Summary Six normal‐conformation and six double‐muscled Belgian White‐blue bulls were involved in a 2 × 2 × 2 factorial experiment to investigate the effect of genotype (normal versus double‐muscled), body weight (400 versus 600 kg) and dietary crude protein (135 versus 165 g per kg dry matter) on voluntary feed intake, digestion and its consequences on the nutritive value, metabolites in blood and urine and nitrogen retention. The diet consisted of concentrate and maize silage (50:50, dry matter basis) and was fed ad libitum. Double‐muscled bulls showed a significantly lower feed consumption (67.1 g DM per kg W0.75) compared to normal bulls (81.5 g). When adjusted for dry matter intake, digestibility was not affected by beef type. Some feed components tended to be better digested when body weight (crude fibre and nitrogen‐free extractives) or dietary crude protein content (dry matter, organic matter, crude protein, nitrogen‐free extractives and energy) were higher. Blood urea nitrogen was not dependent on genotype, but increased with body weight and dietary protein. Creatinine concentration in the blood and daily creatinine excretion in the urine were highest in double‐muscled bulls and heavier animals. Urinary 3‐methylhistidine excretion was not different between double‐muscled and normal bulls, but increased with body weight. This was confirmed by the fact that nitrogen retention relative to intake was similar for both beef types and decreased with a higher body weight. A negative effect of stress on feed intake, muscle protein degradation and nitrogen retention in double‐muscled bulls was not excluded. Zusammenfassung Einfluß von Genotyp, Lebendmasse und Proteingehalt der Ration auf Futteraufnahme, Verdaulichkeit, Metaboliten im Blut und Harn und Stickstoffbilanz. Der Einfluß von Genotyp (konventionell oder Doppellender), Lebendmasse (400 und 600 kg) und Proteingehalt der Ration (135 oder 165 g Rohprotein pro kg Trockensubstanz) auf Verdaulichkeit, Metaboliten im Blut und Harn und Stickstoffbilanz wurde mit 6 konventionellen Bullen und 6 Doppellendern der Belgischen weißblauen Rasse untersucht. Die Ration bestand aus Kraftfutter und Maissilage (50:50 auf Basis von Trockensubstanz) und wurde ad libitum gefüttert. Die Trockensubstanzaufnahme der Doppellender lag niedriger im Vergleich mit den konventionellen Bullen (67, 1 bzw. 81, 5 g pro kg LM0.75). Nach mathematischer Anpassung an die verschiedene Trockensubstanzaufnahme war die Verdaulichkeit nicht durch den Genotyp beeinflußt. Die Verdaulichkeit einiger Futterkomponenten lag höher, wenn die Lebendmasse (Rohfaser, N‐freie Extraktstoffe) und der Proteingehalt (Trockensubstanz; Organische Substanz, Protein, N‐freie Extraktstoffe und Energie) höher waren. Die Blutharnstoffkonzentration war nicht abhängig vom Genotyp, aber sie erhöhte sich mit der Lebendmasse und dem Proteingehalt. Die Blutkreatininkonzentration und die tägliche Exkretion im Harn lagen höher bei den Doppellendern und den schweren Tieren. Die 3‐Methylhistidinexkretion im Harn war nicht verschieden...

Introduction  Even at a similar energy concentration of the diet, energy source may affect animal performance. O wens et al. (1997) reported that daily dry matter (DM) intake tended to be lowest for wheat‐based diets and highest for milo and oat‐based diets. O’M ara et al. (1997) found a lower pH and less ammonia in the rumen of lactating cows, when unmolassed beet pulp was replaced with ground wheat. Contrary to the results of O’M ara et al. (1997), M alestein et al. (1984) found a greater risk for lactic acidosis for citrus and beet pulp than for maize meal and tapioca. For years it has been known that rapidly degradable carbohydrates may provoke acidosis (H untington and B ritton 1979; F iems et al. 1993). Furthermore, low ruminal pH may inhibit cellulose digestion (M ould et al. 1983) and decrease efficiency of microbial protein synthesis (R ussell et al. 1979). As energy concentration of the diet is important for finishing cattle (B oucqu& eacute; et al. 1980), the amount of roughage is rather limited. This may result in sub‐clinical acidosis with a negative impact on animal performance (O wens et al. 1998), especially when the diet is rich in rapidly fermentable carbohydrates. Therefore an experiment was conducted to investigate the impact of energy source in the finishing diet on voluntary daily feed intake, daily liveweight gain, feed efficiency, blood metabolites and carcass quality. Energy source may also affect meat quality. C asteels et al. (1969) found differences in meat colour when concentrates were based on cereals or sugarbeet pulp. W ood (1984) reported that the concentrate : forage ratio in the diet affects the fatty acid composition of body fat through an increase in propionate production in the rumen. Therefore the effect on meat quality was also studied.

No abstract