Carcass Fat Content Research Articles

Effect of ractopamine on carcass characteristics and joint-cartilage soundness in finishing pigs

One hundred and fifty crossbred pigs (Camborough × Canabrid, equal numbers of gilts and barrows) at an average live weight of 64.2 kg were randomly assigned to diets containing 17 or 20% crude protein (with 0.8 or 1.1% lysine, respectively) and 0 or 20 ppm ractopamine. Pigs were slaughtered at an average live weight of 102.2 kg. Supplementation of ractopamine in pig diets significantly increased average daily gain (P < 0.005) and decreased feed to gain ratio (P < 0.001), with no effect on daily feed intake. Ractopamine feeding increased total lean (P < 0.001) and decreased total bone (P < 0.05) and total fat content (P < 0.001) of carcasses. The decreased fat content was largely due to the reduction of subcutaneous fat (P < 0.001). Cartilage visual scores and cartilage uronic acid concentrations of weight-bearing areas of humeral and femoral condyles were not affected by feeding ractopamine. Correlations between visual scores and uronic acid concentrations of joint cartilage and performance parameters and carcass characteristics were not significant. These results demonstrated that feeding ractopamine can increase pig growth rate and carcass leanness without detrimental effect on joint cartilage. Key words: Ractopamine, growth rate, uronic acid, cartilage, osteochondrosis, pigs

Recombinant bovine and porcine somatotropin: Safety and benefits of these biotechnologies

This article reviews the literature about the safety and benefits of two recombinantly derived proteins, bovine somatotropin (bST) and porcine somatotropin (pST), that likely will be used in animal agriculture in the future. When administered to dairy cows, bST increase milk production per cow approximately 15% to 20% and improves productive efficiency approximately 10%. Administration of pST to growing pigs reduces carcass fat content by as much as 70% to 80% and improves productive efficiency 15% to 35%. Because meat is a major source of total fat and saturated fatty acids in the diets of human beings, pST will allow consumers to include leaner, more nutrient-dense pork in their diets and still meet current dietary guidelines. Although these biotechnologies have not yet received regulatory approval from the Food and Drug Administration (FDA) for commercial use, information published by the FDA, the National Institutes of Health, the US Congress Office of Technology Assessment, and the American Academy of Pediatrics, as well as an extensive body of scientific evidence, indicate that these products are safe for the consumer. Nonetheless, it is important that consumers understand the benefits and safety of these biotechnologies. Dietitians can play an important role in providing information to consumers about the safety and benefits of bST and pST.

Evaluation of Australian merino and U.S. sheep breeds for growth and carcass traits.

One hundred twenty 4-mo-old wether lambs born to Targhee ewes and sired by six rams each from Merino (Finewool, FM and Strongwool, SM), Rambouillet (Dubois, DR and Texas, TR), and Targhee (T) breeds were randomly assigned to predetermined slaughter weight groups of 43, 48, 52, and 57 kg and evaluated for growth and carcass traits. Overall mean ADG and feed conversion rate (FC, kilograms of feed/kilogram of gain) were .28 and 6.4 kg, respectively; T grew the fastest (.31 kg) and FM grew the slowest (.23 kg). Targhee and SM had the best FC (6.2), whereas FM (6.8) had the poorest FC (P < .05). Overall mean backfat thickness (BT) and carcass fat (CF) were 4.8 mm and 25.6%, respectively. Targhee had the lowest (24%) and FM the highest (27.8%) CF percentage (P < .05). Differences (P < .05) were observed for BT and CF among slaughter weight groups; overall means for both traits gradually increased from the 43- to the 57-kg groups. Separate analysis of the 43- and the 48-kg groups indicated nonsignificant breed differences for feed traits, whereas significant differences still existed for CF. It was concluded that Merino strains grew more slowly, were less efficient in postweaning growth, and had higher carcass fat content than U.S. breeds at a constant slaughter weight; SM were more comparable to U.S. breeds than were FM. Merino-cross lambs should be slaughtered at lighter BW to avoid excessive carcass fat.

Body and carcass composition of Angus and Charolais steers as affected by age and nutrition.

The objectives of this study were to examine the effects of a low vs moderate rate of gain during the growing phase on empty body and carcass composition during finishing of Angus and Charolais steers of two ages. Forty-eight Angus and 48 Charolais steers that were either spring-born (OLDER) or fall-born (YOUNGER) were fed two diets (alfalfa pellets [CON] or cubed grass-alfalfa hay, wheat straw, cottonseed hulls, and soybean meal [RES]) for a growing period followed by a conventional feedlot period. The feedlot period started when the YOUNGER-CON steers weighed the same as the OLDER-RES steers. At that time, an interaction of age x diet occurred in empty body fat content (P < .10), whereas breed and age x diet affected carcass fat content (P < .01). OLDER-CON steers were larger (average 378 kg empty BW) and fatter than the other, smaller groups (average 222 kg). Angus carcasses were fatter than Charolais carcasses (P < .01). At the end of the finishing phase, compensating steers (OLDER-RES) had fatter carcasses than OLDER-CON steers. Empty body fat content was affected by a breed x age x diet interaction (P < .10). Allometric regressions (Y = aXb) of fat on empty BW indicated that empty body fat accretion was greater in Angus than in Charolais and in YOUNGER than in OLDER steers. A breed x age x diet interaction (P < .10) indicated that OLDER-Angus had higher fat accretive rates than YOUNGER-Angus, whereas OLDER-CON-Charolais steers deposited fat more slowly than the remaining groups. These data suggest that steers receiving feedlot diets at light weights, whether young in age or previously restricted, accumulate fat more rapidly than do larger steers. This feeding strategy may be an advantage in late-maturing types, but moderate growth through approximately 75% of slaughter weight is recommended for early-maturing types.

Correlated responses in slaughter and carcass traits of crossbred progeny to selection for carcass lean content in sheep

AbstractCorrelated responses in slaughter and carcass traits to divergent selection for high or low carcass lean content in Texel-Oxford sheep were measured in the crossbred progeny of 23 rams. Rams were selected using the selection index: -0·995 FATD + 0·206 WT20, where FATD and WT20 are the ultrasonic backfat depth and live weight at 20 weeks of age, with both traits standardized to have zero mean and unit phenotypic variance. A total of 329 crossbred lambs were slaughtered at 16 weeks of age and 250 lambs were slaughtered at fixed weight, 38 to 40 kg for castrated males and 36 to 38 kg for ewe lambs. Progeny from high-line rams grew faster, as indicated by the heavier slaughter weight of lambs slaughtered at fixed age (04 (s.e.d. 0·5) kg) and the lower age at slaughter for lambs slaughtered at fixed weight (-5 (s.e.d. 3) days). Subcutaneous and internal fat scores and the Meat and Livestock Commission carcass appraisal and conformation scores were all lower in the high line than in the low line and the magnitude of the selection line differences for lambs slaughtered at fixed weight was essentially double that of lambs slaughtered at fixed age (0·8 v. 0·5 score units).Shoulder joints of 254 lambs, slaughtered at fixed age, were dissected and half carcasses were dissected on 66 of the lambs. Carcass and shoulder joint information was combined with double-sampling methodology, using multiple regression equations to predict carcass composition. For each tissue type, viz. lean, subcutaneous fat, internal fat and bone, the correlations between carcass content and shoulder joint content were at least 0·90 and the proportions of variation in carcass tissue content accounted for by the prediction equations were also at least 0·90. Progeny of high-line rams had higher carcass lean weight, (402 (s.e.d. 140) g) than progeny from the low line, with no difference in carcass fat weight, such that carcass lean content was higher, (10 (s.e.d. 5) g/kg), and carcass fat content was lower, (-10 (s.e.d. 7) g/kg). Based on the slaughter and carcass traits of these crossbred progeny, divergent selection for high and low carcass lean content has established lines of animals with different rates of lean growth but similar rates offat deposition.

Research Note: Effect of 2,4-Dinitrophenol on Growth and Body Composition of Broilers

The effects of 2,4-dinitrophenol (DNP) on growth, feed efficiency, fattening, and mitochondrial functions of liver and skeletal muscle were studied in broilers. The DNP was added at levels of 100, 200, and 400 mg/kg of diet. Feed intake was not changed with administration of DNP except at 100 mg/kg of diet. Body weight was significantly decreased by administration of DNP at 400 mg/kg of diet compared with those at 0 and 100 mg/kg of diet. Feed efficiency was significantly reduced by administration of DNP at 400 mg/kg of diet. Abdominal fat and carcass fat contents, expressed either as absolute values or relative percentages of body weight, were significantly decreased with increasing dietary DNP concentration above 200 mg/kg of diet. These results showed that administration of DNP reduced body fat, which may be associated with the change in feed efficiency. No reduction in adenosine triphosphate:oxygen ratio with increasing DNP concentration was observed in hepatic and skeletal muscle mitochondria isolated from broilers fed experimental diets containing DNP.

The effects of plane of nutrition and slaughter weight on performance and carcass composition of beef cattle

Current consumer demand for leaner beef necessitates a reduction in the fat content of a major proportion of beef carcasses. Recent studies have shown that a greater reduction in carcass fat content can be achieved when plane of nutrition is reduced by reducing the quantity of food given rather than reducing the energy content of a diet given ad litibum. An experiment lias been carried out to examine the effects of restricting food intake during the finishing period on the performance and carcass composition of beef cattle.Two hundred and ten 12 month old Friesian (F), Limousen x F and Belgian Blue x F bulls, steers and heifers, which had been reared under uniform management and nutrition were used. They were purchased directly from dairy farms between mid October and mid December, at approximately two weeks of age, were artificially reared and were put to pasture from late April until early October.

Effects of clenbuterol on skeletal muscle mass, body composition, and recovery from surgical stress in senescent rats

Aging decreases skeletal muscle mass and strength, which may be exacerbated by age-related diseases. There is a need for therapeutic agents to prevent or restore loss of skeletal muscle in elderly subjects with muscle wasting disorders. Clenbuterol, a β 2-adrenergic agonist, dramatically increases skeletal muscle mass in young animals and partially prevents or restores muscle loss in experimental models of muscle wasting. However, the protein anabolic and fat catabolic effects of clenbuterol have not been studied in senescent animals. To determine whether this drug has potential for preventing or repairing muscle loss in elderly subjects, we have examined its effects in young and old rats. Clenbuterol was administered by implanted osmotic minipumps to Fischer-344 rats ages 3, 12, and 23 months, at a dose of 1.5 mg/kg/24 h for 3 weeks. The weights of five hindlimb muscles and carcass protein and fat content were determined. Clenbuterol treatment increased the weight of skeletal muscles 22% to 39% in 3-month-old rats, 19% to 35% in 12-month-old rats, and 22% to 25% in 23-month-old animals. Likewise, clenbuterol increased carcass protein content 19% in 3-month-old rats, 16% in 12-month-old rats, and 24% in 23-month-old animals. Conversely, the drug reduced carcass fat content 36% in 3-month-old rats, 32% in 12-month-old rats, and 38% in 23-month-old rats. Therefore, clenbuterol had similar anabolic and catabolic effects in all age groups. In addition, clenbuterol stimulated recovery of skeletal muscle protein lost following pump implantation in senescent rats. These findings suggest that clenbuterol or similar drugs may prove useful in stimulating skeletal muscle hypertrophy in elderly subjects with muscle wasting disorders.

Growth and Development of Leghorn Pullets Subjected to Abrupt Changes in Environmental Temperature and Dietary Energy Level

Four trials were conducted to note the response of pullets to changes in environmental temperature and energy level at 56 days of age. In each trial, birds were fed diets providing either 2,500 or 3,000 kcal ME/kg throughout rearing, or with a single diet change from 2,500 to 3,000 and 3,000 to 2,500 kcal ME/kg occurring at 56 days. Each of the four diet scenarios was tested with six replicate caged groups each containing 10 pullets. In Trials 1 and 2 environmental temperature was maintained at 18 and 30 C, respectively, to 126 days. In Trials 3 and 4, temperature was changed at 56 days from 18 to 30 C and 30 to 18 C, respectively.Regardless of environmental temperature conditions, diet change per se had minimal effect on growth and development. Rather dietary energy level used from 56 to 126 days had the greatest effect on growth, with birds fed the highest energy content diet generally being heaviest. However, this effect was not significant (P>.05) in all trials, which is probably related to a lack of effect on energy intake under such conditions. Final body weight was more closely associated with energy intake than with protein intake and energy intake was maximized when high-energy diets were used after 56 days of age. Consumption of high-energy diets after 56 days, regardless of trial conditions, always resulted in increased carcass fat content at 126 days.It was concluded that abrupt and major changes in environmental temperature or dietary energy as used in these trials have little deleterious effect on pullet development. Conditions prevailing during later stages of growth have a far greater effect than changes per se in these parameters.

Effect of Dietary Protein Level and Length of Feeding on Performance and Abdominal Fat Content of Broiler Chickens

Dietary CP levels influence carcass fat content of chickens but the length of time necessary to feed higher levels in order to increase carcass fat is not known. Studies were conducted to evaluate the effects of length of feeding of different levels of dietary CP on broiler performance and abdominal fat deposition. All diets were calculated to be isocaloric at 3,200 kcal ME/kg. Broilers fed 23% CP for 0 to 21 days, 20% CP for 21 to 42 days, and 18% CP for 42 to 49 or 42 to 56 days served as the control group in each of two trials. In the first trial, broilers were fed constant levels of CP from day-old to market age with CP levels ranging from 15 to 27% (amino acids adjusted in proportion to CP level). Other broilers were fed 23% CP for 0 to 21 days and then fed either 15, 17, 19, or 21%CP to market age. In the second trial, broilers were fed constant levels of CP (18, 20, or 23%) from day-old to market age.Feeding CP levels lower than those fed the control group had a more pronounced effect on males than on females, with the primary effects being reduced body weight, poorer feed utilization, and increased carcass fat content. Feeding CP levels higher than those fed the control group generally did not increase final body weight but generally improved feed utilization and decreased carcass fat content. The economics of improved feed utilization and reduced carcass fat must be considered in determining dietary CP levels to use at different ages for growing broilers.

Estimation of Fat Content of Poultry Carcasses from Dry Matter Data

Chemical analyses of 519 poultry carcasses, ranging from 475 to 3,679 g in weight, were statistically analyzed to ascertain whether fat contents could be estimated from DM data. The data included analyses of males and females, whole birds and eviscerated carcasses, sexually mature and immature birds, and young and old birds kept under various management systems and subjected to widely differing nutritional treatments.Regression slopes of the 15 sets of analyses were not significantly different from each other, this permitted a common regression to be fitted to all data. A high coefficient of determination (R2 = .953) indicated that the regression equation ŷ = −30.79 +1.22 x, where ŷ = fat content and x = DM, could be satisfactorily used to estimate fat content from DM data.

Body fat accretion

A rat model for studying causes of body fat accretion was developed. Employing this model, it was possible to produce a 108 g difference in carcass fat content between two groups of rats simply by selecting the seven fattest and the seven leanest animals from a group of 100. The results of this study provide evidence that the gastrointestinal tract was not a site of caloric wastage, that total energy excreted in feces and urine was directly proportional to caloric intake, that differences in brown adipose tissue thermogenesis were not responsible for the twofold difference in adiposity between the lean and fat rats, and that a family of hepatic lipogenic enzymes was not up-regulated even though the habitual consumption of a diet rich in carbohydrate was greater in the fat vs lean rats. The fat rats also had a greater lean body mass. Therefore, the additional calories consumed by the fat rats could have contributed to their greater adiposity and/or could have been channeled to sustain more active tissue. Finally, evidence was presented to show that the experimental selection process is an important consideration when determining the relationship between caloric intake and body fat content.

Effect of early weaning one lamb in a triplet lamb rearing system

ABSTRACTThirty-seven Cambridge (C) and Suffolk (S) × C ewes and their lambs were housed and penned individually in family groups for 35 days post partum and then grazed on pasture until the lambs reached slaughter weight. Lambs were reared as twins (TR-TW). The lambs weaned at 35 days were artificially reared and formed the TR-AR group.Dry matter intake of the complete diet and hay offered ad libitum during the housing period was unaffected by rearing type. TR-TR and TR-TW ewes produced more milk at 10 days than TW-TW ewes, 4·4 and 4·2 v. 3·6 (s.e.d. 0·257) kg/day. From 35 days onwards the decline in milk yield tended o t be greater in the TW-TW and TR-TW ewes which also gained more condition than TR-TR ewes, 0·33 and 0·37 v. 0·01 (s.e.d. 0·139) of a score.TW-TW lambs grew faster than TR-TW and TR-TR lambs during the housed period, 336 v. 295 and 292 (s.e.d. 9·8) g/day but after 35 days TR-TW, TR-AR and TW-TW lambs had similar growth rates, 348, 350, and 348 (s.e.d. 14·2) g/day respectively whereas TR-TR lambs grew less quickly at 310 g/day. Forty-two male lambs were slaughtered. TR-AR lambs had a higher killing-out proportion and carcass fat content than naturally reared animals. In the latter group carcass fat content was negatively related to time reared as triplets and the kidney knob and channel fat weight was significantly lower in the TR-TR group. Crossbred lambs grew faster, had a higher killing-out proportion and greater weight of m. longissimus dorsi and m. psoas major in the half carcass.It is concluded that weaning one lamb at 35 days provides a suitable alternative system for rearing triplets and that it is possible to produce good quality carcasses with some desirable reduction in fat content from lambs reared as triplets throughout their life.

Carcass and Tissue Fat Content in the Pregnant Rat

The present study in rats was aimed at determining the specific day of pregnancy on which maternal body fat accumulation starts and which tissues are involved. Most of the body weight increase at day 12 of gestation corresponded to conceptus-free maternal weight which progressively increased until the 19th day of gestation after which maternal weight stabilized and the rate of conceptus weight gain became maximal. Maternal carcass fat content progressively increased until day 18 of gestation, increased very markedly on day 19, stabilized between day 19 and 20 and then decreased on day 21. These changes were the opposite of the course of the specific-gravity values. The fresh weight of lumbar fat-pads and mesenteric adipose tissue reflected the changes in carcass fat content throughout gestation. Periuterine adipose-tissue mass declined on day 12 of gestation to be recuperated later, subcutaneous adipose tissue increased on day 12 to decline progressively thereafter and interscapular brown adipose tissue remained stable until day 20 and increased on day 21. With only a few exceptions, the lipid concentration in all these adipose tissues remained stable throughout gestation. Mammary glands and liver weights increased intensely from day 12 and, whereas the lipid concentration in the former was stable, in the latter it decreased on day 12 and increased on days 18 and 19. These results show that in the rat (a) maternal carcass fat accumulation during gestation is not paralleled by the size of the different fat-storing tissues and (b) mammary-gland fat accumulation also contributes to maternal fat storage.

Production results, serum cholesterol concentration and carcass composition of broiler chickens fed diets based on bran or inner endosperm from oats with and without enzyme supplementation

AbstractBroiler chickens were fed diets based on bran or inner endosperm from oats (Avena sativa L), given with or without a supplementary fibre‐degrading enzyme, in order to study the effects of the dietary fibre on production results, carcass composition and serum cholesterol concentration. Enzyme supplementation of the oat‐bran‐based diet significantly improved production results and caused an increase in total serum cholesterol concentration and carcass fat whereas carcass crude protein and water content decreased. On enzyme supplementation of the diet based on inner endosperm, a significant although less pronounced improvement in production results was obtained. Chickens fed the inner endosperm diet generally had higher total serum cholesterol concentrations which increased further on enzyme supplementation. Carcass fat content also increased on enzyme supplementation, and at day 27 chickens fed the enzyme‐supplemented diet based on inner endosperm had the highest carcass fat content in comparison with all other diets. The results show that dietary fibre exerts a greater influence on total serum cholesterol concentration than energy or fat intake since chickens fed the enzyme‐supplemented oat‐bran diet had the highest intake of metabolisable energy and fat but still displayed lower total serum cholesterol concentrations than chickens fed the enzyme‐supplemented low fibre diet based on inner endosperm.

Interrelationships between exogenous porcine somatotropin (PST) administration and dietary protein and energy intake on protein deposition capacity and energy metabolism of pigs.

Exogenous porcine somatotropin (PST) administration stimulates protein deposition and inhibits lipogenesis, resulting in dose-related improvements in growth performance and reduction of carcass fat content. However, the associated impacts of this technology on dietary nutrient requirements and energy partitioning between maintenance, protein, and fat remain unclear. Studies with pigs between 25 and 60 kg body weight indicate that, because of unknown improvements in amino acid utilization and(or) in the energy available for protein synthesis, only marginal increases in dietary protein percentage are required to support 20 to 25% improvements in protein deposition induced by PST administration. In contrast, an increased dietary protein concentration is required to support maximal protein deposition in pigs 60 to 100 kg. Exogenous PST administration increased the maintenance energy requirement and altered the relationship between energy intake and protein deposition, although the magnitude of these changes and the consequent effects on expression of dietary protein (amino acid) requirements was influenced by gender. Albeit limited, information suggests that PST alters nutrient demand at the tissue level. Information of this type will form the basis for rational decisions concerning the method for expression of dietary nutrient requirements (% vs g/d) for PST-treated pigs. Further quantitative information is required on the effects of PST dosage on the relationship of protein deposition to energy intake and on any underlying changes in amino acid utilization and metabolism.

Influence of dietary protein and recombinant porcine somatotropin administration in young pigs: growth, body composition and hormone status2

The influence of dietary protein and recombinant porcine somatotropin (rpST) administration on growth and body composition was investigated in barrows. Ten groups of six pigs starting at 30 kg were restrictively fed (approximately 80% of ad libitum) one of five diets containing 11, 15, 19, 23 or 27% protein. Diets contained skim milk (12%). Soybean meal diluted with cornstarch was used as the supplemental source of dietary protein. Diets were isocaloric (3.8 Mcal DE/kg) and all contained the same amount of lysine (18 to 20 g/kg). Thirty pigs were treated daily with rpST (100 micrograms/kg) by i.m. injection; the remaining pigs were treated with sterile diluent (control) for 42 d. Growth rate was greater in rpST-treated pigs at all levels of protein intake; however, the magnitude of the response to rpST treatment was lowest among pigs fed the diet containing 11% protein. Feed:gain ratio, backfat depth and carcass fat content were decreased in rpST-treated pigs compared to respective controls. Additionally, the concentration of carcass fat decreased concomitantly with an increase in dietary protein intake. Concentration of carcass protein increased linearly as dietary protein increased in control and rpST-treated pigs. In contrast, treatment with rpST was associated with an increased visceral mass; the concentration of protein and fat in the viscera was influenced by protein intake but not by rpST. These results, characterized by few treatment interactions, suggest that when energy intake is kept constant and appropriately fed pigs serve as controls, dietary protein and rpST influence growth and body composition by independent mechanisms.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of Feed Restriction During the Rearing Period on the Growth Rate and Carcass Composition of Turkey Breeder Hens

An experiment with Nicholas parent-stock turkey breeder hens was designed to determine the effect of feed restriction on body weight and carcass composition. The following six feeding programs were compared using four replicate pens of 15 or 16 poults each: ad libitum intake of conventional corn and soybean diets (Ad), skip 1 day per week (S1), skip 2 days per week (S2), 95% of ad libitum (95%), 90% of ad libitum (90%), and 85% of ad libitum (85%). At 29 weeks of age, Ad birds were heavier than restricted birds (P<.05); there were no differences among S1, S2, and 95% or between 90% and 85% treatments. The 95%, 90%, and 85% hens did not have as much carcass fat as did Ad hens (P<.05); there were no differences among Ad, S1, and S2 treatments. The results of the present study show that feed restriction during the rearing period reduces the growth rate of turkey breeder hens. Quantitative feed restriction (95%, 90%, and 85%) appears to be the most effective method to reduce carcass fat content.

Processing Losses, Carcass Quality, and Meat Yields of Broiler Chickens Receiving Diets Marginally Deficient to Adequate in Lysine Prior to Marketing

A feed based on com, soybean meal, and sesame meal containing .85% lysine was supplemented with L-lysine HCl to provide .95 and 1.05% of total lysine. Each lysine level was given to broilers from 28 to 42 days of age in which the sexes were reared separately. No differences occurred in BW because of lysine, but feed conversion decreased as the lysine level increased. The holding loss prior to slaughter was greater with the birds that had received .95% lysine versus those that had received .85 and 1.05% lysine, respectively; however, no effects were detected on the chilled-carcass yield after processing. The extent of carcass finish increased as the lysine decreased. The fat content of the whole chilled carcass increased along with finish, while protein and ash were to the reverse. The percentage of fat in the skin and in the thigh meat were altered in parallel with the whole carcass, but the breast meat was unaffected. Cutting sample carcasses into commercial parts revealed that the proportions of breast and thigh increased with lysine at the expense of back both on a raw and a cooked basis. The cooked meat from the breast, wings, and back increased, the skin decreased. Both sexes responded similarly to lysine.

Carcass composition of serially slaughtered Friesian, Hereford × Friesian and Charolais × Friesian steers finished on two dietary energy levels

ABSTRACTThe carcass composition of Hereford × Friesian (HE), Friesian (FR) and Charolais × Friesian (CH) steers finished on diets of high (H) and medium (M) dietary metabolizable energy (ME) concentrations and slaughtered at low (L), normal (N) and heavy (W) carcass weights was examined in a 3 × 2 × 3 (no. = 9 per individual treatment) factorial experiment. A pre-finishing slaughter group of nine animals of each breed type was also included, giving a total 189 animals in 21 experimental groups. ME concentrations of the H and M diets which were offered ad libitum were 12·6 and 10·4 MJ/kg dry matter. Target carcass weights for L, N and W were 260, 300 and 340 kg for HE and FR and 260, 320 and 380 kg for CH.Carcass side weights (before tissue separation) of the HE, FR and CH pre-finishing slaughter groups were 90·8, 970 and 101·0 (s.e.d. 3·9) kg. Corresponding tissue proportions were 188, 199 and 200 (s.e.d. 4·3) g/kg bone, 663, 686 and 690 (s.e.d. 5·3) g/kg muscle and 135, 99 and 96 (s.e.d. 5·7) g/kg fat. Main effect side weights of the finished groups were 152·3, 151·4 and 162·2 (s.e.d. 1·4) kg for HE, FR and CH. 158·5 and 152·2 (s.e.d. 1·1) kg for H and M and 131·2, 155·2 and 179·6 (s.e.d. 1·4) kg for L, N and W, respectively. Tissue proportions in the same order were 146, 160 and 157 (s.e.d. 2·0), 149 and 159 (s.e.d. 1·6) and 163, 154 and 146 (s.e.d. 2·0) g/kg bone, 579, 601 and 635 (s.e.d. 5·5), 600 and 610 (s.e.d. 4·5) and 637, 599 and 574 (s.e.d. 5·5) g/kg muscle and 264, 228 and 195 (s.e.d. 6·4), 240 and 219 (s.e.d. 5·2) and 188, 235 and 264 (s.e.d. 6·4) g/kg fat. CH had more (P &lt; 0·001) of their muscle in the pelvic limb and less (P &lt; 0001) in the thorax than HE and FR. HE had more (P &lt; 0·001) of their carcass fat in the subcutaneous depot and less (P &lt; 0·001) in the intermuscular depot than FR and CH. The allometric regression coefficients for the main joint and tissue weights on side weight were &lt;1·0 for both limbs, loin, bone and muscle. Coefficients were &gt;1·0 for the thorax, ribs, flank and fat. The regression coefficients for the main muscles of the pelvic limb and loin and total thoracic limb muscle on total side muscle were &lt;l·0, while the coefficients for the flank, ribs and thorax muscles were &gt;1·0. Similarly the regression coefficients for the bones of the two limbs on total side bone were &lt;10, while the coefficients for the loin, ribs and thorax bones were &gt;10. It was calculated (for the H diet) that at a carcass weight of 300 kg, HE, FR and CH would have carcass tissue proportions of 576, 600 and 642 g/kg muscle and 261, 227 and 180 g/kg fat. The three breed types would have similar carcass fat contents at carcass weights of 264, 300 and 376 kg for HE, FR and CH, respectively.