“The calving pattern will be the outcome of the preceding season, even at a herd level,” Brownlie said.
This meant improving the six-week in-calf rate would be a slow and incremental process, he said.
With the industry-led induction reduction policy meaning in the 2014-15 season a maximum of 4% of any single herd can be induced, ticking the management boxes that lead to improved six-week in-calf rate are critical.
Some of those management boxes identified by Brownlie were improving submission rates through well planned and executed heat detection, considering culling late calving cows, and if purchasing cows, making sure they are likely to calve in the first six weeks of the calving period.
Getting heifers to calve early and keeping them calving early could be another key factor in tightening the calving spread. Brownlie said this was a process that started right from birth, laying the foundations by giving potential heifer replacements the best start in life.
“The moment the calf hits the ground, the health of that calf affects the likelihood that it will hit liveweight targets.”
Weighing and condition scoring a relatively large sample of heifers was part of the fertility study, showing that 66% of those animals did not hit the industry target of 90% of their adult liveweight (based on liveweight breeding values) at 22 months.
Brownlie said research currently in the pipeline strongly suggested this gap would also lead to a legacy effect in subsequent lactations, with reduced milksolids production and potentially higher rates of attrition or culling.
He recommended regular weighing and making management decisions based on individual animal data rather than working with a mob average.
Body condition score (BCS) of the milking herd was another contributing factor to the six-week in-calf rate that should be managed by individual animal data rather than an average value. Brownlie said there was plenty of research showing the importance of having mixed-age cows at a BCS of between 5.0 and 5.5.
“The less the condition score, the less likely it is that it will be an early-calving animal.
“While there is also a ‘fat cow effect’, where physiologically it can depress reproduction, according to my body condition score results only 3% of the national herd have a body condition score in excess of 6.0 whereas we have 66% that are 4.5 or below.”
Brownlie said to improve herd reproductive performance, farmers should target having fewer than 15% of their herd at a pre-calving BCS of less than 5.0.
