Introduction
Environmental factors including disease exposure, social stress and less than optimal stocking density limit growth. As a result, pigs managed under commercial conditions are unlikely to express their maximum potential protein accretion, even when allowed ad-libitum access to a high quality, nutrient dense diet. The operational protein accretion is the maximum protein accretion rate that pigs can achieve under specified commercial conditions. This definition implies that for a given genotype, the maximum achievable lean growth rate is limited by the environmental conditions under which the pig is raised. Lean growth curves can be used to estimate the magnitude at which environmental conditions (health status, facilities, stressors) limit the expression of the pig’s genetic potential for lean growth. A substantial difference between on-farm and maximum achievable protein accretion or lean growth rates is indicative of major environmental limitations. In such cases, the commercial producer must evaluate the benefits and costs of environmental-management changes.
Material and Methods
A commercial swine operation in northeast Missouri was used for this study. The operation was a 3-stage, one-site, farrow-to-finish, 130-sow farm stocked with PIC Camborough-15 sows and Line-326 boars. The health status of the herd was considered average for the industry, with a moderate level of respiratory disease in the grower and finisher stages. The sow herd was serologically positive for porcine reproductive and respiratory syndrome virus (PRRS), swine influenza virus (SIV), Actinobacillus pleuropneumoniae(APP) serotype 7, and Mycoplasma hyopneumoniae (MHYO). The herd was selected due to a history of consistently slow-average growth in the grower and finisher stages.
A total of 48 barrows were selected at the completion of the all-in, all-out nursery stage, at 11 weeks of age and an average weight of 65 pounds. The animals were blocked by weight and randomly assigned to either remain in the commercial facility (COMM, n=24) or to be transported to research facilities providing an unrestricted environment (UNRES, n=24). All pigs were individually identified with ear tags, weighed, and measured by real-time ultrasound for backfat and loin eye area at allotment.
The COMM pigs were moved as a group to fill one pen in the on-site grower building. The grower building was a power ventilated, total slat/pull-plug building containing 16 pens. The COMM grower building was managed continuous flow, as two age groups occupied the building at any one time. The trial pen measured 12′ x 13′, providing approximately 5.5 ft2/hd. The pen contained one 8-hole feeder and 2 nipple waterers. The room temperature in the grower ranged from 64 to 86ºF during the 8 weeks in which the COMM pigs were in the room. The COMM pigs were moved as a group to a pen in the on-site finisher at 19 weeks of age, consistent with the typical pig flow of the commercial operation. The COMM finisher was a naturally ventilated, double curtain sided, partially slatted building that was run all-in, all-out by room. The trial pen measured 8′ x 23′, providing approximately 7.6 ft2/hd. The pen contained one 32″ diameter round feeder and 2 nipple waterers.
The UNRES pigs were transported to a research facility at Iowa State University. The facility contained 8 pens on solid concrete floors with solid steel gating between pens. The room was positively power ventilated and was isolated from other swine during the course of the trial. Each pen measured 8′ x 9′ and provided approximately 23 ft2/hd with one 2-hole feeder and 1 nipple waterer. The room temperature in the research facility was held constant between 60 and 69ºF for the entire trial period. The UNRES pigs were assigned to one of eight pens by weight in order to equalize mean weights for each pen at the initiation of the trial. UNRES pigs remained in their assigned pens for the entire length of the trial.
All pigs were weighed every 2 weeks following a...
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