Meriville Outstanding-P, one of our polled Milking Shorthorn bulls
I will explain here how the polled trait is inherited. I will then go into some technical detail with some diagrams for those who are interested in what is behind it.
“Polled” means naturally hornless. (Some polled animals may have scurs, which are small, harmless growths in the horn area.) Many farmers prefer polled because it saves the trouble and expense of dehorning. Animal welfare issues are also a factor.
Polled animals can be either heterozygous or homozygous, and you can’t tell by looking at them which they are, though if you know that one parent was horned, they must be heterozygous. However, if one or both polled parents are heterozygous, only a DNA test or checking a large number of offspring will tell you if the animal is homozygous or heterozygous. This is why we have our polled bulls tested if there is a chance they are homozygous.
A heterozygous polled bull will transmit the polled gene half the time, so if you use him on horned cows, on the average half of the calves will be polled. If you use him on heterozygous polled cows, on the average ¾ of the calves will be polled.
A homozygous polled parent will have all polled calves, regardless of whether the other parent is polled or horned.
We now have two homozygous polled Milking Shorthorn bulls, Wildflower-PP and Outer Star-PP. We also have three heterozygous polled MS sires: King Oscar-P, Outstanding-P (pictured above), and Matchmaker-P.
We currently have one polled Dutch Belted bull, Fortified-P, and are raising another promising young sire that is polled.
Bestyet Fortified-P, our first polled Dutch Belted sire
We also offer polled Jersey sires from other grass-based breeders.
Below we show several Punnett squares, such as you may have seen in high school biology class, to visualize the inheritance of horned/polled. In preparing this discussion, I referred to the textbook Biology, God’s Living Creation, c1997 Pensacola Christian College.
I recently read a fascinating biography of Gregor Mendel, the German monk who discovered these basic inheritance patterns by studying pea plants at his monastery in the mid 1800’s.
Genes come in pairs, and the parent transmits one gene for each trait to the offspring. If both genes are the same for a certain trait, we say the parent is homozygous. If one gene is different from the other, the parent is heterozygous.
We represent dominant traits with capital letters (such as P for polled), and recessive traits are shown with lower case letters (such as h for horned). Dominant traits such as polled show up in the offspring even if the different trait is also genetically present.
In the Punnett square, we show the gene pairs from one parent across the top, and the gene pairs from the other parent along the side. By filling in each box with the trait from the corresponding column and row, we can visualize all the possible combinations that offspring of that mating may receive.
Below are the two Punnett squares showing the results of mating a heterozygous polled animal with a horned animal (left drawing) or with another heterozygous polled animal (right drawing).
The Punnett squares below demonstrate what happens when a homozygous polled animal is mated with a horned animal (left drawing) or with a heterozygous polled animal (right drawing).
When we say ½ of the offspring will be polled, we mean each offspring has a 50% chance of being polled, just like the chance of being one gender or the other. Of course in real life, there will be instances where more or less than half are polled, but over a large number on the average it would be 50%.
Even such a brief survey of genetic principles clearly demonstrates the complexity and order of Creation, thus the awesome wisdom of our Maker.