Effects of spring-calving compared to autumn-calving on the lactation curve and milk quality in Norwegian herds

The objective of this work was to study the effects of spring calving in comparison with autumn-calving on the trajectory of both milk yield and quality (percentages of protein, fat and lactose, and also somatic cell counts (SCC) and urea). On average, autumn-calvers had 0.8 and 1.2 kg higher daily milk yield and ECM (energy-corrected milk), respectively, than those calving in the spring, due to a higher yield in mid- and late lactation. Milk fat and lactose were also higher and SCC lower for those calving in autumn, and the reduction of protein and fat percentages in early lactation was lower. These results suggest that maintaining a high milk yield is a greater challenge for spring-calving cows on pasture feeding than for autumn-calving cows fed indoors.