Body Condition Scoring
When Slimmer is Better
Widely recognized as a valuable dairy management tool, body condition score (BCS) assessment has been used to recommend the amount of body fat your cows should be carrying at various stages in their lactation cycle. Recent research suggests we need to slim down those recommendations at calving and peak lactation.
The five-point North American scale considers 1 as a very thin cow and 5 as an over-conditioned animal. In other parts of the world, the scale may differ but the concept is the same: assess the animal's body fat reserves.
You could be tempted to measure body weight to estimate body fat reserves, but this measurement alone is a poor indicator. Factors such as age, stage of lactation, frame size, pregnancy status and breed would affect your interpretation.
Moreover, in early lactation, body fat mobilization takes place as feed intake increases. Increased amounts of feed ingested when rumen-fill is greater can sometimes mask actual tissue mobilization.
In early lactation, when dairy cows cannot get enough energy through their daily ration to support high milk production, they use body fat reserves to compensate for the energy deficit. This phase can last 50 to 100 days after calving.
The BCS profile is similar to an inverted lactation curve. The lowest point of the BCS curve usually shows up around peak lactation. Cows with superior milk production genetics have a higher lactation curve and tend to have a depressed BCS profile.
A particular cow's genetic make-up tends to dictate the target BCS level she strives to achieve at a certain point in lactation. Research findings demonstrate dry matter intake increases when the BCS deviates from cow-specific targets. This dry mater intake increase persists until she replenishes her body reserves. These findings explain why fatter cows tend to have depressed dry matter intake.
During the first 30 days after calving, management and feeding have little effect on BCS loss. This is mostly due to hormonal adjustments. After that four-week period, research has shown, management and diet can play an important role in reducing the length of time a cow uses her body reserves. Eventually, when conditions allow it, she replenishes what she lost.
This BCS fluctuation is perfectly normal, and improved feeding cannot completely eliminate it. Traditionally, nutritionists came up with early-lactation rations that would provide all the energy a cow needed to prevent as much as possible any body reserve losses. We now know BCS change is a genetically regulated process-beneficial as long as it is not drastic (less than a point of BCS).
Since several researchers have demonstrated a ration's inability to influence the early-lactation rate of BCS loss, it seems management of calving BCS is the primary way to control the extent of BCS variation and lowest point after calving.
This is why monitoring BCS in mid to late lactation is also critical. During this period, the intended calving BCS can be more efficiently managed to achieve the optimal objective. It is less efficient to adjust the BCS in the dry period.
First-calf heifers are unable to achieve a rapid BCS gain after hitting their lowest point after calving. This highlights the necessity of specific management practices for these animals so they can reach optimal BCS at their second calving. Practices include using a separate milking heifer group, ensuring adequate bunk space and minimizing situations that permit competitive behaviours from boss-cows toward subordinate animals. Keep in mind that optimal BCS at calving is an important factor influencing the fertility outcome later in lactation.
The effect of energy status (BCS at a specific point in time) and energy balance (BCS gain or loss and rate) on reproductive performances is well documented. In fact, energy balance is probably the most important non-management factor influencing reproductive performance.
The most recent studies tend to demonstrate successful pregnancy can be achieved earlier when the BCS low point and reserve replenishment happens early in lactation. It also seems the optimal BCS at the onset of the breeding period should range between 3.0 and 3.5. For cows above or below this range, successful heat detection decreases rapidly.
As well, research shows cows with high BCS at calving have a much greater risk of coming down with metabolic problems later on. Recent studies demonstrate even a small amount of over-conditioning substantially increases odds of metabolic problems showing up.
A 2006 study, for example, reported a 30 per cent increase in the risk of milk fever if a cow's BCS was greater than 3.5 at calving. Similarly, another study reported a doubling of ketosis risk in dairy cows calving at a BCS greater than 3.5 compared to cows calving at 3.5.
Generally, it appears, over-conditioning-BCS greater than 3.5-rather than a low BCS increases risk of metabolic disorders around calving time. BCS has also been linked to lameness.
Recent findings suggest previous BCS recommendations need to be lowered slightly. Optimal BCS at calving should range between 3.0 and 3.25, and the loss of BCS after calving should be no more than 1 point to a lowest score of 2.25.
This article first appeared in the Ruminations column of The Milk Producer Magazine in February 2011.
Optimal range of Body Condition Score according to days in milk
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