Introduction

There has been and will continue to be much speculation on what influences the length of productive life of a sow within a sow herd. There have been studies completed that report both management and genetic history do contribute to the length of a sow’s stay within the herd. Throughout much of today’s pork industry the genetic development and management history of a prospective replacement gilt is not controlled by the sow farm where she will live her adult life. Thus sow farms have little influence on invoking any management practices that may impact a female’s subsequent reproductive life until the gilt arrives to the breeding herd. However there are two areas that sow farms can actively manage to improve the length of time females remain in the herd.

Feet and Leg Structure and Underline Soundness

Figure 1. Two Examples of Rear Leg Conformation

Conformation among breeding animals has long been considered an important characteristic for improved length of productive life. In addition, an age old recommendation has been that replacement females should have at least 6 evenly spaced teats on each side of their underline. Recently a report from Switzerland1 evaluated performance data from Large White sows maintained within their national recording system. Within their recording scheme replacement females had conformation scores for rear leg set, side view angle, pastern angle and a score describing dew claws. These scores were formulated into an index with seven categories. Females with a score of 0 had optimal conformation while gilts with a score of 6 had the most detrimental conformation score. In addition the total number of teats was recorded for each female. The analysis included data from 5,077 sows collected during 4 consecutive years. These females averaged 342 days of age at first farrowing. Length of productive life was defined as the number of days between first farrowing and culling.

There were dramatic differences for length of productive life among sows which differed for leg index scores. Among sows with a score of 0, considered most optimum, 48% were still retained in the herd two years after their first farrowing while 32% which had an intermediate score were still retained within the herd. Among those with the worst index score for rear leg soundness, less that 20% had been retained for two years after their first farrowing. Females with good conformation had improved length of productive life and were retained within sow herds longer (Figure 1). There are several examples available for use as a guide in evaluation of feet and leg conformation. The National Hog Farmer published several posters for use on hog farms that describe differences in conformation for replacement females. Copies of these, in limited quantities, can be obtained from MSU from the author (Ron Bates). In addition the National Pork Board has available pocket guides for conformation evaluation.

The Swiss study also evaluated teat counts and related it to length of productive life. The analysis revealed that females with 13 or fewer teats were more likely to be culled than females with 14 or greater teats. Females with 13 or less teats were retained in sow herds for an average 459 days (15.2 months) after their first farrowing, whereas females with 14 or more teats had an average time of retention of 600 days (19.8 months) after their first farrowing.

Lactation Feed Intake

Pork producers know that sow feed consumption during lactation is important for both the growth of the litter as well as how well the sow will return to estrus after weaning. However, there is a multitude of feeding schemes used across the industry regarding how a sow should be fed on differing days of her lactation. Most would probably agree that it is important to have sows consume as much feed as possible (within reason) without causing the sow to go off feed. The need to have sows on “full feed” during lactation is of little debate. However how to bring a sow into “full feed” is often the topic most debated.

In a study which used data from sows which were included in the Maternal Line comparison conducted by NPPC in the late 90’s, daily feed consumption during lactation was evaluated for its impact on longevity. Feed consumption was corrected to constant number of pigs weaned. Daily feed consumption did influence length of productive life for 5 of the six crossbred sow types evaluated. Across crossbred sow type, the likelihood that sows remained in the herd increased 2 to 4 times when lactation feed consumption increased by approximately 2 lb per day.

The industry differs widely on how quickly sows should be allowed to consume “full feed”. A study was recently published that evaluated the amount of feed sows consumed during each day of lactation and how that influenced the ability of the sow to stay productive in the herd. Average daily feed consumption in this study was 15.2 lb/day. Sows lactated for approximately 19 days. This study confirmed the importance of lactation feed consumption and found that for every 2 lb increase in daily feed consumption the likelihood of being culled before a sow’s next farrowing decreased by 30%. Also this study determined that consumption during the first two weeks of lactation also influenced the sow’s ability to remain in the herd. Sows that consumed less than 7 lb any day during the first two weeks of lactation, (day 2 through day 14), had a greater risk of being culled compared to sows which ate 7 or more lbs per day each day during the first two weeks of lactation. Furthermore sows which did not consume any feed during any day during the first weeks of lactation (day 2 to 14) had the greatest risk of being culled.

Certainly, lactation feed consumption has an important role in maintaining reproductive function. Sows which do not eat enough feed during lactation or go off feed during lactation have a greater risk of being culled. Tracking daily feed offered to each sow during lactation and having a pre-planned strategy on how to progress a sow to full feed is important when trying to have sows milk well during lactation and maintain reproductive function and longevity after weaning.

Final Thoughts

Sow farms should have a well though through plan on how to evaluate gilts before they enter the sow herd. Gilts should have acceptable feet and leg conformation and underline conformation with 14 more total teats. There are several good tools available to assist sow herd personnel in developing this type of evaluation system.

In addition, sow feed intake during lactation plays an important role in the growth of the nursing pigs and the longevity of the female within the herd. Sows should start consuming 7 lb per day or more, within reason, on the second or third day of lactation and then progressed to full feed as soon as feasible. A good publication for review on this topic is, “Feeding the Lactating Sow” by Dr. Frank Aherne.

Literature Cited

1Tarres, J., J.P. Bidanel, A. Hofer and V. Ducrocq. 2006, Analysis of longevity and exterior traits on Large White sows in Switzerland. J. Anim. Sci. 84: 2914-2924.
2Serenius, T., K.J. Stalder, T.J. Baas, J.W. Mabry, R. N. Goodwin, R.K. Johnson, O.W. Robison, M. Tokach and R. K. Miller. 2006.
National Pork Producers Council Maternal line National Genetic Evaluation Program. J. Anim.
Sci. 84: 2590-2595.

May 2007