Evaluation of mating systems involving five breeds for integrated beef production systems: I. Cow-calf segment.

Deterministic computer models were used to simulate the cow-calf segment of an integrated production system. Angus, Charolais, Hereford, Limousin, and Simmental breeds were included in three mating systems: pure-breeding (PB) or two- (2R) or three-breed (3R) rotational crossbreeding. Breed data were taken from the literature. Herds were evaluated over the production year. Sires represented breed averages and were available from sources outside their herds, and 100 replacement heifers were saved annually. Females in 3R had the highest average energy requirements (8,144 Mcal of ME.cow-1.yr-1) and production costs ($322.31.cow-1.yr-1), and PB females had the lowest average requirements (7,748 Mcal of ME.cow-1.yr-1) and costs ($313.2.cow-1.yr-1). Purebred systems were the least biologically and economically efficient (64.9 Mcal of ME/kg of steer equivalent, $2.35/kg of steer equivalent), respectively, and 3R systems were the most efficient (56.6 Mcal of ME/kg of steer equivalent, $1.95/kg of steer equivalent). On average, 3R systems were more efficient biologically and economically than 2R systems. However, some 2R systems were as efficient as some 3R systems. Crossbred combinations containing Angus and(or) Hereford ranked more biologically and economically efficient than other breed combinations. Conversely, British purebreds ranked more biologically efficient, whereas Continental purebreds ranked more economically efficient.     

Evaluation of mating systems involving five breeds for integrated beef production systems: III. Integrated system.

Angus (A), Charolais (C), Hereford (H), Limousin (L), and Simmental (S) breeds were included in deterministic computer models simulating integrated cow-calf-feedlot production systems. Three mating systems were used: pure-breeding and two-and three-breed rotational crossbreeding. Breed information was taken from the literature. Herd sizes were unrestricted; however, 100 heifers were saved as replacements. Cows were removed for reproductive failure, age (greater than 10.5 yr), or death. Calves produced in the cow-calf segment were fed in a custom feedlot to four slaughter end points: 440 d, 457 d, 288-kg carcass weight, and low Choice. All animals were fed to requirements. Cull cows were slaughtered after weaning. Biological and economic efficiencies improved with crossbreeding; however, rankings of breed combinations depended on how efficiencies were measured (weight, lean, or value basis). Among purebreds, reproductive performance had a large influence on breed rankings at age and weight end points, whereas feedlot performance was important at the low Choice end point. Crossbred combinations involving British (A or H) and Continental (C or S) breeds were more efficient than other crossbred combinations at all end points. However, choosing specific breed combinations for integrated systems depends on slaughter end points, market end points (weight vs lean), and measures of efficiency (weight, lean, or value basis).     

Evaluation of Egyptian sheep production systems: II. Breeding objectives for purebred and composite breeds

Objectives for this study were to estimate relative economic weights for performance traits for two native and two composite sheep breeds under two management systems in Egypt. Breeds studied were Rahmani (R), Ossimi (O), 3/4R-1/4Finnish Landrace (RFR), and 3/4O-1/4Finn (OFO); OFO and RFR were composite breeds. Management systems were one mating season per year (1M) and three mating seasons per 2 yr (3M). A dynamic computer model was used to simulate animal performance and enterprise efficiency and profit. Input parameters for the model were obtained from published results and analyses of data collected from experimental flocks of the same genetic stocks in Egypt. Responses for two measures of life-cycle feed conversion and one measure of enterprise profit were evaluated. Life-cycle feed conversion was calculated as kilograms of TDN input per kilogram of empty body weight output (TDN/EBW) and kilograms of TDN input per kilogram of carcass lean output (TDN/CLN). Profit was measured as annual gross margin/ewe (GM/EWE). Traits evaluated were conception rate (CR), lambing rate (LR), mortality rate (MR), mature weight (MW), and milk production (MK). Based on responses to percentage changes in trait means, CR was most important for TDN/EBW, followed by LR and MR. For TDN/CLN, LR, MR, and CR were most important. For GM/EWE, CR was most important, followed by LR, MW, and MR. In the systems studied, there was little response to changes in MK. Based on changes in GM/EWE per genetic standard deviation change, LR was most important, followed by CR, MR, MW, and MK in all systems. Relative economic weights for O and OFO were similar, as were weights for R and RFR. Differences in economic weights between management systems for the same breed were not large enough to justify separate selection lines within breeds.     

Evaluation of crossbreeding systems for small beef herds: II. Two-sire systems

Stochastic computer models were used to evaluate nine crossbreeding systems in beef herds consisting of two bulls, 50 cows and 15 replacements. Systems examined were: 1) purebred (PB), 2) two- and three-breed rotations using natural service (2R and 3R) or artificial insemination (2RAI and 3RAI), 3) two-breed roto-terminals not exploiting complementarity using natural service (2RT) or AI (2RTAI) and 4) two-breed roto-terminals exploiting complementarity using natural service (2RTC) or AI (2RTCAI). Average heterosis estimates were taken from literature sources. Replacement females were produced within the herd; sires were purchased. Estimates of calf and dam heterosis were used to calculate performance of calf weight weaned and sold, cow and total weights sold and gross calf, cow and total incomes. All crossbred systems were superior to PB for weights sold and income. The natural-service systems (2R, 3R, 2RT and 2RTC) utilized 90 to 98% of the heterosis available in their AI counterparts (2RAI, 3RAI, 2RTAI and 2RTCAI). No differences were found between corresponding natural-service and AI systems for weights sold and incomes. Increasing the complexity of the system did not provide important improvements in traits measured.     

Forage systems for beef production from conception to slaughter: II. Stocker systems.

Fall weaned Angus calves grazed stockpiled 1) tall fescue (Festuca arundinacea Schreb.), 2) tall fescue-red clover (Trifolium pratense L.), or 3) tall fescue-alfalfa (Medicago sativa L.) or were barn-fed, 4) tall fescue hay, 5) orchardgrass (Dactylis glomerata L.)-alfalfa hay, or 6) tall fescue silage from late October to early April during each of 5 yr. Infection of the fescue with Acremonium coenophialum ranged from 0 to 55%. There were two replications each of steers and heifers for each forage system in a completely random design. Each replicate was grazed by three Angus stockers, except for System 1, which was grazed by six stockers, for a total of 420 stockers. Each pasture replicate contained .8 ha (except System 1, which was 1.6 ha), and the stocking rate was one stocker per .27 ha. Fescue hay and silage were harvested each spring for barn-fed systems from the area stockpiled for grazing by cattle in System 1. Nitrogen fertilizer (90 kg/ha) was applied in early spring and again in early August, before stockpiling; no N was applied to stockpiled fescue grown with legumes. Daily gains by calves grazing stockpiled fescue-alfalfa were greater (P less than .01) than by calves grazing stockpiled fescue-red clover or N-fertilized stockpiled fescue (.50, .33, and .34 kg/d, respectively), but fescue-alfalfa calves required more days (P less than .01) of supplemental hay feeding (105, 60, and 36, respectively). Calves fed fescue hay in the barn gained more (P less than .01) than those fed fescue silage.(ABSTRACT TRUNCATED AT 250 WORDS)     

Evaluation of cattle breeds for beef production in New Zealand—A review

Important differences are noted between the New Zealand and European cattle industries, in terms of both breeds and farming systems. Under pasture feeding, experimental data strongly suggest that selection and genetic evaluation for growth performance should be based on weight-for-age rather than on post-weaning weight gains. Carcass merit is more appropriately measured by the yield of trimmed boneless retail cuts than by accepted commercial grades.Relative to the nationally predominant Angus beef breed, research results demonstrate an advantage in final and carcass weight per animal of 5–10% for the Hereford and 20–30% for the Friesian, with the superiority being approximately halved in crossed with the Angus. In terms of weaning performance, the Friesian dam is greatly superior, the Hereford slightly inferior, to the Angus. Heterosis for growth traits is of the order of 5%.In crosses over Jersey cows the Charolais sire is superior to the Hereford but not to the Friesian for total meat output. Carcasses from the dairy breeds and dairy x beef crosses slaughtered at the same age contain a higher bone percentage and are less acceptable on traditional export grading standards than those of the British beef breeds, but nevertheless achieve high output and quality of lean meat.Preliminary results from current large-scale trials suggest that the larger European breeds have potential for improving growth rate and meat yield in crosses with local Angus and Hereford cattle but are more prone to difficult calvings and show later sexual maturity.     

Economic evaluation of alternative crossbreeding systems involving four breeds of swine. II. System efficiency

A static, deterministic computer model was used to calculate production efficiency (cost per kg of product) for four purebred and 69 alternative crossbreeding systems involving the Duroc, Yorkshire, Landrace and Spotted breeds of swine. Crossbreeding systems were defined as including all purebred, crossbred and commercial matings necessary to maintain a total of 10,000 farrowings. Driving variables for the model were predicted mean conception rates, litter size born, preweaning survival rate, postweaning average daily gain, feed-to-gain ratio and carcass backfat. Predictions were computed using breed effect and heterosis estimates obtained from experimental data involving the four breeds collected at the Oklahoma Agricultural Experiment Station between 1976 and 1979. The most efficient breed combinations for each of the nine types of crossbreeding systems evaluated were predicted to reduce cost per kg of product by 6.7 to 10.5%, relative to the most efficient purebred (Duroc). The Duroc X (Yorkshire, Landrace, Spotted) four-breed rotaterminal was predicted to be the most efficient system, followed by the Duroc X (Yorkshire, Landrace) rotaterminal. Duroc X (Spotted X Landrace) and Duroc X (Spotted X Yorkshire) static systems ranked third and fourth overall, respectively. Sensitivity analysis indicated that ranking of systems predicted to be most efficient under the default model was reasonably robust to varying input economic, genetic and management parameter values. Results of this study suggested that three- or four-breed rotaterminal or static systems should maximize effective use of heterosis and breed complementarity in swine production systems.     

Bioeconomic evaluation of embryo transfer in beef production systems: II. Economic evaluation of steer production.

A bioeconomic model was developed and used to evaluate economic implications of embryo transfer for steer production. Sensitivity analysis indicated that the net returns were strongly influenced by pregnancy and growth rates. Matching of recipient and embryo sizes reduced dystocia prevalence and resulted in as much as a $98 saving per transfer in costs associated with dystocia. Optimal weight and age and net returns at slaughter were found to be a function of mature size and growth rate. Varying growth rates resulted in optimal slaughter weight and net present value (NPV) ranging from 403 to 494 kg and $156 to $273, respectively, for medium-sized steer genotypes characterized by a mature size of 600 kg. The optimal slaughter weight ranged from 456 to 607 kg and NPV from $182 to $344 for large-sized steer genotypes characterized by a mature size of 750 kg. The results showed that high pregnancy rates and embryos with high growth rates generated the greatest profitability from investment in embryo transfer. The model has a wide potential application in formulating optimal biological and economic strategies for matching embryo genetic resources to physical and economic environments for commercial beef production.     

Record systems for beef stocker production enterprises.

The accelerated growth of individual animal identification systems is likely to generate significant amounts of data that need to be synchronized, filtered, analyzed, managed, and acted on in real time by data-mining software and animal health professionals who possess a dual understanding of beef systems production and technology associated with management information and record-keeping systems. Ultimately, the resulting information can be used seamlessly throughout a vertically coordinated production system to conduct management and animal health compliance audits, initiate timely animal and product recall measures, and reveal complex biologic and economic relations.     

Forage systems for beef production from conception to slaughter: I. Cow-calf production.

Six year-round, all-forage, three-paddock systems for beef cow-calf production were used to produce five calf crops during a 6-yr period. Forages grazed by cows during spring, summer, and early fall consisted of one paddock of 1) tall fescue (Festuca arundinacea Schreb.)-ladino clover (Trifolium repens L.) or 2) Kentucky blue-grass (Poa pratensis L.)-white clover (Trifolium repens L.). Each of these forage mixtures was combined in a factorial arrangement with two paddocks of either 1) fescue-red clover (Trifolium pratense L.), 2) orchardgrass (Dactylis glomerata L.)-red clover, or 3) orchardgrass-alfalfa (Medicago sativa L.), which were used for hay, creep grazing by calves, and stockpiling for grazing by cows in late fall and winter. Each of the six systems included two replications; each replicate contained 5.8 ha and was grazed by eight Angus cow-calf pairs for a total of 480 cow-calf pairs. Fescue was less than 5% infected with Acremonium coenophialum. Pregnancy rate was 94%. Cows grazing fescue-ladino clover maintained greater (P less than .05) BW than those grazing bluegrass-white clover, and their calves tended (P less than .09) to have slightly greater weaning weights (250 vs 243 kg, respectively). Stockpiled fescue-red clover provided more (P less than .05) grazing days and required less (P less than .05) hay fed to cows than stockpiled orchardgrass plus either red clover or alfalfa. Digestibilities of DM, CP, and ADF, determined with steers, were greater (P less than .05) for the orchardgrass-legume hays than for the fescue-red clover hay. All systems produced satisfactory cattle performance, but fescue-ladino clover combined with fescue-red clover required minimum inputs of harvested feed and maintained excellent stands during 6 yr.     

Evaluation of life-cycle herd efficiency in cow-calf systems of beef production

A deterministic beef efficiency model (BEM) was used to evaluate life-cycle herd efficiency (LCHE) in cow-calf beef production systems using four breed groups of beef cattle. The breed groups were Beef Synthetic #1 (SY1), Beef Synthetic #2 (SY2), Dairy Synthetic (DS), and purebred Hereford (HE). The LCHE was defined over the lifetime of the herd as the ratio of total output (lean meat equivalent) to total input (feed equivalent). Breed differences in LCHE were predicted with the larger/slower maturing DS being most efficient at each age of herd disposal and reproductive rate. This was mainly because, at any average age at culling, the dams of DS breed group were less mature and so had been carrying relatively lower maintenance loads for shorter periods and positively influencing LCHE. Higher LCHE was predicted with improvement in reproductive performance if there were no associated extra costs. However, this declined markedly if there was a delay in marketing of offspring. As average age at culling increased from 4 to 6 yr, efficiency declined sharply, but it began to recover beyond this age in most breed groups. We concluded that the slower maturing DS breed group may be more efficient on a herd basis in cow-calf systems and that improvements in reproductive rate not associated with extra costs improve life-cycle efficiency. Culling cows soon after their replacements are produced seems efficient.     

Comparison of alternative beef production systems based on forage finishing or grain-forage diets with or without growth promotants: 1. Feedlot performance, carcass quality, and production costs

Forty Angus-cross steers were used to evaluate 5 beef cattle management regimens for their effect on growth performance, carcass characteristics, and cost of production. A 98-d growing phase was incorporated using grass silage with or without growth promotants (trenbolone acetate + estradiol implants, and monensin in the feed) or soybean meal. Dietary treatments in the finishing phase were developed, with or without addition of the same growth promotants, based on exclusive feeding of forages with minimal supplementation or the feeding of barley-based diets. Overall, ADG for animals treated with growth promotants or fed supplemented diets (soybean meal and barley) was increased (P < 0.01) by 25 and 21%, respectively, compared with steers reared on grass silage alone and not treated with growth promotants. Except for HCW (P < 0.01), the use of growth promotants did not affect carcass measurements. Increasing the proportion of barley in the diet of steers finished on forage produced a heavier HCW (P < 0.01) and a greater (P < 0.01) quality grade. Because of their lower HCW and quality grade, cattle targeted to a forage-fed, nonimplanted beef market would need to garner a 16% premium to be economically competitive with cattle finished conventionally.     

五种肉牛品种杂交改良青海黄牛的效果对比

蓝白花牛、皮埃蒙特牛、利木赞牛、夏洛莱牛、德国黄牛都是我国引进的大型肉牛品种,用于改良本地黄牛.为了探讨不同肉牛品种杂交改良青海黄牛的效果,从而筛选最佳品种杂交组合,互助县于2002-2004年利用蓝白花牛、皮埃蒙特牛、利木赞牛、夏洛莱牛、德国黄牛细管冻精与青海黄牛进行杂交,对杂种F1牛进行了不同生长发育阶段的体重及体尺测定,以研究不同品种杂交牛的生长发育情况及产肉性能.     

Simulated efficiency of range beef production. II. Fertility traits

A modified version of the Texas A&M University Beef Cattle Production Model was used to simulate the effects of changes in potential for age at puberty (AAP), potential for probability of conception (PCA) and winter feed levels on biological and economic efficiency of beed production in a northern plains, range environment. Two management systems were simulated: a weanling system in which all calves except replacement heifers were custom fed in a feedlot immediately post-weaning; and a yearling system in which calves were kept on the ranch through their second summer, then custom-fed. Biological efficiency was defined as the ratio of TDN input to product output, and economic efficiency was defined as the ratio of total dollar cost to 100 kg product output. A simulated increase in AAP from 365 to 425 d resulted in slightly decreased economic efficiency under a yearling system of management. An increase in PCA from .75 to .85 caused decreased biological efficiency under both weanling and yearling management systems, suggesting biological inefficiencies associated with maintaining mature cows. Simulation results indicate that optimal supplementation levels and corresponding levels of observed fertility depend on the value of product derived from cull cows relative to the value of product derived from fed animals and on the costs of developing replacement heifers relative to the costs of maintaining mature cows. Decreased fertility causes change in the sources of products, not product loss per se. For this reason, survivability may be a more important aspect of reproduction than fertility.     

Breeding objectives for beef cattle used in different production systems: 1. Model development

A bio-economic model was developed to evaluate utilization of beef bulls in a variety of production systems. The model can simulate life-cycle production of both beef and dairy cow herds with or without an integrated feedlot system. The Markov chain approach is used to simulate herd dynamics. The herd is described in terms of animal states and possible transitions among them. Equilibrium herd structures of the integrated production systems are calculated in their stationary states. The economic efficiency of each system is a function of biological traits of animals and of management and economic parameters. The model allows estimation of marginal economic values for 16 traits separately in each system. The economic weight for each trait or direct and maternal trait component in each selection group and breed of interest is then calculated as the weighted sum of the economic values for the trait in all production systems in which the selection group has an impact. Weighting factors for each system are computed as the product of the number of discounted expressions for direct and maternal trait components transmitted in that system by the selection group and the proportion of total cows belonging to each system.     

Evaluation of intensive vs extensive systems of beef production and the effect of level of beef cow milk production on postweaning performance

Charolais-sired calves from three groups of beef cows, similar in growth potential and mature size but different in genetic potential for milk production (5.6, 7.7, 9.0 kg/d; low, medium, and high, respectively), were allotted to two beef production systems each year for 3 yr. At weaning, calves in an intensive (Int) system went directly into the feedlot for finishing (236 d); calves in an extensive (Ext) system were wintered on corn residues (195 d), grazed pasture (115 d) and then were finished (122 d). Postweaning effects of increased weaning weight due to increased level of milk were small and not affected by growing-finishing system. Only the steer calves from the low milk-producing cows showed evidence (P less than .01) of compensatory growth postweaning in response to reduced levels of milk during the suckling phase. Cattle from the Ext system were heavier (P less than .01) before (388 vs 233 kg) and after (595 vs 531 kg) the finishing phase than Int system cattle. During finishing, cattle from the Ext system made more rapid gains (1.70 vs 1.36 kg/d) and consumed more feed (12.4 vs 8.5 kg/d, 2.52 vs 2.19% of average BW) but were less efficient (.137 vs .160, gain/feed) than cattle from the Int system (P less than .05). Extensive systems of beef production produced more total kilograms of beef per animal but they were 196 d older at slaughter.     

Bioeconomic evaluation of embryo transfer in beef production systems: I. Description of a biological model for steer production.

Concepts used to derive a deterministic model for evaluating embryo transfer for commercial steer production taking into consideration genetic merit for growth and mature size, herd feed supply, and recipient maternal environment are discussed. Genetic potential of an embryo is used to derive optimal growth rates that can be sustained by available herd feed per animal per day. Equations are provided for various measures of performance as functions of the feed, genotype of the embryo, and recipient maternal contribution. To assess the value of a particular line of embryos, interactions between genotype and nutrient environment are quantified, so that the benefits of embryos of high genetic merit are evaluated objectively. Product quality and weight are predicted from the model to provide a framework that will allow commercial beef producers to determine marketing strategies likely to result in optimal return.