تأثیر پروتئین هیدرولیز شده کنجاله پنبه‌دانه بر عملکرد و پاسخ‌های فیزیولوژیکی جوجه‌های گوشتی در جیره‌های کم‌پروتئین

Introduction: Cottonseed meal (CSM), a readily available byproduct of the cotton oil industry, presents a promising candidate with a substantial protein content ranging from 30% to 50%. However, its incorporation into poultry diets at high inclusion levels has been historically constrained by the presence of antinutritional factors (ANFs), primarily gossypol, which can adversely affect animal health and performance. To overcome this limitation, various processing techniques have been developed to degrade these ANFs and enhance the nutritional value of plant protein sources. Among these, enzymatic hydrolysis has gained significant attention for its ability to break down proteins into smaller peptides and free amino acids. This process not only improves protein digestibility but also generates bioactive peptides (BPs) that possess "extra-nutritional effects," including potent antioxidative, antimicrobial, and immunomodulatory properties. While the application of bioactive peptides from sources like soybean and canola meal has been relatively well-documented in broiler nutrition, research on the potential of cottonseed meal bioactive peptides (CSBP) remains scarce. Furthermore, there is a growing interest in formulating low-protein (LP) diets for broilers to reduce nitrogen excretion, improve litter quality, and mitigate environmental pollution. However, such diets often lead to compromised growth performance due to amino acid deficiencies. Therefore, identifying nutritional strategies that can sustain broiler performance under reduced protein conditions is of paramount importance.
Materials and methods: The experiment employed a completely randomized design with a 3x3 factorial arrangement of treatments. Six hundred and forty-eight one-day-old Ross 308 broiler chickens were randomly allocated to nine experimental groups, each with six replicates of twelve birds. The factors consisted of three dietary crude protein levels (standard, 7.5% reduction, and 15% reduction from the Ross 308 recommendations) and three levels of CSBP supplementation (0, 15, and 20 g/kg of diet). All diets were formulated to be isocaloric and to meet or exceed the essential amino acid requirements for the starter (1-15 days) and grower (16-35 days) phases. The hydrolyzed cottonseed meal was produced using a modified enzymatic method involving a cocktail of five food-grade enzymes (Alcalase, chymotrypsin, pepsin, trypsin, and pancreatin). Performance traits (body weight, weight gain, feed intake, feed conversion ratio-FCR, and mortality) were recorded throughout the study. At 35 days of age, blood samples were collected to analyze serum uric acid, creatinine, nitric oxide (NO), total antioxidant capacity (TAC), plasma protein fractions (albumin, globulins), and liver enzymes (ALP, ALT, AST, CK). Carcass traits and relative weights of internal organs were also determined. Intestinal morphology, including villus height, crypt depth, villus width, and goblet cell count in the duodenum and jejunum, was assessed at 15 days of age. Data were subjected to statistical analysis using a two-way ANOVA procedure in SAS, with mean separation conducted by Tukey's HSD test.
Results and discussion: The results unequivocally demonstrated that reducing dietary protein by 7.5% and 15% linearly and significantly decreased body weight, weight gain, and feed intake, while increasing FCR. These LP diets also led to elevated serum uric acid levels, indicating potential inefficiency in nitrogen utilization, and significantly increased the concentrations of liver enzymes (ALT, AST, CK, ALP), suggesting heightened metabolic stress and possible hepatocellular and muscle tissue damage. Furthermore, LP diets negatively impacted carcass characteristics, resulting in lower carcass yield and higher abdominal fat deposition, and induced adverse changes in intestinal morphology. Supplementation with CSBP at both 15 and 20 g/kg levels effectively mitigated these detrimental effects. CSBP significantly improved body weight and FCR in birds fed LP diets. It enhanced the antioxidant status, as evidenced by increased serum TAC and NO levels. CSBP supplementation also significantly increased plasma albumin concentration and positively influenced beta globulin levels, indicating improved protein metabolism and potential immune modulation. A notable reduction in the serum activity of liver enzymes (ALT, AST, CK, ALP) was observed with CSBP, pointing towards reduced metabolic load and improved liver health. Carcass analysis revealed that CSBP increased dressing percentage and reduced abdominal fat. Morphologically, CSBP supplementation improved jejunal architecture by increasing villus width and the villus height-to-crypt depth ratio, while decreasing crypt depth and goblet cell numbers, which is indicative of enhanced digestive and absorptive capacity. The most pronounced benefits were often observed at the 20 g/kg supplementation level, particularly when combined with the standard protein diet.
The significant improvements in body weight, feed conversion ratio, and key blood parameters such as albumin and nitric oxide underscore CSBP's role in enhancing protein utilization and metabolic homeostasis. The reduction in liver enzyme concentrations and the positive morphological changes in the jejunum further indicate that CSBP alleviates metabolic stress and promotes intestinal health, likely through the action of its bioactive peptides. These results align with previous research on hydrolyzed protein sources but uniquely highlight the efficacy of cottonseed meal as a sustainable alternative. Future studies should focus on isolating the specific bioactive peptides responsible for these benefits and evaluating their effects under commercial-scale farming conditions to facilitate widespread adoption.
Conclusions: This study provides compelling evidence that reducing dietary crude protein levels adversely affects broiler growth, metabolic health, and carcass quality. However, the supplementation of diets with cottonseed protein hydrolysates (CSBP) effectively counteracts these negative impacts. CSBP enhances growth performance, improves nutrient utilization, boosts antioxidant capacity, supports liver function, and promotes intestinal health. These benefits are attributed to the improved digestibility of hydrolyzed protein, the bioactive properties of the constituent peptides, and the resultant reduction in metabolic stress. Consequently, CSBP emerges as a highly valuable functional feed ingredient that can facilitate the use of more sustainable low-protein diets in broiler production without compromising performance or animal well-being, thereby contributing to the reduction of the environmental footprint of poultry operations.