Effects of time of calving on the productivity of pasture-based dairy systems: A review

Effects of season of calving, date of calving within season, and pattern of calving on different components of pasture-based systems of dairying and o n the system as a whole are reviewed. Season and pattern of calving can inf luence the shape of the lactation curve (by influencing the level of yield at peak of lactation, the rate of decline after the peak, or the total days in milk), the annual milk yield and milk composition, the herd's reproduct ive performance, and animal health. For systems in which the cows calve in spring, an earlier study reported small advantages from later calving, wher eas more recent studies have shown advantages from earlier calving. These l atter advantages resulted from extra days in milk, provided that sufficient feed was available for the herd in early lactation. A combination of early calving and extra feed in early lactation may achieve the benefits and avo id the disadvantages of early calving. Comparisons between autumn and sprin g calving systems showed that autumn-calved cows require more supplements d uring early lactation (winter) and usually have lower daily milk yields at peak lactation than spring-calved cows. However, autumn-calved cows can hav e higher annual yields of milk and milksolids than spring-calved cows, main ly as a consequence of both longer lactations and higher daily milk yields during late lactation. Time of calving is a key element in construction of the farming system, which can be integrated with stocking rate, pasture sup ply, and availability of supplementary feed.