Differences in nitrogen and urea metabolism between goats bred for fibre production (Angora goat) or meat production (Boer goat)

Author: P.B. Cronjé
Year: 1992
Issue: 5
Volume: 22
Page: 143 - 148

This experiment was conducted to determine whether selection for fleece weight is accompanied by changes in the efficiency of nitrogen utilization, using Angora and Boer goats as models of animals bred for fleece or meat production respectively. A diet, containing a protein: energy ratio of 12 g CP/ MJ ME, was fed at either 77, 88.5, 100, 111.5 or 123% of estimated maintenance energy requirements. Mean N digestibility was 5% lower in Angora goats (P < 0.01), but Angoras retained 33% more N (P < 0.01). N retention increased quadratically (P < 0.01) with level of feed, but there was no interaction between diet and breed (P> 0.05). When expressed on a metabolic weight basis, urea N plasma flux rate was 14% higher in Angoras (P < 0.05), but 18% less urea N was excreted in the urine (P < 0.01). Urea N recycling was 48% higher in Angoras (P < 0.01). Angoras partitioned 62% of flux to recycling and 38% to excretion; in Boer goats proportionately less was recycled (48%) and more was excreted (52%) (P < 0.01). Urea N flux and recycling rates (g N/d) increased (P < 0.05) as the amount of diet fed was increased. It is suggested that higher N retention and urea recycling could be an adaptative mechanism consequent to increasing the demand for amino acids via selection for fleece production.

 

Keywords: Angora, goat, metabolism, nitrogen, nutrition, recycling, retention, ruminant, urea.
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