As dairy cows begin their lactations, energy quickly becomes the first limiting ‘nutrient.’ Body fat reserves are a source of energy in early lactation as milk energy output exceeds feed energy intake. Change in body condition score (BCS) is an effective way to evaluate shifts in the cow’s energy status during lactation and gestation periods.
The amount of fat cover around the ribs, spine, rump, and other body areas can be used to estimate body reserves. The BCS system of 1 (very thin) to 5 (fat) is used to numerically score or rate the animal. These scores are not related to frame size or breed. BCS reflects the impact of milk yield, dry matter intake, and stress (such as environmental stress, sore feet, twins, and metabolic disorders) on the cow’s energy status. Investing an hour with an experienced BCS evaluator will train most individuals to accurately assign BCS consistently.
Each person will develop her or his approach and parts of the cow used to score cows. I use the rib, thigh, and spine areas when evaluating cows below BCS 3. I will focus on the tail head, brisket, rump, and withers areas for cows over BCS 3.
The key is to consistently score cows and monitor changes during the lactation cycle. Generally, I will score cows 0.25 to 0.5 point higher than veterinarians and consultants, but we will rank cows in the same BCS order.
The following points can be helpful when interpreting BCS changes.
1 - One BCS is equal to 120 pounds of body weight based on New York research results. One pound of mobilized body fat can support six pounds of milk energetically.
2 - Cows should not drop more than one BCS in early lactation (for example shifting from 3.5 to 2.5). Cows that drop below BCS 2 cannot gain back enough weight during lactation to be a BCS 3.5 when cows dry off.
3 - Weight loss should be limited to less than two pounds per day in early lactation. Greater weight losses can lead to ketosis, reduced dry matter intake, and metabolic disorder risks. Some computer ration programs will calculate this value for cows at peak milk yield.
4 - If a cow gains one pound of weight starting at 140 days after calving, she could/will gain 120 pounds or 1 ½ BCS when she is dried off.
5 - To replace one pound of body weight will require an additional 2.33 megacalories of net energy lactation or three pounds of shelled corn (as fed basis).
6 - If the dry cow is below 3.5 when she enters the dry period, 60 pounds of gain or 0.5 BCS can be added during the 60 day dry period. More aggressive weight gains can lead to metabolic disorders due to high energy intakes.
7 - Optimal BCS for dry cows is controversial. Researchers suggest lower BCS (less than 3.25) will reduce metabolic risks. Dairy managers generally want dry cows at 3.5 to 4.0 because the extra energy reserve can support higher milk yields in early lactation. The following guidelines reflect the manager’s ability to manage health risks while harvesting the extra milk potential.
Cows scored monthly or bi-monthly provide valuable management information. Summary of BCS by milk yield groups, days in milk, lactation number, and feed groups allows the manager to focus on key areas. Another approach is to monitor BCS at critical time points.
Another method is to evaluate BCS based on one visit. Be sure to score several cows in each of the categories below.
In summary, body condition scores are another tool that allow dairy managers to evaluate energy status of their dairy cows which is impacted by ration energy concentration, dry matter intake, and metabolic disorders. Happy scoring!
Reprinted with permission from
AGRI-VIEW, March 5, 1998
Written by Mike Hutjens, Extension Dairy Specialist, University of
Illinois at Urbana-Champaign