تأثیر مرحله فنولوژیکی بر ترکیب شیمیایی، قابلیت هضم و ویژگی‌های تخمیری گیاه سلمه‌تره (Chenopodium Album L.) در شرایط آزمایشگاهی

Introduction
Rangelands are among the most fundamental resources for livestock feed in animal production systems and play a crucial role in sustaining livestock production, reducing feeding costs, and conserving natural resources. The quality and quantity of rangeland forages directly affect feed intake, digestibility, nutrient balance, and ultimately the productive performance of ruminant animals. Rangeland plants exhibit considerable variation in chemical composition, cellular structure, and ruminal fermentability, which are influenced by plant species, climatic conditions, rangeland management practices, and, in particular, phenological stage. As plants mature, substantial changes occur in their chemical composition, characterized by increases in cell wall components and lignin content, and reductions in soluble constituents such as crude protein and fermentable carbohydrates. These changes are generally associated with decreased digestibility, metabolizable energy content, and microbial protein synthesis efficiency. Therefore, determining the optimal harvesting or grazing time is essential to maximize the nutritional value of rangeland forages. Common lambsquarters (Chenopodium album L.) is an annual plant widely distributed in rangelands and agricultural fields of northern Iran. Due to its rapid growth, high biomass production, and relatively good tolerance to environmental stresses, this species is naturally abundant in many regions. In addition to its traditional use as human food in some regions, common lambsquarters contains substantial amounts of crude protein, minerals, and bioactive compounds, indicating its potential as a forage resource for ruminants. However, information on changes in nutritional value, digestibility, and ruminal fermentation characteristics of this plant across growth stages is limited, and most previous studies have focused primarily on its chemical composition. Therefore, a comprehensive evaluation integrating chemical composition, digestibility, fermentation characteristics, and gas production is required to understand the feeding value of this plant better. Furthermore, comparison of common lambsquarters with conventional feedstuffs such as alfalfa hay and wheat straw can provide practical insights into its potential use in ruminant diets. Accordingly, the objective of this study was to investigate the effects of phenological stage on chemical composition, digestibility, and in vitro gas production parameters of common lambsquarters and to compare its nutritional value with alfalfa hay and wheat straw under laboratory conditions.
Method
This study was conducted in the spring of 2023 at the Animal Nutrition Laboratory, Faculty of Agriculture, Gonbad Kavous University. Samples of common lambsquarters were collected at three phenological stages, including vegetative, flowering, and seed-setting stages, from farms located in Bandar Gaz County, Golestan Province, Iran. After transport to the laboratory, the samples were initially wilted in the open air and subsequently oven-dried with alfalfa hay (second cut, harvested at the early-flowering stage) and wheat straw. All samples were then ground using a suitable mill and sieve to obtain homogeneous material for laboratory analyses. The experimental treatments consisted of five feeds: wheat straw, common Lamb’s quarters at the vegetative stage, common Lamb’s quarters at the flowering stage, common Lamb’s quarters at the seed-setting stage, and alfalfa hay. Chemical composition analyses, including dry matter, crude protein, and ash, were performed according to standard procedures. Neutral detergent fiber (NDF) and acid detergent fiber (ADF) contents were determined using the Van Soest method. Net energy values, total digestible nutrients, and metabolizable energy were calculated using reference equations. To evaluate fermentation characteristics, in vitro gas production was measured using a pressure transducer system. Rumen fluid was collected from rumen-fistulated male sheep, filtered, and mixed with artificial saliva. Gas volume was recorded at incubation times of 2 to 96 hours, and gas production parameters, including potential gas production and gas production rate, were estimated using a nonlinear model. Dry matter digestibility and organic matter digestibility were determined using the closed culture technique. Microbial indices, including the partitioning factor, microbial biomass, and the efficiency of microbial biomass production, were calculated. Statistical analysis was performed using the GLM procedure, and mean comparisons were conducted using Duncan’s multiple range test at a significance level of 5%.
 Results
The results indicated that phenological stage significantly affected the chemical composition and nutritional value of common lambsquarters. The highest contents of crude protein, ash, total digestible nutrients, and metabolizable energy were observed in the vegetative stage. As plant maturity advanced toward flowering and seed-setting stages, crude protein content decreased, while NDF and ADF concentrations increased, reflecting the accumulation of structural components in the plant cell wall. Compared with wheat straw, common lambsquarters exhibited higher nutritional value at all growth stages, and at the vegetative stage, it even surpassed alfalfa hay in some nutritional parameters. In vitro gas production results showed that alfalfa hay had the highest potential gas production, whereas common lambsquarters at the seed-setting stage produced the lowest amount of gas. However, the rate of gas production was higher in common lambsquarters at the vegetative stage, indicating more rapid fermentation of soluble components. Dry matter and organic matter digestibility were highest in alfalfa hay and lowest in wheat straw. In common lambsquarters, although digestibility generally declined with advancing maturity, a relative improvement in some digestibility indices and microbial parameters was observed at the seed-setting stage due to the presence of seeds and softer plant tissues. Increased microbial biomass and partitioning factor at this stage suggested more efficient utilization of fermentable organic matter by rumen microorganisms.
 Conclusions
Overall, the findings showed that the nutritional quality of Chenopodium album declines with advancing phenological stage. Crude protein, metabolizable energy, digestible organic matter, and volatile fatty acids decrease during plant maturation, while NDF, ADF, and lignin contents increase. The vegetative stage exhibited the highest nutritional quality, as assessed by chemical composition, digestibility, and gas production. Therefore, harvesting Chenopodium album at the vegetative stage can provide higher nutritional value for ruminants and may serve as a suitable supplementary forage source in their diets.