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Napier or groundnut hay as supplements in diets of sheep consuming poor quality natural pasture hay 1. Effect on intake and digestibility
Livestock
Production
Science 49 (1997) 33-41
Napier or groundnut hay as supplements in diets of sheep consuming poor quality natural pasture hay 1. Effect on intake and digestibility B. Manyuchi
a-*, F.D. Deb Hovel1 b, L.R. Ndlovu ‘, J.H. Topps ‘, A. Tigere d a Africa University, P.B. 1320, Mutare, Zimbabwe b Rowett Research Institute, Aberdeen, ScotlandAB2 9SB, UK ’ University of Zimbabwe, Harare, Zimbabwe * Grasslands Research Station, Marondera, Zimbabwe Accepted
11 February
1997
Abstract
Three experiments, each of a 5 X 5 Latin square design, were carried out using sheep to assess the effect of supplementing poor quality natural pasture (veld) hay with graded levels of napier or groundnut hay on intake and digestibility. In Expt 1, napier hay was fed at 0, 100, 200, 300 g/day or ad libitum. In Expt 2 the same levels of feeding were used with groundnut hay, while in Expt 3 napier and groundnut hay were each fed at 0, 150 or 300 g/day to enable a direct comparison of the two supplemental forages. All the forages used were chopped to a particle size of about 1 cm prior to feeding. The veld hay was supplemented with 1 percent urea and was always offered ad libitum. The forage supplements were fed separately. In all the experiments, the forage supplements increased total feed intake (P < 0.05). In Expt 1, total feed intake was greatest with the daily supplement of 300 g napier. The forage supplements did not reduce intake of veld hay. After correcting for differences in the digestibility, intake of veld hay was always greater than anticipated if there had been simple substitution. Although the forage supplements increased digestibility, differences were only significant (P < 0.05) between the 0 and 300 g forage supplemented diets. In all the experiments, nitrogen retention was also increased by supplementation (P < 0.05). Response to supplementation was similar between groundnut and napier. These results demonstrated that small amounts of forage supplements can be effective in increasing nutrient intake when animals consume poor quality forages. 0 1997 Elsevier Science B.V.
1. Iutroduction The use of high quality forage supplements in diets for ruminants consuming low quality forages continues to receive considerable attention. M&t of the research has involved the use of legume forages
* Corresponding
author.
0301-6226/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SO301-6226(97)00019-S
(e.g. Minson and Milford, 1967; Siebert and Kennedy, 1972; Mosi and Butterworth, 1985) and high quality grass (Mbatya et al., 1983; Silva, 1985). In all the experiments, forage supplements increased total feed intake. With low levels of forage supplementation, some increase in the intake of the poor quality forage above the level achieved with the unsupplemented diet was observed. As the level of forage supplement is increased, especially beyond 20
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B. Manyuchi et al. / Livestock Production Science 49 (1997) 33-41
to 40 percent, the intake of the basal diet falls below the level achieved with the unsupplemented basal diet. Since in many of the experiments reported, the basal diet was deficient in nitrogen, this has led to the hypothesis that the increase in feed intake is due to the stimulatory effect of increased dietary nitrogen intake, while the substitution is due to the bulk effect of the legume forage. However, in other experiments (e.g. Silva, 1985; Manyuchi et al., 1992), similar responses to forage supplements have been observed when the basal diet was supplemented with nitrogen, suggesting that the response can not be entirely due to nitrogen. Most of the reported experiments show a consistent increase in vivo digestibility of the total diet (Minson and Milford, 1967; Mosi and Butterworth, 1985; Smith et al., 1989). However, in some of these experiments, it has not been possible to show any positive associative effect of the high quality forage on the digestibility of the low quality forage. Siebert and Kennedy (1972) observed very small and nonsignificant improvements in digestibility of the diet, although total feed intake was increased substantially. The authors concluded that digestibility of the high quality forage was probably decreased as the level of supplemental forage was increased due to increased rate of digesta passage. The current study was therefore carried out to examine changes in feed intake and digestibility, when a basal diet of poor quality natural pasture (veld) has was supplemented with either groundnut or napier hay.
2. Materials and methods Veld hay was supplemented with amounts of napier (Expt 1) or groundnut 2). In Expt 3 different levels of napier or hay were used in the same experiment direct comparison of the supplements.
different hay (Expt groundnut to enable
2.1. Source of forages Veld hay was harvested, when the natural pasture was mature and dormant. The hay consisted of a mixture of grasses dominated by Hyperrhenia species. Napier hay was from a hybrid cross between napier
grass (Pennisetum purpureum) and pearl miller (Pennisetum americanum). The napier was grown as a single sward and the hay was harvested during the wet season at approximately 1 m height (4 weeks growth) and was chopped and sun dried. Groundnut (Arachis hypogea) hay was harvested when the crop was mature. After removing the pods the forage was sun-dried for approximately 3 days. All forages were chopped prior to feeding using a hammer mill fitted with a 14 mm screen to achieve a particle size of about 1 cm. 2.2. In sacco degradation of forages In sacco degradation of veld hay, napier hay and groundnut hay was determined in steers using the nylon bag method outlined by Orskov et al. (1980). Four Hereford X Nkone steers with an average weight of 550 kg and each fitted with rumen cannulae of 900 mm internal diameter were used. The steers were housed in individual pens and offered a standard diet of high quality star grass (Cynodon nefluensis) hay ad libitum. After an adaptation period of 21 days, 2 g samples of veld hay, napier hay or groundnut hay milled through a 3 mm screen, were placed in nylon bags and incubated in the rumen for 6, 12, 24, 48, 72 and 96 hours. After incubation, the samples were rinsed under running tape water and oven dried at 60°C for 24 hours in order to estimate dry matter (DM) loss by difference. Samples of forages were placed in the nylon bags and washed without incubation and dried to give an estimate of ‘zero’ time loss of DM. Soluble DM loss was determined by washing the forage samples through filter paper (Whatman No 1) using warm water. DM losses to rumen in sacco incubation were fitted to a non-linear negative exponential model given by: p = a + b( 1 - epC’) (Orskov and McDonald, 1979). Where p is the degradation loss at time ‘t’ hours, a is the intercept by &rapolation of the degradation curve to t = 0, b is the asymptote of the exponential and c is the fractional rate constant of the exponential. The total amount of material potentially degradable is given by a+b.
B. Munywhi et al. /Livestock
2.3. Intake and digestibility studies 2.3.1. Animals
Five male sheep of the Dorper X Merino breed with an average live weight of 65 (+0.6 kg were used in each experiment. The sheep had been fitted with rumen cannulae of 3 cm internal diameter. In each experiment, the sheep were allocated to five dietary treatments in a 5 X 5 Latin square design. The three experiments did not use the same five sheep. 2.4. Dietary treatments 2.4.1. Experiment
1
Five dietary treatments were formulated in which veld hay with 1% urea fed ad libitum alone (Control) or the Control diet supplemented with either 100 g napier hay (100 Nap), 200 g napier hay (200 Nap) or 300 g Napier hay (300 Nap). The fifth diet was napier hay fed ad libitum on its own. 2.4.2. Experiment 2 Five dietary treatments were formulated as in Expt 1, with the exception that groundnut hay was used as a supplement i.e. Control, Control + 100 g groundnut hay (100 Gnut), Control + 200 g groundnut hay (200 Gnut), Control + 300 g groundnut hay (300 Gnut) or groundnut hay fed ad lib&m on its own (Gnut). 2.4.3. Experiment 3 Five diets were used in this experiment. In common with Expts 1 and 2, veld hay with 1% urea was used as a basal diet. The basal diet was fed either alone (Control> or supplemented with 150 g or 300 g of either napier hay or groundnut hay (150 Nap, 150 Gnut, 300 Nap, 300 Gnut respectively). In all the experiments, the supplemental forages were fed at 0890 h and consumed within 30 minutes after which veld hay was offered ad libitum for the rest of the day. 2.5. Management
of the animals and measurements
The sheep were housed in individual pens. Each pen had separate water and feed troughs. During each experimental period of the Latin square, collec-
Production Science 49 (1997133-41
35
tion of excreta and intake measurements were carried out after a minimum of 21 days adaptation to the diet. At the end of the adaptation period, the animals were moved into metabolism crates to enable total collection of the dung and urine. The measurement period lasted for 5 days. During the period, the weight of faeces and urine produced by each animal were recorded at 0890 h every morning. Faeces were then dried at 60°C for 48 hours and re-weighed to give daily faecal DM excretion. A sub-sample of about 10 percent of total was taken and milled trough a 2 mm screen prior to analysis. Daily urine was collected over 5 ml of 20 percent sulphuric acid, bulked and a sub-sample of about 10 percent of total was taken at the end of the collection period and stored at - 16°C pending analysis for nitrogen. Daily feed refusals were dried at 60°C for 48 hours and weighed to give DM refused. A representative of the feed was taken and dried in a similar manner in order to obtain an estimate of DM content of feed which was then used to calculate DM offered daily. Daily DM intake was calculated as the difference between DM offered and DM refused. 2.6. Veld hay equivalent of napier hay supplement The veld hay equivalent of the supplement (V,) was calculated by multiplication of the intake of the napier supplement (Z,) by the ratio of the measured digestibility of the veld hay given alone (I$) to the calculated digestibility of the napier supplement (5,) in the mixed diets. Thus:
v,=r,x; d
The calculated digestibility of the supplement (5,) was estimated as the intercept of the linear regression of diet digestibility (dependent variable) on the proportion of veld hay in the diet (independent variable). Anticipated intake of veld hay was calculated by subtracting the veld hay equivalent of the supplement from the intake of veld hay on the unsupplemented Control diet. The gain in veld hay intake was calculated as the difference between the anticipated intake and the observed intake of veld hay.
36
B. Manyuchi et al. /Livestock Production Science 49 (1997) 33-41
3. Analysis
Table 2 In sacco dry matter degradation (%o)of the experimental forages determined in the mmen of tistulated steers
3.1. Chemical analysis
The DM content of samples was determined in a forced draught oven at 60°C for 48 hours, ash was determined by incineration in a muffle furnace at 550°C for 12 hours, nitrogen was analyzed using the kjeldhal method and neutral and acid detergent fibre were analyzed using the method of Goering and Van Soest (19701. 3.2. Statistical analysis Data from each Latin square were analyzed using analysis of variance procedure for a balanced Latin square design with 12 degrees of freedom in the residual. Differences between treatment means were tested using t-test.
4.1. Chemical analysis When compared with groundnut and napier hay, veld hay had a very low nitrogen (N) and high fibre content (Table 1). Over 60% of the total nitrogen in veld hay was associated with ADF. The percentage of total N associated with the ADF fraction was 36% and 21% for groundnut and napier hay respectively. In vitro DM digestibility were lowest with veld hay, but similar for groundnut and napier hay. Table 1 Chemical composition and in vitro digestibility of veld hay, napier hay and groundnut hay Veld
’ Tilley and Terry (1963).
In sacco degradation Incubation time (h) 6 IL
24 48 72 96 Degradability constants d 6 a+b c (I/h)
Napier hay
Groundnut hay
5.64 13.17 7.53
20.28 31.53 11.25
26.98 37.35 10.37
9.48 21.68 28.10 42.58 52.80 58.13
37.06 51.17 65.20 76.72 81.15 83.94
50.96 60.02 66.22 71.46 72.78 73.73
4.50 61.76 66.26 2.09
21.57 61.62 83.19 5.21
40.36 32.35 72.7 1 6.93
a Determined by washing forage samples through a filter paper (Whatman No. 1). b Determined by washing samples through nylon bags. ’ Zero time washing loss minus water soluble fraction. d Constants in the model: p = a+dl - e-“1 (0rskov and McDonald, 1979).
4. Results
Dry matter(g/kg) Ash (g/kg DM) Nitrogen (g/kg DM) Neutral Detergent Fibre (g/kg DM) Acid Detergent Fibre (g/kg DM) Nitrogen in ADF (g/kg DM) In vitro DM digestibility ’
Water soluble DM (%) a Zero time washing loss (%) b Loss of small particles (%) ’
Veld hay
hay
Napier hay
Groundnut hay
901 115 3.8 848
897 65 22.1 700
916 70 21.0 455
524
329
330
2.4 0.384
4.6 0.672
7.7 0.649
4.2. In sacco DM degradation of forages Both DM solubility and ‘zero’ time DM loss were very low on veld hay (Table 2). Groundnut hay had DM solubility that was 25 and 79% higher than that of napier and veld hay respectively. The degradation curve for veld hay had a flat shape, which resulted in an overestimation of the asymptote. Compared with veld hay and napier, groundnut hay had the smallest and least degradable ‘b’ fraction. The rate of DM degradation of veld hay was 5 to 9 times slower than that of napier and groundnut hay respectively (Table 21. 4.3. Dry matter intake Expts 1 and 2 (Tables 3 and 4) where the supplemental forage was fed on its own, intake was substantially greater than when veld hay was fed on its own or when veld hay was supplemented with napier or groundnut hay. However in Expt 1 intake was similar (P > 0.05) on 300 Nap and Nap diets. In In
37
B. Manyuchi et al. /Livestock Production Science 49 (1997) 33-41
Table 3 Expt 1. Feed intake measured in sheep given veid hay with 1% urea alone (Cont), napier hay alone (Nap) or veid hay with 1% urea plus 100 g, 200 g or 300 g napier hay (100 Nap, 200 Nap, 300 Nap, respectively). Values am means of five observations) SED
Diet Cont
100 Nap
200 Nap
300 Nap
Nap
Dry matter intake (g/d): Veld hay
812
889
846
987
0
_
Napier hay Total Total (g/W 0.75) Napier hay in the diet (%) Veld hay equivalent of napier supplement Anticipated veld hay intake (g/d) d
0 812 ’ 35.7 a 0 812
89 978 a,b 43.1 a.b 9 72 740
178 1025 b 41.5 a,b 17 145 667
267 1254 ’ 55.3 b 21 212 595
1194 1194 b,c 52.6 b 100 _ -
99.4 8.1 _ _ _
149
179
392
(g) d
Gain in veld hay intake (g) d a,b,c Means in the same row with different superscripts d See text for details.
are significantly
different (P < 0.05).
Table 4 Expt 2. Feed intake measured in sheep given veld hay with 1% urea alone (Cont), groundnut hay alone (Gnut) or veld hay with 1% urea plus 100 g, 200 g or 300 g Gnut hay (100 Gnut, 200 Gnut, 300 Gnut, respectively). Values are means of five observations) SED
Diet
Dry matter intake (g/d): Veld hay Groundnut hay Total Total (g/W 0.75) Groundnut hay in the diet (%) Veld hay equivalent of Gnut supplement(g) Anticipated intake of veld hay d Gain in veld hay intake (n) d qb’c Means in the same row with different
Cont
100 Gnut
200 Gnut
300 Gnut
Gnut
912 0 912 a 48.4 ’ 0
896 90 986 a.b 52.1 a,b 9 56 856 40
905 180 1085 b 57.5 b 17 111 801 104
785
0
_
270 1055 b 56.0 b 26 167 745 40
1656 1656 ’ 87.8 ’ 100 _ _ -
58.0 4.6 -
912
d
superscripts
are significantly
different (P < 0.05).
d See text for details.
Table 5 Expt 3. Feed intake in sheep fed a basal diet of veld hay with 1% urea alone or supplemented with 150 g or 300 g of napier or groundnut hay (150 Nan, 150 Gnut, 300 Nan, 300 Gnut. resnectivelv). Values are means of five observations Diet
SED
Cont
150 Nap
150 Gnut
300 Nap
300 Gnut
997 0 997 = 46.0 = 0 997
996 135 1131 a 52.3 a*b 12 107 890 106
956 135 1091 a 50.3 a.b 12 126 871 85
944 270 1214 b 56.0 b 22 214 783 161
989 270 1259 b 58.4 b 21 252 745 244
Dry matter intake (g/d): Veld hay Supplement Total Total (g/W 0.75) Supplement in the diet (%) Veld hay equivalent of supplement (g) ’ Anticipated intake of veld hay (g/d) ’ Gain in veld hay intake (g) ’
ab Means in the same row with different superscripts ’ See text for details.
are significantly
different (P < 0.05).
71.5 71.5 4.5
38
B. Manyuchi et al. /Livestock Production Science 49 (1997) 33-41
Table 6 Expt 1. Digestibility and nitrogen retention measured in sheep given veld hay plus 1% urea alone (Cod), napier hay alone (Nap) or veld hay with 1% urea plus 100 g, 200 g or 300 g napier hay (100 Nap, 200 Nap, 300 Nap, respectively). Values are means of five observations) Diet
Total DM intake (g/d) Total N intake (g/d) Faecal DM excretion (g/d) Faecal N excretion Urinary N excretion Apparent total DM digestibility Nitrogen retention (g/d)
SED
Cont
100 Nap
200 Nap
300 Nap
Nap
812 a 6.50 a 410a 4.34 B 1.21 a 0.458 a 0.94 B
978 a*b 9.08 b 527 b 5.23 a,b 1.53 B 0.461 a 2.32 ’
1025 b 10.04 = 562 b 5.47 a,b 1.61 a 0.451 a 2.96 aSb
1254 = 14.53 d 593 b 6.14 b 1.70 a 0.527 b 6.69 b
1194 b-c 26.26 e 450 Kb 9.15 c 8.10 b 0.623 ’ 9.16 ’
‘b*c Means in the same row with different
superscripts
are significantly
Expt 1, intake of veld hay was increased by supplementation with napier hay. In Expt 2, intake of veld hay tended to be depressed with the highest level of groundnut hay supplementation (300 Gnut diet) while in Expt 3 (Table 51, supplementation with groundnut or napier hay did not cause a change in intake of veld hay. In all the three experiments, intake of veld hay was always above the intake anticipated had the effects of the supplement been one of simple replacement after correcting for differences in the digestibility of veld hay and the supplemental forage (Tables 3-5). 4.4. Digestibility In all the experiments digestibility of dry matter (DM) was increased by supplementation (P < 0.05; Tables 6-8). In Expts 1 and 2, digestibility of DM
99.4 1.26 40.3 1.26 1.87 0.023 2.00
different (P < 0.05).
and OM of napier and groundnut hay when fed alone were higher than the other diets (P < 0.05). The relationship between DM digestibility (Y) and proportion of veld hay in the diet (X) was calculated using linear regression. The value of the intercept (0.659 k 0.051, 0.779 * 0.038 for Expts 1 and 2, 0.65 f 0.041 and 0.587 f 0.035 for napier and groundnut hay in Expt 3) and representing digestibility of the forage supplement used to calculate the veld hay equivalent of the supplement as described previously. Faecal DM excretion was increased by supplementation. In all the experiments there was a linear (P < 0.05) relationship between DM intake (Y) and faecal DM excretion (X); Y = 0.33X + 165.19 (r = 0.712; Expt 11, Y = 3.01X - 384.06 (r = 0.839; Expt 2) and Y = 1.79X + 158.79 (r = 0.825; Expt 3).
Table 7 Expt 2. Digestibility and nitrogen retention measured in sheep given veld hay with 1% urea alone (Con& groundnut hay alone (Gnut) or veld bay with 1% urea plus 100 g, 200 g or 300 g Gnut hay (100 Gnut, 200 Gnut, 300 Gnut, respectively). Values are means of five observations) SED
Diet
Total DM intake (g/d) Total N intake (g/d) Faecal DM excretion (g/d) Faecal N excretion (g/d) Urinary N excretion (g/d) Apparent DM digestibility Nitrogen retention (g/d)
Cont
100 Gnut
200 Gnut
300 Gnut
Gnut
912 a 7.03 a 471 a 5.36 ’ 0.79 a 0.484 a 1.14 a
986 a*b 9.06 ’ 475 a 4.94 a 0.64 a 0.517 =sb 3.50 b
1085 b 11.42 b 504a 6.34 a.’ 0.85 ’ 0.533 b 4.19 b
1055 b 12.42 ’ 480 = 5.98 aSb 0.95 b 0.546 b 5.49 b
1656 ’ 34.78 d 604b 7.86 b 3.06 h 0.636 ’ 23.86 ’
ab’c Means in the same row with different superscripts
are significantly
different (P < 0.05).
58.0 1.09 35.9 0.83 0.22 0.020 1.00
39
B. Manyuchi et al. / Livestock Production Science 49 (1997) 33-41
Table 8 Expt 3. Digestibility napier or groundnut
and nitrogen retention in sheep fed a basal diet of veld hay with 1% urea alone or supplemented with 150 g or 300 g of hay (150 Nap, 150 Gnut, 300 Nap, 300 Gnut, respectively). Values are means of five observations SED
Diet
Total DM intake (g/d) Total N intake (g/d) Faecal DM excretion (g/d) Faecal N excretion (g/d) Urinary N excretion (g/d) DM digestibility N retention (g/d)
Cont
150 Nap
150 Gnut
300 Gnut
300 Gnut
997 = 7.97 = 494 a 4.93 1.53 0.505 = 1.51 a
1131 a 11.00 b 549 a 5.97 1so 0.515 a 3.93 b
1091 a 11.32 b 546 a 5.33 1.64 0.500 a 4.35 b
1214 b 13.62 ’ 662 b 5.93 1.72 0.545 b 5.98 ’
1259 b 13.99 c 666 b 5.94 1.38 0.529 ab 6.67 ’
‘b,c Means in the same row with different
superscripts
are significantly
4.5. Nitrogen retention
The nitrogen retentions obtained in the three experiments and given in Tables 6-8, show that supplementation increased nitrogen retention in all cases. The all napier and all groundnut hay diets gave the highest nitrogen retention values (P < 0.05).
5. Discussion 5.1. Intake of ueld hay
In Expt 1 and 3, increasing amounts of forage supplements did not cause a decrease in veld hay intake relative to intake of veld hay on the unsupplemented Control diet. In Expt 2, there was some indication of substitution, with 26 percent groundnut hay supplement causing a 14 percent decrease in the intake of veld hay. In most experiments where forage supplements have been used, it has been shown that high levels of forage supplements will cause substitution of the basal diet, i.e. intake of the basal diet on the supplemented diet will be lower than on the unsupplemented Control diet. Minson and Milford (1967) postulated that substitution resulted from the bulk effect of the forage supplement. When compared with concentrates, forage supplements have a lower soluble fraction and a high fraction that degrades with time. It is conceivable that forage supplements will cause greater substitution of the basal diet compared to concentrates.
71.5 0.57 30.9 0.37 0.19 0.014 0.54
different (P < 0.05).
In considering substitution it is not accurate to calculate it on a 1:l basis. Differences in the digestibility of the basal diet and the supplement should be corrected for as the two feeds will have different contribution to bulk per unit weight. The higher digestibility of the supplement implies that the supplement will occupy less space in the rumen compared with veld hay. In this study the veld hay equivalent of the forage supplement was calculated by correcting for the differences in the digestibility of the forages. The digestibility of the supplement was estimated by regression to reduce errors due to effect if changes in outflow rate on the digestibility of the supplement. Despite the low correlation between level of supplement and digestibility of the supplement was the most appropriate. The low correlation coefficients were caused by the low and nonsignificant change in digestibility following supplementation. When substitution is calculated after correcting for digestibility, it is evident that forage supplements increased intake of veld hay above the level anticipated if there was simple substitution. 5.2. Digestibility One of the benefits of using high quality forage supplements is that they supply rumen degradable nitrogen which is deficient in poor quality forages. The additional nitrogen supplied by the forage supplement will stimulate rumen digestion resulting in an increase in feed intake (0rskov, 1994). In the current study, digestibility of the diet tended to be increased by supplementation, with differences being
40
B. Manyuchi et al. / Lioestock Production Science 49 (1997) 33-41
significant only between the Control and the highest level of forage supplementation. The digestibility figures show no evidence of positive associative effects of the forage supplement on digestibility of the poor quality veld hay. This lack of a positive associative effect of the supplement on digestibility of veld hay was confirmed by the lack of improvement in in sacco degradability of veld hay (see second paper in this series). Siebert and Kennedy (1972) observed very little change in the in vivo digestibility of the diet following supplementation of poor quality pangola hay with luceme. The authors concluded that the digestibility of the supplemental luceme was probably reduced due to the high rate of passage of digesta associated with an increase in feed intake as a result of supplementation. In the current study, the increase in total feed intake was associated with an increase in faecal excretion (r = 0.71 to 0.82), evidence that digesta outflow was increased by supplementation. These results suggest that with poor quality forages, an increase in feed intake does not always result from an improvement in digestibility per se. 5.3. Nitrogen retention In the current study, forage supplements increased nitrogen retention. Similar results are reported in the literature (e.g. Mosi and Butterworth, 1985; Smith et al., 1989). 5.4. Differences between napier and groundnut hay Groundnut and napier hay differed in degradability patterns (Table 2). Groundnut hay had a large soluble fraction and a small fraction that degrades with time, while napier hay had a smaller soluble fraction and a large fraction that degrades with time. These differences are typical of the differences between legumes and grasses (Van Soest, 1982). The results of this study show no meaningful differences between groundnut and napier when they supplemented veld hay. 6. Conclusion This study confiis the benefits of forage supplements in increasing intake of nutrients when animals
consume poor quality forages. The absence of significant substitution of veld hay by napier or groundnut indicate an efficient use of the high quality forage supplement.
Acknowledgements This study was sponsored by the Overseas Development and Natural Resources Institute (UK) and the Ministry of Lands, Agriculture and Water Develop ment (Zimbabwe). We grateful to staff at the Rowett Research Institute (Scotland, UK) and Grasslands Research Station (Zimbabwe) for their assistance.
References Gcaing,H.K.
and Van Soest, P.J., 1970. Forage fibre Analyses. United States Department of Agriculture Hand Book Number 379. Manyuchi, B., (Ilrskov, E.R., Kay, R.N.B., 1992. Effects of feeding small amounts of ammonia treated straw on degradation rate and intake of untreated straw. Animal Feed Science and Technology 38, 293-304. Mbatya, P.B.A., Kay, M., Smart, RI., 1983. Methods of improving the utilization of cereal straw by ruminants. 1. Supplements of urea, molasses and dried grass and treatment with sodium hydroxide. Animal Feed Science and Technology 8, 221-227. Minson, D.J., Milford, R., 1967. The voluntary intake and digestibility of diets containing different proportions of legume and mature pangola grass (Digitaria decumbens). Australian J. Experimental Agriculture and Animal Husbandry 7,545-551. Mosi, A.K., Buttenvorth, M.H., 1985. The voluntary intake and digestibility of cereal crop residues and legumes hay for sheep. Animal Feed Science and Technology 12, 241-251. 0rskov, E.R., McDonald, I., 1979. Evaluation of protein degradability from incubation measurementS weighted according to rate of passage. J. Agriculture Science Cambridge 92.499-503. 0rskov, E.R., 1994. Recent advances in understanding of microbial transformation in the rumen. Livestock Production Science 3, 53-60. p)rskov, E.R., Hovell, F.D. Deb, Mould, P., 1980. The use of the nylon bag technique for the evaluation of feedstuffs. Tropical Animal Health and Production 3,9-l 1. Siebert, B.D., Kennedy, P.M., 1972. The utilization of spear grass (Heteropogon contortus). 1. Factors limiting intake and utiliition by sheep. Australian J. Agricultural Research 23, 35-44. Silva, A.T., 1985. Assessment and control of condition in the rumen to increase utilization of fibrous roughages in ruminant. Ph.D Thesis, University of Aberdeen. Smith, T., Manyuchi, B. and Miiayiri, S., 1989. Legume supple-
B. Manyuchi et al. /Livestock Production Science 49 (1997) 33-41 mentation of maize stover. In: eds. B.H. Dzowela, A.N. Said, A. Wendem-Agenehu and J.A. Kategile, Utilization of Research Results on Forage and Agricultural By-Product Materials as Animal Feed Resources in Africa. JLCA, Addis Ababa, Ethiopia, pp. 303-320.
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Tilley, J.M.A., Terry, R.A., 1963. A two stage technique for in vitro digestion of forage crops. J. British Grassland Society 18, 104-111. Van Scest, P.J., 1982. Nutritional Ecology of the Ruminant. 0 and B Books, Inc. United States.
Production
Science 49 (1997) 33-41
Napier or groundnut hay as supplements in diets of sheep consuming poor quality natural pasture hay 1. Effect on intake and digestibility B. Manyuchi
a-*, F.D. Deb Hovel1 b, L.R. Ndlovu ‘, J.H. Topps ‘, A. Tigere d a Africa University, P.B. 1320, Mutare, Zimbabwe b Rowett Research Institute, Aberdeen, ScotlandAB2 9SB, UK ’ University of Zimbabwe, Harare, Zimbabwe * Grasslands Research Station, Marondera, Zimbabwe Accepted
11 February
1997
Abstract
Three experiments, each of a 5 X 5 Latin square design, were carried out using sheep to assess the effect of supplementing poor quality natural pasture (veld) hay with graded levels of napier or groundnut hay on intake and digestibility. In Expt 1, napier hay was fed at 0, 100, 200, 300 g/day or ad libitum. In Expt 2 the same levels of feeding were used with groundnut hay, while in Expt 3 napier and groundnut hay were each fed at 0, 150 or 300 g/day to enable a direct comparison of the two supplemental forages. All the forages used were chopped to a particle size of about 1 cm prior to feeding. The veld hay was supplemented with 1 percent urea and was always offered ad libitum. The forage supplements were fed separately. In all the experiments, the forage supplements increased total feed intake (P < 0.05). In Expt 1, total feed intake was greatest with the daily supplement of 300 g napier. The forage supplements did not reduce intake of veld hay. After correcting for differences in the digestibility, intake of veld hay was always greater than anticipated if there had been simple substitution. Although the forage supplements increased digestibility, differences were only significant (P < 0.05) between the 0 and 300 g forage supplemented diets. In all the experiments, nitrogen retention was also increased by supplementation (P < 0.05). Response to supplementation was similar between groundnut and napier. These results demonstrated that small amounts of forage supplements can be effective in increasing nutrient intake when animals consume poor quality forages. 0 1997 Elsevier Science B.V.
1. Iutroduction The use of high quality forage supplements in diets for ruminants consuming low quality forages continues to receive considerable attention. M&t of the research has involved the use of legume forages
* Corresponding
author.
0301-6226/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved. PII SO301-6226(97)00019-S
(e.g. Minson and Milford, 1967; Siebert and Kennedy, 1972; Mosi and Butterworth, 1985) and high quality grass (Mbatya et al., 1983; Silva, 1985). In all the experiments, forage supplements increased total feed intake. With low levels of forage supplementation, some increase in the intake of the poor quality forage above the level achieved with the unsupplemented diet was observed. As the level of forage supplement is increased, especially beyond 20
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B. Manyuchi et al. / Livestock Production Science 49 (1997) 33-41
to 40 percent, the intake of the basal diet falls below the level achieved with the unsupplemented basal diet. Since in many of the experiments reported, the basal diet was deficient in nitrogen, this has led to the hypothesis that the increase in feed intake is due to the stimulatory effect of increased dietary nitrogen intake, while the substitution is due to the bulk effect of the legume forage. However, in other experiments (e.g. Silva, 1985; Manyuchi et al., 1992), similar responses to forage supplements have been observed when the basal diet was supplemented with nitrogen, suggesting that the response can not be entirely due to nitrogen. Most of the reported experiments show a consistent increase in vivo digestibility of the total diet (Minson and Milford, 1967; Mosi and Butterworth, 1985; Smith et al., 1989). However, in some of these experiments, it has not been possible to show any positive associative effect of the high quality forage on the digestibility of the low quality forage. Siebert and Kennedy (1972) observed very small and nonsignificant improvements in digestibility of the diet, although total feed intake was increased substantially. The authors concluded that digestibility of the high quality forage was probably decreased as the level of supplemental forage was increased due to increased rate of digesta passage. The current study was therefore carried out to examine changes in feed intake and digestibility, when a basal diet of poor quality natural pasture (veld) has was supplemented with either groundnut or napier hay.
2. Materials and methods Veld hay was supplemented with amounts of napier (Expt 1) or groundnut 2). In Expt 3 different levels of napier or hay were used in the same experiment direct comparison of the supplements.
different hay (Expt groundnut to enable
2.1. Source of forages Veld hay was harvested, when the natural pasture was mature and dormant. The hay consisted of a mixture of grasses dominated by Hyperrhenia species. Napier hay was from a hybrid cross between napier
grass (Pennisetum purpureum) and pearl miller (Pennisetum americanum). The napier was grown as a single sward and the hay was harvested during the wet season at approximately 1 m height (4 weeks growth) and was chopped and sun dried. Groundnut (Arachis hypogea) hay was harvested when the crop was mature. After removing the pods the forage was sun-dried for approximately 3 days. All forages were chopped prior to feeding using a hammer mill fitted with a 14 mm screen to achieve a particle size of about 1 cm. 2.2. In sacco degradation of forages In sacco degradation of veld hay, napier hay and groundnut hay was determined in steers using the nylon bag method outlined by Orskov et al. (1980). Four Hereford X Nkone steers with an average weight of 550 kg and each fitted with rumen cannulae of 900 mm internal diameter were used. The steers were housed in individual pens and offered a standard diet of high quality star grass (Cynodon nefluensis) hay ad libitum. After an adaptation period of 21 days, 2 g samples of veld hay, napier hay or groundnut hay milled through a 3 mm screen, were placed in nylon bags and incubated in the rumen for 6, 12, 24, 48, 72 and 96 hours. After incubation, the samples were rinsed under running tape water and oven dried at 60°C for 24 hours in order to estimate dry matter (DM) loss by difference. Samples of forages were placed in the nylon bags and washed without incubation and dried to give an estimate of ‘zero’ time loss of DM. Soluble DM loss was determined by washing the forage samples through filter paper (Whatman No 1) using warm water. DM losses to rumen in sacco incubation were fitted to a non-linear negative exponential model given by: p = a + b( 1 - epC’) (Orskov and McDonald, 1979). Where p is the degradation loss at time ‘t’ hours, a is the intercept by &rapolation of the degradation curve to t = 0, b is the asymptote of the exponential and c is the fractional rate constant of the exponential. The total amount of material potentially degradable is given by a+b.
B. Munywhi et al. /Livestock
2.3. Intake and digestibility studies 2.3.1. Animals
Five male sheep of the Dorper X Merino breed with an average live weight of 65 (+0.6 kg were used in each experiment. The sheep had been fitted with rumen cannulae of 3 cm internal diameter. In each experiment, the sheep were allocated to five dietary treatments in a 5 X 5 Latin square design. The three experiments did not use the same five sheep. 2.4. Dietary treatments 2.4.1. Experiment
1
Five dietary treatments were formulated in which veld hay with 1% urea fed ad libitum alone (Control) or the Control diet supplemented with either 100 g napier hay (100 Nap), 200 g napier hay (200 Nap) or 300 g Napier hay (300 Nap). The fifth diet was napier hay fed ad libitum on its own. 2.4.2. Experiment 2 Five dietary treatments were formulated as in Expt 1, with the exception that groundnut hay was used as a supplement i.e. Control, Control + 100 g groundnut hay (100 Gnut), Control + 200 g groundnut hay (200 Gnut), Control + 300 g groundnut hay (300 Gnut) or groundnut hay fed ad lib&m on its own (Gnut). 2.4.3. Experiment 3 Five diets were used in this experiment. In common with Expts 1 and 2, veld hay with 1% urea was used as a basal diet. The basal diet was fed either alone (Control> or supplemented with 150 g or 300 g of either napier hay or groundnut hay (150 Nap, 150 Gnut, 300 Nap, 300 Gnut respectively). In all the experiments, the supplemental forages were fed at 0890 h and consumed within 30 minutes after which veld hay was offered ad libitum for the rest of the day. 2.5. Management
of the animals and measurements
The sheep were housed in individual pens. Each pen had separate water and feed troughs. During each experimental period of the Latin square, collec-
Production Science 49 (1997133-41
35
tion of excreta and intake measurements were carried out after a minimum of 21 days adaptation to the diet. At the end of the adaptation period, the animals were moved into metabolism crates to enable total collection of the dung and urine. The measurement period lasted for 5 days. During the period, the weight of faeces and urine produced by each animal were recorded at 0890 h every morning. Faeces were then dried at 60°C for 48 hours and re-weighed to give daily faecal DM excretion. A sub-sample of about 10 percent of total was taken and milled trough a 2 mm screen prior to analysis. Daily urine was collected over 5 ml of 20 percent sulphuric acid, bulked and a sub-sample of about 10 percent of total was taken at the end of the collection period and stored at - 16°C pending analysis for nitrogen. Daily feed refusals were dried at 60°C for 48 hours and weighed to give DM refused. A representative of the feed was taken and dried in a similar manner in order to obtain an estimate of DM content of feed which was then used to calculate DM offered daily. Daily DM intake was calculated as the difference between DM offered and DM refused. 2.6. Veld hay equivalent of napier hay supplement The veld hay equivalent of the supplement (V,) was calculated by multiplication of the intake of the napier supplement (Z,) by the ratio of the measured digestibility of the veld hay given alone (I$) to the calculated digestibility of the napier supplement (5,) in the mixed diets. Thus:
v,=r,x; d
The calculated digestibility of the supplement (5,) was estimated as the intercept of the linear regression of diet digestibility (dependent variable) on the proportion of veld hay in the diet (independent variable). Anticipated intake of veld hay was calculated by subtracting the veld hay equivalent of the supplement from the intake of veld hay on the unsupplemented Control diet. The gain in veld hay intake was calculated as the difference between the anticipated intake and the observed intake of veld hay.
36
B. Manyuchi et al. /Livestock Production Science 49 (1997) 33-41
3. Analysis
Table 2 In sacco dry matter degradation (%o)of the experimental forages determined in the mmen of tistulated steers
3.1. Chemical analysis
The DM content of samples was determined in a forced draught oven at 60°C for 48 hours, ash was determined by incineration in a muffle furnace at 550°C for 12 hours, nitrogen was analyzed using the kjeldhal method and neutral and acid detergent fibre were analyzed using the method of Goering and Van Soest (19701. 3.2. Statistical analysis Data from each Latin square were analyzed using analysis of variance procedure for a balanced Latin square design with 12 degrees of freedom in the residual. Differences between treatment means were tested using t-test.
4.1. Chemical analysis When compared with groundnut and napier hay, veld hay had a very low nitrogen (N) and high fibre content (Table 1). Over 60% of the total nitrogen in veld hay was associated with ADF. The percentage of total N associated with the ADF fraction was 36% and 21% for groundnut and napier hay respectively. In vitro DM digestibility were lowest with veld hay, but similar for groundnut and napier hay. Table 1 Chemical composition and in vitro digestibility of veld hay, napier hay and groundnut hay Veld
’ Tilley and Terry (1963).
In sacco degradation Incubation time (h) 6 IL
24 48 72 96 Degradability constants d 6 a+b c (I/h)
Napier hay
Groundnut hay
5.64 13.17 7.53
20.28 31.53 11.25
26.98 37.35 10.37
9.48 21.68 28.10 42.58 52.80 58.13
37.06 51.17 65.20 76.72 81.15 83.94
50.96 60.02 66.22 71.46 72.78 73.73
4.50 61.76 66.26 2.09
21.57 61.62 83.19 5.21
40.36 32.35 72.7 1 6.93
a Determined by washing forage samples through a filter paper (Whatman No. 1). b Determined by washing samples through nylon bags. ’ Zero time washing loss minus water soluble fraction. d Constants in the model: p = a+dl - e-“1 (0rskov and McDonald, 1979).
4. Results
Dry matter(g/kg) Ash (g/kg DM) Nitrogen (g/kg DM) Neutral Detergent Fibre (g/kg DM) Acid Detergent Fibre (g/kg DM) Nitrogen in ADF (g/kg DM) In vitro DM digestibility ’
Water soluble DM (%) a Zero time washing loss (%) b Loss of small particles (%) ’
Veld hay
hay
Napier hay
Groundnut hay
901 115 3.8 848
897 65 22.1 700
916 70 21.0 455
524
329
330
2.4 0.384
4.6 0.672
7.7 0.649
4.2. In sacco DM degradation of forages Both DM solubility and ‘zero’ time DM loss were very low on veld hay (Table 2). Groundnut hay had DM solubility that was 25 and 79% higher than that of napier and veld hay respectively. The degradation curve for veld hay had a flat shape, which resulted in an overestimation of the asymptote. Compared with veld hay and napier, groundnut hay had the smallest and least degradable ‘b’ fraction. The rate of DM degradation of veld hay was 5 to 9 times slower than that of napier and groundnut hay respectively (Table 21. 4.3. Dry matter intake Expts 1 and 2 (Tables 3 and 4) where the supplemental forage was fed on its own, intake was substantially greater than when veld hay was fed on its own or when veld hay was supplemented with napier or groundnut hay. However in Expt 1 intake was similar (P > 0.05) on 300 Nap and Nap diets. In In
37
B. Manyuchi et al. /Livestock Production Science 49 (1997) 33-41
Table 3 Expt 1. Feed intake measured in sheep given veid hay with 1% urea alone (Cont), napier hay alone (Nap) or veid hay with 1% urea plus 100 g, 200 g or 300 g napier hay (100 Nap, 200 Nap, 300 Nap, respectively). Values am means of five observations) SED
Diet Cont
100 Nap
200 Nap
300 Nap
Nap
Dry matter intake (g/d): Veld hay
812
889
846
987
0
_
Napier hay Total Total (g/W 0.75) Napier hay in the diet (%) Veld hay equivalent of napier supplement Anticipated veld hay intake (g/d) d
0 812 ’ 35.7 a 0 812
89 978 a,b 43.1 a.b 9 72 740
178 1025 b 41.5 a,b 17 145 667
267 1254 ’ 55.3 b 21 212 595
1194 1194 b,c 52.6 b 100 _ -
99.4 8.1 _ _ _
149
179
392
(g) d
Gain in veld hay intake (g) d a,b,c Means in the same row with different superscripts d See text for details.
are significantly
different (P < 0.05).
Table 4 Expt 2. Feed intake measured in sheep given veld hay with 1% urea alone (Cont), groundnut hay alone (Gnut) or veld hay with 1% urea plus 100 g, 200 g or 300 g Gnut hay (100 Gnut, 200 Gnut, 300 Gnut, respectively). Values are means of five observations) SED
Diet
Dry matter intake (g/d): Veld hay Groundnut hay Total Total (g/W 0.75) Groundnut hay in the diet (%) Veld hay equivalent of Gnut supplement(g) Anticipated intake of veld hay d Gain in veld hay intake (n) d qb’c Means in the same row with different
Cont
100 Gnut
200 Gnut
300 Gnut
Gnut
912 0 912 a 48.4 ’ 0
896 90 986 a.b 52.1 a,b 9 56 856 40
905 180 1085 b 57.5 b 17 111 801 104
785
0
_
270 1055 b 56.0 b 26 167 745 40
1656 1656 ’ 87.8 ’ 100 _ _ -
58.0 4.6 -
912
d
superscripts
are significantly
different (P < 0.05).
d See text for details.
Table 5 Expt 3. Feed intake in sheep fed a basal diet of veld hay with 1% urea alone or supplemented with 150 g or 300 g of napier or groundnut hay (150 Nan, 150 Gnut, 300 Nan, 300 Gnut. resnectivelv). Values are means of five observations Diet
SED
Cont
150 Nap
150 Gnut
300 Nap
300 Gnut
997 0 997 = 46.0 = 0 997
996 135 1131 a 52.3 a*b 12 107 890 106
956 135 1091 a 50.3 a.b 12 126 871 85
944 270 1214 b 56.0 b 22 214 783 161
989 270 1259 b 58.4 b 21 252 745 244
Dry matter intake (g/d): Veld hay Supplement Total Total (g/W 0.75) Supplement in the diet (%) Veld hay equivalent of supplement (g) ’ Anticipated intake of veld hay (g/d) ’ Gain in veld hay intake (g) ’
ab Means in the same row with different superscripts ’ See text for details.
are significantly
different (P < 0.05).
71.5 71.5 4.5
38
B. Manyuchi et al. /Livestock Production Science 49 (1997) 33-41
Table 6 Expt 1. Digestibility and nitrogen retention measured in sheep given veld hay plus 1% urea alone (Cod), napier hay alone (Nap) or veld hay with 1% urea plus 100 g, 200 g or 300 g napier hay (100 Nap, 200 Nap, 300 Nap, respectively). Values are means of five observations) Diet
Total DM intake (g/d) Total N intake (g/d) Faecal DM excretion (g/d) Faecal N excretion Urinary N excretion Apparent total DM digestibility Nitrogen retention (g/d)
SED
Cont
100 Nap
200 Nap
300 Nap
Nap
812 a 6.50 a 410a 4.34 B 1.21 a 0.458 a 0.94 B
978 a*b 9.08 b 527 b 5.23 a,b 1.53 B 0.461 a 2.32 ’
1025 b 10.04 = 562 b 5.47 a,b 1.61 a 0.451 a 2.96 aSb
1254 = 14.53 d 593 b 6.14 b 1.70 a 0.527 b 6.69 b
1194 b-c 26.26 e 450 Kb 9.15 c 8.10 b 0.623 ’ 9.16 ’
‘b*c Means in the same row with different
superscripts
are significantly
Expt 1, intake of veld hay was increased by supplementation with napier hay. In Expt 2, intake of veld hay tended to be depressed with the highest level of groundnut hay supplementation (300 Gnut diet) while in Expt 3 (Table 51, supplementation with groundnut or napier hay did not cause a change in intake of veld hay. In all the three experiments, intake of veld hay was always above the intake anticipated had the effects of the supplement been one of simple replacement after correcting for differences in the digestibility of veld hay and the supplemental forage (Tables 3-5). 4.4. Digestibility In all the experiments digestibility of dry matter (DM) was increased by supplementation (P < 0.05; Tables 6-8). In Expts 1 and 2, digestibility of DM
99.4 1.26 40.3 1.26 1.87 0.023 2.00
different (P < 0.05).
and OM of napier and groundnut hay when fed alone were higher than the other diets (P < 0.05). The relationship between DM digestibility (Y) and proportion of veld hay in the diet (X) was calculated using linear regression. The value of the intercept (0.659 k 0.051, 0.779 * 0.038 for Expts 1 and 2, 0.65 f 0.041 and 0.587 f 0.035 for napier and groundnut hay in Expt 3) and representing digestibility of the forage supplement used to calculate the veld hay equivalent of the supplement as described previously. Faecal DM excretion was increased by supplementation. In all the experiments there was a linear (P < 0.05) relationship between DM intake (Y) and faecal DM excretion (X); Y = 0.33X + 165.19 (r = 0.712; Expt 11, Y = 3.01X - 384.06 (r = 0.839; Expt 2) and Y = 1.79X + 158.79 (r = 0.825; Expt 3).
Table 7 Expt 2. Digestibility and nitrogen retention measured in sheep given veld hay with 1% urea alone (Con& groundnut hay alone (Gnut) or veld bay with 1% urea plus 100 g, 200 g or 300 g Gnut hay (100 Gnut, 200 Gnut, 300 Gnut, respectively). Values are means of five observations) SED
Diet
Total DM intake (g/d) Total N intake (g/d) Faecal DM excretion (g/d) Faecal N excretion (g/d) Urinary N excretion (g/d) Apparent DM digestibility Nitrogen retention (g/d)
Cont
100 Gnut
200 Gnut
300 Gnut
Gnut
912 a 7.03 a 471 a 5.36 ’ 0.79 a 0.484 a 1.14 a
986 a*b 9.06 ’ 475 a 4.94 a 0.64 a 0.517 =sb 3.50 b
1085 b 11.42 b 504a 6.34 a.’ 0.85 ’ 0.533 b 4.19 b
1055 b 12.42 ’ 480 = 5.98 aSb 0.95 b 0.546 b 5.49 b
1656 ’ 34.78 d 604b 7.86 b 3.06 h 0.636 ’ 23.86 ’
ab’c Means in the same row with different superscripts
are significantly
different (P < 0.05).
58.0 1.09 35.9 0.83 0.22 0.020 1.00
39
B. Manyuchi et al. / Livestock Production Science 49 (1997) 33-41
Table 8 Expt 3. Digestibility napier or groundnut
and nitrogen retention in sheep fed a basal diet of veld hay with 1% urea alone or supplemented with 150 g or 300 g of hay (150 Nap, 150 Gnut, 300 Nap, 300 Gnut, respectively). Values are means of five observations SED
Diet
Total DM intake (g/d) Total N intake (g/d) Faecal DM excretion (g/d) Faecal N excretion (g/d) Urinary N excretion (g/d) DM digestibility N retention (g/d)
Cont
150 Nap
150 Gnut
300 Gnut
300 Gnut
997 = 7.97 = 494 a 4.93 1.53 0.505 = 1.51 a
1131 a 11.00 b 549 a 5.97 1so 0.515 a 3.93 b
1091 a 11.32 b 546 a 5.33 1.64 0.500 a 4.35 b
1214 b 13.62 ’ 662 b 5.93 1.72 0.545 b 5.98 ’
1259 b 13.99 c 666 b 5.94 1.38 0.529 ab 6.67 ’
‘b,c Means in the same row with different
superscripts
are significantly
4.5. Nitrogen retention
The nitrogen retentions obtained in the three experiments and given in Tables 6-8, show that supplementation increased nitrogen retention in all cases. The all napier and all groundnut hay diets gave the highest nitrogen retention values (P < 0.05).
5. Discussion 5.1. Intake of ueld hay
In Expt 1 and 3, increasing amounts of forage supplements did not cause a decrease in veld hay intake relative to intake of veld hay on the unsupplemented Control diet. In Expt 2, there was some indication of substitution, with 26 percent groundnut hay supplement causing a 14 percent decrease in the intake of veld hay. In most experiments where forage supplements have been used, it has been shown that high levels of forage supplements will cause substitution of the basal diet, i.e. intake of the basal diet on the supplemented diet will be lower than on the unsupplemented Control diet. Minson and Milford (1967) postulated that substitution resulted from the bulk effect of the forage supplement. When compared with concentrates, forage supplements have a lower soluble fraction and a high fraction that degrades with time. It is conceivable that forage supplements will cause greater substitution of the basal diet compared to concentrates.
71.5 0.57 30.9 0.37 0.19 0.014 0.54
different (P < 0.05).
In considering substitution it is not accurate to calculate it on a 1:l basis. Differences in the digestibility of the basal diet and the supplement should be corrected for as the two feeds will have different contribution to bulk per unit weight. The higher digestibility of the supplement implies that the supplement will occupy less space in the rumen compared with veld hay. In this study the veld hay equivalent of the forage supplement was calculated by correcting for the differences in the digestibility of the forages. The digestibility of the supplement was estimated by regression to reduce errors due to effect if changes in outflow rate on the digestibility of the supplement. Despite the low correlation between level of supplement and digestibility of the supplement was the most appropriate. The low correlation coefficients were caused by the low and nonsignificant change in digestibility following supplementation. When substitution is calculated after correcting for digestibility, it is evident that forage supplements increased intake of veld hay above the level anticipated if there was simple substitution. 5.2. Digestibility One of the benefits of using high quality forage supplements is that they supply rumen degradable nitrogen which is deficient in poor quality forages. The additional nitrogen supplied by the forage supplement will stimulate rumen digestion resulting in an increase in feed intake (0rskov, 1994). In the current study, digestibility of the diet tended to be increased by supplementation, with differences being
40
B. Manyuchi et al. / Lioestock Production Science 49 (1997) 33-41
significant only between the Control and the highest level of forage supplementation. The digestibility figures show no evidence of positive associative effects of the forage supplement on digestibility of the poor quality veld hay. This lack of a positive associative effect of the supplement on digestibility of veld hay was confirmed by the lack of improvement in in sacco degradability of veld hay (see second paper in this series). Siebert and Kennedy (1972) observed very little change in the in vivo digestibility of the diet following supplementation of poor quality pangola hay with luceme. The authors concluded that the digestibility of the supplemental luceme was probably reduced due to the high rate of passage of digesta associated with an increase in feed intake as a result of supplementation. In the current study, the increase in total feed intake was associated with an increase in faecal excretion (r = 0.71 to 0.82), evidence that digesta outflow was increased by supplementation. These results suggest that with poor quality forages, an increase in feed intake does not always result from an improvement in digestibility per se. 5.3. Nitrogen retention In the current study, forage supplements increased nitrogen retention. Similar results are reported in the literature (e.g. Mosi and Butterworth, 1985; Smith et al., 1989). 5.4. Differences between napier and groundnut hay Groundnut and napier hay differed in degradability patterns (Table 2). Groundnut hay had a large soluble fraction and a small fraction that degrades with time, while napier hay had a smaller soluble fraction and a large fraction that degrades with time. These differences are typical of the differences between legumes and grasses (Van Soest, 1982). The results of this study show no meaningful differences between groundnut and napier when they supplemented veld hay. 6. Conclusion This study confiis the benefits of forage supplements in increasing intake of nutrients when animals
consume poor quality forages. The absence of significant substitution of veld hay by napier or groundnut indicate an efficient use of the high quality forage supplement.
Acknowledgements This study was sponsored by the Overseas Development and Natural Resources Institute (UK) and the Ministry of Lands, Agriculture and Water Develop ment (Zimbabwe). We grateful to staff at the Rowett Research Institute (Scotland, UK) and Grasslands Research Station (Zimbabwe) for their assistance.
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Tilley, J.M.A., Terry, R.A., 1963. A two stage technique for in vitro digestion of forage crops. J. British Grassland Society 18, 104-111. Van Scest, P.J., 1982. Nutritional Ecology of the Ruminant. 0 and B Books, Inc. United States.