Mating success
What really matters when it comes to fertility? The collective efforts of the dairy industry have identified that in seasonal calving herds, the 6-week in-calf rate is as important as the final empty rate to assess reproductive performance.
The main drivers of the 6-week in-calf rate are the 3-week submission rate (SR) and conception rate. The target submission rates are 90% by three weeks and 95% by six weeks. The major influences on SR are the number of non-cycling cows and heat detection. The non-cycling rate at the start of calving limits 6-week in-calf rate and the target is 15% or less.
Non-cycler rates are affected most significantly by body condition at calving and weight loss after calving. Both are affected significantly by management decisions such as drying-off dates and feed budgeting and so have implications beyond herd fertility. In terms of monitoring where the herd sits during the year, regular body-condition scoring (BCS) is an objective way to check progress. The times to BCS are pre-calving, pre-mating, after mating and at drying-off. This information is used to plan feed budgets.
Calving pattern is both an influence and a consequence of mating success. Late-calving cows are more likely to be non-cycling and have lower conception rates during AI. Extending mating to lower empty rates spreads the calving pattern which has a negative impact on the subsequent mating. This highlights the need to achieve good in-calf rates early in the mating period.
Heat Detection
A missed heat is a loss worth about $200.[MSOffice1] Heat detection is worth doing well! Mating activities should be the responsibility of experienced staff, particularly heat detection. If experience is an issue, then invest time in training staff either yourself or with our help.
Heat detection aids
Tail paint - apply early (32 days before planned start of mating) to detect pre-mating heats. Paint is best applied as a 20cm by 5cm strip from the base of the tail and forward. The hair should be well covered but not so thick that hair fibres cannot be identified. Tail paint should be touched up at least weekly.
Heat mount detectors - improve detection rates. They are increasingly popular and are now more user-friendly than ever.
Conception Rate (CR)
The influences on CR are more difficult to quantify. We know that cow health, in particular the presence of endometritis, has a significant negative impact. Identifying and treating endometritis was discussed in August's VetNotes. Suffice to say it should be dealt with in the lead-up to mating.
We also know that the first heat after calving has a low CR of around 35%. The CR for subsequent heats rises quickly towards a normal rate of around 60%, so the number of cows having their first heat during the first or second round of mating will therefore lower the overall CR.
All of the effects already discussed such as body condition, calving pattern, non-cyclers and heat detection are therefore likely to influence CR and improvements in all these areas will lead to better outcomes overall.
Bull Mating
Sufficient numbers and a healthy bull team are obvious requirements. The rule of thumb for bull numbers is 3% of the number of cows to be mated plus one (the plus one is to make sure there is always more than one bull with the herd at all times). The number of cows refers to the number that are not in-calf at the end of AI. For a 6-week AI period this is typically 35-40% of the herd.
Health requirements are bulls that are tested for and vaccinated against BVD, have had a fertility test, have no history of illness within two months of the start of mating and are not lame.
Totally Vets currently tests a large number of beef bulls and can efficiently test dairy bulls for semen quality and assess serving ability at the same time.
