Influences of dietary-reduced nitrogen (N) and phosphorus (P) on chemical body composition, N and P retention and health traits of contemporary barrows.

Farmgate balances are used as a tool for monitoring nutrient surpluses at farm level. In Germany, preparation of farmgate balances is legally mandatory and also requires data on chemical body composition, especially concentration of nitrogen (N) and phosphorus (P), of farm animals. It is well known that increased N and P efficiency results in lowered N and P excretions with the manure and therefore mitigates negative consequences of high N and P release into the environment (e.g. eutrophication of surface waters), especially in areas with high livestock density. In this context, feeding N- and P-reduced diets can be a strategy for increasing N and P efficiency in fattening pigs. To investigate the influence of N- and P-reduced diets on chemical body composition of barrows and to update current used data basis, 8 barrows were slaughtered after a balance trial and their bodies were subjected to full body analysis. During the balance trial, pigs received the control diet (CON) meeting common nutrient requirements or the N- and P-reduced diet (NPred) in a three-phased feeding regimen (n = 4/diet, 3 weeks/phase). Pigs were slaughtered with an average live weight (LW) of 123.3 ± 7.5 kg and carcasses were manually dissected in four fractions. Fractions were analysed for nutrient concentration. Furthermore, organs were weighed individually and blood serum was sampled during exsanguination. Serum samples were analysed for clinical-chemical traits. Chemical body composition did not significantly differ between NPred- and CON-fed pigs. N concentration was 23.3 ± 0.3 and 24.5 ± 1.0 g/kg, P concentration was 5.2 ± 0.1 and 5.5 ± 0.4 g/kg in the empty body of NPred- and CON-fed pigs (p = 0.073, 0.164). N and P retention between the experiment's start and slaughter did not differ between the feeding groups (p = 0.641, 0.240). Variables related to liver integrity, energy metabolism and electrolytes were similar between CON- and NPred-fed pigs. Traits related to protein metabolism showed significantly reduced concentrations of urea and albumin in NPred-fed pigs (p = 0.013, 0.025), but no hypoalbuminaemia. Results suggest that N- and P-reduced feeding does not significantly affect chemical body composition of contemporary barrows.

Effects of dietary-reduced nitrogen (N) and phosphorus (P) on N and P balance, retention and nutrient digestibility of contemporary fattening pigs fed ad libitum.

The reduction of nitrogen (N) and phosphorus (P) in fattening pigs' diets is one possible approach to lower N and P excretion in livestock farming relative to N and P intake. Due to the implementation of the European Nitrates Directive and the consecutive amendments to the German fertiliser legislation since 2017, N- and P-reduced diets for fattening pigs are becoming more and more important and are increasingly used in practice. To investigate the effects of such diets on N and P balance and retention as well as on nutrient digestibility of contemporary fattening pigs, a balance experiment was performed with eight barrows (average live weight = 61.5 ± 2.1 kg) which were surgically fitted with a simple T-cannula at the terminal ileum. The pigs received a control diet meeting nutrient requirements (CON) and an N- and P-reduced diet (NPred) ad libitum (n = 4/diet) in a 3-phased feeding regimen (3 weeks/phase). In the last week of each phase, faeces and urine were collected quantitatively for 5 days followed by a 2 × 12 hours collection of ileal digesta. Daily feed intake, live weight gain and feed-to-gain ratio did not differ between CON and NPred. NPred-fed pigs consumed 10.5% (p = 0.006) and excreted 28.3% (p = 0.028) less N than CON-fed pigs. Phosphorus excretion was lowered by 15.1% in NPred-fed pigs (p = 0.012). N and P retention did not differ between CON and NPred, but were elevated in comparison to other studies. N and P efficiency, expressed as nutrient retention divided by nutrient intake, was higher in NPred - than CON-fed pigs (N: 68 vs 60%, P: 54.2 vs 49.3%). Apparent post-ileal digestibility coefficient (DCpost-ileal) and apparent total tract digestibility coefficient (DCtotal) of crude protein were higher in NPred - than CON-fed pigs (p < 0.013), but apparent precaecal digestibility coefficient (DCpc) of crude protein was unaffected by diet. DCpc, DCpost-ileal and DCtotal of P were similar for CON- and NPred-fed pigs. NPred-fed pigs showed an elevated DCpc and DCtotal of organic matter, N-free-extractives and starch compared to CON-fed pigs. DCpc of calcium was also higher in NPred-fed pigs. In conclusion, the results suggest that N- and P-reduced feeding of fattening pigs remains an effective strategy to lower the N and P release into the environment. Furthermore, results indicate that N- and P-reduced feeding leads to a higher N and P efficiency in contemporary fattening pigs.