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Veterinarian View | May/June 2023

Current Issues for Spring 2023

contributed article by Dr. Vince Collison, Collison Embryo and Veterinary Services,

Rockwell City, Iowa



One of the bigger issues for this spring has been the shortage of FSH for stimulation of donor cows. For conventional flushing, it is an essential hormone for the process. Without stimulation there will only be one oocyte ovulated, resulting in a single embryo collection. Fortunately, aspirations can be done for IVF without FSH. When aspirating cows for IVF there are two schools of thought. IVF production with stimulated versus non-stimulated donors.


At the time we started IVF we were strictly aspirating all donors as non-stimulated. Over time we have started to collect more of the IVF donors with stimulation. I think the decision to stimulate or not to stimulate an IVF donor needs to be on a case-by-case basis. For many of the cows the non-stimulation has worked very well. Yet for some cows it seems that to get the best results, they need stimulation with FSH.


Non-Stimulation

Advantages of the non-stimulation is the labor savings due to no trips through the chute other than to do the collection. Also, there is less expense from not using FSH. Many producers also like the idea of not giving exogenous hormones to their donor cows.


When we aspirate follicles, we are collecting a group of follicles that would normally be present anyway. So, the disadvantage of non-stimulations is that collections are done at a random point in time during a follicular wave. Therefore, you really don’t know if the collection occurs during the early part of the follicular wave when the follicles are growing or if it’s during the later part of the wave when the follicles are regressing.


When a follicle is in a regressive phase, the oocyte is probably not going to be competent for fertilization. There are typically 2 to 3 waves of follicles that occur during a cow’s 21-day cycle. When a follicle is growing, the oocyte inside the follicle starts to undergo changes that prepare it to be fertilized resulting in a competent oocyte. Once the follicle reaches the end of the follicular wave development it will start to regress and the oocyte will start to lose its competence to become fertilized. So, if a non-stimulated cow is collected during the regressive part of a follicular wave there is a good chance these oocytes will not fertilize very well. I feel this is often what is happening when a non-stimulated cow has a nice collection of 20 or more oocytes and then comes back with a very low embryo development rate or often just a total bust resulting in no embryos.


Stimulation

We feel this is the big advantage of stimulating IVF donor cows. The FSH puts the follicles in a growth phase and increases the chance of collecting a competent oocyte. The other advantage is you may see slightly higher numbers of oocytes recovered on stimmed cows. While the actual number of follicles available to collect does not change, you may cause a few extra follicles to enlarge slightly and make them easier to collect.


With the current shortage of FSH this winter and spring, it has been necessary to do as many IVF collections without stimming as possible. One thing that can be done to a non-stimmed donor as well as stimmed donors to increase their chances of inducing oocyte competence is to give an injection of GNRH five days prior to the oocyte collection date. This will help to reset a new follicular wave and hopefully have a new cohort of growing follicles in the ovary at the time of her collection. This is a very inexpensive way to reset the follicular wave and potentially can get similar benefits without the cost of FSH.


Calf Health

Even more important has been the challenges with calf health seen this spring. The weather conditions this winter have been harsh on both cows and calves. We feel that some of the diets fed to cows have been short on some of the key micronutrients needed for calf health. Vitamin A deficiency has continued to be an important issue for many this spring. With a combination of drought causing poor vitamin A content in harvested forages and the fact that many producers are moving to more of a silage, distillers, and corn stover type of diet for their cows. This type of diet is usually going to be low on vitamin A.


It has been very common to see low vitamin A in liver samples we have submitted on calves to the diagnostic lab. A couple of things could be going on. The main source of vitamin A for new calves is from the colostrum they get nursing shortly after birth. So, if you see low vitamin A levels in a calf that is only a few days of age it could be that they did not get enough colostrum at birth. This would also mean there is probably a failure of passive transfer which results in the calf being much more prone to illness.


The other issue can be that the cow is low on vitamin A and just doesn’t have it to put into the colostrum. Also, the weather has put a lot of extra stress on these cows this winter and may adversely be affecting colostrum.


As a final note, continue to make colostrum intake at birth a priority to give the calf high immunity from the start. Use calving pens in the first 24 hours, if possible, to improve the pair bonding and nursing of the new calf in the first 24 hours of life. Use vitamin A premix in situations where you’re feeding diets to cows that have the potential to be very low in vitamin A. Also keep a good trace mineral product in the ration or out in front of the cows and calves at all times.



Dr. Vince Collison is co-owner of Collison Embryo and Veterinary Services PAC

in Rockwell City, Iowa.

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