Effects of Protein Supply on Growth Performance, Body Composition and Tissue Deposition for Piglets Fed Diets With or Without Antibiotics
Authors: Hou Lei , Wang Li , Zhu Cui , Wen Xiaolu , Xiao Hao , Wu Qiwen , Lin Zeling , Wang Zhikang , Qiu Yueqin , Yang Xuefen , Gao Kaiguo , Jiang Zongyong 
Published: August 2020

Abstract
Background: With increasing concerns about antibiotic-resistant bacteria that pose a threat to human and animal health, in-feed antibiotics have been banned since 2006 in Europe and 2020 in China. However, previous studies on crude protein (CP) and amino acids (AA) requirements of pigs were mostly based on the diets with antibiotics. The objective of this study was to evaluate the effects of CP supply on growth performance, body composition and tissue deposition for piglets fed diets with or without antibiotics. Methods: A total of 250 newly weaned piglets were randomly assigned to 1 of 10 dietary treatments (5 replicate pens per treatment with 5 animals per pen) in a 5 × 2 factorial arrangement with 5 CP levels (16, 18, 20, 22, 24 %) and 2 antibiotic supplementations (with or without antibiotics). Treatment diets were fed for 14 d to test treatment effects, and then a nursery diet (19% CP) without antibiotics was fed to all piglets until they had an average body weight of 25 kg to determine if carryover effects of treatment diets existed. An additional 5 piglets at the start were slaughtered to determine initial body composition. At the end of each period, 1 pig close to the average BW of each pen was slaughtered to determine body composition and tissue deposition.Results: Increasing dietary CP level linearly improved (P < 0.05) average daily gain (ADG), average daily feed intake (ADFI), and gain:feed (G:F) during the treatment period, while antibiotics tended to improve ADG of piglets (P < 0.10). The ADG during the carryover period tended to be improved (P < 0.10) with the increase of dietary CP level, but there was no difference in ADG during the entire nursery period (P > 0.10). Neither CP level nor antibiotic supplementation affected (P > 0.10) the incidence of diarrhea in each period. With the increase of dietary CP level, weights of fasted body, empty body, eviscerated carcass, and organs at d 14 were linearly improved (P < 0.05). Neither CP level nor antibiotic supplementation had a significant effect on the physical body composition of pigs at the end of the nursery period (P > 0.05). Body protein content at d 14 linearly improved (P < 0.05) with increasing CP level, whereas body ash content, lipid:protein and ash:protein ratio linearly decreased (P < 0.05). Increasing dietary CP level resulted in a greater (P < 0.05) deposition rates of body water and protein during the treatment period, while antibiotics tended to increase (P < 0.10). There was no effect (P > 0.05) of CP level or antibiotic supplementation on the chemical body composition at the end of the nursery period. However, increasing CP level quadratically improved (P < 0.05) deposition rates of body water, protein and lipid during the carryover period as well as deposition rates of protein, lipid and ash during the entire nursery period. According to the model with the minimum AIC, the CP requirement based on ADG was 23.01 and 22.65%, and based on protein deposition (PD) was 24.00 and 23.29% for antibiotic-free diet and antibiotic diet, respectively. Conclusions: Increasing dietary CP level increased the growth performance and protein deposition of piglets during either the treatment period or the carryover period. The CP requirement for piglets with high health status fed antibiotic-free diet was slightly higher than those fed antibiotic diet.