Optimal level of rapeseed meal in diets of lambs.
S.N.M. Mandiki1, J.L. Bister1, G. Derycke1, J.P. Wathelet2, N. Mabon2, M. Marlier2 and R. Paquay1
1. Facultés Universitaires Notre-Dame de la Paix, Physiologie Animale, 61 Rue de Bruxelles, B-5000 Namur, Belgium. e-mail : Raymond.Paquay@fundp.ac.be
2. Faculté Universitaire des Sciences Agronomiques, Unité de Chimie générale et organique Passage des Déportés 2, B-5030 Gembloux, Belgium.
Two experiments were carried out in order to improve the strategy of rapeseed meal (RPM) incorporation in the diets of lambs. In a first experiment, the effects of RPM obtained from either a high-glucosinolate (HG) cultivar (Honk RPM) or a double-low strain (Samourai RPM) were studied. Two types of concentrates containing 25% of RPM were compared to a Control. In a second experiment, the effects of various proportions (0 – 40%) of an industrial low glucosinolate (LG)-RPM were studied in order to determine the disorder-threshold in diets for young ruminants. One hundred forty six Texel, Suffolk or crossbred lambs ranged in age from 1 to 2 months were used. Neither the Samourai nor the Honk RPM did affect negatively animal performance whatever the parameter considered (growth, food intake and conversion, slaughter performances). Low (P < 0.05) proportions of C10:0, C12:0 and C14:0 and high (P < 0.05) contents of C18:1trans, C22:2 were determined in the perirenal fat of lambs receiving the Honk RPM. The industrial LG-RPM had no negative effects on animal performance, best results were obtained with 25 and 30% of RPM. The Samourai RPM had no effect on the thyroid weight, whereas, the Honk RPM modified (P < 0.05) the histology of this organ; the percentages of large thyroid follicles being higher (P < 0.05) in the Honk group than in the Control and Samourai groups. High levels of industrial LG-RPM (20-40%) induced also an hyperthyroidism. The Samourai and Honk RPM decreased (P < 0.05) the secretions of thyroid hormones while the industrial LG-RPM did not affect these hormones in any way. LG-RPM had no significative effects on other hormones. It was concluded that disturbance in thyroid histology and activity induced by the ingestion of RPM did not affect the physiology and performance of lambs and that the levels between 25 to 30% of a LG-RPM were optimal for growing and fattening lambs.
Keywords : Rapeseed meal, disorder-threshold, lambs, performance, physiology.
Introduction
Data concerning the maximal proportions of rapeseed meal (RPM) in diets of ruminants are not well defined although it is known that the effects of antinutritional factors vary among species and depend upon the age of animal (Bell, 1993 ; Mawson et al. ; 1993, 1994). Contents of erucic acid and some types of glucosinolates have been reduced in rapeseed by the way of genetic improvement but concentration in other antinutritional factors, such as progoitrin is still important in some rape cultivars and their effects depend upon the amount of rapeseed meal in the diet. So, the general objective of our experiments was to determine the optimal amount of RPM which may be included in the diet of young lambs for optimisation of growing and fattening.
In a first experiment, the effects of RPM from either a high-glucosinolate (HG) cultivar (Honk RPM, 33 µmoles of glucosinolates/g DM of seed ) or a double-low strain (Samourai RPM, 15 µmoles/g DM of seed) were studied. Two types of concentrates containing 25% of RPM were compared to a Control; they contained respectively 1.95 and 4.22 mmoles of glucosinolates/g DM. Sixty six Texel, Suffolk or crossbred lambs (± 1 month of age) were used. From weaning (88 ± 8 days) to slaughter weight concentrates were the sole component of the diet apart from a small quantity of hay (0.4 kg/day/animal). In a second experiment, the effects of various proportions (0 – 40%) of an industrial low glucosinolate (LG)-RPM were tested in order to determine the disorder-threshold in diets of lambs. Eighty lambs (± 2 months of age) receiving concentrates with 0, 5, 10, 15, 20, 25, 30 and 40% of RPM as major component of their diet were used. The experimental concentrates contained 0.70, 1.73, 2.66, 3.76, 4.91, 6.31, and 8.37 mmoles of glucosinolates/g DM, respectively.
For the two experiments, growth performances, feed intake, slaughter parameters, thyroid weight and histology and circulating hormones were investigated. In order to compare the size of thyroid follicles, slices of thyroid tissue (7µm) were submitted to histological staining before being photographed. The pictures were stored in JPEG format and were analysed using a photosharp program. All the follicles observed on pictures taken with low magnification were classified by their diameter into three classes, ranging from 25 (small), 50 (medium) and > 75 (large) pixels. Plasma hormone concentrations were quantified by radio-immunoassay. For Experiment 1, the fatty acids of perirenal fat were determined by gas-liquid chromatography.
For animal performance, no significant effects of RPM were observed whatever the parameter considered. Only the quality of perirenal fat showed some modifications. The concentrates with RPM induced a significant (P < 0.05) decrease in the percentages of some saturated acids (C10:0, C12:0 and C14:0). Moreover, an increase (P < 0.01) in C22:2 was noted for the two experimental concentrates and this was also apparent for trans C18:1 for the Honk group. The cholesterol concentrations were respectively of 0.52 ± 0.13 ; 0.54 ± 0.08 and 0.66 ± 0.13 mg/ml for the Samourai, Honk and Control groups.
Thyroid weights were comparable for the Control and the Samourai groups, in contrast, they were 15 or 18% higher (P < 0.05) in the Honk group than in the Control. Moreover, the proportion of small follicles was significantly lower (P < 0.05) in the Honk group compared to the Control group but the difference between Honk and Samourai groups was not significant. The proportions of large thyroid follicles were significantly higher (P < 0.05) in the Honk than in the Samourai and Control. Values were comparable among the three groups for medium follicles. No significant difference was calculated between groups concerning the surfaces of the largest thyroid follicles. Plasma T3 , T4 and insulin concentrations were higher (P < 0.05) in the Control than in the Samourai and Honk groups. Values for other hormones (GH and cortisol) did not differ among groups.
Experiment 2 (Table 2)
As in Experiment 1, no detrimental effect of LG-RPM was detected apart from a low concentrate intake which was compensated by a high ingestion of hay. For groups receiving 25 and 30% of RPM, the growth rate was comparable to the Control group; this was associated with a low concentrate intake and a best feed conversion.
Thyroid weights were higher (P < 0.05) for proportions between 20 to 40% than those between 0 to 15%. This increase in thyroid weight was associated with large surface follicles. Plasma T3 concentration was comparable among groups; plasma T4 did not also differ between Control group and groups with LG-RPM except for low values (P < 0.05) in lambs receiving 15, 20 and 40% of LG-RPM. In contrast to results obtained in Experiment 1, the ingestion of LG-RPM lowered (P < 0.05) the concentration in plasma cortisol. Plasma insulin was not modified except an increase (P < 0.05) for group receiving 15% of RPM.
In agreement with previous reports (Mawson et al., 1994; Hopkins et al., 1995) the results in the current studies show that the incorporation of LG-RPM (< 10 mmoles of glucosinolates g-1 diet, Mawson et al., 1994) in the diet of lambs has no detrimental effects on animal performance. Indeed, large amount of LG-RPM (25-40%) obtained from either a HG or 00-rapeseed induced any depression in the zootechnical performance. No relation was established between the levels of LG-RPM in the diet and the zootechnical parameters. However, best growth rate associated with a low feed intake and efficiency was observed for groups receiving 25 and 30% of LG-RPM. The use of LG-RPM improved the quality of perirenal fat since the ratio of unsaturated-saturated fatty acids increased as observed in milk from dairy cows fed with high proportion of LG-RPM (Mawson et al., 1994). The improvement in the quality of perirenal fat is related to the distribution of fatty acids in the RPM for whom the high content in poly-unsaturated fatty acids has been reported (Emanuelson et al., 1991).
The Samourai RPM obtained from a double-low cultivar had no effect on the thyroid, whereas the Honk RPM from a HG-variety as well as high levels of industrial LG-RPM modified the weight and the histology of this organ. The changes in weight agree with previous report by Hill et al. (1991) that the hyperthrophy of the thyroid is positively related to the content in glucosinolates in the diet. The histological disturbance in the thyroid induced by the ingestion of RPM was not associated with significant changes in circulating hormones. Changes in some hormones such as, T3, cortisol and insulin could not be confirmed between the two experiments or were not strictly related to the ingestion of RPM.
It was concluded that the disturbance in thyroid histology and activity induced by the ingestion of large amount of LG-RPM did not affect the animal physiology and performance, and that levels between 25 - 30% of a LG-RPM were optimal for growing and fattening lambs.
This work was supported by the General Office of Research and Development of the Belgian Agricultural Ministry and by the General Direction of Technologies, Research and Energy of Ministery of "Region Wallonne" in Belgium. The authors are grateful to M.A. Bouckoms-Vandermeir of the laboratory of Animal Physiology of Namur, the staff of the Ovine Research Centre of Faulx-les-Tombes, and to M. Hardenne of the Department of General and Organic Chemistry of Gembloux for their technical assistance.
Bell, J.M., 1993. Factors affecting the nutritional value of Canola meal: a review. Can. J. Anim. Sci., 73, 679-697.
Emanuelson M.; Murphy M. and Lindberg J.E., 1991. Effects of heat-treated and untreated full-fat rapeseed and tallow on rumen metabolism, digestibility, milk composition and milk yield in lactating cows. Anim. Feed Sci. Techno., 34, 291 - 309.
Hill, R., 1991. Rapeseed meal in the diets of ruminants. Nutr. Abstr. Rev., 61(3), 139-155.
Hopkins, D.L., Beattie, A.S. and Pirlot, K.L., 1995. Meat quality, carcass fatness and growth of short scrotum lambs grazing either forage rape or irrigated perennial pasture. Australian Journal of Experimental Agriculture, 35, 453-459.
Mawson, R., Heany, R.K., Zdunczyk, Z. and Kozlowska, H., 1993. Rapeseed meal-glucosinolates and their antinutritional effects. Part II. Flavour and palatability. Die Nährung, 37, 336 - 344.
Mawson, R., Heany, R.K., Zdunczyk, Z. and Kozlowska, H., 1994. Rapeseed meal-glucosinolates and their antinutritional effects. Part III. Animal growth and performance. Die Nährung, 38, 167-177.
Table 1. Animal performance, weight and histology of thyroid and plasma hormone concentrations (Experiment 1).
|
|
Control |
Samourai RPM |
Honk RPM |
|
Animal performances Liveweight at weaning (kg) Weight at slaughtering (kg) Daily gain after weaning (g/d) Concentrate intake after weaning (g DM/lamb/d) Feed conversion Carcass weight (kg) Dressing percentage Carcass classification (Score 1 – 6) |
23.1 ± 6.0 35.0 ± 1.9 262 ± 45
847 3.41 17.0 ± 1.6 48 3.7 |
24.5 ± 4.4 35.3 ± 2.7 270 ± 70
915 3.48 17.4 ± 1.6 49 3.7 |
23.9 ± 6.8 35.7 ± 2.5 258 ± 57
849 3.61 17.2 ± 1.2 49 3.6 |
|
Thyroid Weight (g) Surface of follicles (p2) Proportions of follicles (%) - small (25 p) - medium (50 p) - large (> 75 p) |
2.6 ± 0.5a 27.8 ± 16
42 ± 27a 46 ± 20 12 ± 14a |
2.7 ± 0.6a 24.1 ± 5
29 ± 13b 57 ± 7 14 ± 10a |
3.0 ± 0.8b 27.9 ± 7
24 ± 15b 49 ± 12 27 ± 18b |
|
Plasma hormone concentrations T3 (ng/dl) T4 (µg/dl) GH (ng/ml) Cortisol (µg/dl) Insulin (µUI/ml) |
356 ± 8.8 a 8.6 ± 1.7a 8.1 ± 7.6 4.1 ± 1.3 24.0 ± 8.6a |
304 ± 70b 7.3 ± 1.7b 9.5 ± 4.1 3.6 ± 1.2 14.5 ± 3.7b |
315 ± 77b 7.4 ± 1.2b 9.0 ± 3.1 4.2 ± 1.2 14.6 ± 5.0b |
a – b : significantly different means (P < 0.05). 1 : percentages of follicles per unit of thyroid tissue. p = pixel.
Table 2. Animal performance, weight and histology of thyroid and plasma hormone concentrations (Experiment 2).
|
|
0% |
15% |
20% |
25% |
30% |
40% |
|
Animal performances Liveweight at weaning (kg) Weight at slaughtering (kg) Daily gain after weaning (g/d) Concentrate intake after weaning (g DM/lamb/d) Feed conversion Carcass weight (kg) Dressing percentage (%) Carcass classification (SEUROP) |
19.4 ± 2.2 34.5 ± 2.3 252 ± 50a
871 4.02 17.0 ± 0.8 49 2.1 |
19.2 ± 3.1 36.4 ± 2.2 229 ± 86b
790 3.92 17.7 ± 1.2 49 2.4 |
18.1 ± 3.2 35.9 ± 3.4 228 ± 74b
625 3.18 17.5 ± 2.0 49 2.1 |
19.0 ± 2.7 36.0 ± 3.3 247 ± 54a
745 3.58 17.5 ± 1.3 49 2.0 |
19.6 ± 2.7 36.4 ± 3.2 252 ± 61a
782 3.61 18.0 ± 1.4 49 2.0 |
19.9 ± 3.4 35.3 ± 3.4 225 ± 43b
787 4.05 16.9 ± 0.0 48 2.4 |
Thyroid
Weight (g) Surface of follicles (p2) |
3.1 ± 0.7a 17.1 ± 4a |
3.0 ± 0.4a 16.4 ± 3a |
4.5 ± 1.2b 22.1 ± 2b |
4.1 ± 1.2b 19.0 ± 3b |
3.9 ± 1.3b 21.0 ± 7b |
4.4 ± 1.5b 21.1 ± 5b |
|
Hormone concentrations T3 (ng/dl) T4 (µg/dl) Cortisol (µg/dl) Insulin (µUI/ml) |
136 ± 20 4.4 ± 0.8a 2.7 ± 0.5a 29.1 ± 7a |
105 ± 11 3.0 ± 0.4b 2.0 ± 0.2b 40.7 ± 17b |
117 ± 25 3.1 ± 0.7b 1.8 ± 0.3b 34.2 ± 9b |
149 ± 32 4.1 ± 0.8a 1.7 ± 0.3b 24.9 ± 6a |
120 ± 20 3.6 ± 0.3a 2.1 ± 0.3b 35.6 ± 11b |
140 ± 17 3.0 ± 0.6b 1.9 ± 0.3b 25.9 ± 8a |
a – b : significantly different means (P < 0.05). 1 : percentages of follicles per unit of thyroid tissue. p = pixel.