Four Belgian Blue double-muscled type (BBDM) bulls, four Belgian Blue dual-purpose type (BBDP) bulls and four Holstein bulls were used in a fattening trial in order to relate differences in the extent of muscle development and adiposity to differences in digestibility, endocrine status, protein and lipid metabolism. The larger muscle development in BBDM animals was associated with a trend to higher nitrogen retention, higher food conversion efficiency (p < 0.05) and lower apparent digestibility (p < 0.05). No difference was found between the groups for plasma glucose concentration. Higher creatinine, lower alpha-amino nitrogen, lower triglycerides and higher non-esterified fatty acid plasma levels were observed in BBDM as compared to Holstein bulls (p < 0.05), the BBDP group being intermediate. A trend to a higher cholesterol plasma level was found in BBDM animals. There was no difference between the three groups in plasma fatty acid composition, except for the C14:0 content. Some of the differences in plasma metabolites were related to carcass composition and endocrine regulation, a decrease in muscle development and an increase in adiposity being associated with lower growth hormone production (p < 0.05) and higher insulin (p < 0.05) and IGF secretions. The insulin/growth hormone ratio at the end of the fattening period was 0.0011, 0.0018 and 0.0069 in BBDM, BBDP and Holstein bulls, respectively, and was directly associated with fat deposition.

Two experiments were carried out with growing-fattening bulls, offered a fattening diet based on concentrate and supplemented with soya oil or steam-flaked linseed. Soya oil (200 g/kg) was mixed with middlings (800 g/kg). Linseed (500 g/kg) and whole barley (500 g/kg) were steam flaked. The fat incorporation resulted in an increase of the ether extract content from 26·5 g/kg dry matter to about 45 g/kg. The incorporation of soya oil increased the average daily gain (P> 0·05). The saturated: unsaturated fatty acid ratio was reduced in perirenal fat due to an increase of oleic acid and a reduction of stearic acid. The inclusion of steam-treated linseed resulted in a lower slaughter weight (P< 0·05) and a shorter fattening period (P> 0·05). The fatty acid composition of perirenal fat was affected significantly: the concentrations of oleic, linoleic and linolenic acid were increased and the concentrations of myristic, palmitic and stearic acids were reduced. This resulted in a reduced saturated: unsaturated fatty acid ratio.In a third experiment, samples of the two fat concentrates were incubated in nylon bags in the rumen. The ether extract disappearance was high with both concentrates. Furthermore, the fatty acid composition was altered to a large extent for soya oil while large proportions of unsaturated fatty acids were still present with steam-flaked linseed.

Summary — Incorporation of rapeseed meal extracted by pressure in a diet for growing fattening bulls. I. Intake, digestibility and fermentation in the rumen. Intake, digestibility, degradation kinetic and fermentation were studied with bulls offered fattening diets with four different incorporation rates of rapeseed meal obtained by pressure; the ether extract content was 8.6% and the glucosinolate content 17,6 pmolg. The control diet was made of sugar beet pulp, cereals, soya bean meal and linseed meal. In the three other diets, nitrogen from rapeseed meal provided 33, 66 or 100% of nitrogen from soya bean meal or linseed meal. The intakes of the control diet were 94.3 + 7.3 g/kg metabolic body weight. Intakes were maintained high in the diet with 33, 66 or 100% of protein from rapeseed meal at 93.5 ± 7.7; 93.0 ± 5.0 and 93.5 ± 7.7 g/kg, respectively. The apparent digestibility of rapeseed meal in the ration containing only rapeseed meal was high at 74.9 ± 1.9% for dry matter, 76.5 ± 2. I % for organic matter, 69.9 ± 3.9% for nitrogen, 59.1 ± 4.8% for ADF and 74.6 ± 6.9 % for ether extract. Dry matter of rapeseed meal was less degradable (57.8 ± 5.0%) than that of soya bean meal (65.5 ± 2.6%) or of linseed meal (61.6 ± 4.2%) but was not as well protected than that of protected soya bean meal (43.6 ± 2.6%) (P < 0.001 Similar trends were observed for the degradability of nitrogen (P < 0.001). Ether extract of rapeseed meal was more degradable than that of linseed meal (P < 0.001). 93,5 ± 7,7 ; 93,0 ± 5,0 et 93,5 ± 7,7 g/kg de poids métabolique. La digestibilité apparente du tourteau de colza dans la ration qui contenait uniquement le tourteau de colza a été particulièrement élevée : 74,9 ± 1,9 % pour la matière sèche ; 76,5 ± 2,1 % pour la matière organique ; 69,9 ± 3,9 % pour les matières azotées ; 59,1 ± 4,8 % pour l'acid detergent fiber (ADF) et 74,6 ± 6,9 % pour l'extrait éthéré. La matière sèche du tourteau de colza a été moins dégradable (57,8 ± 5,0 %) que celle des tourteaux de soja (65,4 ± 2,6 %) et de lin (61,6 ± 4,2 %), mais n'a pas été aussi fortement protégée que celle du tourteau de soja protégé (43,6 ± 2,6 %) (p < 0,001 ). Des tendances similaires ont été observées avec la dégradabilité des matières azotées du tourteau de colza et les différences ont été significatives (p < 0,001

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Since CAP reform and environmental problems, there is, in agriculture, a tendency to reduce the production. Reduction of nitrogen fertilizer was suggested to decrease intensification. Nowadays, high quality milk has to be produced for the dairy industry, in order to be processed as cheese, butter,... Another aspect in milk production is the payment based on the composition (Beguin, 1994). The aim of this experiment was to study the effects of a reduction in nitrogen fertilizer on milk yield, butterfat, protein, urea and cells contents. The trial was repeated over four years consecutively.