Impact of nutritional and environmental factors on plasma urea and amino acid concentrations in pigs

Abstract

<p>A series of experiments were conducted to study variables that may affect concentrations of the blood plasma urea nitrogen (PUN) and free amino acids (AA) in 60 kg pigs. Pigs fed twice daily had postprandial peak PUN at 5 h and peak AA at 2 h after feeding. Pigs with ad libitum access to feed exhibited an almost constant PUN and AA during the 24-h period. Thirteen plasma nonprotein AA varied less than 10 essential or 9 non-essential AA in response to sampling times and two feeding methods. Adding cation (Na) to a corn-soybean diet elevated plasma citrulline but did not affect growth performance, PUN and plasma pH. Also, the Na addition shifted the forms of N excreted in the urine by increasing urea and decreasing ammonia, but total N from urea, ammonia and allantoin was the same for both groups. Water intake at 1.5 times feed intake as compared with 3 times feed intake increased PUN but did not affect ADG, feeding efficiency or plasma urea-cycle AA concentrations. A 2[superscript]3 factorial experiment with sex, CP at 13 or 15% and K added at 0 or.4% of diets resulted in greater PUN for barrows than gilts, for the pigs fed 15% CP and for those fed added K. A 2 x 2 x 3 factorial experiment with sex, ME at 3.33 or 3.55 Mcal/kg and CP at 13, 15 or 17% of diets resulted in a tendency for PUN to be greater in barrows than gilts, and a linear increase in PUN but linear decrease in total nonessential AA with increasing CP levels. In the two factorial experiments, barrows and gilts had similar AA; the sex difference in PUN suggested that gilts were more efficient in use of dietary N than barrows. The data also support the idea that more plasma essential AA were used for weight gain with increasing CP levels at high energy than at low energy intake. The curvilinear decline of PUN with energy intakes indicates that as lean tissue growth approached a plateau, further increases in ME intake resulted in relative more fat than protein deposition. The nine AA that differed between breed combinations have active AA transport systems that are Na[superscript]+ dependent, suggesting a breed difference in availability of energy for AA transport. This research demonstrates that, to effectively use PUN and plasma AA as indicators of rates of N deposition, it is necessary to control certain environmental variables. (Abstract shortened by UMI.)</p>