PHA and TH bulls

[Finley Club Calves]

What is the risk of breeding to PHA and TH positive bulls? ??? I am new to the whole breeding club calves thing. Any help would be greatly appreciated!

 

[OKshorthorn]

Breeding 2 carriers together goes like this. 25% chance calf will be free of defects. 50% chance the calf will be a carrier of defects. And a 25% chance the calf will be dead.

If you breed a carrier bull with a clean cow, then it is just 50/50 as to whether or not the calf will be a carrier of defects, but will not result in a defective (dead) calf.

 

[Finley Club Calves]

Ok, thank you! (clapping) what are the defects?

 

[OKshorthorn]

DL on here would be the best at telling you the exact defects associated with TH and PHA. You can also use the "search" tab and find other threads about it that go into depth about it.

Basically with PHA, to my knowledge, if they are not in the 25% defective (dead) from breeding 2 carriers there are no side effects. It is just a defective gene that they are carriers of, they don't show signs of being a carrier and you do not know they are unless tested.

They same goes for TH, with the exception that some believe that TH carriers have superior bone and hair compared to non-carriers.  

Here are a couple links to old threads on this subject.
http://www.steerplanet.com/bb/index.php?topic=28689.0
http://www.steerplanet.com/bb/index.php?topic=39638.0
http://www.steerplanet.com/bb/index.php?topic=22124.0

 

[JTM]

You never want to breed a carrier to another carrier. I know the science says that the chances are 25% defective calf, but I would submit that the actuals in reality are much higher. The smart thing to do would be to build a herd with non carrier cows and then if you are dead set on using a carrier bull you can breed them with no risk. The bad part about that is that some people won't buy carrier females. Just depends on your market. Good luck to you!

 

[knabe]

why would pha be more special than any other defect with respect to ratios?

what does much higher mean?  do you have a number in mind?

 

[twistedhshowstock]

It is no more special than any other recessive deffect.  Both TH and PHA are recessive deffects, which means for there to be any physical affect from the deffect then the calf must be homozygous for the trait(posess 2 rececessive, deffect genes).  If a calf is heterozygous(carries 1 recessive, deffect gene and 1 dominant, normal gene) then the dominant, normal gene will override the recessive, deffective gene and the calf will physically be normal.  With both PHA and TH positive, or homozygous calves are lethal either at or shortly after birth.  PHA is a deffect with lung development, these calves are almost always dead at birth. Because of the lung deffects they tend to retain fluid and be HUGE, PHA calves often have to be cut out via C-Section and run a high risk of losing the cow as well.  TH is a deffect with tibial development, the legs often apear to be twisted.  Many TH positive calves from my experience and research are born alive and cows dont typically have issues having them unless they are high birthweight calves which is an entirely different issue.  TH positive calves often die or are put down shortly after birth. Because of the leg deformity they will never be able to stand.
As far as genetic probability it works like this.  We will call the Dominant(normal) gene "D" and the recessive(deffective) gene "r".  All animals carry 2 chromosomes with one copy of each gene on each chromosome.  So an animal that is clean of the deffect would be DD, and animal that is a carrier would be Dr, and an animal that is positive would be rr.  However sperm and egg cells are only single chromosomed cells, they do not become dichromatic until they join together, thus a carrier bull or heifer can only pass on one of the genes not both.  So if a carrier bull is mated to a carrier cow and the bull passes on gene D it will either join with an egg carrying gene D resulting in a DD(clean) calf or an egg carrying gene r resulting in a Dr(carrier) calf.  If the bull passes on gene r it will also either join with an egg carrying gene D resulting in a rD(carrier) or an egg carrying gene r resulting in a rr(positive)calf.  Thus you have 4 possible gene combinations but 2 of them result in a carrier calf, so you have a 50% probability of having a carrier calf, a 25% probability of having a clean calf, and a 25% probability of having a positive calf.  These percentages are for that one individual breeding, this is not saying that if you bred that exact same cow and bull 4 times that you would get 2 carrier calves, 1 clean calf, and 1 dead calf , we have no way of predicting that. 
As far as the risk goes its pretty simple 75% chance is your calf wont have any physical issues, the other 25% is a chance that the calf will be lethal.  I guess it all comes down to this, is the chance of a mating producing a superior calf worth it to you enough for you to be willing to take a 25% chance on losing a calf and possibly a cow? If not, then dont breed a carrier to a carrier.  If it is worth it in your opinion then that cow must be pretty special and the mating for me would most likely be a flush and recips would carry the calves, because I wouldnt want any known calculated risk of loosing a cow of that caliber.

 

[OKshorthorn]

Well said twisted. I know of a guy that runs over 100 cows, mostly for a club calf operation. He breeds carriers to carriers all the time, because he firmly believe it makes a difference. He claims that the percentage of a lethal calves vary by cow. He said that he has had a few cows that have had almost 100% defective calves while others have never had one, over a period of several years. They have all been tested and in his opinion some cows have a highers percentage of lethal calves. I have no idea, personally. I'm in the camp of never breeding 2 carriers together. We have had a TH calf, from unknowingly breeding 2 carriers, and it sucks. It's simply not worth it for us.

 

[knabe]

as anyone knows that's taken stats, you can flip a coin and get heads a few times in a row.

maybe some of these people that are getting all these pha calves in a row can go to reno and beat the odds too.

i've heard people make lots of money gambling.

 

[DL]

I sent FCC a link to some articles - hopefully they will be helpful to him

A point to emphasize - especially when someone says "well this cow family never has calves dead from a lethal recessive defect even thought we always mate carriers to carriers"

the risk is the same for every single mating, its probabilities  - think of a coin toss - every time you toss a coin the chance that it is heads is 50% and the chance that it is tails is 50% - just because you just got heads doesn't mean the next toss will be tails - the risk for the next toss is independent of all previous tosses and that is basically the same for a mating of 2 carriers (of the same lethal recessive defect)

So if you breed 2 carriers of the same lethal recessive mutation

Your risk of having a dead calf is 1 in 4 (25%) for this mating and every other carrier to carrier mating

Your risk of having a carrier calf is 2 in 4 (50%) for this mating and every other carrier to carrier mating

Your risk of having a non carrier is 1 in 4 (25%) for this mating and every other carrier to carrier mating

and just like sometimes you toss a coin and get all heads for what seems like for ever, you can get a "run of dead calves" from a carrier to carrier mating or a "run of live calves" but it doesn't imply anything special about that cow - she just got unlucky or lucky but she is not more likely to have a live non carrier calf next time than she was with any other breeding

There are (however) some defects (ie NH) where there is a high percentage of early embryonic loss or abortions which makes the risk appear different but in reality of the calf aborted early from a lethal recessive defect it is technically a dead NH calf - just early

 

[knabe]

one of the first uses of sequencing in cattle will be to screen snps in parents that don't occur in offspring, meaning they are potentially lethal and no calf is ever found to help ID defects we don't know anything about because no dead or sloughed calf is ever found.  should be interesting.

super cool.

 

[JTM]

Knabe, I'm just saying that in life, when you play with fire, more times than not you are going to have problems. The science is the science, but reality is what happens when that coin is flipped.