The aim of this research has been to assess the effect of the dietary protein level on piglet growth and post-weaning diarrhea (PWD) incidence. Piglet fecal microbiota and feces composition were also assessed. The experiment was carried out on 144 weaned piglets (Duroc × Large White; 72 piglets per treatment) and lasted from weaning (at 25 days of age) until the end of the post-weaning phase (at 95 days). Two dietary protein levels were compared: high (HP; 17.5% crude protein on average, during the experiment) and low (LP; 15.5% on average). Lower (p < 0.01) average daily gain and feed conversion ratio were observed in LP piglets in the first growth phase. However, at the end of the post-weaning period, the growth parameters were not significantly different in the two diets. Diarrhea scores were lower in piglets fed LP diets than in piglets fed HP diets (28.6% of the total vs. 71.4% in the HP piglets). Fibrobacteres, Proteobacteria, and Spirochaetes were more abundant in the feces of the piglets fed LP diets. Feces nitrogen content was lower in piglets fed LP diets. In conclusion, low protein levels in the diet can reduce the incidence of PWD while only marginally affecting growth parameters.

The trial explored innovative low-protein diets for weaning piglets, testing the elimination of fish meal and blood derivatives. The trial compared three treatments, each with two post-weaning feeds: control feed with blood plasma and fishmeal; T1: low-protein feed with seven amino acids, fishmeal, and blood plasma; T2: low-protein feed with seven amino acids without fishmeal and blood plasma. The trial tested 180 weaned piglets, 24 days of age, evenly distributed by weight, age, and litter of origin. At the end of the first phase, T1 and T2 recorded a significantly higher average weight, ADG, and FCR compared with the control feed. At the end of the second phase, the T2 group maintained a significantly better weight, ADG, and FCR than the control group. Considering the entire test period (phase 1 and phase 2), the T2 thesis appears to have a significantly higher average weight, ADG, with a lower FCR compared to the control group. The T2 thesis fixed a significantly (p < 0.01) greater quantity of nitrogen compared to the T1 thesis and control feed (T2 58.71% vs. T1 54.13% and control 54.02%). In conclusion, a low-protein diet without raw materials of animal origin proved more efficient in terms of performance and nitrogen retention.

Italian pigs for slaughter weigh between 150 and 170 kg, and their breeding is strictly regulated by the Protected Designation of Origin. Intensive production raises environmental concerns, in particular, nitrogen (N) emissions. To address these issues, low-crude-protein diet strategies have been proposed. However, few experiments have tested the effects of very low crude protein levels on performance and nitrogen efficiency, above all, in heavy pigs. The aim of our study was to explore new feeding solutions, compared to traditional ones, in accordance with PDO regulations, from 50 kg live weight to slaughtering: (1) traditional diet based on soy and maize; (2) iso-protein diet protein that is pea-based; and (3) low-crude-protein (−24.5% vs. C and T1 diets) diet that is cereal-based. Our results show that the use of different protein sources and the very low crude protein levels did not influence the technical efficiency and quality parameters; instead, a highly significant difference (p < 0.01) was recorded in the nitrogen efficiency of the cereal-based diet both in terms of nitrogen excretion and efficiency, achieving −28% and +21%, respectively. These results open up very interesting scenarios regarding the future feeding of heavy pigs and the cropping systems on which this is based.