Having a breeding objective implies a desire to change an animal genetically. This in turn implies a need to improve an animal’s performance or productivity, as breeding is undertaken—or should be—with end users in mind.
But the end animal should also be considered. Its health, welfare and the system it is raised in all contribute to an end product and ultimately influence profitability.
Take dairy cattle. A cow in Africa may produce just over half a litre of milk a day, while in developed countries a cow can produce as much as 34 litres a day. This improvement has come from many generations of selecting for large udder size amongst other things. But how much larger can an udder get before a cow literally falls apart? Modern dairy cows already suffer complications from swollen udders, such as mastitis and lameness. Is continuing to breed for yet more milk production really the way to go? At what point is continual, linear, “improvement” no longer an improvement?
There is a phrase worth noting in any breeding programme: intermediate optimum. This is the value for a trait at which function or profitability is optimal.
A dairy cow may have optimal profitability with a “just right” udder size at which milk production, health and wellbeing are in equilibrium. Too small an udder, and production and profit drop. Too big, and health problems overwhelm production and profit.
An example of optimal function is hock set in animals, or the angle at the hock. Horses are especially prone to lameness if this angle is smaller or larger than the optimum. There is no valid reason to change this phenotype once the ideal angle is consistent amongst a breed.
Thus “improvement” doesn’t have to mean continual and linear change. “Improvement” instead could be the continual increase in uniformity across a breed by selecting for animals that meet optimum or near optimum performance for certain traits.
- Davis, K Jr. 2018. The Cash Cow of Africa (Part I): Dairy. Retrieved 24th March, 2018.