BRIEF COMMUNICATION: The effect of concentrate supplementation on milk production during an extended lactation in grazing dairy cows

摘要

Extended lactation systems where cows are milked for longer than 300 days, provide an opportunity for farmers to use the lactation potential of genetically superior cows, reduce calving and mating costs, even-out labour requirements, and/or build herdsize by retaining non-pregnant cows. However, depending upon cow genetic strain and nutrition, milk production can be reduced in an extended lactation system relative to a 'normal' lactation of 260 to 300 days (Kolver et al., 2007; Grainger et al., 2009). Winter-feeding levels are potentially important in contributing to the success of extended lactations in a pasture-based system. Cows fed pasture-based diets have a second lactational peak during the second spring of extended lactation, coinciding with an increase in the availability and quality of pasture (Kolver et al., 2007; Grainger et al., 2009). Increased nutrition stimulates secretory activity and proliferation of mammary epithelial cells during early lactation (Norgaard et al., 2005), and strategic use of supplementation during winter pasture deficits may improve milk production responses to extended lactations through a similar mechanism.