The Simbra Breed

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(From “Polled Simmentals” by ASA, USA)

(Due to the sex influenced African Horn gene, these procedures do not always apply to animals of Bons Indicus breeding and is therefore not necesarily applicable to the Simbra's)

The polled gene (P) is dominant to the horned gene (p).  So when an animal inherits the dominant P gene from one parent and the recessive p gene from the other parent, it is the dominant P that shows up in the individual’s appearance as the polled trait.  The only time the recessive horn gene (p) can express itself is when the dominant P gene is not present.

There are three possible gene combinations: They are PP, Pp, pp, and half of each combination is inherited from each parent.

The PP individual is said to be homozygous polled because it possesses two identical genes (“homo” means “the same”).  It will have all polled offspring regardless of whether the other parent is horned or polled, because it has only the dominant P gene to pass on to its progeny.  PP bulls are sometimes referred to as 100% dehorners.

The Pp individual, on the other hand, is heterozygous (“hetero” means “not the same”).  Fifty percent of the time, the Pp individual will pass on the horn gene, p, to its progeny.

The pp individual is horned, and is also homozygous because it has two identical genes.  The pp individual will always pass on the p gene to its progeny because that is all it possesses.

Summary
PP x PP = All calves PP
PP x Pp = 50% PP and 50% Pp
PP x pp = 100 Pp
Pp x pp = 50% Pp and 50% pp
Pp x Pp = 25% PP, 50% Pp and 2
5% pp.

Testing criteria for homozygous polled

Individual animals need a minimum confidence level of 99.9% based on progeny test.  If animals produce horned calves, they cannot qualify as homozygous polled.  To reach the minimum level of confidence (99.9%), one of the following procedures must be used:

    ■  A bull with polled parents would need a minimum of:
               10 polled calves from horned cows or
               25 polled calves from known heterozygous polled cows or
               38 polled calves from polled cows of unknown genotype..

    ■  A female with polled parents would need a minimum of:
               10 polled calves from horned bulls or
               25 polled calves from known heterozygous polled bulls.

    ■  Progeny from parents which both qualify as homozygous polled.

 

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