Effect of feeding urea treated wheat straw based diet on biological performances and economic benefits of lactating Boran-Friesian crossbred dairy cows

Grazing and crop residues are major source of basal feeds.  Grazing is diminishing by the ever expansion of land for cultivation of food crops.  In the highlands substantial amount of crop residues are produced every year, which makes this feed resource available. Crop residues, particularly cereal straws and stovers, however, are poor quality feeds. The major production limitations on feeding straw to cattle include low N higher mass of lignifications and lower digestibility (40 – 50%). Thus it doesn’t provide much energy to the animal. It has also problems of low intake (1.6–2kg/100kg body weights). Lower content of the important minerals and vitamin such as P, S, Na and Vitamin A are also the inherent problems. Thus it cannot support for production more than for maintenance (Schiere and Ibrahim 1989). Further more wheat straw is the poorest of all straws in nutrient content and digestibility (Yitaye et al 2000).

Urea treatment can overcome the limitations imposed by low nutrient supply. Research results revealed that, as a result of urea treatment, the crude protein and digestibility barley straw increases from 40 to 105 g/kg DM and 425 to 516g/kg DM. Similarly, intake increases from 4.9kg/head/day-5.22kg/head/day Hadjipanayiotou et al 1997). According to (Schiere and Ibrahim 1989) the intake of treated straw can be increased from 2–2.7kg per 100kg body weight, depending on straw quality, type and amount of supplement and the production of the animal

a trial of treating teff and barely straws with urea, CP has increased from 38 to 89g/kg and 40 to 74g/kg DM respectively. Similarly, the IVOMD has increased from 566 to 608 and 464 to 594g/kg DM respectively. Feeding urea treated straws to milking cows as supplemented by concentrate feeds, had replaced hay-based diet (Rehrahie and Ledin 2001). Experience of farmers in sellale (North Shoa) showed that feeding urea treated straw to crossbred dairy cows can increase milk production by 0.5–2L/day, it enhances feed intake and water consumption and it contributes to improvement of body condition of cattle. Farmers have been performing the practice using family labor.

Urea treated straws and stovers are deficient in minerals and vitamins such as P, S and V-A which are useful for the activity and growth of rumen microbes and milk production. In this regard, minerals can be supplied from bone meal and mineral lick and vitamin A can be supplied from green grass. The demand of dairy cows for propionate is greater than other classes of cattle. This nutrient can be supplied from concentrate feed. Strategic supplementation of concentrate inclusive of minerals and common salt and a constant supply of drinking water are advisable ways with feeding urea treated straw to milking cows (Schiere and Ibrahim 1989). The objective of this experiment therefore was to know the feeding value of urea treated wheat straw for crossbred dairy cows as compared to untreated straw.

Materials and methods 

Site of the study

The study was carried out on station, Holetta Research Center.  The area is among the places that are known to be potentially high for dairy production.  The center is located 45 km West of Addis Ababa, the capital city of Ethiopia.  The place is situated at an altitude of 2400 m above sea level, 9⁰ 3, North and 38⁰ 38’ East longitude.  It receives an annual rainfall of about 1100 mm with an average maximum temperature of 21.3⁰C.

Experimental feeds

The treatments were three:

• Hay ad libitum + 0.5kg concentrate/L milk/day/cow,

• un-treated wheat straw ad libitum + 0.5kg concentrate/L milk + 1 kg elephant grass/day/cow and

• treated wheat straw ad libitum + 0.5 kg concentrate/L milk + 1 kg elephant grass/day/cow.

Experimental cows and management

Nine Boran-Friesian crossbred dairy cows were selected from the herd of dairy cattle at Holetta Agricultural Research center.  The cows have calved in the same month.  They were in different parity ranging 2-4 lactations.  The weight range during the start of the experiment was 243-396 kg.  The experiment was started after the cows have passed the lactation peak.  The cows were dewormed for internal parasites one week before the commencement of the experiment.

The experimental feeds were allocated randomly for three groups of cows.  A shift of feeds among the groups was performed every period.  Urea treated straw was aerated for about 2 hours before offering to cows.  The experimental feeds have been offered little by little through out the day and night, beginning at 08:00 hrs Am. To fulfill V–A requirement of milking cows, one kg elephant grass was offered for those groups fed urea treated wheat straw and untreated straw.  Experimental cows have also been provided with mineral block containing major and minor minerals to lick for about 1 hr every day. The experimental cows were allowed to drink water freely and were let exercise out of doors for about 30 minutes every morning.

Experimental design

Latin Square design was used for handling the experiment. The experimental cows were grouped in to three according to previous milk production.  Three treatments:  hay based diet, untreated wheat straw based diet and urea treated wheat straw based diets were the experimental feeds. The treatments were allocated randomly into three groups. The experiment was conducted for three periods, 21 days each.  In each period 7 days for adaptation and 14 days for data collection was allotted.

Methods of urea treatment

The spray method of alkali treatment (Wilson and Pigden 1964) that has given promising and viable procedure for improving poor quality crop residues was used for the treatment.  The straw was treated with urea in three compartments.  The compartments were constructed using wood.  A shade was also constructed to protect the treated straw from direct sunlight and rain fall.

Five kg urea, 10 liter molasses and 80 liter water was used for 100 kg straw.  Five kg urea was diluted into 80 liter water.  Ten liter molasses then was added into this solution and diluted.  Treatment of straw with the solution was based on a batch of 20 kg straw at a time to make the practice easy and the treatment efficient. Sixteen liters of urea-molasses solution was uniformly sprayed over 20 kg straw and was mixed properly.  About 4 people pressed this.  Following the same procedure, the straw that can be fed for the given cows for a week was treated.  The stack was covered with polythene plastic sheet.  This was then kept for 14-21 days before feeding.

Measurement, sampling and chemical analysis

Morning and afternoon milk of the experimental cows were measured and total milk yield was recorded daily. Milk samples were taken fortnightly and analyzed for fat, protein, lactose and total solids by Lacto scope (Automatic milk composition analyzer). The cows were weighted every two weeks and recorded.

Samples from each feed treatment were taken ever day, pooled to a weekly basis and analyzed for DM, Ash and CP by the methods described in (Schiere and Ibrahim 1989).  IVOMD was determined by the procedures described by (Tilley  and Terry 1963). Metabolizable energy was derived from % IVOMD: ME = 0.016 * g IVOMD/kg according to (McDonald et al 1995). Similarly samples taken every day from each treatment, pooled for a period were analyzed for NDF by the method described in (Van Soest and Robertson 1985).

Samples taken every day from each treatment, pooled for a period were used to determine degradability. Samples were milled using 2 mm mesh sieve.  Each type of sample was put into Dacron bags with a dimension of 140 x 90 mm and uniform pore size of 40µm.  Three gm samples from each feed treatment were put into nylon bags in duplicate and incubated into rumen of three fistulated-crossbred bulls for 0 hr, 6 hr, 12 hr, 24 hr, 48 hr, 72 hr and 96 hr. Fistulated animals have been fed hay adlib and 2 kg concentrate per day. On the termination of each incubation period, the bags were taken out from the rumen and the lose substances adhering to the outer surface of the bags were removed with cool tape water.  The bags then were dried in an oven at 650 c for 72 hrs, cooled in desiccators and reweighed.

Method of data analysis

From the 21 days data in each period, data of the 14 days excluding the first 7 days data were used for analysis. DM intake, daily milk yield, milk fat and milk protein were subjected to Analysis of Variance using General Linear Model (GLM) procedures of Statistical Analysis System (SAS 1999).  The statistical model used was: 

Y_ijk = µ + r_i + c_j + t_k(ij) + e_ijk

Where: 

Y_ijk  - Dependent variable (feed intake, milk yield, milk compositions)

µ  = Over all mean

r_i  = Effect of lactation stage (Period effect)

c_j  = Effect of cows (column effect)

t_k(ij) = Effect of feed treatment

e_ijk   = Error term

Economical analysis

The economical evaluation was based on calculation of total cost of production (cost of feeds, plastic sheet, urea, labor and wood).  Milk price was considered Based on the price paid by private consumers.

Results and discussions 

Chemical composition of untreated and urea treated wheat straws

The chemical compositions of urea treated and untreated wheat straws are presented in Table 1 and 2. 

As a result of urea treatment, CP and IVOMD content have increased.  The improvement in nutrient content due to urea treatment is in agreement with the results reported by Rehrahie and Ledin (2001).  The CP content of Teff and barley straw has increased from 3.8% and 4% to 8.9% and 7.4% respectively. Several authors also reported similar results:  The CP content of urea treated paddy straw had increased from 4.47 to 7.69. Agrawal et al (1989) reported that treatment of rice straw increased the protein content from 3.94% to 12.96% and that wheat straw from 3.43% to 7.83%. In another trial, the CP content of paddy straw due to urea treatment increased from 3.2% to 6.4% (Agrawal et al 1989). With regard to IVOMD, teff and barley straw has increased from 56.6% and 46.4% to 60.8% and 59.4% respectively. This is lower than the IVOMD% gained in urea treated wheat straw of the current study. This is because, wheat straw as low quality feed (2% CP and 31.1% IVOMD) has relatively better response to urea treatment. This idea agrees with the result of (Chenost and Kayouli 1997) that straw with lower nutrient content showed better response to urea treatment.

Ash content has increased (Table 1). The present study appeared to be similar with the study reported by (Rehrahie and Ledin 2001) that Ash content of teff and barley straw has increased from 3.8% and 4% to 8.9% and 7.4% respectively. (Zaman and Owen 1995) reported in similar manner that the Ash percentage increased from 3.8% to 4.1%. Musimba (1981) noted that the increase in ash percent is due to straws treated with urea, soluble nutrients like CP, nitrogen free extract (NFE), and ether extract (EE) and soluble carbohydrates are dissolved and lost in solution, resulting in increased crude fiber, associated cell wall constituents and Ash contents. The Author supported this statement by the findings that 30 - 40% EE and 30 – 65% CP had been solublized when wheat straw was treated with NaOH. 

With regard to fiber content, NDF has decreased from 808.2 g/kg to 761 g/kg (Table 2).

Neutral detergent fiber has reduced by 5.8% after it was treated with urea. (Givens et al 1988) noted that the reduction in NDF and hemicelluloses might be explained by the dissolving effect of urea on the hemicelluloses fraction and subsequent removal from the cell wall constituents. Consequently the amount of cell wall immediately soluble in the rumen increases, which is likely to improve the supply of fermentable sugars in the rumen.  Hence measuring the hemicelluloses fraction helps to asses how effective treatment with urea had been (Zaman and Owen 1995).  Determination of ADF and lignin is useful as there is a good statistical correlation with its digestibility. The NDF% doesn’t show the feed intake. The fiber fraction of a food has great influence on its digestibility, and both the amount and chemical composition of the fiber are important.  The amount of fiber and lignin/silica/tannin determine the digestibility (McDonald et al 1995).

Rumen degradability of the experimental feeds

Rumen degradability of all the experimental feeds has increased with incubation hrs (Table 3).

Across all incubation hrs, concentrate mix has the highest degradability as compared to roughage. Urea treated straw has higher degradability than untreated straw. As a result of alkali treatment, the degradability of sheep fed NaOH treated barley straw has increased from 33.5% to 57.4% Kudo et al 1994). 

Compared with the value of IVOMD, hay has higher rumen degradability (Table 4).

Urea treated wheat straw has higher IVOMD (435g/kg) than the value of rumen degradability, which is 412g/kg.  Untreated what straw has higher rumen degradability (345 g/kg) than the value of IVOMD, which is 311 g/kg. Concentrate has higher IVOMD (792g/kg) than the value of rumen degradability, which is 785 g/kg. The variation in value of rumen degradability and IVOMD arise from the variation of individual samples. Among the incubation hours in which experimental feeds are kept, highest degradability was recorded in 96 incubation hours.

Daily dry matter feed and nutrient intake of experimental cows

The DM feed and nutrient intake is presented in table 5.

There were highly significance (P<0.0001) differences between roughage intakes. Cows fed hay based diet had higher intake (9.03 kg ± 0.12) than cows fed treated wheat straw (5.53 kg ± 0.12) this then was higher than    cows fed untreated wheat straw (5.11 kg ± 0.12). The result is in agreement with Talukder et al (1990) in which, indigenous cows in Bangladish fed urea treated and untreated rice straw have consumed 9.4 and 8.1kg/day respectively. Biswas et al (2002) have found an increase in DM feed intake from 4.6kg/day in the untreated form to 5.6kg/day in the treated straw. 

There were significant (P<0.0001) differences between concentrate intakes. Cows fed hay based   diet had higher concentrate intake (4.29kg ± 0.07) than cows fed urea  treated straw (4.22 ± 0.07) these cows then have higher concentrate intake than cows fed untreated wheat straw based diet (4.03 kg ± 0.07). Highly significance (P<0.0001) difference on total DM intake of the experimental diets was observed. Cows fed hay based diet have consumed higher (13.29kg ± 0.15) total dry matter intake than cows fed urea treated wheat straw based diet (10.2kg ± 0.15) these cows then have consumed higher total dry matter intake than cows fed untreated wheat straw based diet (9.6 kg ± 0.15). This indicates intake to feed supplements increase with feeding nutritionally qualified roughages. Accordingly, cows fed hay based diet have consumed higher total dry matter intake than cows fed urea treated wheat straw based diet and these cows have consumed higher total dry matter intake than cows fed untreated wheat straw based diet.

Highly significant (P<0.0001) difference in total CP intake was shown between the experimental feeds.  Cows fed hay-based diet have consumed higher total CP (1508.39 g/c/d ± 16.5) than cows fed urea treated straw based diet (1248.9 g/c/d ± 16.5) these cows then have consumed higher total CP than cows fed untreated straw based diet (1047 g/c/d ± 16.5). Highly significance (P<0.0001) difference in total ME were observed between the experimental feeds. Cows fed hay based diet have consumed higher total ME (133.4 MJ/c/d) than cows fed urea treated straw based diet (92.94 MJ/c/d) these cows then have consumed higher total ME than cows fed untreated straw based diet (82.44 MJ/c/d). The result is in agreement with (Talukder et al 1990) in which indigenous cows in Bangladish fed urea treated and untreated rice straw have consumed 9.4 and 8.1kg/day respectively. Biswas et al (2002) have found an increase in DM feed intake from 4.6kg/day in the untreated form to 5.6kg/day in the treated straw. 

There were highly significance (P<0.0001) differences between roughage intakes. Cows fed hay based diet had higher intake than cows fed treated wheat straw this then was higher than cows fed untreated wheat straw.  This indicates intake to feed supplements increase with feeding nutritionally qualified roughages. Accordingly, cows fed hay based diet have consumed higher total dry matter intake than cows fed urea treated wheat straw based diet and these cows have consumed higher total dry matter intake than cows fed untreated wheat straw based diet.

In this experiment, the intake of both treated and untreated straw was reduced. The lower feed intake with urea treated wheat straw might be due to the fact that feed intake on some diets bears no relationship to digestibility and is much more influenced by supplementation (Preston 1995).  Moreover, there is also a fact that, the intake of roughage reduces as the amount of concentrate increases. Heifers fed urea treated cane sugar residue and supplemented with 3 kg concentrate have consumed more roughage than when they were supplemented with 4kg concentrate (Hassoun et al 2002).  The concentrate: roughage ratio in this experiment for hay based diet, untreated straw based diet and urea treated straw based diet respectively was 32:68, 44:56 and 43:57. The daily allowance of concentrate for the experimental cows under each treatment was based on their milk production.  The amount of roughage intake would increase if the treatments had formulated based on the requirement of cows. The level of concentrate supplementation to various urea treated crop residues was observed to be 30% of the total diet (Hassoun et al 2002).  Literature is mentioning that treatment of straw with urea has an effect on increasing dry matter intake 10 – 15% or 1kg. The digestibility and intake of feeds may be reduced by either deficiency and or excessive supply of nutrients or other constituents like lignin, silica and tannin (McDonald et al 1995).  In our case cows are expected to consume extra nutrients from the concentrate supplement.

The major control of milk production resides in dry matter intake, however, dry matter intake may be controlled to some extent by nutrient deficiency. The amount of glucose synthesized represents about 20% of the digestible energy of the diet, which is approximately the proportion of the digestible energy available from rumen propionate when propionate is 20-25% of the VFA and under these conditions propionate production may be so low as to represent less than 10% of the digestible energy available. This suggests that the animal fed straw diets are precariously balanced for glucose precursor.

As presented in Table 5, cows fed hay-based diet had consumed the highest total CP and ME.  Accordingly, they have produced the highest milk yield. Regarding the live weight gain however, cows fed urea treated wheat straw based diet have got the highest live weight gain. Cows fed hay based diet have got higher weight gain than cows fed untreated wheat straw based diet. This shows that nutrients in urea treated wheat straw have contributed more to weight gain than nutrients in the hay-based diet.  In the case of untreated wheat straw based diet which constitute the least CP and ME have produced the relatively least weight gain.

Effect of experimental diets on milk yield, milk fat, milk protein, lactose, total solids and weight gain

The effect of experimental diets on milk yield, milk fat, protein, lactose, total solids and weight gain is presented in table 6.

Highly significance (P<0.0001) differences on average daily milk yield was observed between the experimental diets. Cows fed hay based diet have produced on average higher milk yield (10.5 1iters/cow/day ± 0.08) than cows fed urea treated wheat straw based diet (8.99 1iters/cow/day ± 0.08) these cows then have produced higher milk yield than cows fed untreated wheat straw based diet (8.12 liters/cow/day ± 0.08). Gir cows, from South East Asia fed urea treated rice straw have produced 52% more milk yield than those fed untreated straw (Doyle 1982). The current result appeared to be similar to those reported from elsewhere: indigenous cows in Bangladesh fed urea treated and untreated rice straw have produced 3.25 and 2.88kg milk/day.

However, the effects of the experimental diets on the milk fat, lactose and total solids have not differed significantly (P>0.05). Rehrahie and Ledin (2001) reported that the effect of hay based diet, urea treated teff straw based diet and urea treated barley straw based diet on milk fat percent didn’t differed significantly.  Values of milk fat for hay based, urea treated teff straw based and urea treated barley straw based diet was 4.23%, 4.42% and 4.52% respectively.  Where as, highly significance (P<0.001) difference on milk protein was observed between the experimental diets. Cows fed hay based diet have produced higher milk protein (3.34%/cow/day ± 0.05) than cows fed urea treated straw based diet (3.11%/cow/day ± 0.05) these cows then have produced higher milk protein than cows fed the untreated wheat straw based diet (3.06%/cow/day ± 0.08).  Though not differed significantly, cows fed hay based diet produced higher milk fat (4.23%/cow/day) than cows fed the other experimental diets.  Cows fed both urea treated and untreated wheat straw produced similar percentage of milk fat (4.07%/cow/day). Result of the present study is relatively lower than the results obtained by Rehrahie and Ledin (2001). Doyle (1982) however reported that yield of milk fat in Gir cows fed urea treated rice straw was doubled those of the untreated straw. Cows fed hay based diet have produced higher milk protein (3.34%/cow/day) than cows fed urea treated straw based diet (3.12%/cow/day) these cows then have produced higher milk protein than cows fed untreated wheat straws based diet (3.06%/cow/day). A relatively higher milk protein (3.47%, 3.36% and 3.35%) than the present study were observed in a trial of feeding crossbred dairy cows fed hay based diet, urea treated teff straw based diet and urea treated barely straw based diet respectively.  Like milk fat, effect of the experimental diets on milk lactose didn’t differed significantly.  Cows fed hay based diet produced relatively higher milk lactose (4.11%) than cows fed urea treated wheat straw (4.09%), these cows then have produced relatively higher milk lactose than cows fed untreated wheat straw based diet (4.06%). Sanh et al (2002) in feeding of urea treated rice straw to crossbred lactating cows reported an increase in fat concentration.

The effects of experimental diets on milk total solids haven’t differed significantly.  Cows fed hay based diet have produced relatively more total solids (12.96%) than cows fed both urea treated wheat straw and untreated wheat straw based diets (12.71% and 12.84%) respectively.

On average basis of the entire experiment, cows fed urea treated wheat straw based diet have got higher live weight gain (370 kg) than cows fed hay based diet (362 kg) these cows then have got higher weight gain than cows fed the untreated wheat straw based diet (357 kg). Talukder et al (1990); Doyle (1982) found a significant improvement in feed conversion rate from 52 kg DM per kg gain in the untreated straw to 13kg DM per kg gain in the treated straw in cows and buffaloes. Growth performance and feed utilization efficiency were not improved by straw treatment in the absence of concentrate supplement. The nutrients provided by the concentrate play an essential role in permitting the additional digestible energy to be used for productive purposes.  Feeding trial conducted with sheep demonstrated that urea treated straw plus mineral supplement was capable of maintaining live weight.  Farmers who witnessed first-hand the superior feeding value of urea treated straw were quick to repeat the practice and often treating larger amounts straw. The technology was simplified to the point where farmers could, after one or two demonstrations, carry out the task themselves (O'Donovan et al 1997)

With feeding urea treated straw, lactating cows require supplementation with concentrate feeds. The type of feed supplement should be any source of rumen un-degradable protein and energy feed. The feed supplement in the current trial was a mixture of wheat bran, wheat middling, noug cake and salt.  Several Authors have witnessed the importance of supplementing rumen un-degradable protein and energy feed sources to be available for digestion in the lower tract of the ruminant. Talukder et al (1990) reported that the response to rumen un-degradable protein is better with urea treated rice straw than untreated rice straw. Khan et al (1990) also indicated that fish meal should be supplemented to native lactating cows of Bangladesh fed urea treated rice straw.

Urea treated straw is not complete feed.  Some nutrients like V-A and minerals are lucking in straws. Cows under this trial were supplemented with green elephant grass and minerals lick to supply the V-A and mineral requirement of dairy cows respectively. Biswas (2002) in their feeding trial with urea treated rice straw to milking cows in India have included mineral mixture during treatment to support the mineral that is lacking in the straw and thus found better intake and milk production. Gebrehiwot et al (1994) have supplemented urea-molasses block to cows fed urea treated rice straw to help cows get complete feed including minerals and the effect of the lick block supplementation significantly increased the milk yield of cows. Prasad et al (1998) from their feeding urea treated rice straw noted that the extra concentrate supplement is offered to meet the production requirement. Sanh et al (2002) in a feeding trial of crossbred lactating cows with urea treated rice straw noted that replacement of green grass by urea treated straw with a ration of 50:50 is as good as feeding 100% green grass in terms of milk yield, body weight gain and feed conversion.

Economic analysis

The costs for feed and materials used in the experiment and the cost-profit analysis are shown in Table 7 and 8 respectively.

Based on milk price paid by private consumers, with 8.00 Birr/1t milk, cows fed hay based diet have got the highest net return 58.88 ETB /cow/day. This was followed by urea treated straw based diet which has better a net return of 52.55 ETB than untreated wheat straw based diet which had  a net return of 48.96 ETB /cow/day. The economic advantage of feeding urea treated straws over untreated straw to milking cows has reported by different Authors. Prasad et al (1998) in feeding urea treated rice straw to crossbred milking cows concluded that the cost of feeding per kg FCM yield was lower with rations containing urea treated rice straw. Feeding of urea ensiled paddy straw becomes economically attractive practice for cattle-owning paddy cultivators (Doyle 1982). Feeding urea treated wheat bhusa to crossbred cows in India brought about a net saving of Rs 18/day.

Conclusions and recommendations 

• Treatment of straw with urea has improved the crude protein, In vitro organic matter digestibility and rumen degradability.

  
  

• Among the treatments, cows fed hay based diet has produced the highest milk.

  
  

• Compared to untreated straw, cows fed urea treated wheat straw based diet has produced higher milk 

  
  

• Among the treatments, hay based diet was the most economically profitable.  This was followed by urea treated wheat straw and the least profitable was untreated wheat straw.

  
  

• Experimentation should be carried out to know the appropriate level of concentrate supplementation with feeding urea treated wheat straw to dairy cows.

  
  

• Since the price of molasses is getting increasing and is becoming inaccessible, information is needed on how to replace molasses with other locally available degradable feeds.  

  
  

• Investigation is also required on how to replace urea with other nitrogen rich compounds available locally.

References 

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Received 11 October 2010; Accepted 3 November 2010; Published 9 December 2010

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