Why it is that cows have equal numbers of male and female calves? Apparently, from the point of view of natural selection and evolution, this is the optimum model for the species. Though it’s not ideal for farmers as farmers need many female calves for replacement heifers. This is according to Oliver McGrath of Teagasc.
“Commercially available sexed semen offers farmers the opportunity to choose the sex of the calf, which would obviously be hugely beneficial within a breeding strategy,” he outlined recently.
“Dairy farmers currently decide how many replacements they need for their herd and serve an appropriate number of cows with dairy genetics. Roughly five straws are currently used per heifer that will enter the herd.”
According to McGrath, who is based in Teagasc Listowel, Co Kerry, male dairy calves with limited potential as beef animals, are an inevitable by-product.
“With sexed semen, dairy farmers could potentially produce a heifer from almost every cow in the herd as sexed semen is about 90 per cent accurate. As well as reducing the number of male dairy calves, this would allow rapid expansion of milk production if required. However this strategy would be very expensive.”
Alternatively, farmers could use dairy genetics with sexed semen on relatively few cows and the maiden heifers secure in the knowledge that they will produce about 90 per cent daughters,” he added.
“The remainder of the dairy herd could be served with semen from beef bulls or a beef stock bull could be used.”
In addition, McGrath stressed that beef suckler farmers using AI could benefit from sexed semen by opting for a higher proportion of male calves. “Additional benefits to both beef and dairy farmers could include improved bio-security: herd size can be increased rapidly without buying in live animals.”
So how close is the practical use of sexed semen? This latest technology does pose some challenges, according to McGrath. “While this sounds like an excellent result, there’s a catch, or indeed, several. The process of sorting the sperm is slow and many sperm are lost or damaged. As a result, only two million sperm are typically included in a sexed semen straw versus 20 million for a conventional straw.”
As a result sexed semen is consequently costly, €18 more per straw, and conception rates are lower than for conventional straws, partly due to the lower number of sperm present, and partly due to sperm damage during the sorting process.
In addition, he outlined that sexed semen is mainly used on maiden heifers because maiden heifers are inherently more fertile.
“Maiden heifers should be well grown and healthy and a good heat detection programme should be in place,” the Teagasc expert advises. “It would be ideal if they were located in a paddock near the yard to enable easy access to the yard. There are a variety of dairy bulls and beef bulls available with sexed semen this year.”
Friesian weanling heifers. Photo O’Gorman Photography.