First year start-up data on six genetic lines in the NPPC Maternal line study provides clues about gilt handling, performance differences.

The reproductive life expectancy of replacement gilts has far-reaching, bottom-line effects in today's pork production systems. The purchase of specialized maternal lines represents a significant investment. For producers to realize a sufficient payback, those gilts must be long lived and produce fast-growing, lean market hogs with good meat quality.

The largest study of commercial sow efficiency, including longevity, has completed its first year. Sponsored by the National Pork Board and conducted by the National Pork Producers Council (NPPC), this three-year study is evaluating the reproduction, growth, carcass traits, and meat quality performance of six maternal genetic lines under modern-day commercial management and facilities.

The six genetic lines are being tested for longevity through four parities. Lifetime production of each sow line will be evaluated to determine the economic value of each line.

Testing Protocol A total of 3,560 gilts from 39 different farms were delivered to wean-finish units last spring. The 10-15 day old gilts represented six commercially available genetic lines. Seedstock suppliers participating include: American Diamond Genetics, Danbred USA, DeKalb Swine Breeders (two lines), National Swine Registry and Newsham Hybrids USA. About 590 gilts per line were delivered, grouped 25/pen. Each wean-finish building held about 1,100 pigs.

All gilts were vaccinated for Porcine Reproductive and Respiratory Syndrome (PRRS) and swine influenza virus (SIV) in the wean-finish units. Ivomec was used at entry along with a three-day Naxcel protocol. Mecadox was fed to young pigs according to label directions.

The gilts were fed a 23% protein (1.7% lysine) diet until they weighed 20 lb. From 20-30 lb., a diet with 1.5% lysine was fed. As pigs reached 30 lb. they were switched to a corn-soy starter diet that contained 1.35% lysine and added fat. These diets all contained Mecadox.

>From 70-150 lb., pigs were fed a corn-soy grower diet that contained 1.2% lysine with added fat. Tylan was added to the grower diet at 40 g./ton. The gilt developer diet was corn-soy with .8% lysine. Complete diet formulations are available from NPPC.

All gilts were weighed after 50 days on feed and again at about 165 days of age. Gilt performance in the wean-finish buildings was excellent. Table 1 shows the average gilt performance and a comparison of the best and poorest lines.

The 50-day gains in the wean-finish units compared very favorably with previous research conducted by NPPC using specialized hot nursery buildings. Record analysis verifies the value of heavier pigs at weaning. A 1-lb. heavier pig on delivery translates to a 2-lb. heavier pig at 50 days and 3-lb. heavier at 150 days.

The number of gilts moved to the sow units divided by the number of young gilts placed in the wean-finish buildings is the survival rate listed in Table 1. Gilts weighing less than 7 lb. at entry had a survival rate of 85% while gilts heavier than 7 lb. had a 94% survival rate.

As gilts approached 165 days of age (150 days in the wean-finish unit) they were evaluated for health concerns and abnormalities by the attending veterinarian, the unit manager and an NPPC project manager.

About 3% of the gilts were culled for umbilical hernias, chronic illness and severe injuries. Mortality rate was 5%. The remaining 92% (3,284) of the gilts were given electronic ear tags and moved to two new, 1,600-sow breeding-gestation-lactation units in Iowa. This move occurred when all gilts were 165 days old or younger. No gilts were culled for growth or backfat.

Gilt Prep and Mating Gilts were vaccinated for leptospirosis and parvovirus and housed in gestation stalls. They were ad libitum fed a corn-soy diet with .65% lysine upon arrival to the sow units.

These gilts were exposed to vasectomized boars daily to stimulate estrus. Gilt age at first-observed estrus varied by line. The average was 193 days of age; the best line averaged 178 days, the poorest line, 201 days of age.

The program protocol requires gilts to be mated at the second or later estrous period. Eligible gilts - those exhibiting their second estrus - were mated after they were 205 days old. Gilts were bred when found in estrus and every 24 hours while in estrus. All gilts were artificially inseminated (AI).

Gilts were given three mating periods (60 days) to conceive. Failing that, they were culled. And, any gilt not showing estrus by 300 days of age was culled. All gilts (433) failing these two standards were slaughtered and their reproductive tracts were evaluated by Don Levis, swine reproductive specialist at the University of Nebraska (See Table 2.).

The 108 "normal cycling" gilts in Table 2 included 81 gilts that were found in estrus and bred (some during up to three estrous periods), but never settled, or gilts with their first estrus identified; but subsequent estrous periods were not seen. No gilts were bred on their first estrus. That left only 27 gilts identified in the slaughter checks as"normal cycling" females that were never detected in heat by the farm managers - an excellent result.

Interestingly, 60 of the gilts recorded as displaying estrus actually never cycled, therefore landed in the "not cycling" status when the slaughter checks were complete. Because the program protocol required mating of gilts at second estrus, herdsmen may have reported these gilts in heat if there was any question, thus allowing them to be bred on the next estrus.

The four pregnant gilts listed in Table 2 are victims of unrecorded, weekend matings. By totaling the gilts that were mated, those that cycled normally, those that quit cycling and those found pregnant in the slaughter check, we recorded 89.3% of the gilts entering the sow units as being potentially fertile.

Feeding Feed was restricted to 4 lb./day for the first 14 days after mating, then fed 4.5-5.0 lb./day for the remainder of the gestation period. A lactation diet with 1.2% lysine is fed three times daily to encourage consumption.

After their first parity, sows are fed, ad-lib, from weaning to mating. When bred, all sows are fed 4 lb. daily for 14 days after mating. Thereafter, the amount fed in gestation is based on each sow's weight, lactation weight loss and desired second parity weight gain. Sows are fed to optimize each individual's performance.

Gilt Performance To Date One year after the early weaned gilts arrived at the wean-finish units, 2,679 still remained in the two sow units. That is slightly over three-fourths (75.3%) of the gilts. The best line for survival from early wean entry to one year of age was 86%, the poorest, 70%.

Those 2,679 gilts represent 81.6% of gilts that entered the sow units at 165 days of age. The best line has 93% of the gilts surviving since their move to the sow units, the poorest line has 77%.

The value of early weaned gilts is greatly influenced by the number of gilts surviving, the length of their reproductive life and their reproductive output while in the herd. Likewise, there is a significant investment in developing the gilts and value in acquiring an improved herd health status.

Table 3 shows start-up, first-parity reproduction performance in the farrowing units from December 20, 1997 to March 15, 1998. About two-thirds of the gilts (66%) have farrowed their first litter. On average, the first-litter gilts from the six genetic lines are performing admirably.

In addition to the reproductive performance tracking, backfat loss and weight loss during the first (and subsequent) litters is being recorded. Last rib backfat is measured on all sows as they enter the farrowing crate and within two days after they are weaned. The last rib measurement was chosen because researchers felt it could be measured with more consistency in sows. The Sonic Industries' A-Scan is used.

To date, first-parity gilts have averaged .88 in. last rib backfat going into the crates, ranging from .31 to 1.49 in. The average lactation backfat loss has been .13 in., ranging from zero to .58 in.

Scales strategically located in the alley between the farrowing and breeding-gestation units have made collecting sow weights easy. The average weight of first-parity sows going into the farrowing crates has been 440.5 lb., ranging from 270 to 570 lb. The average weight loss during lactation has been 58.8 lb./sow, but the range was between 2.0 and 140 lb./sow.

Recap The results of Maternal Line Program gilt development project has shed some light on recent trends to early wean gilt purchases. Realizing that information on all first-litter gilts is not in and the results should be treated as "preliminary," these points should be considered:

* Gilt weight on delivery is important. Smaller gilts have a lower survival rate.

* Seedstock supplier history of leg unsoundness and umbilical hernias in gilts. These two factors prevented good gilts from moving into the sow units.

* About 8-10% of gilts moved to the sow units may have reproductive problems that will prevent them from ever conceiving. There appears to be real differences between lines, verified by slaughter checks conducted in this project. Ask for references to check other producers' experience with specific lines. Poor estrous detection could inflate the percentage of gilts blamed with reproductive problems.

* The early weaned gilt value depends on survival rate through breeding.

An extension of this maternal line program is the progeny testing of one pig from each gilt litter. A pig/litter will be randomly selected, then tested for growth, feed efficiency, carcass and meat quality traits. The first group is on test now. Producers will have extensive information to compare the economic values of maternal lines when complete program results are presented in 2000.

This information was compiled and written by Rodney Goodwin, NPPC Director of Production Research, with the assistance of Dave Boyd, NPPC Research Programs Manager. For more information contact Goodwin or Boyd at NPPC, P.O. Box 10383, Des Moines, IA 50306 (515-223-2600).