INFLUENCE OF AVILAMYCIN AND TYLOSIN ON RETENTION AND EXCRETION OF NITROGEN IN GROWING PIGS

In two trials with growing pigs the effect of zero, 40 mg Avilamycin/kg and 40 mg Tylosin/kg feed on the N balance at varying dietary crude protein concentrations was investigated. The dietary crude protein contents in the first trial were 17% and 15.5%, and in the second trial they were 18.5%, 17.5%, 16.5% and 14%. The 14% protein level was fortified with L-Lys, DL-Met, L-Thr and L-Trp to the amounts of the 17.5% protein level. In trial 1 Avilamycin and Tylosin increased N retention by a joint average of 3.5% and 4.7% of both protein levels. The rise was due primarily to improved N digestibility. N excretion relative to N retention was reduced by 7% and 8% through the additives. Reducing dietary protein significantly decreased N retention. In trial 2 Avilamycin and Tylosin improved N retention by a joint average of 5% and 6% for all protein levels. The higher retention was due both to improved N digestibility and to lower urinary N excretion. N excretion relative to N retention declined by 11% with both additives. Reducing dietary protein from 18.5% to 16.5% led to a proportional reduction of N retention. The 14% protein level after supplementation with amino acids was comparable to the 16.5% level in terms of N retention, but N utilization was improved by 10 percentage points. There were no interactions between the feed additives and the protein levels. It was concluded form these results that by using the feed additives a 6% saving of dietary protein can be achieved without reducing N retention. This implies that 11% less nitrogen is excreted. These findings illustrate the contribution of these feed antibiotics towards reducing environmental pollution with nitrogen.