Each winter the team of MSU Extension dairy nutritionists hosts a series of Nutrition Roundtable meetings for dairy nutritionists practicing in Michigan and northern Indiana. In December 2010 and January 2011, five meetings were held across the state. We discussed a variety of current topics, new products, and new nutrition research. This article highlights three areas that were especially ‘hot topics’ at the last series of meetings.
Optimal Body Condition Score through Transition
Optimal body condition score (BCS) at calving was discussed extensively in the Roundtables. This topic also was addressed by Dr. Phil Garnsworthy (University of Nottingham, UK) at the American Dairy Science Association Discover Conference on Transition Cow Biology and Management in September 2010. 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 prone to develop health disorders and have an extended period of negative energy balance, reducing reproductive performance. We also know that inadequate BCS at calving can result in lower milk yield and decrease reproductive performance. It is clear that there is an optimum for the range among cows within a management group. And, variation among cows should be minimized by focusing attention on cows in late lactation.
Garnsworthy’s recommendation is consistent with the theory that feed intake of cows in the transition period is controlled by hepatic oxidation of fatty acids. Cows with greater BCS will mobilize more fat and have greater plasma non-esterified fatty acid (NEFA) concentrations for a longer period of time. According to the hepatic oxidation theory, uptake and oxidation of this mobilized fat in liver suppresses feed intake decreasing energy intake and extending the period of 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 postpartum. So, a BCS of 3.5 to 4.0 was often recommended. Since then we have realized that fat mobilization is the main reason that feed intake is suppressed and we have recommended lower BCS at calving. As more information becomes available, recommendations for optimal BCS at calving may be fine-tuned further.