Effect of grass nitrogen protection by Acacia cyanophylla on nitrogen balance and sheep milk production

Abstract

Tunisian dairy sheep is localized in sub humid area characterized by a high forage production and prairie growing. Nevertheless, young grass is characterized by a high level of soluble nitrogen which generates an important loss of urinary nitrogen leading to environment pollution. The objective of this work is to study the natural protection of protein by acacia tannins and its effect on urinary losses and milk production. An experimental sheep flock conducted on ray-grass grazing was divided into three homogeneous groups according to lactation rank. The first group (Control, C) received 300 g of concentrate, the second group (C-A) 300 g of concentrate and 100 g acacia, the last group only 100 g acacia (A). The nitrogen balance was realized on individual boxes with a daily cut herb. The dairy control was twice a month. Total milk production was higher for C-A group than for other groups, 48, 45 and 42 l for C-A, C and A respectively. Nitrogen intake varied significantly according to the concentrate and/or acacia supply. The average values were 22, 20 and 15 g/day for C-A, C and A group respectively. Urinary nitrogen excretion decreased from 6.5 g/d for C group to 4.5 g/d for C-A one, consequently to acacia intake. Conversely, the nitrogen retention significantly increased with acacia intake from 6 for C group to 10 g/d for C-A one. In conclusion, the acacia supply is a valid way to increase nitrogen retention and to manage the loss of nitrogen and environment.