Effect of lime and/or urea treatment of sesame (Sesamum indicum L.) straw on feed intake, digestibility and body weight gain of sheep

Teferi Aregawi, Getachew Animut¹, Kefelegn Kebede¹ and Habtemariam Kassa¹

Humera Agricultural Research Center, P.O.Box 65, Humera, Ethiopia
teferia2005@yahoo.com
¹School of Animal and Range Sciences, Haramaya University, P.O.Box 138, Dire Dawa, Ethiopia

Abstract

This study was carried out to determine effect of lime and/or urea treatment of sesame straw (SS) on intake, digestibility and daily body weight (BW) gain (ADG) of sheep. Twenty four yearling intact male Begait sheep with initial BW of 29.2+2.79 (mean+SD) were grouped into six blocks of four animals each and randomly assigned to four dietary treatments. Treatments were untreated SS (CT), 3% lime treated SS (L3), 4% urea and 3% lime mixture treated SS (L3U4) and 4% urea treated SS (U4). The straw was fed ad libitum and each animal was supplemented with concentrate mixture composed of 184g dry matter (DM) sesame seed cake and 87g DM wheat bran. The experiment consisted of a feeding trial of 90 days and digestibility trial of 7 days.

The crude protein (CP) content of SS in CT, L3, L3U4 and U4 were 4.44, 4.01, 7.88 and 7.92 % DM. Total DM intake was 1034, 957, 995, 1323 g/day (SEM = 22.2) and was highest for U4 followed by CT then L3, while the value for L3U4 was similar with CT and L3. Intake of CP was in the order of U4 > L3U4 > CT > L3 (45.9, 38.4, 78.4 and 105 g/day for CT, L3, L3U4 and U4, respectively). Digestibility of DM was higher for L3U4 (58%) and U4 (62%) as compared to CT (43%) and L3 (50%). Digestibility of CP ranged 28% for CT and 51% for U4 and was in the order of U4 > L3 > CT, while the value for L3U4 was similar with L3 and U4. ADG was in the order of U4 > L3U4 > L3 = CT (29, 37, 51, 67 g/day (SEM = 2.7)) for CT, L3, L3U4 and U4, respectively. Results of this study suggested that urea treatment of SS positively impacts intake, digestibility and body weight gain of Begait sheep. Conversely, lime treatment failed to improve the feeding value of SS to sheep. Moreover, treatment of SS with a combination of lime and urea did not have an additive effect in enhancing the feeding value of SS. Therefore, according to the current results SS treatment with urea solution along with supplemental protein and energy source is a good option in improving the utilization of the sesame straw.

Key words: begait sheep, chemical composition, sesame seed cake, wheat bran

Introduction

Under nutrition, due to inadequate or fluctuating nutrient supply is a major constraint limiting the productivity of livestock in Ethiopia. Under traditional system of production, ruminant animals mainly rely on mature grasses and crop residues (Seyoum and Zinash 1989), which are characterized by low to moderate digestibility, and low levels of nitrogen, protein and minerals (Preston 1995). In the lowlands of Ethiopia, the most important feed resources available to livestock are native grasses and browse with crop residues increasing in importance as livestock feed (Alemayehu 2004). The continued growth in human population have increased competition for natural resources, particularly land, in recent decades resulting in large areas of natural grasslands to be converted into arable lands and settlements. The expansion of cropping at the expense of grazing lands that in turn increases availability of crop residues, results in significant increase of the degree of integration between crop and livestock.

Sesame straw is abundantly produced in the Northwestern lowlands of Ethiopia since sesame is widely cultivated in the area. Similar to other crop residues, sesame straw (SS) is generally low in nutritional value with low level of protein (4-5% DM), high fiber content (NDF > 50% DM) and low digestibility (37-42% DM) (Teferi et al 2013). This demands for designing appropriate strategies to enhance the feeding value of sesame straw to increase feed intake and digestibility. So far, limited research has been published concerning methods to improve sesame straw as livestock feed.

Various treatment methods have been used to improve nutritive value of straw including physical, biological and chemical treatments (Ibrahim 1983). Method of processing straws such as chopping has been shown to affect feed intake and utilization (Lu et al 2005). Different chemicals are also used to upgrade the nutritive value of straws. Lime (CaO) can be used to enhance the utilization of crop residues and the level of calcium (Ca) in straws (Chaudhry 1998). Urea is a commonly used chemical for straw treatment to improve nutritive value (Sundstol and Coxworth 1984). Although urea treated straw has been used for straw treatment, the cost was relatively high due to increasing price of urea (Trach et al 2001). Fadel Elseed et al (2003) suggested that when amount of urea was reduced and combined with lime, it could improve rumen degradability. Such a mixture would be able to combine treatment effects of both chemicals (Sirohi and Rai 1999), with resultant increase of Ca and nitrogen in the treated straw. Moreover, mould inhibition is an important effect of ammonia released from urea from lime urea mixture in moist straws (Zaman et al 1994; Zaman and Owen 1995; Pradhan et al 1997). However, alkali treatments of straws may have variable effects on animal production (Williams et al 1997) because of various factors such as straw genotype (Habib et al 1998) and level of calcium hydroxide and urea, moisture, treatment time and temperature (Zaman et al 1994). The objective of this experiment was therefore; to evaluate the effect of urea and/or lime treatment of SS on feed intake, digestibility and body weight gain of sheep.

Materials and methods

Description of the study area

The experiment was conducted during February - May 2013 at Humera Agricultural Research Center, which is located in the Northwestern lowlands of Ethiopia 960 km from the capital Addis Ababa. The area is located at a latitude and longitude of 14^o15’ N and 36^o35’E, respectively. The altitude of the area is 568 meters above sea level. The maximum temperature varies between 33 ^oC in April and 42 ^oC in August, while the minimum temperature ranges from 17.5 ^oC in July to 22.2 ^oC in May. The mean annual temperature is 26 ^oC and the average annual rainfall is 448 mm. Most of the rainfall occurs during June to September (MOA 1998).

Experimental feeds preparation and feeding

Sesame straw from Hirhir cultivar was collected after grain harvest from Humera Agricultural Research Center’s seed multiplication farm. The collected straw was hand chopped to a size of about 4-5 cm length to facilitate packing during ensiling with 4% urea, or 3% lime or a mixture of 4% urea and 3% lime (w/w). Six pits (two pits for urea treatment, two for mixture of  urea and lime treatment, and two pits for lime treatment), each having a size of 6 m³ were prepared for ensiling the straw. The wall of the pits was covered with polyethylene sheet. Fertilizer grade urea and lime was dissolved in water to assure 50% moisture in the treated material (Zaman et al 1994). Sesame straw was sprayed with 4% urea, 3% lime, or a mixture of 4% urea and 3% lime solution layer by layer until the pit was filled, and thoroughly mixed. The straw was well pressed by trampling before placing the next layer and finally sealed using polyethylene sheet and loaded on top by mass of soil to make it airtight. It was, then, left unopened for twenty-one days as per the recommendations of Zaman et al (1994) and Sirohi and Rai (1998) and a portion of the straw was taken daily and ventilated overnight before offering to the animals.

Sesame seed cake was purchased from traditional sesame oil expellers in Humera town, while wheat bran was purchased from Gonder town flour mill factory. The basal diet, i.e., treated and untreated SS were offered ad libitum ensuring 20% refusal in excess of the previous day straw intake. All animals received supplemental feed composed of 184g DM of sesame seed cake and 87g DM wheat bran in two equal portions at 0800 and 1600 hours in a separate feeding trough. Fresh clean water and common salt block were available to the animals all the time throughout the experiment. Animals were adapted to the respective experimental diets for 15 days before the commencement of the actual data collection.

Experimental animals and management

Twenty four yearling intact male growing Begait sheep with initial body weight of 29.2+2.79 (mean+SD) were purchased from the market in Humera. Age of the animals was determined by their dentition and information obtained from the owners. The experimental animals were ear tagged for identification, quarantined for 15 days. During this time each animal were treated against internal parasites (broad spectrum anthelmintic), sprayed (Accaricide) against external parasites and vaccinated against sheep pox, ovine pasteurellosis and anthrax based on the recommendation of a veterinarian.

Experimental design and treatments

The experiment consisted of 90 days of feeding and 7 days of digestibility trials. There were four treatments in this study. Treatments were untreated SS (CT), 3% lime treated SS (L3), 4% urea and 3% lime mixture treated SS (L3U4) and 4% urea treated SS (U4). The levels of urea and lime used in this study were determined based on the better in vitro organic matter digestibility and in sacco dry matter degradability results obtained in a companion study that used different levels of urea and lime treatment of SS. The experiment design used in this study was randomized complete block design (RCBD). At the end of the quarantine period, animals were weighed and blocked based on initial body weight into six blocks of four animals each. The four treatment diets were randomly assigned to each animal in a block, making six animals per treatment. Animal were placed in individual pens equipped with watering and feeding troughs.

Feeding trial

The amounts of feed offered and refused were recorded daily for each animal and the daily feed intake was determined by difference. Representative samples of basal feeds offered and refused after thoroughly mixing on daily basis as well as sesame seed cake and wheat bran per batch were collected and a sub-sample was taken for chemical analysis. Straw treated with urea was placed in bags and kept in deep freezer to prevent ammonia loss until sub-sampled for analysis. The metabolizable energy intake (MJ/day) of experimental animals was estimated from in vivo digestible organic matter intake (DOMI) values by using the equation of AFRC (1993), as ME (MJ/day) = 0.0157*DOMI.

Body weight of each animal was measured at the onset of the experiment, and every ten days interval subsequently. Body weights were taken in the morning before the daily feed was offered using spring balance having a sensitivity of 100g. Average daily body weight gain (ADG) was calculated as the difference between final and the initial body weights of the animals divided by the number of experimental days. Feed conversion efficiency (FCE) of the animals was determined as a ratio of daily weight gain to the daily DM intake.

Digestibility trial

Digestibility trial was conducted following the feeding trial using the same animals and similar dietary treatments. The animals were fitted with fecal collection bags for fecal collection. They were adapted for three days to carrying the fecal collection bags followed by seven days of feces collection during which daily feed offered and refused for each animal was recorded for the determination of daily feed intake. Samples of feed offered and refused were taken daily, and were composited per feed type for the feed and per treatment for refusals for chemical analysis. Daily collected feces for each animal were weighed in the morning before feeding and 10% representative samples were taken and kept in dip freezer at -20^OC. On the last day of the collection period, the composite fecal samples for each animal was thawed, thoroughly mixed and sub sampled for chemical analysis. Apparent DM and nutrients digestibility was determined as the difference between nutrients intake and that recovered in feces expressed as a proportion of nutrient intake.

Chemical analysis

Samples of feed offered and refused, and fecal samples were dried at 60C for 48 hours, ground to pass 1 mm screen in a Willey mill and stored pending chemical analysis. Dry matter (DM), ash and nitrogen (N) were assayed using the method described by the AOAC (1990). The crude protein (CP) content was determined by multiplying the N value by a factor of 6.25. Neutral detergent fiber (NDF), acid detergent fiber (ADF) and acid detergent lignin (ADL) were determined following the procedure of Van Soest and Robertson (1985). Hemicellulose and cellulose contents were determined as a difference between NDF and ADF and ADF and ADL, respectively.

Statistical analysis

Data were subjected to Analysis of Variance (ANOVA) using the General Linear Model (GLM) procedure of SAS (SAS 2002). Differences among treatment means were tested using least significance difference (LSD) test.

The model for data analysis was:

Yij  = m + ti + bj + Îij, where, Yij = is the response variable, m = the overall mean, ti = the treatment effect, bj = the block effect, and Îij = is the random error.

Results and discussion

Chemical composition

As expected lime treatment reduced the OM content presumable due to the added Ca to SS from the lime used to treat the straw (Table 1). On the other hand urea treatment of SS almost doubled the CP content of the straw, obviously due to the incorporated nitrogen from urea into the SS. The increase in CP content with urea treatment of SS is consistent with reports of other ammoniation studies of teff straw (Getahun 2014) and wheat straw (Moss et al 1994). The CP content of the untreated SS used in this study was quite low, while that of the treated SS was about the 8% level of CP required to satisfy the maintenance requirement of ruminants (Norton 2003). Roughage feeds with NDF content of more than 65% DM were categorized as low quality roughages (Singh and Oosting 1992). Thus, based on the NDF content, both treated and untreated SS used in the current study may be classified as low quality roughages that may impose limitations on the productivity of livestock. This suggests that supplementation with protein and energy rich dietary ingredients are required to supply nutrients needed for production. Thus, the use of supplementary sesame seed cake and wheat bran that are high in CP and energy, and low in fiber fractions in the current study was in an attempt to provide sufficient nutrients for the growing sheep.

Treatment of SS with lime, urea and urea lime mixture decreased the contents of NDF, ADF and cellulose and increased the level of hemicelluloses of SS. Moreover, sole urea and sole lime treatment were effective in reducing the ADL content of SS. Gao (2000) reported decreased values of NDF, ADF and ADL for urea treated wheat straw. According to Madrid et al (1997) and Trach et al (2001), urea was effective in solublising NDF and hemicelluloses from straws, but did not significantly affect other cell wall components. Moreover, Trach et al (2001) reported that lime, and urea and lime mixture has high effect on delignification as reflected by reduced NDF and ADF levels of rice straw which are in agreement with the results of the present study. Reduction in the levels of cellulose and increase in hemicelllulose contents with alkali treatment observed in this study suggested that the magnitude of effect of alkali treatment to be higher on ADF than NDF and lignin.  

In this study the supplemental feed was totally consumed by the animals. The lower CP and higher fiber content of SS refusals suggested the presence of selectivity by animals against the more fibrous stem part of the SS. However, the selectivity of straw fractions appeared to be relatively less in the treated SS than the untreated straw.

Dry matter and nutrient intake

Sheep that received 4% urea treated SS had the highest basal diet and total DM intake, while animals fed with 3% lime treated sesame straw had lower basal diet and total DM intake than those fed untreated SS (Table 2). Intake of total OM, NDF and ADF was in the order of U4 > CT > L3U4 = L3. Consistent with differences in the CP content of the basal diet and intake of the basal diet, CP intake was in the order of U4 > L3U4 > CT > L3.  Generally intakes of DM and most nutrients from SS were not improved by lime or mixture of lime and urea treatment. The ME intake was improved as a result of treatment with urea and combination of lime and urea treatment of SS as compared to the untreated SS, but ME intake of SS was not increased by sole lime treatment of SS as compared to the untreated straw.

The increase in straw DM intake by urea treatment in the present study was about 38%. This is consistent with the reported of Chenost and Kayouli (1997) that noted a range of 15 to 50% increase in intake of urea treated straws. Sheep fed urea treated wheat straw was also reported to have increased DM intake by 13% (Singh and Klopfenstein 2001) and sheep fed urea treated sorghum stover increased DM intake by 34% (Reddy and Reddy 2002). In the current study lime treatment depressed SS intake by sheep. This is in line with the results of Saadullah et al (1981) that made similar observations on rice straw treated with 4% lime. According to Sarnklong et al (2010), although lime treatments increase the degradability of straw, the dry matter intake decreases, due to a reduced acceptability of the treated feed by animals. To the contrary, increased OM intake (Djajanegara et al 1985) and increased DM intake (Sahoo et al 2002) were observed in calcium hydroxide treated wheat straw. For combination of lime (3%) and urea (2%), Nurfeta et al (2009) found increased intakes of DM, OM, CP, NDF and ADF than the untreated wheat straw, though no difference was found in their ME intake. Moreover, Trach et al (2001) showed that treatment of rice straw with 2% urea and 3% lime was more effective than only 4% urea in terms of DM intake. Reports of Nurfeta et al (2009) and Trach et al (2001) on intakes of DM and nutrients while employing a combination of lime and urea treatment fail to be in agreement with results of the current study. This suggests that the use of lime alone or in combination with urea to treat SS might induce reduced palatability of the straw and consequently reduce intake of SS.   

Dry matter and nutrient digestibility

Apparent digestibility of DM, OM, CP, NDF and ADF digestibility increased by treatment with urea and combination of lime and urea as compared to the untreated SS (Table 3). The apparent digestibility of DM and nutrients between the straws treated with urea and with a combination of lime and urea were similar. Compared with untreated SS, increment in digestibility of nutrients as a result of sole lime treatment was obtained only for CP and ADF, but not for DM, OM and NDF. Animal that received sore urea treated SS had higher digestibility of DM and nutrients than those fed sole lime treated SS, while the latter had similar digestibility values of OM and CP with animals in L3U4.

The 46% increment in DM digestibility due to urea treatment in the present study was higher than the expected increases in digestibility of 5- 10 % and 20% suggested by Preston (1995) and FAO (2002), respectively. This might be due the supplementation of sesame seed cake and wheat bran in the present study which could have improved nutrient supply to the rumen microbes with consequent rise in ruminal digestion of the roughage feeds.

Fall et al (1989) conducted a feeding trial based on urea treatment with additional supplement and arrived at DM digestibility increment of 27, 16, 50, 38 % for treated rice straw, maize, millet and sorghum stovers, respectively, indicating that digestibility SS is more responsive to urea treatment as compared to some other cereal straws. In general, it is noted that the lower the quality of the straw, the higher the response to urea treatment (Mascarenhas-Ferreira et al 1989). Increased digestibility of OM and NDF (Wanapat et al 2009; Trach et al 2001), CP (Wanapat et al 2009; Reddy and Reddy 2002) and ADF (Wanapat et al 2009; Moss et al 1994) of straws due to urea treatments has been noted.

Previous studies showed contradictory results concerning the digestibility of straws as a result of lime treatment. According to Gharib et al (1975), lime appears to increase ADF and cellulose digestibility. Moreover, increased digestibility of DM (Sadullaah et al 1981; Devendra 1979), OM and NDF (Trach et al 2001; Djajanegara et al 1985) were observed in calcium hydroxide treated straws, which were not observed in the present study. Verma (1981) noted that digestibility of straw treated with lime gave poor results due to the high Ça content that can produce an imbalance in the Ça:P ratio. Ammerman et al (1963) have reported that protein and energy digestibility was reduced when cattle were fed a diet containing 4.4% Ca. To the contrary, NRC (1996) indicated high concentrations of dietary calcium are tolerated well by cattle (NRC 1996), and most of the additional calcium is excreted in the faeces (Djajanegara et al 1985). Although ruminants can tolerate wide Ca: P ratios (Call et al 1978), a ratio of Ca: P higher than 7:1 has been reported to reduce growth and feed efficiency (Wise et al 1963; Ricketts et al 1970).

Lime is a weak alkali with low solubility, thus ensiling for longer periods of time seems to be required for effective treatment to increase the straws digestibility (Trach 1998). Moreover, digestibility results in the current experiment should be interpreted cautiously because of the possible impact of high ambient temperature of the experimental site on the effectiveness of lime treatment as the solubility of lime decreases when the ambient temperature is high (Weast 1975).

Similar to result of the current study, mixture of urea and lime treatment of wheat straw improved the digestibility of straw compared to the untreated straw (Sahoo et al 2002). In line with the present study, combined lime and urea treatment fail to show an additive effect on the digestibility of straw and did not further improve digestibility of the straw as compared to the sole urea treated rice straw fed to growing cattle (Trach et al 2001). According to Trach et al (2001) negative interactions between lime and urea might have reduced additive effect in improving digestibility of the treated straw when the straw is treated with a combination of lime and urea. Hadjipanayiotou (1984) and Zaman and Owen (1995) have also reported the possible presence of negative interaction between lime and urea when used in conjunction to treat straws. This may be due to the inhibition of urease activity by high alkalinity induced by lime (Trach et al 2001), that may reduce the formation of ammonia from urea and the consequent effect of ammoniation in improving the feeding value of straws.

Body weight change and feed conversion efficiency

As planned initial body weights of sheep were similar among treatments. Sole urea treatment followed by combination of urea and lime treatment of SS resulted to higher ADG of sheep (Table 4) as compared to the other two treatments. Lime treatment of SS fail to induce a significant increase in ADG as compared to animals fed untreated SS. Feed conversion efficiency was in the order of U4 = L3U4 > L3 > CT. Variation in ADG of sheep among treatments in the present study appears to be consistent with differences in intake and digestibility of DM and nutrients among treatments.  In the current study, positive and significant (P<0.05) correlations (r = 0.43, 0.80, 0.75, and 0.78) were observed between ADG and OM intake, CP intake, digestibility of OM and digestibility of CP, respectively. In agreement with the present finding, previous studies reported increased ADG with increase in nutrient intake such as CP (Dawit  and Solomon 2008; Solomon et al 2003).

Many studies have been carried out to evaluate supplemented untreated and urea treated straws on the performance of sheep. The ADG for sheep fed untreated SS with the level of concentrate supplementation employed in this study (29.2 g/day) was comparable to the value of 35 g/day reported by Meng and Xiong (1993) for sheep maintained on untreated wheat straw supplemented with 400 g /day concentrate mix. A slightly lower ADG of 20 g/day as compared to the current result was reported (Liu et al 1998) for Huzhou lambs maintained on untreated rice straw supplemented with 262 g/day of mustard seed cake. The ADG of 67.4 g/day for sheep maintained on urea treated SS with the level of supplementation used in the current study was somewhat higher than the ADG values of 31.3, 47.2 and 54.4 g/day reported for Washera sheep fed urea treated rice straw supplemented with 300 g/day of noug seed cake and wheat bran (Hailu 2011), for Arsi-Bale lambs maintained on urea treated wheat straw supplemented with 300 g/day of Leucaena leucocephala  foliage hay (Getahun 2014), and for Hararghe highland sheep fed a basal diet of urea treated maize stover supplemented with 250 g/day of concentrate mix (Hirut 2011), respectively. Such comparisons suggests that SS whether untreated or urea treated has a comparable feeding value for sheep with other commonly used crop residues. 

Comparison between urea treated SS in the present study with previous studies (Gallal et al 1979; Abebe 2006; Fentie 2007; Simachew 2009) carried out on a basal diet of hay suggest that hay can be well substituted by urea treated SS. For instance, ADG of 69 g/day was reported for Arsi-Bale sheep fed a basal diet of grass hay supplemented with 300 g/day of linseed cake and wheat bran (Abebe 2006) and 70.9 g/day ADG was noted for sheep supplemented with 300 g/day noug seed cake and wheat bran in hay based feeding (Fentie 2007), the results of which are comparable with the current study for the urea treated SS group. Lower ADG (41 g/day) was reported in Washera sheep supplemented with 300 g/day noug seed cake and maize bran in hay based feeding (Simachew 2009) and 59 g/day for Highland sheep supplemented with 300 g/day concentrate mix to grass hay basal diet (Gallal et al 1979) as compared to the current result for U4. In line with the present finding, Promma et al (1983) also suggested that urea treatment improved the nutritive value of rice straw and made it at least equivalent to grass hay.

Increased ADG by about 130% due to urea treatment of SS (U4) as compared to the untreated straw (CT) in the present study was higher than the ADG increment of 13% (Al-doori et al 2011) and 62% (Getahun 2014) reported for lambs fed on urea treated wheat straw compared to untreated wheat straw. Similarly, Mattoni et al (2007) reported 24 and 29% increment in ADG of sheep fed urea treated millet and sorghum straw compared to sheep on untreated straw at equal amount of supplementation. Higher increment in ADG of sheep fed on urea treated SS over untreated straw in this study as compared to other studies with other crop residues may suggest the considerable potential of urea treatment in improving the nutritive value of SS. Generally, SS can have a good potential as roughage source for sheep in areas like the Northwestern lowlands of Ethiopia where a significant increase in expansion of cropping at the expense of grazing lands (Binyam 2012) is occurring.

Conclusion

• Results of this study suggested that urea treatment of SS positively impacts intake, digestibility and body weight gain of Begait sheep. Conversely, lime treatment failed to improve the feeding value of SS to sheep. Moreover, treatment of SS with a combination of lime and urea did not have an additive effect in enhancing the feeding value of SS. Therefore, according to the current results SS treatment with urea solution along with supplemental protein and energy source is a good option in improving the utilization of sesame straw.

Acknowledgements

The authors are greatly indebted to the Rural Capacity Building Project (RCBP) through Ethiopian Institute of Agricultural Research (EIAR) for funding this research. Assistance from experts of Humera Agricultural Research Center as well as laboratory technicians at Holleta Agricultural Research Center Animal Nutrition Laboratory is duly acknowledged.

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Received 16 July 2014; Accepted 19 July 2014; Published 1 August 2014

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