To reliably evaluate a sire within a herd, he should have progeny in three or more contemporary groups to improve the accuracy of his EBV or EPD predictions. Sires represented within a contemporary group should never be unique to that contemporary group alone. Within a contemporary group at least one sire should have progeny in another contemporary group. This will likewise improve the evaluation of a boar in both a within and across herd evaluation. Reproductive or farrowing traits are typically those collected on females at farrowing, weaning, and rebreeding.
Females are often of different parities and ages.
A reproductive contemporary group or farrowing group are those females of the same breed and have minimal age differences among litters. All females that farrow a litter should be measured. Furthermore, litter size should be standardized soon after farrowing. Thus, if litter size between sows is relatively the same, differences in the number and weight of pigs at a target lactation age will more reflect genetic differences for milking ability among sows. Designation of farrowing groups must occur with the same if not more forethought as that of post-weaning contemporary groups.