-cine, leucine) were greater (P<0.05) for Spanish versus Angora doelings.
4. Discussion
4.1. DM intake and BW gain
The low level of mimosine in the leucaena used might be attributable to plant strain variation, stage of growth or method of drying (Garcia et al., 1996). The ruminally undegraded protein concentration for leu-caena fell within the wide range of values previously reported (Garcia et al., 1996). This level is similar or slightly less than that in corn, for which leucaena was
partially substituted for. The dietary level of cotton-seed hulls also decreased as level of leucaena increased, although cottonseed hulls are low in pro-tein. Because of these factors and the small increase in total dietary crude protein concentration as level of leucaena increased, dietary concentration of ruminally undegraded protein presumably increased slightly as leucaena level increased.
The increase in DM intake as level of leucaena increased to 45% of the diet agrees with ®ndings of Virk et al. (1991). In the present experiment, except for 60 l, treatments with high DM intake relative to other treatments had low DM digestibility. This and the similar ruminal ¯uid concentration of total volatile fatty acids among diets suggest that total energy absorption was not markedly in¯uenced by dietary inclusion of leucaena or its level.
Virk et al. (1991) demonstrated that goats could maintain BW on diets consisting of as much as 60% leucaena. Likewise, in the present experiment 60 l doelings increased in BW, although BW gain:DM intake values indicate that performance was more ef®cient for lower leucaena levels. A number of factors could be responsible for this ®nding, such as protein binding by condensed tannins, since the level of tannin in leucaena ranges from 1 to 9% (Garcia Table 6
Effects of dietary leucaena level on plasma amino acid concentrations (mmol lÿ1) at 3 h post-feeding in Angora and Spanish goatsa
Item Dietb SEM Breed Significance levelc
CS 15 l 30 l 45 l 60 l Angora Spanish Diet Breed Diettime
Glutamate 148 191 195 178 156 16 183 165 NS NS NS
Serine 119 b 165 a 108 b 96 b 11 b 14 174 65 0.01 0.01 0.05
Glycine 620 710 620 600 600 50 770 490 NS 0.01 NS
Threonine 74 abc 64 c 73 bc 88 ab 93 a 7 82 75 0.02 NS NS
Alanine 186 236 209 211 198 12 225 190 NS 0.01 NS
Arginine 162 c 170 c 199 bc 231 ab 251 a 15 180 230 0.01 0.01 NS
Tyrosine 56 49 55 56 55 4 52 57 NS NS NS
Valine 286 ab 173 d 205 cd 242 bc 298 a 17 210 270 0.01 0.01 NS
Methionine 27 24 25 30 27 2 20 33 NS 0.01 NS
Phenylalanine 41b 43 a 54 a 54 a 63 a 4 50 51 0.01 NS NS
Isoleucine 73 bc 65 c 80 bc 86 ab 99 a 6 70 92 0.01 0.01 NS
Leucine 134 ab 89 c 110 bc 121 ab 146 a 9 103 137 0.01 0.01 NS
Lysine 67 b 72 b 89 ab 107 a 95 a 7 80 90 0.01 NS NS
Proline 115 a 82 b 86 b 98 ab 87 b 7 90 100 0.04 NS NS
aWithin a row, means with different letters differ (P<0.05).
bCS: Formaldehyde-treated casein; 15, 30, 45 and 60 l15, 30, 45 and 60% leucaena leaf meal, respectively.
cNS: Nonsigni®cant (P>0.05).
et al., 1996; Jackson et al., 1996). Chronic leucaena toxicosis is possible as well but not strongly indicated. High blood levels of 2,3-or 3,4-DHP can limit DM intake, and low ADG and T4concentration in plasma are symptomatic of leucaena toxicosis (Megarrity and Jones, 1983; Jones and Hegarty, 1984; Jacquemet et al., 1990). These conditions have previously been observed in goats subjected to long-term (e.g., more than 3 weak) feeding of diets composed of 40% or more leucaena, providing 250 (our unpublished observations) to 600 mg kgÿ1 BW of mimosine (Megarrity and Jones, 1983). However, our leucaena was low in mimosine compared with other reports (e.g., 2 to 14%; Garcia et al., 1996), resulting in a range in mimosine intake of approximately 40 mg kgÿ1
BW to slightly more than 200 mg kgÿ1 BW. Consequently, the concentration of T4was not in¯uenced by diet, although effects on T3 concentra-tion at 0 and 3 h post-feeding imply an effect of feeding on release of stored T3and subsequent oppo-site effects at 0 h, the magnitude of which varied with level of leucaena in the diet.
Mimosine may interfere with some aspects of amino acid metabolism. For example, Crounse et al. (1962) suggested that mimosine acts as a tyrosine analogue and Prabhakaran et al. (1973) reported that mimosine inhibits activity of some enzymes involved in tyrosine metabolism. Ter Meulen et al. (1981) observed that mimosine included in the diet of rats reduced serum tyrosine concentration. Mimosine inhi-bits activity of pyridoxal-requiring enzymes (Hylin, 1969) and, thus, could decrease methionine conver-sion to cysteine via the transulfuration pathway. In accordance, in recent studies with Angora and Alpine goats both mimosine and 2,3-(DHP) in¯uenced plasma amino acid concentrations. Parenteral admin-istration of mimosine (Sahlu et al., 1995; Smuts et al., 1995) or a perfusion of an area of skin (Puchala et al., 1996) reduced concentrations of some amino acids in plasma, but effects were variable. The administration of 2,3-DHP increased plasma concentration of some amino acids (Puchala et al., 1995; Sahlu et al., 1995). However, in the present experiment the lack of marked adverse effects of dietary inclusion of up to 45% leucaena does not indicate substantial deleterious effects on amino acid or nitrogen metabolism in animal tissues. Similarly, it does not appear that long-term feeding of leucaena, relatively low in
mimosine concentration, adversely affected goat BW change.
4.2. Fiber
Though leucaena used was relatively low in mimo-sine, mimosine intake in the preliminary period was suf®cient to induce alopecia in many of the goats. Alopecia has been previously observed without other symptoms of leucaena toxicity (Reis et al., 1975), and is elicited by mimosine rather than DHP (Reis et al., 1999). Within 48 h of the ®rst exposure to dietary leucaena, ruminal microorganisms of sheep adapt to convert mimosine to DHP (Reis et al., 1975); there-fore, as in this study, alopecia is a transitory, short-term occurrence.
DHP has depressed plasma thyroid hormone con-centrations, which are thought to have permissive roles in ®ber growth; treatment with thyroid hormones has increased wool growth rate (Ferguson et al., 1965) and thyroidectomy reduces wool follicle division rate (Hynd, 1994). However, plasma T3and T4 concentra-tions in the present experiment do not clearly indicate any such effects of dietary leucaena inclusion level. Correspondingly, the ®ber measures do not suggest substantial effects of long-term feeding of leucaena-containing diets on ®ber growth for either Angora or Spanish goats, with 45% or less leucaena in the diet. Although, mohair ®ber diameter was greater for CS than for diets with leucaena, which was at least partially responsible for numerically greatest mohair growth rate among treatments. This may have been a response to a difference in the level or array of dietary amino acids passing from the rumen intact, since leucaena contains only 0.7% sulfur-containing amino acids (D'Mello and Acmovic, 1989).
Methionine, isoleucine, leucine and lysine were identi®ed by Reis and Tunks (1978) as the most important amino acids for wool growth. In accor-dance, the high ®ber-producing Angora goats in the present experiment had lower concentrations of these amino acids than Spanish goats. However, it should be cautioned that numbers of observations per breed were not large. Nonetheless, breed differences in plasma concentrations of ®ve essential amino acids measured suggest that a substantial effect of diet on amino acid use in ®ber growth would be re¯ected in plasma amino acid concentrations.
Factors responsible for effects of dietary leucaena level on plasma concentrations of many amino acids without coincident impact on ®ber growth are unclear. However, one possible explanation, as alluded to before and supported by change in plasma urea con-centration with increasing leucaena level and also by the steady methionine level, is that total amino acid absorption in the small intestine increased as the dietary level of leucaena increased. Use of absorbed amino acids for BW gain presumably was limited by the low to moderate level of metabolizable energy intake and relatively low growth potential of these animals. Furthermore, incorporation into ®ber protein could have been restricted as well, if the pro®le of available amino acids was suboptimal for ®ber protein synthesis.
5. Conclusions
These results indicate that diets containing moder-ate to high levels of leucaena, at least up to 45%, can be fed to goats without adverse effects on BW gain or ®ber growth or characteristics. Moreover, the lack of interaction between dietary treatment and breed (i.e. Angora versus Spanish) for most variables suggests that differences among animals in ®ber production do not have appreciable impact. However, leucaena used in this experiment was relatively low in mimosine, and factors such as the amino acid composition of rumin-ally undegraded protein of leucaena deserve consid-eration and further study.
Acknowledgements
This research was supported by USAID Grant No. PCE-5053-G-00-3066-00.
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