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A 4-year experiment has been conducted on finishing Belgian Blue cull cows of double-muscled type in order to study the effects of diets containing adequate levels of metabolizable protein, but either normal (NENP), low (LENP) or medium (MENP) levels of metabolizable energy, on animal performance, carcass and meat characteristics, and plasma metabolites and hormones. The LENP diet was offered during the whole (LENP group) or second half of the finishing (NENP-LENP groups), and the MENP diet during the whole finishing (MENP group). The degree of fatness required for the slaughter of animals from NENP groups was close to 4-5 (scale from 0 (very lean) to 5 (very fat)). In each underfed group, the slaughter of the animals was synchronized to that of NENP cows, by degressive degree of fatness. The same duration of finishing was thus obtained for all groups.The experimental feeding strategies reduced the amounts of fat deposited in the carcass and the meat while muscle deposition was remarkably preserved. The proportions of saturated and monounsaturated fatty acids in intramuscular fat were also decreased while their proportions increased in plasma free fatty acids. Plasma insulin levels were also reduced and those ofIGF-1 were, surprisingly, maintained. The low energy diet promoted thus the settlement of a discrete lipolytic state while high levels ofIGF-1 preserved muscle deposition. This feeding strategy should be evaluated in other breeds of cattle.

The aim of this experiment was to determine the extent of variation in the eating quality of beef from light or heavy steers and young bulls from extreme dairy or beef cross dairy breeds of cattle. High genetic merit New Zealand Holstein–Friesian dairy progeny (NZ), high genetic merit European/North American Holstein–Friesian dairy progeny (EU) and Belgian Blue beef cross Holstein–Friesian progeny (BB) (32 per genotype) were reared from birth to slaughter as light (620 kg) steers, heavy (720 kg) steers, light young bulls or heavy young bulls. Quality assessments of M. longissimus dorsi were: pH, Warner Bratzler shear force (WBSF), sensory attributes, cooking loss and chemical composition. Variances were compared using Bartlett's test. Bulls were more variable than steers for ultimate pH, WBSF after 2 and 7 days postmortem, flavour after 14 days postmortem and cooking loss after 2, 7 and 14 days postmortem. Within genotype, the BB breed was less variable for moisture and intramuscular fat concentration than the dairy breeds, but the variance for eating quality characteristics was similar for the three breeds. Within weights, the heavy animals were more variable for ultimate pH and cooking loss after 2 and 7 days postmortem. Within each factor, more than 81% of samples were considered acceptably tender after 14 days ageing postmortem. Further work should focus on reducing this residual variation.

The objective of this study was to investigate a potential association of an inactive myostatin allele with early calf mortality, and evaluate its effect on growth and carcass traits in a crossbred population. Animals were obtained by mating F1 cows to F1 (Belgian Blue x British Breed) or Charolais sires. Cows were obtained from mating Hereford, Angus, and MARC III (1/4 Hereford, 1/4 Angus, 1/4 Pinzgauer, and 1/4 Red Poll) dams to Hereford, Angus, Tuli, Boran, Brahman, or Belgian Blue sires. Belgian Blue was the source of the inactive myostatin allele. Myostatin genotypes were determined for all animals including those that died before weaning. Early calf mortality was examined in the F2 subpopulation (n = 154), derived from the F1 sires mated to F1 cows from Belgian Blue sires, to evaluate animals with zero, one, or two copies of inactive myostatin allele. An overall 1:2:1 ratio (homozygous active myostatin allele:heterozygous:homozygous inactive myostatin allele) was observed in the population; however, a comparison between calves dying before weaning and those alive at slaughter showed an unequal distribution across genotypes (P < 0.01). Calves with two copies of the inactive allele were more likely (P < 0.01) to die before weaning. Postweaning growth traits were evaluated in the surviving animals (n = 1,370), including birth, weaning, and live weight at slaughter, and postweaning ADG. Carcass composition traits analyzed were hot carcass weight, fat thickness, LM area, marbling score, USDA yield grade, estimated kidney, pelvic, and heart fat, retail product yield and weight, fat yield and weight, bone yield and weight, and percentage of carcasses classified as Choice. Charolais lack the inactive myostatin allele segregating in Belgian Blue; thus, in the population sired by Charolais (n = 645), only animals with zero or one copy of the inactive myostatin allele were evaluated. Animals carrying one copy were heavier at birth and at weaning, and their carcasses were leaner and more muscled. In the population sired by Belgian Blue x British Breed (n = 725), animals with two copies of inactive myostatin allele were heavier at birth, leaner, and had a higher proportion of muscle mass than animals with zero or one copies. Heterozygous animals were heaviest at weaning and had the highest live weight, whereas animals with zero copies had the highest fat content. The use of the inactive myostatin allele is an option to increase retail product yield, but considerations of conditions at calving are important to prevent mortality.

The objectives of this study were (a) to compare muscle and adipose tissue colour of male progeny of two strains of high genetic merit Friesian cows (New Zealand [NZF] and Irish [DAF]) with those of beef (Belgian Blue)×dairy (Holstein-Friesian) [BBHF] male progeny; (b) to compare bulls and steers (gender) of these genotypes and (c) to examine the effects of slaughter weight (SW) on these quality traits. Bulls (n=48) and steers (n=48) of the three genotypes were grown to nominal target liveweights of 550 kg (light) and 630 kg (heavy). Adipose tissue from the NZF genotype was more yellow (P0.05) than from DAF or BBHF, regardless of gender or SW. For longissimus dorsi (LD) pH, bulls and heavy animals had higher pH (P0.05) than steers or light animals, respectively, while NZF and BBHF bulls had higher pH than steers. LD muscle from the BBHF genotype had lighter colour (P0.05) and lower haem pigments (P0.01) than NZF or DAF progeny. There was no difference in muscle `L' value between light bulls and steers but heavy bulls had darker muscle than heavy steers. There was an interaction between genotype, gender and SW for LD redness. Thus, NZF animals were most red when slaughtered as light or heavy bulls, but there were no differences between genotypes slaughtered as light or heavy steers. These data demonstrate differences in colour of beef, especially from progeny of NZF, which produced the most yellow adipose tissue and the most red muscle tissue.

The volatile compounds of cooked meats from differently fed Belgian Blue, Limousin and Aberdeen Angus bulls were isolated in a model mouth apparatus. Their odour activity was determined by gas chromatography-olfactometry based on a detection frequency method. A total of thirty compounds possessed an odour activity in cooked beef meat. Significant influences of breed and diet on the development of the odour-active compounds of cooked beef meat were observed. The meat of Belgian Blue seemed to generate more odour-active compounds and to be more influenced by the feeding diet than the other breeds. This could be the consequence, at least in part, of its double-muscle condition. However, no obvious justifications could be given to explain the influence of the diet. Different chemical compositions are factors of importance for explaining the different aroma profiles between breeds, but some other parameters should also play an important role.

A factorial experiment was conducted to investigate the effect of dietary protein level on animal performance, and carcass and meat quality. Eighty-four culled double-muscled Belgian Blue cows, with an initial age and live weight (LW) of 1791 ± 660 days and 659 ± 96 kg, respectively, were used. Maize silage was fed ad libitum and supplemented with concentrate, fed at 10 g/kg of LW. Concentrates were formulated to contain a low or a high DVE-level (110 and 140 g true protein digested in the small intestine/kg dry matter (DM)) and a low or a high OEB-level (-30 and +30 g degraded protein balance in the rumen/kg DM), resulting in average dietary concentrations of 84 (low) and 98 (high) g DVE, and -38 (low) and -11 (high) g OEB/kg DM. Results were split into two classes, being cows with an initial age below or above 4 years. Daily DM intake (P < 0.001), net energy intake (P < 0.001) and protein intake (P < 0.05) were lower for younger cows, while N deposition, efficiencies of utilization of DM and energy, and N deposition were higher, compared with older cows. Daily LW gain (P = 0.108), N deposition (P = 0.076), protein intake (P < 0.01) and DM and energy efficiencies (P < 0.05) were negatively affected by a low DVE concentration. Daily intake of DM, energy and protein were also negatively affected by a low OEB concentration (P < 0.05). The efficiency of N deposition was low, averaging 125 g/kg N intake, but was not affected by DVE, while the dietary OEB level had a significant effect. Few interactions between DVE and OEB occurred, while an interaction between age, DVE and OEB occurred for most intake data. Carcass and meat quality parameters were little affected by the dietary protein supply. The optimum DVE concentration in diets, with a net energy content for fattening of 7.5 MJ/kg DM, is 95-100 g/kg DM for older, as well as for younger, double-muscled cull cows to realize maximum growth rate and feed efficiency. Dietary OEB levels below -15 g/kg DM should be avoided at this DVE concentration to prevent a lower intake.

Chemical composition, digestibility, nutritive value and intake of hay from an agri-environmental management (EH) were compared with those from hay (Lolium perenne) from an intensive management (IH). IH was of low to moderate quality because of unfavourable weather conditions. EH was harvested mid-June of 2000 (EH1) and 2001 (EH2) on the same sward that had not received mineral fertilizer for 10 years. The EH was characterized by a species-rich botanical composition. On average, it had lower contents of protein (32%), NDF (9%) and ash (35%), and a higher concentration of water-soluble carbohydrates (117%) than IH. Digestibility of dry and organic matter, determined with sheep, was not different between IH and EH and averaged 59 and 63%, respectively. Crude fibre and NDF digestibility were lower in EH (58 and 57%, respectively) than in IH (70 and 69%, respectively). Net energy value for lactation did not differ between IH and EH and amounted to 4.78 MJ per kg DM. True protein digested in the small intestine and rumen degraded protein balance were lower in EH (63 and -60 g per kg DM) than in IH (71 and -33 g per kg DM). Intake of hay was investigated in Holstein-Friesian heifers and Belgian Blue double-muscled heifers (mean BW 280 +/- 22 kg and 269 +/- 21 kg, respectively), and in Belgian Blue non-lactating and non-pregnant double-muscled cows (initial BW 642 +/- 82 kg), using a cross-over design. Hay was freely available. It was supplemented with 1 kg concentrate daily. Dry matter intake from hay was higher for EH than for IH in heifers (4% and 13%, respectively in Holstein-Friesian and Belgian Blue heifers) and in cows (22%). Hay from an agri-environmental management may be used for low-performing animals, as energy intake only exceeded maintenance requirements by 20 to 35%. Several characteristics of EH were different between years, such as dry matter digestibility, net energy value for lactation and fermentable organic matter content.

The objective of this experiment was to determine the effectiveness of current “best-practise” management of steers pre- and post-slaughter in reducing variation in the eating quality of beef. Steers sired by one Belgian Blue bull from Holstein–Friesian cows were managed optimally from birth to slaughter. Animals were slaughtered at target body weights and subcutaneous fat scores of 620 kg and 4L (LH) ( n =23) or 720 kg and 4H (HH) ( n =24). On each slaughter occasion, commercial steers with similar carcass weights and classification scores to the homogenous steers were selected from the factory lairage; n =19 for light commercial steers (LC) and n =20 for heavy commercial steers (HC). Carcasses were hung by the pubic bone at 10 °C for 10 h and 2 °C until 24 h postmortem, when M. longissimus dorsi and M. semimembranosus muscles were excised. Following ageing for 2, 7 and/or 14 days postmortem, eating quality was assessed. Muscle from HH steers was more variable in terms of tenderness, protein, moisture and water-holding capacity compared to muscle from LH steers within LD muscle. Muscle from HC steers was more variable in terms of tenderness, redness colour, protein and intramuscular fat compared to muscle from LC steers within LD muscle. Applying best practice management to the homogenous and commercial steers in the present experiment reduced variances in Warner Bratzler shear force (25.69 and 23.9, respectively) compared to variance (154.9) of previous research carried out by the present authors.

In a 2-year experiment, 66 Belgian Blue (BB) double-muscled culled females have been divided in three groups according to the calving number (heifers–H, cows culled after two calvings–C2 or four calvings–C4) and finished on a maize silage-based diet in order to compare animal performance and evolution of carcass and meat characteristics with age. Four females per group were slaughtered on day 0 to assess carcass and meat characteristics of lean animals. The initial and final live weights, the carcass weight and the daily food intake increased with advancing age, while the live weight gain and feed efficiency decreased. The H presented the higher killing-out and muscle proportions and the lower adipose tissue proportion. Their meat was less dark and less red than that of older cows. The lowest protein content and the highest fat content in meat dry matter were found in the C2. In the three groups, the carcass and meat became fatter with finishing process. The amplitude of fat deposition was the highest in C2. It can be concluded that the performance of BB culled females vary with age. The carcass and meat characteristics differ mainly between H and cows, few differences appearing between cows.

Two groups of 12 Belgian Blue double-muscled cull females were used successively in a 2-year repeated experiment and divided into three groups according to age, allowing four animals per group each year. The aim of the trial was to relate, during the finishing period, the metabolic and endocrine parameters with age. Females were fattened with a diet based on maize silage and were blood sampled on several occasions. The average daily gain (ADG) decreased with the age of the cows. Plasma glucose and triglycerides decreased also with age while the youngest females showed lower concentrations of urea than those older. The composition of plasma non-esterified fatty acids also differed considerably between groups. The hormones that best related with ADG were IGF-1 and insulin. Plasma concentrations of thyroid hormones were lower in the oldest animals. No difference between groups was found for GH. Heifers presented lower concentrations of GH and IGF-1 than those reported elsewhere in fattening bulls of the same breed. It may be concluded that in Belgian Blue double-muscled females, glucose, IGF-1 and insulin are good indicators of the growth potential. Young adult cows presented intermediate characteristics of metabolic and endocrine status that were close either to younger or to older cows.

Various strains of Holstein–Friesian cattle have been imported into Ireland in recent years. The objective of this study was to evaluate for beef production the male progeny of New Zealand (NZ) and European/American (EU) Holstein–Friesians, and Belgian Blue×Holstein–Friesians (BB). The NZ animals were imported from New Zealand as embryos which were implanted into Irish heifers. The EU animals were the progeny by artificial insemination (AI) of high genetic merit Irish cows and high genetic merit European/North American-bred bulls. The BB animals were the progeny both by AI and natural mating of Belgian Blue bulls and Holstein–Friesian cows on commercial farms. A total of 96 spring-born male cattle (32 per genotype) were reared from calfhood to slaughter. They spent their first summer together at pasture and they were then blocked on weight to a 3 genotypes (NZ, EU and BB)×2 production systems (bulls and steers)×2 slaughter weights (550 and 630 kg) factorial experiment. After slaughter, carcasses were measured and the ribs joint was dissected into subcutaneous fat, intermuscular fat, muscle and bone. For NZ, EU and BB, respectively, mean daily gains from arrival to slaughter were 773, 822 and 850 (S.E.D. 9.8) g, mean carcass weights per day from arrival were 425, 459 and 528 (S.E.D. 3.8) g, mean kill-out proportions were 496, 508 and 554 (S.E.D. 2.8) g/kg and mean carcass weights were 284, 302 and 339 (S.E.D. 3.0) kg. Carcass conformation score, carcass fat score, fat depth and m. longissimus area did not differ significantly between NZ and EU, but BB had higher values for carcass conformation and m. longissimus area and lower values for the fatness indicators. Compared with NZ, EU had more muscle and bone and less fat in the ribs joint, while BB had more muscle and less fat and bone than the dairy strains. Bulls had significantly higher slaughter and carcass weights per day from arrival than steers and also had a higher proportion of muscle and a lower proportion of fat in the ribs joint. Delaying slaughter increased slaughter and carcass weights but there was no significant effect on ribs joint composition. It is concluded that EU were slightly superior to NZ for beef production and BB were considerably superior to both dairy strains. Rearing as bulls rather than as steers improved carcass traits and retaining animals to a heavier slaughter weight improved carcass compactness with little effect on rib joint composition.

The objective of this study was to evaluate the differences in biochemical, sensorial and quality characteristics of retail beef in Belgium. Four types of beef (Belgian Blue double-muscled, Limousin, Irish and Argentine) and two different muscles (longissimus lumborum and semimembranosus) were bought at the retail level and compared with regard to colour, shear force, collagen content, fatty acid analysis, taste panel evaluation as well as flavour analysis. Belgian Blue and Limousin beef had a paler colour, lower collagen and intramuscular fat contents. Fatty acid profiles were significantly different between the four types, with significantly higher PUFA/SFA and n-6/n-3 ratios for Belgiam Blue and Limousin beef compared to Argentine and Irish beef. There were significant differences between the meat types for taste panel tenderness and shear force, however both measurements did not fully correspond. Flavour analysis by gas chromatography-mass spectrometry as well as sensory analysis demonstrated that Irish and Argentine beef had a higher flavour intensity related to higher contents of volatile compounds. Differences in tenderness and flavour between the meat types were probably affected by differences in ageing time, related to import vs local production of meat.

Summary A cDNA encoding the bovine dopamine receptor 1 (DRD1) was isolated from a bovine cDNA library, cloned and completely sequenced. The coding region showed 93 and 91% sequence identity on DNA level and 96 and 94% on protein level with its respective porcine and human orthologs. The bovine DRD1 and dopamine receptor 5 (DRD5) were mapped, respectively, to BTA10 and 6 by radiation hybrid mapping. One SNP was found in DRD1 and four in DRD5. Using polymerase chain reaction–restriction fragment length polymorphism, 11 different European cattle breeds were screened for the presence of the DRD1 and DRD5 substitutions. Allele frequencies for DRD1 and DRD5 alleles were very similar across all the breeds examined. Allele frequency discrepancies were found between Belgian Blue beef breed and the other breeds.

Postweaning growth, feed efficiency, and carcass traits were analyzed on 1,422 animals obtained by mating F1 cows to F1 (Belgian Blue x British breeds) or Charolais sires. Cows were obtained from mating Hereford, Angus, and MARC IIIHereford, 1/4 Angus, 1/4 Pinzgauer, and 1/4 Red Poll) dams to Hereford or Angus (British breeds), Tuli, Boran, Brahman, or Belgian Blue sires. Breed groups were fed in replicated pens and slaughtered serially in each of 2 yr. Postweaning average daily gain; live weight; hot carcass weight; fat depth; longissimus area; estimated kidney, pelvic, and heart fat (percentage); percentage Choice; marbling score; USDA yield grade; retail product yield (percentage); retail product weight; fat yield (percentage); fat weight; bone yield (percentage); and bone weight were analyzed in this population. Quadratic regressions of pen mean weight on days fed and of cumulative ME consumption on days fed were used to estimate gain, ME consumption and efficiency (Mcal of ME/kg of gain) over time (0 to 200 d on feed), and weight (300 to 550 kg) intervals. Maternal grandsire breed was significant (P < 0.01) for all traits. Maternal granddam breed (Hereford, Angus, or MARC III)was significant (P < 0.05) only for fat depth, USDA yield grade, retail product yield, fat yield, fat weight, and bone yield. Sire breed was significant (P < 0.05) for live weight, hot carcass weight, longissimus area, and bone weight. Sex class was a significant (P < 0.001) source of variation for all traits except for percentage Choice, marbling score, retail product yield, and fat yield. Interactions between maternal grandsire and sire breed were nonexistent. Sire and grandsire breed effects can be optimized by selection and use of appropriate crossbreeding systems.

Carcass and meat quality of 37 bulls and 91 cows of the Belgian Blue breed (double-muscled type) were compared. Age at slaughter averaged 648±73 and 1820±689 days, respectively. Both groups of cattle were finished on maize silage supplemented with concentrate, and were slaughtered at about 750 kg live weight. Females had a lower (P=0.004) cold carcass weight (469.7 kg) in comparison with bulls (500.8 kg), due to a reduced dressing percentage (63.8 vs. 66.6; P

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One hundred and eleven 5-month-old Belgian Blue double-muscled bulls were divided into three feeding management groups. Group I was turned out on pasture with a daily supplement of 2 kg of beet pulp during the summer period and was fed grass silage to appetite and 2 kg of concentrate during the winter period. The other groups stayed permanently indoors and were fed on maize silage and concentrate (67:33 dry matter basis). Intake was limited for group II to have a daily liveweight gain of 0.85 kg, while the feeds were freely available for group III. From 400 kg onwards, all animals were finished indoors on a diet of maize silage and concentrate (50:50). Within each group, half of the animals were slaughtered at either 650 or 725 kg. Below 400 kg, the daily liveweight gain averaged 0.76, 0.83 and 1.16 kg, respectively (P < 0.05). Above 400 kg, the animals of groups I and II gained faster and gain was more efficient in comparison with group III. Slaughtering at 725 kg tended to decrease daily liveweight gain during the finishing period (P = 0.13) and had a negative effect on feed conversion (P = 0.013) in comparison with 650 kg. Overall daily liveweight gain was lower in groups I and II and these animals needed more time to achieve the same finishing weight (P < 0.001) compared to group III. The bulls, which grazed during the growing period, showed a lower dressing percentage and a tendency for a lower meat content in the carcass. Slaughtering at a heavier live weight also increased fat content of the carcass. Furthermore, significant interactions were found between feeding management and slaughter weight for total number of experimental days, overall daily liveweight gain, dressing, carcass composition and meat production coefficient. It is concluded that animal performance of double-muscled bulls is affected by feeding management during the growing period and liveweight range during the finishing period. Reduced growth rate during the growing period was not fully compensated afterwards, and it did not result in a reduction of carcass fat content. Double-muscled animals mostly behave in a similar way as non-double-muscled animals with regard to compensatory gain. Energy supplementation of light animals at pasture should be advised.

Relative quantities of five collagen crosslinks in meat from Belgian Blue normal, heterozygous and homozygous double-muscled (DM) bulls ( n =31, mean age=20 months) were investigated using m. gluteobiceps, m. semitendinosus and m. pectoralis profundus . The crosslinks pyridinoline, dihydroxylysinorleucine (DHLNL), hydroxylysinorleucine (HLNL), histidinohydroxymerodesmosine (HHMD) and Erlich chromogen (EC) were measured. Concentrations (per mol collagen) of pyridinoline and DHLNL were greater in the DM animals than normal and heterozygous animals for the muscles combined; HHMD was lower. The collagen content in the DM animals was about 65% of the normal animals; that of the heterozygous animals was about 87%. Consequently, the HHMD, HLNL and EC crosslink concentrations (per g wet meat) were significantly lower in the DM animals than in normal and heterozygous animals. All other measured crosslink concentrations and the thermal solubility of the collagen were not significantly affected by the animal type.

Une methode en trois etapes a ete utilisee pour determiner le besoin en acides amines (AA) totaux et celui du premier AA limitant chez les taurillons Blanc Bleu Belge culards (BBBc) en periode de finition.Dans une premiere experience, trois taurillons BBBc (505 ′ 21 kg) ont recu une ration pauvre en proteines digestibles se composant de 25% de foin de prairie et de 75% de concentre. L'apport d'energie nette etait satisfaisant pour maximiser le croit quotidien grâce a la perfusion continue de dextrose dans le duodenum. La digestibilite intestinale apparente des AA essentiels atteignait en moyenne 70.8% et variait de 61.3% pour l'histidine a 79.9% pour l'arginine. Dans une seconde experience, quatre taurillons BBBc (517 ′ 16 kg) ont recu la meme ration accompagnee d'une perfusion duodenale de dextrose et de quatre doses de caseinate de Na (17, 33, 50 et 66% des AA digestibles dans l'intestin grele fournis par la ration epreuve) selon un carre latin 4 x 4. La retention azotee pour la ration de base seule et les quatre complements de caseinate de Na a atteint respectivement 61, 64, 74, 75 et 78 g j - 1 . Un apport de 720 g j - 1 d'AA digestibles a ete defini comme optimalisant l'utilisation de l'N pour la croissance des animaux. Sur base des concentrations plasmatiques, la methionine et la phenylalanine etaient probablement les AA limitants. Dans une troisieme experience, cinq taurillons BBBc (513 ′ 60 kg) nourris avec la ration epreuve, ont recu une perfusion duodenale de dextrose et d'AA equivalente a la dose optimale definie dans la seconde experience a l'exception de l'apport de methionine digestible (12.8, 15.1, 17.6, 20.1, 22.6 et 25.1 g j - 1 ) variant selon un dispositif experimental en carre latin 6 x 6 avec un animal manquant. Sur base de la retention azotee, le besoin en methionine digestible a ete estime a 22.8 g j - 1 et correspondait a 360 mg de methionine digestible par gramme d'azote retenu.

The critical roughage part (CRP) of 2 diet types was determined in a cross-over design with 6 double-muscled and 6 normally conformed Belgian Blue bulls fitted with rumen cannulae. The roughage:concentrate ratio was lowered weekly until signs of a lack of physical structure were observed. For diet 1, consisting of maize silage and concentrates, the initial proportion of maize silage was 25% of DM but it decreased weekly with 5% units of DM. For the second diet, consisting of wheat straw and concentrate, 12% straw (DM basis) was provided during the first week and thereafter the proportion of straw decreased weekly with 3% units of DM. Several directly observable parameters (rumen pH, feed intake, bloat, faecal consistency) were evaluated weekly for each bull. Apart from these direct indicators of acidosis, also other parameters, whose results were only available after the end of the trial, were determined (volatile fatty acid profile, lactic acid concentration, chewing time). The roughage part between the part fed when signs of a lack of physical structure was first observed and the part that was fed the week before, was considered as the CRP. Most animals showed no acute signs of clinical acidosis (directly observable parameters) and finished the trial on a 100% concentrate diet. However, in sacco rumen DM-degradabilities of maize silage, grass silage and wheat grain was depressed considerably when low roughage diets were fed. Based on all observed parameters, the mean CRP was calculated to be 14.7% for diet 1 and 8.1% for diet 2. The beef type (double-muscled or not) had no influence on the CRP.

The minimal amount of dietary physical structure for Belgian Blue double-muscled fat- tening bulls was investigated with four feeding regimens. The trial involved 52 bulls weighing 330 kg at the start and 680 kg at slaughter. All diets were fed ad libitum and consisted of concentrates and maize silage in different ratios. The structural value (SV), currently in use in Belgium as an index of dietary physical structure for dairy cattle, of the diets amounted to 0.79, 0.62 and 0.45 units per kg DM for the HSV (high), MSV (moderate) and LSV (low) group, respectively. The fourth group (LSVs) received the same diet as the LSV group, but additional straw was provided ad libitum, to evaluate whether bulls were capable of compensating for a possible lack of physical structure by eat- ing straw. From the start until 600 kg no differences in growth rate were found. From 600 kg until slaughter (680 kg), the LSV group had the highest growth rate (1.35 vs. 1.14 kg·d -1 ). That same group also had the highest DM- and NEF-intake during the first 84 days of the trial. Although not signifi- cantly different, the MSV group had the highest amount of lean meat in the carcass (776 g·kg -1 ) and the lowest amount of fat (100 g·kg -1 ). The level of physical structure did not affect meat quality. Over- all, no external signs of subclinical or clinical acidosis were observed. The length of the rumen papillae was not affected by the diets. Histological examination of the ruminal epithelium revealed that MSV and LSV exhibited the severest morphological changes. However, it is unclear whether the welfare of these animals was endangered by a shortage of physical structure. Based on the zootechnical performances, no adverse effects were found when feeding a diet with an SV of 0.45·kg -1 DM.

Double-muscled animals are of particular interest to meat producers because they are characterized by an exceptional muscular development and an increased carcass lean to fat ratio. The term is mainly restricted to cattle, but functional mutations in the myostatin gene causing this phenotype are also described in other species. The condition is associated with altered physiological and histological characteristics that bring about not only differences in meat quantity but also in animal performances and in meat quality. Therefore, the exploitation of double muscling has to be considered carefully. This article mainly focuses on observations in cattle.

In this paper we present results from a genetic characterization of a herd of the Danish Jutland cattle breed named the Kortegaard herd (n = 135; 57 males and 78 females). The herd is genotyped on the Bovine HD BeadChip microarray with 697,548 evenly spaced SNP across the bovine genome. The aim of the study was to characterize the genetic profile of the Kortegaard herd, which has been closed for several generations, by quantifying the degree of genetic homogeneity within the herd and to compare its genetic profile to that of other cattle breeds. A total of 868 animals from the Angus, Belgian Blue, Charolais, Friesian, Hereford, Holstein, Holstein-Friesian crosses, Limousin, and Simmental breeds was used for genetic profile comparisons. The level of genetic variation within the breeds were quantified by the expected heterozygosity (HE), observed heterozygosity (HO), average minor allele frequency (MAF), the degree of polymorphism, and runs of homozygosity (ROH), which are contiguous lengths of homozygous genotypes of varying length. Interestingly, the Kortegaard herd had the lowest within-breed genetic variation (lowest HE, HO, and MAF), showed moderate levels of short ROH (5 Mb) compared to all the other breeds. This is possibly due to recent consanguineous matings, a strong founder effect, and a lack of gene flow from other herds and breeds. We further examined whether the observed genetic patterns in the Kortegaard herd can be used to design breeding strategies for the preservation of the genetic pool by focusing on a subset of SNP outside homozygote regions. By calculating the pairwise identical-by-state between all possible matings, we designed a breeding plan that maximized heterozygosity in the short term. The benefits and limitations of such a breeding strategy are discussed.