[Jacob-list] Results of ram lamb vs ewe lamb study

[SteffArce at aol.com]

Hi all,
Regarding ram lambs vs ewe lambs:  Survey Results:
I looked at the information I received from 5 people on the list  on their 
Jacob's (and other breeds) regarding feed, age of rams, etc....
There are more variables than number of sheep looked at!
So I watched questions being asked on the list and  wrote Gary Anderson. With 
his permission I have copied his response to my questions.

> -----Original Message-----
> From: SteffArce at aol.com [mailto:SteffArce at aol.com]
> Sent: Thursday, March 08, 2001 7:40 AM
> To: GBAnderson at ucdavis.edu
> Subject: Questions on Jacob Sheep
> 
> 
> Dr. Anderson, I have a small flock of Jacob Sheep in Central Oregon. My 
> questions to you are from a group of people on the Jacob List. We were 
> interested in study results that may have already been completed. We have 
> these questions. 
> 
> Who determines the sex of the lambs---Ram or Ewe? 
> Is there an influence on the sex because of the age of the Ram---ram lamb 
> vs 
> mature ram? 
> Is there a tendency for first time bred ewe's to have ram lambs? 
> I understand that "flushing" will increase the number of eggs available for 
> fertilization, Is there an influence on the type of feed ie.. could one 
> flush 
> using alfalfa instead of grain? 
> Many on the list are looking for ways to increase number of ewes verses 
> rams 
> (: 
> We are looking for information that shows if you provided 'this' type of 
> food 
> with 'this' age group of ewes and rams you will/may get 'this' sex of lambs 
> and 'this' number of lambs. 
> Your input, suggestions would be greatly appreciated. 
> I had asked for data from different members only to find multiple variables 
> from each. No place to start with a constant. 


> Thank you for your time, 
> Stephanie Arceneaux 
> SteffArce at aol.com



Subj:   RE: Questions on Jacob Sheep    
Date:   3/9/01 3:57:58 PM Pacific Standard Time 
From:    GBAnderson at UCDavis.Edu (Anderson, Gary B.)
To:    SteffArce at aol.com ('SteffArce at aol.com')
    
    


The sex is determined by the ram, or more correctly the fertilizing sperm 
cell.  Each sperm cell carries either an X chromosome or a Y chromosome.  
Each egg carries only a single X chromosome.  If the egg is fertilized by an 
X-bearing sperm cell, producing an XX embryo, the lamb will be female.  If 
the egg is fertilized by a Y-bearing sperm cell, producing an XY embryo, the 
lamb will be male.
 
Theoretically, 50% of a ram's sperm cells carry an X chromosome and 50% carry 
a Y chromosome; thus, 50% of a ram's lambs should be ewe lambs and 50% ram 
lambs.  When a breeder say, "My ram produced 9 ram lambs in a row!"  it's 
most likely by random chance and not anything special about the ram.  The 50% 
male/female ratio can appear to be off when dealing with a relatively small 
number of lambs, but were the same ram to sire, for example, 100 lambs, the 
ratio is likely to be 50%/50%.
 
In cattle where AI (artificial insemination) bulls can sire tens of thousands 
of calves, individuals are known in which the sex ratio is, for example, 
48%/52%, and because the numbers of calves is so large, the deviation from 
the expected 50%/50% ratio can be 'statistically significant,' which is a 
scientist's way of determining if something is 'real' or just occurring by 
chance.  (The 9 ram lambs in a row is probably just by chance and not a real, 
biological phenomenon.)  The slight deviation is probably due to greater 
embryonic mortality (during pregnancy) in one sex versus the other, most 
likely do to a genetic defect.
 
Rarely, and I mean RARELY, a male (for example, a ram) is found that truly 
has a large deviation from a 50/50 ratio of offspring sex (much more rarely 
than you'd expect based on anecdotes passed among breeders).  The most 
logical explanation is that the ram carries a defective gene that is killing 
embryos/fetuses of one sex or the other, most likely the males so that 
predominantly females survive to term.
 
Sex of lambs is not influenced by the age of the ram.  Nor is there an effect 
of first-time lambing ewes to have one sex or the other.
 
Flushing increases the number of eggs ovulated.  With flushing ewes are more 
likely to ovulate two versus one egg compared with had the ewes not been 
flushed; thus, a breeder is more likely to get twins than with not flushing, 
and the breeder will get MORE EWE LAMBS (by virtue of getting more lambs) but 
NOT more ewe lambs relative to ram lambs.  There's no way to feed a ewe (or 
ram) to alter the sex ratio.
 
There are two, and only two, scientifically proven ways to alter the sex 
ratio.  Both require treating semen to separate the X- and Y-bearing 
spermatozoa, and thus the procedures require AI or in vitro fertilization 
(IVF).  One of the two methods seems to work somewhat in humans (and is used 
in some IVF clinics) but hasn't worked in other animals.  The other one was 
developed at USDA in Beltsville, MD and is being commercialized by a company 
associated with Colorado State University.  The latter is being tested 
primarily in cattle, and is a ways off from practical use (although it does 
work in small-scale projects).
 
I hope that I've answered your questions.  Please let me know if something is 
unclear.

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