LOW-GLUCOSINOLATE CANOLA IN LAYING HEN DIETS

Lloyd D Campbell¹, Bogdan A Slominski¹, Kevin C Falk²

and Yuqiong Wang¹

¹Department of Animal Science, University of Manitoba,

Winnipeg, Manitoba, Canada R3T 2N2

²Agriculture and Agri Food Canada, Saskatoon, Saskatchewan, Canada S7N 0X2

e-mail address: campbel13@ms.umanitoba.ca

ABSTRACT

Two experiments were conducted to evaluate the feeding value of low-glucosinolate canola meal for laying hens. Low-glucosinolate and commercial canola meal diets and a control diet were fed to laying hens over a 5-month period in one experiment and diets varying in glucosinolate content were used in a second experiment. In both experiments treatment effects were assessed by measuring productive performance characteristics and by a determination of organ weights, plasma thyroid hormone levels and liver enzyme levels in representative birds sacrificed at the termination of the trials. Hen-day egg production, feed consumption, feed conversion efficiency and mortality levels were parameters used to assess productive performance. Thyroid status was determined by thyroid weight and levels of thyroid hormones (T₃ and T₄). Incidence of liver hemorrhage, liver glutathione levels and activities of xenobiotic metabolizing enzymes in liver tissue were measured to assess antinutritive effects. Egg production was maintained at a high level for all treatment groups throughout the experimental period and liver hemorrhage mortality or evidence of an antinutritive effect of glucosinolates were not apparent for hens fed the low-glucosinolate canola meal. A high feeding value was demonstrated for the low-glucosinolate canola meal and the data indicated that the meal may be used in laying hen formulations based on its nutritive value in comparison to other protein sources with no need for an upper-limit constraint.

KEYWORDS: Canola meal, glucosinolates, laying hens, antinutritive.

INTRODUCTION

Glucosinolates have long been considered as the major antinutritive factor in rapeseed meal and plant selection programs have resulted in the development of cultivars of rapeseed with low levels of glucosinolates (Bell, 1982). In Canada, low-glucosinolate rapeseed meal, or canola meal, became available for use over 20 years ago and the canola meal is used extensively in diets for livestock and poultry but an upper-limit constraint is still recommended for its use in the diet of the laying hen (Hickling and Freig, 1997). Lines of canola with glucosinolate levels below that in commercial canola varieties have been developed in Canada and studies with laying hens conducted with meal produced from these lines have shown promising results (Campbell and Slominski, 1991). Further developments have been made in the reduction of the level of glucosinolates in canola lines and this paper will present studies on the nutritive value of low-glucosinolate canola meal for the laying hen.

EXPERIMENTAL

An experiment was conducted with laying hens (1280 Dekalb SCWL) over a 5 month period to determine the feeding quality of low-glucosinolate canola and in particular to assess the antinutritive effects. The low-glucosinolate canola (a Brassica campestris cultivar from Agriculture and AgriFood Canada, Saskatoon) was processed in a pilot plant and the resulting meal was incorporated into cereal-based diets at levels of 10 and 20% of the diet. Two commercial canola meal diets (10 and 20%) along with a non-canola control diet were also used in the experiment (Table 2). A companion experiment in which laying hens were fed diets containing graded levels of glucosinolates (0 - 25% commercial canola meal as the protein supplement) was also conducted to obtain data on responses to diet glucosinolate level that would facilitate the interpretation of the results for the low-glucosinolate meal.

Table 1. Composition (%) of diets used in the evaluation of low-glucosinolate canola meal (CM).

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Ingredient Diet type_____________________________ Control Low-glucosinolate CM Commercial CM 10% 20% 10% 20%
Wheat	51.06	47.05	42.78	45.43	39.07
Barley (hulled)	20.00	20.00	20.00	20.00	20.00
Canola meal	–	10.00	20.00	10.00	20.00
Soybean meal	13.81	6.00	–	8.20	3.15
Meat meal	3.00	3.00	3.00	3.00	3.00
Tallow	--	1.23	2.50	1.45	3.07
Vegetable oil	2.00	2.00	2.00	2.00	2.00
Limestone	8.20	8.10	8.00	8.10	8.00
Calcium phosphate	0.39	0.29	0.20	0.29	0.20
Premix¹	1.55	1.53	1.52	1.53	1.51

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¹ Premixes contained DL methionine, vitamins and minerals to meet NRC specifications. All diets were iso-caloric (2750 kcal/kgME) and iso-nitrogenous (18.0% protein).

Treatment effects were assessed by measuring productive performance characteristics and by a determination of organ weights, plasma thyroid hormone levels and liver enzyme levels in representative birds sacrificed at the termination of the trial. Hen-day egg production, feed consumption, feed conversion efficiency and percent medium, large and extralarge eggs were parameters used to assess productive performance. Mortality levels, including incidence of liver hemorrhage as a cause of mortality, were also monitored. Thyroid status was determined by thyroid weight and levels of plasma thyroid hormones (T₃ and T₄). Liver glutathione levels (Baker et al., 1990) and activities of xenobiotic metabolizing enzymes (Cytochrome P₄₅₀; Guengerich et al., 1994 and glutathione-S-transferase; Habig et al., 1974) were measured to assess antinutritive efffects.

The glucosinolate content of the new cultuvar is shown in Table 2. The level of 1.80 F mol/g meal of total glucosinolate represents a level substantially below that normally found in commercial canola meal (10 - 15 F mol/g; Slominski and Campbell, unpublished results). As indicated in Table 2, the low-glucosinolate meal contained a low level of myrosinase activity. This may be explained by the fact that the meal was produced in a pilot plant and not by the commercial crushing process. Whole seeds (5.2% by weight) in the meal may have contributed the active enzyme.

Table 2. Glucosinolate of low-glucosinolate canola meal.

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Glucosinolate F mol/g oil-free-meal
3-butenyl	0.35
4-pentenyl	0.13
2-0H-3-butenyl	0.47
2-0H-4-pentenyl	0.07
4-0H-benzyl	0.05
3-indolylmethyl	0.00
4-0H-3-indolylmethyl	0.73
Total	1.80
Myrosinase activity	0.024 units¹

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¹ 1 unit myrosinase activity equals the hydrolysis of 1 F mole glucosinolate per minute.

Egg production was maintained at a high level throughout the production trial for all treatment groups indicating a high feeding value for low-glucosinolate canola meal (Table 3).

Table 3. Productive performance of laying hens fed control, low-glucosinolate and commercial canola meal (CM) diets over a 5 month feeding period.

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Parameter Diet______________________________ Control Low-glucosinolate CM Commercial CM 10% 20% 10% 20%
Feed intake, g/hen/day	102.2a¹	100.7ab	99.2b	99.9b	99.8b
Egg production (%)	90.1	89.4	90.5	90.7	89.4
Feed/egg (g/g)	1.95	1.91	1.87	1.88	1.89
Mortality (LH/total)²	0/0	0/2	0/0	1/2	1/7
Medium eggs (%)	19.0ab	21.6ab	22.9a	22.6ab	17.0b
Large eggs (%)	62.7	60.7	62.2	59.9	62.1
Extralarge eggs (%)	17.8ab	16.7ab	14.7b	16.8ab	20.8a

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¹ ab (P<0.05). ² Number of hens dying due to liver hemorrhage (LH) and total mortality numbers.

Feed consumption was lower for hens fed commercial canola meal and the 20% low-glucosinolate canola meal diet than for hens fed the control diet. This may reflect the over-formulation of added fat in the canola diets to produce isocaloric diets. In this regard, the canola diets resulted in superior feed conversion efficiency in comparison to the control (soybean meal) diet. Egg weight measurements were similar for all treatment groups although hens fed 20% commercial canola meal had a greater percentage of extralarge eggs and fewer medium eggs. The reason for this is not clear and is contrary to previous results in which egg weight tended to be depressed in hens fed diets of high glucosinolate content (Campbell and Schöne, 1998). The results of the current companion experiment also showed the depressing effect of diet glucosinolate content on egg weight (data now shown).

Liver hemorrhage mortality was not evident among hens fed the low-glucosinolate canola meal although mortalities were recorded among hens consuming the commerical canola meal (Table 3). A lack of an antinutritive response to glucosinolates among hens fed the low-glucosinolate canola meal was corroborated by similar thyroid weights, liver glutathione levels and plasma thyroid hormones (T₃ and T₄) in comparison to control. Similarly, no response was noted in liver content of cytochrome P₄₅₀ or glutathione-S-transferase activities (data not shown). In contrast elevated levels of these antinutritive responses were evident among hens fed the 20% commercial canola meal diet which has been demonstrated in previous experiments (Campbell and Slominski, 1991) and were noted in the companion experiment involving graded levels of dietary glucosinolate (data not shown).

Table 4. Organ weight, plasma thyroid hormone (T₃, T₄) levels and liver glutathione levels in hens fed control, low-glucosinolate and commercial canola meal (CM) diets over a 5 month feeding period.

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Parameter Diet P value Control Low-glucosinolate CM Commercial CM 10% 20% 10% 20%
Thyroid weight mg/100g BW	13.1	12.6	12.7	14.3	14.5	0.18
Liver weight g/kg BW	29.1	30.0	30.3	29.4	27.8	0.52
Plasma T₃ ng/dl	120.8	119.5	124.8	116.8	117.7	0.96
Plasma T₄ Fg/dl	0.77	0.62	0.71	0.78	0.72	0.19
Liver glutathione mg GSH/g	2.77	3.03	3.01	3.04	3.42	0.06

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CONCLUSIONS

The data indicate a high feeding value for low-glucosinolate canola meal. The lack of an antinutritive effect at a dietary glucosinolate level of 0.4 Fmol/g diet would suggest that low-glucosinolate canola meal may be used in laying hen formulations based on the nutritive value of the meal in comparison to other protein sources with no need for an upper-limit constraint.