H . Ben Salem et al. Livestock Production Science 64 2000 51 –60
55
variance using the SAS general linear models pro- blocks containing 6, 12, 18 and 24 of PEG
cedure of the SAS 1987 for a completely random- respectively. The highest increase in acacia intake
ised design. The linear and quadratic effects of PEG was obtained with the PEG rate of 18 as the
rate in feed blocks were detected using polynomial highest rate of PEG did not lead to a further increase
contrasts. in acacia consumption.
The positive effect of PEG in feed blocks on acacia intake was reflected in sheep growth. Sheep
3. Results given feed blocks containing PEG gained more than
those on feed blocks without PEG. The response was 3.1. Feed composition
linear and significant P , 0.001 although the gains
with the rates 18 and 24 of PEG were similar. Nutrient contents of acacia foliage and feed blocks
are given in Table 2. Acacia foliage had a relative 3.3. Feed intake by adult sheep and diet
high content of CP, lignin and CT. Including PEG in digestibility
feed blocks had no effect on their chemical com- position. CP contents of the five types of feed blocks
Feed intake and digestibility values are given in were quite similar and somewhat high, ca. 21 g 100
Tables 4 and 5, respectively. There was no effect of g of DM. In contrast, all the feed blocks had low
PEG inclusion on feed block intake P . 0.05. The
contents of NDF and ADF. positive effect of PEG on acacia intake by growing
sheep was observed also on adult sheep. DM intake 3.2. Feed intake during the growth trial and daily
of acacia foliage increased linearly with the rate of gain
PEG in feed blocks P , 0.001 with increases of 22,
25, 56 and 71 with the rates 6, 12, 18 and 24 of DM intake of feed blocks by growing sheep
PEG respectively. Feed block intake by adult sheep ranged from 130 to 150 g day and was not affected
was greater than that measured on yearling sheep by PEG supply P
. 0.05 Table 3. Sheep receiv- ranging from 150 and 210 g DM day or 15.5 and
0.75
ing feed blocks without PEG consumed a small 24.3 g kg W
.
0.75
amount of acacia DM 37.7 g kg W . There was
The digestibilities of DM, organic matter, CP and a linear increase of acacia intake with the rate of
NDF of acacia supplemented with feed block without PEG in the feed blocks P
, 0.001. Increases of PEG was low. They were substantially increased by
about 25, 35, 56 and 46 were obtained with feed feeding PEG. Sheep offered blocks containing 18 or
Table 2 Chemical composition of acacia foliage and feed blocks of DM
a
DM OM
CP NDF
ADF ADL
CT Acacia
27.1 90.9
15.2 50.3
27.7 11.9
3.2 Feed block ingredients
Olive cake 75.3
95.0 5.4
78.7 56.8
29.0 –
Wheat bran 86.5
94.4 18.1
45.5 12.4
2.1 –
Wheat flour 84.7
98.0 15.3
17.8 9.1
1.9 –
Feed blocks containing 0 PEG
69.1 75.1
21.4 20.6
13.3 3.6
– 6 PEG
71.0 73.8
21.2 21.2
13.0 4.5
– 12 PEG
68.2 74.0
20.8 20.2
12.6 3.8
– 18 PEG
70.5 75.5
21.0 20.9
12.1 3.3
– 24 PEG
68.9 76.4
20.9 21.0
13.5 4.2
–
a
CT, methanol extractable condensed tannins equivalent catechin g 100 g of DM.
56 H
. Ben Salem et al. Livestock Production Science 64 2000 51 –60 Table 3
Feed intake and sheep growth growth trial
a
PEG in feed blocks Contrasts
6 12
18 24
S.E. Linear effect
DM intake g day Acacia
357 429
461 539
516 13.4
Feed block 129
150 145
128 145
23.7 ns
Diet 486
578 606
667 660
29.2
0.75
DM intake g kg W Acacia
37.7 47.1
50.9 58.8
54.8 1.47
Feed block 13.7
16.5 16.0
14.0 15.2
2.61 ns
Diet 51.4
63.5 67.0
72.8 70.0
3.30 PEG intake g day
7.1 13.0
19.5 28.0
– –
b
PEGi CTi 0.52
0.88 1.13
1.70 –
– Daily gain g day
14 39
50 61
63 3.2
a
Whenever significant, quadratic effects are reported in the text.
b
Amount of PEG consumed to the amount of condensed tannins consumed ratio. P
, 0.001, ns not significant P . 0.05.
24 of PEG increased DM digestibility of the diet ty and negative values of ADF digestibility indicated
by approximately 13 and 21 percentage units, respec- an analytical problem which is discussed below.
tively. The rate 6 of PEG was too low to make any The
positive effect
of including
increasing significant improvement of diet DM digestibility. In
amounts of PEG in feed blocks on acacia intake and contrast, even with the lowest rate of PEG there was
diet digestibility resulted in an improvement of the a significant increase P
, 0.001 of diet CP di- energy and nitrogen value of diets. The amounts of
gestibility of 1 7.4 percentage units. Higher rates of
digestible OM intake DOMI and digestible CP PEG 12, 18 and 24 led to further improvement in
intake DCPI were significantly increased. The CP digestibility but the rate of increase was lower.
highest increase was recorded with the 24 PEG- PEG supply improved cell wall digestibility of the
rate, 89 and 78, respectively. It should be noted diet. Nevertheless, the low values of NDF digestibili-
that the lowest rate of PEG used in this experiment
Table 4 Feed intake by rams digestibility trial
PEG in feed blocks Contrasts
6 12
18 24
S.E. Linear effect
DM intake g day Acacia
351 468
473 609
697 41.7
Feed block 207
189 194
151 180
26.8 ns
Diet 558
657 667
760 877
54.4
0.75
DM intake g kg W Acacia
39.9 48.5
50.0 62.4
68.2 3.80
Feed block 24.3
19.6 20.3
15.5 17.7
2.96 ns
Diet 64.2
68.1 70.3
77.8 85.9
5.06 PEG intake g day
9.0 17.4
23.0 34.8
– –
a
PEGi CTi 0.62
1.17 1.21
1.56 –
–
a
Refer to Table 2 footnote. P
, 0.01, P , 0.001.
H . Ben Salem et al. Livestock Production Science 64 2000 51 –60
57 Table 5
Effect of the level of PEG in feed blocks on nutrient digestibility of acacia-based diets fed to sheep PEG in feed blocks
Contrasts 6
12 18
24 S.E.
Linear effect Diet digestibility
DM 28.8
36.8 37.7
42.2 50.2
2.95 OM
33.3 39.5
40.3 43.2
51.2 2.67
CP 43.5
50.9 54.9
55.1 57.2
2.31 NDF
2 8.4 5.8
14.8 17.5
26.3 6.79
ADF 2 86.5
2 52.0 2 67.3
2 65.8 2 41.0
8.69
a
Feeding value of diets DOMi
20.5 23.9
24.8 29.9
38.7 3.20
DCPi 46
63 58
69 82
7.7 NDCP
104.2 82.1
75.3 73.2
69.8 3.42
a 0.75
DOMi, digestible organic matter intake expressed as g kg W ; DCPi, digestible crude protein intake expressed as g day; NDCP, non
digestible crude protein expressed as g kg dry matter intake. P
, 0.05, P , 0.01, P , 0.001.
6 was sufficient to increase intake of the acacia percent of N intake, when increasing amounts of
supplemented with unmolassed feed blocks to cover PEG were included in feed blocks P
, 0.001. The maintenance requirements of sheep.
increase of N retention resulted from the positive effect of PEG on N intake which was associated to a
3.4. Nitrogen balance and microbial synthesis decrease of faecal P
, 0.05 and urinary P , 0.01 N excretions.
Excretion and retention of N, urinary excretion of The amount of allantoin excreted in urine was
allantoin and estimated microbial synthesis are given higher in sheep receiving PEG-containing feed
in Table 6. N retention was low for sheep receiving blocks than in those on the feed block without PEG
feed blocks without PEG. There was a linear in- P
, 0.01. The rates 12, 18 and 24 of PEG crease of N retention, expressed as g day or as
increased allantoin excretion by 19, 17 and 27 mg
Table 6 Nitrogen balance and microbial sytnthesis by sheep given acacia foliage and graded levels of PEG in feed blocks
PEG in feed blocks Contrasts
6 12
18 24
S.E. Linear effect
g day N intake
16.7 18.4
17.9 19.8
22.9 1.60
Faecal N 12.0
10.6 11.1
11.6 12.7
0.62 ns
Urinary N 6.2
6.6 5.1
5.7 5.1
0.69 ns
N retention 2 1.5
0.8 1.7
2.5 5.1
0.99 Percentage of N intake
Faecal N 72.8
57.8 63.3
59.7 56.0
3.49 Urinary N
37.0 37.1
29.4 28.3
22.4 3.60
N retention 2 9.7
2.3 7.6
12.2 21.8
4.63 Allantoin in urine
0.75
mg kg W 35.8
49.8 54.5
59.1 62.9
2.27
a
Microbial N 4.9
6.7 9.5
11.5 12.4
1.04 g kg DOMi
a
Microbial nitrogen expressed as g kg of digestible organic matter intake.
58 H
. Ben Salem et al. Livestock Production Science 64 2000 51 –60
0.75
kg W , respectively, as compared with the control
increasing amounts of PEG in feed blocks signifi- diet with blocks without PEG. The optimal responses
cantly increased acacia DM intake by sheep. Similar of N retention as well as allantoin excretion were
findings were reported by Silanikove et al. 1996 obtained in sheep receiving feed blocks containing
who distributed tannin-containing leaves of Quercus 12 of PEG. Animals on acacia foliage sup-
calliprinos , Pistacia lentiscus and Ceratonia siliqua
plemented with PEG-containing feed blocks ex- to goats. Estimated amounts of PEG consumed by
hibited higher microbial synthesis as compared to adult sheep averaged 9.0, 17.4, 23.0 and 34.8 g day
those given feed blocks without PEG. The optimal and ratios of PEG:condensed tannins of 0.62, 1.17,
response in this case was also obtained with the PEG 1.21 and 1.56 with feed blocks containing 6, 12, 18
rate of 12. The further increase of the amount of and 24 of PEG, respectively. The optimal acacia
microbial nitrogen which was obtained with the two intake was obtained with the 18 PEG rate corre-
highest rates of PEG 18 and 24 was not signifi- sponding to the PEG consumed:condensed tannins
cant as compared to that obtained with the 12 PEG consumed ratio of 1.13 or 1.21, respectively for
rate. growing and adult sheep Tables 3 and 4. According
to Silanikove et al. 1996, the amount of PEG needed to produce a maximal increase in feed intake
4. Discussion by goat varied with shrub species. Highest DM
