Uniformity or variation, that is the question. Uniform products in retail outlets and genetic variation in selection populations are desired. More uniform -birth weight in pigs,- color of eggs and -milk production per day in cattle makes life of the farmer easier and improves product quality. Phenotypes within families show genetic variation in variation; some families are more uniform than others.

Background: Consumers in Japan are frantic about uniformity and pay readily higher prices for uniform consistent food. Uniformity and predictability is high on the agenda of farmers too. Litter size of sows is between 5 and 25 piglets per litter. Life of piglets and farmers would be much easier if variation would be between 12 and 18 piglets.

Methodology: Standard genetic modeling includes environmental and genetic effects and the inevitable residual. Interestingly part of this residual variation is heritable. Some families fit their expectation better than others. A second step, therefore, analyses the residual variance for genetic components. Iteration links both models for highest likelihood. The carrot here is that the protocol can be applied to all traits under selection, and help to improve robustness to environmental challenges in animals and, hence, decrease stress and disease pressure, reducing the use of medication and increasing welfare

Results: Interpretation of the results is not straightforward since the method involves a double hierarchical generalized linear model . One of the very few traits to test methodology is within litter standard deviation of birth weight in pigs, since it can be analyzed as a trait of the sow and analyzed as a trait of the individual piglet. Results of both methodologies are highly similar (Sell-Kubiak et al.,2014)

Implications and further study: Methodology can help product quality through uniformity, it can help animals and farmers in more balanced levels of production, without extreme outliers and it can definitely help to adapt animals to their environment. The latter is a risk too, since environments can change, in the wild and in human restricted situations.

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