The resolution season is here again. Many people all over the world eagerly await December 31 to make resolutions for 2024. Whether the resolutions are implemented or not is another story altogether.
One of my dairy clients told me two months ago that she wanted to switch to sexed semen in the New Year. She wanted to know if technically it was a good idea. She had been discouraged from using sexed semen in the past and said it had very poor performance compared to conventional semen.
I would not do justice to the question without first explaining the two types of semen. First, sexed semen is used in both dairy and beef cattle. Conventional semen is the normal semen harvested from a bull and used either fresh at room temperature or frozen and stored in liquid nitrogen at negative 196 degrees Centigrade.
The disadvantage of room-temperature semen is that it has to be used within a very short time after harvesting. For that reason, it can only be used in the locality of the harvesting facility or transported by expensive means, such as aeroplanes if it is to be used in far-off places.
Frozen semen has the advantage of the ability to be stored for many years and can be used anywhere in the world as long as it is stored continuously in liquid nitrogen. The advent of frozen semen immensely changed animal breeding and enabled high-quality or special breeds of animals to be distributed globally.
As a young boy, I could not help wondering why calves born of artificial insemination were called in my language “plastic cattle”. I came to learn it was because the semen was stored in plastic straws and delivered to the cow through a plastic straw.
We had been used to natural bull insemination until the government embarked on massive artificial insemination in our area in the early 70s. Soon, the whole countryside was filled with very beautiful Friesians and Ayrshires.
Our small East African zebu breed completely disappeared by the mid-1980s. I can therefore bear witness to the effectiveness of frozen semen in distributing cattle genetics.
Natural insemination and frozen semen have an approximate chance of 50:50 for a cow to give birth to a male or female calf in both dairy and beef animals. Incidentally, beef farmers prefer male calves, while dairy ones are biased on heifers. This is not, emotionally, but rather, driven by the products of each type of farming.
Beef farmers are about meat and they slaughter bulls while females are kept for breeding. Bulls produce more meat, gain weight faster and fetch better prices than heifers when sold for slaughter. Unlike beef farms, dairy farms loath bull calves and seek to dispose of them soon after birth. The reason is that bulls in a dairy farm are very expensive to rear for meat.
Second, they are not required for breeding because most farms use artificial insemination
Some farms kill the bull calves after birth, an action that has become very unpopular with animal welfare advocacy. Other farms sell the calves to those farmers who have pastures to rare the bulls for meat.
The success of artificial insemination got scientists thinking of how they could improve the chances of selectively producing calves of one gender depending on the farmer’s preference. That led to the technology of sorting male from female sperms and gave rise to what is now called sexed or sex-sorted semen.
The gender of the calf is determined by the sperm that fertilises the mother’s egg. Female eggs all contain genetic material called the X-chromosome. Each sperm or male egg from a bull contains either the male Y-chromosome or the female X-chromosome in equal or differential numbers.
The egg can only be fertilised by one sperm for there to be a viable pregnancy and calf. If the X-carrying sperm fertilises the egg, the foetus will be an XX and female, while an XY results if a Y-carrying sperm is the lucky one; resulting in a bull calf.
Therefore, in all mammals, it is the male that determines the gender of the offspring. I recall, with amusement, how I once advised a farmer to stop blaming his wife for the girls-only brood in the family. It was his fault. The wife later told me privately that even two others nested elsewhere secretly by the husband were girls. I was happy I scientifically made peace in that home.
So, should my client resolve to use sexed semen?
My answer is yes but with some caveats. It turns out the more we advance, the more we become accurate but less precise. Natural insemination has the highest chance of pregnancy but less accurate on the gender of the heifer preferred by the farmer.
Artificial insemination with frozen semen gives many calves for each bull, but the pregnancy rates on first insemination are lower than for natural insemination. Sexed semen is highly accurate, starting from 90 percent in producing calves of the desired gender, but the pregnancy rate is about 43 percent in heifers and a bit lower in cows. This means that for every 100 heifers inseminated with sexed semen, 43 will give birth to approximately 39 heifer calves and four bulls in the first insemination.
When one considers the same ratios will be repeated in the second and third insemination, it is clear that a farmer can quickly expand her herd by using sexed semen to get heifer calves. The current cost of sexed semen in Kenya is about Sh4,500 to 6,000 per dose.
This cost is good value for money for a 90 percent chance of getting a heifer calf. To improve the success of breeding with sexed semen, I advise farmers to use the semen on heifers and cows that are known to conceive easily.
