Effect of high oxalic acid intake on growth performance and digestion, blood parameters, rumen fermentation and microbial community in sheep

Oxalic acid, a crucial secondary metabolite prevalent in most plants, often constitutes an unavoidable component of the diet for grazing animals, particularly in saline-alkaline grasslands. This research focused on examining the effects of elevated oxalic acid consumption on various aspects of sheep health and metabolism, including growth performance, nutrient digestibility, blood biochemical indices, rumen fermentation, and microbial populations. Employing a single-factor experimental model, 24 six-month-old German Merino sheep (with an average body weight of 32.08 ± 3.43 kg) were systematically segregated into three distinct groups. Each group contained eight replicates, with each replicate comprising a single sheep. The diet of the experimental groups was enhanced with oxalic acid concentrations of 1 % (T1) and 2 % (T2), whereas the control group received no oxalic acid addition. Under ad libitum feeding, the duration of the experimental phase spanned a total of 60 days. Outcomes demonstrated that a 2 % oxalic acid augmentation notably diminished the sheep's daily weight gain (ADG) (P<0.05), elevated the feed conversion ratio (FCR) (P<0.05), and reduced the ruminal pH levels (P<0.05), compared to both control group and 1 % oxalic acid group. This pH reduction markedly curtailed the synthesis of essential ruminal constituents such as acetic acid, propionic acid, and butyric acid (P<0.05). Furthermore, there was a notable decline in serum alkaline phosphatase (ALP) levels, alongside rises in both blood urea nitrogen (BUN) and serum creatinine (CREA)(P<0.05), coupled with a significant reduction in serum calcium concentrations (P<0.05) in 2 % oxalic acid group, compared to both control group and 1 % oxalic acid group. Moreover, the 2 % oxalic acid addition adversely impacted the digestibility of neutral detergent fibre (NDF) and acid detergent fibre (ADF), as well as the concentration of NH₃-N in the rumen fluid (P<0.05), compared to both control group and 1 % oxalic acid group. Pertaining to rumen microorganisms, there was a significant escalation in the relative abundance of Proteobacteria at the phylum level, contrasted by a substantial reduction in the presence of Fibrobacteres (P<0.05). At the genus level, an increased concentration of oxalic acid in the diet correlated with a pronounced decline in the relative abundance of Prevotella_1, and a substantial decrease was observed in the relative abundance of Ruminococcaceae_UCG-014 (P<0.05). In summary, while sheep can acclimate to an inclusion of 1 % oxalic acid in their diet, an augmentation of 2 % oxalic acid appears detrimental, impinging upon growth performance, fiber and crude protein (CP) digestibility, blood calcium levels, rumen pH, volatile acid content, and the microbial ecosystem within the sheep’s rumen.