Efficiency traits in dairy cows: definition - classification - implementation

In dairy cattle, efficiency is required both in breeding and in farming practice. However, there are considerable uncertainties about definition, classification, and implementation of efficiency criteria. Present paper offers criteria to be considered as well as background information. According to its origin in economy, efficiency aims at the maximization of an output trait per unit of a production factor (e. g. kg energy-corrected milk per MJ energy intake). Efficiency traits do not consider advantages and disadvantages that arise elsewhere. The high milk yield in the first third of lactation is largely decoupled from feed intake which results in a numerically high efficiency. However, this is based on an increased loss of body reserves that is not accounted for in simple efficiency definitions. If cattle breeding and nutrition strive for a high efficiency in the short term, further losses in health, fertility and metabolic stability must be expected. However, with regard to economics and environmental impact, animals with high longevity are preferable. The key for an efficient animal is a comprehensive consideration of its performance and its requirements across its lifetime. More sophisticated efficiency traits take loss and gain of body reserves (e. g. a change of body condition score) into account. They also consider a longer time period and more performance traits, e. g. milk and meat. Apart from efficiency at the animal level, defined by efficient conversion of nutrients, the required feed quality and its effects on environment and feed versus food competition, there are further levels of efficiency. Efficiency at farm level focuses on feed or nutrient losses in feed and manure management. Efficiency at the system level examines models of milk and meat production systems and shows how changes at the animal or farm level affect environment, food security or profitability. Regardless of whether the animal, farm or system levels are considered: Focusing on a single aspect of efficiency cannot account for the complexity of the subject and will give rise to problems elsewhere.