The optimal body condition score (BCS) at calving was discussed by Dr. Phil Garnsworthy (University of Nottingham, UK) at the American Dairy Science Association Discover Conference on Transition Cow Biology and Management this past September. He said that a BCS loss of 0.5 unit (1 to 5 scale) is acceptable for fresh cows and that cows should calve with "BCS between 2.5 and 3.0 to optimize health, fertility and lifetime performance". This is lower than the commonly recommended range of 3.0 to 3.5. We know that cows that are excessively fat at calving are more likely to develop health disorders and an extended period of negative energy balance, decreasing reproductive performance. We also know that inadequate BCS at calving can result in lower milk yield and reproductive failure. It is clear that there is an optimum for the range and variation among fresh cows should be minimized by focusing attention on cows in late lactation.
Dr. Garnsworthy's recommendation is consistent with the theory that feed intake of cows in the transition period is controlled by oxidation of fatty acids in the liver. Cows with greater BCS will mobilize more fat and have higher plasma lipid concentrations for a longer period of time. According to the hepatic oxidation theory, uptake and oxidation of fat in the liver suppresses feed intake decreasing energy intake and extending the length of time in negative energy balance. A couple of decades ago we thought that cows needed more condition at calving to provide energy while feed intake was suppressed following calving and a BCS of 4.0 was often recommended. Since then we have realized that fat mobilization is the reason that feed intake is suppressed and we have recommended lower BCS at calving. Therefore, BCS should be adjusted in late lactation to reduce the range in BCS among cows at calving and the optimal average score is likely close to 3.0. Adding a maintenance group will help accomplish this.