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Genotype x environment interaction (G x E) effects on live weaning weights of lambs were studied by using the 2 breeds Norwegian White sheep (NWS; heavy, long-tailed) and Spel sheep (Spel; lighter, short-tailed) as genetic groups (G). A total of 37,338 NWS lambs and 30,075 Spel lambs born from 1989 to 1999 on 40 farms that kept both breeds together were included in the analyses. Environment was characterized by farm x year (E). In a mixed linear model framework, significance of the random G x E effect and breed-specific environmental variances were tested by using a log-likelihood approach. Directions and magnitudes of the effect were described through variance component estimates. An across-genotype environmental correlation was also used. There was a significant G x E effect on lamb BW; significant breed differences were found for variance of flock x year effects, indicating different phenotypic plasticities with changing flock x year environments, with the NWS being more sensitive to environmental change. Further, the breed-specific residual variance was greater for NWS, indicating that the effects of environmental variation were larger for the weaning weights of the NWS breed within flock and year. Further, the correlation between flock x year effects for the 2 breeds was significantly different from unity (0.82 [+ or -] 0.02), indicating that the common environment is 'perceived' differently in the 2 breeds. The best environment for one breed is not necessarily best for the other breed, and vice versa. Solutions of flock x year effects may be used to describe how environmental characteristics such as climate and topography affect the production of different genotypes, and for clustering of environments, thus facilitating improvement of breeding programs and management schemes for domestic and wild ungulate populations. Key words: breed, genotype by environment interaction, phenotypic plasticity, sheep, weaning weight

Genetic correlations between reproduction and production traits were estimated in swine. Reproduction traits investigated were age at first service (AFS), number of live-born piglets in the first litter (NB[A.sub.1]), interval from weaning to first service after first litter (WT[S.sub.1]), number of live-born piglets in the second litter (NB[A.sub.2]), and interval from weaning to first service after the second litter (WT[S.sub.2]). Females generating the data were Norwegian Landrace born in nucleus herds between 1990 and 2000, and the number of records ranged from 13,792 to 56,932. Genetic correlations were estimated among the main production traits in the breeding goal: adjusted age at 100 kg live weight (A100), percentage of lean meat content (LMC), individual feed consumption from 25 to 100 kg (FC), and bacon side quality (BSQ). Average adjusted backfat thickness (BF) was included as a production trait. The A100 and BF traits were recorded on gilts on-farm with 190,454 records, whereas LMC, BSQ, and FC were recorded on-station with the number of records ranging from 12,487 to 12,992. Analyses were carried out with a multivariate animal model using average information restricted maximum likelihood procedures by first running each reproduction trait with A100 and BF, followed by each reproduction trait with LMC, BSQ, and FC. Average heritabilities for reproduction traits were as follows: AFS (0.38), NB[A.sub.1] (0.11), WT[S.sub.1] (0.06), NB[A.sub.2] (0.12), and WT[S.sub.2] (0.03); and for production traits: A100 (0.30), BF (0.44), FC (0.22), LMC (0.58), and BSQ (0.23). The highest genetic correlation was estimated between A100 and AFS ([r.sub.g] = 0.68), also resulting in a positive genetic correlation between FC and AFS. Growth (A100) was negatively (i.e., unfavorably) genetically correlated to NB[A.sub.1] and NB[A.sub.2] ([r.sub.g] = 0.60 and [r.sub.g] = 0.42 respectively), and so the genetic correlation to FC also became unfavorable ([r.sub.g] = 0.23 and [r.sub.g] = 0.20). Single-trait selection for enhanced LMC would also affect NB[A.sub.1] and NB[A.sub.2] unfavorably ([r.sub.g] = -0.12 and [r.sub.g] = -0.24). Correlations between BF at 100 kg live weight and reproduction traits were close to zero; however, a low genetic correlation between BF and WT[S.sub.1] was obtained ([r.sub.g] = -0.12), indicating that selection toward reduced BF at 100 kg live weight may have an unfavorable impact on WT[S.sub.1]. Key Words: Genetic Parameters, Heritability, Litter Traits, Pigs, Production, Reproduction

The overall twinning rate was shown to increase from .6% in the first parity to 4.0% in the sixth parity, and a positive phenotypic trend for twinning rate was observed during the time period considered (1978 to 1995). The distribution of bulls according to the average percentage of multiple births of daughters in first and second parity showed that some bulls had an extremely low twinning frequency and others exceeded the population mean by approximately six times. (Co)variance components were estimated for twinning in first and second parities using a linear sire model. The analysis included either first- and second-crop daughters (1.4 and .9 million records for first- and second-parity cows, respectively) or first-crop daughters only (.6 and .4 million records for first- and second-parity cows, respectively) from 2,043 sires. Heritability estimates were .7 to .8% in the first parity and 2.8% in the second parity. The genetic correlation between twinning in the first and second parities was approximately 1. Part of the phenotypic trend observed can be explained by a genetic trend for twinning rate. Key Words: Twinning, Norwegian Cattle, (Co)variance Components, Genetic Trend