Nitrogen and lysine utilization efficiencies, protein turnover, and blood urea concentrations in crossbred grower pigs at marginal dietary lysine concentration

Abstract

Nitrogen utilization efficiency (NUE) and lysine utilization efficiency (LUE) are key indicators of sustainable pork production and vary depending on nutritional and non-nutritional factors. The objective was to study NUE and LUE together with concentrations of blood urea nitrogen (BUN) and other metabolites in growing pigs fed diets with marginal Lys concentrations at 11–13 weeks (40.5 kg mean BW) and 14–16 weeks (60.2 kg mean BW). The cereal grain-soybean meal-based diets contained 10.6 and 7.9 g Lys/kg DM in periods 1 and 2, respectively. Feed intake and BW were measured for 508 individually penned pigs, and blood samples were collected 5 h after morning feeding at weeks 13 and 16. A subgroup of 48 barrows was used in a nitrogen (N) metabolism trial at weeks 13 and 16. In this subgroup, the mean N retention of pigs (27.3 g N/d) and mean LUE (70%) were not different between the periods, but NUE was higher in Period 1 (47%) than in Period 2 (43%) (P < 0.001). After administration of a single dose of 15N labeled glycine and measurement of 15N recovery in urine, the calculated whole-body protein turnover did not differ between the periods. The rate of protein synthesis was positively correlated with NUE (P < 0.001), but protein degradation was not. Excretion of urea-N in urine accounted for 80% of the total urinary N and was positively correlated with BUN. The N retention of all 508 pigs was estimated using an equation that was derived from the N metabolism data. N retention was on average 31.4 g/d, equal in both periods, and higher in barrows than in gilts in Period 2, but not in Period 1 (P = 0.003). The calculated NUE was, on average, 47% and was lower in barrows than in gilts (P < 0.001) and higher in Period 1 than in Period 2 (P < 0.001). The calculated LUE was, on average, 71%, and was lower in barrows than in gilts in Period 2, but not in Period 1 (P < 0.001). The BUN concentration was higher in barrows than in gilts (P < 0.001) and higher in Period 1 than in Period 2 (P < 0.001). BUN concentration was negatively correlated with NUE in Periods 1 (r = -0.50) and 2 (r = -0.15) (P < 0.05). We concluded that the maximum LUE was in the range of 70–72% under the conditions of this study, and only small differences between the periods and sexes existed. Protein synthesis, rather than degradation, appears to affect NUE. BUN concentration may be useful for estimating NUE in a large group of animals fed a diet with a marginal Lys concentration.

Microbial signatures and enterotype clusters in fattening pigs: implications for nitrogen utilization efficiency

“…In total 508 crossbreed pigs (German Landrace×Piétrain) with defined family structures were kept under standardized conditions and investigated into 21 cohorts. A detailed description of the experimental design and procedures is given in Berghaus et al (2023) . Briefly, at the 11th week of life, cohorts were moved into the experimental barn for individual housing.…”

“…At the end of the experiment, the BW was 96.0 ± 9.5 kg. A subgroup of pigs ( n = 48) were randomly selected throughout the experimental period for N balance measurement in combination with stable isotope tracer technique as described in detail in Berghaus et al (2023) .…”

“…On all days of the respective SP, fecal samples were collected from each pig to measure total N and dry matter (DM; Berghaus et al, 2023 ). Blood samples were collected to determine the BUN level, serum cortisol (Cor), and serum insulin-like growth factor 1 (IGF-1).…”

“…For the pigs subjected to balance measurement, daily urinary N excretion and daily fecal N excretion were determined in addition to DNI. These values and blood metabolite concentrations were used to estimate daily nitrogen retention (DNR) for all pigs by multiple regressions and further calculate NUE ( Berghaus et al, 2023 ). Those pigs ( n = 446) whose fecal samples in both SPs passed the bioinformatic quality control described below, were divided into two groups (low and high) within each SP based on their NUE.…”

“…Blood urea nitrogen (BUN) can be used to predict urinary N excretion in pigs of comparable production stages within a study ( Kohn et al, 2005 ), and a negative correlation between BUN and NUE in growing pigs is described ( Tran-Thu, 1975 ; Berschauer, 1977 ; Whang et al, 2003 ; Schmid et al, 2024 ). BUN concentration appears to be a useful auxiliary feature for determining the NUE, in groups with large numbers of animals that have a limited lysine supply ( Berghaus et al, 2023 ).…”