Using sexed semen in the suckler herd

Artificial insemination (AI) is a breeding technology that has been around for a long number of years. However, only 17% of suckler calves are born from AI sires, despite AI being the fastest way of making genetic improvement in the herd.

Using AI also avoids the hazard, purchase and maintenance costs of a stock bull, providing the ability to produce replacement heifers and eliminating the risk of stock bull infertility, Aisling Molloy, Future Beef Advisor, discusses more on AI and sexed semen usage in this article.

Why use sexed semen?

Sexed semen has become a more viable option for herds in recent years. Developments in the sexing technology, herd trials which show improved conception rates and the introduction of two sexed semen labs in Ireland have increased the availability of sexed beef straws for suckler farmers this spring.

The advantages of using sexed semen are:

• 90% chance of a heifer calf;
• Can breed replacements early in breeding season;
• Genetic gain;
• Can breed more cows to a terminal sire to increase beef output on the farm.

While sexed semen will provide an excellent opportunity to herds, it does come with challenges. Some of the disadvantages are: lower conception rates (85% of conventional rates); much smaller breeding window after heat is detected; and slightly higher cost.

Steps for success with sexed semen

It is recommended that sexed semen insemination should be restricted to the first three weeks of the breeding season, so that the herd calving spread is not negatively affected. Some other main points to consider are outlined below.

1. Herd suitability. You should:

• Have used AI successfully in the past;
• Have a fertile herd, i.e. >70% six-week calving rate, 356-day calving interval and >0.95 calves per cow per year.

2. Choose your females carefully. They should:

• Be your most fertile females that have calved in the first half of the season;
• Be >35 days calved;
• Have cycled more than once before breeding;
• Have had less than four calves;
• Heifers should be at target body weight for breeding, e.g. over 400kg for continental heifers;
• Have a body condition score of 3;
• Be on a good plane of nutrition with no sudden changes in their diet before or after breeding.

3. For replacements, pick a bull that:

• Has a higher Replacement Index than your herd index at over 70% reliability;
• Has a positive daughter milk figure;
• Has a negative daughter calving interval figure;
• Has a daughter calving difficulty figure of less than 8% at >70% reliability if being used on heifers;
• Note that not all sexed bulls are going to breed suitable replacements for your herd, so make sure to choose them carefully.

 4. Communicate with your AI technician:

• Let them know that you are planning to use sexed semen and to check if they will have the flexibility to call when needed;
• Discuss what AI straws you want to use to ensure they are available.

 5. Heat detection - crucial for success

• Frequent observation is essential – 20 minutes 4-5 times per day is recommended;
• Heat detection aids such as tail paint, kamars, scratch cards, vasectomised bull with a chin ball etc. should be used;
• Automated heat detection options such as tags, collars and boluses are also available.

 6. Timing of AI

• 14-20 hours after heat onset (first standing mount);
• Practice AM/PM rule if possible;
• If using once a day AI, use conventional semen if time of AI is <14 hours after heat onset.

Table 1: Recommended breeding times for sexed semen

7. Straw handling

• Ensure the AI straws are easily identified in the flask if doing DIY AI, ideally in a single goblet;
• Thaw a maximum of two straws at any one time;
• Thawing time is a minimum of 45 seconds at 35-37^o;
• Ensure the straws are fully dry before insemination;
• Load straws into a pre-warmed AI gun and keep it warm;
• Deposit semen into the uterine body;
• Use the thawed straws within five minutes.

How many sexed semen straws do I need to use?

In a suckler herd of 30 cows with a replacement rate of 20%, six replacement heifers will be needed per year. The expected conception rates for sexed semen in heifers is 60% and 50% for cows for the first serve.

If sexed semen is only used for the first three weeks of the breeding season and the six heifers are bred, you would expect a conception rate of 60%. Allowing for 90% sex bias towards heifers, you would expect to produce three replacement heifers from sexed semen. Heifers that repeat can be served again with conventional semen from a maternal bull.

Three further heifers are required to be produced from the suckler cows in the herd. Allowing for 50% conception rates and a 90% sex bias, seven cows will have to be bred to sexed semen straws.

This means that 13 sexed semen straws are required in the herd to produce six replacement heifers. Note that this does not allow for any embryo loss, abortions or mortality after birth.

Eamon and Donnchadh McCarthy, Future Beef farmers

Eamon and Donnchadh McCarthy in Co. Waterford are using 10 sexed female straws on suckler cows from Curaheen Gunshot P (SI4147) in their 31 cow herd this spring. At a 50% conception rate from the first serve to sexed semen and 90% sex bias, they expect to produce four or five female replacements.

However, as conventional straws are available for the same bull, these will be used on some maternal cows to increase conception rates, although the chance of a female replacement is reduced to 50%.

The McCarthys selected SI4147 for sexed straws as he has a Replacement Index of €191, which is higher than the herd average of €123. He has a carcass weight figure of +33.3kg, daughter milk of +9kg and a daughter calving interval of -6.1 days. His cow calving difficulty figure is 7.2% at 99% reliability, but his heifer calving difficulty figure is 14.4% so he is not suitable for use on maiden heifers. Conventional straws from another three replacement bulls are also being used on the farm.

Future Beef Programme

Follow the breeding progress on the Future Beef farms here.