Stephen Butler, reproductive physiology specialist at Teagasc, discussed how to achieve high conception rates when using sexed semen in a recent episode of the Teagasc Dairy Edge podcast.
He feels farmer’s confidence and enthusiasm for sexed semen has increased in the last three years.
The reproductive physiology specialist acknowledges that many farmers want to use high-EBI bulls.
He stated that unless it is imported from a country with similar genetics to Ireland, sexed semen imported will have a poorer EBI and not be as attractive to farmers.
“We want to use semen from Irish bulls; the problem is that in Ireland right now, there is no lab for making sexed semen straws,” Butler told podcast presenter, Emma-Louise Coffey.
Currently, bulls are going abroad to sexed semen laboratories in the UK or Europe.
“The problem is for a bull to go to a laboratory they have to spend time in quarantine, the bull is not being collected during that time. So, it is not very attractive to send the very best bulls because their downtime is too long.”
“That is typically what is made available to farmers here, bulls that are not the best of the best. It is important to point out. The best bulls are often young bulls, which may not be suitable for sexed sorting anyway. Once they are 2-years-old, they should be for producing sexed-semen.”
“To have a laboratory here, there needs to be a lot of interest from dairy farmers that they are going to engage with this technology and use it to generate their replacements. So, for the breeding companies in Ireland, it is a gamble to develop a sexed semen lab.”
Most effective use
Stephen advises farmers to consider the bull team they are going to utilise, selecting sires with the best EBI available.
“The important thing, when you are picking a bull, is that you pick a good-sized team; the bigger the team of bulls, the better. If you like the EBI/genetic background of a bull, you might be attracted to using a lot of semen from that one bull, but that is a very risky strategy.”
“Some bulls have a big reduction in fertility after sorting. Some bulls have almost no reduction in fertility after sorting. The problem is you do not know until you use it. Here, the control strategy is to use a big team of bulls, a small amount of semen from multiple bulls.”
“Which animals are you going to use it on? The economical choice would be to use it on the heifers. They are going to have the best pregnancy rates. They are also going to be the highest EBI animals in the herd.”
“That is not going to give you enough pregnancies to meet all your replacement heifer requirements. So, pick the best fertility cows, younger cows in the herd with the best EBI.”
Furthermore, he advises using sexed semen at the beginning of the breeding season in seven to ten days if possible.
When to AI
He explains that the day of insemination is crucial to achieving high conception rates from sexed semen.
Stephen outlines how with conventional AI, it is advised to inseminate the cow 10-12 hours after the onset of heat, whereas he feels this is too early with sexed semen.
“The sexed semen procedure is a damaging procedure to the sperm. Once you inseminate the cow, its life span in the reproductive tract is shorter than what you achieve with conventional semen. So, the objective is to get the semen in closer to the time of ovulation.”
“Inseminate cows 14-20 hours after heat onset. If you are AI’ing only once a day, it is not going to be possible to use sexed semen on all animals. It is not worth your while putting sexed semen into cows that have just come into heat.”
“One thing to consider is whether or not fixed-time AI is a useful strategy. If you want to use sexed semen on all your heifers or 20-30% of your cows, you can synchronise those animals to get bred on the mating start date,” Stephen adds.
He also emphasises that sexed semen is a more fragile product than conventional semen, and advises only thawing two straws at a time, putting them into prewarmed AI guns. By the time you thaw the straw, you should complete the insemination within five minutes.
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