The ability of pigs to reach full value by finishing closeout is dependent on their ability to survive to weaning, thrive through the nursery period and grow to a minimum market weight and acceptable quality at marketing. The impact of birthweight on these preharvest landmarks was studied on 5,727 pigs from 463 litters farrowed by Large White x Landrace sows and sired by Duroc boars.

All pigs farrowed on a commercial swine farm during a four-week period were individually weighed and identified within 24 hours of birth. Pigs were weaned in four separate weekly groups and transferred to an off-site nursery where they spent seven weeks before being placed in a finishing site. However, data was collected only on pigs from weaned groups #2 and #3 after finishing placement.

Pigs were weighed at weaning, when placed in the finisher and at 16-week post-finisher placement. At weighing, pigs were also given a visual quality score (3 = acceptable weight and health; 2 = somewhat lightweight and/or minor injury; 1 = severely lightweight and/or injury).

Individual survival was tracked for each phase of production (preweaning, nursery, finishing). To predict if pigs would be full value, a combination of weight, quality score and survival was used. Pigs were deemed non-full value on the 16th week in the finisher if they received a quality score of 1, weighed less than 155 lb. or had died.

Figure 1 graphically shows the impact that birth weight had on pre-weaning survival, nursery survival, quality score and weight at 16 weeks in finishing, and full-value classification. The values are presented as percentage deviations from the mean (average) of the respective traits.

Birth weight affected all traits, especially for pigs with the lightest birth weights. The impact of birth weight was reduced as birth weight increased, particularly for preweaning survival and the likelihood of a pig attaining full value. The total impact of birth weight on likelihood of a pig being full value is a combination of each of these traits.

Researchers noted that as birth weight increases, a level is reached where a further increase in weight does not lead to any advantage in off-test weight and much smaller advantages in survival and pig quality and value. For example, an increase in birth weight from 3.5 to 3.6 lb. has much less impact on the survival, performance and value of the pig than an increase from 2.0 to 2.1 lb. of birth weight.

These results confirm the dramatic impact of birth weight on production parameters. Therefore, selection strategies and management practices should be devised to limit the impact or reduce the incidence of light-birth-weight pigs in order to optimize the amount and value of pork marketed.

Researchers: Justin S. Fix and M. Todd See, North Carolina State University, Raleigh, NC. Contact Fix by phone at (919) 515-5914 or e-mail jsfix@ncsu.edu.