Otto J. Loewer

Modeling the Physiological Growth of Swine Part I: Model Logic and Growth Concepts

This article is Part 1 in a series of three articles describing the computer model (NCPIG) that was developed to simulate the physiological growth of swine. The methods and techniques used to simulate the interaction of feed intake and the various metabolic processes for the growing swine are presented. These processes include nutrient digestion, nutrient storage in the blood, body maintenance, lean mass growth, excess fat growth, and waste and urine production. Animal heat production and thermal energy balance is described in Part 3 of this series. The model was shown to provide reasonable predictions of the empty body weights used to develop the supporting body component growth curves

A body composition model for predicting beef animal growth

Abstract Two beef animal growth computer simulations were compared as to the effects of altering feed energy density. Steers of varying initial degrees of fatness were evaluated. The BEEF-NC114 model used NRC regression equations to predict growth while the BEEF-S156 model used physiological age and body components. Otherwise, the models were essentially identical. On average, the predictions of both models were reasonably close to each other. However, the BEEF-S156 model was more sensitive to extreme conditions of high or low nutrition.

Mathematical-Logic to Simulate the Growth of Two Perennial Grasses

ABSTRACT MATHEMATICAL-logic was developed to reflect the relationships between growth (accumulation of dry matter) and air temperature, day length, leaf area, photoperiod, and rainfall. These relationships were incorporated in a nonspecific crop growth model (GROWIT). The validity of the model was demonstrated by simulating experiments with fescue and coastal bermuda grass. The simulated yields of dry matter did not differ significantly from the experimental yields. Yields of fescue were significantly lower in 1976 than in 1977, and the model indicated that insufficient water during critical periods was responsible, even though the rainfall for 1976 was only 5% below normal. Yields of coastal bermuda grass were lower in 1965 than in 1966, and the model showed that air temperature and rainfall were constraints on growth during 1965 as compared to 1966.

Incorporation of environment and feed quality into a net energy model for beef cattle

Abstract The California net energy system has gained wide acceptance as a method for predicting rates of gain in growing and finishing beef animals. Researchers at the University of Kentucky, in co-operation with agricultural scientists in two regional research projects, NC-114 and S-156, have developed an interactive model that enhances the usefulness of the net energy system by including skeletal size, feed quality, temperature and relative humidity to determine feed intake and utilisation. Basically, the intake based on feed availability, nutrient composition, potential skeletal size and heat loss potential. After the feed is consumed, it is utilised according to the productive status of the animal, i.e. growth, lactation, foetal development, etc., using a modified form of the net energy system to predict weight change. The model allows a researcher to easily modify environment, feed, breed characteristics and productive status so as to evaluate their influence on the performance of the animal.

Dynamic Simulation of Animal Growth and Reproduction

ABSTRACT A rather unique systems analysis approach has been made to simulate the utilization of dry matter by ruminant animals, and the natural breeding and reproduction process within a herd. Physiological factors occurring over time and the time related effects of these factors are simulated.

A Simulation Model for Assessing Alternate Strategies for Beef Production with Land, Energy and Economic Constraints

ABSTRACT A computer model has been developed to analyze alter-nate management strategies and energy and economic constraints. Daily production of beef animals and growing crops is simulated in response to prevailing conditions and system interactions using the GASP IV simulation language. Complete inventories of plant dry matter, animal status, production resources and economic net worth are maintained over the simulation period.

Grain Flow Restrictions in Harvesting-Delivery-Drying Systems

ABSTRACT A model has been developed which simulates the har-vesting, delivery, and handling of grain for any specified grain production enterprise. This study describes the procedures used in validating the model. A time and motion analysis was used with three sets of ac-tual field observations. A comparison is made between simulated and measured values for total grain harvested, number of combine and field unloadings, and vehicle wait time.

Economics of High Temperature Solar Grain Drying

ABSTRACT IF solar energy is to be used by farmers in grain drying, it must be economically competitive with other available energy sources. An economic analysis of high temperature solar grain drying has been made through a computer model that designs and calculates the economic feasibility of this system. A description of the model and a sensitivity analysis is presented.

Economics of Stirring Devices in Grain Drying

ABSTRACT THE addition of a stirring device to three in-bin drying methods was analyzed with regard to economics. It was concluded that adding stirrers to a functioning in-bin drying system (a) was generally economical for layer drying; (b) was not generally economical for natural air drying; (c) was economical for low-temperature drying only with larger bin diameters and relatively higher corn prices

Finite Element Model of Heat Transfer in the Bovine Part 1: Theory

ABSTRACT A transient, polar coordinate (two-dimensional) finite element model of the bovine body is described. The model includes the core, muscle, fat, skin and hair coat components. The model simulates heat transfer due to conduction and convective blood flow within the animal and by convection, radiation and evaporative cooling from the hair coat. Internal metabolic heat generation, shivering and respiration are also included. Theoretical details of the model are emphasized in this paper..