The American Kerry Cattle Association
The Kerry Cow - Ireland's Native Dairy Breed

Milk Gene Tests

Shannon Nichols

Many French and NZ bulls are tested for milk genes to assess their suitability for the production of cheese or other manufactured products. Some variants are specific to a breed or breed family. In general, breed associations test for the more popular variants. When there is a variant that is traditional to a particular breed, they should be identified and tested for in that breed. An example of this is the c-variant of Kappa Casein in the Tarantaise breed. Traditionally this breed is used in the production of alpine cheeses. Identifying other variants and their traditional use may help breeders select animals for that variant and traditional dairy product.

The more conventional dairy breeds, (Ayrshire, Guernsey and Milking Shorthorn) will need to go through USDA to have these tests become an official part of bull proofs. Bulls from NZ and other countries have this data collected. Taurus is a great example of a semen company advertising bull genetics from milk genotyped animals.

Bulls and cows can be selected for the following milk genes:

• Beta Casein
Beta Casein has many different variants. The most common are A, B, Al and A2. The current trend in niche fluid milk consumption is for milk to have the A2 variant. While ALBC will not make claims related to A2 milk, the ability for breeders to use this test in selecting animals for the variant will allow them to sell breeding stock to people marketing this milk. There are serious patent issues involved with this test. It may not be worth it, and breeders should be careful using this as a sole criteria for selecting animals.

• Beta Lactoglobulin
This is a whey protein. The two most common variants are A and B. The variants behave differently when heated. BB is more desirable for cheese making and milk powder manufacturing.

• Kappa Casein
There are nine known variants of the Kappa Casein in milk. The genotyping of x-casein alleles (A and B) is of practical importance, since the B allele is found to correlate with commercially valuable parameters of cheese yielding efficiency. Cows with BB genotype have been found to have a 10% better yield than cows with the A.A. The B allele was found to be associated with thermal resistance, shorter coagulation time, better curd formation and micelles of different sizes, which are preferable in cheese making (Schaar et al., 1985; Marziali and NgKwai-Hang, 1986) The AA genotype is more desirable for milk powder production.

• Alpha S I -Casein*
In this gene it is the BB and CC variant that is identified. BB cows showed significant increases in milk yield, fat and protein than BC cows. They also show higher per lactation cheese yields compared to cows with BC and CC genotypes.


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