Total teat number in a Large White and a British Landrace population had a modal number of 14. The trait was highly leptokurtic, indicated by the fact that 086 of the population falls within one standard deviation of the mean. There was no sex difference in total teat number, although a small but significant breed difference existed. Heritability of the trait was low, of the order of 0·10 to 0·20 based on the sire component of variance. Larger dam terms suggested a maternal effect.Severely inverted teats (nipple invisible) were observed in 0·17 of gilts. Mean number of inversions was 0·738 in the entire population but 4·01 in affected gilts. The heritability of the trait was of the order of 0·20 and a maternal component was possibly involved.Inverted teats are not distributed at random. They occur most frequently in the umbilical and anterior regions and diminish sharply in frequency towards the rear. In this study 0·97 of all affected pigs had one or more inverted teats in the umbilical and anterior regions.

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1. Analyses of records of eight-week body weight in broiler chickens have been carried out to estimate the effect of management level (measured by mean body weight of all varieties on each farm) on the components of variance due to differences between and within varieties, and to find out if there is any evidence of genotype-environment interaction.2. It was found that as management improved, the between-variety genetic variance remained constant or possibly increased whilst the withinvariety (genetic and environmental) variance decreased markedly. The cause of these regressions is not known.3. In four cases out of six there were significant genotype-environment interactions. In two cases, the genetic correlation between the performance of varieties on different locations was significantly different from 1·0.4. It is suggested that on the basis of these findings it would be necessary to select between varieties on records taken from chickens maintained under conditions similar to those in which they will eventually be used. However, fewer chickens would be required to measure, with a predetermined level of accuracy, mean differences on well managed farms than on poorly managed ones.