OPtimization of rapeseed meal use for fattening bulls
R. Paquay1, S.N.M. Mandiki1, J.L. Bister1, G. Derycke1, J.P. Wathelet2, N. Mabon2 and M. Marlier2
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 conducted in order to optimize the incorporation of rapeseed meal (RPM) in diets for growing and fattening of bulls. In a first experiment, the effects of 20% of a low glucosinolate (LG)-RPM (3.14 mmoles/g DM of concentrate) were studied. In a second experiment, various proportions (0, 10, 20, 34%) of an industrial LG-RPM were tested in order to determine the optimal level in diet of young bulls. Thirty six young Belgian White Blue bulls were used. In the two experiments, large amount of LG-RPM (20 - 34%) did not reduce animal performance whatever the parameter considered (liveweight, daily weight gains, food intake, feed conversion, carcass weight, dressing percentages). Values did not also vary with the level of LG-RPM in the diet. Any effects were observed on the thyroid weight and the size of thyroid follicles. The secretion of thyroid hormones was not affected by RPM except for a decrease (P < 0.05) in the production of thyroxin by thyroid tissue of bulls which received 34% of RPM in Experiment 2. Results concerning plasma testosterone and cortisol were inconsistent between the two experiments with negative effects or no influence of LG-RPM. It was concluded that levels between 20 – 34% of LG-RPM in diet may be used for fattening bulls but investigations are still needed to outline the long-term effects on steroids and reproductive performance.
Keywords : Rapeseed meal, disorder-threshold, bulls, performance, physiology.
Introduction
It is well known that the effects of rapeseed antinutritional factors vary among species and depend upon the age of animal (Fiems and Bell, 1985; Bell, 1993; Mawson et al., 1993, 1994). Studies on the use of rapeseed meal in feeding of ruminants are still incomplete, especially investigations are still needed to establish the maximal amount of RPM which may be included in the diet of young animals. Therefore, the objective of our experiments was to determine the optimal amount of RPM which may be included in the diet of bulls for growing and fattening.
In a first experiment, a concentrate with 20% of LG-RPM obtained from a double-low cultivar (Synergy variety, 20.94 mmoles of glucosinolates/g DM of seeds) was compared to a control without RPM. The experimental concentrate contained 3.14 mmoles of glucosinolates/g DM (in which 51% of progoitrin). Twelve Belgian White Blue bulls (± 280 kg) were used. From their 9th month of age to slaughter (± 650 kg), they received ad libitum concentrates as the sole component of their diet apart from wheat straw. In a second experiment, the effects of various proportions (0, 10, 20 and 34%) of an industrial LG-RPM were tested. These experimental concentrates contained 1.67, 3.73 and 6.36 mmoles of glucosinolates/g DM, respectively; with the percentages of progoitrin varying between 43 – 48%. Twenty four Belgian White Blue bulls allocated to 4 groups received ad libitum concentrates as the sole component of their diet apart from wheat straw from their 9th month of age (±300 kg) till slaughter weight (± 620 kg).
For the two experiments, growth, feed intake, slaughter parameters, thyroid weight and histology and circulating hormones (triiodothyronin-T3, thyroxin-T4, testosterone, cortisol, insulin) 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.
Results
No significant effects of Synergy RPM were observed except for high weight values at slaughtering in the Control group (P < 0.05) due to a large intra-variability.
Thyroid weight and size of thyroid follicles were not affected by the ingestion of the Synergy RPM. The ingestion of Synergy RPM decreased (P < 0.05) plasma testosterone concentration while values for other hormones (T3, T4, cortisol and insulin) were comparable to the Control group.
Experiment 2 (Table 2)
As in Experiment 1, the industrial LG-RPM did not induce a reduction in animal performance whatever the parameter considered. Daily weight gain and feed conversion were comparable between the Control and group with 34% of RPM ; values were slightly higher in groups with 10 and 20% of RPM in relation to the initial growth rate (1.35, 1.55, 1.58 and 1.28 kg/d, respectively).
Thyroid weight values were comparable among groups. No relation was calculated between the level of RPM in diet and the size of thyroid follicles. Indeed, the percentages of medium follicles were similar among groups; values for large follicles were comparable between the Control and group receiving 34% of RPM. In addition, the percentages of large follicles were higher (P < 0.05) in the Control than in groups with 10 and 20% of RPM. In contrast to the results obtained in Experiment 1, the industrial LG-RPM enhanced (P < 0.05) plasma cortisol concentration while no negative effect was observed concerning plasma testosterone. Values for other plasma hormones (T3, T4 and insulin) were comparable among groups.
The results of the current study show that LG-RPM (< 10 mmoles of glucosinolates g-1 diet, Mawson et al., 1994) had any negative effect on animal performance as previously reported (Mawson et al., 1994, Hopkins et al., 1995). In addition, they indicate that high levels ranging from 20 - 34% of RPM in the diet may be used for growing and fattening bulls. This agrees with the recommendation of Canola Council of Canada that LG-RPM can make up to 25% of concentrate mixes for cows prepared on a cereal base (Mawson et al., 1994).
LG-RPM used in our experiments did not affect negatively the weight or histology of thyroid whatever the level in the diet of bulls. With LG-RPM detrimental effects were only observed for lambs relatively more younger (Mandiki et al., 1999) than bulls used in the current study. Except a depression in the production of thyroxin by thyroid tissues in bulls fed with 34% of RPM, the secretion of thyroid hormones were not influenced by the ingestion of LG-RPM. It has been reported that a long-term feeding by 00-RPM has negative effect on thyroid hormone release in primiparous (not in pluriparous) cows (Ahlin et al., 1994). As for thyroid hormones, plasma insulin concentration was not not affected by LG-RPM in the two experiments. Data on testosterone and cortisol were inconsistent between the two experiments indicating either negative effects or no influence of RPM. Recent studies have shown an enhancement of steroid-3-beta-dehydrogenase activity associated with a low number of Leydig cells, a degeneration and necrosis of seminiferous epithelium in boars submitted to a long-term feeding with 00-RPM (Rotkiewicz et al., 1997). Such data are not yet available for bulls.
It was concluded that levels between 20 - 34% of LG-RPM in diet may be used for fattening bulls but investigations are still needed to outline the long-term effects on steroids and reproductive performance.
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 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.
Ahlin K.A., Emmanuelson M. and Wiktorson H., 1994. Rapeseed products from double-low cultuvars as feed for dairy cows : effects of long-term feeding on thyroid function, fertility and animal health. Acta Vet. Scand. 35 :37-53.
Bell, J.M., 1993. Factors affecting the nutritional value of canola meal: a review. Can. J. Anim. Sci., 73, 679-697.
Fiems, L.O. and Buysse, F.X., 1985. Aperçu de l'utilisation de tourteaux de colza en tant que source de protéines dans les rations pour ruminants. Revue de l'Agriculture (Belgium), 2(38), 261-274.
Mandiki S.N.M., Bister J.L., Derycke G., Wathelet J.P., Mabon N., Marlier M. and Paquay R., 1999. Optimal level of rapeseed meal in diets of lambs. Proceedings 10th International Rapeseed Congress, Australia, Canberra (in press).
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.
Rotkiewicz T., Bomba G., Falkowski J., Glogowski J., Kozera W., Kozlowski M., 1997. Studies on a log-term use of rapeseed products in diets for boars: pathomorphological changes in the reproductive system, liver and thyroid gland. Reprod. Nutr. Dev. 37: 675-690.
Table 1. Animal performance, weight and histology of thyroid and plasma hormone concentrations (Experiment 1).
|
|
Control |
Synergy RPM |
|
Animal performances Initial liveweight (kg) Weight at slaughtering (kg) General daily liveweight gain (kg/d) Concentrate intake (kg DM/animal/d) Feed conversion Carcass weight (kg) Dressing percentage |
278 ± 60 658 ± 35a 1.39 6.83 5.6 429 ± 16 65 ± 1.3 |
281 ± 43 630 ± 18b 1.30 6.63 5.8 409 ± 15 65 ± 0.1 |
|
Thyroid Weight (g) Surface of follicles (p2) Proportions of follicles (%) - small (25 p) - medium (50 p) - large (> 75 p) |
36.0 ± 23 49 ± 25
32 ± 14 31 ± 10 37 ± 26 |
38.6 ± 14 42 ± 11
31 ± 15 28 ± 4 41 ± 21 |
|
Plasma hormone concentrations T3 (ng/dl) T4 (µg/dl) Testosterone (ng/ml) Cortisol (µg/dl) Insulin (µUI/ml) |
136 ± 7 6.1 ± 0.6 0.82 ± 0.4a 1.47 ± 0.7 18.6 ± 2.8 |
137 ± 22 5.9 ± 1.2 0.61 ± 0.4b 1.37 ± 0.6 26.3 ± 16.8 |
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% |
10% |
20% |
34% |
|
Animal performances Initial liveweight (kg) Weight at slaughtering (kg) General daily weight gain (kg/d) Concentrate intake (kg DM/animal/d) Feed conversion Carcass weight (kg) Dressing percentage (%) |
303 ± 20 618 ± 33 1.46 7.51 6.04 415 ± 16 67.5 ± 2 |
302 ± 23 629 ± 27 1.60 7.47 5.50 413 ± 8 66.0 ± 2 |
300 ± 14 614 ± 32 1.58 7.47 5.44 416 ± 19 67.5 ± 1 |
300 ± 22 605 ± 34 1.47 7.56 6.00 411 ± 23 67.9 ± 2 |
ThyroidWeight (g) Proportions of follicles (%) - small (25 p) - medium (50 p) - large (> 75 p) |
16.2 ± 1.3
17 ± 10b 29 ± 6 54 ± 16a |
14.5 ± 2.8
29 ± 10a 32 ± 10 38 ± 11b |
17.8 ± 1.2
22 ± 16a 31 ± 8 47 ± 18b |
16.9 ± 3.8
12 ± 5b 29 ± 7 59 ± 14a |
|
Hormone concentrations T3 (ng/dl) T4 (µg/dl) Testosterone (ng/ml) Cortisol (µg/dl) Insulin (µUI/ml) |
75.1 ± 5.6 1.12 ± 0.1 1.87 ± 0.26 0.47 ± 0.1a 13.2 ± 2.7 |
64.8 ± 3.0 1.00 ± 0.1 2.05 ± 0.6 1.20 ± 0.2b 13.9 ± 2.6 |
71.5 ± 2.6 1.11 ± 0.1 2.38 ± 0.4 1.50 ± 0.2b 14.9 ± 1.7 |
71.0 ± 4.4 0.95 ± 0.0 1.93 ± 0.8 1.29 ± 0.3b 11.0 ± 1.3 |
a – b : significantly different means (P < 0.05). 1 : percentages of follicles per unit of thyroid tissue. p = pixel.