Field data analysis of cytoplasmic inheritance of dairy and fitness-related traits in cattle

Abstract

Field data of the Austrian Simmental population were analysed using restricted maximum likelihood (REML) with an animal model where additive direct, additive maternal and cytoplasmic effects were treated as random and the effect of the year of first calving as fixed. Traits analysed were milk yield, fat and protein content, persistency, days open and herd life. All dairy traits were pre-adjusted for best linear unbiased prediction (BLUP) herd-year effects, milk yield additionally for season, age at first calving and days open. After applying specific data restrictions, the number of records for the various traits ranged from 3360 to 51889. Identification of cow lineages was based on pedigree information from the official milk recording scheme, with a span of at least four and up to 16 generations. The number of lineages per trait varied and ranged from 484 to 3195, with an average size of 15 members (for herd life 7). Evaluations of the relevant variance components for the dairy and fitness-related traits investigated were separate for the first three lactations.The estimated variance components for cytoplasmic effects were close to zero for all dairy traits with the exception of first lactation milk yield, where a significant value of 2.0% of the total phenotypic variance was found. Significant contributions of cytoplasmic lineages to total variance in all lactations, however, were estimated for persistency (2·6 to 3.8%), days open (1·8 to 2.9%) and for both true and functional herd life (4.6% each). The portions of additive maternal variance and covariance between additive direct and additive maternal effects on total variance were very close to zero for all traits investigated. The maximum differences between BLUP lineage effects were 373 kg for first lactation milk yield, 44 days for days open (first lactation), 1·6 and 2·8 years for true and functional herd life and, on average, 1·0 kg for standard deviation of test day milk yields (persistency) of the first three lactations.Removing the cytoplasmic effect from the model led to increased estimates of the additive direct heritability. Further model aspects such as interaction between additive and cytoplasmic gene effects and possible confounding between cytoplasmic and herd effects are discussed.

Effects of cytoplasmic inheritance on preweaning traits of Hereford cattle

“…Roughsedge et al (1999) confirmed a significant effect of maternal lineage on fat yield (5% of the phenotypic variance) in a Holstein Friesian herd. Interestingly, Schnitzenlehner and Essl (1999) detected a significant maternal line contribution to variance in fitness-related traits (persistency, days open and herd life) in Austrian Simmental cattle. Analysis of a Holstein cattle data set by Albuquerque et al (1998) concluded that the contribution of the cytoplasmic line to the total variance of milk yield was only 1.1%, to fat yield 0.8% and to percentage fat 0.9% and were too small to be relevant to genetic evaluations, a conclusion subsequently supported by the work of Rorato et al (1999) who found that in the same data set the maternal lineage only accounted for 1.1% of the phenotypic variance of milk yield.…”

“…biometric or molecular) over the other. While some workers have reported a significant influence of mitochondrial genes on performance (Schutz et al, 1994;Mannen et al, 1998;Roughsedge et al, 1999;Schnitzenlehner and Essl, 1999) others have concluded that the effect of such genes is negligible (Rohrer et al, 1994;Albuquerque et al, 1998;Rorato et al, 1999) and it therefore appears that the importance of mitochondrial genome on cattle performance has not yet been fully elucidated.…”

Exploration of cytoplasmic inheritance as a contributor to maternal effects in Welsh Mountain sheep

“…Some authors have commented that analyses on small datasets from a limited number of populations may reduce the ability of tests to find significant differences between maternal lines [9,12,15,16]. Mezzadra et al [12] examined the influence of cytoplasmic inheritance by a method of assigning maternal lines, in addition to analysing the direct association between mitochondrial DNA polymorphisms and productive traits.…”

“…It should be noted, however that the same mitochondrial genotype can occur in different families. It was pointed out by Schnitzenlehner and Essl [15] that treating animals as members of a maternal line to have the same mitochondrial genome can become more unreliable with increasing numbers of generations, since the probability of mutation increases with increasing distance from the foundation dam.…”

“…Mannen et al [10] studied the association between the variation of transcribed mtDNA and variation in carcass traits in beef cattle, and it was suggested that one polymorphism was associated with meat quality traits, the longissimus muscle area and beef marbling score. Schnitzenlehner and Essl [15] found that cytoplasmic effects were non-significant for dairy traits, but significant for fitness traits in cattle. Nevertheless, even if associations between mitochondrial polymorphisms and economically important traits exist, Sutarno et al [20] commented that mitochondrial markers were less valuable than nuclear ones in marker-assisted selection because they are maternally inherited, and because selection intensities in females are much less than in males, and producing far fewer progeny than males.…”