| Livestock Research for Rural Development 9 (3) 1997 | Citation of this paper |
Agricultural Research Institute, 1516 Nicosia, PO Box 2016, Cyprus
Email:miltos@arinet.ari.gov.cy
Six trials with Friesian cows and one digestibility experiment with sheep were carried out. Four dairy cow trials were on a research station (ORST) and two on private farms (OFT). In ORST 1 (high yielding cows, 27 kg/day) and ORST2 (medium yielding cows, 17 kg/day) were given urea-treated straw (UTS) offered with a low protein (LP) concentrate mixture and compared with untreated straw (US) given with a low (LP) or higher (HP) protein mixture ( provided by soybean meal or combination of soybean and urea (LP+U). In ORST 4, liberal feeding of UTS along with a LP mixture was compared with US offered with a mixture of high CP content. In trial 5 on a research station, and trials 6 and 7 on private farms (OFT) (OFT1 at Dhali and OFT2 at Aradippou), the effect on the lactation performance of replacement of barley hay with UTS was studied.
Treatment of straw improved its in vivo and in vitro digestibility and N-content. UTS
fed along with a low CP content mixture (ORST1, 2 and 4) resulted in similar lactation
performance to cows on US offered with a HP content mixture supplied from soybean meal
(SBM). It must be underlined, however, that although cows on US with the low CP mixture
gave the lowest yield, differences between diets were not significant. ORST 5 and OFT 1
and 2 showed that UTS can replace barley hay, a roughage source of relatively good quality
(D= 55-60%). It is concluded that UTS can replace barley hay in diets of lactating cows,
and that while UTS of higher energy and nitrogen can improve the economics on high levels
of SBM inclusion, the benefit may in some instances be relatively marginal.
Key words: Friesian cows, urea-treated straw, milk yield, milk composition
Straw is the most abundant of all agricultural residues and has a great potential as a feedstuff for ruminants in most semi-arid and sub-tropical regions. However, voluntary intake and digestibility of straw are limited by its high lignin content, the manner by which lignin is bound to digestible materials, and its low nitrogen content (Coxworth et al 1977).
Chemical treatment to improve the nutritive value of poor quality roughage has been proposed for enhancing greater and improved use. Despite the fact that NaOH was the first chemical used, its use is not recommended any more. Although treatment of low quality roughage with ammonia has been effectively tested in Scandinavian countries (Sundstol et al 1978), the latter method of treatment cannot be applied in many countries , and/or regions within countries because of lack of infrastructure for delivering anhydrous ammonia. Therefore, treatment of straw with urea which is converted to ammonia has been used by others (Jackson 1978; Saadullah et al 1981; Hadjipanayiotou 1982; Williams and Innes 1982; Cloette and Kritzinger 1984; Dias-Da-Silva and Sundstol 1986). There is considerable amount of research work showing positive responses to ammoniated straw feeding of growing bulls, steers and heifers (Kristensen 1984). In areas where straw is a predominant feedstuff, chemical treatment has boosted animal output and resulted in greater economic returns to the farmer, with China being the major example of the successful use of the technology at commercial level ( (Tingshuang et al 1993; Tingshuang and Zhenhai 1996).
It must be underlined however, that only a limited number of experiments has been carried out with ammoniated straw in rations of dairy cows (Kristensen 1984; Rissanen et al 1981; Orskov et al 1988; Brown et al 1990) and goats (Hadjipanayiotou 1984).
The objective of the present studies was to study the effect of feeding urea-treated
straw (UTS) to Friesian cows at different levels and stages of production and whether UTS
can be used instead of barley hay of relatively good quality.
The Norwegian stack method (Sundstol et al 1978) was used for treating rectangular bales (90 x 47.5 x 33.7 cm) of long barley 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.
Preparation of stacks took place from late spring to early autumn. Stacking, spraying, and covering and sealing of stacks with polyethylene sheet as outlined by Sundstol et al (1978) were completed in 4-6 hr. The bottom and cover sheet were sealed together with a layer of soil. Stacks were opened after a period of at least six weeks.
Representative samples from morning and afternoon milking were analyzed for fat, crude protein, ash, and total solids as outlined by MAFF (1973). 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, in duplicate.
Two separate trials with Friesian cows, one in which the average initial milk yield was 26.8±4.67 kg/d (ORST-1) and another with 17.9±3.75 kg/d (ORST-2), were carried out to study the effect of feeding UTS with a low protein (LP) mixture (mixture 2, Table 1) or US with the same low protein mixture, and/or with a high protein or high protein/non-protein nitrogen (HP) mixture from either soybean meal (mixture 1) or a combination of soybean meal and (LP+U) urea (mixture 3).
Animals, within trials, were separated into six blocks of four animals each. Cows within each block were randomly allocated to one of the four treatments. Milk yield was recorded morning and afternoon. Milk samples were analyzed for fat at weekly intervals, and for N, TS and ash twice (after the second and the last week on test) during the course of the 60-day trial. Animals in this and all other ORST trials were weighed for two consecutive days at the commencement and at the end of the trial. Cows were offered 9.5 kg of US or UTS/ head daily plus concentrate (11.3 MJ ME/kg as fed) to meet their ME requirements according to NRC (1989). Feed allowance was adjusted at fortnightly intervals. For the estimation of the energy intake from straw the energy value of US and UTS was taken as equal to 5.88 MJ ME/kg (as fed). Concentrates were offered individually and roughage in groups twice daily. Data collected were analyzed by two way analysis of variance (treatment, block and their interaction).
Apparent digestion coefficients of the four diets fed to high yielding cows (ORST-1) were measured using Chios wether sheep (ORST-3) fed at 1.1*maintenance energy requirements. Sixteen mature wethers were divided into four groups that were randomly allocated onto one of the four treatment diets. Sheep within dietswere offered the experimental diets in groups for a period of 4-weeks before being placed in metabolic crates designed for the separate collection of urine and faeces. Animals were in metabolic crates for 17 days; the first 10 days served as adaptation period and the last seven as collection period. Feed intake was kept constant throughout the last 10 days. Concentrate and roughage were offered twice daily from separate feed troughs. Collection, processing and analyses of feed, faeces and urine samples were as outlined by Hadjipanayiotou (1982). Data collected were analyzed by one-way analysis of variance.
Eighteen lactating Friesian cows, 145 days in milk (range 50-227 days) and producing on average 19.4 kg milk daily (range 14.5-24.5) at the commencement of the trial, were used to study the effect on milk yield, milk composition and live weight changes of feeding large quantities of urea-treated or untreated straw with a concentrate mixture of low (mixture 7) or high (mixture 6) protein content, respectively. Cows were stratified (pairs) based on individual milk yield and allocated to the two treatments at random. Animals were offered concentrates individually in two approximately equal portions per day. The amount of concentrate (11.3 MJ ME/kg as fed) offered was adjusted to meet the deficit of energy required (NRC 1989) after subtracting the amount of energy supplied by straw (see experiments 1 and 2). UTS or US (10 kg/day as fed) were offered per animal on a group basis. The animals were on test for 42 days following a 7-day adaptation period. Data collected were analyzed by one way analysis of variance.
The effect of replacing barley hay by UTS (1:1 DM basis) on the performance of lactating Friesian cows was studied in ORST-5. Animals (6/treatment) with an average initial milk yield of 24.6 kg daily, and 135 days in milk (range 57-199), were used. Allocation of animals to treatments and feeding (barley hay or UTS) was as in experiment 4. All animals were offered 4 kg of US daily and an equal quantity of either barley hay (7.11 MJ ME/ kg as fed) or UTS, plus concentrate (mixture 8) to meet the total ME requirements (NRC 1989). The daily feed allowance was offered on a group basis in approximately two equal portions. Milk samples were analyzed for fat once a week, and once for N, ash and TS during the 49-day trial. Data collected were analyzed by one way analysis of variance.
Two trials, one at Dhali (Expt 6, OFT-1) and one at Aradippou (Expt. 7, OFT-2), using
16 and 12 animals, respectively, were carried out to study the effect of replacing barley
hay with UTS. The average initial milk yield of the experimental animals at Dhali and
Aradippou was 20.8 kg/d (range 16-24) and 23.2 kg/d (range 19-27, respectively. Allocation
of animals to treatments, method of feeding, data collection, feed sampling and chemical
and statistical analyses were as in experiments 4 and 5. Both OFT studies were of 45-day
duration. Percentage composition of individual ingredients used in the concentrate
mixtures are not known. No urea or any other non-protein nitrogen source was present in
the mixture. Milk yield was recorded at fortnightly intervals, and milk samples were also
analyzed for fat , protein, ash and TS.
Percentage composition and chemical analyses of concentrates used in the various ORST are shown in Table 1. The corresponding chemical analyses of concentrates used in the OFT trials and of roughage used in the OFT and ORST are in Table 2. In all cases treatment of straw with urea increased digestibility in vitro (Table 2) and in vivo (Table 3), and N content compared to US straw (Tables 2 and 3). Of the total urea-N sprayed on the straw (around 110-115 g N*6.25) only 50% was retained (equal to about 50 g N*6.25). Assuming a constant (80%) DM digestibility of the concentrates used in the in vivo digestibility trial, the DM digestibility of UTS (calculated by difference) was estimated as 10 (range 8.1-11.1) percentage units greater than that of US (Table 3).
Though there were no significant differences (P>0.05) in milk yield, milk composition and live weight changes between the four diets fed in the ORST-1 (Table 4) and ORST-2 (Table 5), it is worthwhile mentioning the trend towards lower milk yield in the diets where US was fed with concentrate mixtures 3 and 2 (ORST-1), and 4 (ORST-2).
With the exception of lower (P<0.05) milk protein content of cows on the UTS (Table 6, ORST-4) fed with a low protein content mixture (mixture 7) as opposed to those on US fed with a high protein (HP) content mixture (mixture 6), there were no differences (P>0.05) for absolute and FCM (4%) yield, fat, ash and TS content of milk and/or live weight changes and voluntary feed intake of cows on US or UTS.
In all three trials [ORST-5 (Table 7) and OFT-1 and OFT-2 (Table 8)], where barley hay
was completely replaced by UTS there were no differences (P>0.05) for absolute and FCM
(4%) yield, fat, CP, ash and TS content of milk (Tables 7 and 8).
In line with previously reported studies (Sundstol et al 1978; Hadjipanayiotou 1982), ammoniation of straw resulted in an improvement of N*.25 content and digestibility. Solaiman et al (1979) and Hadjipanayiotou (1982) reported values of 34.9% and 44.4% of the applied N in the form of NH4OH and urea (1.8 g per 100 g DM), respectively, to be retained in the straw. In the present studies, N-retained was somewhat higher (around 50%), and closer to the values reported by Lawlor and O'Shea (1979). Unlike our previous studies (Hadjipanayiotou 1984), where treatment resulted in an increase in digestibility of straw offered alone, but not when offered with concentrates, in the present study UTS had a higher digestibility than US, even when combined with concentrates.
The initial FCM (4% fat) yield (kg/head/d) was 23.1, 16.3, 17.7, 20.8, 16.8 and 18.7 in the ORST 1, 2, 4 and 5 and OFT 1 and 2, respectively. At these levels of production, a dietary N*6.25 concentration ranging from 12.5 to almost 16% (DM basis) is recommended by NRC (1989). In the present ORST not only the negative control (ORST-1 and ORST-2), but also all other diets were below the NRC (1989) recommended requirements for dietary N*6.25; indeed, the deficit was more evident in the diets with UTS than US, and this may have adversely affected yields to a greater extent in the UTS treatments.
Barley hay was successfully replaced by UTS in all three experiments. Our findings are in line with those of rskov et al (1988) where both the milk yield and live weight loss of cows fed good quality straw treated with ammonia were similar to that expected using good quality silage or hay. UTS was also used as partial replacement for concentrates and of a leguminous hay in diets of lactating ewes in Syria (Hadjipanayiotou et al 1993). It is possible that the relatively short duration of the experiments, the small number of animals per treatment and the high level (about 50%) of concentrate in the diet were factors masking the expression of the superior nutritive value of the urea-treated straw. It must be mentioned, however, that response to treatment was similar throughout the trials, and that in the dry sub-tropics, where there is a scarcity and high costs of roughage, the use of relatively high levels of concentrate in the diet of Friesian cows is a common practice, and is economically feasible.
A significant response to treatment (37 to 40% increase) has been reported in dairy animals of low milk potential that were offered large quantities of straw (Verma and Jackson 1984). In contrast, in studies with Friesian cows, only marginal differences were obtained (Kristensen 1984), which did not compensate for additional treatment expenses.
Although differences between diets were not significant in our experiments, an
assessment was made of the economic consequences of using urea-treated straw (Tables 4, 5
and 6). Cost of urea for straw treatment is CYP (Cyprus pounds) 4.96 per tonne of straw.
The return above feed costs (ORST 1, 2 and 4) ranged from nil to 35/tonne of straw (see
Tables 4, 5 and 6) that may be used to cover labour, plastic and other expenses associated
with treatment. The economics of using urea-treated straw are also affected by current
prices of barley grain and soya bean meal. In the studies of Hadjipanayiotou (1982), rskov
and Ryle (1990) and Sundstol et al (1993), urea treatment was considerably more effective
than urea spraying prior to feeding for upgrading the nutritional value of straw. The
former is in line with our data where urea addition in the mixture was less economically
effective than when used for reacting with the straw. Urea-N in UTS which is consumed in
small frequent meals, compared with concentrates that are consumed quickly, may have
resulted in more uniform rumen ammonia levels throughout the day leading to better
microbial growth. Furthermore, UTS that is more degradable in the rumen than US, may have
enhanced microbial activity. The lack of any economic benefit from UTS in trial 4 may be
ascribed to a wastage of ammonia due to the high intakes of UTS.
It is concluded that urea treatment improves the nutritive value of straw, and that UTS can effectively replace barley hay in diets for Friesian cows containing relatively high levels of concentrates. When used to complement soya bean meal for cows fed high levels of concentrates it is proposed that it is economically beneficial to use the urea to treat the straw rather than incorporate it in the concentrate mixture.
The authors are grateful to Drs F Sundstol and A Mavrogenis for reviewing the
manuscript and M Theodoridou, M Karavia and the staff of the central chemistry laboratory
for skilled technical assistance. The work had the generous support of the International
Development and Research Centre of Canada (IDRC).
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Received 1 June 1997