Development and evaluation of polymer coated urea as a potential slow-release urea supplement for ruminants

[摘要] ENGLISH ABSTRACT:The rate of hydrolysis of urea in the rumen of animals is a major limitation whenconsidering the substitution of natural protein with urea in the formulation of rations.The aim of this study was to evaluate polymer coated urea prills with variable coatingthickness and evaluate its potential as a slow-release NPN compound. A new slowreleaseurea compound, made by coating prilled feedgrade urea with a co-polymerof urea-formaldehyde resin and a castor-coconut alkyd was initially evaluated forurea-nitrogen concentration in distilled water in order to evaluate its potential as aslow-release urea product for ruminants. Amino/alkyd or polyester blends areamong the cheapest of the modern synthetic systems and are considered because itis non-toxic, low-cost, biodegradable and easy to manufacture. A 2 x 2 x 2 x 2factorial design was used and 16 individual products were made and evaluated. TheWurster method was used to encapsulate urea prills. The slopes of the urea releasecurves represented the release rate of the encapsulated products and werecompared to identify the process variables, which had an effect on release rate. Twoof the coating variables, coating weight and alkyd: resin ratio, had a major effect (P =0.0001) on the release rate of urea. The crushing strength of encapsulated productswas significantly (P = 0.0001) higher than that of untreated urea. Results motivatedthe evaluation of the products in the rumen of sheep in terms of rumen ammonia andblood urea N concentrations. Four slow-release products were made afterinterpreting results from the first study, and differed on account of the coating weight and the composition of the co-polymer. Fifteen fistulated wethers were randomlyallotted into 5 groups and intraruminally received an equivalent of 15g urea. Rumenammonia and blood ammonia were taken at 0, 1, 2, 4, 6, 8, 12, 16, 20, 24, 36 and 48h after administration of the various treatments. Slow release urea (SRU) resulted insignificantly lower rumen ammonia peaks (P = 0.0001) than untreated urea, while thepeaks were also significantly delayed. Untreated urea resulted in the maximumconcentration at two hours after administration of the urea (P = 0.0685) while theSRU's reached a maximum at six hours after administration in the rumen. Nosignificant differences between the four different SRU types were found. Responsesin blood urea-N was similar to that observed for rumen ammonia nitrogen. Theencapsulation was effective in decreasing the rate of ammonia release from the ureafor up to six hours after administration. In a third trial four Dehne Merino wetherswere used in a 2 x 2 Latin square design. They received a SRU product equivalent to0.4 g urea per kg body weight orally. Rumen liquor and blood samples were taken at0, 1, 2, 4, 6, 8, 12, 16, 20, 24, 36 and 48 h after intake. Difficulty was initiallyexperienced with ingestion and palatability of the SRU products due to the strongformaldehyde and butanone odour present in the coating. The maximum rumenammonia (NH3) concentration for the SRU were lower than that of untreated urea(17.5 mg N/dl vs. 66.9 mg N/dl). The time to reach blood urea levels also differedconsiderably (6 h vs. 24 h for blood urea nitrogen) between treatments.The encapsulation of urea prills shows potential solutions to reduce the solubility ofurea and also reduce the hygroscopic nature of urea and improve the palatability andstorage characteristics thereof.Keywords: Slow-release urea, encapsulate, copolymer, urea formaldehyde rumenammonia, blood urea nitrogen, solubility, palatability, storage characteristics.

[发布机构] Stellenbosch University