Focus on condition of individual cows

The optimum BCS for mature cows at calving is 5.0. Heifers and young cows in their second lactation should calve at a score of 5.5. DairyNZ principal scientist animal science, John Roche, discusses the issue.

Cows that calve at BCS 5.0 instead of BCS 4.0: 

• produce 12-15kg more milksolids cycle 7-10 days earlier 
• are 0.75 BCS fatter at mating 
• are therefore more likely to be pregnant after six weeks of AI 
• are more likely to give birth to a heifer calf the following year.

If all that doesn’t convince you of its importance, the people who judge us by looking over the fence will think fatter cows are in a better welfare state than thin cows. It is difficult to put a value on this. It is also important to realise that you cannot ‘fix’ a low BCS cow after calving.

Too fat is equally bad. Although in the past, BCS advice has focused mainly on thin cows gaining BCS to meet targets at calving, a five year research partnership between DairyNZ and AgResearch has highlighted that fat cows may be equally compromised. For example, 40% of mature cows that calved at BCS 5.5 showed signs of ketosis after calving, even when well fed. In comparison, none of the cows that calved at BCS 4.5 to 5.0 showed signs of ketosis. All the research efforts point to BCS 5.0 as the optimum mature cows  and BCS 5.5 for first and second calvers.

It is important to treat cows as individuals. All these results highlight the need to focus on the condition of individual cows, not just the herd average.

Having a herd average of 5.0, when one third of the herd is BCS 5.0, one third is BCS 4.0, and one third is BCS 6.0, will not provide you with the desired outcome. 

In this situation, the cows at BCS 6.0 have been overfed during late lactation and the dry period, they do not return sufficient milk for the feed expense and are at an increased risk of metabolic diseases after calving. 

In comparison, the cows at BCS 4.0 have been underfed, will cycle late, produce less milksolids than they should and will be thin at mating, reducing the likelihood of an AI calf next year.

So, what needs to be done?

Cows need to be condition scored in February and thin cows identified. These cows need special attention; consider the following options:

Dry them off early and feed them preferentially during the dry period. With current low milk prices this is probably the best option.

They could be milked once-a-day. Although this will increase BCS, the effect is small. Eighty days of milking cows once-a-day increased BCS by only 0.2 BCS compared with cows milked twice-a-day.

Continue to milk them and feed them preferentially. Although this seems logical, preferential feeding of thin cows in late lactation generally results in them producing more milk and has only a small effect on BCS. In addition, with the current milk price it may not be economic to do this.

It must be remembered that cows require adequate time and feed to gain condition. Cows gain very little condition in the month before calving because of the energy requirements of the growing calf and it is rare for cows to gain more than 0.5 BCS a month during the dry period – and this is presuming they are well fed. 

To achieve calving BCS targets, cows at BCS 4.0 need to be dry for three months before calving and cows at BCS 3.5 need four months dry.

To gain BCS during the dry period, the cow needs to eat more. 

The amount of feed required by a dry cow to gain condition can be found in the BCS reference guide on the DairyNZ website. 

As an example, to gain half a BCS, a Friesian cow (about 500kg) needs to eat about 100kg DM pasture, 80kg DM pasture silage or maize silage, 60kg DM PKE, 110kg DM kale, 90kg DM swedes or 75kg DM of fodder beet in addition to the energy required for maintenance, pregnancy and limited activity. 

• This article first appeared in Inside Dairy March 2015.