Effect of processing methods on the degradability of rattle box (Crotalaria retusa) plant in Yankasa rams

Abstract

Crotalaria as a feed has great ability to serve as a source of energy and protein in dry season feeding due to the fact that it has good crude protein content comparable to other well-known forage legumes. The study was designed to evaluate the nutritive compositions of Crotalaria retusa leaves subjected to various processing. The processing methods that the crotalaria leaves were subjected to include: sun drying, oven drying, shade drying and fresh, and thereafter, the chemical analysis of the variously processed leaves was determined. Similarly, the rumen degradation was determined. The results showed a significant difference in the fresh leaves for all the parameters determined. Dry matter degradability showed a general increase with increase in the incubation time, and there was also a general decrease in passage rate with increase in outflow rate (‘k’ value). Sun drying reduces the protein content for ruminant use as such Crotalaria can serve as a source of protein for ruminants especially in dry season when there is scarcity of protein sources for ruminants.

Keywords:

• Crotalaria retusa
• degradability
• processing
• rams

Introduction

Research on indigenous wild legumes has been very limited when compared with improved legumes. Tropical legumes which are used for forage have been cultivated during the last 50 years (Sarwatt 1986), yet the volume of unexplored genetic resources remains very vast.

Crotalaria retusa L usually known as rattle box plant is a leguminous plant (Milford 1967). It belongs to the genus Crotalaria and it is widely found in tropical Africa in open places from mountains to semi-deserts with over 500 species among which is C. retusa L. Most of the species are annuals, semi-perennials with few perennials herb or shrubs, and they establish during the late rains (August–September). They start flowering in November and they remain green up to February–March. They also have the potential of augmenting the scarce crop residue during the critical period of the dry season (Martin and Lewnard 1970). The leaves are either simple or compound with three, five or seven leaflets (Polhill 1982).

There are many crop legumes that produce grains for human consumption and forage for livestock. Some at the stage of seed maturity lose their leaves and becomes stemmy, resulting in decline in their nutritive value. Dried legume residues like groundnut haulms, cowpea hay, lablab hay and mucuna hay play a very important role in small ruminant production. They are often fed as supplement to grass basal feed. Their prohibitive cost hinders them being used as commonly as basal feed for small ruminants even though feeding them has been proven to be cost effective. Leguminous plants are useful supplements in meeting the nitrogen requirements in small ruminants (La Crotalaria … 1965; Lakpini 2002)

The availability of nutrients in forage legumes for an animal is determined by the digestibility and the nature and quantity of antinutritional substances it may contain while some are legumes that are rich in nutrients but not available to the animal because either they are not palatable or contain large quantity of crude fibre which makes them inaccessible for digestion or degradation. These types of legume forages can be processed to improve their nutrients value (Lakpini 2002). There are a number of ways by which these antinutritional factors can be radically reduced or eliminated from the plant. Post-harvest processing techniques like sun drying, shade drying and others are ways by which these antinutritional factors and toxins in the forage can be lowered (Lyon 1985; D'Mello and Devendra 1995; Lakpini 2002; Adeleke 2008).

This study, therefore, is to determine the nutritional composition and dry matter degradation of Crotalaria plant subjected to different processing methods.

Materials and methods

The experiment was conducted at the Livestock Unit, Department of Animal Science, Ahmadu Bello University, Zaria, Nigeria. C. retusa plants were collected from the Institute for Agricultural Research (IAR) research farm. The plants were subjected to four different treatment methods: shade drying, sun drying, oven drying and fresh.

Shade drying

The harvested C. retusa leaves were air-dried under shade for three days until when the leaves becomes crisp, the samples were then ground using hammer mill and stored in an air tight plastic bags in readiness for proximate and incubation into the rumen of the animals.

Sun drying

The leaves were dried in the open sun for three days, the samples were then ground using hammer mill and stored in an air tight plastic bags in readiness for proximate and incubation into the rumen of the animals.

Oven drying

The sample was oven dried at 60°C as not to lose its nutrient content for three days. The samples were then ground using hammer mill and stored in an air tight plastic bags in readiness for proximate and incubation into the rumen of the animals.

Fresh sample

This sample was not subjected to any treatment before incubation.

Three fistulated rams were used, with an average live weight of 20 kg. The three animals were used as replicates to determine in sacco dry matter degradability of differently processed C. retusa plant. The animals were housed in individual pens and fed ad lib with hay and concentrated (12% Cp) 70:30 ratio, water and mineral block at 10.00 hours. The animals were adapted to the basal feed for two weeks prior to suspension of the bags.

Rumen degradation was measured using the techniques described by Ørskov et al. (1980). The incubation times were 3, 6, 12, 24, 36 and 48 hours. Effective degradability (ED) of the samples was calculated using the outflow rates of 0.02, 0.03, 0.04 and 0.05/hour, according to Ørskov et al. (1980) model:

where ED is effective degradability; ‘a’, ‘b’ and ‘c’ are the constants; ‘k’ the rumen fractional outflow rate (constant), as described in the exponential equation (Ørskov et al. 1980).

Dried milled samples of the variously treated leaves were analysed for proximate compositions using the procedure of AOAC (1990). A small portion of the plant from each treatment was taken to the laboratory for analysis of proximate composition according to Proximate chemical and mineral analysis using the procedure AOAC (1990). Data obtained were subjected to one-way analysis of variance using ANOVA procedure of SAS (1990), significant treatment means were compared using the Duncan Multiple Range Test of the same package.

Results and discussion

Table 1 presents the proximate composition of the feed samples. The result obtained for dry matter ranged from 58.06% for the fresh sample to 99.67% for shade dried leaves. The value obtained for fresh leaves was low because of the moisture content as compared to the dry samples. Subsequently, the values obtained for oven dried and sun dried were 99.42% and 98.30%, respectively. The values were similar probably due to the similar range of temperature they were exposed to.

Table 1. Proximate composition of variously treated Crotalaria retusa leaves.

Treatment	DM (%)	CP (%)	CF (%)	EE (%)	ASH (%)	NFE (%)
Fresh	58.06	15.69	24.55	0.93	6.87	51.96
Oven dried	99.42	15.44	24.42	0.79	7.09	52.26
Sun dried	98.30	12.31	22.86	0.72	6.02	58.09
Shade dried	96.67	14.00	29.91	0.68	7.73	47.68

The crude protein content ranged from 12.31% in the sun dried leaves to 15.69% in the fresh leaves. The difference in crude protein contents could be due to the effect of the processing methods. The crude protein contents were within the range of 10–35% of Crotalaria species as reported by Balaraman and Vankaterkrishman (1974) and Sarwatt (1986). This also present a promising feed material when compared with the reported range of crude protein content of the general tropical legumes which ranges between 5.6 and 35.8% as reported by Minson (1977).

The crude fibre content varied from 22.86% in sun dried leaves to 29.91% in the shade dried. The differences may be due to differences in levels of lignin present and processing methods. The values obtained are within the range reported by Sarwatt (1986), the crude fibre of forage is an important measure of dry matter in take and in vivo dry matter digestibility (Sarwatt 1986). The Ash content ranges from 6.02% to 7.73%. This may be due to the different methods of processing. Although, most of the values were within the ash values as reported by Sarwatt 1986.

Table 2 shows the effect of processing on the dry matter degradation of C. retusa leaves after incubation in the rumen of Yankasa rams. The rumen degradation of the C. retusa leaves generally increases with increase in the incubation time from 0 hour to 48 hours for all treatments. There was significant (p>0.05) difference in DM degradation following the different methods of processing. The result showed that fresh, sun dried and shade dried have the same pattern of degradation at 3 hours, 12 hours and 48 hours incubation times. Fresh leaves were highest at these times and significantly different (p<0.05) compared with sun dried and shade dried, although there was a significant difference (p>0.05) between sun dried and shade dried at all these times, while oven dried was the lowest at all these times.

Table 2. Effect of processing method on the dry matter degradability of Crotalaria leaves.

	Treatments
Incubation time (hour)	Fresh	Oven dried	Sun dried	Shade dried	SEM	LOS
3	86.00^a	39.33^c	46.00^b	49.67^b	0.60	*
6	91.00^a	43.33^d	47.67^c	57.00^b	0.44	*
12	93.00^a	58.00^c	67.67^b	70.00^b	0.51	*
24	97.00^a	72.00^b	73.67^b	74.67^b	0.45	*
36	97.67^a	77.67^c	76.67^d	79.33^b	0.19	*
48	98.00^a	78.00^c	80.00^b	81.00^b	0.17	*
^a,b,c,dMeans with different superscript letters within the same row differ significantly.
p<0.05. SEM=Standard Error of Means; LOS=level of significance.

Figure 1 shows the graphical illustration of the degradation characteristics. The figure shows that the fresh leaves had the highest degradation levels, followed by shade dried leaves, and then the lowest was oven dried. This difference continues with rapid degradability until a time of 30 hours when the degradability becomes less rapid. The different roughage degradability in the rumen could be as a result of the different processing methods which affects their chemical composition, which may affect the microbial degradation in the rumen (Mahadeevan et al. 1980; Adeleke 2008). Mahyuddin et al. (1988) has reported that drying of some high phenol forages may reduce fibre digestibility.

Figure 1.  Graphical outlook of disappearance of experimental material with time.

Table 3 shows degradation characteristics of the Crotalaria leaves. The ‘a’ value obtained for the fresh leaves (71.00) was significantly different (p<0.05) and higher than those of oven dried (85.00), sun dried (40.00) and shade dried (35.00). Sun dried was also significantly (p<0.05) different and higher than those of oven dried and shade dried which was the same. The ‘a’ value indicates a value that is essentially similar to the very rapidly disappearing fraction which is the intercept and highly correlated with the water soluble fraction of the experimental material. This implies that the plant (C. retusa) is a succulent legume. These values are similar to those reported by Adeleke (2008). The difference in solubility might be due to different fibre content due to the different methods of processing (Adeleke 2008).

Table 3. The effect of processing on the degradation characteristics of the experimental material.

	Processing methods
Degradation characteristics	Fresh	Oven dried	Sun dried	Shade dried	SEM
a	71.00^a	35.00^c	40.00^b	35.00^c	0
b	98.00^a	78.00^c	80.00^b	81.00^b	0.17
a + b	169.00^a	113.0 0^d	120.00^b	116.00^c	0.17
c	1.58^a	0.74^b	0.58^c	0.56^c	0.01
^a,b,c,dMeans with different superscript letters within the same row differ significantly.
p<0.05. SEM=Standard Error of Means; LOS=level of significance.

Low solubility values have also been demonstrated by Kamande (1988) and Akinlade et al. (2001) both for pasture grasses and legumes. Van Soest (1982) and Preston and Leng (1987) have also demonstrated that the degree of lignifications has a negative effect on cell wall degradation in forage.

The ‘b’ values were significantly (p<0.05) different ranging from 98.00 in the fresh (the highest) to 78.00 (the lowest) in the oven dried. There was no significant (p>0.05) difference between sun dried (80.00) and shade dried (81.00), but shade dried was slightly higher than sun dried. The ‘b’ value is the portion of the feed which will degrade in time ‘t’ (Ørskov et al. 1980). This implies that microbial breakdown of fresh leaves was better than that of shade dried which in turn is slightly better than that of sun dried and which is also better than that of oven dried leaves. This result is contrary to that of Adeleke (2008), who reported a lower value for fresh sample (13.33) and a higher value for dried sample (32.57).

The (a+b) were significantly different (p<0.05) ranging from 113.00 to 169.00. The asymptote (a+b) gives potential degradability of the tested material (Ørskov and McDonald 1979). This shows that the fresh leaves had the highest rate degradability.

The rate of degradation (c) differed significantly (p<0.05) among processing methods with fresh leaves (1.58) having the highest value and shade dried (0.56) the least. The values were higher than those reported by Adeleke (2008), who reported 0.251 for fresh sample and 0.182 for dried sample. This implies that the rate of degradation of the dried samples is better than in other plants.

Table 4 shows the effect of processing passage rate of the Crotalaria plant at different outflow rate. At ‘k’ value of 0.02, fresh leaves were highest with a value of 167.78 followed by sun dried (117.34), oven dried and shade dried were lowest with no significant difference (p>0.05). At ‘k’ values of 0.03, 0.04 and 0.05, there were significant difference (p<0.05) with fresh leaves always the highest, followed by sun dried, and then oven dried always the lowest.

Table 4. The passage rate of the Crotalaria retusa leaves at different outflow rates.

	Processing methods
Outflow rate (k)	Fresh	Oven dried	Sun dried	Shade dried	SEM	LOS
0.02	167.78^a	112.30^c	117.34^b	113.23^c	0.45	*
0.03	167.18^a	109.99^d	116.06^b	111.88^c	0.16	*
0.04	166.59^a	109.05^d	114.84^b	110.59^c	0.16	*
0.05	166.00^a	108.12^d	113.65^b	109.36^c	0.16	*
^a,b,c,d means with different superscript letters within the same row differ significantly.
p<0.05. SEM=Standard Error of Means; LOS=level of significance.

Figure 2 is the graphical illustration of the passage rate of experimental material at different outflow value. The figure shows a general decrease in passage rate with increase in ‘k’ value. These values do not agree with those of Adeleke (2008), and Mupangwa et al. (1997) who reported that there was a decrease in outflow rate with increase in k for all the fresh and the dried samples. ‘k’ is a constant at a particular time called rumen outflow rate. It ranges from 0.02 to 0.05 (Ørskov and McDonald 1979).

Figure 2.  Graphical illustration of rate of passage of experimental material at different outflow rates.

Conclusion and recommendation

The nutrient profile of C. retusa holds a good potential for use as a rich source of protein in the dry season for ruminants. Since sun drying reduces the protein content, therefore, shade drying would significantly improve the utilisation of Crotalaria as a sheep feed and could still be used to preserve the plant for dry season feeding.