Potential “Benchmarks” For Sow Longevity

An examination of today’s lifetime productivity expectations and litter of origin characteristics.

by W.L. Flowers, Department of Animal Science, N.C.S.U., Raleigh, North Carolina

High replacement rates for gilts and young sows have skewed current parity distributions on many farms towards younger females that haven’t reached their peak productivity.

Identifying potential causes of this reduced longevity is challenging because many factors affect reproductive performance, and it is reasonable to speculate that these probably differ among farms and possibly within the same farm over time.

Previous research using a technique called multiple regression analyses has shown that close to 50 percent of the variation observed in sow lifetime productivity on commercial farms can be explained by aspects of the litter from which the replacement gilt was weaned.

These are commonly referred to as “litter of origin” traits and include things such as the number of pigs born, nursing, and weaned; birth and weaning weights; and weaning age (Figure 1).

From a practical perspective, this means that if the difference between the most and least productive sows in a herd was, for example, 10 pigs weaned over six parities, then five of these were likely due to their neonatal management, or litter of origin. Collectively, these observations provide an opportunity for using production data collected between birth and weaning as a “benchmark” for estimating the future lifetime productivity of replacement gilts.

chart of relative contribution of litter - origin traits to lifetime productivity

Birthweight, weaning weight, and weaning age had a positive relationship with adult reproductive performance, while a negative relationship was present for the numbers of pigs born, nursing, and weaning, so any of these could be viewed as potential benchmarks for lifetime productivity.

Of these, weaning weight appears to be one of the better candidates because: it is measured at the end of the neonatal period; is influenced to some extent by all the other litter of origin traits mentioned; and is relatively easy to collect.

Accordingly, gilts from the same dataset used in the multiple regression analyses were placed into three equal groups based on their weaning weight: the upper, middle, and lower one-third of the entire population. Average weaning weights for these three groups were 21.5 lbs., 16.1 lbs., and 13.2 lbs., respectively, and at rebreeding after parity 3, corresponding percentages of sows still in production for each of these groups were approximately 60 percent, 40 percent, and 20 percent (Figure 2).

chart comparing weaning weight and sow longevity

It is important to recognize that neither the initial multiple regression nor the subsequent weaning weight analyses establish cause-and-effect relationships between litter of origin traits and lifetime productivity.

While both are indicative of a strong positive relationship between the two, the true definition of a cause-and-effect relationship is when a management change is initiated first and then subsequent improvements in production occur in “response.” These types of evaluations are done quite often on commercial swine farms and typically involve collecting data before and after a management change is implemented.

While there are obvious drawbacks to this approach, if the same management change is implemented across many different farms and the responses are very similar, then this provides good support for the conclusion that the management change caused the production effect.

With regards to using weaning weight as a possible “benchmark” for sow lifetime productivity, a logical management change would be setting a minimum weaning weight for all replacement gilts.

Females meeting this minimum would be managed accordingly post-weaning, while those that did not would essentially become market animals along with the maternal-line barrows. Once delivered to commercial farms, some measure of longevity, such as the parity at which sows are culled and/or the total number of pigs weaned per sow prior to culling, would need to be recorded.

This is currently being done within some commercial production systems, and initial comparisons before and after the comparisons are shown in Table 1.

chart comparing farms - sows rebred after parity 3 and total pigs weaned parities 1 - 3
Table 1. Preliminary Data from Commercial Sow Farms Before and After Implementation of Weaning Weight Selection Criteria for Replacement Gilts

For this dataset, the weaning weight minimum for potential replacement gilts was 14 lbs. and based on the analyses similar to those described earlier. This data has also been restricted to parity 3. This was done because several of the farms did not have quite enough observations from older parities to obtain a good enough estimate of what longevity means.

The general trend for all the farms shown is for the proportion of sows still in production at rebreeding after parity 3 and the total number of pigs weaned over three parities to be statistically better after the weaning weight selection criteria was implemented at the multiplication farm.

The degree to which these increased varied considerably among farms. This should not be surprising.

If a litter of origin traits accounts for 50 percent of the variation in these traits, then the “other” 50 percent is most likely associated with the production environment on commercial sow farms. It is interesting to note that the farms with better lifetime production before screening replacement gilts for weaning weight tended to have smaller positive changes.

For Farm No. 2 (in Table 1), the reproductive tracts of gilts delivered to the farm but never detected in estrus are being examined once these females are culled.

Ovaries from most of the gilts examined prior to the use of the weaning weight criteria were small, avascular, and tended to contain low numbers of follicles and corpora lutea (Figure 3, top image).

photos of corpora albicantia and corpora lutea

These characteristics are consistent with an underdeveloped, sub-functional ovary and are likely linked to poor growth and development during the neonatal period.

In contrast, most of the ovaries from their counterparts after implementation appeared to be large, vascular, and contained large numbers of follicles and corpora lutea (Figure 3, bottom image). This suggests that the failure to detect estrus was probably technical (people) rather than biological (pigs).

Although these preliminary results are encouraging, it would be unwise to make definitive conclusions or recommendations with regards to the value of using the weaning weight of gilts as a benchmark of their adult reproductive function, because things could be significantly over parities three through six.

Interestingly, the most important aspect of this study may very well be the process rather than the result.

The process is the following: a qualitative analysis that identifies possible benchmarks; a quantitative assessment to establish specific criteria for a given “benchmark”; and an implementation prospectively to determine the actual responses.

It is quite possible and probable that all of these could differ among different production systems or within the same production system over time.

Dr. William L. Flowers

Dr. William L. Flowers joined the Animal Science Department at North Carolina State University in 1987, and is currently a William Neal Reynolds Distinguished Professor. His research program focuses on improving fertility in swine and has resulted in over 170 peer-reviewed publications and 485 popular press and extension articles.