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).     

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 calving seasons and marketing strategies in Northern Great Plains beef enterprises: I. Cow-calf systems

A bioeconomic computer model was used to evaluate alternate calving seasons in a cow-calf enterprise under range conditions representative of the Northern Great Plains. The simulated ranch utilized a rotational breeding system based on Hereford and Angus and had a fixed forage base (4,500 animal unit months of native range, 520 t of grass hay, and 183 t of alfalfa hay). Calving seasons studied were spring (SP, beginning March 15), summer (SU, beginning May 15), and fall (FA, beginning August 15). Weaning dates were October 31, December 15, and February 1, for SP, SU, and FA. The SP system was also simulated with a 5% increase in calf mortality (SP-IM), and SU with early weaning on October 31 (SU-EW). Herd size for the fixed resource was 509, 523, 519, 560, and 609 cows exposed per year for SP, SP-IM, SU, SU-EW, and FA, respectively. Corresponding values for weight weaned per cow exposed were 206, 186, 193, 153, and 145 kg. Steer calves, nonreplacement heifer calves, and cull cows were sold at the time of weaning. Quarterly cattle and feed prices used were representative of the peak, descending, valley, and ascending phases of the 1990s cattle cycle adjusted for inflation. Estimates of ranch gross margin (gross returns minus variable costs) were greatest for SP, followed by SP-IM, SU, SU-EW, and FA, and the ranks were consistent across phases of the cattle cycle. Differences between ranch gross margin for SP-IM and SU were small. In beef enterprises representative of the Northern Great Plains, with a restricted grazing season, limited access to low-cost, high-quality grazeable forage, and with calves sold at weaning, switching from early spring to a summer or fall calving date is not expected to improve profitability. If delaying calving improves calf survival, then calving in early summer may be a competitive choice.     

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.     

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.     

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.     

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)     

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.     

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: 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.     

Serving capacity of crossbred yearling beef bulls. I. Single-sire mating behavior and fertility during average and heavy mating loads at pasture

Eighty crossbred, virgin, yearling beef bulls were subjected to three serving capacity (SC) tests. Ten low SC (LSC) and 10 high SC (HSC) bulls similar in weight (avg wt = 452 kg), testicular size and seminal traits but differing in average services were selected. Objectives were to evaluate the mating behavior and fertility of LSC and HSC bulls at pasture when exposed to an average and a heavy mating load and to determine the effect of sexual activity on body weight and testicular characteristics. One LSC and one HSC bull per block were exposed single-sire to 25 naturally cyclic (N) cows for 3 d and to 9 estrus-synchronized (S) cows for 1 d in a randomized complete block design consisting of 10, 4-d blocks. Bulls were fitted with pedometers to record distance travelled. Behavioral data were collected by periodic visual observation. During the N cow treatment, LSC bulls had fewer (P less than .05) services per cow, total services and a higher mount to service ratio than HSC bulls. During the S cow treatment, LSC bulls showed increased sexual activity, though they achieved fewer (P less than .09) services per cow. Pregnancy rates for LSC and HSC bulls did not differ (P greater than .20) and across SC groups averaged 53.6% for N cows and 31.9% for S cows. Distance travelled also was similar (P greater than .20) between SC groups for both treatments. Sexual activity during pasture exposure had no effect (P greater than .20) on testicular characteristics but resulted in an average decline in body weight of 25.7 kg across SC groups during the 4-d period. Post-exposure SC tests found that LSC bulls had increased (P less than .05) services, decreased mounts and mount to service ratio compared to pre-exposure measurements, but LSC were still lower (P = .06) than HSC bulls for average services. These results suggest that LSC virgin, yearling bulls should be offered sexual experience and retested before their inherent SC can be determined.     

Simulated efficiency of range beef production. III. Culling strategies and nontraditional management systems

A modified version of the Texas A&M Beef Cattle Production Model was used to simulate life-cycle biological and economic efficiency of various culling strategies and non-traditional management systems in a northern plains, range environment. Biological efficiency was defined as the ratio of TDN input (kg) to product output (kg), and economic efficiency was defined as the ratio of cost ($) to product output (100 kg), where products were live weight at weaning (LWW), empty body weight at slaughter (EBW) and fat-free weight at slaughter (FFW). Several economic scenarios were simulated. Culling cows at younger ages increased biological efficiency, but not necessarily economic efficiency. The simulated optimal age at culling was 8 yr, the same age at which simulated feed intake and milk production began to decline. Finishing young cows in the feedlot had little effect on biological efficiency and generally increased economic efficiency, although specific results depended on feed prices and relative values of cull cows vs fed animals. A simulated sex-controlled system in which only heifer calves were produced, while extremely biologically efficient for production of lean, resulted in relatively little output and was not economically efficient in most cases. Sex control combined with feeding of 2-yr-old cows was economically efficient, but not markedly more efficient than a conventional system. Results suggest that sex-controlled systems may be more appropriate where emphasis is on lean product and heifers can be bred at very early ages. General results indicate that producers should pay attention to relative values of cull cows and fed animals in choosing culling strategies and management systems.     

Simulation of cow-calf production systems in a range environment: I. Model development

A mathematical computer model of beef cattle production systems was developed at Montana State University. The objective of this report was to describe the rationale and procedures used to simulate animal and system performance. The model was designed to simulate the dynamic relationships among cattle genotype, physiological state, forage quality, and management in range environments. Forage intake, energy and protein metabolism, growth, reproduction, lactation, and changes in chemical body composition are simulated for individual animals over complete life cycles. Expenses driven by animal performance, management decisions, and land resources are tabulated. Several biological and economic measures of system performance can be computed, including ratios of inputs (e.g., DM, CP, ME, dollars) to outputs (e.g., weight, lean), break even prices, and annual gross margin per cow or ranch. Primary uses of the model include the evaluation of system responses to changes in breeding strategies and management in range production/marketing systems.     

Opportunities for conservation and utilisation of local pig breeds in low-input production systems in Zimbabwe and South Africa

Purpose and methods

In situ conservation of pig genetic resources requires understanding of the farming systems under which the pigs are kept. The objective of the study was to characterise smallholder pig production systems where indigenous pigs are kept in order to assess opportunities for in situ conservation of these pigs. Factors influencing pig herd sizes, ranking of pigs in smallholder production systems, breeds and breed preferences, pig ownership patterns, traits preferred by farmers and constraints to production were investigated in a survey involving 199 farmers from Chirimhanzu District of Zimbabwe, Vhembe, Alfred Nzo and O. R. Tambo Districts of South Africa.

Results

Income was the major factor influencing most pig production related parameters. Most pigs (69.67 %) were owned by women, with most of the women falling into the very low income group. Farmers kept pigs for several reasons that were common across geographical zones and income groups. The odds of a farmer ranking pigs first in the production system depended on the absence of other livestock (P?<?0.05). Farmers in the higher income group tended to mention poor feed resources and access to information as constraints (P?<?0.05) compared to the very low income group. There was preference heterogeneity in the breeds kept and the reasons for breed choice across the income groups and geographical zones. Fewer farmers in the very low income group (42.62 %) recognised the need to conserve local pigs compared to the low income group (80.49 %), the medium income group (50.00 %) and the high income group (100.00 %; χ ²?=?19.14; P?<?0.001).

Conclusions

It was concluded that farmers see value in local pigs and are willing to conserve them. In situ conservation programmes are possible and these should recognise the role of poor women in conserving and enhancing indigenous pig genetic resources.     

An economic evaluation of the differences between intensive and extensive beef production systems

A model to evaluate economic criteria involved when cattle are raised on high-forage diets prior to finishing or finished directly after weaning was developed using data from two experiments. In Exp. 1, each year for 3 yr, 136 Charolais-cross calves were weaned and allotted to either an intensive system, in which they were immediately finished on a high-grain diet, or an extensive system, in which they were wintered on crop residues, grazed on summer pasture and finished on a high-grain diet. In Exp. 2, 160 British breed steers were wintered, in one of eight different wintering systems utilizing crop residues, using supplemental protein and(or) alfalfa hay. After wintering, the steers grazed summer pasture and then were finished on a high-grain diet. Overall cost of gain and final "break-even" price were lower for cattle finished through the extensive system except when the price of corn was very low in relationship to other inputs. Interest costs were higher for cattle in the extensive system. Increasing the feeder calf purchase price had almost no effect on differences between the systems. Corn price and purchase price affected both systems similarly, whereas interest rate, wintering yardage and finishing yardage affected each system differently. Because of the additional weight produced through the extensive system, it yielded lower final "break-even" prices in most situations.     

Effects of creep feeding, zeranol implants and breed type on beef production: I. Calf and cow performance

A 2-yr study was conducted to evaluate the effects of a high-energy creep feed, preweaning zeranol implants and breed type on calf and cow performance. Two hundred calves sired by Brahman and Romana Red bulls out of Angus and Angus x Brown Swiss reciprocal crossbred (F1) dams were stratified by breed type and sex to three creep treatments: no creep feed (NC); long-term creep (LC), creep-fed from 56 to 210 d of age (weaning); and short-term creep (SC), creep-fed from 146 to 210 d of age. Alternate calves within sex, breed type and creep treatment were implanted with 36 mg of zeranol at an average of 56 d and reimplanted 90 d later. The LC and SC calves had heavier (P less than .001) 210-d weights than NC calves (264 and 257 vs 231 kg, respectively), and the LC calves were heavier (P less than .001) at 146 d than NC calves. The LC calves had higher (P less than .001) ADG from 118 to 210 d of age and higher 146 and 210-d condition scores than did NC calves. Pregnancy rate was not affected (P greater than .46) by creep treatment of calf. Zeranol implants increased (P less than .01) 146- and 210-d weights (184 vs 175 kg and 259 vs 243 kg) and ADG during all periods to weaning. Brahman-sired calves had higher (P less than .005) 146- and 210-d weaning weights and frame scores than Romana Red-sired calves.(ABSTRACT TRUNCATED AT 250 WORDS)     

About camel breeds: A reevaluation of current classification systems

SUMMARY: This article revaluates the current dromedary breed classifications based on Leese's (1927) division into hills, riverine and plains camel according to camel breeding zones, and the even earlier distinction by Cross (1917) and Leonard (1894) between baggage and riding camels. It is suggested that these classifications are inappropriate to portray the wide variety of camel breeds actually existing, since they do not accurately reflect the ecological context of camel breeding and also depict incompletely the actual uses to which camels are put in camel pastoral societies. The breeding practices of traditional camel pastoral societies are described and discussed, and it is concluded that these have been conducive to the development of a large number of specialized camel breeds. It is pointed out that many camel breeds are endangered, and that it is imperative to take steps for their documentation. ZUSAMMENFASSUNG: Kamelrassen: Revision des gegenw?rtigen Klassifikationssystems In diesem Artikel werden die heute gebr?uchlichen Klassifikationssysteme für Dromedarrassen einer Prüfung unterzogen: Diese beruhen auf der Einteilung von Leese (1927) nach Kamelzuchtgebieten in Berg-, Flu?- und Flachlandkamele und der noch ?lteren Unterscheidung von Cross (1917) und Leonard (1894) zwischen Reit- und Lastkamelen. Es wird vorgeschlagen, da? diese Einteilungen der tats?chlichen Variabilit?t zwischen Kamelrassen nicht gerecht werden, weil sie die ?kologischen Bedingungen, unter denen Kamelzucht betrieben wird, nicht richtig reflektieren und die tats?chlichen Nutzungsweisen, denen das Kamel in Kamelhirtenkulturen unterzogen wird, nur unvollst?ndig wiedergeben. Die Zuchtmethoden traditioneller Kamelhirten werden beschrieben und diskutiert, und es wird die Schlu?folgerung gezogen, da? diese für die Herausbildung vieler spezialisierter Rassen ideale Vorbedingungen darstellten. Auf die gro?e Gefahr des Verlustes vieler dieser Rassen und die Notwendigkeit diese zu katalogisieren wird hingewiesen.     

Computer simulation model of swine production systems: I. Modeling the growth of young pigs

Theoretical concepts and relationships were used to develop a deterministic pig growth model. The model predicts, in a continuous form, growth and body composition of boars, barrows, and gilts according to genotype, diet, and management conditions. The model is aggregated at the whole-animal level with three main elements of body composition; total body DNA, total body protein mass (PT), and total body mass of lipids, with PT determining the secondary elements of ash and moisture. The primary factors regulating growth were associated with cellular hyperplasia and hypertrophy in agreement with the basic concepts described by Baldwin and Black (1979). Differential equations representing DNA accretion and protein synthesis and degradation were adapted from Oltjen et al. (1985). Normal pig protein growth was characterized from published data. Body PT was used to reflect several metabolic activities related to animal size and age, as in some prior models. Dietary energy and protein were used in sequence until requirements are satisfied, first for maintenance, then for protein growth, and finally for fat deposition. A comparison between experimental and simulated results illustrates that the model may simulate growth and body composition of young pigs adequately.