Changes in body condition score and in its genetic variation during lactation

Abstract The foundation of the complex of production efficiency and metabolic stress of lactating cows is the dynamics of energy balance (EB) during lactation, for which body condition score (BCS) may be a useful monitoring tool. Energy balance, or imbalance, is the difference between energy expenditure including yield and energy sources from intake nutrients and mobilized body reserves. Both milk yield and dietary intake, their amounts and compositions, can be measured readily and frequently, at least on experimental farms, but body reserves cannot be. Potentially, BCS can be used to indicate the mobilization and deposition of body reserves during lactation. This paper examined changes in BCS during lactation in different breeds, parities and feed levels. Also examined were changes in additive genetic and other variance components of BCS during lactation. Ample additive genetic variation in BCS was found to allow for fruitful genetic selection. If genetic selection is to be practiced, it appeared that shape of the curves during lactation in BCS could be changed genetically. Body condition score assessments were highly correlated within parity and between parities. Strategically, the best period to score a cow's body condition during lactation appeared to be the recovery period from negative energy balance, during which the greatest variances were observed.