Effect of level of rapeseed (Brassica carinata) cake in rations on broiler performance 

D Tadelle, Y Alemu*, H M Moges** and K Fasil* 

Humboldt University of Berlin, Animal Breeding for Tropics and Sub-tropics
Philippstrass 13, Haus 9, 10115 Berlin, Germany
sarmeder@hotmail.com 
*Debre Zeit Agricultural Research Centre PO Box 32, Debre Zeit, Ethiopia
** Faculty of Veterinary Medicine, PO Box 34, Debre Zeit, Ethiopia
 

Abstract

 

A study was carried out to determine the effect of level of inclusion of rapeseed cake (RSC) in the diet on broiler performance. In a seven-week feeding trial with chicks of the Hubbard genotype, rapeseed cake was included at levels of 0, 7, 14, 21, 28, and 35% in broiler rations as a protein source instead of Noug (Guizotia abyssinica) cake.  Data on performance and histopathological effects of the different levels of rapeseed cake were collected.

 

The results indicate that there was depression (p<0.05) in feed intake and live weight gain by birds on the diets containing RSC. The broilers on the 21 and 28% RSC had significantly better (p<0.05) performance compared to the 35% level and also quantitatively better (though not significant) relative to the lower RSC levels. Histopathological examination of thyroid gland samples showed reduced secretory activity with increased RSC inclusion in the ration. The findings in the present study indicated a tendency towards developing a colloid goitre, particularly in the 35% group. Economic analysis showed that the 28% RSC diet resulted in the highest net benefits.

 

Findings from this trial indicate that the 28% inclusion of rapeseed could be recommended for practical diet formulation.

 

Key words: Broilers, glucosinolate, oil cake, rapeseed,

  

Introduction 

Production of rapeseed  (Brassica carinata) covers an area of 15,000 ha, representing 85 % of the total area of land devoted to the production of Brassica species in Ethiopia (IAR 1986). The production of Rapeseed (RS) in Ethiopia is estimated at about 22,000 metric tons (Solomon Mogus 1992). A large proportion of this crop is processed for oil production that results in substantial quantity of Rape Seed Cake (RSC) as a by-product. RSC is a potentially good source of plant protein for farm animals. However, feeding of RSC can have a negative impact on the health and production of farm animals associated with its content of glucosinolates. Goitrin, (5-vinyl-oxazolidine-2-thionine) derived from degradation of glucosinolates by enzymes contained in the feed or in the animal bacterial flora is known to inhibit thyroid function by blocking the incorporation of iodine into thyroxin precursors and by suppressing thyroxin secretion from the thyroid gland (Wheater et al 1987). Proper function of the thyroid gland is important in growth promotion.

 

Although low glucosinolate cultivars of rapeseed have been developed, these are not widely available in Ethiopia and farmers have to depend on high glucosinolate varieties. The current recommendation is that only 5 to 10% of RSC from high glucosinolate cultivars should be included in poultry diets (Schloffel et al 1993; Göhl 1981, Thomas et al 1983).

 

In Ethiopia, rapeseed cake is available in large quantities and costs less than other oil cakes. Large quantities of this valuable ingredient are wasted.  If used in broiler rations at high levels of inclusion it could have important implications for reducing costs of broiler production. However, the histopathological and consequent effects on broiler productivity of high levels of feeding of RSC of Ethiopian origin need to be investigated.

 

The present study was carried out to determine the effect of increasing RSC levels in the diet on broiler performance.

Materials and Methods 

Treatments,  rations and animal management

Three hundred day-old mixed-sex Hubbard broiler chicks obtained from a local hatchery were divided into six treatment groups of 60 chicks each. Each group was further randomly sub-divided into three replicates of 20 chicks and placed in deep litter pens heated by electric bulbs. Tef (Eragrostis tef) straw was used as litter. Replicate groups were similar in weight within and across treatments. Six treatment rations were used during each phase of the study. Diet 1 did not contain RSC while diets 2 to 6 contained 7, 14, 21, 28, and 35 % RSC, respectively. The RSC level in the rations was increased by replacing Noug (Guizotia abyssinica) Seed Cake (NSC), the most commonly used oil cake in Ethiopia. Data on composition of the rations are presented in Table 1 (starter rations) and Table 2 (finisher rations). The rations were randomly assigned to the replications. The diets were formulated to be iso-energetic and iso-nitrogenous.  

 

Birds were provided daily with a known amount of feed ad libitum. Feed refusals were measured and recorded daily for each treatment and replicate group. Water was offered ad libitum. Routine vaccination and health care were given as necessary. The birds in each replicate were weighed as a group each week. Mortality was recorded as it occurred. The trial lasted for 48 days (0-26 days starter phase and 27-48 days finisher phase).

 

Two birds from each replication and from each treatment were slaughtered at the end of starter and finisher phases to allow histopathological diagnosis and, at the end of the finisher phase, for determination of dressing percentage. The slaughter method and dressing percentage determinations followed procedures recommended by Kubena et al (1974).

 

For the histopathological analysis, thyroid gland tissue samples were collected in 10% buffered formalin, dehydrated in alcohol, embedded in paraffin and sectioned at 4-5 µm sections. These were stained with Haematoxylin-Eosin staining procedure and examined using a light microscope.

 

Representative samples of the feed ingredients were analysed for proximate principles following standard procedures of AOAC (1980). Metabolisable energy was estimated by employing the formula developed by King and Travener (1975). Rations were formulated based on these analyses.

 

Experimental design and statistical analyses

 

The experimental design employed in this study was the Completely Randomised Design (CRD). Data were analysed using SAS (1987). When the analysis of variance revealed the existence of significant differences among the treatment means, the Duncan Multiple Range Test (Duncan 1955) was used to locate treatment means that were significantly different from one another. Mortality data were subjected to square root transformation before analysis because of deviations from assumptions of analysis of variance. Treatment effects on mortality are presented as untransformed means.

 

Partial budgeting, dominance and marginal analysis (CIMMYT 1988), were used to compute the effects of the different levels of RSC in the diets of broiler chicks on economics of the operation. Input variable cost (cost of feed consumed) and carcass sale were used for economic feasibility evaluation (profitability). The average carcass weights were adjusted downward by 10% to more accurately reflect the difference between experimental (on-station) carcass yield and the carcass yield that farmers could expect from the same treatment due to differences between experimental management and farmer management practices.

 

Results  

Performance and Histopathology

Starter phase

 

 Total body weight gain per bird and mean daily gain per bird were highest for the control (0%) diet (Table 1). Feed intake was highest for the control diet while there was a significant (p<0.05) decrease in rations with 7 and 14% inclusion of RSC. The decrease was not significant for the higher levels. Water intake was not significantly (p>0.05) influenced by RSC level. Feed conversion ratio was better at levels beyond 21% RSC inclusion in the diet where the broiler chicks required relatively less feed per unit of gain. Lowest feed requirement per unit gain was for the diet containing 28% followed by that containing 35% RSC. Mortality was not related to RSC level.  

Variation in secretory activity was the only abnormality noted in histopathological examination of the thyroid gland. The size of the follicles increased in the glands of birds on rations containing more than 21% RSC. Medium to large sized follicles dominated at the 21% RSC while that of birds on the diet containing 35% RSC was dominated by larger follicles. Epithelial cells were more cuboidal in the control and low RSC diets (7 and 14%) but were dominated by flat to low cuboidal cells in treatments with higher RSC levels (21, 28 and 35% RSC). Wheater (1987) reported that the size of follicles corresponds with the secretory activities, being small with small amount of colloid in an active gland. The follicles in less active glands are enlarged due to stored colloid and the epithelial cells are flat. The decrease in activity was apparent histologically at the 28 and 35% levels of RSC inclusion. 

Finisher phase  

Comparison among diets containing RSC (Table 4) indicates that increasing levels of RSC in the diet up to 28% improved weight gain. Increasing RSC to 35% significantly (p<0.05) depressed gain and resulted in the lowest performance. Feed intake did not significantly (p>0.05) differ among broiler finishers subjected to diets containing 7, 14, 21, 28 and 35% RSC. Birds on the control diet consumed significantly (p<0.05) more feed than those fed diets containing RSC. Water intake was not affected by level of RSC in the diet. Broilers fed diets containing 21 and 28% RSC showed increased (p<0.05) feed conversion compared with other treatments. Mortality was significantly (p<0.05) higher for 28% RSC in the diet. There was no difference among the other treatments. Dressing percentage was not significantly (P>0.05) affected by RSC level in the diet.  

Table 4. Mean values for effect of  level of rape seed cake in the diet on the performance of broiler finishers (27-48 days of age).
Parameters	Level of rapeseed cake in the diet, %						SEM	Signif.
	0	7	14	21	28	35
Gain, g/d	41.2 ab	39.8 ab	40.4 ab	42.5a	42.1a	37.5 b	1.11	*
Feed intake, g/d	117 a	105 b	108 b	108 b	106b	105 b	2.18	*
Water intake, ml/d	304	286	301	297	312	296	8.41	NS
Feed/gain	2.9 a	2.7 bc	2.7 c	2.6c	2.5c	2.8 ab	0.06	*
Mortality, %	0.3b	0.7b	1.0 b	0.7b	2.7 a	0.7 b	0.49	*
Dressing %	69.8	69.4	71.4	70.7	71.9	71.7	1.14	NS
abcd Means within a row followed by different superscripts are significantly different *= P<0.05;  **= P<0.01; ***= P<0.001;  NS= Not significant

During the finisher phase, birds on the 21, 28 and 35% RSC levels showed slight to moderate enlargement of the thyroid gland. The enlargement was mainly bilateral but at times unilateral. Histologically, large follicles lined with mainly flat to low cuboidal cells dominated the follicles of these three groups. The colloid particularly in the 35% group was deep pinkish in some follicles showing condensation of the colloid. The gland in these three groups seemed to be less active progressively decreasing in activity with increasing RSC inclusion. The observations indicate a tendency towards developing a colloid goitre, particularly in the 35% group. 

Whole period  

Performance of broilers over the whole experimental period, expressed as on total gain, average daily gain or average final weight was not significantly (p>0.05) affected by inclusion of RSC up to 35% of the ration (Table 5). Feed intake was, however, significantly (p<0.05) lower for broilers on the rations containing RSC compared to the ration that did not contain RSC. Broilers on the ration containing 28% RSC required the lowest quantity of feed per unit gain and had the highest dressing percentage. 

Economic analysis 

Partial budget analysis revealed that the level of RSC inclusion in the diet affected net benefit.  Initially, the net benefits decreased as the level of RSC increased. There was then an increase before a drop at the end. The highest net benefit was obtained from inclusion of 28% RSC in the diet (Table 6). 

Levels of RSC listed in order of increasing total variable cost are shown in Table 7. Net benefits increase for the 28 and 35% levels of RSC inclusion rates which means no farmer would choose the other levels relative to these levels because of the higher costs coupled with lower net benefits. Thus, levels that contain 0, 7, 14 and 21% RSC are dominated. 

Marginal Rate of Return (MRR), the relation between the variable costs and net benefits for the two non-dominated levels, indicates that the farmers can expect to gain, on the average, 1655% in return for their investment by opting for the 28% RSC in the ration

 

Discussion

 

Inclusion of high levels of RSC in poultry diets has been reported to result in reduction of growth rate and /or poorer efficiency of feed utilization (Schloffel et al 1993) although the maximum level of RSC that can be included is unclear and dependent on the cultivar and content of Glucosinolates. (Kellems and Church 1998)

 

The overall results of this study show that the weight gain of the broilers was slightly less than would be expected from the breed used (Esonu 2002). This was particularly evident during the finisher phase. The histopathological findings also indicate that the effects of feeding RSC on the thyroid gland were more evident during the later (finisher) phase of the study. Leung and March (1976) reported that the effects of RSC feeding varied in magnitude according to the length of time over which RSC is fed. Findings in this study also agree with this suggestion. Capen (1993) also reports formation of colloid goitre due to glucosinolates similar to the observation in this study for broilers on the higher levels of RSC (28 and 35%) inclusion in the diet.

 

Reduced performance of birds on treatments containing RSC could partly be due to their reduced feed intake compared to the control. Comparison among RSC containing diets showed higher gains with increasing levels of RSC in the diet up to 28% during the finisher phase. This may be explained by the added advantages of a larger assortment of protein sources resulting in amino acid complementarity that satisfies requirements of the broilers better (McDonald et al 1995). The sharp decline at the 35% level could be due to the combined effects of the absence of Noug cake as a protein source in the mix at this level and possibly the increased glucosinolates resulting from the increased RSC in the diet. The situation was similar during the starter phase also.

 

The final judge in any feeding program is the economics of the operation. The economic analysis results indicated that both practices (feeding diets with and without RSC) provided positive net benefits at all levels. Highest net benefit was, however, obtained from the 28% RSC inclusion. Broilers on this ration required the lowest quantity of feed per unit gain and had the highest dressing percentage.

 

Thus, from the overall results of this study, it would appear that a 28% inclusion level of RSC could be used for both starter and finisher phases of broiler feeding.
 

 

Acknowledgements

 

The authors would like to acknowledge the Ethiopian Government for financing the study through the Ethiopian Agricultural Research Organization (EARO).  Thanks are also due to the Debre Zeit Agricultural Research Centre for provision of research facilities.

 

References

 

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