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Growth is an integrated process, resulting from the response of cells dependent on the endocrine status and nutrient availability. During feed restriction, the production and secretion of growth hormone (GH) by the pituitary gland are enhanced, but the number of GH receptors decreases. Changes of GH binding proteins induce GH resistance and are followed by reduced insulin-like growth factor-I (IGF-I) secretion. On the other hand, high circulating levels of GH enhance the mobilization of fatty acids, which are used to support energy requirements. Thus, when feed restriction in growing animals is moderate, there is mainly protein but barely fat accretion. By contrast, a severe feed restriction enhances the release of catabolic hormones and stimulates, from muscle cells, the liberation of amino acids, which are used by hepatocytes for gluconeogenesis. During refeeding and compensatory growth, the secretion of insulin is sharply enhanced and plasma GH concentrations remain high. This situation probably allows more nutrients to be used for growth processes. The role of plasma IGF-I during compensatory growth is not clear and must be explained in connection with changes of its binding proteins. Thyroxin and 3,5,3'-triiodothyronine seem to have a permissive effect on growth. The simultaneous occurrence of puberty with refeeding can exert a synergistic effect on growth. Initially, compensatory growth is characterized by the deposition of very lean tissue, similar as during feed restriction. This lasts for some weeks. Then, protein synthesis decreases and high feed intake leads to increased fat deposition.

An experiment was conducted to study effects of dietary vitamin E supplementation on animal performance, slaughter characteristics and meat quality traits in Belgian Blue double-muscled bulls. Two groups of six bulls each were offered (close to ad libitum) a fattening diet based on sugar beet pulp for 154 days, at which time they were slaughtered. The diet given to the control group (CG) contained 12.5 mg vitamin E / kg concentrate. The vitamin E-treated group (VG) received the same concentrate plus a supplement of 1000 mg vitamin E per bull daily. Steaks from m. longissimus thoracis were used to determine meat quality characteristics, alpha tocopherol concentration and thiobarbituric acid reactive substances content (TBARS), an indicator of oxidation rancidity. Supplementation had no influence on animal performance or carcass characteristics. The main findings were that vitamin E doubled the muscle alpha tocopherol level (1.9 vs. 0.9 mg / kg; P , 0.001), lipid oxidation was suppressed as indicated by TBARS values (P , 0.01 at days 7, 9, 11 and 14 after slaughter), but muscle colour was not significantly affected although a* (redness) tended to be higher for VG. © 2000 Elsevier Science B.V. All rights reserved.

The objectives of this study were to evaluate the effect of feed restriction and re-alimentation on the onset of puberty and IGF status in peripubertal male calves and to compare the radioimmunoassay (RIA) and western ligand blotting (WLB) methods for bovine IGFBP-2. Twelve prepubertal 290 d-old Belgian Blue bulls (mean weight: +/- 290 kg) were randomly assigned in three groups: a control group (NG; n = 4) receiving a classic fattening diet to induce "normal" growth (1.48 kg/d), a feed restricted group (RG; n = 4) to obtain reduced growth (0.50 kg/d) and, a severely restricted group (SG; n = 4) to nearly stop growth (0.08 kg/d). The feed restriction period was maintained over a period of 114 d. After the period of differential feeding, all animals received the control feed regime over a period of 100 d. Blood samples were collected at fortnightly intervals. Circulating IGF-I was measured by RIA whereas plasma IGFBPs was evaluated by WLB; IGFBP-2 was additionally quantified by RIA procedure. At the beginning of the trial, IGF-I levels were low (

Fifty double-muscled Belgian Blue bulls were divided into five groups. The first group (control, CG) was given, on an ad libitum basis, a fattening diet based on sugar-beet pulp. In G2 and G3, fattening was interrupted 103 and 187 days, respectively after the beginning of the experiment, by approximately a 2-month period of food restriction during which the animals received a maintenance ration. The last two groups, namely G4 and G5, received for about 4 months a limited amount of the restriction diet to support growth of 0·5 and 0 kg/day, respectively, before being fattened as CG. The average daily gain was 1·48 kg/day in CG v. 1·33, 1·30, 1·43 and 1·61 kg/day during the period of ad libitum feeding in G2, G3, G4 and G5. Higher nitrogen (N) balance during compensatory growth in G2, G4 and G5 (78·8, 81·0 and 74·6 v. 53·3 g N per day in CG, P < 0·001) resulted mainly from a higher efficiency of N retention. In G3, however, compensatory growth was characterized by lower N digestibility and efficiency of N retention. Muscle proportion in the carcass was higher in G3 while fat plus connective tissue proportion was lower (P < 0·05). Muscle pH values in CG were lower than in the other groups (P < 0·01) but ether extract values were higher. The intramuscular fat of G2 and G3 was characterized by higher proportions of polyunsaturated fatty acids.

Nitrogen balance and myofibrillar protein breakdown were studied in 16 double-muscled Belgian Blue bulls during a low growth period (0.5 kg d−1) (LGP) of 4 mo (L4), 8 mo (L8), or 14 mo (L14) and the subsequent fattening period (rapid growth period, RGP). The control group (CG) was given a conventional fattening diet; the others received a low-energy, low-protein diet during LGP, and the same diet as the CG during RGP. Measurements were made halfway through the LGP, l mo after the beginning of the fattening period, and 1 mo before slaughter. Nitrogen balance was about half of CG (P −1, for CG, L4, L8, and L14, respectively. Between LGP and RGP, N balance increased by about 18 g N d−1 above the control in the compensating groups L4, L8 and L14. This was due to the higher digestibility and the higher metabolizability of the nitrogen in the fattening diet. Lower muscle protein accretion during the LGP resulted from decreased synthesis (P

A comparison was made between fattening systems with Belgian Blue bulls of the double-muscle type, in order to assess the reponse in terms of compensatory growth when the bulls were grazed at a high stocking rate. Two groups of eight bulls were grazed on Lolium perenne and Trifolium repens pasture during an initial period of 135 days (period I). One group grazed at a stocking rate of six animals per ha allowing for normal growth at pasture (NGP); the other group grazed at stocking rate of 10 animals per ha (low growth at pasture, LGP). Both groups were then finished indoors (period II) with a concentrate based on dried sugar-beet pulp. Eight control bulls were also fattened indoors on the concentrate diet during periods I and II (CG). The bulls were slaughtered according to similar finishing fattening state. Live-weight gains were 1·47, 1·10 and 0·52 kg/day (P < 0·002) during period I in CG, NGP and LGP groups respectively. Corresponding live-weight gains during period II were 1·22, 1·37 and 1·50 kg/day (P > 0·05). The LGP group had lower food conversion ratios, slaughter weights (P < 0·05) and dressing proportions (P < 0·01). The meat from the grazed bulls had lower cooking losses (P < 0·05) and tended to have lower drip losses (P > 0·05) and higher tenderness (P > 0·05). It also had a higher cholesterol (P < 0·05) content. Large differences were observed in the fatty acid composition according to fat location (subcutaneous, intermuscular or intramuscular). The proportions of mono and polyunsaturated acids were increased in the fats of the animals previously grazed (P > 0·05, P < 0·05).

The aim of the present study was to evaluate the effects of three fibres (sugar-beet fibre, guar gum and inulin) incorporated in the basal diet of healthy dogs at 7 per cent of dry matter (DM). Parameters examined included stool output, water consumption, nutrient digestibility and fasting and postprandial plasma metabolites. All fibres increased wet faecal output; an increase in faecal DM output being observed with sugar-beet fibre only. Sugar-beet fibre and inulin increased daily water consumption. Sugar-beet fibre and guar gum decreased DM digestibility. The three fibres diminished organic matter and crude protein digestibility while ether extract digestibility was decreased by guar gum and inulin. Guar gum induced lower postprandial insulin, alpha-amino-nitrogen and urea plasma concentrations. Guar gum also lowered fasting cholesterolaemia. Sugar-beet fibre and inulin showed no metabolic effects. These physiological properties suggest that guar gum would be a suitable ingredient for dietary therapy of chronic diseases such as diabetes mellitus or hyperlipidaemia in the dog.

Influence of milk in diet of growing fattening Belgian Blue bulls on animal performances and on fatty acid composition in subcutaneous, intermuscular and intramuscular fats. The use of milk as component of a fattening diet for bulls was studied in an experiment carried-out over 2 years with Belgian Blue bulls. The animals weighed 305 kg at the beginning of the experiment. In all, 15 bulls were given a control concentrate fattening diet (control group, CG), while 11 others were fed concentrate plus 6.5 to 11 1 whole milk per day according to weight or age (milk group, MG). The fattening period lasted for 174 and 181 d respectively in groups CG and MG. The MG-group had a higher killing-out percentage (P < 0.01) and the meat was characterized by a lower b∗ value and a lower dry matter content (P < 0.1). Whole milk in the diet increased the proportion of shorter chain and saturated fatty acids in fat (P < 0.001) and reduced the proportion of mono- and polyunsaturated acids (P < 0.05; P < 0.1). The extent of the changes were larger in subcutaneous and intermuscular fats than in intramuscular fat.

Une serie de deux essais concernant deux modes de distribution de la paille dans une ration d'engraissement a base de concentre destinee a des taurillons est presentee. Le premier essai concerne l'aspect metabolique et le second se rapporte aux performances zootechniques. L'aspect metabolique a ete etudie sur huit taurillons Blanc Bleu Belge du type mixte repartis en deux groupes de quatre, munis d'une canule du rumen et maintenus sur des stalles a metabolisme pendant une periode de 112 j divisee en deux. Durant la premiere periode, le premier groupe recevait separement le concentre d'engraissement compose de pulpes de betteraves sechees (40,8 %), cereales (37 %), tourteaux (18 %), melasse (3 %), et un melange mineral (1,2 %) a l'auge et la paille dans un râtelier. Le second groupe de taurillons recevait le meme concentre d'engraissement dans lequel etait incorpore grâce a une melangeuse distributrice de la paille hachee a raison de 9 % pour 91 % de concentre. Durant la seconde periode, les deux rations ont ete inversees. Dans l'essai zootechnique, les memes regimes ont ete distribues dans des conditions identiques du debut jusqu'a la fin d'engraissement a deux groupes de six taurillons âges de ± 10 mois et maintenus en loges semi-paillees. La duree d'engraissement a ete de 153 et de 144j respectivement pour les animaux du premier et du second groupe. La digestibilite apparente a ete systematiquement plus elevee lorsque la paille a ete incorporee au concentre. La degradabilite dans le rumen, determinee par la technique des sachets de nylon, a ete plus importante avec la paille hachee en melange pour des aliments contenant de l'amidon (p < 0,001) et des fibres a fermentation lente (p < 0,05). Le pH du rumen a ete systematiquement plus eleve chez les taurillons qui avaient recu la paille hachee en melange indiquant un effet tampon important lie au mode de distribution de la paille. La longueur des papilles dans le rumen ainsi que l'epaisseur des couches de cellules keratinisees ont ete plus elevees avec la paille hachee en melange. Les quantites ingerees ont ete un peu plus elevees pour les taurillons qui recevaient la paille separement tant dans l'essai metabolique que dans l'essai zootechnique. L'indice de consommation a ete plus faible (7,0 vs 7,4 kg/kilo) alors que le gain quotidien moyen (1,5 vs 1,4 kg/jour) et le poids de carcasses (402,7 vs 371,0 kg) ont ete plus eleves avec la paille hachee en melange. Une tendance vers des valeurs plus elevees pour le rendement d'abattage (65,8 vs 62,6 %) et la proportion des muscles (83,7 vs 78,3 %) a ete observee chez les taurillons nourris avec la paille hachee en melange.

The effect of growth rate and protein supplementation on muscle metabolism of eight bulls from the Belgian Blue breed, double-muscled type, was investigated by the arterio-venous difference technique. A low growth (LG) group was maintained at a low growth rate over 36 d, and a rapid growth (RG) group for 28 d before receiving a fattening diet allowing for a rapid growth. At the end of the RG period the RG bulls received a supplement of protected soybean meal. Animals were fitted with an aortic ultrasonic blood flow probe and with catheters in the aorta and the vena cava. The blood flow in the hindlimbs of bulls varied greatly by time of the day but was higher in the RG group. The RG group had a higher arterio-venous difference (AVD) and uptake of alpha-amino nitrogen while AVD in essential amino acids was four times higher and uptake eight times higher. Significant higher AVD or uptake was observed in individual amino acids such as leucine, isoleucine and lysine. The supplementation with protected soybean meal had significant negative effect on the uptake of several amino acids. It was concluded that caution should be exercised when measuring punctually blood flow in muscle tissue, for example by dilution techniques. At high growth rate, the requirements for amino acids are larger than for glucose. Excess protein provides no additional benefit. Key words: Bull, hindlimb catheterism, growth rate, protected soy bean, metabolite

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.

A comparison was made between two different finishing systems with Belgian Blue bulls. Two groups of bulls were grazed during an initial 140-day period and then finished indoors with concentrates. There were two stocking rates during the grazing period: a medium at six bulls per ha (MGFI) and a high at eight bulls per ha (HGFI). A third group of bulls was finished indoors on a concentrate diet during the whole finishing period (FI). The experiment was repeated over 2 years consecutively. The pasture which was grazed at the medium stocking rate was characterized by a higher sward height (P < 0·01), more refusals (P < 0·001), less Lolium perenne (P < 0·05) and more Trifolium repens (PP < 0·001) and improved the gain indoors (1·24 v. 1·01 kg/day, P < 0·001). In the groups which were initially grazed when compared with the indoor system, the fattening period was longer (236·0 and 241·0 v. 186·9 days, Pv. 1·44 kg/day, P < 0·001 for MGFI, HGFI and Fl respectively). The dressing proportion was greater also (P < 0·05), and there were higher concentrations of muscles (P < 0·05) and bones (P < 0·05) in the carcass of the bulls which were grazed initially. With these bulls, the lean meat was darker (P

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.

Two groups of six bulls were offered a fattening diet based on barley or sugar-beet pulp in the proportions of either 500: 200 g/kg or 200: 500 g/kg to compare the effects of starch and degradable fibre on rumen fermentations, plasma hormones and metabolites. The bulls were fed twice daily at 08.00 and 16.00 h.The large proportion of sugar-beet pulp in the diet induced higher levels of acetic and butyric acids and less propionic acid than the high proportion of barley. The diurnal patterns over a 24-h period of rumen pH, volatile fatty acids, glucose and ammonia were characterized by two cycles. Sugar-beet pulp in large proportions induced more even fermentations as indicated by flatter curves with less extreme values than those produced by a large inclusion of barley in the diet. Ammonia concentration was high before feeding and decreased subsequently during 4 to 6 h after the meal.No typical patterns were observed in plasma concentrations of glucose and alpha-amino nitrogen. Plasma urea concentration rose 2h after feeding and dropped during the following 6 to 8 h. There were no effects of dietary carbohydrate composition on growth hormone concentration but plasma insulin was significantly reduced with the diet high in sugar-beet pulp. Furthermore, the insulin profile showed peaks after each meal with the barley diet but only after the afternoon feeding with the diet high in sugar-beet pulp.

Insulin-like growth factor-I and -II (IGF-I, IGF-II) circulate in biological fluids bound to six different IGF-binding proteins that regulate IGF bioactivity. The IGF-binding protein-2 is regulated by growth hormones, and its concentration depends on nutrition and physiological state. Specific antibodies directed against bovine IGF-binding protein-2 were produced, and IGF-binding protein-2 levels in bovine blood samples were quantified by radioimmunoassay. Parallel displacement curves showed strong cross-reactivity with bovine and ovine plasma, were low with porcine plasma, and no cross-reactivity with rat or chicken plasma. Addition of IGF-I or -II to a control pool of bovine plasma did not significantly alter control IGF-binding protein-2 values in a radioimmunoassay. Six nycthemeral periods, determined for three young bulls bled on two occasions, showed that IGF-binding protein-2 plasma levels were stable throughout the day; two or three samples were sufficient to characterize the animal. Cows treated with recombinant bovine somatotropin (bST) had significantly lower serum levels of IGF-binding protein-2 than did control cows. Furthermore, IGF-binding protein-2 levels were dramatically increased at the onset of lactation. This radioimmunoassay for bovine IGF-binding protein-2, which enables quantitative assessment of IGF-binding protein-2 concentration in cattle, confirmed that IGF-binding protein-2 concentrations are depressed by administration of bST, enhanced after calving, and showed absence of diurnal variation.

Plasma metabolites and hormones were studied in 16 double-muscled Belgian Blue bulls maintained at low growth (.5 kg/d) for 114 (G2), 243 (G3), or 419 (G4) d (low growth period, LGP) before fattening (rapid growth period, RGP). Animals from the control group (CG) were fed a diet high in energy and protein. The animals from G2, G3, and G4 were fed a restricted amount of a diet low in energy and protein during LGP and the same diet as CG during RGP. Plasma glucose, alpha-amino nitrogen (AAN), NEFA, urea, creatinine, thyroxine (T4), 3,3',5'-triiodothyronine (T3), and IGF-I were measured in blood samples taken fortnightly. Plasma GH and insulin (I) profiles were measured in serial blood samples obtained at three times during growth. The RGP was characterized by an initial compensatory growth, by higher plasma glucose, AAN, and urea levels, and by lower plasma NEFA and creatinine levels. Plasma GH concentration decreased after refeeding. Plasma T4 increased linearly during refeeding, as opposed to T3, which showed a different profile in each group. Plasma IGF-I showed a curvilinear increase during RGP and reached a plateau after 3 mo in each compensating group. In G4, changes of plasma metabolites and hormones differed often distinctly from G2 or G3. During refeeding, higher nutrient supply improved the functionality of the somatotropic axis and increased the concentration of anabolic hormones, allowing rapid muscle deposition. However, animals underfed the longest period behaved differently from the other groups, possibly because they reached a more complete sexual maturity.

Thirty double-muscled Belgian Blue bulls were maintained at a rate of gain of .5 kg/d during four periods of time, 115 (G2), 239 (G3), or 411 (G4) d (low growth period, LGP), before fattening (rapid growth period, RGP). Ten control animals (CG) were fed a diet rich in energy and protein. The G2, G3, and G4 were fed a diet low in energy and protein and the same diet as CG during RGP. Live weight was recorded biweekly, feed intake (FI) daily, and nitrogen balance at three times for each group. At the slaughterhouse, the 7, 8, and 9th ribs were removed to determine carcass composition, meat quality, and meat and fat composition. Compensatory growth reached a maximum 2 mo after refeeding and then decreased rapidly, leading to a sharp increase in the feed conversion ratio. Nitrogen balance was higher in compensating groups ( P < .05). Compensating animals had higher carcass connective and adipose tissue contents (P < .05) but lower meat fat content (P < .05). Cattle exhibiting compensatory growth had higher redness, yellowness, cooking losses, and drip losses, but had lower Warner-Bratzler peak shear force values. The saturated fatty acid content of the fat decreased with the duration of the LGP. During the first 2 mo after refeeding, compensatory growth in double-muscled bulls was ascribed to one or more of the following mechanisms: higher FI, lower maintenance requirements, or better efficiency of lean meat production. Compensatory growth at the expense of higher FI increased peripheral fat but decreased intramuscular fat deposition.

Metabolism of muscle growth in the hindquarter was investigated by the arterio-venous difference (AVD) technique in Belgian Blue double-muscled type bulls at maintenance or at fattening. The bulls were fitted with an aortic ultrasonic blood flow probe and with catheters in the aorta and vena cava. They were offered a diet allowing for maintenance (MP) during a period of 15 d, at the end of which measurements were made over 3 d. Bulls were then given a fattening diet (FP) and the measurements were repeated. Arterial blood flow was approximately 1 L/min greater when the bulls were standing than when lying. Blood flow was 2 L/min higher during FP than during MP. The AVD and uptake of glucose were maximal at 1400 and 1600. Uptake of alpha-amino nitrogen decreased immediately after a meal. The increase in glucose from MP to FP fitted very well with the calculated energy needs for muscle growth. The AVD and uptake of alpha-amino nitrogen, total amino acids, and total nonessential amino acids were negative during MP and positive and significantly higher during FP. There was also a significant increase in AVD and uptake of essential and branched-chain amino acids when the bulls were changed from MP to FP. When changing from maintenance to fattening, the incremental glucose and amino acid hindquarter uptake provided energy and supply for muscle protein accretion, respectively. The level of alanine transamination was also sharply reduced.

We investigated continuous profiles and within-day variations of some metabolites and hormones in four nonpregnant, nonlactating cows fed hay-based diets in two equal meals. Diets supplied either too much or too little N (approximately 1.3 or .8 times the maintenance requirements) and NE1 (approximately 1.2 or .8 times). Continuous collection of ruminal liquor, blood, and urine samples was performed for 42 consecutive hours, the last 16 h covering a period without feed. For twice-daily feeding, nitrogenous and energetic underfeeding decreased average ruminal propionate and the insulin:growth hormone ratio. However, only the energetic underfeeding increased plasma 3-methylhistidine and urinary excretion of 3-methylhistidine, and decreased body weight and ruminal acetate, butyrate, and total VFA. Conversely, only the nitrogenous underfeeding decreased glycemia. Whatever the dietary level, the 42-h patterns of metabolites and hormones were mainly affected by the time from the last meal. An energy deficit progressively took place during feed deprivation and the nocturnal interprandial period but not during the diurnal interprandial period. During the feed deprivation and nocturnal periods, glycemia was maintained despite a shortage in ruminal propionate. We conclude that in twice-daily fed cattle 1) the dietary supply of energy is the main trigger for an energy deficit and the subsequent muscle protein mobilization; 2) the nocturnal interprandial period may be considered as short-term feed deprivation; 3) the diurnal patterns of metabolites and hormones are not affected by the nitrogenous and(or) energetic supplies of the diet.

Lorsqu’on les compare à des sujets mixtes de la même race, les taurillons Blanc Bleu Belge (BBB) culards réalisent des gains quotidiens moyens au moins aussi élevés tout en consommant moins d’aliments. L’amélioration de l’efficacité alimentaire est expliquée principalement par la composition des gains de poids : la carcasse d’un sujet BBB culard contient au moins 60 kg de muscle en plus et 30 kg de graisse en moins que celle d’un sujet mixte abattu au même poids vif. Lorsque le poids vif augmente, on observe, dans les deux types, une augmentation du rendement à l’abattage et de la proportion de viande maigre dans la carcasse. La composition chimique et les qualités organoleptiques des viandes sont, elles aussi, influencées par le caractère culard. La teneur en gras est réduite et la proportion d’acides gras polyinsaturés est augmentée chez le culard, ce qui constitue un avantage nutritionnel. L’évolution plus rapide du pH post mortem chez le taurillon culard ne peut expliquer que très partiellement les différences observées pour les qualités sensorielles. La couleur plus pâle de la viande est liée en grande partie à sa faible teneur en myoglobine. L’avantage du culard en matière de tendreté, expliqué par une teneur faible en collagène, n’apparaît pas dans un morceau noble de la carcasse à faible teneur en collagène. Enfin, dans la majorité des études disponibles à ce jour, la capacité de rétention d’eau de la viande produite par les culards apparaît peu différente de celle des non culards. Les concentrations de plusieurs métabolites sanguins indiquent une répartition des nutriments favorable au dépôt de protéines et défavorable au dépôt de graisses chez le culard. Lors de l’engraissement, les particularités endocriniennes concernent essentiellement l’hormone de croissance et l’insuline ; elles peuvent expliquer la répartition particulière des nutriments., When compared to animals of the dual purpose type in the same breed, Belgian Blue double muscled bulls exhibit, at least, similar average daily gain with lower feed intake. The higher feed efficiency in the double muscled type is mainly explained by the composition of the weight gains, the muscle content is minimum 60 kg higher and the fat content 30 kg lower than in the dual pur pose type when slaughtered at a similar live weight. In both types, the dressing percentage and the lean meat proportion in the carcass increase with final liveweight. The chemical composition and the sensory characteristics of meat are also influenced by double muscling. The fat content is reduced and the polyunsaturated fatty acids proportion is increased in the double muscled type, resulting in a nutritional advantage. The difference in sensory characteristics could be, only partially explained by the fas ter post mortem pH drop. The paler meat is mainly related to the myoglobin content. The advantage of the double muscled type in terms of tenderness, due to a low collagen content, is not exhibited in a << choice >> cut of the carcass with a low level of collagen, Finally, according to most of the available data, the water holding capacity of meat of double muscled animals seems not very different. The concentrations of several blood metabolites indicate a partition of the absorbed nutrients propitious to protein deposition and unpropitious to fat deposition in double muscled animals. During the fattening period, this specific partition can be related to endocrine characteristics, mainly growth hormone and insulin.

The purpose of this study was to characterize circulating growth hormone-binding proteins (GHBP) and prolactin-binding proteins (PRLBP) in cattle blood plasma. In particular, the 24-hr profile of these molecules was investigated. The preincubation of bull plasma with iodinated bovine growth hormone (bGH) or bovine prolactin (bPRL), followed by gel filtration chromatography (Superdex 200; 1.6 x 60 cm column), resulted in the formation of essentially two complexes. The majority of [125I]bPRL eluted with the first one (M(r) approximately 600 kDa), whereas [125I]bGH mainly appeared in the second one (M(r) approximately 70 kDa). The fractions corresponding to these two peaks were analyzed by western ligand blotting (WLB), under reducing conditions. WLB revealed, respectively, 190-, 56-, 52-, and 28-kDa bands for the first peak and only 52- and 28-kDa bands for the second one. The nature of the 600-kDa peak is at present undetermined, but the 70-kDa one was previously identified as high-affinity GHBP. Displacement studies demonstrated that bGH and bPRL were both able to bind to this GHBP, because the bGH- and bPRL-binding activities of this protein could be saturated by an excess of either of these two hormones. This was indirectly confirmed by the close correlation (r = 0.615; P = 0.0001; n = 155) observed between plasma bGH- and bPRL-binding activities, because this correlation could suggest that both ligands are bound to the same proteins. The temporal concentrations of plasma GHBP were measured in samples collected at 20-min intervals for 24 hr from 8 young bulls. The evaluation of GHBP was realized by WLB, followed by densitometric analysis. Some fluctuations were observed, but these were not correlated with bGH release, even with a +/- 2-hr lag period. In summary, we found that bovine high-affinity GHBP binds not only bGH, but also bPRL. A second type of protein, of higher molecular weight, also binds these two hormones, but further investigations are needed to determine its nature. Finally, GHBP concentrations in cattle blood plasma apparently show fluctuations over a 24-hr period, but no correlation was found between these fluctuations and plasma growth hormone concentrations.

An experiment was conducted to determine the effects of a single low-dose administration of adrenocorticotrophic hormone (ACTH) on milk yield, plasma cortisol, free amino acids, urea and glucose in lactating cows. The animals were treated with either 6 IU synthetic ACTH or 5 ml physiological saline (control) administered intravenously via a jugular vein catheter. Blood was withdrawn 60 and 5 min pretreatment (baseline), and 10, 20, 30, 60, 120, 180, 240, 300, 360, and 420 min post-treatment. A rapid positive response (P0.05) in plasma cortisol occurred within 10 min of administration of 6 IU ACTH. The maximum increase in plasma cortisol concentration occurred at 1 h post-ACTH treatment and plasma cortisol returned to baseline 4 h later. Until 7 d after ACTH administration, no effect on milk yield was recorded. In comparison with the saline-treated group, the ACTH-treated group exhibited a significant (P0.05) increase in the plasma concentrations of 3-methylhistidine, glycine, histidine, isoleucine, leucine, lysine, valine, and glucose. In contrast, the concentrations of alanine, aspartate, glutamate, glutamine and proline decreased significantly (P0.05) after ACTH treatment. Hormone administration had no effect on the plasma arginine, asparagine, methionine, phenylalanine, serine, threonine, tyrosine, and urea. These results demonstrate that the bovine species behaves like other mammalians with respect to its metabolic response to stress. Thus, during stress, ACTH increases adrenal cortical activity which, in turn, stimulates protein catabolism in muscle and gluconeogenesis from some non-essential amino acids.

Six Belgian Blue bulls (double-muscled type) and six Friesian bulls were offered a fattening diet for 34 weeks. Plasma samples were obtained once a week and also every 20 min over a 24 h period, 7 weeks before slaughter. No differences were observed between the breeds in plasma glucose, urea and free amino nitrogen concentrations, while creatinine was significantly higher in the Belgian Blue bulls. Tri-iodothyronin, tetra-iodothyronin, insulin-like growth factor 1, insulin and testosterone concentrations were higher in the Holstein group. In contrast, the Belgian Blue bulls appeared to produce more growth hormone. The slaughter weight, carcass weight, dressing percentage and proportion of lean meat were significantly higher in the Belgian Blue group. The characteristics of muscle mass (carcass weight, dressing percentage and proportion of lean meat) were positively correlated with creatinine and with the total peak area or peak amplitude of growth hormone. The insulin concentration was positively correlated with the proportion of adipose tissue in the carcass and negatively correlated with the proportion of muscle. There were no correlations between the carcass characteristics and insulin-like growth factor 1 or testosterone. No further information was provided when the ratios of the hormones were correlated with carcass characteristics.

Nitrogen balance was studied in 5 bulls fed a concentrated diet containing 0 or 4 ppm cimaterol. Cimaterol increased nitrogen retention, mainly by reducing urinary nitrogen excretion due to decreased body protein degradation. There was a tendency for reduced nitrogen utilization efficiency when treatment was prolonged.

By contrast to bulls, fattening cull cows deposite large amounts of fat in the carcass. Furthermore, the live weight gain are low. Methionine (M) is a limiting amino acid for muscle growth in Belgian blue cattle (Hornick et al., 1997). Supplementation with M in fattening diets for cattle could therefore improve weight gain or feed conversion ratio. An experiment was thus conducted in Belgian Blue cull cows in order to assess the effects of M in fattening diet on characteristics of tissue deposition.Twenty four Belgian Blue females from double muscled type -8 heifers (H), 8 cows with 2 calving (C2) and 8 cows with 4 calving (C4)- were used. In each group, 4 animals received a control fattening diet (M0) based on maize silage complemented with cereals, sugar beet pulp and protein from vegetable origin (10.3 MJ ME and 160 g/ kg CP per kg DM), while 4 other received similar diet but with 3.5 g of rumen protected methionine (M1).

As far as consumers are concerned, the major quality characteristics of beef meat are an attracting color and tenderness (Smulders et al., 1991). The chemical composition - protein, fat and fatty acids contents mainly - is of importance for the dietitian. These parameters are influenced to a large extent by the management - diet and environment - of the fattening animals. The aim of the present paper is to relate some parameters of meat quality and meat composition with animal performance in growing fattening bulls.

Hay is an usual component of horse diet. Nevertheless, it is suspected to provide some spores causing chronic obstructive pulmonary disease. Grass silage has been suggested as forage in the diet to overcome the problem. It was therefore of interest to assess the nutritive value of grass silage in horses.Three silages with different dry matter (DM) content were compared. Since horses dislike grass silage with a low DM content, wilted silages only were compared. The first two were first cut grass silages with a low DM content at 427.3 g/kg (LGS) or a medium DM content (661.7 g/kg - MGS). They were compared with a second cut silage from grass grown under very dry conditions (HGS - 787.5 g/kg). The grass was ensiled in square big bales. The 3 silages were offered alone and ad libitum to 4 sport horses in 3 consecutive periods,each silage being offered during one period.

In Belgium, beef meat is traditionally produced with growing fattening bulls kept indoors and fed concentrate. Alternatives exist to this technic. Dufirasne et al. (1995) showed that young bulls may spend one season on pasture before a finishing period indoors. It has been reported recently that the finishing of young Belgian Blue bulls at grass did not provide carcasses with the required qualities (Hornick at al., 1995). The supplementation at grass has been suggested as an alternative. The aim of the present experiment was to study the effects of supplementation of bulls finished at grass on animal performance, carcass and meat characteristics.

Belgian Blue bulls fattened at grass are not slaughtered directely out of pasture. They are always finished in a stanchion barn with concentrate diets, in order to provide a meat which corresponds to the market demand. So, no data are available on the influence of grass on meat and fat characteristics of bulls from the Belgian Blue breed. The objective of this experiment was to compare meat quality and fat composition of bulls which carried out a complete fattening period either on pasture or indoors.

Aside from its function of contraction, the muscle is also a pool of mobilisable protein which may be released or stored according to the needs of the animal. An approach of this aspect can be theorically studied by measure of arterio-venous differences of plasma metabolites from blood in the muscle mass. The aim of this experiment was to study uptake of α amino-nitrogen, glucose and urea across the hind-limb of bulls from a breed with large muscle development.Three bulls from the Belgian Blue breed-double muscled type-were used. They weighed about 300 kg when an ultrasonic flow probe (Transonic Systems, Inc.,Ithaca, NY) was implanted around the abdominal aorta, back to the renal vessels, in order to measure the blood flow in the hind-leg (Eisemann et al., 1987). After an one month recovery period, circumflex iliac artery and vein were implanted with catheters. During the periods of surgery, the bulls were offered hay only at a rate of three kg daily. Ten days after the second surgery, increasing amounts of concentrate were given with the hay so that the animals received one kg concentrate on day 1 (level 1), three kg concentrate on day 3 (level 3), five kg concentrate on day 5 (level 5).

Fat supplementation is commonly used in feedstufs for high yielding cows or ewes. The diet for growing-fattening bulls in Belgium are usually high in concentrate. The fat content.of such diets .is low at .about 2.51. Over the recent years, feed manufacturers have incorporated fat in diets for growing-fattening animals (Clmquart, Istasse, Dufrasne, Mayombo, Van Eenaeme, Bienfait, 1991). In most of the reported works the fat supplemented diets were offered during the whole fattening period according to Brandt, Anderson and Elliot (1988) and Zinn (1989), differences in performance could be expected when the fat supplement is offered only during the finishing period. An experimental was designed to compare the effects of fat supplementation during the last part of the fattening period on the performance and meat characteristics of fattening bulls.

Beef meat in Belgium is mainly produced from growing fattening bulls. In the usual technique, the average daily gain is about 1.0 kg/day during the growing period while it is about 1.4 to 1.5 kg/d during the fattening period (Clinquart et al., 1991). The aim of the present trial was to study another growth curve characterized by a low growth rate during the growing period and to assess the effects in terms of coipensatory growth during the fattening period.

The degree to which growth patterns are modified after a period of food restriction affects the compositional changes of the carcasses(Carstens et al., 1992), furthermore, the growth rate has a direct effect on the physical properties of meat (Fishell et al., 1985). The objective of this experiment was to evaluate the effects of a severe food restriction at a early stage of maturity on the slaughter characteristics and meat quality of Belgian Blue bulls.Twelve Belgian Blue bulls (dual purpose type) weighing 233 kg were offered two different planes of nutrition during the growing period. Six bulls (Group-) received a restricted diet so that their average daily gain was 0.34 kg/d (Group+) during 202 days. By contrast six other bulls were given a more conventional growing diet and their average daily gain was 1.13 kg/d. Both Groups were fattened with similar diet and slaughtered when the live weight was close to 600 kg. Carcass weight was measured and killing-out proportion calculated, the composition of the carcass was estimated after dissection of ribs 7, 8, 9 removed 48 h post-mortem.

The Holstein and Belgian Blue double muscle type (BBDM) are two cattle breeds extremely different in extent of muscle proportion (Istasse, Van Eenaeme, Evrard, Gabriel, Baldwin, Maghuin-Rogister and Bienfait, 1990). In BBDM, the proportions of lean meat and fat are high and low respectively. Opposite trends are found in Holstein, the Belgian Blue dual purpose type (BBDP) being intermediate. This experiment was carried out to compare lipid metabolism in these 3 breeds.Four bulls of these 3 breeds were used in a fattening trial. The initial weight was 340 kg. They were given a sugar beet pulp based diet supplemented with cereals, by-products and protein sources or vegetable origin. After a 145 days fattening period the final weight was 540 kg. Non esterified fatty acid (NEFA), triglycerides (TG) and cholesterol concentrations in the plasma were measured every 4 weeks during the fattening period. The plasma fatty acid composition was determined by gas chromatography. The 7, 8 and 9 ribs were removed at slaughter and cholesterol concentrations were measured in Longissimus Dorsi samples.

The incidence of human coronary heart disease has been correlated with the serum cholesterol level and a high consumption of saturated fat. Furthermore the cholesterol level can be raised by shorter chain fatty acids (Rose, 1990). It was therefore interesting to compare breeds extreme in terms of fatness. The adipose tissue proportion of the Belgian Blue double muscled type (BBDM) is low while that in Holstein is high, the Belgian Blue dual purpose (BBDP) type being intermediate. The present experiment was designed to investigate how large difference in degree of fatness can be associated with differences in fatty acid composition.Four bulls of the 3 breeds were used in a fattening trial. Their initial weight was 340 kg. Biopsy samples were taken from the Longitimus Dorsi (LD) at weeks 5 and 16 of the fattening period. They were slaughtered after 145 days. The 7-8-9 ribs and perirenal fat (PR) were removed at slaughter. Intramuscular (M) and intermuscular (IM) fats of the LD were obtained after dissection of the 7-8-9 ribs.

Soya oil at an inclusion rate of 33 g/kg in a concentrate diet for growing-fattening bulls tended to increase the production of volatile fatty acids and the dry matter disappearance from nylon bags incubated in the rumen. It also slightly improved apparent digestibility of dry matter, organic matter and fiber and significantly increased the ether extract digestibility (Clinquart, Van Eenaeme, Istasse, Neirinck, Midy and Bienfait, 1991). It was therefore interesting to assess the effects of soya oil supplementation on animal performance. The linoleic acid content of soya oil is about 0.50. Such fat could be used to increase the unsaturated fatty acid proportion in order to produce a more dietetic fat.

The diets for growing-fattening bulls in Belgium are usually high in concentrate (Van Eenaeme, Istasse, Gabriel, Clinquart, Maghuin Register and Bienfait, 1990). The fat content of such diets in usually low at about 0.025. Over the recent years, feed manufacturers have incorporated fat in fattening diets. The incorporation rates are usually rather low so that the ether extract content is about 0.05 in fat supplemented regimes. At such rates upsets of intake and digestion and depression of growth could be avoided (Zinn, 1989). The fat concentrates which are incorporated are usually blends of various and very often unknown origins. Conflicting observations were reported on the effects of fat supplementation. Two experiments were carried out to assess the effects of soya oil on metabolism in the rumen and on apparent digestibility.

Growing fattening bulls in Belgium require diets high in concentrate and low in roughages in order to achieve large live weight gains and high quality carcasses. Sugar beet pulp is usually incorporated at a high inclusion rate in fattening diets. It is supplemented with cereals, by-products like wheat bran or glutenfeed and protein supplements very often of vegetable origin. The fat content of such diet is low. Over the recent years, there has been an increasing pressure from the industry to incorporate fat in fattening diets. Each company produces its own fat concentrate. They are blends of various origins. The present experiments were carried out to assess the effects, on animal performances, of soya oil and linseed, two fat concentrates of vegetable origin incorporated in fattening diets.