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Dairy vet advice: Pregnancy rate will be good indicator of skill

Achieving high pregnancy rates will depend on how good you are at spotting bulling cows and achieving good conception rates. 

 

Vet Rose Jackson, from Scarsdale Vets in Derbyshire, gives us a few pointers.

 

Sperm were first discovered in 1678, although the scientist who saw them under a microscope thought they were a parasite.

 

It took a further 100 years of research to realise that sperm were the agents of fertilisation, and another 100 years after that to clearly understand the detailed events that are necessary for fertilisation.

 

In 400BC, before science even knew about sperm, it was thought that the right testicle produced male offspring and the left produced females, so by tying up the left testicle, you were guaranteed a boy!

 

Sexed semen technologies have advanced since then and been with us for more than 30 years.

 

Flow cytometry is the technology that made sexed semen commercially available in cattle and is still in use today.


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Because the X chromosome (female) is bigger than the Y (male), it takes up more of the fluorescent dye. This then enables the sperm to have a different electric charge applied according to how much they show up the dye.

 

X (female) sperm have a positive charge and are pulled in one direction when an electric charge is applied, whereas Y (male) sperm are pulled in the opposite direction and are sorted into separate collection tubes.

 

In 2017, one of the big AI companies launched a new sexing technology. It still uses flow cytometry, but instead of applying an electric charge, the Y sperm are disabled using a laser.

 

This technique should, theoretically, be less damaging to the female sperm as everything ends up in the same collection tube.

 

Initial results from the USA look good, but it will be interesting to see data from the UK now it has been commercially available for more than 12 months.

 

There are obvious benefits to using sexed semen, like fewer unwanted bull calves, increased genetic gain when used on maiden heifers (particularly if used in conjunction with genetic testing) and increased milk.

 

Heifers which give birth to heifers at their first calving give +445kg milk in their first lactation, compared to those that have
bull calves.

 

We are quick to blame cows for poor fertility rates, but we don’t often review our own AI techniques.

 

Only 50% of Holstein cows will show standing to be mounted (STBM), therefore it is important to optimise heat detection, insemination technique and semen quality.

 

Some 94% of ovulations are 16-40 hours after onset of heat. The recommendation for sexed semen is to AI 14-20 hours after observed heat.

Check on your thawing technique at 35-37°C for minimum of 45 seconds. Insert straw into a pre-warmed gun, AI cow within 10 minutes, and only thaw one straw at a time. And semen should be placed in the body of the uterus not in the horns i.e. just through the cervix.

We at Scarsdale Vets have been offering AI training for farmers for more than 20 years. This involves one intense day of theory, including practising on post-mortem uteri, followed by three practical days out on farms using cull cows.

Doing your own AI has a number of advantages over using an AI technician. You can be far more flexible than when using a technician, and cows are less stressed as they aren’t left waiting for hours which can interfere with conception.

And, of course there is the cost, although I do accept there will need to be an initial outlay on equipment to get started.

Traditional measures of fertility focus on the ‘outputs’. Calving interval requires a cow to calve down before a figure is produced, which means it is too historical to be make assumptions on the current fertility levels and can also be manipulated by high culling rates.

In order to assess the current fertility performance on a farm, we can look at fertility efficiency (sometimes referred to as pregnancy rate) which looks at the ‘inputs’ of fertility. This is illustrated in the graph which is divided into 21-day intervals.

The yellow bar shows the number of eligible cows, the blue bar is the number of these which are served and the green bar is the number that are confirmed pregnant.

The lines are the rolling % served (red) and rolling % PD (pregnancy diagnosis) positive (dark blue).

This helps to identify whether we have problems with heat detection or conception rate (or both), which then enables us to further analyse the situation.

 

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