There has been a lot of discussion on these topics this winter. Many inseminators are in such a hurry they put the straw directly into the AI gun unthawed, theorizing the cow’s body temperature will thaw it adequately. Others, especially those trained by CRI Genex, are using “pocket thaw” rather than the universally recommended warm water bath.
CRI Genex (and Taurus Service) were the only major AI companies to use whole milk as a fluid extender for semen straw packaging. “Cream” is the natural substance most able to protect the sperm cells through the critical temperatures at which water crystallizes. Thus they could get away with recommending “pocket thaw”, knowing full well that this would damage sperm cells extended in the more common egg yolk, powdered citrate, or soybean oil fluids used by their AI competitors. In our opinion, given you generally do not know which choice was made for the bulls you buy, warm water thaw bath at temperatures between 92 F and 98 F are your best bet, especially for late fall, winter, and early spring when air temperatures are well below a cow’s body temp.
Why was whole milk not universally used? (1) the cream content of commercial “whole” milk varies by 40% (3.25% minimum to over 4% blended average); (2) it is the most difficult media to be able to see the motility and acrosomal retention on sperm cells, requiring more expensive magnification. Volume semen produced in AI studs goes more smoothly with other extenders.
The bigger issues affecting conception rates over longer-term semen storage
Prior to 1968, semen was generally packaged in 1.0 or 1.2 cc pyrex (glass) ampules. These are easier to transfer between tanks, can be stored virtually indefinitely without loss of potency, BUT required eight to ten minutes thawing time (in 40F ice water) to fully liquify. Even after experimentation with warm water thawing, you still need two minutes to reach body temps.
From 1968 forward, the French straw system took over, using a 1/2cc plastic wand that took up less tank space (10 on a cane compared to 6 or 8 ampules) AND would thaw out in 40 seconds in warm water. The stainless steel breeding guns offered a bit more rigidity than the plastic tubes used with ampules. Under optimal handling, conception rates initially rose from this switch from ampules to straws, as faster freezing and thawing saved sperm cells.
However, the transfer of straw canes between tanks had to be done faster (eight seconds or less is recommended), and the longer straws are stored, the risk of exposure damage to straws in the upper cups on canes was greater. Canisters holding the canes should not be lifted above the neck tube when extracting a straw to breed a cow. ALSO once thawed that straw needs to be in the cow within 15 minutes and protected from temperature drops (“wind chill”) once the AI gun is loaded. It is also advantageous to warm the AI gun before inserting the straw. None of these precautions were necessary in the days of ampules and ice water thawing.
Gender-sorted semen (and most imported sires) are in the even more fragile 1/ 4 cc ministraw.
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