Holstein strain affects energy and feed efficiency in a grazing dairy system

Context Improving the partitioning of the energy consumed by dairy cows towards milk-solid production is a priority in grazing diary systems because energy efficiency has been associated with sustainability. Different selection criteria in the Holstein breed have led to divergent Holstein strains with different suitability to grazing systems. Aim The objective of this work was to quantify and evaluate the energy partitioning between maintenance and milk production of two divergent Holstein strains (New Zealand Holstein and North American Holstein) in a grazing system without supplementation of concentrate. Methods New Zealand Holstein and North American Holstein cows, nine of each, in mid-lactation (183±37 days in milk, mean ± s.d.) were allocated in a randomised block design and evaluated under grazing conditions. The cows were managed under a daily strip-grazing system and grazed perennial ryegrass as the only source of nutrients. After an adaptation period of 14 days, heat production, retained energy in milk and metabolisable energy intake were measured over 7 days, and animal behaviour was simultaneously recorded. Key results Milk yield did not differ between Holstein strains, but fat and protein content were greater for New Zealand than North American Holstein cows; consequently, retained energy in milk was 13% greater for the former strain. Heat production did not differ between Holstein strains, but metabolisable energy intake (kJ/bodyweight0.75 .day) was greater for New Zealand than North American Holstein cows, which was associated with a greater pasture dry matter intake relative to their body weight. Both feed and energy efficiency were greater for New Zealand than North American Holstein cows. Conclusions The results supported that the New Zealand Holstein strain has greater energy and feed efficiency, demonstrating that it could be more suitable to be managed under a grazing dairy system without supplementation than the North American Holstein strain. Implications The New Zealand Holstein strain may be suited to selection as a dairy cow with the capacity to fulfil energy requirements from pasture, which is a key factor to improve production efficiency of grazing dairy systems.