Sow Longevity Genetic Differences

Rodney Goodwin, National Pork Board

Improving the average herd life of breeding females reduces genetic costs and gilt development costs. And, there’s the added advantage that sows tend to wean heavier pigs than gilts and have acquired immunity to specific herd diseases. Therefore, sows that remain productive through more parities can increase herd output while reducing cost of production.

Fertility and prolificacy serve as the productivity yardsticks by which sow herd output is measured. Swine breeders have made great efforts to improve prolificacy traits such as number of pigs born and litter weaning weights. Both traits are easily measured by breeders and the commercial producers using their genetic lines. Low heritabilities for these prolificacy traits and joint selection for lean growth to ever heavier market pig weights have kept genetic improvement of prolificacy traits at a relatively slow but constant rate.

Fertility traits, such as age to puberty and farrowing rate, have been given less attention by breeders because of the great difficulty in getting reliable data. Records of '0' or no performance are important when evaluating fertility. Commercial producers ignore such records routinely. Comparisons of fertility traits depend on all records whereas many sow recordkeeping programs only account for prolificacy traits. In other words, they only track sows that mate and/or farrow. However, fertility traits greatly influence the reproductive efficiency of the sow herd.

How can you predict which sows will stay in your herd and which will not? The checkoff funded Maternal Line National Genetic Evaluation Program (MLP) Results gives us some clues. The goal of the MLP was to evaluate the six genetic lines through four parities. An important design requirement of the MLP was that no gilt or sow could be culled for poor reproductive performance (small litters, poor milker, etc). The only way that a female could leave the program was death, injury or failure to conceive within fifty days of weaning.

Genetic lines of females in the MLP were American Diamond Swine Genetics, Danbred USA, Monsanto Choice Genetics (two lines), National Swine Registry (Yorkshire*Landrace F1 crossbred), and Newsham Hybrids. Each line was represented by about 600 females. There were 3600 gilts delivered to the program at 10-20 days of age and grown in wean-finish barns.

The 3,283 gilts entered the MLP reproduction tests at about 165 days of age. Gilts were placed in two new, 1,600-sow breeding-gestation-farrowing facilities. No gilts were culled for poor growth or backfat. Only gilts that died, were injured, had an abnormality (hernia, etc), or were rejected by herd veterinarian and manager as 'stunted' were excluded from the reproduction tests.

The 3283 gilts entering the sow facilities were checked for heat (estrus) daily and serviced on their second or later heat period. All matings were done by artificial insemination using fresh semen from one unrelated sire line. Matings started when gilts reached 210 days of age and were on their second or later estrus. Gilts that were not successfully mated by 300 days of age or had failed to conceive after three mating periods were slaughtered.

Sows were given 50 days after weaning to conceive. No gilt or sow was culled due to poor litter size or low litter weight.

The amount of daily gestation feed given each sow was determined by her weight and desired weight gain before farrowing. All sows were fed three times daily during lactation with the goal of maximum intake. Daily lactation feed disappearance for each sow was recorded. Average weaning age was 15.4 days.

The sow loss rate of the Monsanto GPK347 line was different from the other five genetic lines. The sow loss rates of the other five lines are pooled and shown in Table 1.

Table 1. MLP sow loss rates by age of breeding females.

* 150-330 days old, %	331-450 days old, %	451-570 days old, %	571-690 days old, %	691-810 days old, %	** Sold after fourth parity, %	Genetic Line
18	11.7	8	6.4	5.3	50.6	Avg 5 lines
6.1	8.8	4.9	5.7	4.6	69.9	Monsanto GPK347

* Includes culling of gilts not expressing estrus by 310 days of age.

** All sows were sold after weaning their fourth parity litter.

Results of Table 1 show that the greatest barriers to sow longevity are gilt and post first parity sow loss due to fertility. The major component of sow loss prior to 450 days of age is reproductive failure. Gilts that are never serviced or fail to conceive make the difference between the GPK347 and other lines prior to 330 days of age. Many producers fail to account for the cost of days on feed and facility space occupied by these gilts. The NPPC Financial and Production Standards require entering all gilts into the sow herd when delivered or selected. Litters and/or pigs per sow year ratios will be reduced to their true value with these Standards, sometimes more than a producer or his banker would like. Failure to rebreed is the major component of sow loss between 331-450 days of age.

MLP records were grouped according to how long a sow remained in the herd (longevity group) and then further divided into parity groups. Only sows of the five lines that farrowed at least one litter are included in Table 2. The Monsanto GPK347 females had different performance indicators for many traits and are not included in Table 2. The first four columns show the performance of parity 1 females. The first column is parity 1 performance of females that were lost from the herd after first parity (longevity 1). The second column is the parity 1 performance of females that were lost from the herd after two parities (longevity 2). The other columns follow this pattern until the last column shows the parity 4 performance of females that completed the MLP with four parities (longevity 4). This table allows us to search for performance indicators at the end of each parity that might predict sow loss.

Table 2. Litter Parity by Herd Longevity Group performance in the MLP, average of five lines.

Parity by Life	P1-L1	P1-L2	P1-L3	P1-L4	P2-L2	P2-L3	P2-L4	P3-L3	P3-L4	P4-L4
Sows*	318	203	261	1042	187	257	1029	243	1032	994
Age at first heat, days	228	227	226	220
Age at first farrow, days	376	378	378	365
Sow wt, lbs	466	469	458	452	510	509	503	517	518	524
Wt loss, lbs	63	54	53	55	46	49	51	42	39	44
Sow BF, in	.85	.86	.82	.84	.81	.77	.78	.71	.75	.70
BF loss, in	.09	.09	.08	.08	.06	.06	.04	.05	.05	.02
Pigs born	10.4	10.4	10.4	11.1	10.0	10.9	10.6	10.8	11.3	10.9
Pigs born alive	9.4	9.6	9.6	10.2	9.2	9.9	9.8	9.6	10.3	9.8
Pigs nursed	10.1	10.2	10.0	10.2	9.9	10.2	10.0	9.9	10.4	10.0
Pigs weaned	9.2	9.1	9.1	9.2	9.0	9.2	9.2	9.1	9.3	9.1
Weaned wt, lbs	105	110	111	108	113	117	121	110	114	112
Day 1-7 lactation feed, lbs	45	54	55	53	69	76	73	82	84	85
Day 8-14 lactation feed, lbs	76	82	85	82	91	99	96	105	112	109

* Number of sows with complete 14 day daily feed intake records.

The number of sows with complete daily lactation feed disappearance records is slightly different within herd longevity groups due to occasional missing records.

Age at first was the age of first detected estrus, observed by sow managers. Table 2 shows that the gilts that showed heat younger stayed in the herd longer. Sows that finished four parities (P1-L4) were a week younger than other sows when showing first heat. The Monsanto GPK347 gilts were 12 days younger than the other lines.

Age at first farrowing. The P1-L4 sows were 10-13 days younger when they farrowed their first litter. The Monsanto GPK347 gilts were 12-17 days younger at first farrowing.

All gilts were fed about five lbs daily during gestation. The sow weight at first parity shows the longer lived sows were actually slightly smaller at first parity. All sows grew larger as they got older. The individual sow gestation feeding program was designed to maximize the growth and reproductive performance of each sow.

Sows that were lost after first parity (P1-L1) had the greatest lactation body weight loss, 63 lbs.

Sow backfat thickness, measured at the last rib, was not different for any herd longevity group. The lactation backfat loss for each herd longevity group was also the same within each parity. Even though the sows grew heavier during each gestation period they did not completely replaced their lactation backfat loss. The sows had their greatest backfat thickness at first parity farrowing.

Total pigs born and number of pigs born alive were different only for the Parity 1 herd longevity groups. Sows that weaned four litters (P1-L4) had more P1 pigs and live pigs born than the other three longevity groups.

Each female was given an equal chance to raise a litter. Within 24 hours of farrowing all litters were cross-fostered to about 10 pigs per sow. The number nursed reflects this practice. The number of pigs farrowed did not affect the number of pigs allowed to nurse.

The number of pigs weaned and litter weaning weights are not different for the herd longevity groups.

The first week lactation feed disappearance records show a lower feed intake, at least 1 lb per day, by parity one sows that did not complete parity two(P1-L1), at least a pound of feed per day. The second week feed lactation records also show a lower feed intake for P1-L1. These P1-L1 sows were weaning just as many pigs as the other parity one sows.

What can we conclude from Table 2? It is very difficult to predict sow longevity from performance data, there are very few real differences among sow longevity groups shown in Table 2. The strongest signals are age at first farrowing, lactation feed disappearance and sow weight loss during lactation. Problems in those areas could prevent a sow from expressing post-weaning estrus, resulting in a sow culled for reproductive failure.

The MLP results of the Monsanto GPK347 line females confound some of the observations just made from the other five lines’ performance. These females were smaller, lost more weight during lactation, ate less feed during lactation, yet farrowed more pigs and bred back more readily after weaning. About 70% of Monsanto GPK347 line females survived through four parities versus 50% of the other five lines. Nearly all of the longevity difference was due to fertility differences prior to 450 days of age.

The NPB Maternal Line National Genetic Evaluation Program (MLP) reported the performance of six genetic lines through four parities. However, NPB continued to measure sow performance on the MLP lines after the official test was completed. Data is now compiled and evaluated through their sixth parities (see Tables 3 and 4).

Use of 'cohort' analysis gives a more complete picture of sow performance. More precisely, a cohort is defined in the National Pork Producers Council’s (NPPC) Production and Financial Standards as “a group of animals that shares a common event within a defined period of time.”

The advantage of cohort comparisons is it allows us to target groups of gilts as they enter the sow herd and follow them through multiple parities. This approach requires close accounting of all gilts entered into the herd. In the end, longevity is a reflection of a sow’s fertility traits.

The 25 female cohorts shown in Table 5 are formed by line-age-facility subclass at 165 days of age, as reported previously through four parities. Large lifetime differences in cohort performance were found between genetic lines, highlighting the opportunity for improved total herd efficiency by selection of sow genetic line.

Ranges in output of the 130 cohorts show the great biological opportunity in production efficiency that is still possible. Table 6 shows the extremes in production from a 25-sow cohort. The total possible litters born from a 25-female cohort over six parities is at 150. Actual records show a range of 40 litters for the worst cohort group to 127 litters for the best.

The most productive cohort farrowed 1,347 live pigs during its 6-parity productive life while the poorest farrowed only 397.

Clearly, measuring and comparing these fertility traits give a more complete measure of performance than single sow prolificacy traits.

The combination of superior sow longevity and superior number of live pigs born/litter gives the Monsanto GPK347 line female a lifetime live pig born output advantage of 48 % over the average of the other five lines. (This genetic line was originally called Dekalb Monsanto MXP200.) Note that this advantage is due mostly to the superior fertility of GPK347 gilts and first parity sows (Table 3). This line produced 36% more litters through their sixth parity.

After the first two parities, the percentage of sows leaving the herd due to illness, injury, death and infertility is nearly the same in each parity for all genetic lines (see Table 4).

The figures in Table 4 reinforce that an opportunity to improve sow longevity exists by developing gilts with the highest P1 farrowing rate. Simply stated, the gilt must farrow a first litter. Anything done to improve her first parity farrowing rate should indirectly improve sow longevity.

The first opportunity for improving herd performance is selecting a maternal line with higher fertility. Of course, this is easier said than done given the lack of reliable data available. The heritablities of fertility traits are low to medium so improving the environment in which gilts are developed should improve farrowing rates. Sow longevity may be improved by implementing gilt development programs (i.e. gilt nutrition, boar stimulation, acclimatization) that better prepare gilts for mating success.

There has been remarkable improvement in prolificacy traits, such as pigs weaned/litter, throughout the industry. The results presented here show that great opportunity remains for increasing breeding herd output. Greater attention to fertility traits is needed to capture this opportunity.

Table 3. Percent of 3283 entered females that produced litters by line and parity.

Genetic Line	P1, %	P2, %	P3, %	P4, %	P5, %	P6, %
American Diamond Genetics	77	64	57	50	40	30
Danbred USA	77	63	56	48	39	26
Monsanto DK44	75	65	57	50	39	32
Monsanto GPK347	92	83	77	70	63	51
National Swine Registry	76	63	57	52	43	32
Newsham Hybrids USA	78	65	59	52	43	30
Total Litters	2602	2206	1984	1750	1459	1104

Table 4. Parity to parity loss of females by line.

Genetic Line	P1, % *	P2, %	P3, %	P4, %	P5, %	P6, %
American Diamond Genetics	23	13	7	7	10	10
Danbred USA	23	14	7	8	9	13
Monsanto DK44	25	10	8	7	11	7
Monsanto GPK347	8	9	6	7	7	12
National Swine Registry	24	13	6	5	9	11
Newsham Hybrids USA	22	13	6	7	9	13

*Percent of entered gilts that never farrowed a litter.

Table 5. Production of 130 cohorts through six parities.

Genetic Line	Total sow days	Ave sow life, days	Total pigs born	Total pigs born live	Live pigs / sow day	Total litters born
ADG	14138 b	566 b	835 c	758 c	.054 d	79.7 b
DB	13632 b	545 b	860 bc	767 bc	.056 cd	76.9 b
DK44	14009 b	560 b	944 b	843 b	.060 b	80.5 b
GPK347	17197 a	688 a	1312 a	1172 a	.068 a	109.0 a
NSR	14033 b	561 b	871 bc	790 bc	.056 c	80.6 b
NSH	14230 b	569 b	870 bc	790 bc	.055 cd	81.4 b

Means with the same superscript are not different (P>.05).

Table 6. Six parity output among the 130 MLP cohorts.

Trait	Best cohort	Worst cohort	Goal
Total litters born	127	40	150
Live pigs born	1347	397	1575*
Ave sow life, day	781	358	900
Total sow days	19542	8957	22500**

* 10.5 live pigs born per litter

** 900 day life times 25 sows

Sow longevity is a complex goal that involves genetics, nutrition, herd health and breeding herd management. Improvement must include a strategy that includes all areas of management. Detailed reproductive records, starting when gilts enter the herd, and sow feed consumption records may be the best tools to maintaining high performance sows in the herd.