Everything You Need to Know About Bull Semen — And How to Choose the Right One for Your Cows

*By KilimoDairy | Farm Intelligence Series*

If you use artificial insemination (AI) on your farm — or you are thinking about starting — one of the most important decisions you will make is which bull semen to use. The right choice can mean daughters that produce 5, 8, even 10 more litres of milk per day than their mothers. The wrong choice can set your herd back by years.

This guide explains everything in plain language. No complicated science. Just what you need to know to make a smart decision.

What Is Bull Semen, and Why Does It Matter So Much?

When a cow gives birth to a calf, that calf gets half its genetics from the mother and half from the father (the bull). The bull's genetics determine a lot — how much milk his daughters will produce, how healthy they will be, how long they will last on your farm, and even how easy they will be to milk.

When you use artificial insemination, a technician deposits a small straw of frozen bull semen into your cow. That single straw contains the genetics of one of the best bulls in the world — genetics you could never afford to have on your farm as a live animal.

This is the power of AI: it puts world-class bull genetics within reach of every farmer, at the cost of a single straw.

Where Does Bull Semen Come From?

Bull semen is collected from carefully selected bulls at special breeding centres. The bulls are chosen because their daughters — tested on hundreds or thousands of farms — have proven to be exceptional milkers, healthy animals, and long-lasting cows.

In Kenya, you can get semen from two main sources:

KAGRC (Kenya Animal Genetics Resource Centre) This is Kenya's national semen production centre, based in Naivasha. KAGRC collects and sells semen from bulls that have been evaluated in Kenya and East Africa. Because these bulls' daughters have been tested locally, their performance figures reflect what you can realistically expect on a Kenyan farm. KAGRC semen is widely available through government AI services and is generally the most affordable option — roughly KES 300–600 per straw.

Imported Semen from International Companies Companies like GENEX, Semex, ABS Global, and Select Sires sell semen from bulls proven in Europe, North America, and other parts of the world. These bulls often have very high production figures — but those figures were recorded on farms with very different conditions from Kenya. Imported semen can cost KES 800–4,000 per straw for conventional semen, and more for sexed semen.

Both sources have their place. KAGRC semen tends to work well for crossbreeding programmes. Imported semen is popular for farmers who want to introduce top international genetics into their herd.

Conventional Semen vs. Sexed Semen — What Is the Difference?

Conventional semen contains roughly equal numbers of male and female sperm cells. When used for insemination, you have approximately a 50/50 chance of getting a heifer (female) calf or a bull calf. Heifers are the valuable ones on a dairy farm — they are the future milkers.

Sexed semen has been sorted in a laboratory to contain mostly female sperm cells — typically around 90% female. This means when you use sexed semen, approximately 9 out of 10 calves born will be heifers.

The trade-off: Sexed semen is more expensive (often 2–3 times the price) and has a slightly lower conception rate than conventional semen because the sorting process affects the sperm. However, for many farmers, the value of getting more heifer calves outweighs the extra cost.

A practical tip: Use sexed semen on your best, most fertile young cows. Use conventional semen on older cows or those with a history of conception difficulties.

How to Read a Bull's Numbers

Every AI bull comes with a set of numbers that tell you what his daughters are expected to perform like. These numbers look confusing at first, but once you understand what they mean, they become very useful.

Here are the most important ones — explained simply:

### PTA Milk (or EBV Milk) This is the most important number for a dairy farmer. It tells you how many extra litres (or kilograms) of milk per lactation the bull's daughters are expected to produce compared to an average bull.

A bull with PTA Milk of +800 kg means his daughters should produce around 800 kg more milk per lactation than daughters of an average bull. That is roughly 2–3 extra litres per day over a 305-day lactation — which adds up to real money very quickly.

Positive numbers are better. Higher is better.

### PTA Fat % and PTA Protein % These tell you about milk quality — how rich the milk is in fat and protein. If you sell milk to a processor that pays a premium for higher fat or protein content, these numbers matter to you.

### Somatic Cell Score (SCS) This measures how resistant the bull's daughters are likely to be to mastitis (udder infection). Lower is better. A bull with a low SCS produces daughters that are less likely to get mastitis — saving you treatment costs and milk losses.

### Productive Life (PL) This tells you how many extra months the bull's daughters are expected to remain productive on the farm before needing to be culled. A bull with PL of +2.5 means his daughters last about 2.5 months longer than average. Longer-lasting cows mean lower replacement costs for you.

### Daughter Pregnancy Rate (DPR) This measures how easy it is to get the bull's daughters pregnant again after calving. Higher is better. A cow that gets pregnant quickly after calving gives you a calf every year — which is what you want for maximum milk production and income.

### Net Merit (NM$) or Total Merit Index This is a single combined score that adds up all the traits above (and more) into one number, weighted by their economic importance. It is a useful shortcut when you want a quick comparison between two bulls.

When in doubt, compare bulls by their Net Merit score. It accounts for the full picture, not just one trait.

What Breed of Semen Should You Use?

The right breed depends on your situation. Here is a simple guide:

Friesian (Holstein-Friesian) The world's top milk-producing breed. Friesian bulls produce daughters that can milk 20–30 litres per day or more under good management. However, pure Friesians can struggle with Kenya's heat and are more demanding on feed quality. Best for farmers with reliable feed supply and good housing.

Ayrshire A hardy breed that performs well in Kenya. Ayrshire milk is naturally high in fat and protein, making it attractive to processors. Ayrshire cows adapt better to local conditions than pure Friesians and are a popular choice for smallholder farmers.

Jersey The smallest of the common dairy breeds but produces milk with the highest fat content of all. Jersey cows are very heat-tolerant and feed-efficient — they produce a lot relative to what they eat. A good choice if you are selling cream or making cheese.

Sahiwal Kenya's own elite indigenous dairy breed. Sahiwal cows are highly resistant to ticks and local diseases, thrive on natural pasture, and can produce up to 3,500 litres per lactation under good management — impressive for a breed that needs none of the climate babying of exotic breeds. Sahiwal semen is widely available through KAGRC.

Crossbreeding For most Kenyan smallholder farmers, a cross between an exotic breed (Friesian or Ayrshire) and local genetics gives the best balance of production and hardiness. A 50–75% exotic cross tends to perform best where feeding is good but not perfect. If you are just starting to upgrade your herd, begin with Sahiwal or Ayrshire crosses before moving to higher-grade Friesian genetics.

Common Mistakes Farmers Make When Using AI

1. Using semen without reading the bull's numbers Choosing a bull based only on breed or price is like buying a cow without looking at her milk records. Always check PTA Milk, SCS, and Net Merit before buying.

2. Poor heat detection AI only works if you inseminate at the right time — when the cow is in heat. Signs of heat include restlessness, standing to be mounted by other cows, reduced milk production that day, and a clear discharge from the vulva. Missing the heat window is the biggest reason AI fails on smallholder farms.

3. Improper semen handling Semen straws are stored in liquid nitrogen at -196°C. Once removed from the tank, they must be thawed correctly — typically in water at 35–37°C for 30–45 seconds — before use. Exposing them to the wrong temperature, sunlight, or delays kills the sperm cells and wastes your money.

4. Inseminating a cow that is not healthy A cow under stress — from illness, poor nutrition, or recent calving complications — will have a much lower conception rate regardless of the semen quality. Get her healthy first.

5. Using the same bull generation after generation If you always use the same bull, your herd's genetics stop improving. Rotate bulls thoughtfully, choosing ones with higher merit scores each generation.

How KilimoDairy Helps You Make Better Semen Choices

Choosing the right bull used to mean relying on your AI technician's recommendation, a printed catalogue from a semen company, or asking a neighbour. KilimoDairy changes that.

### Browse Over 9,000 Bulls in One Place KilimoDairy's bull catalogue brings together semen from GENEX, Semex, ABS Global, Select Sires, and KAGRC — all in one searchable database on your phone. You can filter by breed, sort by PTA Milk or Net Merit, and compare any two bulls side by side before you make a decision.

### Understand Every Bull in Plain Language Each bull in the catalogue has an AI-generated description written in simple language — explaining what his numbers mean for your farm in practical terms. No agricultural degree required.

### Record Every Service Against the Right Cow When you use a straw of semen, KilimoDairy records it against the specific cow: which bull, which date, and which method (AI or natural service). The system then calculates the expected calving date automatically and reminds you to confirm the pregnancy. Nothing falls through the cracks.

### Track What Is Actually Working on Your Farm Over time, KilimoDairy shows you which bull combinations are producing your best calves — and which are underperforming. You can make your next semen order with confidence, knowing you are building on what has worked rather than guessing again.

### Heat Detection Reminders Based on your cows' recorded cycle history, KilimoDairy reminds you when each cow is approaching her expected heat window. Fewer missed heats means better conception rates and less wasted semen.

A Simple Step-by-Step: Using AI on Your Farm

1. Observe your cow for heat signs — restlessness, standing to be mounted, reduced milk
2. Call your AI technician as soon as you confirm she is in heat. AI is most successful 12–18 hours after heat begins
3. Choose your bull using KilimoDairy's catalogue — check PTA Milk, SCS, and Net Merit
4. Let the technician handle the insemination — proper technique and equipment matter
5. Record the service in KilimoDairy — bull name, date, cow ID
6. Watch for return to heat 21 days later — if she comes back into heat, she did not conceive and needs to be re-served
7. Confirm pregnancy at 45–90 days via rectal palpation or ultrasound by a vet
8. Prepare for calving — KilimoDairy will remind you when the expected date approaches

The Bottom Line

Bull semen is not just a farm input. It is a long-term investment in the genetics of your herd. A good choice today produces daughters that milk better, stay healthier, and breed more reliably for the next 10 years. A poor choice — or no choice at all, just using whatever is available — means you are farming the same herd your grandfather farmed.

The good news is that making the right choice has never been easier. With KilimoDairy's bull catalogue, plain-language descriptions, and complete breeding records, every Kenyan dairy farmer now has the information they need to breed smarter — starting today.

*Explore the KilimoDairy Bull Catalogue and start upgrading your herd's genetics. Visit [kilimodairy.co.ke](https://kilimodairy.co.ke) to get started.*