BCS is the single most important factor influencing the health of the transition cow and her milk production and reproductive success following calving. DairyNZ principal scientist John Roche explains.
- Body condition score at calving is the most important factor affecting the health of a transition cow and her performance post-calving.
- March is the time to assess how to manage your herd’s BCS.
- Drying-off cows is the best way to increase BCS. For late calvers, once-a-day-milking (OAD) and supplementary feed can also help.
When most people hear the term ‘transition cow’ or ‘transition period’, they immediately think of short days and cold wet weather – calving time. However, research in New Zealand and internationally has now identified that the transition period actually starts much earlier.
The most important management factor influencing the incidence of metabolic disease at calving, and levels of milk production and reproductive success in lactation, is body condition score (BCS) at calving. The optimum BCS at calving for mature cows is 5. Heifers and second calvers should be 5.5 BCS at calving.
The second factor influencing cow health around calving is pre-calving feeding.
So, management decisions for calving BCS and feeding cows around calving should be considered at the same time.
Calving BCS and transition cow health
Although the effect of BCS on milk production and reproduction has been accepted for decades, much less was known about the effect of BCS on transition cow health, because it was unclear whether poor health caused thin cows, or thin cows were simply more likely to get sick. Recent DairyNZ experiments were designed to answer this question.
The results indicate that cows were healthiest if they calved between BCS 4.5 and 5. If thinner than BCS 4.5, they had poorer immune function and were more at risk of a uterine infection. However, if fatter than this (i.e. BCS 5.5), there was an increased risk of ketosis and other metabolic diseases, particularly if they were being fed high quality feed during the weeks before calving (i.e. consuming more than 100 MJ metabolisable energy/day). These metabolic diseases also increase the risk of uterine infections and mastitis.
Therefore, the cow’s calving BCS determines the effect of transition cow nutrition on the incidence of disease.
Achieving optimum BCS
From March, most cows are 120 to 150 days (North Island) or 150 to 180 days (South Island) away from the planned start of calving. Generally, cows lose a little BCS during the two weeks following dry-off and cows do not gain BCS in the month before calving. Therefore, early-calving cows only have 75 to 100 days during which they can gain BCS.
A cow will gain BCS if:
- she eats more and does not produce more milk, or
- she eats the same amount but produces less milk.
There are, therefore, three strategies for BCS gain:
- changing from twice-a-day to once-a-day (OAD) milking
- feeding supplementary feeds to milking cows and dry cows
- drying off cows early.
An effective strategy to achieve calving BCS generally involves a mix of all three.
Changing cows from twice-a-day to OAD milking
Cows milked OAD in late lactation gain about 0.25 BCS units more in three months than cows milked twice a day over the same period5. This can be part of an effective strategy to keep cows milking and gain BCS if OAD milking starts in January/February. However, cows must be offered the same amount of feed as if milked twice a day. At this stage (i.e. March), changing from twice-a-day to OAD milking is only an option if cows are BCS 4 or greater, as the amount of BCS that will be gained before dry-off is very small.
Feeding supplement to milking cows and dry cows
When fed supplements and presuming pasture is not wasted (i.e. grazing residuals are no higher than 3.5-4 cm or 7-8 clicks on the plate meter), cows will partition the extra energy into producing more milk. This means that providing supplements to milking cows is not a very effective strategy for gaining BCS, although it can prevent BCS loss when grazing residuals are less than 3.5-4 cm (7-8 clicks on the plate meter).
Offering supplements to dry cows will increase BCS, but different feed types have different effects on the amount of BCS cows gain/100kg DM of supplement fed. For more information on the effect of different supplements on BCS gain, refer to DairyNZ Body Condition Scoring – the reference guide for New Zealand dairy farmers (dairynz.co.nz/publications/animal/body-condition-scoring-reference-guide/).
Drying-off cows early
Cows need time to gain BCS as well as more energy. Therefore, drying-off thin cows (i.e. less than BCS 4) at least 14 weeks before the planned start of calving is required to achieve BCS targets. A maximum gain of 0.5 BCS units/month is a good rule of thumb, taking account of no BCS gain in the final month of pregnancy.
The best strategy for BCS gain
To manage calving BCS targets, the herd must be assessed in early March. OAD milking and feeding milkers supplements are not effective ways to gain BCS in early-calving cows at this time. To hit targets, cows should be dried-off based on their individual BCS, their approximate calving date, and the amount of supplementary feed available for autumn feeding. A timeline relative to calving date is presented in Table 1.
For later-calving cows, OAD milking and supplementary feeds can form a part of the strategy for BCS management. But the time taken to gain the necessary BCS must be considered. Particular attention must be paid to R2s and heifers finishing their first lactation.
For more information on dry cow feeding requirements refer to the April 2014 Technical Series article - Feeding for BCS gain.
Table 1. Days required from drying-off until calving to achieve the target calving BCS, based on cow age and BCS at dry-off, when fed pasture only or pasture and a high quality supplement.
|Body condition score||Days cow need to be dry before calving|
|Mature cows||Rising three-year-old||Autumn pasture (days)||Autumn pasture and high quality supplement (days)|
Note: Includes 10 days when cows are being dried off and not gaining BCS and 30 days when cows do not gain BCS before calving. For this strategy to work, dry cows must be allocated a minimum of 9-11kg DM/day (depending on breed)
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