A couple of weeks into the breeding season, a lot of farmers will begin to wrap artificial insemination (AI) and let out stock bulls to run with the herd for the next number of weeks.
It is not unusual for farms to only AI for three to five weeks in order to get the majority of cows in-calf to AI, as serving cows for about four to five weeks will mean that many of the first round repeats will also get served.
If 90% of cows are submitted in a 100-cow herd at a 60% conception rate in the first three weeks, it means that 54 cows will hold to first service and many of the 36 repeats – along with the few more that come bulling – should be served again before the bulls are let out.
For many farmers, it has been a tiresome few weeks getting cows back into calf, which may result in an eagerness to let out the stock bull.
Many spring calving herds are now five weeks into the breeding season and hopefully the majority of the herd is served by now, so it might be time for the stock bull to play a role
Stock bull
Getting the stock bull out at the right time is crucial. If he is let out too early, there may be too many cows to be served and – with the shortage of dairy replacements looming as well – you need to make sure you have enough cows served to dairy AI.
A mature stock bull should be able to cover about 30 cows within three weeks, which means the bull will be serving about 1.4 cows/day.
Not having enough bulls is often where empty rates derive from.
If there are a lot of repeats or more cows coming into heat in the next few weeks, the bull will more than likely be overworked.
Farmers should aim to have one young bull for every 10 empty females, or one mature bull for every 20 to 30 empty females.
Teagasc recommends that if more than two cows are in heat per mature bull on one day, then these additional cows should be inseminated to take the pressure off the bull.
When synchronisation programmes are being used, it is advised to serve the first round of repeats as that number of females coming into heat at the one time will be too much for a bull to deal with in a short space of time.
It is a good idea to read back through your records to get an idea of the number of cows potentially in calf, although it may be difficult to get an exact number.
All dairy farmers should first calculate the number of replacement heifers they want, and then calculate the number of dairy AI straws needed to generate that number of replacements.
Your stock bull should ideally be a beef breed, easy calving, and short gestation, that is also genomically tested.
Transitioning from AI
Many farmers will be letting out their stock bull in the coming weeks, and whether it be a dairy ‘sweeper’ bull or a beef-bred bull, the timing is essential to make sure you have bred your replacements.
Quite often, when a farm moves from using AI to letting out the stock bulls, a lull in the following calving season can be experienced.
The stock bull in most scenarios will have spent months on a silage-only diet doing minimal daily walking. Turning it out with a flurry of cows in heat and expecting it to get them all covered is a task that is next to impossible.
The bull is going to be going from barely moving to pacing up and down laneways and paddocks and mounting cows, which is going to test their feet, and so the bull’s feet should be monitored monthly and ran through the foot bath every few weeks.
Farmers should continue to AI cows along with the introduction of the bull for at least a week, as this will ensure there is no lull in the following calving season, ensuring the bull has time to settle in before getting to work.
