Improving Bull Performance

Improving Bull Performance
Conception rates in dairy herds are dictated by AB management and by bull management. Bull numbers are often underestimated in New Zealand. There is no doubt that bulls can be a costly and messy addition to your farming enterprise, but getting bull management right helps to promote a condensed and efficient calving pattern, ultimately influencing the reproductive success of your herd.
There are three aspects to bull management which should be considered:

1) Bull selection
Selecting bulls that are tall enough to service your cows is paramount. Bulls that are too short or under-grown will not be able to perform. Usually, selecting two year old bulls is a good idea for your herd as yearling bulls are often too small.

BVD testing and vaccination is also vital to prevent the detrimental effects on fertility caused by the BVD virus. There is no point in vaccinating animals for BVD that have not first been tested clear of the virus. Bulls born with BVD will not respond to vaccination, so animals should be tested first to prove they are not persistently infected (PI). BVD vaccination is a two shot vaccination programme with the booster given four weeks after the initial injection. Bulls need two shots before they are ready to work so the BVD vaccination programme needs to begin five to six weeks before bull mating begins.

Anexa FVC offers a bull fertility testing service. This involves collection of a semen sample from an animal and immediate examination of the sample under a microscope to assess sperm quality. A bull ‘firing blanks’ will not get your cows in calf, so identification of these bulls is important.

2) Bull power
The InCalf book recommends bull numbers depending on the number of cows still not pregnant at the end of the AB period. Intuitively, the longer you do AB for, providing submission and conception rates during the AB period are reasonable, the more cows will be in calf. The table (shown below) estimates the number of bulls needed depending on cow numbers and the percentage of the herd pregnant at the start of the bull mating period. Remember that these numbers are the numbers of bulls that are needed in with the herd at any one time, so essentially you will need to double these numbers to allow for resting bulls.

3) Bull day to day management
Bulls become fatigued and will not inseminate cows effectively if they are tired. Resting your bulls for two to three days and working them for two to three days is advisable. Alternatively, day and night bulls can be used.

Lame bulls should be swapped out immediately. Lame bulls will be infertile because they often have high temperatures and will be less keen to mount cows. It is obviously easier to swap out lame bulls if they are leased. Bought in bulls will also need to be monitored closely too, but may be less easy to swap out. In any case, you will need enough bulls to have bulls resting, and possibly having spare bulls on farm should be considered.

Date Added: Saturday, 1st October 2016