A statistical approach is presented for selection of best performing lines for commercial release and best parents for future breeding programs from standard agronomic trials. The method involves the partitioning of the genetic effect of a line into additive and non-additive effects using pedigree based inter-line relationships, in a similar manner to that used in animal breeding. A difference is the ability to estimate non-additive effects. Line performance can be assessed by an overall genetic line effect with greater accuracy than when ignoring pedigree information and the additive effects are predicted breeding values. A generalized definition of heritability is developed to account for the complex models presented.

The optimum duration of test for measurement of growth rate, feed intake, feed conversion, and residual feed intake was examined using postweaning feed intake and weight data from 760 Angus, Hereford, Polled Hereford, and Shorthorn heifer and Angus bull progeny from 78 sires. Variance components, heritability, phenotypic and genetic correlations, and the efficiency of selection using shortened tests compared with a 199-d test were used as criteria to assess the optimum test length. The results indicated that a 35-d test was sufficient for measurement of feed intake, whereas a 70-d test was required to measure growth rate, feed conversion, and residual feed intake without compromising the accuracy of measurement. When a 70-d test is used to measure growth rate, feed conversion, and residual feed intake there is minimal loss in accuracy when weights are collected every 2 wk instead of weekly, but a further increase in the interval between weights to 5 wk caused a decline in the accuracy of the test. Therefore a 70-d test with cattle weighed every 2 wk seems to be optimal for measuring these traits in British breed cattle.

The fatty acid composition of the triacylglycerol fraction of shoulder fat from Limousin and Jersey yearling heifers, yearling steers, and non-lactating cows was investigated. Significant breed differences in the degree of fatty acid saturation were apparent between Jersey and Limousin cows, but were not observed in the yearlings. Jersey cows had less saturated fatty acids than the Limousin. Jersey cows showed an increased percentage of monounsaturated fatty acids compared with the Jersey yearlings. In contrast, the level of monounsaturated fatty acids in the Limousin cows was the same as in the Limousin yearlings. The calculated indices of enzyme activities also differed between the breeds. Jersey cows had higher indices of Δ9-desaturase and elongase activities than Limousin. This was also reflected by differences in the ratios of total unsaturated and polyunsaturated to saturated fatty acids. Breed differences were also observed in the triacylglycerol fatty acid chain length. In this case, however, yearlings showed significant breed differences that were not detected in the cows. Limousin yearlings had more long chain fatty acids (C16 and C18) than the Jersey yearlings. Limousin yearlings also had a higher elongase activity index than their Jersey counterparts. Thus, breed and age affect the fatty acid composition in these cattle.

A quantitative trait locus (QTL) was identified by linkage analysis on bovine Chromosome 19 that affects the fatty acid, myristic acid (C14:0), in subcutaneous adipose tissue of pasture-fed beef cattle (99% level: experiment-wise significance). The QTL was also shown to have significant effects on ten fatty acids in the milk fat of pasture-fed dairy cattle. A positional candidate gene for this QTL was identified as fatty acid synthase (FASN), which is a multifunctional enzyme with a central role in the metabolism of lipids. Five single nucleotide polymorphisms (SNPs) were identified in the bovine FASN gene, and animals were genotyped for FASN SNPs in three different cattle resource populations. Linkage and association mapping results using these SNPs were consistent with FASN being the gene underlying the QTL. SNP substitution effects for C14:0 percentage were found to have an effect in the opposite direction in adipose fat to that in milk fat. It is concluded that SNPs in the bovine FASN gene are associated with variation in the fatty acid composition of adipose fat and milk fat.

A statistical approach for the analysis of multi-environment trials (METs) is presented, in which selection of best performing lines, best parents, and best combination of parents can be determined. The genetic effect of a line is partitioned into additive, dominance and residual non-additive effects. The dominance effects are estimated through the incorporation of the dominance relationship matrix, which is presented under varying levels of inbreeding. A computationally efficient way of fitting dominance effects is presented which partitions dominance effects into between family dominance and within family dominance line effects. The overall approach is applicable to inbred lines, hybrid lines and other general population structures where pedigree information is available.