Prediction of empty body components in steers by urea dilution

Empty body composition of 68 mixed-breed and 50 Angus steers was determined by chemical analysis of the right half-carcass and entire noncarcass fraction of each steer. Chemical composition was used to develop prediction equations for empty body protein (EBPRO) and fat (EBFAT) in steers using urea space (US) and body weight measurements. Previous research showed a significant positive correlation between empty body water (EBH2O) and urea space in these steers. For all steers studied, the percentage of EBH2O ranged from 44.8 to 69.2 (mean = 56.0), the percentage of EBPRO ranged from 14.1 to 19.8 (mean = 17.0) and the percentage of EBFAT ranged from 6.1 to 38.1 (mean = 22.1). The best predictions obtained were multiple regression equations with actual weight of body components as dependent variables and US and empty body weight (EB) as independent variables. Urea space alone was a poor predictor of EBFAT, but US improved predictions based on live weight (LW) or EB alone. Coefficients of determination for the best predictions of percentage of composition were not as high as coefficients of determination for the best predictions of actual weight of body components. These data suggest that US measurements can be used to predict empty body composition of live steers, but this may require repeated measurements and an independent estimate of EB from LW for greatest accuracy.     

Efficacy of the urea dilution technique in estimating empty body composition of pigs weighing 50 kilograms

The efficacy of the urea dilution technique in estimating the empty body composition of pigs weighing 50 kg was evaluated in three trials using 17 contemporary (Large White X Landrace X Hampshire X Duroc) and 8 Nebraska Gene Pool X contemporary pigs. Blood samples were collected via ear catheter before infusion (-60, -30 and 0 min) and at various times (3 to 90 min) after urea infusion (2.16 mmol/kg live BW), and analyzed for plasma urea. Backfat thickness of live pigs from the contemporary line was measured ultrasonically. Pigs then were killed by euthanasic injection, and total bodies (with gastrointestinal contents removed) were analyzed for water, protein and fat. In Trials 1 and 2, there were linear relationships (P less than .001) between chemically determined body water and fat and between body water and protein. Urea space was related (P less than .05) to empty body components with few exceptions, but regression coefficients for urea space in Trial 3 were different from those of Trials 1 and 2. Inclusion of additional independent variables with urea space improved estimation of empty body components. Although backfat alone did not estimate empty body components (except fat) as well as urea space alone, the addition of other common independent variables resulted in better estimates using backfat than urea space. The results of this experiment indicate that the urea dilution technique can be used to estimate the body composition of growing pigs. However, the accuracy obtained depended on the population of pigs being investigated and was no greater than the accuracy with appropriate equations based on backfat.     

Evaluation of the use of deuterium oxide dilution techniques for determination of body composition of beef steers

Body composition as estimated by a one- or two-compartment deuterium oxide dilution technique was compared with directly measured body composition of 15 large- and 15 small-frame steers. Body composition of the steers was measured at 219, 412 and 603 kg live weight. Empty body protein was overestimated (P less than .05) 3.6% from a one-compartment model (1 CM, using the slope, intercept method), while empty body protein was underestimated (P less than .05) 5.4% from a two-compartment kinetic model (2CM). Empty body ether extract estimated by 1 CM was not significantly different from the direct method, although 4.7% larger. Empty body ether extract was overestimated (P less than .001) 32.2% by the 2CM. Empty body water was accurately estimated from the 1CM when a 3.2% correction factor was used for the overestimation of total body water by the 1CM, but water in gastrointestinal tract contents was overestimated (P less than .001) 13.4% by the 1CM. Empty body water was underestimated (P less than .001) 7.8% by the 2CM, and water in gastrointestinal tract contents was overestimated (P less than .001) 41.8% by the 2CM due to its dependence on regression equations that differ between groups of cattle. The 2CM offered no advantage over the 1CM. A three-compartment model was not better than the 2CM in estimating body water compartments. Assuming the amount of empty body water associated with either empty body protein or ash to be constant seemed to be valid. Suggested values calculated from data presented in the literature for growing cattle with an empty body weight greater than 175 kg are .302 and .0668, respectively, for the ratios of protein and ash to water. The relationship between empty body fat and water was, percentage empty body fat = 94.27--(1.267)(percentage empty body water), which had a 1.25 residual standard deviation and a .98 coefficient of determination.     

Anabolic implant and frame size effects on growth regulation, nutrient repartitioning and energetic efficiency of feedlot steers

Rates of growth and partitioning of nutrients among tissues were measured in large (Simmental x [Hereford x Brahman]; n = 34) and very large (Chianina x Angus and Maine Anjou x Angus; n = 37) steers implanted with different anabolic growth regulators. All cattle were fed individually a whole shelled corn (13% crude protein) diet. Implant strategies were: none (n = 13), Ralgro 36 mg (n = 15), Ralgro 72 mg (n = 14), Synovex-S (n = 15) and Ralgro 36-Synovex-S (n = 14) administered at d 0 and 90. Empty body composition of all cattle was measured initially and at 90 d by D2O dilution procedures and at slaughter (average, 182 +/- 4.1 d) by carcass specific gravity. Empty body weight for large and very large cattle averaged 274 and 324 kg (P less than .05) initially and 497 and 603 kg (P less than .05) at slaughter. Empty body protein differed (P less than .05) for large and very large steers and averaged 51 and 61, 67 and 79, and 87 and 103 kg initially, at midpoint and at slaughter, respectively. Percentage empty body fat was lower for very large steers (13.5 vs 15.6%) initially (P less than .05) but was similar for very large and large steers at the midpoint (18.7 vs 18.1%) and at slaughter (23.2 vs 21.9%). Daily rates of empty body gain (DEBG) were greater (P less than .05) for very large vs large steers for both growing and finishing periods and averaged 1.53 vs 1.26 kg/d overall. Daily rates of protein gain (DPG) were similar for very large and large steers for the growing phase (204 vs 202 g/d) but greater (P less than .05) in very large steers for the finishing phase and overall (253 vs 204, and 229 vs 202 g/d). All implant strategies, except R36, increased DEBG and DPG and tended to decrease the percentage of fat in daily gain. In both large and very large cattle, implant growth regulators increased growth rate and partitioned nutrient use away from fat toward protein accretion, with the magnitude of partitioning toward protein increasing with greater rates of growth. These data indicate that anabolic growth regulators are viable strategies to enhance lean beef production in steers, regardless of animal size.     

Relationship between fatty acid-binding protein activity and marbling scores in bovine longissimus muscle

Studies were conducted in an attempt to establish a relationship between fatty acid-binding protein (FABP) activity and marbling score in bovine longissimus muscle. Longissimus muscle was obtained from four 20-mo-old Charolais-Hereford crossbred heifers, three 16-mo-old Angus steers, and four 18-mo-old Angus steers. Immediately after slaughter, longissimus muscles were removed for the extraction of FABP. Supernatant (S104) fractions containing 41.3 to 144 mg of protein (depending on animal group) were eluted over Sephadex columns, and elution fractions were analyzed for the binding of radiolabeled palmitoyl-coenzyme A (CoA). Specific activities of FABP were 23, 32, and 101 nmol palmitoyl-CoA bound/mg protein for the Charolais-Hereford, 16-mo-old Angus, and 18-mo-old Angus cattle, respectively. These preliminary results suggested that longissimus muscle FABP activity was positively correlated with marbling score. To test specifically for this possibility, longissimus muscle was obtained at slaughter from each of four Wagyu steers, Angus heifers and Braford heifers. Marbling scores taken at the 12th-13th rib junction were Sm45, Sm43, and SI50 for the Wagyu, Angus, and Braford cattle, respectively. Interfascicular adipose tissue was exhaustively removed from sections of the 5th to 8th thoracic region of the longissimus muscle to eliminate any contribution of adipose tissue to FABP activity. For each animal, 300 mg of the S104 were eluted over Sephadex columns. Specific activities for the Wagyu, Angus, and Braford longissimus muscle FABP were 3.1, 3.8, and 3.9 pmol palmitoyl-CoA bound/mg protein, respectively, and were not different (P greater than .05) among the three animal groups.(ABSTRACT TRUNCATED AT 250 WORDS)     

Periodic changes in body composition and in priorities for tissue storage and retrieval in mature beef cows.

Sixty mature (4 to 6 yr), nonpregnant, nonlactating beef cows of two breed types, Angus (n = 30) and Simmental (n = 30), were used in a four-period, split-plot study (371 d) to determine the seasonal differences in body composition. Periods were chosen to represent each of the four seasons in one year that ran consecutively from June 14, 1986 to June 20, 1987. Initially, all cows were assigned randomly within breed type to one of four feeding levels based on the cows' estimated maintenance requirement (75, 87.5, 112.5, and 125% of weight maintenance) and were rotated such that all animals were fed at all four feeding levels during the course of the study. Body composition was estimated via isotope dilution initially and at the end of Periods 1 through 3 and via derived regression relationships after Period 4. Body composition differed by breed; Simmental cows had greater (P less than .05) amounts of empty body protein (79.4 vs 55.8 kg, respectively) and less (P less than .05) empty body fat (85.3 vs 93.9 kg, respectively) than the Angus cows. These differences also were apparent when expressed as a percentage of live weight. Season altered components of the empty body. On the average, both breeds mobilized (P less than .05) empty body protein (-3.6 and -5.4 kg for Angus and Simmental cows, respectively) in the summer while simultaneously gaining (P less than .05) empty body fat (15.3 and 30.1 kg for Angus and Simmental cows, respectively). Both breeds subsequently tended to gain empty body protein in the winter and spring.(ABSTRACT TRUNCATED AT 250 WORDS)     

Relation of feedlot performance and certain physiological responses to the metabolizable protein and urea content of cattle diets

An experiment was conducted to test the accuracy of the metabolizable protein system in predicting the amount of urea that would be useful in a corn-based cattle diet. Treatment diets included a basal, low-protein (7.8% CP) negative control (NC) with no supplemental N and a positive control (PC) that contained soybean meal. Urea was added to the NC diet in quantities calculated to be either 25% deficient (LU), equal to (MU) or 25% in excess (HU) of the urea fermentation potential ( UFP ). In vitro rumen fermentation studies were used to determine sequential ammonia production and digestible dry matter content of the diets. In a growth trial, 12 individually-fed Angus, Hereford and Angus X Hereford steers weighing an average of 213 kg were assigned randomly to each treatment diet. At the conclusion of the 112-d trial, rumen ammonia and jugular blood urea N (BUN) concentrations were determined on two steers from each treatment before feeding and at 1, 2, 3, 4 and 5 h postfeeding. In vitro ammonia concentrations of the NC and PC treatments were lower (P less than .05) than that of urea containing diets. In vivo rumen ammonia concentrations at 1 h postfeeding and BUN levels at 3 h postfeeding were low for both the NC and PC diets compared with urea-containing diets. Both of these values increased with each successive increase of added urea to the NC diet. During the initial 70 d of the growth trial, daily gains were improved (P less than .05) by addition of urea up to the MU level, which fulfilled the calculated UFP .(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of live weight gain of steers during winter grazing: I. Feedlot performance, carcass characteristics, and body composition of beef steers

Two experiments were conducted to examine the effect of previous BW gain during winter grazing on subsequent growth, carcass characteristics, and change in body composition during the feedlot finishing phase. In each experiment, 48 fall-weaned Angus x Angus-Hereford steer calves were assigned randomly to one of three treatments: 1) high rate of BW gain grazing winter wheat (HGW), 2) low rate of BW gain grazing winter wheat (LGW), or 3) grazing dormant tallgrass native range (NR) supplemented with 0.91 kg/d of cottonseed meal. Winter grazing ADG (kg/d) for HGW, LGW, and NR steers were, respectively, 1.31, 0.54, 0.16 (Exp. 1) and 1.10, 0.68, 0.15 (Exp. 2). At the end of winter grazing, four steers were selected randomly from each treatment to measure initial carcass characteristics and chemical composition of carcass, offal, and empty body. All remaining steers were fed a high-concentrate diet to a common backfat end point. Six steers were selected randomly from each treatment for final chemical composition, and carcass characteristics were measured on all steers. Initial fat mass and proportion in carcass, offal, and empty body were greatest (P < 0.001) for HGW, intermediate for LGW, and least for NR steers in both experiments. Live BW ADG and gain efficiency during the finishing phase did not differ (P = 0.24) among treatments, but DMI (% of mean BW) for NR and LGW was greater (P < 0.003) than for HGW steers. Final empty-body composition did not differ (P = 0.25) among treatments in Exp. 1. In Exp. 2, final carcass and empty-body fat proportion (g/kg) was greater (P < 0.03) for LGW and NR than for HGW steers. Accretion of carcass fat-free organic matter was greater (P < 0.004) for LGW than for HGW and NR steers in Exp. 1, but did not differ (P = 0.22) among treatments in Exp. 2. Fat accretion in carcass, offal, and empty body did not differ (P = 0.19) among treatments in Exp. 1, but was greater (P < 0.05) for LGW and NR than for HGW steers in Exp. 2. Heat production by NR steers during finishing was greater (P < 0.02) than by HGW steers in Exp. 1 and 2. Differences in ADG during winter grazing and initial body fat content did not affect rate of live BW gain or gain efficiency during finishing. Feeding steers to a common backfat thickness end point mitigated initial differences in carcass and empty-body fat content. However, maintenance energy requirements during finishing were increased for nutritionally restricted steers that were wintered on dormant native range.     

Feedlot performance of Brahman x Angus versus Angus steers during cold weather

Ten Angus and 10 Brahman x Angus F1 steers were used in a 184-d trial to compare feedlot performance during cold weather (-9 to 26 degrees C). Both groups of steers were exposed to the same environment for the same amount of time. All steers were fed for the same number of days regardless of frame score to avoid frame score x environment interactions. Brahman x Angus steers were 30.7 kg heavier (P less than .05) than Angus steers at the start of the trial. Differences in age (Brahman x Angus 40 d younger) for the two breed groups did not affect final live weight or carcass weight. Brahman x Angus steers consumed .2% less feed (P less than .05) as a percentage of BW than Angus steers; however, there was no difference in overall feed efficiency. Angus steers had a higher yield grade, more fat at the 12th rib (P less than .05), and graded 90% Choice; only 10% of the Brahman x Angus were graded Choice. Brahman x Angus steers were taller at the hip (P less than .05) and longer from first rib to aitch bone (P less than .05) and from thoracic vertebrae (T12/T13) to point of hock (P less than .05). Hide thickness determined at the neck, belly, and rump was found to be similar (7.7 mm) between the two groups. Sample hair weight and diameter did not differ between groups. Fiber, fat, protein, and DM digestibility coefficients were similar between groups but Brahman x Angus feces had a higher DM content.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of sodium thiosulfate as an extracellular water marker in cattle.

Two studies were conducted to determine whether sodium thiosulfate (THS) can estimate extracellular water (ECW) in beef cattle in conjunction with empty body water (EBW) estimation by urea space. Experiment 1 used 24 steers (366 kg) to determine the clearance parameters for THS and urea. Blood samples were taken over 1 h. A two-component curve, Y = A1ek1(t) + A2ek2(t), (t = hours after infusion) fit the clearance of both markers; intercepts (A1, A2) and clearance coefficients (k1, k2) were 44.8, 44.4, -25.8, and -2.24 mg/dL, respectively, for THS (r2 = .98, Sy.x = 2.72, animal effects removed and 24.4, 10.5, -21.7, and -.71 mg/dL, respectively, for urea (r2 = .98, Sy.x = 1.49). Sodium thiosulfate equilibrated with ECW 5 to 10 min after infusion. Experiment 2 consisted of 22 steers (483 kg) infused with a combination solution of 20% urea, 10% THS, and 4% sodium thiocyanate (SCN; equilibration time = 28 min); half the steers were implanted with estradiol. Empty body water increased with implantation (P less than .01). Extracellular water tended to increase in implanted steers as measured by THS (12 min, P = .14) and SCN (P = .10). The estimation of ECW at 12 min was not different (P greater than .2) from the SCN estimate at 28 min (SCN = 3.7 + .873 THS; r2 = .70; P less than .001). Sodium thiosulfate gave reasonable estimates of ECW (22 to 26% of BW) and required only 0- and 12-min blood samples.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lipogenesis in acute and 48-hour cultures of bovine intramuscular and subcutaneous adipose tissue explants

In this study, the interactions among breed of cattle, adipose tissue site and specific incubation conditions were investigated. Subcutaneous and i.m. adipose tissues were obtained from 10 Angus and 9 Santa Gertrudis steers immediately postmortem. Adipose tissue explants were incubated acutely for 2 h immediately at slaughter or after being cultured 48 h with or without 1 mU/ml insulin and 30 mg/ml bovine serum albumin; the incorporation of 14C-labeled acetate and glucose (5 mM, plus 5 mM unlabeled lactate) into lipid fractions was measured. AT the same chronological age, Angus steers had a more youthful lean maturity score, higher USDA marbling score and higher USDA quality grade (P less than .05) than did carcasses from Santa Gertrudis steers. The lower marbling score of the Santa Gertrudis steers was paralleled by smaller i.m. adipocytes (P less than .05) relative to Angus steers. Pentose cycle reductase and NADP-malate dehydrogenase activities were greater in Angus i.m. adipose tissue than in Santa Gertrudis i.m. adipose tissue, which would provide more reducing equivalents (NADPH) and glycerol for fatty acid biosynthesis and triacylglycerol esterification. Correspondingly, Angus i.m. adipose tissue exhibited a greater rate of lipogenesis from acetate and glucose (P less than .05) than did Santa Gertrudis i.m. adipose tissue in acute incubations. The presence of insulin resulted in higher rates of lipogenesis from acetate in Angus s.c. adipose tissue than in Santa Gertrudis s.c. adipose tissue after 48 h of explant culture. These data indicate that i.m. and s.c. adipose tissues exhibit aspects of lipid metabolism unique to each tissue and suggest that breed-related differences in adipose tissues may explain the divergent responses to insulin observed in different laboratories.     

Growth and metabolism in somatotropin-treated steers: II. Carcass and noncarcass tissue components and chemical composition

Carcass and noncarcass tissue compositional characteristics were determined in growing Hereford steers treated with daily subcutaneous injections (20.6 mg/d) of recombinantly derived bovine somatotropin (rBST) for 112 d. For carcass primal cuts, weights and rates of gain of bone, lean and total fat and site of fat deposition were not significantly affected by rBST treatments with the exception of a few tissues (loin total weight, flank total and lean weight and shank total weight). Lean to fat ratios, however, were greater (P less than .1) for the loin, flank, chuck and brisket. Weights and growth of individual muscles from the hindquarter were not affected by rBST administration. Weights and(or) average daily gains of the liver, kidneys, lungs and trachea and head were greater (P less than .05) in rBST-treated animals. Weights and (or) average daily gains were greater (P less than .1) in rBST-treated steers for water in the total body and carcass, for CP in the total body and noncarcass, and for ash in the total body, carcass and noncarcass. Ratios of CP to ether-extractable fat in the total body were greater (P less than .1) in rBST steers. These data indicate that rBST modified carcass lean and fat composition in cattle, but responses were modest compared to effects of somatotropin treatment of swine.     

Influence of zeranol and breed on growth, composition of gain, and plasma hormone concentrations

Seven Angus and six Brangus steers averaging 225 and 245 kg, respectively, were assigned randomly to zeranol (36 mg) implant (I) and no implant (NI) treatments. Steers had ad libitum access to a corn silage diet plus .68 kg of a soybean meal-based supplement fed daily. Steers were bled via jugular catheters on d 0, 28, 56, and 84 at 15-min intervals for 4 h before and 4 h after feeding. Concentrations of growth hormone (GH), insulin (INS), triiodothyronine (T3), thyroxine (T4), and glucose were determined. Whole-body protein and fat contents were monitored. A breed x I interaction (for d 56 to 84 and d 0 to 84) was observed for ADG (P less than .05 and P less than .07, respectively), feed conversion (P less than .05 and P less than .07, respectively), and protein deposition (for d 0 to 29 and d 0 to 84; P less than .07 and P less than .05, respectively). These interactions were attributed to a greater response to I by Angus than by Brangus steers. A feeding x period interaction (P less than .10) was observed for mean GH concentration, and INS, T4, and T3 concentrations were higher (P less than .05) during the 4-h postfeeding period than during the 4-h prefeeding period. The implant increased (P less than .08) mean GH concentration but did not alter the frequency, duration, or amplitude of plasma GH peaks. Steers that were implanted had lower (P less than .05) plasma T3. Brangus steers had lower (P less than .05) plasma glucose, T3, and T4 concentrations than Angus steers. Results indicate that growth factors beyond those measured are responsible for the anabolic response to zeranol.     

Hormone secretory patterns, pituitary characteristics and selected blood metabolites in feedlot steers implanted with growth stimulants

Twelve Charolais-crossbred steers (256 kg) received one of three treatments: nonimplanted controls (C), implanted initially and at 84 days with 36 mg zeranol (Ralgro, R) and implanted initially and at 84 days with 200 mg of progesterone and 20 mg of estradiol benzoate (Synovex-S,S). All steers were fed a corn-based diet (calculated metabolizable energy 2.89 Mcal/kg dry matter) ad libitum. In a parallel comparative slaughter trial, rates of empty body protein accretion were increased 14% in R and 24% in S steers (P less than .01). R and S steers in the present study had heavier pituitary weights (P less than .001), more pituitary growth hormone content (P less than .04) and more pituitary weight/unit live weight (P less than .05) than did C steers. Cattle implanted with R or S exhibited an increased growth hormone (GH) secretory response to a pituitary challenge with thyrotropin releasing hormone (TRH). Plasma insulin profiles were not significantly altered, but tended to be greater for steers given implants. Overall 9-hr GH secretory profiles were not affected by implantation. Plasma urea N at 94 days post-implantation was decreased (P less than .01) by implantation. Plasma glucose was increased (P less than .04) at both 94 and 199 days in R and S vs C steers. Overall mean and total (integrated area) plasma GH, as well as secretory profile components (baseline mean, amplitude of secretory spikes) were negatively correlated with body weight and size on days 94 and 199. Overall mean, baseline and integrated area of plasma insulin on days 94 and 199 were positively related to body weight and size. Thus positive protein anabolic growth responses from implantation (parallel comparative slaughter trial) were coupled with increased pituitary GH content and little change in circulating plasma GH concentrations between implanted and control steers. This may suggest that changes in tissue sensitivity, an increased plasma clearance rate of GH and/or a direct effect on target tissues may be involved in the improved growth performance of cattle implanted with R or S.     

Procedural and mathematical considerations in urea dilution estimation of body composition in lambs

Two experiments (n = 46 and 56, respectively) were conducted to evaluate urea dilution as an estimator of body composition in lambs and to address certain procedural and mathematical considerations in this technique. In Exp. 1, 14 blood samples were taken over 240 min after urea infusion. The equation describing the urea clearance curve was: delta PUN = 9.7e-.1727(min) + 10.4e-.0021(min), pools 1 and 2, respectively (r2 = .99, P less than .001; individual lamb effects removed). In the combined experiments, urea space (US) was related to percentage of empty body water (PEBH2O) by the equation 31.7 + .471 US (empty body weight basis; r2 = .56, P less than .001). The regression equation indicates that the US-PEBH2O relationship in lambs is different from that reported in cattle, even though urea clearance kinetics are similar. Although the prediction equations appeared to be biologically valid, considerable error was associated with the composition estimates. The PEBH2O was predicted as well by live weight (r2 = .69; SEy.x = 3.0) as by US in these experiments. The two-sample method (T12 minus T0) to determine the change in marker concentration was shown to be related more closely (r2 = .56) to PEBH2O than the standard multisample extrapolation to T0 method (r2 = .0 and .38 for pools 1 and 2, respectively). An equilibration time of 9 to 12 min provided the best estimate of body composition in lambs.(ABSTRACT TRUNCATED AT 250 WORDS)     

Anabolic effects on rate, composition and energetic efficiency of growth in cattle fed forage and grain diets

The effects of anabolic implants on rate, composition and energetic efficiency of growth were determined in steers fed diets varying in forage and grain content. Santa Gertrudis-cross steers averaging 337 kg were group-fed (n = 72) or individually fed (n = 45) ad libitum one of three diets and either not implanted or implanted (90-d intervals) with Ralgro or Synovex-S implants. Steers were fed to a similar empty body weight (463 kg). Initial empty body composition of individually fed steers was determined via D2O dilution, and final composition of all steers was determined by carcass specific gravity. Rate of empty body gain increased (P less than .05) from 695 g/d for nonimplanted steers to 798 and 844 g/d for Ralgro- and Synovex-implanted steers. Anabolic implants increased (P less than .01) daily empty body protein gain from 91 to 119 and 133 g for Ralgro and Synovex, an increase of 31 and 46%, respectively. The fraction of protein in empty body gain increased (P less than .01) from 13.8% to 15.6 and 15.9%, and the percentage of fat in empty body gain decreased (P less than .01) from 41.7% to 32.9 and 31.3% with Ralgro and Synovex, respectively. Daily rates of protein deposition increased at a decreasing rate, and rates of fat deposition increased at an increasing rate with increasing rate of empty body gain. Implanted steers deposited more protein and less fat at any rate of growth; the magnitude of this shift in nutrient partitioning from fat to protein growth increased with rate of growth.(ABSTRACT TRUNCATED AT 250 WORDS)     

Nitrogen metabolism in crossbred steers with varying levels of Brahman using a nitrogen depletion-repletion regimen

Nine N metabolism trials were conducted in a N-depletion-repletion regimen using five breed crosses of steers with 0, 25 or 50% Brahman. Three steers from each breed cross (avg initial wt 239 kg) were standardized for 3 wk on an 18% protein diet and depleted for 5 wk on a 7.5% protein diet and then repleted for 4 wk on the 18% protein diet. Nitrogen balance and blood and urinary N metabolites were monitored to determine changes in metabolic status due to changes in dietary N intake. Reduced N intake during the depletion period almost completely inhibited fiber digestion (P less than .01), while ruminal ammonia concentration fell from an average concentration of 156 during standardization to 22 mg/liter (P less than .01) during depletion. Organic matter digestion was depressed (P less than .05) due to the reduced fiber digestion. Absolute amounts of intake, fecal, urinary, absorbed and retained N were severely depressed during depletion. Apparent digestibility of N was reduced from an average of 68% during standardization to 42% (P less than .05) during depletion, but truly digested N was not affected. Nitrogen retained, as a percentage of intake, or absorbed was reduced only during the first week of depletion. Urea N comprised the major identified urinary fraction during standardization and repletion, whereas creatinine was the major fraction during depletion. Brahman-cross steers excreted more urinary N (P less than .1) and retained less N (P less than .13) during repletion than Angus X Hereford steers. Creatinine excretion was also higher (P less than .01) during depletion for Brahman-cross steers. Blood urea and albumin N concentrations were higher (P less than .05) during both depletion and repletion among Brahman crosses. These experiments suggest that blood measurements were more sensitive than N balance to changes in dietary N state and that faster recharge of blood N measurements in Brahman cattle may help mitigate adverse effects of N depletion stress.     

Dietary energy density and frame size effects on composition of gain in feedlot cattle

Experiments were conducted to evaluate the effects of dietary energy density or genetic background on protein and fat gain of growing cattle. In Exp. 1, 24 Limousin steers were used in a growing-finishing trial. A 2 X 2 factorial arrangement was used with steers randomly allotted to four treatment combinations and fed the following diets: 80% concentrate, high moisture corn-corn silage diet (HI) or a corn silage diet (LO) during both the growing (GRO) and(or) the finishing (FIN) phases. Body composition for both experiments was determined by a deuterium oxide dilution technique. Empty body weight gains were greater (P less than .05) for HI during GRO, FIN and the total trial. Daily protein gains (DPG) were greater (P less than .05) for HI during GRO and FIN, while cattle receiving HI during at least FIN had the greatest (P less than .05) overall DPG. Daily fat gains (DFG) followed the pattern of DPG, being more rapid (P less than .05) for cattle fed HI during either GRO or FIN. Cattle fed the HI diet also tended to be more energetically efficient. In Exp. 2, large frame (LG) and small frame (SM) cattle were used for the evaluation of frame size effects on protein and fat deposition. Steers were individually fed an 80% concentrate, corn-based diet during the entire trial. Average daily gains and daily dry matter intake (P less than .05, P less than .01) were greater for LG, while feed efficiency was similar for both cattle types. Large cattle had greater (P less than .05) DPG than SM cattle, however, DFG were not different. Small frame steers were energetically more efficient (P less than .05), apparently due to composition of gain difference.     

安秦F_1代、和秦F_1代与秦川牛生长性能比较

[目的]为探讨安秦F1代与和秦F1代与秦川牛的生长发育情况。[方法]选择安秦、和秦、秦川公牛各10头作为2个试验组和1个对照组,测定6、12、18、24月龄的空腹体重、体长、体高、胸围数据,并进行比较分析。[结果]表明,在集约化饲养条件下,6～24月龄的安秦F1代体重及各项体尺指标,均显著高于秦川牛（P〈0.05）,和...     

Factors influencing intermuscular fat and other measures of beef chuck composition.

Carcasses from 59 steers produced from the mating of Braford, Simbrah, Senepol, and Simmental bulls to Brahman- and Romana Red-sired cows and Brahman bulls mated to Angus cows were used in this study. Effects of sire breed and feeding calves vs yearlings on fat depots in the chuck, when steers were fed to 1.0 cm external fat, were determined. Breed of sire and feeding calves vs yearlings had no effect (P greater than .05) on percentage of intermuscular fat. However, carcasses from Braford-sired steers had a higher (P less than .05) percentage of dissectable subcutaneous fat on the chuck than did those from other breed groups. Carcasses from Simmental-sired steers were superior (P less than .05) to those from Braford-sired steers in USDA yield grade and had a higher average marbling score (P less than .05) than the Simbrah-sired group. Estimated kidney, pelvic, and heart (KPH) fat was higher (P less than .05) in carcasses from Brahman-, Simbrah-, and Senepol-sired steers than in Braford-sired steers. Steers fed as calves had higher percentages (P less than .05) of KPH fat and major chuck muscles than did those fed as yearlings. The best single predictor of percentage of intermuscular fat within the chuck was adjusted fat over the ribeye (R2 = .46).