KEEP CONDITION SCORING COWS AT GRASS

NWF Technical Manager Tom Hough explains why regularly measuring body condition score (BCS) should be an essential management technique this summer.

While many farmers routinely condition score cows when they are housed, very few continue once the cows are out at grass. Yet energy intakes at grazing will vary far more than when cows are on conserved forages, making the risk of negative energy balance significantly greater when cows are turned out.

The problem is most acute with high yielding cows who quite often are expected to work too hard at grazing. Unless condition score is monitored and supplementary feeding adjusted accordingly the consequence is that they will spend too long in negative energy balance.

Negative energy balance is where the demands of the cow outstrip the energy she can consume and the physiological response is to mobilise body tissues and to lose weight There are limits to how much condition a cow can, or should lose and excess loss can have significant consequences.

Modern Holsteins commonly experience negative energy balance during the first eight weeks of lactation but this can extend to as far as week 20. Consequences of negative energy balance can include reduced fertility, low peak yields and poor lactation persistency and an increased number of problems around calving.

Managing energy balance and body condition is a year round task and requires regular body condition scoring and adjustment to the diet as required. While this can be quite precisely managed on TMR diets, it is more of a challenge at grass.

The aim is to manage cows so that they don’t lose too much condition in early lactation, but also don’t gain too much from mid lactation to calving, while ensuring all changes are gentle. The rate of change in body condition is as important as the actual body condition scores.

When you condition score a cow you are assessing the amount of subcutaneous fat on the cow and gauging how much it is changing through lactation. As such, cow groups should be condition scored monthly to expose any BCS faults within the herd.

It is important to be consistent about how and when you condition score cows. It should be done each month by the same person using the same hand. Cows should be scored at five set times: in late lactation, at drying off, at calving, 4 weeks post calved and at peak lactation – 90 days post calved.

The target is to keep cows within a set of guidelines based on stage of lactation so that they don’t get too thin but also aren’t allowed to get too fat. While thin cows suffer from low milk proteins, poor fertility and less persistent lactations, overly fat cows also have fertility problems, are more prone to calving difficulties, have poor appetite in early lactation and suffer excessive condition loss post calving.

If high yielders lose excessive condition at grazing it may be advisable to reduce the time they are allowed to graze and increase the proportion of buffer feed to ensure dry matter intakes are adequate.

Mid and late lactation diets should be reviewed to encourage an increase in condition so cows dry off at the target score. However if there is plenty of grazing there is no reason why they should not be challenged to milk from grass and also gain condition providing grazing quality and quantity are sufficient. Providing supplementary feed may actually make cows gain condition too quickly leading to them being too fat when they dry off.

In late season the risk is that there can seem to be plenty of grass available but low dry matters and digestibility mean the feed value is poor leading to cows losing condition, often resulting in poor performance in the run up to Christmas.

Taking the time to condition score cows and fine tuning diets will make a difference to how cows perform this summer, and next winter.