Focusing on heifer rearing
Many farmers are now considering an expansion in cow numbers. This increase in herd size is heavily reliant on increasing the number of heifer calves born, which are successfully reared until calving down, ideally two years later.
Many farmers have endeavoured to maximise the number of dairy heifer calves born. With this in mind, they now use AI or dairy stock bulls on heifers and cows, and extend the period of AI mating, etc. Unfortunately, this is the easy bit.
So why focus on heifer rearing when the majority of spring calves are weaned? The stark reality is that as herd size and heifer numbers increase, the performance and liveweight (LW) gain tends to decrease. It's from now on that a large divergence in size and weight of heifers results, and the bottom 25pc is very evident and noticeable.
Regrettably, it often isn't until mating that we realise there are a number of heifers which are too small. At this point, you either breed them on time, breed them later, or carry her over until next year -- all of which have significant losses of production, efficiency and profit. Small heifers have significantly lower production levels in first and second lactation (eg heifers 50kg behind target liveweight at calving produce around 300 litres less over two years).
Higher replacement rates also reduce herd milk yields. Therefore, in the expansion phase, these two factors will substantially reduce overall output per cow and potential profitability of the herd. Small heifers often won't go in calf early because of delayed oestrus.
However, to offset the reality of small heifers, some decide to mate all the heifers later. This results in a poorer calving spread of the herd and a substantially reduced longevity of the heifers.
And don't leave the bull in with heifers too long. A maximum of 12 weeks from start of mating is sufficient. Others opt to roll over light heifers, which gives them a chance of herd longevity, but the extra year comes at a cost. So, instead of the above, give all heifers a fair chance by maximising the liveweight gain in this critical period from now until winter.
What are the targets? To avoid any negative impacts of liveweight on reproductive performance at mating (target 60pc of LW) and subsequent lactation, heifers need to be 30pc of mature liveweight at six months and 40pc of mature liveweight at nine months. For a spring calving herd, which starts calving in February, this relates to heifer liveweight in August and November respectively.