Agricultural Research Institute, 1516 Nicosia, PO
Box 2016, Cyprus
Eleven trials with growing Friesian heifers of different ages were carried out. In trials 1, 2 and 6, the voluntary intake of untreated (US) and urea-treated straw (UTS) was measured with Friesian heifers offered a constant allowance of a concentrate mixture. The effect of feeding a high (HP) or low protein (LP) concentrate mixture along with US or UTS, respectively was studied in four trials (trials 3, 9, 10 and 11). In another three trials (trials 4, 5 and 7), UTS offered with a LP content concentrate mixture was compared with US given along with a HP mixture provided by soybean meal (HP) or a combination of soybean meal and urea (LP+U). Finally, in trial 8 the effect of complete replacement of barley hay by UTS, both offered ad libitum, was studied over the period of 4-6 months of age.
UTS had greater crude protein (98 vs 43 g/kg DM) and in vitro digestibility (53.2 vs 44.9%) than US. Voluntary intake of UTS was greater by 3.2% (trial 1), 8.6% (trial 2) and 10% (trial 6) compared to US. There was no difference (trials 3, 6, 9, 10 and 11) in the performance of heifers on US and UTS fed along with a HP and LP mixture, respectively. With the exception of trial 5, there was an overall increase (12.4%) in weight gain of heifers on the urea-treated than the urea-supplemented diets. Finally, UTS successfully replaced barley hay (trial 8). Based on animal performance data, and the feeding costs obtained in the present studies, urea treatment expenses ranging from CYP 12.04 - 45.80 may be justified. It is concluded that under certain conditions urea treatment of straw is economically viable and treatment may enhance straw utilization.
High prices of cereal grain and protein sources, combined with inadequate supplies of conventional roughages have enhanced the potential for using crop residues in ruminant rations. However, cereal straws are characterized by low crude protein, high lignin and low available energy content resulting in low intakes and utilization (Sundstol et al 1978). Mechanical and chemical methods of processing have been proposed for upgrading the nutritional value of poor quality roughages. Kay (1972) reported that straw consumption may be increased by grinding and pelleting, while alkaline treatment or anhydrous ammonia may improve both digestibility and intake (Garrett et al 1974). Rather recently (Saadullah 1981; Hadjipanayiotou 1982, Cloete and Kritzinger 1984; Dias-Da-Silva and Sundstol 1986; Chenost and Kayouli 1997), there has been considerable interest in the use of urea as a precursor of ammonia for the upgrading of cereal straws. Large scale on-farm application of the ammoniation technique using urea, and feeding the treated straw to ruminants has been extensively promoted in China (Tingshuang et al 1993; Tingshuang and Zhenhai 1996).
In an intensive dairy cattle production system that is widely practised in many sub-tropical countries, heifers are fed to reach mating at 14-16 months of age on very limited quantities of conventional forages. For milk production systems with cows of high production potential, the available limited quantities of moderate to good quality forages are spared for dairy heifers in their early post-weaning life and for the late pregnancy and early lactation stages. As a result, heifers are given large quantities of high price concentrate mixtures based on cereal grains and protein sources.
Treatment of crop residues has been shown to upgrade their nutritional worth (intake, N-content and digestibility) and may facilitate their greater contribution in the diet of growing heifers at the expense of concentrates. The experiments reported in the present study were designed to measure:
The Norwegian stack method (Sundstol et al 1978) was used for treating rectangular bales (90 * 47.5 *33.7 cm) of long straw of about 10-12 kg each. A 10% urea solution (4% urea w/w) was applied with a sprayer mounted on a tractor at the rate of 400 litres per tonne of straw, after each layer of straw of known weight. Stacks ranging from 4 to 9 tonnes each were prepared between June and September. The processing of the straw (stacking, spraying, covering and sealing of the stacks with polyethylene sheet) as outlined by Sundstol et al (1978) was completed in 4-6 hours. The bottom and cover sheet were sealed together with a layer of soil. Stacks were opened after a period of at least six weeks.
Animals were weighed at the beginning, at the end, and at monthly intervals during the course of each trial. Group feed residues were recorded at weekly intervals. Concentrates and roughage were offered twice daily. Samples of feed offered were collected routinely, bulked and analyzed in duplicate for proximate constituents (MAFF 1973), dry matter digestibility in vitro (Tilley and Terry 1963), acid (ADF) and neutral detergent fibre (NDF) (Harris 1970). Total nitrogen in UTS, US, barley hay and concentrate mixtures (macro-Kjeldahl method) was determined routinely. The percentage composition of the concentrates used in all trials is shown in Table 1.
Twenty Friesian growing heifers were used in each experiment. Animals within experiments were stratified (in pairs) based on individual body weight and allocated to the two treatments (ad libitum feeding of US or UTS). Within treatment, there were two age groups. Animals were group housed and fed in four adjacent pens. In experiment 1, animals of the younger (5.5-9.5 months-old) and older (10-15.6 months-old) age groups were offered 3 and 3.5 kg of a concentrate mixture (Table 1), respectively.
In the second experiment, animals were offered 2 kg/head of the same concentrate mixture (Table 1) plus US or UTS ad libitum. Animals were on test for 28 and 21 days in experiments 1 and 2, respectively. In this, and the following experiments, data collected were analyzed by one-way analysis of variance. Daily straw intake of the groups was measured.
Ten, 30, 12 and 16 heifers were used in experiments 3, 9, 10 and 11, respectively. Stratification and allocation to treatments were as in experiments 1 and 2. There were two treatment diets (US and UTS) in each experiment. US was offered along with a HP concentrate mixture, whereas UTS was supplemented with a LP mixture (Table 1).
Heifers (10.9-17.3 months-old) in experiment 3 were housed in two adjacent pens and were offered 4 kg of concentrate and 4 kg of US or UTS throughout the 42-day experiment. In experiment 9, heifers were placed on trial at the age of about 10 months and they remained on test (259 days) until 4 months prior to calving. At the commencement of the experiment animals were offered daily 3.5 kg concentrate (Table 1) and 3.5 kg straw, which was changed to 4 kg of each at about midway of the test.
Experiments 10 and 11 were carried out on private farms. Animals were stratified (pairs) based on their initial body weight, and randomly allocated to the two treatment diets (US plus HP mixture or UTS plus LP mixture). Animals within diet were housed in groups in two adjacent pens, and were offered 4.5 kg/head/day of concentrate (Table 1) and 4 kg of US or UTS per head daily. Heifers were on test for 70 and 86 days in experiments 10 and 11, respectively.
Fourteen Friesian heifers were used. Allocation of animals to treatments, housing and other management practices and data collection and analysis were as in previous experiments. Animals were offered US or UTS ad libitum along with a constant amount of concentrate. US was offered along with LP+Urea, and UTS with a LP concentrate mixture (Table 1). During the periods 1-30, 31-63 and 64-83 days on experiment animals were offered 2, 2.5 and 3 kg of concentrate/head daily.
Eighteen, 24 and 30 heifers were used in experiments 4, 5 and 7, respectively. Animals, within experiment, were stratified (in threes) based on individual body weight and randomly allocated to the three treatment diets. US was offered along with a HP or a LP+Urea concentrate mixture (Table 1), whereas UTS was given with a LP mixture. Heifers were on test for 85, 60 and 84 days in experiments 4, 5 and 7, respectively. Animals in experiments 4 and 5 were housed in three adjacent pens (one pen/treatment), whereas in experiment 7 there were two pens/treatment: one for older (322 kg) and one for younger (268 kg) animals. From 250 to300, 301-350 and over 351 kg body weight, the groups were given per head daily 3.5 kg concentrate and 3.5 kg straw, 4.0 kg concentrate and 4 kg straw, and 4.5 kg concentrate and 4.5 kg straw, respectively.
Forty heifers were stratified (pairs) based on individual body weights at
four months of age, and allocated to the two treatments at random. Heifers were
on test from 4 to 6 months of age. Animals on both treatments were offered a
constant allowance of 3 kg concentrate/head/day (Table 1) plus barley hay or UTS
offered ad libitum.
There were no health problems with the heifers fed UTS; in experiment 5, one
heifer on US and the LP+U mixture had a health problem that was not related to
the treatment. The animal was removed from the pen and the data were excluded
from the analysis.
Chemical composition of the concentrates and roughages is shown in Tables 1 and 2, respectively. Urea treatment of straw resulted in an increase in nitrogen content and in in vitro digestibility but there were no differences (P>0.5) between US and UTS for ADF, NDF and ash content. These findings are in agreement with the conclusions of Chenost and Kayouli (1997) concerning effects of urea treatment on chemical composition of straws.
In all three experiments (experiments 1, 2 and 6) where US and UTS were
offered ad libitum along with constant quantities of concentrate (Table 3),
voluntary intake of UTS was greater by 3.2% (experiment 1), 8.6% (experiment 2)
and 10.0% (experiment 6) compared to US. Furthermore, heifers on UTS had better
growth rates of 3.7% (experiment 1), 9.0% (experiment 2) and 33.5% (experiment
6) than those on US. In experiments 1, 2 and 6, heifers on UTS gained 39, 62 and
189 g more body weight daily at the expense of 150, 470 and 440 g/d of extra
treated straw. In addition, it must be underlined that in experiment 6, the
extra weight gain was attained even with a concentrate mixture of lower protein
The performance of heifers on US and UTS fed along with a HP and LP mixture,
respectively, is in Table 4. In all 4 experiments (3, 9, 10 and 11), there was
no significant difference (P>0.05) between diets for initial and final body
weight and daily body weight gain.
Performance data of Friesian heifers on US offered either with a HP or a
LP+Urea concentrate mixture and on UTS fed along with a LP mixture are in Table
5. With the exception of experiment 5, where animals on all three treatments had
similar performance, in the other experiments (experiment 4 and 7), heifers on
US fed along with the LP+U mixture had the poorest performance; the difference
between the other two diets being small and non-significant.
Voluntary intake of UTS and barley hay, and the performance of heifers on the
two roughages is in Table 6. The consumption of UTS was lower (28%) than that of
barley hay, and heifers on the latter roughage grew faster (12%) than those on
Urea-treatment of straw resulted in an increase of nitrogen content and digestibility. The amount of N that was retained on the straw ranged from 39.1 to 59.5% of that applied (1.8 g/100 g DM), and was very close to previously reported values (Hadjipanayiotou 1982; Lawlor and O'Shea 1979). Similarly, the increase (6 to 14.6 percentage units) in in vitro organic matter digestibility obtained as a result of treatment, was almost identical to previously reported values (Hadjipanayiotou et al 1997).
With the exception of experiment 5, where urea supplementation resulted in almost similar weight gains compared with urea treatment, there was an overall increase of 12.4% in body weight gain of heifers on the ammoniated compared with the urea-supplemented straw; the corresponding difference between the urea and soybean meal supplemented US being even greater (15.4%). Superiority of urea treatment as opposed to urea supplementation has been also reported for voluntary intake, digestibility in vivo (Cloete and Kritzinger 1984) and in vitro (Hadjipanayiotou 1982), and milk production (Hadjipanayiotou et al 1997).
In the studies of Cloete and Kritzinger (1984) the voluntary intake of ammoniated wheat straw by sheep was increased by 8.1% and 46.7% over that of urea supplemented and non-supplemented straw. The somewhat lower difference in voluntary intake between US and UTS obtained in the present studies (higher intake of 3.2%, 8.6% and 10% of UTS than US in experiments 1, 2 and 6, respectively) can be related to the fact that both straws were already supplemented with concentrates. The superiority of ammoniation has been ascribed by Orskov and Grubb (1978) to the fact that the latter has the advantage of supplying the supplementary NPN that is required by ruminants when the availability of the energy component in the straw is increased.
An economic evaluation was made of the data obtained in experiments 3, 9, 10 and 11 and 4, 5 and 7. Cost of concentrates was estimated using two prices for barley grain (CYP 42 and 80/tonne), and the prices for the other individual ingredients shown in Table 1. Concentrate feeding costs were less when the LP mixture was fed, followed by the LP+Urea mixture. Weighted (for days on test and number of animals/diet/experiment) means for daily body weight gain in experiments 4, 5 and 7 were 0.786, 0.764 and 0.677 kg for diets HP plus US, LP plus UTS and LP+Urea plus US, respectively. The corresponding values for experiments 3, 9, 10 and 11 were 0.576 and 0.574 for diets HP plus US and LP plus UTS; those for experiment 6 were 0.564 (LP+Urea plus US) and 0.753 (LP plus UTS).
Taking into consideration the price of concentrate mixtures shown in Table 1, and adjusting to similar daily body weight gain for all treatments within each sub-group of experiments, it was estimated when comparing HP with LP diet (sub-group of experiments with two diets) that CYP 34.2-45.8/tonne may be allocated for treating straw with urea. Regarding the other sub-group of experiments with three diets, when comparing the HP with LP diet, it was estimated that CYP 24.3-34.7 could be allocated for straw treatment; the corresponding values when comparing LP with LP+Urea range from 12.0-14.9/tonne. Finally, in experiment 6, CYP 15.8 to 22.0/tonne could be justified/allocated for straw treatment.
Urea treatment of straw resulted not only in saving in the amount of the expensive protein supplement incorporated into the concentrate mixture, but also in an increase of straw intake leading to enhanced growth rates with less quantities of concentrates, and better use of straw offered. In intensive dairy production systems where growing females are fed to reach mating weight of 330-350 kg body weight at the age of 14-16 months, feeding of ammoniated straw will make this possible, as judged by the enhanced growth rates.
In line with previously reported data with lactating cows (Hadjipanayiotou et
al 1997), UTS can replace barley hay in diets of fast growing (750-900
g/head/day) Friesian heifers. Taking into consideration the actual daily weight
gain of 0.764 kg, and an energy value of 11.3 MJ ME/kg for concentrate (as fed
basis), the energy value of UTS is estimated at 8.1 MJ ME/kg (as fed). Assuming
a selling price (CYP/tonne) of 65 and 30 for barley hay and US, respectively,
and following the considerations made in the other experiments, it is estimated
that CYP 14.6 to 24.9/tonne may be justified for treating straw with urea.
It is concluded that urea treatment of straw can improve its nutritional
worth, and that it can replace barley hay in diets of growing heifers.
Non-protein nitrogen in urea-treated straw is more effectively utilized than
urea-N incorporated into the concentrate mixture, and it can partially replace
soybean meal. Based on animal performance data and on feeding costs obtained in
the present studies, straw treatment expenses ranging from CYP 12.0 to 45.8 per
tonne may be justified.
The authors are grateful to M Theodoridou, M Karavia and the staff of the
Central Chemistry Laboratory of the Institute for skilled technical assistance.
The work had the generous support of the International Development Research
Centre of Canada (IDRC).
In this study, treatments were applied to single groups of animals housed in adjacent pens. In certain experiments there were two age groups on each treatment which were housed separately. One-way analysis of variance was used to assess differences between treatments using individual animals as repetitions. This type of analysis can sometimes lead to confusing results as "treatment" effect is confounded with "pen" effect.
Electronically controlled individual feeders allow animals on different treatments to be housed in the same pen and this permits individual animals to be considered as repetitions. But such a sophisticated feeding system is out-with the economic possibilities in most developing countries.
In assessing treatment effects reported in this paper the above considerations should be borne in mind. In fact, the methods used are those typically applied by farmers (as well as by scientists) when they carry out their own research in an "on- farm" situation and are perfectly justified when the intention is to use the results as a guide to policy-making decisions (eg: an economic analysis as reported in the final section of the present paper.) [The Editors of LRRD]
I am aware of the fact that treatments are confounded with pen effects. Pens were of the same size, direction and adjacent to each other. I would not expect asignificant pen effect, large enough to influence/ seriously affect treatment effects, thus causing confusion in interpretation. It is a common practice to house groups of animals of the same treatment in thesame pen; Published data from animals kept/housed in groups can be found in many journals. The disadvantage is the group feed records, which are not analysed. More pens per treatment would be preferable but.....
In the case of the age groups, animals within age group and treatmentwere balanced and stratification within age group was used to assign members of each pair to each of the two treatments. Age group effects should not appear in the linear model (treatments were a priori balanced for those effects).
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Received 13 August 1997
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