Feed intake and growth performance of crossbred dairy calves fed on a basal diet of wheat straw treated with urea-molasses, urea-lime, and effective microorganisms

ABSTRACT

The effects of various treatment options on the nutritional value of wheat straw as well as the growth performance of crossbred calves fed the treated wheat straw were evaluated. Twenty-four female calves (75% Friesian-Borana), weighing 99.3 ± 19.7 kg (aged 6–9 months), were divided into four groups of six animals using a randomized complete block design. The feeding trial lasted approximately 104 days. The dietary treatments were: untreated wheat straw (control T1), wheat straw treated with urea-molasses (T2), urea-lime (T3), and effective microorganisms (T4). Results showed that the treatment options affected the physical silage quality and chemical composition of wheat straw. Calves in the T3 and T4 groups had a higher daily DM intake (3.7 and 3.5 kg/head, respectively) than those in T2 (3.1 kg/head) and T1 (3.02 kg/head) groups. Calves in the T3 (422.7 g/d) and T4 (391 g/d) groups gained greater weight than those in the T2 (281.7 g/d) and T1 (204.4 g/d) groups (P < 0.001). Thus, improving the feed value of wheat straw with urea-lime or effective microorganisms treatment options suggested in this trial could result in cost-effective and significant growth performances when crossbred calves were supplemented with concentrate at a rate of 1.2% of their live weights.

KEYWORDS:

• Crossbred calves
• feed intake
• live weight
• treatment
• wheat straw

1. Introduction

The inadequate supply of feeds for optimum production limits global livestock production (Mahesh and Mohini 2014). Land allocated to forage production is unlikely to increase due to increasing human and animal populations, urbanization, and industrialization. One possible low-cost feed alternative resulting from crop production is crop residue. Crop residues are vital to feeding resources for livestock in tropical and subtropical countries (McDonald et al. 2010). It contributes the most to the overall feed supply, beginning with the harvest of food crops and continuing through wet months when range forage is scarce (Mengistu et al. 2017). The nutritional quality enhancement of crop residue using potential treatment options aims to improve the nutritional value, palatability, intake, and digestibility of feeds in low and middle-income countries (Balehegn et al. 2020). Various physical, biological, and chemical treatment options have been investigated globally to improve the nutritional quality of crop residues (Tesfaye et al. 2011). Crop residues and other roughages contribute up to 30–95% of available feed in Ethiopia. Depending on the production system the current wheat straw yield in Ethiopia, estimated from the (Central Statistics Agency, CSA 2021) grain yield using recommended conversion factors developed by Kossila (1988), is close to 8.7 × 10⁶ tons. Similarly, wheat (Triticum aestivum L.) is Ethiopia’s second most important crop in terms of grain yield (CSA 2021).

Despite the high production, crop residues, particularly wheat straws, are underutilized in Ethiopia due to their low nutritional value. To properly utilize these abundant crop residues, potential treatment options must be identified. However, several studies showed that wheat straw treated with urea increased its crude protien and in-vitro organic matter digestibility and decreased its fiber contents compared to untreated wheat straw (Getahun 2014; Mesfin and ktaw 2010). Similarly, treating wheat straw with urea and ammonium bicarbonate increased its CP from 3.2% (untreated) to 8.7% and 9.5%, respectively (Ali et al. 2002). Furthermore, feeding urea-treated straw was reported to have reduced the need for concentrate supplementation through increased nitrogen content and improved palatability, digestibility, and animal weight during seasons of feed shortage (Abate and Melaku 2009). On the other hand, the combination of urea and lime treatment options increased crude protien and organic matter and also improved dry matter intake and organic matter intake as compared to untreated wheat straw (Can et al. 2004; Nurfeta et al. 2009). Effective Microorganisms (EM) is a culture of coexisting beneficial microorganisms, primarily lactic acid bacteria, photosynthetic bacteria, yeast, fermenting fungi, and actinomycetes, cultured in liquid according to a specific method (Renuka and Parameswari 2012). A study showed that crop residues treated with effective microorganisms had improved nutritive value, digestibility, and intake (Mulugeta 2015). Effective microorganism-ensiled coffee husk was also used as a biological inoculant, and it was revealed that the overall nutritional value of wet-processed coffee husk improved (silage quality, chemical composition, and dry matter digestibility) (Kassu et al. 2014).

However, there is very limited information on the comparative biological and economic responses of dairy calves fed wheat straw treated with various treatment options in Ethiopia. Therefore, this study was initiated to determine the effects of treating wheat straw without nothing or with urea-molasses, urea-lime, or EM followed by ensiling on chemical composition of wheat straw and the intake, apparent digestibility, growth performance, and total feed cost of crossbred calves fed diets containing the treated and untreated straws.

2. Materials and methods

2.1. Experimental animals selection and management

The experiment was conducted at the Holetta Agricultural Research Center (HARC) dairy farm, which is located 29 kilometers west of Addis Ababa at latitude 9° 00’ N and longitude 38° 30’ E. Twenty-four weaned crossbred (75% Friesian-Borana) female calves weighing 99.3 ± 19.7 kg (aged 6–9 months) were selected from the on-station dairy herd. The calves were dewormed for internal parasites three weeks before the experiment started. The calves were individually stall-fed (1.8x1.2) in a well-ventilated barn with a concrete floor and an appropriate slope for drainage and gutters.

2.2. Experimental feed preparations

The wheat straw variety ‘Dandea,’ which is used as a basal diet, was collected from on-station plots in January 2021. Part of the stored baled wheat straw was chopped by hand into 5–10 cm pieces and then treated with one of the three treatment options. The calves in the first treatment group were fed chopped untreated wheat straw (T1) while others were fed chopped straw ensiled after treatment. The wheat straw used as a basal diet for calves in the T2 group was treated with a urea-molasses solution made up of 5% urea, 10% molasses, and 80 liters of water for every 100 kg of air-dried and chopped wheat straw mass (Sundstøl and Owen 1984). The urea-lime (T3) solution was made by combining 2.5% urea, 2.5% quick lime, and 80 liters of water for 100 kg of air-dried and chopped wheat straw mass (Millam et al. 2017). Wheat straw was treated with an effective microbial inoculum for the calves in the last treatment group (T4). The microbial inoculant, also called activated effective microbial solution (EM-2), was purchased from Weljijie, a local private limited company based in Bishoftu, Ethiopia. The activated microbial inoculant (EM-2) was further diluted to produce an extended form of the EM solution from one liter of EM-2 plus one liter of molasses dissolved in 18 liters of water. At a rate of 50 liters per kg straw mass, the final solution was sprayed directly on air-dried and chopped wheat straw (Tibebu et al. 2018). Two above-ground concrete silos with dimensions of 2 × 1.5 × 1 meter (length, width, and height) were prepared for each treatment. The volumes of straw treated at a time were calculated by considering the length of the experiment, the calves’ daily intake, and the total number of experimental animals. The silos’ walls were lined with polyethylene sheets. Each treatment option's uniformly sprayed straws were placed and compacted inside the silo, batch by batch until the silo's capacity was reached. Finally, the silos were sealed and topped with heavy stones to create an airtight enclosure. Wheat straw were fermented in the silo for 21 days for all treatment options, according to the recommendations.

2.3. Experimental design, feeding, and data management

Twenty-four experimental animals were divided into four groups of six animals each to serve as replicate animals. A completely randomized block design (RCBD) was used. Every block’s animals were assigned to one of the four dietary treatments at random. The experiment lasted 104 days in total, including 14 days of adaptation and 90 days of data collection. The four dietary treatments were as follows: – untreated wheat straw ad libitum (T1), urea-molasses-treated wheat straw ad libitum (T2), urea-lime-treated wheat straw ad libitum (T3), and effective microorganisms-treated wheat straw ad libitum (T4) plus concentrate supplemented at a rate of 1.2% of the calves’ live weight. The basal diets were weighed for each animal individually at a rate of 20% refusal from the previous day’s offer. The basal and supplemental feeds were given twice a day, at 7:30 am and 4:00 pm Throughout the experiment, clean and potable water was available at all times.

During the actual feeding period, the daily required amount was taken out of the silo only through an opening in one corner, and the urea-molasses and urea-lime-treated straws were aerated overnight to remove irritating ammonia gas before feeding to the animals. The concentrate allowance for each calf in each dietary treatment was revised every two weeks based on the calves’ live weight conditions. Commercial concentrate mixes for growing calves, sufficient to cover the entire experimental period, were purchased from local feed processing plants. The purchased concentrate feed contains 16.5% crude protein, 42.6% NDF, and 26.2% ADF. According to Kearl (1982), a total diet that could provide 12% CP and 8 Mcal ME per day for calves growing at a rate of 500 g per day is recommended. Individual daily intakes of basal, supplemental, and total feed were recorded for each calf, and treatment options were considered. The difference between the daily amount of feed offered and refused was calculated as the daily feed DM and nutrient intake. The apparent dry matter and nutrient digestibility of the total diet were determined over seven days using the total fecal collection method. To calculate the apparent DM and nutrient digestibility of total feed, the difference between nutrient intake and that recovered in feces was expressed as a proportion of nutrient intake (Khan et al. 2003).

Initial body weight was taken for two consecutive days after overnight fasting of the calves, and the mean weight was taken as the initial weight. Subsequently, each animal was weighed twice a month after overnight fasting before fresh feed and water were offered. The total body weight change was determined as the difference between the final weight and the initial weight. While daily body weight gain was calculated as an average of the fortnightly live weight changes divided by the same number of days, the live weight changes have been recorded for each calf. Calves’ feed conversion ratio was calculated as the ratio of daily DM intake to ADG in experimental animals. It was calculated as follows: $\mathrm{F}\mathrm{e}\mathrm{e}\mathrm{d}\mathrm{c}\mathrm{o}\mathrm{n}\mathrm{v}\mathrm{e}\mathrm{r}\mathrm{s}\mathrm{i}\mathrm{o}\mathrm{n}\mathrm{r}\mathrm{a}\mathrm{t}\mathrm{i}\mathrm{o}\left(\mathrm{F}\mathrm{C}\mathrm{R}\right)={\displaystyle \frac{\mathrm{A}\mathrm{v}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{d}\mathrm{a}\mathrm{i}\mathrm{l}\mathrm{y}\mathrm{i}\mathrm{n}\mathrm{t}\mathrm{a}\mathrm{k}\mathrm{e}}{\mathrm{A}\mathrm{v}\mathrm{e}\mathrm{r}\mathrm{a}\mathrm{g}\mathrm{e}\mathrm{d}\mathrm{a}\mathrm{i}\mathrm{l}\mathrm{y}\mathrm{g}\mathrm{a}\mathrm{i}\mathrm{n}}}$

2.4. Physical evaluation and pH measurement

The visual appraisal, smell, and texture of treated wheat straw silage were evaluated. The subjective evaluation was conducted by five people. Samples were carefully collected by grabbing the treated straw by hand and minimizing air entry into the silage container as much as possible before placing the sample in plastic bags. The parameters for color, smell, and texture were checked, and the result of each test was recorded. The pH values of the treated wheat straw samples were determined by soaking 20 g in 100 ml of distilled water overnight and using the extract’s benchtop digital pH meter (Playne and McDonald 1996).

2.5. Laboratory analytical procedures

Feed offer, refusal, and fecal samples were collected and composited per treatment type for chemical analysis. To determine the response of treated wheat straw to feed chemical composition, five representative samples from different batches were taken from the respective silos. The daily feces collected from each animal were weighed in the morning before the animals were served with fresh feed. Representative fecal samples were taken after sub-sampling of the daily fecal collections and kept in a dip freezer at −20°C. On the last day of the collection period, the composite fecal samples for each calf was thawed, thoroughly mixed, and sub-sampled for DM, total ash, and crude protein (CP) determinations using the procedure of the AOAC (2005). Neutral detergent fiber (NDF), acid detergent fiber (ADF), and permanganate lignin were determined following the laboratory procedures of Van Soest et al. (1991).

2.6. Analysis of feed costs

The calculation of the total feed cost for each calf managed under each dietary treatment was based on a comparison of only the total feed cost (for roughage and concentrate diets) and the straw treatment cost incurred per kilogram of straw mass for the three dietary treatments and the cost incurred per kilogram of untreated straw mass for feeding the calves in the control group. The current market price and cost involved for treating one kg of straw on a DM basis are as indicated below. Wheat straw costs 5.6 Birr per kg, while concentrate feed costs 9.4 Birr per kg. Treatment costs (chemicals, labor for chopping and ensiling the straw) for the three dietary treatments were 3.13, 2.75, and 2.95 birr/kg wheat straw treated using urea-molasses, urea-lime, and an effective microorganism solution, respectively. Costs that didn’t vary over the treatments (fixed costs) were generally not considered in the calculations (1 USD = 48.37 ETB).

2.7. Statistical data analysis

Data were analyzed using the ANOVA procedures in R-software version 4.1.0. The mean separations for all the parameters were subjected to Tukey’s HSD test at P = 0.05. The statistical model used for the feeding trail was: Yij = μ +Ti + Bj + ϵij; where Yij is the response variable, μ is the overall mean, Ti is the treatment effect, Bj is the block effect, and ϵij is the random error. The statistical model for the lab-based trial was: Yji = μ +Ti + ϵji; where Yij is the response variable, μ is the overall mean, Ti is the treatment effect, and ϵij is random error.

3. Results

3.1. Physical evaluation and pH measurement

The effect of treatment on sensory evaluations and the mold prevalence of treated wheat straws are summarized in Table 1. Sensory evaluation of urea-molasses-treated wheat straw (UMTWS) silage showed that it became brownish yellow with a pungent smell and soft texture. In comparison, (ULTWS) contains a minor pungent odor and a soft consistency with a pale-yellow color. There was no fungus observed in the UMTWS or ULTWS. However, effective microorganism-treated wheat straw (EMTWS) has a sweet and yogurt-like odor, a soft consistency, a light-yellow color, as well as some fungus on the silage’s surface. The pH values were 8.63, 8.30, and 4.27 for UMTWS, ULTWS, and EMTWS, respectively. The untreated wheat straw's pH was not evaluated because it had not been ensiled.

Table 1. Sensory evaluation of attributes and pH of treated and untreated wheat straw.

Treatments	Silage color	Silage texture	Silage smell	Mold stratus	pH
UWS	Straw	Hard	–	–	–
UMTWS	Dark yellow	Soft	Pungent	none	8.63
ULTWS	Pale-yellow	Soft	Moderate pungent	none	8.3
EMTWS	Light yellow	Soft	Sweet and yogurt	Some on top	4.27

UWS = Untreated wheat straw, UMTWS = Wheat straw treated with urea-molasses, ULTWS = wheat straw treated with urea-lime, EMTWS = Effective Microorganisms treated wheat straw.

3.2. Chemical composition of experimental feed

The chemical composition of the experimental diet is presented in Table 2. The chemical composition of wheat straw was significantly affected (P < 0.001) by the treatment options. The dry matter percentage was significantly (P < 0.001) higher for UWS followed by that of ULTWS, EMTWS, and UMTWS. The total ash contents of UMTWS and ULTWS were higher (P < 0.001) than the untreated wheat straw (UWS) sample. The crude protein values were significantly (P < 0.001) different between treatments, with a value of 6.31% for UMTWS, 4.88% for ULTWS, 2.94% for UWS, and 2.76% for EMTWS. The percentage CP increments for UMTWS and ULTWS were 2 and 1.5 times greater than that recorded for the control treatment, respectively. Treatment with urea-molasses, urea-lime, and EM improved the cell wall constituents of NDF, ADF, and lignin concentrations over the untreated wheat straw basal diet (P < 0.001). A 23% reduction in NDF obtained from EM treatment over the untreated wheat straw in the present trial was exceptionally higher (P < 0.001).

Table 2. Chemical composition and IVDMD of concentrate mixture; untreated and treated wheat straw and dietary treatments (% DM basis).

Parameters	DM	CP	Ash	NDF	ADF	ADL	IVDMD
Concentrate	89	16.5	10.2	42.6	26.2	5.3	68.3
UWS	93.1^a	2.94^c	10.5^d	76.48^a	53.39^a	6.31^a	47.90^d
UMTWS	69.8^d	6.31^a	11.9^a	74.98^b	51.39^c	5.98^a	52.35^b
ULTWS	75.2^b	4.88^b	11.6^b	72.14^b	52.04^b	5.75^b	50.90^c
EMTWS	71.4^c	2.76^d	11.3^c	53.43^c	51.12^c	5.64^b	53.30^a
SEM	0.0172	0.0001	0.0347	0.1599	0.1212	0.0455	0.2397
P value	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001	<0.001

^a–d Means with different superscript letters in the column show significant differences (P < 0.05), UWS = Untreated wheat straw, UMTWS = Wheat straw treated with urea-molasses; ULTWS = wheat straw treated with urea-lime; EMTWS = Effective Microorganisms treated wheat straw; DM= dry matter as fed basis NDF = neutral detergent fiber; ADF = Acid detergent fiber; ADL = Acid detergent lignin; IVDMD = In vitro dry matter digestibility, SEM = Standard error of means.

3.3. Feed DM and nutrient intake

Feed and nutrient intake of experimental calves fed on untreated and treated wheat straw-based diets are presented in Table 3. The roughage, total dry matter, and organic matter intakes per day of calves were considerably higher (P < 0.001) for the T3 and T4 diets than for the T2 and T1 diets. Dry matter intake expressed as a percent of body weight was not affected by the different treatment options (P > 0.05). On the other hand, the mean CP intake was significantly affected (P < 0.001) by the urea-molasses and urea-lime treatments. As a result, calves fed T2 and T3-based diets consumed 60 g more CP per day on average than calves fed control or T4-based diets. Fiber intakes (NDF and ADF) were also positively affected (P < 0.001) by urea-lime (T3) treatment, except for the comparable ADF intake it had with calves receiving the T4-based diets. The effects of the experimental period on the total feed dry matter intake are presented in Figure 1.Dietary fiber intake (NDF and ADF) was also greater (P<0.001) for the T3 diet relative to others, except for the comparable ADF intake of the T4 diet.

Figure 1. Effects of period on total DM intake per treatment.

Table 3. Dry matter and nutrient intake of calves fed untreated/treated wheat straw (means ± SDs).

Dry matter intake (kg/d)	T1	T2	T3	T4	P value
Roughage	1.63 ± 0.35^b	1.72 ± 0.29^b	2.37 ± 0.44^a	2.15 ± 0.48^a	<0.001
Concentrate	1.40 ± 0.24	1.40 ± 0.30	1.30 ± 0.30	1.40 ± 0.35	NS
Total dry matter	3.02 ± 0.58^b	3.12 ± 0.56^b	3.70 ± 0.70^a	3.52 ± 0.82^a	<0.001
Dry matter (%BW)	3.24 ± 0.53	3.36 ± 0.74	3.46 ± 0.76	3.48 ± 0.88	NS
Total organic matter	2.70 ± 0.52^b	2.74 ± 0.50^b	3.24 ± 0.65^a	3.12 ± 0.73^a	<0.001
Crude protein	0.28 ± 0.05^b	0.35 ± 0.067^a	0.34 ± 0.07^a	0.29 ± 0.07^b	<0.001
Neutral detergent fiber	2.31 ± 0.44^b	2.34 ± 0.42^b	2.78 ± 0.56^a	1.88 ± 0.44^c	<0.001
Acid detergent fiber	1.60 ± 0.31^b	1.59 ± 0.29^b	1.94 ± 0.34^a	1.79 ± 0.42^ab	<0.001

^a–c Means with different superscript letters across the row are significantly different (P < 0.05), NS = nonsignificant, d = day, T1 = untreated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T2 = urea molasses treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calvesT3 = urea lime treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T4 = effective microorganisms treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves.

3.4. Apparent dry matter and nutrient digestibility

The apparent DM, OM, and nutrient digestibility of experimental calves as affected by treatment are presented in Table 4. The apparent digestibility of the DM, OM, CP, and ADF were noted to be significantly (P < 0.01) higher for the treated straw than the untreated straw basal diet. The apparent NDF digestibility of the wheat straw basal diet improved with urea-molasses and urea-lime treatment options was higher (P < 0.001) than that of the untreated and EM-treated straw. Among the treated straw groups, numerically more DM and OM per day were digested by experimental calves in the T3 group, followed by those in the T4 group.

Table 4. Apparent dry matter, organic matter, crude protein and neutral and acid detergent fiber digestibility of untreated and treated wheat straw-based diets (means ± SDs).

Parameters (g/kg DM)	T1	T2	T3	T4	P value
Dry matter digestibility	474.0 ± 52.4^b	611.0 ± 117.3^a	651.0 ± 50.0^a	646.0 ± 77.0^a	<0.01
Organic matter	510.0 ± 53.4^b	635.0 ± 112.2^a	673.0 ± 45.0^a	665.0 ± 73.0^a	<0.01
Crude protein	408.8 ± 64.0^b	604.0 ± 135.0^a	570.6 ± 58.2^a	555.2 ± 112.5^a	<0.01
Neutral detergent fiber	601.5 ± 36.3^b	710.3 ± 80.1^a	739.5 ± 32.7^a	596.5 ± 87.3^b	<0.001
Acid detergent fiber	546.0 ± 32.0^b	643.0 ± 99.0^a	685.9 ± 38.1^a	665.2 ± 75.5^a	<0.01

^a,b Means with different superscript letters across the row show significant differences (P < 0.05), T1 = untreated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T2 = urea molasses treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T3 = urea lime treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T4 = effective microorganisms treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves.

3.5. Growth performance of experimental calves

The growth performance of calves fed untreated or treated wheat straw is presented in Table 5., The final body weight was higher (P < 0.05) for the calves in the T3 and T4 groups than those in the control group (T1). However, there were no differences in final weight among the calves receiving the treated straw-based diets. Live weight changes (LWC) and daily growth rates (ADG) of calves were higher (P < 0.001) for calves in the T3 and T4 groups than calves in the control and T2 groups. Similar trends to those observed for LWC and ADG were observed for the feed convertion ratio (FCR) of experimental calves receiving the different dietary treatment options. Therefore, calves in the T3 and T4 groups consumed less feed per gram of daily growth rate (P < 0.01) than calves in the control group. The effect of the live weight measurement period on the average daily gains of experimental calves per treatment was described in Figure 2. The calves receiving the treated wheat-straw-based diets didn’t differ in their feed conversion ratio across treatment groups.

Figure 2. Effects of period on average daily gain per treatment.

Table 5. Growth performance and feed conversion ratio of calves fed untreated/treated wheat straw-based diets (means ± SDs).

Parameters	T1	T2	T3	T4	P value
Initial body weight (kg)	98.3 ± 16.2	101.5 ± 22.2	97.8 ± 20.9	99.7 ± 24.8	NS
Final body weight(kg)	115.5 ± 18.2^b	125.2 ± 27.7^ab	133.3 ± 29.8^a	132.5 ± 33.7^a	<0.05
Live weight change(kg)	17.2 ± 4.1^b	23.7 ± 8.3^b	35.5 ± 9.2^a	32.8 ± 9.9^a	<0.001
Average daily gains (g)	204.4 ± 49.0^b	281.7 ± 98.9^b	422.6 ± 109.9^a	391.0 ± 117^a	<0.001
Feed conversion ratio (g/g)	15.1 ± 2.79^a	12.1 ± 3.9^ab	8.8 ± 0.78^b	9.4 ± 1.80^b	<0.01

^a,b Means with different superscript letters across the row are significantly different (P < 0.05), NS = not significant, T1 = untreated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T2 = urea molasses treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T3 = urea lime treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T4 = effective microorganisms treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves.

3.6. Analysis of feed costs

The daily basal feed cost per calf was higher (P < 0.001) for the treated wheat straw-based diets than the control-based diets Table 6. But the daily roughage cost among the treated wheat-straw-based diets was higher (P < 0.001) for calves receiving T3 and T4-based diets. The cost of concentrate feeds was not significantly (P > 0.05) different among treatments. Compared to the calves in the control group, approximately 10 and 9 more Ethiopian birr were used to feed the calves in the T3 and T4 groups each day, respectively, while only 4 and 3 more Ethiopian birr were used to feed the calves in the T3 and T4 groups when compared to the daily total fed cost used to feed the calves in the T2 group. The total feed cost per daily weight gain was higher (P < 0.05) for the untreated straw (T1) and T2-based diets than for T3 and T4-based diets. In general, calves in the T3 group spent approximately 34 and 33 percent less Ethiopian birr on feed per kilogram of weight gain than calves in the T1 and T2 groups, respectively. Similarly, 28 and 27 less Ethiopian birr were invested in the feed per kilogram gain for calves in the T4 groups than those in T1 and T2, respectively.

Table 6. Experimental feed cost analysis (means ± SDs).

Parameters (ETB/h/d)	T1	T2	T3	T4	P value
Roughage	9.1 ± 1.96^c	15.0 ± 2.60^b	19.8 ± 3.70^a	18.2 ± 4.10^a	<0.001
Concentrate	13.0 ± 2.30	13.2 ± 2.90	12.2 ± 2.80	12.8 ± 3.30	Ns
Total feed cost	22.2 ± 4.20^c	28.1 ± 5.10^b	32.0 ± 6.44^a	31.0 ± 7.24^a	<0.001
TFC/DWG (ETB-^kg gains)	110.8 ± 19.5^a	109.6 ± 35.40^a	76.7 ± 6.80^b	82.5 ± 15.80^b	<0.05

^a–c Means with different superscript letters across the row are significantly different (P < 0.05), NS = not significant, T1 = untreated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T2 = urea molasses treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves T3 = urea lime treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves; T4 = effective microorganisms treated wheat straw ad libitum plus concentrate supplemented at a rate of 1.2% of the live weight of the calves DWG = daily weight gain, TFC = Total feed cost, 1USD = 48.37 ETB, ETB = Ethiopian birr.

4. Discussion

4.1. Physical evaluation and pH measurement

The visual appraisal, color, smell, and pH results in this study were an indication of good quality and showed EM as a biological inoculant and urea-lime and urea-molasses as chemical additives. . The wheat straw treated with urea molasses had a dark yellow color, a pungent smell, and a soft texture, which agrees with the findings of Kassu et al. (2014), who reported that the dark brown appearance and color of coffee husk silage is an indicator of silage that has good quality. The silage pH observed in the current study (urea-molasses and urea-lime) treatments was consistent with the results of Yalchi (2010), who reported a pH of 8.65 and 9.44 for urea-treated triticale straw at rates of 3 and 4.5%, respectively. Similarly, the increase in pH could be due to the addition of ammonia in the form of urea. This result is in line with the results of Bolsen et al. (1995), who concluded that adding ammonia increases the pH of silage to 8 or 9. With this high pH and ammonia effect on silage, the growth of mold and yeast populations is inhibited, which consequently increases the aerobic stability of the silage materials (Oladosu et al. 2016). The silage color, aroma and pH observed in the EMTWS agreed with the results of Tibebu et al. (2018), who reported teff straw treated with different levels of Effective Microorganisms. Moreover, the pH observed in the EMTWS in the current study is comparable to the results of Taddess et al. (2016), who reported a pH of 4.27 in sorghum straw treated with Effective Microorganisms.

4.2. Chemical composition of experimental feeds

The DM contents of control and treated silages differed significantly. This could be due to differences in the moisture content of the solutions used during treatment. The improvement in the CP contents of straw treated with urea-molasses and the urea-lime solution is attributed to the urea granules in the solution, which are often known for their higher concentrations of elemental nitrogen (the nitrogen content of urea-grade fertilizer is 46%). The observed improvement in the DM, CP, NDF, and ADF in urea-molasses-treated wheat straw in the current study is also in agreement with that reported by Sundstøl (1986) on wheat straw treated with urea-molasses and by Tekliye et al. (2018) for urea-molasses-treated rice straw and by Abera et al. (2016) and Mudavadi et al. (2020) for maize stover treated with urea-molasses. Lime and/or urea-lime inclusions in the treatment of wheat straw have also been reported to have improved CP, reduced cell wall composition, and enhanced rumen degradation (Chaudhry 2000; Can et al. 2004; Millam et al. 2017). Alkaline reactions in the silo due to urea and lime fermentation and acidic pH due to fermentation of the wheat straw with EM inoculant might have contributed to the lower fiber components of NDF, ADF, and lignin concentrations in the ensiled straws. Similar effects noticed previously have been attributed to alkali-induced ‘peeling’ reactions, in which degradation of sugar moieties occurs at the reducing end of hemicellulose chains (Wilkie 1979). Additionally, the improvement in the nutritional value of urea-lime-treated wheat straw in the current study agreed with the previous findings of Wanapat et al. (2013) and Nguyen et al. (2012), who found that the combined use of urea-lime-treated rice straw improved the nutritional value of rice straw. However, the increase in the nutritional value of urea-lime-treated wheat straw as compared to untreated wheat straw in the current study cannot be compared to earlier studies that revealed that a combination of lime and urea did not have an additive effect in enhancing the feeding value of sesame straw (Aregawi et al. 2014). Ash contents for T2 and T3 were significantly affected by treatments, which can be explained by the high mineral concentration in the molasses (Palmonari et al. 2020) and quick lime (CaO) solutions used under the respective treatment options. Furthermore, Dawit et al. (2013) reported a higher (18.4%) ash content in molasses, which could have contributed to the T2.

The reduction in CP content in EM-treated straw as compared to untreated straw was also observed by Kassu et al. (2014) and Begna et al. (2019). This might be due to a biochemical change that occurs in soluble carbohydrates and proteins during fermentation that results in a reduction in CP content (McDonald et al. 2010). According to a study done on different crop residues, wheat straw's CP content did not increase in response to an increase in EM level (Mulugeta 2015). Other studies, however, for example, Getu et al. (2016) and Gulilat and Walelign (2017) , observed higher improvements in CP contents of EM-treated cereal residues compared to those untreated ones. Any nutritional variability between the current and earlier findings could be associated with the straw and varietal types, the level of chemicals or microbial inoculants used in the respective cases, and environmental factors under which the trials were conducted. In general, all treatment options used in the current study resulted in tremendous changes to wheat straw proximate and detergent fractions compared to the untreated straw. This would further imply the wider scope with which the various crop residue treatment options could be exploited under the existing smallholder dairy farmers’ socio-economic and farming system conditions in the country.

4.3. Dry matter and nutrient intake

The increase in the mean daily dry matter and nutrient intakes of the calves fed treated straws agreed with earlier studies by Nurfeta et al. (2009), and Nguyen et al. (2012), which reported improvements in dry matter and nutrient intakes of sheep and buffalo fed urea and quick lime-treated wheat and rice straws, respectively. Similarly, Aredo (2006) reported an increase in the mean daily dry matter and nutrient intakes of the cross-bred calves fed urea-treated maize Stover. Calves in the T2 groups had lower feed DM and nutrient intake performance, which was surprising given that treatment with urea-molasses solution improved the nutritional value of the wheat straw. However, it has been observed that it took a relatively long time for the calves to adapt and stabilize intake on T2. On the other hand, the urea-lime (T3) treatment of wheat straw in the current study resulted in a greater daily feed intake for the calves. The combined action of urea and lime, rather than the urea and molasses used to treat the straw, was most likely responsible for this (Wanapat et al. 2013). The increase in DM and nutrient intake of calves as a result of treatment effective microorganisms agrees with the result of a study on Washara sheep fed on EM-treated finger millet straw (Alemu et al. 2020). Except for the T2 diet, the observed improvement in basal, total feed, and nutrient intake with the treated wheat straw-based diets could be attributed to improvements in wheat straw nutritional values and the corresponding effect on feed and nutrient apparent digestibility values.

4.4. Apparent dry matter and nutrient digestibility

In the current study, improvement of wheat straw using the different treatment options considerably increased DM and nutrient apparent digestibility of the total experimental diet (the exception being OM and NDF digestibility recorded for calves in the T2 and T4 groups) over the untreated wheat straw-based diets. Perhaps this could be linked to the differences in the proximate and detergent fractions of the wheat straw basal diet brought about by the various treatment effects. As was also the case in the present study, Millam et al. (2017) observed improvements in the dry matter, d CP and ADF digestibility of groundnut residue treated with a urea-lime solution but also increased NDF digestibility. Likewise, calves on the urea-molasses-treated wheat straw-based diet had comparable nutrient digestibility values reported in a related study on a urea-molasses-treated maize Stover-based diet by Abera et al. (2016). Despite the recorded poor feed intake, the relatively greater CP contents of T2 might have contributed to the higher apparent feed DM and nutrient digestibility of calves maintained on the same diet. The CP content of the diets were within the range of 6-8%, below which appetite, forage intakes, and digestibility are depressed (Forbes 1995). Treatment of wheat straw with EM improved the digestibility of wheat straw as compared to untreated wheat straw. A comparable effect of EM on finger millet straw was observed by Alemu et al. (2020). Similarly, Chalchissa and Arega (2018) found that feeding treated barely straw improved apparent DM and nutrient digestibility in dairy cows. Greater feed DM and CP digestibility among the treated straw groups indicated that any one of the treatment options could be recommended for use at local field conditions. However, treatment costs per kilogram of straw dry mass and the availability of major inputs required for the specific treatment option under consideration.

4.5. Growth performance of experimental calves

The urea-lime and effective microorganisms treatment options improved the growth performance of the calves, which can be directly related to the improved feed dry matter, nutrient intake, apparent dry matter, and nutrient digestibility of the treated wheat straw-based diets. The increased intake of energy due to greater total DM and OM digestibility of T3 and T4 diets relative to the others may also have resulted in their greater live weight gain compared to the calves receiving the other treatments. The average daily gain achieved from the urea-molasses-treated wheat straw-based diet (281.7 g) could be compared to an earlier finding that Misra et al. (2006) reported on crossbred calves fed urea-treated wheat straw supplemented with de-oiled rice bran and green maize diets (341 g day-1). Similarly, the result from the T2-based diet can also be compared to the results of a similar study by Wodajo (2021) that reported an average daily weight gain of 279.94 ± 3.60 g for post-weaning yearling crossbred calves maintained on the station’s conventional calves’ diet at Holetta Agricultural Research Center, Holetta, Ethiopia. However, the average daily gains of calves fed urea-lime (T3) and effective microorganism-treated wheat straw (T4) from the current study were much higher than the same calves maintained on the station’s standard diet. Similar observations were documented by Egbu (2014) and Aredo (2006), both of whom reported significant increases in the growth of N’Dama and crossbred calves fed urea-treated maize stover-based diets. The average daily gains of calves fed a urea-lime-treated wheat straw basal diet were comparable to those obtained from a study conducted on crossbred heifers fed rice straw treated with a combination of urea (2%) and lime (3%) and supplemented with green feed and concentrate (Trach et al. 2001). The difference in the average daily gains of calves fed untreated and urea-molasses-treated wheat straw in the current study was not significant. This result agreed with that reported by Elias and Fulpagare (2015), who were unable to find a difference in the growth performance of crossbred calves fed on treated and untreated maize stover-based diets. Moreover, the observation with the T2-based diet from the current study fully supports the contention given by Sahoo et al. (2004) that feeding a urea-molasses-treated wheat straw-based diet sustains minimum growth potential in growing animals, addressing future animal productivity.

The calves fed the urea-molasses-treated wheat straw-based ration consumed more dry matter, amounting to 12.1 g/g of daily weight gain. Aredo (2006) reported an FCR of 12.2 in a study on crossbred calves fed urea-treated maize stover, which is consistent with the current finding. Trach et al. (2001) reported comparable FCR for crossbred calves fed urea-lime-treated rice straw supplemented with green feed and concentrates. Published information on the growth response to EM-treated crop residue diets for dairy cattle is scanty. However, comparable results with urea-lime treated straw and higher growth performance relative to calves on the control diet could be attributed to EM’s effect on reducing NDF cell wall constituents. The maximum difference in FCR observed between calves fed urea-lime-treated diets and the untreated group was 6.3 g of feed for each gram of gain, which was more than two-fold compared to the FCR value of 2.9 g of feed for each gram of gain reported for crossbred calves fed on the urea-lime-treated and untreated straw-based diets (Trach et al. 2001). This contrasting result with the latter one might be attributed to the variation in the type of straw and treatment additives used in the respective study cases. These findings suggest that under practical field conditions, either T3 or T4 or both can be recommended to improve the growth rate of 75% Frisian-Borana female crossbred calves.

4.6. Analysis of feed costs

Both roughage and total feed costs for calves in the T3 and T4 groups were comparable and higher than those of the T2 and control groups. Feed cost analysis indicated that each kg of live weight gained by the calves fed urea-lime and effective microorganism-treated wheat straw was achieved at a relatively lower daily feed cost than that of calves maintained on urea-molasses-treated wheat straw and the control diet. This result is comparable to an earlier report by Aredo (2006), who observed only 16% lower r feed costs per kg of daily body weight gains for calves fed urea-treated maize stover than for untreated-based diets. Similarly, in another study, the feed cost per kg body weight of calves receiving ammoniated wheat straw was 16.4% lower compared to calves on untreated wheat straw (Tengyun 2000). The better growth performance and FCR displayed by calves in the T3 and T4 groups might justify the reduction in total feed cost per additional weight gain obtained from low-cost but widely available crop residue-based diets under local conditions for the fast-growing, high-grade dairy cattle.

5. Conclusion and recommendations

This study showed that treatment options affected the physical silage quality and chemical composition of wheat straw as well as the feed intake and growth performance of crossbred calves. The maximum crude protein (CP) and ash contents were observed for wheat straw treated with T2 and T3. The highest DM intake was observed for calves in the urea-lime (T3), and EM (T4). The daily weight gain of experimental calves was increased by feeding treated wheat straw-based diets in that order of importance: T3 = T4 > T2 = T1, with higher FCR recorded for treatment groups compared to the control. The calves fed an untreated wheat-straw-based diet had the highest total feed cost per live weight gain. The overall results further implied that treating wheat straw with urea-molasses, urea-lime, and EM improved nutritional values and enhanced growth performance cost-effectively when fed to crossbred calves supplemented with concentrate at the rate of 1.2% of the fortnightly live weight changes of experimental calves. The optimum amount of lime inclusions in the urea-lime mixtures used for crop residue treatment, however, still needs to be confirmed by more research. We recommend repeating the same feeding experiment conducted on these and other ruminant species under different physiological circumstances to obtain practical, comprehensive, and efficient recommendations.

Authors contributions

KM developed the research concept, carried out the experiment, conducted the data analysis, and wrote and edited the manuscript. GK and BT developed the research concept, supported data analysis, and wrote and edited the manuscript. FF helped to develop the research concept and wrote the manuscript. FF, UG, AK, and DG helped to shape the research concept and assisted with experimental design and data interpretation. MB and AA helped with funding acquisition, writing, and editing the final manuscript. All authors contributed to and approved the final version of the article.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was partially funded by the Bill and Melinda Gates Foundation through the Equip – Strengthening Smallholder Livestock Systems for the Future Project (SUBAWARD agreement no. UFDSP00012156 between UF and EIAR). The assistance obtained from UF, EIAR, Addis Ababa University, Holetta Agricultural Research Center (HARC), and the feed and nutrition research staff of HARC is highly appreciated. Any opinions, findings, conclusions, or recommendations expressed here are those of the authors alone.