Use of lentil screenings in the diets of early weaned
lambs and ewes in the second trimester of pregnancy
K. Stanford
a,*, G.L. Wallins
a, B.M. Lees
b, H.-H. MuÈndel
c aAlberta Agriculture, Food and Rural Development, Agriculture Centre, Bag 3014, Lethbridge, Alberta,Canada T1J 4C7
bWestco, Broxburn Agro Centre, RR 8-32-26 Lethbridge, Alberta, Canada T1J 4P4
cAgriculture and Agri-Food Canada, Research Centre, Box 3000, Lethbridge, Alberta, Canada T1J 4B1
Received 28 December 1998; received in revised form 7 May 1999; accepted 15 June 1999
Abstract
Commercial lentil screenings (LS) were substituted for barley grain and canola meal, and the resulting experimental diets (0, 12.5, 25 and 33% LS; 17±18% CP dry matter) were evaluated in situ and in digestibility and feedlot studies using RomanovSuffolk lambs. Mature Suffolk, Dorset and Rambouillet ewes were used to evaluate LS or whole barley as protein/energy supplements for ewes in mid-gestation receiving barley silage diets. Lentil screenings included 53.4% lentils, 10.6% weed seeds, 8.27% chaff and dust, with the remainder being a mixture of field peas, barley, wheat and canola. For the lamb trial, the control diet consisted of 62% barley, 12.5% canola meal and 20% alfalfa (as fed), while for the ewe study, the control diet consisted of barley silage with a salt-mineral supplement. Comparing dietary constituents in situ, the rates of protein and dry matter (DM) disappearance were 5±6-fold lower (p< 0.05) and effective ruminal degradability of protein (EDCP) was also lowest (p< 0.05) for LS as compared to alfalfa or barley. Digestibilities of DM, organic matter (OM) and neutral detergent fibre (NDF) as well as N retention (% of N intake) linearly decreased (p< 0.001) with increasing dietary LS. In the lamb feeding trial, average daily gain (ADG;p< 0.01), feed intake (p< 0.01) and feed conversion efficiency (p< 0.05) were all linearly reduced with increasing dietary LS, although such reductions were not significant for ewe lambs. Reduced lamb performance with LS was likely related to anti-nutritional factors and the reduced digestibility of LS. Valuing LS at 50% the cost of barley, incorporation of up to 25% LS in feeder lamb diets would be cost effective. In the ewe feeding study, although weight gains over the 50 days of feeding were highest (p< 0.05) in barley-supplemented and LS-supplemented as compared to control ewes, LS-supplemented ewes had fewer (p< 0.05) lambs born per ewe and reduced (p< 0.05) weight of lambs weaned breeding per ewe as compared to control ewes. Consequently, supplementation of barley silage diets with LS may not be beneficial for ewes in mid-gestation.#1999 Elsevier Science B.V. All rights reserved.
Keywords: Lentil; Screenings; Feeding value; Digestibility; Sheep 81 (1999) 249±264
*Corresponding author. Tel.: +403-381-5150; fax: +403-382-4526
E-mail address: stanford@em.agr.ca (K. Stanford)
1. Introduction
Lentils (Lens culinaris) have been recognized as one of the most complete and cheapest sources of vegetable protein for humans (Vidal-Valverde et al., 1994). Lentil seed is low in crude fibre (range 1.4±5.9%; Savage, 1988) and contains an average of 25% protein, 56% carbohydrate and 1% fat (Urbano et al., 1995). Agronomically, lentils are able to tolerate frost after emergence and resistant to high temperatures and drought (Savage, 1988). Due to these aforementioned factors and as a result of the promotion of lentil cultivation by the International Centre for Agricultural Research in Dry Areas (ICARDA), world production of lentils increased by 72% during the 1980s (Frias et al., 1996). In Canada, lentil production has also expanded in the last 30 years. Although lentils were not commercially cultivated in Canada prior to 1969, Canada is now, along with Turkey, the world's leading exporter of lentils (Anonymous, 1997).
Increased cultivation has led to greater availability of non-food-grade lentils for use in livestock diets. Lentils affected with ascochyta blight (Ascochyta lentis) and/or frost-damaged have been previously evaluated for use in pig diets (Bell and Keith, 1986; Castell and Cliplef, 1988). Lentil screenings are another source of lentils for livestock feed. Screenings are a byproduct of seed cleaning and consist of a mixture of the crop in question, cereal grains, weed seeds, chaff and dust (Darroch et al., 1990). Screenings are attractive for use in ruminant diets (McAllister et al., 1999) due to their low cost, which for lentil screenings in western Canada averages half that of feed barley.
In the raw, unprocessed form, all grain legumes contain a variety of anti-nutritional factors (Paduano et al., 1995). Some of the weed seeds present in screenings may also contain anti-nutritional factors (Darroch et al., 1990). Consequently, ruminant diets would be the major use for lentil screenings due to the ability of rumen microbes to adapt to (Birnbreier and Hilliger, 1993) or partially detoxify (Tukur et al., 1993) some factors such as alkaloids which would impair the performance of monogastrics. Although the use of lentil screenings in ruminant diets has not previously been addressed, ewes in the Middle East commonly receive 20% of their winter diet as lentil straw which includes broken branches, pod walls and leaflets (Erskine et al., 1990). In order to further study the use of lentil byproducts in sheep diets, the present series of experiments examined the in situ DM and CP degradation kinetics of lentil screenings, the apparent digestibility of lentil screenings, substitution of lentil screenings for barley and canola meal in the diets of early-weaned feeder lambs and the use of lentil screenings as a protein/energy supplement for ewes in mid-gestation.
2. Materials and methods
2.1. Diets
A composite 4 kg sample of screenings from the Laird variety of lentils (LS) was collected over an eight week period from a commercial lentil contractor/seed cleaning plant in Lethbridge, AB and a 250 g subsample was manually sieved to determine botanical composition (Table 1). Upon arrival at the Lethbridge Research Centre, the LS
were hammermilled to pass through a 3 mm screen and subjected to proximate analysis (Table 1) prior to incorporation into four completely pelleted experimental diets for the lamb study (Table 2). For the lamb study, LS were incorporated at rates of 0% (control), 12.5%, 25% and 33% (dry matter basis), replacing barley and canola meal. Diets for pregnant ewes consisted of barley silage (Table 3) top dressed with either whole barley, LS, or not supplemented (control). Ewes were fed the experimental diets for 50 days, after which all ewes received loose alfalfa hay supplemented with whole barley for the last trimester of pregnancy and during lactation.
2.2. Experiment 1: in situ disappearance
For two weeks prior to, and during the two days of the in situ study, two ruminally cannulated Jersey steers (470 kg) were offered a diet consisting of 50% alfalfa : timothy cubes (70 : 30; 13% CP) and 50% of the 33% LS experimental diet. Dried, pre-weighed nylon bags (10 cm11 cm; 53mm pore size) containing 3.0 g of each dietary constituent (rolled barley, pelleted alfalfa or LS) or pelleted diets (20% LS or 33% LS) were placed in the rumen of each steer. Three bags of each samples type were removed from each steer after 2, 4, 8, 12, 24, 48 and 72 h of ruminal incubation. Dry matter disappearance not attributable to microbial digestion was estimated by incubating bags in water at 378C for 2 min. Bag washing and calculation of DM disappearance were performed as described by McAllister et al. (1990). Residues from the triplicate bags were pooled for N analysis.
Table 1
Botanical composition by weight and proximate analysis of lentil screenings used in the present study Botanical composition Proximate analysis (% by weight)
Cultivated crops
Lentils, whole 37.18 dry matter (%) 90.4 Lentils, broken 16.66 organic matter (DM basis) 89.3 Peas, broken 5.80 crude protein (DM basis) 22.7 Barley 4.70 neutral detergent fibre (DM basis) 29.4 Wheat 8.89 acid detergent fibre (DM basis) 16.1 Canola 7.77 tannina(DM basis) 1.4
Total 81.00
Weed seeds
Stinkweed (Thlaspi arvense) 3.97 Wild oats (Avenua fatua) 3.27 Canary grass (Phalaris arundinacea) 1.76 Lamb's quarters (Chenopodium album) 0.51 Wild buckwheat (Polygonum convulvulus) 0.60 Dandelion (Taraxacum officinales) 0.05 Unidentified weeds 0.40
Total 10.56
Other
Chaff and dust 8.46
aTannin expressed as catechin equivalents.
Digestion kinetics of DM and CP were determined without correction for microbial protein using the equation of érskov and McDonald (1979):
pab 1ÿeÿct (1)
wherepis the proportion of DM disappearance at timet(%),athe soluble fraction,bthe slowly digestible fraction,cthe fractional rate of disappearance ofbandtthe duration of
Table 2
Ingredients (as fed) and composition (DM basis) of experimental diets for lambs Lentil screenings content of diet (%)
0 (Control) 12.5 25 33
Ingredients(kg tÿ1)
Barley grain 625 560 500 420
Canola meal 125 65 0 0
Alfalfa, suncured 200 200 200 200
Lentil screenings 0 125 250 330
Molasses, beet 10 10 10 10
Canola oil 8 8 8 8
Sheep minerala 13 13 13 13
Calcium carbonate 10 10 10 10
Maxi-Pelb 5 5 5 5
Dicalcium phosphate 4 4 4 4
Vitamin A, D, Ec 0.25 0.25 0.25 0.25
Deccoxd 0.13 0.13 0.13 0.13
Analysis
Dry matter (%) 89.64 89.56 89.12 89.91 Organic matter (%, DM basis) 90.18 90.25 90.81 89.41 Crude protein (%, DM basis) 18.71 17.58 17.07 18.04 Neutral detergent fibre (%, DM basis) 34.52 36.44 31.84 29.77 Acid detergent fibre (%, DM basis) 17.27 18.41 17.83 17.52 Acid detergent insoluble N (%, DM basis) 1.12 0.88 0.86 0.94
aContaining: 93.1% NaCl, 1.25% Mg, 0.9% Zn, 0.94% Mn, 0.13% Cu, 0.003% Se, 1.25% S, 1.25% K, 1.25%
Fe.
bFeed pellet binder (Mountain Minerals, Lethbridge, AB).
cContaining 10 000 IU gÿ1Vitamin A, 1250 IU gÿ1Vitamin D, and 10 IU gÿ1Vitamin E. dContaining 60 g kgÿ1decoquinate (RhoÃne-Poulenc Canada, Mississauga, ON).
Table 3
Composition (DM basis) of ewe experimental dietsa
Barley silageb Barley grain Lentil screenings
Analysis
Dry matter (%) 31.5 90.4 91.0
Crude protein (%, DM basis) 11.8 12.6 22.4 Neutral detergent fibre (%, DM basis) 56.5 22.7 30.2 Acid detergent fibre (%, DM basis) 33.4 16.2 16.4
aAlso included free choice 2 : 1 (Ca : P) sheep mineral and cobalt-iodized NaCl. bpH 4.2.
ruminal incubation (h), with the constraint thata+b1. The constraintsa,b, andcwere calculated using the NLIN procedure of the SAS Institute Inc. (1993). Effective rumen degradability of CP (EDCP) was estimated using the equation of érskov and McDonald (1979):
EDCPa bc
kc (2)
with an estimated solid outflow from the rumen (k) of 5% hÿ1 (Windschitl and Stern, 1988). Means were compared using the LSMEAN option of SAS (SAS Institute Inc., 1993).
2.3. Experiment 2: apparent digestibility
In a replicated 33 Latin square with three 21-day periods, six Romanov±Suffolk ram lambs (initial weight 25.00.1 kg) were used to evaluate voluntary feed intake and digestibility of the control, 12.5% and 33% LS diets. For the first 14 days of each period, lambs were individually penned. Orts were removed and weighed on a daily basis, and 10% more feed offered each day than was consumed the previous day. Ad libitum intake was then calculated over five days and the lambs fed at 95% ad libitum for the last nine days of the period. During the last seven days of each period, lambs were moved to metabolism crates for daily collections of faeces and urine. Acid (45 ml of 8N H2SO4) was added each morning to the urine collection jugs to prevent volatization of ammonia from the urine. Faeces and urine were subsampled daily (10%), composited over each period and stored atÿ308C until analysed.
2.4. Experiment 3: lamb feeding trial
Forty-seven RomanovSuffolk lambs were used to evaluate the four experimental diets (Table 2) in an individual feeding trial. The lambs (initial weight 26.50.2 kg, initial age 625 days) were blocked by sex and liveweight and allocated to pens using randomized block design. Access to water and pelleted diets was provided on an ad libitum basis throughout the study. Once daily, lambs were fed 5% more than their estimated consumption for the previous day. Orts were collected and weighed weekly. Lambs were weighed weekly and shipped for slaughter after reaching 45 kg.
2.5. Experiment 4: ewe feeding trial
Fifty days after being exposed to rams, 93 mature Dorset, Suffolk and Rambouillet ewes (age 2±6 year) were weighed, condition scored on a five-point scale where 1 = emaciated and 5 = obese (Scheer, 1987), blocked by breed, weight and age and allocated to group pens (n= 6) using a randomized block design. All ewes received a base diet of7 kg per head barley silage (Table 3). One-third of the ewes (2 pens) received only the base diet, another third received the base diet topdressed with 250 g per head per day LS, while the remaining one-third received the base diet topdressed with 250 g per head day whole barley. Throughout the study, water and salt/mineral supplement were
available ad libitum to the ewes. Ewes were fed once daily, with sufficient bunk space to allow each ewe immediate access to the fresh feed. Ewes received the experimental diets for 50 days and were then weighed and condition scored. Fifty days after the end of the feeding period, the ewes began lambing. Lambing data (proportion of ewes lambing, prolificacy and lamb birthweight) and lamb weaning weights at age 60 days were recorded.
2.6. Chemical analyses
Silage samples were freeze dried in a Virtris 25 XL Sentry (Virtris, Gardiner NY) before subsequent analysis. The remaining feed and faecal samples were dried at 1058C for 24 h to determine DM and ashed in a muffle furnace at 5008C for 5 h to determine OM. Excluding silage samples, faeces and feed were dried at 558C for 48 h before analyses for NDF and N. Faeces and feed were ground through a 1 mm screen for analysis of NDF and ground for 3 min in a Wig-L-Bug1
Amalgamator (Crescent Dental, Lyons IL) prior to N analysis in a Carlo±Erba1
NA 1500 Carbon±Nitrogen elemental analyser (Carlo±Erba Srumentazione, Rodano, Milan, Italy). The procedure of Van Soest et al. (1991) was used to determine NDF, but was modified by addinga-amylase to feed samples to solubilize starch and facilitate filtering. Tannin content of lentil screenings was determined by use of the vanillin±HCL method and expressed as catechin equivalents (Price et al., 1978).
2.7. Statistical analyses
Data were analysed using the regression (REG) and general linear model (GLM) procedures and means compared using the least-squares mean (LSMEAN) option of SAS (SAS Institute Inc., 1993). For the digestibility trial, the model included lamb, diet, period and perioddiet interaction. Data for the individual feeding experiment were analysed with sex, diet, and dietsex interaction included in the model with initial weight as a covariate. Breed, age, diet and two-way interactions were included in the model for analysis of the ewe feeding study after pen effects were found to be non-significant.
3. Results
3.1. Experiment 1: in situ disappearance
Lentil screenings were resistant to protein and DM disappearance in the rumen compared to alfalfa pellets, rolled barley or pelleted diets containing 25% or 33% LS (Table 4). Lag time was 7.4 h before onset of protein digestion in LS, while digestion was immediate for other dietary constituents and complete diets. The soluble DM and protein fractions of LS were reduced 3±4-fold (p< 0.05) compared to all other dietary constituents or complete diets evaluated. The reduced soluble fractions of LS were mirrored by slowly degradable fractions of protein and DM that were higher (p< 0.05) for LS than those of alfalfa, rolled barley, or either of the complete diets. Likewise, the
rates of protein and DM disappearance were reduced 5±6-fold (p< 0.05) for LS compared to those of alfalfa, the dietary constituent with the next lowest rates of protein and DM disappearance. Effective ruminal degradability of protein (EDCP) was also lowest (p< 0.05) for LS compared to the other dietary constituents or complete diets.
The low rate/extent of all measures of LS, DM and CP disappearance was not apparent for the complete diets evaluated (25% and 33% LS, respectively). Generally, the in situ degradation kinetics of DM and CP in the complete diets were intermediate to those of rolled barley and pelleted alfalfa. The slowly degradable and soluble fractions of CP and DM for both complete diets did not differ from those of pelleted alfalfa or rolled barley. For both complete diets, rate of DM disappearance was intermediate to that of alfalfa and rolled barley. Rate of protein disappearance was highest in rolled barley (p< 0.05), followed by the 33% LS diet which in turn had a higher rate of protein disappearance than alfalfa (p< 0.05), with the 25% LS diet equal in rate of protein disappearance to alfalfa and the 33% LS diet . Effective ruminal degradability of protein was highest for rolled barley (p< 0.05) followed by both complete diets which had higher EDCPs than alfalfa (p< 0.05).
3.2. Experiment 2: apparent digestibility
The ram lambs used in the digestibility trial found LS to be palatable as DM intake linearly increased (p< 0.05) with increasing LS content of the diets (Table 5). However,
Table 4
In situ degradation kinetics of DM and CP in dietary constituents and complete diets in steersa
Dietary constitutentsg Complete dietsb,g SEMf alfalfac barleyd LSe level of screenings (DM)
25% 33%
Slowly degradable fraction(%)
Protein 48.27 a 70.60 b 95.35 c 52.38 ab 49.18 ab 4.37 DM 47.51 a 70.66 b 95.65 c 52.00 ab 48.85 ab 7.11
Soluble fraction(%)
Protein 23.59 b 20.64 b 4.02 a 25.51 b 21.65 b 1.67 DM 22.40 b 19.52 b 4.00 a 24.93 b 21.48 b 4.29
Rate of disappearance(% hÿ1)
Protein 7.01 b 21.2 d 1.19 a 10.04 bc 13.82 c 1.43 DM 7.90 b 18.0 c 1.20 a 10.25 bc 13.55 bc 2.83
Effective ruminal degradability(%)
Protein 35.70 b 77.40 d 22.01 a 60.52 c 57.70 c 4.23
aLag time 7.4 h for protein disappearance in LS, 0 h for other dietary constituents and complete diets. bControl diet contained (as fed): 75% barley + 20% alfalfa.
cPelleted alfalfa. dRolled barley grain. eLentil screenings. fStandard error of the mean.
gWithin a row, means followed by different letters differ (p< 0.05).
digestibilities of DM, organic matter (OM) and neutral detergent fibre (NDF) linearly decreased (p< 0.001) with increasing dietary LS. Significant quadratic effects for DM (p< 0.05), OM (p< 0.05) , acid detergent fibre (ADF; p< 0.05) and NDF (p< 0.001) digestibilities with level of dietary LS, indicated that reductions in digestibilities as compared to those of control lambs were minor or non-existent with 12.5% dietary LS and severe for lambs receiving the 33% LS diet.
Although N intake, urinary excretion of N and measures of N digestion were not affected by the level of lentil screenings in the diet, N retention measures (g per day, % of N intake and % of N digested) were all linearly reduced (p< 0.01,p< 0.001,p< 0.01, respectively) with increasing dietary LS. Significant quadratic effects (p< 0.01) were also evident for LS level on N retention. Generally, N retention measures were reduced at least twofold for lambs receiving the 33% LS diet as compared to control lambs, while N retention of lambs receiving the 12.5% LS diet was moderately elevated as compared to that of control lambs.
3.3. Experiment 3: lamb feeding trial
Average daily gain, feed intake and feed conversion efficiency were reduced for ewe lambs as compared to ram lambs (Table 6). When all lambs in the study were considered, initial weight and final weight did not vary according to the level of LS in the diet, although average daily gain and feed intake linearly decreased (p< 0.01) with increasing dietary LS and feed conversion (feed per gain) linearly increased with increasing dietary LS. In contrast, when growth performance data were analysed by sex, level of dietary LS
Table 5
Effect of level of lentil screenings in diets on nutrient digestion and N metabolism in lambs Level of lentil screenings
in diet
SEMa Effect of level of screeningsb
0% (control) 12.5% 33% linear quadratic DM Intake (g dayÿ1) 1330.5 1478.0 1523.9 57.9 * NS
Digestibility(%)
Dry matter 68.3 68.2 63.2 0.7 *** * Organic matter 69.8 69.7 64.9 0.6 *** * Acid detergent fibre 26.0 31.7 23.8 2.0 NS * Neutral detergent fibre 42.2 46.4 26.9 1.2 *** *** N Intake (g per day) 39.7 41.5 43.9 1.7 NS NS Urinary N (g per day) 9.7 8.7 12.0 0.6 NS NS N digested (%) 70.3 69.3 68.6 1.1 NS NS N digested (g per day) 27.1 28.5 27.8 1.3 NS NS N retained (g per day) 5.5 7.0 1.9 0.7 ** ** N retained (% of N intake) 14.0 17.0 4.6 1.7 *** ** N retained (% of N digested) 20.4 24.8 7.3 2.1 ** **
aStandard error of the mean.
bControl diet contained (as fed): 62.5% barley grain + 12.5% canola meal + 20% alfalfa.
*Significant at p< 0.05; ** Significant at p< 0.01; *** Significant at p< 0.001; NS: Not significant,
(p> 0.05).
did not affect any growth performance traits of ewe lambs. For ram lambs, the effects of level of lentil screenings on growth performance traits were similar to the effects noted for when both rams and ewes were considered.
3.4. Experiment 4: ewe feeding trial
Ewes in the three treatment groups did not differ in initial condition score, initial weight or final weight (Table 7), although final condition score was higher (p< 0.05) for ewes receiving supplemental barley than the control or LS-supplemented ewes. When weight gain over the 50 days of the feeding study was considered, unsupplemented control ewes gained an average of 100 g, while barley and LS-supplemented ewes had higher (p< 0.05) gains of 1.84 and 2.04 kg, respectively.
The proportion of ewes lambing and lamb birthweight did not differ between the treatment groups. Prolificacy, the number of lambs born ewe per lambing, was lower (p< 0.05) in the LS-supplemented group than it was for the control- or barley-supplemented ewes. Lamb weaning weight at age 60 days was lower (p< 0.05) for the barley-supplemented ewes than for the other two treatment groups. The weight of lambs weaned ewe per breed was lower (p< 0.05) for LS-supplemented ewes as compared to control ewes, while the equivalent measurement for barley-supplemented ewes was intermediate to those of the control and LS-supplemented ewes.
Table 6
Effect of level of lentil screenings in feedlot diets for lambs on growth performance
Parameters Level of lentil screenings in diet (DM basis) Effect of level of screeningsa 0% (control)b 12.5% 25% 33% SEMc L
Number of lambs 11 12 12 12 ± ± Initial wt (kg) 27.0 26.5 26.1 26.4 0.2 NS Final wt (kg) 44.1 44.3 43.3 42.1 1.3 NS Average daily gain (g) 347 291 291 236 17 *** Feed intake (g DM per day) 1405 1377 1343 1172 48 ** Feed conversion (feed per gain) 4.2 4.8 4.7 5.1 0.2 **
Rams
Average daily gain (g) 427 330 317 240 21 ** Feed intake (g DM day) 1516 1421 1372 1074 75 ** Feed conversion (feed per gain) 3.5 4.3 4.4 4.7 0.2 *
Ewes
Average daily gain (g) 268 253 264 235 21 NS Feed intake (g DM per day) 1294 1333 1315 1269 62 NS Feed conversion (feed per gain) 4.9 5.4 5.0 5.5 0.2 NS
aLinear effect, no quadratic effects were significant (p> 0.05).
bControl diet contained 62.5% barley grain, 12.5% canola meal and 20% alfalfa. cStandard error of the mean.
*Significant at p< 0.05; ** Significant at p< 0.01; *** Significant at p< 0.001; NS: Not significant
(p> 0.05).
3.5. Costs of feeding lentil screenings
For the lamb feeding study, actual 1997 and 1998 feed costs kg per gain are shown in Table 8, along with estimates for feed costs in 1999. Although costs for feed ingredients fluctuate widely, using 1997 and 1998 costs and estimates for 1999, in all cases the least-cost feeder lamb diet contained 25% LS. For the ewe feeding study, least-costs of feeding LS would have two components: (1) actual ewe feed costs during mid-pregnancy; (2) loss of income from reduction in lamb crop compared to unsupplemented controls. Assuming a market value of early-weaned feeder lambs of Can$ 2.00 per kg liveweight,
Table 7
Effects of supplementation in the second trimester of pregnancy with lentil screenings or barley grain on ewe weight and condition score and subsequent lambing performancea
Treatment Barley silage
Initial condition score 3.3 3.4 3.3 0.07 Final condition score 3.2 a 3.4b 3.2 a 0.05 Initial weight (kg) 90.3 90.9 87.4 2.5 Final weight (kg) 91.3 93.3 90.5 1.8 Weight gain (kg) 0.1 a 1.84 b 2.04 b 0.7
Lambing and weaning data
Proportion ewes lambing 95.8 90.6 89.4 4.0 Prolificacy (lambs born per ewe) 1.9 b 2.0 b 1.a 0.1 Lamb birthweight (kg) 4.9 4.7 4.9 0.7 Lamb weaning weight (kg) 22.1 b 20.4 a 23.1 b 0.8 Lamb weaned per ewe bred (kg) 32.6 b 28.4 ab 26.4 a 2.1
aWithin a row, means followed by different letters differ (p< 0.05). bStandard error of the mean.
Table 8
Cost of gain estimates for lamb feedlot diets in which barley and canola meal are replaced with lentil screenings (LS).
Predicted least-cost diet (% LS) 25 25 25
aBased on actual values at the time of the study, fall 1997 where barley = Can$ 140/t, canola meal = Can$
235/t and lentil screenings = Can$ 90/t.
bBased on actual values, fall 1998, where barley = Can$ 115/t, canola meal = Can$ 140/t and lentil
screenings = Can$ 75/t.
cAssuming low-priced barley at Can$ 90/t, canola meal at Can$ 157/t and lentil screenings at Can$ 60/t.
supplementing ewes in mid-gestation with barley or LS would potentially result in lost lamb income of Can$ 8.40 and Can$ 12.40 per ewe, respectively, and an additional feed costs of approximately Can$ 2.00 and 1.00 per ewe compared to unsupplemented ewes.
4. Discussion
4.1. In situ disappearance
As40% of LS consisted of lentil fragments, pea fragments, fine weed seeds, chaff and dust (Table 1), LS were not ground before in situ incubations to prevent excessive loss of DM from the bags. It was expected that the cereal grains and intact lentils present within LS would have been sufficiently battered by the seed cleaning process, that they along with the lentil and pea fragments would have been accessible to microbial degradation. Microbial colonization of feed grains has been demonstrated (McAllister et al., 1990; Wang et al., 1999) to proceed once the pericarp is broken. The barley used in situ was whole, and only lightly rolled to break the pericarp. Similarly, the pericarp of an estimated 80% of lentils in the LS used in situ was also broken. Although lentils had a higher surface area and equivalent weight to barley kernels (data not shown), LS were highly resistant to microbial attack. As microbial digestion of complete diets containing LS, was not inhibited to the same extent as that of 100% LS, damage to the lentil pericarp may not be enough to promote microbial colonization. Consequently, LS should be hammer milled to a particle size of 3 mm or less, or ground to promote digestion by rumen microbes.
In the present study, the most abundant weed seed (by weight) in LS was stinkweed (Thlaspi arvense) which contains high levels of glucosinolates (7±8% on DM basis; Beames et al., 1986). Glucosinolates are metabolized in the rumen to form isothiocyanate which can lead to gastric upset, reduced palatability of feed, depressed growth, goitre and anaemia (Cheeke, 1998). Blackshaw and Rode (1991) found stinkweed seed resistant to digestion in the rumen, retaining 98% viability after 12 h rumen incubation. Other constituents of LS which would be resistant to microbial digestion in situ would include whole canola (Wang et al., 1997) and inorganic matter (dust and small stones).
In addition to effects of processing, the minor changes in soluble fractions of CP and DM, rates of disappearance of CP and DM and EDCP values observed for complete diets containing 20% or 33% LS as compared to 100% LS may also be due to a dilution of the antinutritional/microbial digestion-resistant factors of LS. Unless a threshold level is reached for an antinutritional factor, effects on microbial fermentation would likely be minimal (Paduano et al., 1995), especially when exposure to the factor was of relatively short (14 days) duration.
4.2. Apparent digestibility
Reduction in digestibilities of DM, OM and NDF with increasing dietary LS could be partly attributed to the previously discussed anti-nutritional factors in LS and also to the inherent indigestibility of some of the components of LS. Due to the low digestibility
(43±46%) of lentil straw (Erskine et al., 1990), lentil chaff likely has a low digestibility. The digestibility of many of the weed seeds present in LS is also likely low based on the in situ study of Blackshaw and Rode (1991). The DM, OM and ADF digestibility values reported by Tait et al. (1986) for sheep receiving 30% refuse screenings are in accord with those of the present study for the 33% LS diet. The refuse screenings used in the study of Tait et al. (1986) likely contained many of the weeds present in LS and had levels of inorganic matter and ADF similar to those of LS.
In a study comparing N retention on diets consisting of legume seeds (pea, fenugreek, faba bean, common vetch, lentil), sheep were in negative nitrogen balance for the lentil diet, but retained 1.46±4.37 g N per day on non-lentil diets (Guada-Vallepuga, 1972). Although no lambs in the present study had a negative nitrogen balance, N retention was lowest for lambs receiving the 33% LS diet. The reduced N retention with increased dietary LS was not due to elevated levels of acid detergent insoluble N (ADIN) in the LS, as ADIN levels were comparable among all diets (Table 2). Bell and Keith (1986) attributed a reduced digestibility of CP for pigs receiving lentil diets to possible enzymatic trypsin inhibitors. As trypsin inhibitors are digested and rendered ineffective by rumen microbes (Maynard et al., 1979), other factors must have caused the negative nitrogen balance of the sheep in the study of Guada-Vallepuga (1972).
Lentils have been recognized (Bhatty et al., 1976; Savage, 1988) as having limiting levels of sulfur-containing amino acids such as methionine and cysteine. Lentils also contain significant amounts of tannins (0.27±0.40% expressed as catechin equivalents; Davis, 1981) which are detoxified by methylation, further limiting the availability of cysteine and methionine (Savage, 1988). Relative to pigs or cattle, sheep have a high requirement for sulfur-containing amino acids, particularly cysteine, in order to support wool growth (Russel, 1992). Consequently, N retention may be impaired in sheep consuming a high proportion of lentils due to restricted availability of cysteine and methionine. Lentil screenings in the present study had tannin concentrations of 1.4% (expressed as catechin equivalents), higher than those reported by Davis (1981), but likely due to differences in methodology between studies (Reed, 1995). Tannin concentrations of 1.4% have been reported to reduce N digestion in sheep but would have to be increased fourfold to elicit a similar reduction in fibre digestion (Min et al., 1998). Accordingly, the reduced digestibility of NDF with increasing dietary LS is likely due to factors other than tannins present in LS.
4.3. Lamb growth trial
The impaired N retention and lowered digestibilities of DM, OM and NDF with increasing dietary LS for lambs were consistent with the linearly decreased ADG and reduced feed conversion efficiency with increasing LS for individually-fed lambs on the growth trial. One difference noted between the digestibility and growth trials was in feed intake. Feed intake was linearly reduced with increasing dietary LS (p< 0.01) for lambs on the growth trial, but increased with dietary LS on the digestibility trial. Dietary preferences of sheep are known to be highly individual (Phy and Provenza, 1998) and the six rams on the digestibility trial might have found LS more palatable than did the 47 lambs in the individual feeding study. Additionally, it has been established (Provenza,
1995) that variable lengths of time are required based on post-ingestive feedback in order to set ruminant feed intake/preferences.
Although all diets in the individual feeding study had a CP content of 17% or greater on a DM basis and CP content of the diets should have not been limiting according to NRC recommendations (NRC, 1985) the CP available for rapidly growing ram lambs may have been limited by the anti-nutritional/digestion-resistant factors in LS. In contrast to ram lambs, the growth performance of ewe lambs was not affected by level of dietary LS. Likely, the lower growth rate of ewes (25121 g per day) compared to rams (33021 g per day) and consequently lower CP requirement of the ewe lambs were responsible for the lack of effect of LS on ewe lamb growth performance.
4.4. Ewe feeding study
The higher weight gain of ewes supplemented during the 50-day feeding period with barley grain or LS compared to control ewes would be expected due to the increased density of energy and protein in barley grain and lentil screenings compared to 31.5% DM barley silage. However, the reduction in prolificacy of lentil-supplemented ewes compared to control ewes was not anticipated. The second trimester of pregnancy is the period of maximum growth and development of the placenta (Mellor, 1983). Perhaps anti-nutritional factors in the LS impaired the development of the placenta and led to embryonic mortality in the LS-supplemented ewes. Another possible explanation may be the inverse relationship established by Parr et al. (1993) between feed intake and plasma progesterone concentration of pregnant ewes. Provided the nutritional requirements of the ewes are met, additional protein or energy supplements in mid-pregnancy may be detrimental to ewe prolificacy. Hatfield et al. (1998) found that ewes which had received a low level (68 g per day protein or 136 g per day energy) of supplements in mid-pregnancy had reduced numbers of lambs born per ewe as compared to unsupplemented, grazing ewes.
As ewes are able to supply more milk to a single than a twin (Peeters et al., 1992; Ramsey et al., 1998), weaning weight was lower for lambs of barley as compared to LS-supplemented ewes. The trend toward both lower birthweights and marginally higher prolificacy was likely responsible for the reduced lamb weaning weight of barley-supplemented as compared to unbarley-supplemented ewes. Lower birthweight has a negative impact on lamb survival (Schoenian and Burfening, 1990; Russell et al., 1992), which could have reduced the weight of lambs weaned per ewe bred for the barley-supplemented as compared to the unbarley-supplemented ewes.
Weight of lambs produced annually for each breeding ewe has been recognised as the economic trait that is most important to commercial sheep enterprises (Ercanbrack and Knight, 1998). Supplementing ewes in the second trimester of pregnancy with either barley or LS did not improve lamb production per ewe, and in the case of LS-supplemented ewes, the weight of lambs weaned per ewe exposed was significantly lower (p< 0.05) compared to unsupplemented ewes. Based on the results of this study, the utility of protein and/or energy supplementation to adequately nourished ewes in the second trimester of pregnancy is questionable. Although the cause of the reduced prolificacy of ewes receiving LS in mid-gestation is unknown, LS of similar composition
to that of the present study should not be used as a protein/energy supplement for ewes in the second trimester of pregnancy receiving barley silage-based diets.
5. Conclusions
As with many byproduct feeds, lentil screenings vary in composition. Nutritional value would be influenced by the level of weed seeds and other contaminants (dust, rocks, insects) present in the LS. Lentil screenings similar in composition to those used in our studies represent a valuable feed resource for early-weaned lambs, although for maximum lamb performance, LS should not exceed 25% of the diet. In contrast, supplementing barley silage diets of ewes in mid-pregnancy with LS was detrimental to ewe productivity, while supplementing ewes with barley was not beneficial. Conse-quently, the use of protein or energy supplements during mid-pregnancy is questionable, provided that the ewes enter a rising plane of nutrition during the last trimester of pregnancy.
Acknowledgements
The authors wish to thank Westco for the donation of the lentil screenings, the Western Canadian Sheep Research Committee for funding this study and the Canada-Alberta Livestock Research Trust for provision of the lambs and ewes. Recognition is also due to Andy, Brian and Ray of the LRC Sheep Crew for their excellent feeding and care of ewes and lambs on this study. Thanks also to Wendi Smart for her skilful technical assistance and to Walt Strand of Strand Suffolks for suggesting the topic of lentil screenings.
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