The optimum condition score for mature cows at calving is 5. Heifers and young cows in their second lactation should calve at a score of 5.5. John Roche, Principal Scientist, Animal Science discusses the issue.
What we know about cow BCS
Cows that calve at BCS 5 compared with a BCS 4
- produce 12-15kg more milksolids,
- cycle 7-10 days earlier,
- are 0.75 BCS fatter at mating and are, therefore, more likely to be pregnant after six weeks of AI, and
- are more likely to give birth to a heifer calf the following year.
If all of that isn’t enough to convince you of its importance, the people that judge us by looking over the fence think that 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 predominantly focused on thin cows gaining BCS to meet targets at calving, a fiveyear research partnership between DairyNZ and AgResearch has highlighted that fat cows may be equally compromised. For example, 40 percent 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 showed signs of ketosis. All of the research efforts point to an optimum BCS for mature cows of 5 and BCS 5.5 for first and second calvers.
It is important to treat cows as individuals
All of these results highlight the need to focus on the condition of individual cows and not just the herd average.
Having a herd average of 5, when one third of the herd is BCS 5, one third is BCS 4, and one third is BCS 6 will not provide you with the desired outcome. In this situation, the cows that are a BCS 6 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 that are a BCS 4 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.
What needs to be done?
Cows need to be condition scored in February and thin cows identified. These cows need special attention. There are a number of options to consider for these cows:
- 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 as well as 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 very rare for cows to gain more than 0.5 BCS a month during the dry period (and this is presuming they are well fed). In order to achieve calving BCS targets, cows that are a BCS 4 need to be dry for three months before calving and cows that are a BCS 3.5 need four months dry.
Preferential feeding during the dry period
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 approximately 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. Because of these high requirements for DM intake, it is very difficult for cows to gain more than half a BCS in a month during the dry period.
Which scale should I use?
All New Zealand recommendations are based on the 1-10 scale promoted by DairyNZ. This scale has been defined by more than 30 years of research and is internationally recognised and accepted. Calving targets are based on this system and can be found in the BCS field guide as a reference for scoring cows. Alternatively, employ a certified BCS assessor to ensure consistency and accurarcy.
This article was originally published in Inside Dairy March 2015