Dorset
NSIP Notebook
July 7, 2005 Number 6
David Notter, Larry Kuehn, and Randy Borg
Department of Animal and Poultry Sciences
Virginia Tech
The 2005 Dorset Genetic Evaluation
Introduction
The US National Sheep Improvement Program (NSIP) is pleased to release the results of the 2005 Dorset genetic analysis.
The Data
Data were received from seven flocks: two from Michigan, and one each from Indiana, Illinois, Pennsylvania, Virginia, and West Virginia. Data reported in 2005 included records on 270 adult breeding ewes with mating records that produced 426 live lambs. The lambs were offspring of 22 Dorset rams. Following editing, valid records were received for 2005 on 268 60-day
weaning weights, 122 postweaning (120-day) weights, and 251 litter sizes. The entire NSIP Dorset database now contains valid records on 4,890 60-day weaning weights, 1,544 postweaning (60- to 120-day) gains, and 4,203 litter sizes.
Means for each trait are shown below. Weaning weights were adjusted to a single birth and rearing, adult dam, and ewe lamb basis. Postweaning gains were not adjusted, but male and female lambs were placed in different contemporary groups. Litter sizes were adjusted to an adult ewe basis.
Trait Mean
60-day adjusted weaning weight 63.2 lb
postweaning (60- to 120-day) gain 0.70 lb/day
litter size 1.85 lambs
EPDs were calculated for a total of 8,525 animals, including 2,356 breeding ewes and 483 sires. While most flocks had some level of connectedness with at least one or two other flocks, connections in most cases remained limited. Thus, comparisons between animals from different Dorset flocks should still be made with care.
The 2004 Dorset lambing-weaning data were received at the genetic evaluation center on June 6, 2005. EPD’s were returned to the data coordinator on June 28, giving a processing time of 22 days.
2005 Dorset Sire Summary
The 2005 NSIP Dorset Sire Summary is also now available for distribution to breeders and other interested parties. In order to be eligible for the Sire Summary, a ram must have prediction errors of not more than 1.5 pounds for weaning weight, 2.0 pounds for 120-day postweaning weight, or 1.1 pounds for maternal milk. This year's Dorset sire summary contained EPDs for 45 rams, a 15% increase over last year. The sire summary listing includes only rams born after July 1, 1997 and this year contained 17 rams, a 21% increase over last year. Again, breeders should continue to exercise care in using these results across flocks because of the limited genetic connections.
NSIP Dorset Genetic Trends
Genetic trends in EPDs since establishment of NSIP in 1986 are shown in Figure 1, and document the traits that have received emphasis in NSIP Dorset flocks. Each point represents the average EPD of all animals born in each year since 1986. Substantial fluctuations over years were observed in the early years of NSIP. However, since the advent of the across-flock genetic analysis in 1999, consistent and significant increases have been observed in 60-day weaning and 120-day postweaning weight EPDs. Little change appears to be occurring in maternal milk, but relatively consistent increases in percent lamb crop were observed between 1992 and 1999. Little change in percent lamb crop has been observed since 1999, suggesting that, with a mean litter size in adult Dorset ewes of 1.85, breeders may see little need to further increase litter size. Declines in body weight EPDs for 2005 should be viewed as preliminary only, since the fall-born 2005 lambs are not yet included.
