Nutritional strategies to improve nitrogen use efficiency by grazing dairy cows

Juan Pablo Keim1*, and René Anrique1

Grazing dairy cows are characterized by converting a low proportion of dietary N into milk N. This low N use efficiency (NUE) is mainly due to an excessive supply of crude protein (CP) of pasture with regard to animal requirements. Excess N in the diet has negative effects for the animal; it alters the organoleptic characteristics of milk and pollutes the environment through N excretions. The aim of this review was to analyze the available information on nutritional strategies to improve NUE by grazing dairy cows, such as diluting the dietary N through supplementation, synchronizing ruminal carbohydrate (CHO), and N fermentation rates, and using pastures with a high water soluble carbohydrates (WSC) content. There is a beneficial effect of carbohydrate supplementation on NUE, with an increase in milk yield (MY) of 0.83 ± 0.34 kg milk kg-1 supplement and a reduction of ammonia N (NH3-N) in the rumen. A better synchrony between CHO and rumen N does not improve MY and NUE. However, a positive effect on NUE was identified as a result of increasing the WSC/CP ratio. The use of cultivars with high WSC content increases the dry matter intake (DMI), MY, and milk N production, with no consistent effect on NUE.

Keywords: concentrate supplementation, ruminal synchrony, high sugar ryegrass, crude protein, milk production.
1Universidad Austral de Chile, Facultad de Ciencias Agrarias, Independencia 641, Valdivia, Chile. *Corresponding author (juan.keim@uach.cl).