Nitrate as a fermentable nitrogen supplement for goats fed forage based diets low in true protein

Abstract

The adoption of management practices for ruminants which achieve major reductions in methane release is an issue of high priority to the amelioration of global warming. The biochemical changes when nitrate is converted to ammonia in the rumen of cattle and sheep is known to lower methane production. The present study aimed to demonstrate that nitrate salts could be included safely in low-protein diets fed to goats and that the efficiency of N utilization would be the same as in goats fed urea as the non-protein N source. In Experiment 1, twelve young goats (initial weight 11± 2 kg), housed in individual cages, were fed a basal diet of rice straw and molasses and allocated in a completely random design to two treatments. Eight goats (K-N) received increasing amounts of potassium nitrate; the other four goats (CTL) were fed the same basal diet but without any additional fermentable N. The goats on the K-N diet were step-wise adapted to increasing levels of potassium nitrate, beginning with a concentration of 0.33% KNO₃ in diet DM in week 1, and increasing to 5.33% at the end of week 5. In Experiment 2, the CTL goats were fed iso-nitrogenous levels of N from urea and all goats received additional foliage of 'Sesbania grandiflora'. In Experiment 3, ammonium nitrate was given to 4 of the goats previously fed potassium nitrate. The nutritional density of the diets was increased by treating the rice straw with sodium hydroxide and including cottonseed meal as a source of bypass protein. Overall the study took place over a continuous period of 22 weeks. Nitrogen balance in the goats improved as the amount of nitrate in the diet was increased stepwise at weekly intervals. At zero nitrate in the diet, the N balance was negative but then increased linearly as nitrate was increased reaching positive values by week 3 when the KNO₃ concentration was over 1% in the diet. Growth rates and N retention tended to be higher for the goats receiving nitrate compared with those not having fermentable N in the diet. There were no differences in growth rate and N retention between the nitrate and urea diets at the same level of feeding of the Sesbania. Ammonium nitrate gave similar results as potassium nitrate and both were comparable with urea in providing rumen fermentable N and supporting acceptable growth rates when the goats were fed diets of higher nutritional density.