M Nawanyakpa, T R Preston and R Sayers
International Livestock Centre for Africa
P O Box 5689, Addis Ababa, Ethiopia
Summary
Introduction
Materials and methods
Results and discussion
Conclusion
Acknowledgements
References
A 102-day growth and digestion balance experiment was conducted to study the effects of noug (Guizotia abyssinica) cake and various watering frequencies on the growth rate, and feed intake and utilization of teff (Eragrostis tef) straw (TS) and molasses-urea (MU, 2.5% urea) by male castrated highland sheep. Four of 12 sheep (average initial weight: 16.9 ± 0.17 kg) were subjected to one of three watering frequencies (WFs); once every 3 days for 30 minutes, once/day for 30 minutes and ad libitum.
Noug cake, which constituted 13.7% of the total DM intake of half of the sheep, had a substitution effect on the intake of TS. Sheep offered NC consumed 36% less straw than those without noug. However, sheep fed NC had significantly (P<0.05) higher apparent dry matter (73%) and nitrogen (70%) digestibilities and growth rate (23 g/day) than those without the meal (65, 63% and -6 g/day respectively).
Sheep on the ad libitum regime consumed more MU, total feed and water, digested DM, N and fibre better, and gained more weight than those on the other WFs. In general, sheep on the once/day WF performed the poorest, while the performance of those watered once/3 days was intermediate.
Rumen ammonia concentrations increased as the interval of watering increased. Rumen ammonia in sheep fed NC was eight percentage units higher than in those not fed NC, but fibre digestibility was lower in the sheep given noug. This suggested that the fibre in NC is fairly indigestible, probably because NC contained 61% more lignin than TS. Molasses-urea intake was negatively correlated with that of straw (r = -0.67, P<0.017). Intake of MU depressed fibre digestion.
There were no apparent digestive or metabolic disturbances in sheep on any WF, eventhough MU constituted 59 to 66% of total DM intake. Thus, watering once/3 days instead of once/day or ad libitum, restricted feeding of an oilseed cake and free feeding of MU could be important components of a strategy for enhancing survival of sheep during drought.
Ethiopia has the largest livestock population in Africa. About 80% of these animals are raised in the intensely cultivated highlands (Bisrat, 1985). Livestock productivity in the Ethiopian highlands is suppressed by inadequate feed and water supplies, disease and poor utilization of agro-industrial byproducts such as noug (Guizotia abyssinica) cake (NC) and molasses (Bisrat, 1985).
Another constraint to livestock productivity in the Ethiopian highlands is the inadequacy of data on livestock resources and livestock performance. The objective of this study was to determine the effect of three watering frequencies, and the feeding of teff (Eragrostis tef) straw and molasses-urea with and without NC on sheep growth rate, rumen ammonia levels, feed intake and nutrient utilization.
General procedures
The experiment was arranged as a 2 (0 and 100 g noug cake (NC)/sheep/day) x 3 (watering frequency) factorial. There were four male castrated sheep on each watering interval (average initial weight: 16.9 + 0.17 kg) two with and two without NC. All sheep were drenched with a broad spectrum anthelminthic 2 weeks before initiating the trial. Sheep were housed in metabolism crates.
Molasses-urea (2.5% urea w/w) was fed ad libitum in a small can placed securely in a compartment within each metabolism crate. Each sheep's NC, served as one meal each morning, was placed in the other compartment. Teff straw (TS) was fed ad libitum (i.e., 125% of the realized intake during a 10-day preliminary period) and was divided into two equal portions given in the morning and afternoon.
Water was served in plastic buckets tied securely on to the crates and was weighed before and after being offered. Water for sheep on the restricted watering frequencies (WFs) was offered after straw, NC and molasses-urea (MU) had been given.
The trial consisted of three periods: feeding and growth (days 1-84, including a 10-day adaptation period), digestion balance (days 86-100) and rumen fluid collection (days 101 and 102).
Feeding and growth period
Samples of TS, NC and MU offered were taken weekly, bulked at the end of the period, subsampled and dried in a forced draft oven for 24 hours at 60° C. The samples were then ground through a 1 mm screen and analysed for dry matter (DM), ash, nitrogen (N), acid-detergent fibre (ADF), neutral-detergent fibre (NDF) and lignin.
Samples were dried, in duplicate, in a forced air oven overnight at 100°C and subsequently placed in a muffle furnace overnight at 550°C, for DM and ash determinations respectively (AOAC, 1975). Nitrogen was analysed using a Kjeldahl digestion and distillation procedure (AOAC, 1975). Samples were digested at cat 400°C in digestion tubes containing concentrated sulphuric acid (specific gravity, 1.84) and a Se-based catalyst tablet. Aliquots of digests were steam-distilled after reduction with 40% NaOH (w/v). The distillate was collected in 2% boric acid solution and titrated against standard HCl (0.10 N). Neutral-detergent fibre, ADF and lignin were determined according to van Soest and Robertson (1979).
Sheep were weighed weekly, without prior fasting. All sheep were weighed on the same day, which was the day before sheep on the once/3 days WF were to receive water. The chemical composition of feeds offered is presented in Table 1.
Table 1. Chemical composition of feed ingredients offered.
|
Feed ingredient |
Crude protein |
Acid-detergent fibre |
Neutral-detergent fibre |
Lignin |
Ash |
|
% |
DM basis |
||||
|
Teff straw |
3.0 |
41.8 |
70.5 |
5.2 |
8.0 |
|
Noug cake |
32.3 |
32.7 |
34.0 |
13.3 |
11.5 |
|
Molasses/ urea |
12.7 |
- |
- |
- |
17.3 |
Digestion balance period
This consisted of two digestion periods of 7 days each, during which urine and faeces were collected over 24 hour periods. For sheep on the once/3 day WF, urine and faecal collections began on the day before water was to be given.
Daily faecal excretions were collected quantitatively in canvas bags lined with plastic bags. Urine collected passed between the wooden slats of the crates and drained on to zinc urinary trays (required frequent cleaning) and into plastic buckets. This method of urine collection made it difficult to determine N retention with certainty.
Five ml of concentrated sulphuric acid was placed in each bucket to acidify and preserve each sheep's urine output. Each sheep's daily urine output was agitated vigorously to ensure a good blend and measured volumetrically. At least a 30% aliquot of the well-mixed urine was added to the sample of the previous day(s) which was then refrigerated and subsampled at the end of each period for N analysis. Fifty percent of each sheep's faecal output was dried daily at 105°C for 24 hours for DM determinations and the remaining 50% was bulked and refrigerated. At the end of each period, the composited faecal samples were mixed well, subsampled, dried at 60°C for 24 hours, ground and used for chemical analyses as specified above.
Samples of feeds offered were collected daily and composited weekly. Feeds refused were recorded daily and composited weekly on an individual sheep basis. The weekly composites were divided into two portions - one dried at 60°C and the other at 105°C, for chemical analyses and DM determinations respectively. Digestion coefficients were calculated according to standard procedures (Schneider and Flatt, 1975).
Rumen fluid collection period
Rumen fluid samples were taken using a suction pump and stomach tube. A stainless steel strainer, used for excluding large particulate matter from the rumen fluid samples, was attached to the end of the tube that was inserted through the mouth into the rumen of each sheep. Rumen fluid samples were collected before feeding (0 h) and again at 1/2, 1, 2, 3, 4 and 5 h post-feeding, placed in plastic bottles each containing 3 ml of concentrated sulphuric acid, and analysed for ammonia after Kjedahl digestion and distillation methods (AOAC, 1975).
All data were subjected to analysis of variance and differences among treatments were detected using l-tests (Snedecor and Cochrane, 1967).
Growth period
Interaction between level of NC and WF was not significant (P<0.05) for any of the parameters measured (Tables 2 and 3). Sheep given NC ate less TS, consumed more MU and more total feed DM, drank more water and gained more weight than those without access to the meal.
Straw consumption was significantly depressed by the availability of noug cake (equivalent to about 13.7% of the diet DM intake) and intake of molasses (r = -0.67, P<0.017). The reduction in straw intake by MU and NC may have been due to a substitution effect.
Sheep on the ad libitum WF ate more MU and total feed, drank more water and gained faster than those on the other WFs. However, sheep given free access to water consumed less TS than those watered once/3 days. For all parameters, except water intake, sheep on the once/day WF performed the poorest. Performance of sheep watered once/3 days exceeded that of those watered once/day, probably because of the sharp increase in total feed and water intake in the former group on the day that water was provided. On average, the increase in feed intake by sheep watered once/3 days, on the day that water was given, was 60-90% more than the average feed intake during the following 2 days of water deprivation.
Total DM intake was lower in sheep on the two restricted WFs than in those given free access to water, in agreement with Balch et al (1953) and Asplund and Pfander (1972). Asplund and Pfander (1972) stated that reduced feed intake under restricted watering occurs because a certain amount of water is necessary to allow normal passage of DM through the digestive tract.
Water intake in sheep on the once/3 day, once/day and ad libitum WFs were 1.10, 1.18 and 1.83 litres/sheep/day respectively, similar to results obtained by Taneja (1965). In that study, grazing sheep were watered once/day, once/2 days, once/3 days and once/4 days. Those receiving water once/3 days drank 1.32 litres/sheep/day.
Table 2. Feed and water consumption and liveweight change.
|
Measurements |
Watering frequencies |
||||
|
Once/3 days |
Once/day |
Ad libitum |
SEx |
||
|
Feed intake (g/day) |
|
|
|
|
|
|
|
1. Straw (as-fed) |
|
|
|
|
|
|
Without noug |
302 |
200 |
239 |
44 |
|
|
With noug |
160 |
141 |
175 |
|
|
|
2. Molasses/urea (as-fed) |
|
|
|
|
|
|
Without noug |
449 |
542 |
600 |
60 |
|
|
With noug |
700 |
593 |
813 |
|
|
|
3. Noug (as-fed) |
|
|
|
|
|
|
Without noug |
- |
- |
- |
- |
|
|
With noug |
100 |
100 |
100 |
|
|
|
4. Total DM* |
|
|
|
|
|
|
Without noug |
564 |
532 |
605 |
30 |
|
|
With noug |
694 |
607 |
780 |
|
|
|
Water intake (litres/day) |
|
|
|
|
|
|
Without noug |
0.90 |
1.00 |
1.45 |
|
|
|
With noug |
1.30 |
1.35 |
2.20 |
0.07 |
|
Liveweight change (g/day) |
|
|
|
|
|
|
|
Without noug |
-13 |
-17 |
13 |
|
|
|
With noug |
33 |
-6 |
43 |
8.0 |
* Includes straw, molasses/urea and noug cake at DM contents of 90, 65 and 95% respectively.
Table 3. Nutrient digestibilities, rumen ammonia concentration and urine excretion.
|
Measurements |
Watering frequencies |
||||
|
Once/3 days |
Once/day |
Ad libitum |
SEx |
||
|
Digestibilities (%) |
|
|
|
|
|
|
|
1. Dry matter |
|
|
|
|
|
|
Without noug |
60.7 |
60.1 |
73.2 |
|
|
|
With noug |
71.8 |
70.3 |
78.0 |
3.40 |
|
|
2. Nitrogen |
|
|
|
|
|
|
Without noug |
61.8 |
57.5 |
69.3 |
|
|
|
With noug |
70.7 |
65.4 |
74.3 |
1.97 |
|
|
3. Acid-detergent fibre |
|
|
|
|
|
|
Without noug |
48.9 |
43.5 |
53.7 |
|
|
|
With noug |
44.8 |
30.8 |
35.9 |
1.34 |
|
Rumen ammonia concentration (mg %)* |
|
|
|
|
|
|
|
Without noug |
7.6 |
14.5 |
19.9 |
|
|
|
With noug |
22.3 |
21.9 |
21.2 |
3.03 |
|
Urine excretion (ml/day) |
|
|
|
|
|
|
|
Without noug |
100 |
197 |
279 |
|
|
|
With noug |
233 |
420 |
442 |
11.9 |
* Mean ammonia concentration in rumen fluid samples taken before feeding, and at 0.5, 1, 2, 3, 4 and 5 hours post-feeding.
Under drought conditions, there is a cyclical weight loss between watering. This is caused by high water consumption on the day of watering. For example, camels may drink up to 140 litres of water on the day water is given and this may increase the dehydrated weight by 25% (Field, 1985). A precaution against this increase in liveweight was taken during the current study by weighing all sheep on the day before sheep on the once/3 days watering regime were to receive water.
Digestion balance and rumen fluid collection periods
Dry-matter and N digestibilities were higher in sheep fed NC than in those deprived of the meal. These results may have been a reflection of the increased N status of sheep fed noug. Because N deficiency is the primary nutritional limitation in cereal crop residues (Butterworth and Mosi, 1985; Mosi and Butterworth, 1985), strong positive relationships have been found between increasing N intakes and cellulose digestibility, intake of low quality roughages and bodyweight gains in young animals. These effects of N intake in ruminants may be mediated through the rumen microbial population, as indicated by the highly significant relationship found between direct counts of rumen bacteria and N intake (Moir and Harris, 1962).
Although the concentration of rumen ammonia in the rumens of sheep given noug was 8 percentage units higher than in those without the meal (Table 3), fibre digestion was lower in the former group, possibly because of the depressing effects of sugars on fibre digestion (i.e., sheep fed noug ate more molasses/urea than those without noug) and because of the increase in indigestible fibre from noug cake. Noug cake is obtained through expeller or solvent extraction. The cake remaining after oil has been removed has a very high percentage of seed hulls which account for the high fibre and lignin contents of noug (Table 1).
The concentration of rumen ammonia increased as WF increased (Table 3), possibly because the intake of MU increased as the watering interval was increased. Asplund and Pfander (1972) reported that the rumens of sheep on very restricted watering ("high feed, low water") were more acidic and contained higher levels of volatile fatty acids than those of sheep on "low feed, low water" and "high feed, high water".
Dry-matter, N and fibre digestibilities tended to be higher in sheep watered once/3 days than in those watered once/day (Table 2), in agreement with the findings of Balch et al (1953), Thornton and Yates (1968) and Asplund and Pfander (1972). Asplund and Pfander (1972) suggested that drastic curtailment of defecation (not observed in the current study) and exaggerated accumulations of DM in sheep under water restriction caused elevated digestibilities of DM and N. Inadequate water causes DM accumulation in the digestive tract (probably the rumen) by slowing down the rate of passage of feed residues (Belch et al, 1953). A progressive slowing down of the rate of passage would result in higher apparent digestibilities without any alteration in digestive function or rumen kinetics (Asplund and Pfander, 1972). These data infer that high digestibilities in ruminants undergoing severe water restriction may be an artifact.
The phenomenon of exaggerated digestibilities has often been observed in short-term studies on water restriction. For example, in the study of Asplund and Pfander (1972), digestion data were collected after a 14-day adaptation period. Digestion data in such trials are perhaps collected before animals have adapted physiologically to water restriction (Asplund and Pfander, 1972). The current experiment is one of the most long-lasting experiments on water restriction. The phenomenon of high digestibilities under water restriction appeared to have occurred in this trial, despite the fact that digestion data were taken after sheep had been on their watering regimes for nearly 3 months.
The main daily urine output of sheep on the once/3 days, once/day and ad libitum WFs were 167, 309 and 361 ml respectively. This means that sheep on the ad libitum WF excreted 14 and 54% more urine than those watered once/day and once/3 days respectively. Water intake in sheep watered ad libitum was 36 and 40% greater than in those allowed to drink once/day and once/3 days respectively (Table 2). Because the percentage difference in urine excretion between sheep on the ad libitum WF and those watered once/3 days was much greater than the difference in their water intake, it can be said that water conservation was highest in sheep watered once/3 days and lowest in those on the free choice watering regime.
Asplund and Pfander (1972) reported reduced faecal and urinary water excretion under severe water restriction and concluded that this water-conserving mechanism is more efficient in sheep than in cattle.
Ethiopia has the largest livestock population in Africa; 80% of these animals are found in the Ethiopian highlands. Livestock deaths caused by drought are a perpetual problem in this and some other African countries. However, no data from work done in the Ethiopian highlands have been reported on the long-term effects of water restriction and noug cake feeding on growth rate, rumen parameters, and feed intake and utilization in sheep given molasses/urea free choice.
Data from this experiment, one of the most long-lasting studies on water restriction for domestic ruminants, suggest that after a long period of water restriction, sheep adapted physiologically to infrequent watering. These adaptations were manifested through reduced urinary water excretion and increased feed consumption on the day of watering, and were demonstrated most vividly in sheep watered once/3 days. Sheep given noug cake digested dry matter better and grew faster than those without the protein cake. In light of the continuing drought problems facing Ethiopia, it is concluded that watering highland sheep once every 3 days for 30 minutes, instead of ad libitum or once/day for 30 minutes, is an economical and labour-saving "drought response" watering frequency, and that providing at least 14% of the diet DM as noug cake may enhance the survival of sheep during drought.
The authors gratefully acknowledge the assistance of Mr Aklilu Askabe for procuring the feeds used in this experiment and for his administrative supervision over the research assistants involved. The role of Messrs Fikru Teka, Sisay Dibbaba, Mulugeta Habte Michael and Anbase Kasahun as the primary research assistants during this experiment is gratefully acknowledged. Deepest appreciation is extended to Mrs Genet Asafa who served as the senior author's laboratory/research technician.
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