Blood urea and amino acid concentrations in pigs of two breed combinations as affected by energy intakes.

Abstract

Forty-eight barrows (61 kg), 24 Yorkshire x Landrace (YL) and 24 YL x Duroc x Hampshire (YLDH), were used to evaluate the effect of six dietary ME levels on concentrations of plasma urea nitrogen (PUN) and free amino acids. All pigs consumed equal amounts of each nutrient, except for energy. As energy intakes increased from 12.42 to 35.01 MJ/d of ME (34 to 97% of NRC recommendations), ADG increased linearly (P < .001) and concentrations of PUN decreased linearly (P < .01) and quadratically (P < .05). There was a tendency (P = .09) for an interaction of breed combinations and energy intakes on ADG. In general, increasing energy intake decreased plasma concentrations of essential amino acids and increased plasma concentrations of nonessential amino acids. Exceptions were a lack of change in plasma lysine and glutamic acid, an increase in histidine, and decreases in tyrosine and aspartic acid. Concentrations of most plasma amino acids were similar between the two breed combinations, but 9 of 27 amino acids that were measured were different (P < .05) between the breed combinations. The linear response of ADG was probably attained through a relatively constant lean-to-fat deposition ratio in the body over the levels of ME intakes. The curvilinear decline of PUN to increasing energy intakes was probably because at low energy intakes, amino acids were oxidized to furnish energy for maintenance and at increasing energy intakes there was increasing accretion of body proteins.