The National Genetic maternal Line Evaluation Program (MLP), completed three years ago, showed distinct reproductive advantages for an F1 female that was a cross of the Nebraska Line (NI) line with Monsanto Choice Genetics maternal lines.

Since then, pigs of the NI line were released to several breeding organizations that have marketed NI line cross females to commercial producers. Data on the performance of these gilts are beginning to accumulate. This report summarizes that information with the objective of determining whether the NI cross gilts are living up to their reputation derived from the MLP results.

Monsanto Choice Genetics has since obtained exclusive rights to the line outside of Nebraska.

Development of NI Line

For those unfamiliar with the hyper-prolific NI line, it was developed in a selection experiment at the University of Nebraska, begun with a cross of Large White and Landrace in 1979. After two generations of random mating to mix the genes from the two breeds, index selection for increased ovulation rate and increased embryonic survival was initiated in 1981.

Index selection was practiced until 1991, a total of 11 generations. From 1991 to 1996, selection has focused on increased litter size at birth, emphasizing total number born. After 1996, emphasis was placed on number of live pigs born. Selection for increased growth rate and decreased backfat was included in the selection objective in the last three years.

Litter size in the NI line in the last generations has ranged from 13.5 to 14.2 pigs/litter — approximately four pigs/litter greater than a randomly selected control line. Until selection for growth and fat was initiated in 1999, no correlated changes in growth or carcass traits had occurred.

MLP Results Overview

In 1996, a cooperative effort between the University of Nebraska and Monsanto Choice Genetics provided gilts from a cross of NI lines with Monsanto lines to be evaluated in the checkoff-funded MLP test. Performance of these females was compared with that of females of five other industry lines through four parities, with approximately 625 gilts per line.

Table 1. Comparison of Performance of Nebraska Index (NI) Line Cross Females and Standard Cross Females in Herds in Which Both Types of Females Were Contemporary (6 Herds Represented)
NI line cross females Standard cross females
Trait Number Mean Number Mean Percentage advantage
Age at 1st service, days 679 219 1,865 221 0.9
Farrowing rate, % 2,019 84.9 3,439 79.3 7.1
Total born/litter 2,327 12.8 4,799 11.9 7.7
Pigs born live/litter 2,327 11.7 4,799 10.9 7.3
Weaning-to-service interval, days 530 6.9 1,805 7.2 4.2


Results of the MLP were widely published (see “Maternal Line Genetics” Blueprint, National Hog Farmer, April 15, 2000).

The bottom line, the total production of the NI cross gilts was 30 to 50% greater than other lines. Identified as MXP200 females in the test, but subsequently renamed GPK347 by Monsanto, the gilts bred at a younger age, and sows had greater conception rate, litter size, and shorter weaning-to-estrus intervals through four parities. Economic value of this enhanced reproduction was partially offset by slower growth and somewhat fatter carcasses in the progeny of GPK347 dams.

NI Lines Released

A controlled release of breeding animals from the NI line was approved in 1996. An advisory group representing Nebraska pork producers and several breeding organizations developed the guidelines by which the line would be made available to breeding organizations.

The first release occurred in 1997 to a breeding organization in Brazil known then as Granja Rezende S.A. Over the next two years, pigs were released to 10 additional breeding organizations including Newsham Hybrid, Monsanto Choice Genetics, Cotswold Pig Development Company, Premier Swine Breeding Systems, Hermitage Exports Ltd., Danbred North America, National Genetic Technology, two private breeders in Nebraska (Waldo Farms, C. Papenhausen), and a consortium of Iowa-Missouri breeders (B. Sleazer, P. Howerton).

Table 2. Mean Performance of Nebraska Index (NI) Line Cross Females Across Herds
Trait No. herds No. records Mean Range (min. and max. herd means)
Age at 1st service, days 1 679 219
Farrowing rate, % 15 4,261 82.1 62.5 - 90.9
Total born/litter 15 4,569 12.3 10.9 - 13.8
Pigs born live/litter 15 4,569 11.2 10.0 - 12.4
Pigs weaned/mated female/year 8 1,973 22.6 20.8 - 26.2
Weaning-to-service interval, days 11 5,811 8.2 5.9 - 11.5


Most organizations obtained pigs of one sex only or obtained small numbers of pigs of both sexes. Monsanto sampled significant numbers of both males and females and is the only organization to have sampled in a way that will permit the line to be maintained long-term as a pure-line population.

The NI line samples were incorporated into the respective breeding organization lines in a variety of ways, ranging from continued pureline production to development of composite populations.

For the most part, breeding organizations are using their new maternal line composites to produce F1 gilts with either 50% or 25% NI line genes. At this point, a significant number of these crossbred females have been tested in commercial herds and a limited amount of information is available.

NI Line Genetics Field Data

No official data are available on the number of herds or sows of NI line descent being used in the industry. The performance data available from commercial herds are presented in Tables 1 and 2.

Table 1 compares the performance of females with NI line cross genes with standard cross females across six herds in which both types of females were contemporary. Average parity of females was approximately 1.6 for NI line cross females and 1.8 for standard cross females. The “means” are weighted averages across parities and herds.

The data shows NI line cross females had advantages over standard cross females that ranged from 0.9% for age-at-first service, to approximately 7.5% for litter size. Differences were similar across all parities and are similar to differences between GPK347 females and other crosses found in the MLP test.

Data in Table 2 show the performance of more than 4,500 NI line cross females across 15 herds. These data include production of only NI line cross females with no comparison to other crosses. They should be used only to get a general sense of levels of production being realized with these females in a variety of commercial settings. Considerable variation among herds in all traits existed, which is clearly illustrated by the range in number of pigs weaned/mated female/year, which went from 20.8 to 26.2 pigs.

General Comments

Crossbred females with NI line genes are expressing levels of performance in commercial herds that are very similar to those seen in the MLP results. Improvements in fertility, litter size and rebreeding performance are realized in crosses of this line with a wide range of other maternal lines. Breeding organizations with these pigs are continuing to develop and evaluate not only the maternal performance of the lines, but also the growth and carcass merit of terminal cross progeny.