  BeefTalk:
Selection in Bull Buying Can Lessen Surprises in Calf Crop
By Kris Ringwall, Extension Beef Specialist,
NDSU Extension Service
Beef producers commonly ask, "Why didn’t the bull I purchased breed
true?" Upon reviewing the calf crop, most of the calves look somewhat
similar, but there may be those occasional calves that just don’t fit the
mold.
Often, the value of the last calf on the truck may very well be your profit,
so the question is a very serious concern. The core of the problem (if you can
even call it a real problem) is livestock producers do not control what genetic
material (ie. genes) a bull actually passes on to his offspring.
A live calf is assured by the presence of many highly conserved genes. In
other words, genes which assure your calves will have tails, are fairly secure.
Granted, a tailless calf could be born, but generally it’s one of those events
you actually invite the neighbors over to see, since the fore-drawn conclusion
is, "I won’t see this again". Another way of putting the equation,
we are 100 percent certain when a bull breeds a cow, a calf, not a lamb will be
produced.
This may sound like an oversimplification but the preservation of species is
a very delicate matter, and the genetic code takes things very seriously. The
genetic code equates the DNA bases within chromosomes to a corresponding amino
acid, which ultimately makes proteins. The proteins are the basis for life,
since every gene codes for a protein.
These proteins determine how a calf survives, functions and ultimately, what
the calf looks like. Unfortunately, the naked eye does not see DNA strands, nor
the individual proteins. However, with the aid of a microscope, we can see the
chromosomes that contain the DNA.
The end product of a bull is directly related to what genes are contained in
his chromosomes and what sample of genes are passed to the calf. The biology of
a cell, and management of chromosomes is very similar to running a train
station.
There are 60 trains (chromosomes) in every cell of a bull, cow or calf. These
trains are genetically coded and every cell does what that cell was predestined
to do. In a healthy animal, all 60 trains are running well. This is true for all
cells, except the reproductive cells. These cells have only one primary
function, to continue the ancestry of the bull through the sperm cell or
ancestry of the cow through the egg. This is a huge undertaking, since cattle,
just like humans where not made to naturally clone themselves.
The sperm and egg cells go through a process of division, with an end result
of decreasing the number of trains (chromosomes) in half. To better understand
the process, in a size we can comprehend, the cell has two train masters
controlling the 60 trains. As the point of separation approaches, each train
master aligns all the trains and pairs each train (chromosome) with it’s
matching train. Once every thing is lined up, each train master takes thirty
trains, one from each pair, (chromosomes) and they arrive at a new station and
the cell divides, one set of 30 trains (chromosomes) in each cell. This cell, if
in a male becomes a sperm cell, and if in a female becomes an egg.
Upon fertilization, the sperm cell delivers 30 trains and the egg cell
delivers 30 trains, and a new life is created. The important point is this: no
matter how much selection effort you apply, you can never control which trains
go to which sperm cell. A bull produces billions of sperm cells, each with a
unique combination of trains and cars. This process is known as independent
assortment and random segregation, a process designed to keep us all honest.
Selection will increase the probability of a particular gene being in a sperm
cell, but will never control which gene goes into a particular sperm cell. Keep
in mind, every gene is paired, and the bull only sends one, not two. So if the
calf doesn’t meet your expectations, well, that is just the way it is.
May you find all your ear tags.
Your comments are always welcome at www.BeefTalk.com.
For more information, contact the North Dakota Beef Cattle Improvement
Association, 1133 State Avenue, Dickinson, ND 58601 or go to www.CHAPS2000.COM
on the Internet. In correspondence about this column, refer to BT0131.
###
Source: Kris Ringwall, (701) 483-2427, kringwal@ndsuext.nodak.edu
Editor: Tom Jirik, (701) 231-9629, tjirik@ndsuext.nodak.edu
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