Michael Catley, Otorohanga
As I write this, hail is hitting our heads and lightning strikes are causing us to duck for cover. But, life must go on with calving and feeding cows/calves (more like wading through paddocks) still the top priority. It makes for a grim thought, but hopefully that is all that it is with a change to sun on our backs and mating underway in October/November. A few thoughts spring to mind after the first months of the new milking season;
How well have the cows milked and how is their condition leading into AI?
What were my levels of spring mastitis compared to previous years? Am I happy with this level?
How have I managed the anoestrus cows into the start of AI and what result do I expect to get in return?
Although these are very important, I will concentrate on another aspect of reproduction that may be overlooked or considered less important; bull management. Depending on your 6-week in-calf rate, the importance of optimal bull management can vary. But the sooner your cows get pregnant to natural mating, the earlier they will be in milk.
Mature bulls – a mature healthy bull makes for a good sire. Like heifers, he needs to be 50% mature weight at 12 months and up to 85% at two years. Keep in mind breed differences.
Selection - as always assess the risk for breed and look to add value to the calves and don’t forget easy-calving and short gestation sires.
Examine the bulls closely – two/three months out from mating you want them on farm, on good tucker and in good condition to optimise sperm production. Look for the obvious lameness issues but don’t forget genital soundness (pizzle and testicular) and be wary of aggressive bulls.
Managing bulls in work - ensure there are at least two sexually active bulls with the herd at all times (three is even better) – regularly observe for activity. Try to avoid bulls coming onto concrete yards to prevent lameness issues and maintain at least two mobs of bulls and have spare bulls in case of failure.
Bull Numbers - one bull for every 30 cows/heifers is needed to get them pregnant early on in natural mating, BUT double your bulls needed for post-synchrony cows/heifers as large numbers can return at the same time.
For example: A 300 cow herd with a 60% 6-week in-calf rate this means 120 cows must be served by four sexually active bulls. Another four bulls should be on hand for changeover every three days and cautious farmers will have one-two bulls as back-ups on farm. Three bulls are needed for the heifers (25% replacement rate), giving a total of at least 13 bulls.
A simple plan that allows for the inevitable lame or aggressive bull means optimum bull performance, early take to bulls in natural mating and fewer ‘missed’ cows. A lot of us look at the bull numbers and think it’s unnecessary, but carrying a few extra bulls is easy and the best insurance policy.