Resumen

KEIM, Juan Pablo  y  ANRIQUE, René. Nutritional Strategies to Improve Nitrogen use Efficiency by Grazing Dairy Cows. Chilean J. Agric. Res. [online]. 2011, vol.71, n.4, pp.623-633. ISSN 0718-5839.  http://dx.doi.org/10.4067/S0718-58392011000400019.

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.

Palabras clave : Concentrate supplementation; ruminal synchrony; high sugar ryegrass; crude protein; milk production.

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