Protein Content in the Diet Influences Growth and Diarrhea in Weaning Piglets

SIMPLE SUMMARY: Weaning (that is, removal from the sow) and the following two months are the riskiest periods in a pig’s life, especially for pig’s gastrointestinal health. The change in diet due to the suspension of the mother’s milk, accompanied by an acceleration of both morphological and enzymatic maturation of the intestinal mucosa of the piglets, can worsen digestion and absorption. In this context, the protein requirement of piglets, which are in a phase of rapid growth, may be greater than the intestine’s ability to digest proteins. Undigested proteins are the best pabulum for the proliferation of the pathogenic bacterial flora that causes diarrhea. Since these problems can no longer be resolved with prophylactic use of antibiotics, the best balance between intestinal health and growth performance must be found. A diet low in crude protein and supplemented with synthetic amino acids can help achieve this goal. ABSTRACT: 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.