Effects of concentrate and Acacia cyanophylla foliage supplementation on nitrogen balance and milk production of grazing ewes

This study was conducted to evaluate the effects of natural protection of protein from microbial degradation in the rumen by acacia tannins on digestibility, nitrogen (N) retention and milk production in dairy ewes. An experimental sheep flock grazing rye grass pasture was divided into four groups. Indoor, animals were supplemented with 300 g of concentrate, 300 g of concentrate + 100 g Acacia cyanophylla foliage (acacia), 300 g of concentrate + 200 g acacia for C, C1A, C2A groups, respectively, and only 100 g of acacia for group A. Digestibility and N balance were measured for animals in metabolic cages fed with cut fresh grass.Acacia tannins interact with concentrate supply and significantly affected digestibility. Higher OM and CP digestibility was observed for C1A and C2A groups in comparison with the A group. Digestibility of OM, NDF and CP was higher for animals supplemented with concentrate than for those not supplemented. N retention increased with ration CP content. Acacia tannins led to a high increase of N retention for C1A and C2A groups compared to C group (10.3 vs. 5.8 g/day for animals fed acacia and those not fed acacia, respectively). So, urinary nitrogen excretion decreased from 6.5 g/day for C group to 4.5 g/day for C1A. Milk yield was the highest for C1A group (555 ml/day) and the lowest for A group (500 ml/day) whereas it was intermediate for other groups. Milk fat content decreased with groups fed acacia in comparison to groups not fed acacia (7.3 vs. 7.6%). Milk protein content decreased when ewes received acacia and concentrate.