The next month is a crucial one for managing spring-born replacement heifer calves because you can actually influence growth rates on the next generation of milking cows that will calve down on your farm in 30 months. You need to keep calves that are behind target moving along in terms of weight gain, so they reach the target of 330-350kg next May.

Hypothetically, if they are behind target now and let’s say we get a bad weather month at grass, then this subset of calves could end up well behind target going into winter. This can happen quickly if they are running in big groups with stronger comrades.

The first thing you can do now is weigh the spring-born calves. While the average figure for the bunch of calves is often talked about, it means very little.

Really, you need to know and identify the bottom 10% in terms of actual weight and those heifer calves that are behind target.

So what is the target at this time of the year? Effectively, the best way to look at this is to count back from 350kg next May.

Let’s divide the intervening time up into likely feeding scenarios and see where we need to be. The best scenario is where you have the weanlings at grass next March and April.

During those two months they will gain 1kg/day, so that’s 60kg of liveweight. Now let’s assume for November to February they are inside on grass silage and 2kg of meal. For that 120-day period, on average they will gain 0.5kg/day, so that’s another 60kg of liveweight.

We have 10 days left in September and 30 in October, so, again, let’s assume best-case scenario they gain 1kg/day for the next 40 days, so that’s another 40kg liveweight.

So in total for those on dry farms, we can expect 160kg liveweight for the next eight months – this means to hit 350kg target weight at bulling the heifers need to be 190kg now.

Now some farmers will say the heifer calves will be indoors for six months (October to March) because they have heavy land or they want to keep grass for milking cows, etc.

While this is a higher cost, it also leads to lower weight gain, so factor that in.

On average, research results show that this means you can only bank on 0.5kg/day for that six-month period (180 days), so that’s 90kg of liveweight instead of 120kg if you could get them out to grass earlier.