Degree Type


Date of Award


Degree Name

Doctor of Philosophy


Animal Science


The "systems" concept of swine production research incorporates an awareness that there is more to consider than merely the level of production and implies that an enterprise is a system of many components which all play a part in determining net return. While level of production is an important factor affecting profitability, production costs are equally important. Numerous factors influence swine production and this information must be integrated to determine how enterprise profitability is affected. Five pork production systems were simulated using a deterministic computer model to analyze the effect that lactation length, estrus at initial mating, estrus at post-weaning mating and maximum parity have on the efficiency of producing 200 litters per year. Under this approach, production inputs were treated as dependent variables determined by animal performance. Mating gilts at first estrus does not appear to provide a means to improved efficiency, but this system does reduce overall facility requirements, which in turn reduce capital outlay and risk. Mating sows at first versus second estrus following weaning after a 35-day lactation improved feed efficiency and facility utilization. Production costs declined from 98.11 to 94.73 per 100 kg of pork marketed, increasing net profit by 5086. Decreasing maximum parity from five down to one increased the number of replacement gilts entering the breeding herd annually which resulted in poorer reproductive performance, fewer market hogs, and a larger percentage of pork marketed as culled breeding stock. Reducing maximum parity from five to one decreased income as well as increased production costs. Production efficiency improved when lactation length declined from 35 to 18 days as a result of decreased feed, depreciation and capital charges. This result occurred in spite of a decline in litter size due to early weaning. The simulated results conclude that increasing reproductive rhythm, tightening farrowing schedules and farrowing continuously offer producers opportunities to boost sow productivity, make more efficient use of facilities and improve herd efficiency.



Digital Repository @ Iowa State University,

Copyright Owner

Michael M. Miller



Proquest ID


File Format


File Size

129 pages