The effect of conocarpus processed with tannase-producing bacteria on feeding behavior, nutrient digestibility, blood metabolites and rumen fermentation parameters in Arabi lamb

Conocarpus is an ornamental plant common in tropical and subtropical regions that is usually seen as a shrub with a height of 1.5 to 4 meters. Due to resistance and adaptation to hot and dry environment, poor drainage, air pollution and dense soils, its cultivation has increased in the last decade in the country and especially in Khuzestan (Mohammadabadi 2020). Al-Koaik et al (2014) reported the amount of crude protein and fiber of conocarpus leaves were 96.6 and 134.7 g/kg, respectively. Also, Direkvandi et al (2020) reported the amount of crude protein, NDF and ADF of conocarpus silage were 114, 473 and 371 g/kg DM, respectively, which can be used as feed with suitable nutrients in animal feeding. However, one of the things that should be considered about conocarpus as animal feed is the presence of secondary compounds such as phenolic compounds (tannins) (Mohammadabadi 2020). Treatment with microbial additives has been suggested to reduce tannins (Konda et al. 2007). These microbes contain the tannin acyl-hydrolase (tannase) enzyme, which hydrolyze tannin to gallic acid and glucose (Jafari-Tapeh et al 2012)

In this experiment, 16 Arabi lambs (average body weight, 25 ± 3 kg) were used in a completely randomized design with 4 treatments and 4 replicates. The experimental period was 60 days (10 days adaptation and 50 days trial period). Four treatments were included; (1) Control group (without conocarpus); (2) BA6, diet containing conocarpus treated with bacterium A6; (3) BA8; diet containing conocarpus treated with bacterium A8; (4) WB, diet containing untreated conocarpus. During the experimental period, the complete mixed ration (based on 50% forage and 50% concentrate) was provided for each lamb twice daily at 8:00 am and 16:00 pm (allowed 5% of orts) (NRC, 2007). Lambs had free access to fresh water and salt licks. At the end of the experiment, feed intake (daily basis), feeding behavior (in a 24-hour period), nutrient digestibility (sampling on days 45 to 50 according to Givens et al 2000) and rumen fermentation parameters (pH, ammonia-N, volatile fatty acids and protozoa population; sampling on day 50 of the experiment at 0, 3 and 6 hours after morning feeding), were evaluated. Also, blood sample (approximately 10 mL) was collected from jugular veins using tubes containing an anticoagulant (heparin) on day 50 of the experiment at 0, 3 and 6 hours after morning feeding. Glucose, triglycerides, blood urea nitrogen (BUN), cholesterol, low-density lipoprotein (LDL), high-density lipoproteins (HDL), alkaline phosphatase (ALP), aspartate aminotransferase (AST) and alanine transaminase (ALT) were determined by using enzymatic methods and spectrophotometer.

Results showed that the amount of feed intake decreased by experimental treatments (P <0.05) and in all cases the lowest amount of feed intake was observed in WB treatment (P <0.05). Similarly, Hosseini (2018) reported that the use of conocarpus silage reduced feed intake compared to control. Reduction of feed intake in treatments containing conocarpus is probably due to less palatability of these treatments. Feeding time and the rate of chewing was significantly decreased by the experimental treatments (P <0.05). The lowest rumination rate was observed in BA8 treatment (P <0.05). In contrast, the lowest rest period was observed in control and BA6 treatments (P <0.05). The highest digestibility of organic matter was observed in BA6 treatment (P <0.05). The lowest digestibility of NDF and ADF was observed in WB treatment (P <0.05). Digestibility of NDF and ADF showed no significant difference between BA6, BA8 and control (P <0.05). According to our results, Mohammadabadi et al (2021) also reported an increase in digestibility of cell wall as a result of treated with tannin-degrading bacteria. The highest and lowest pH values were observed in control and WB treatments, respectively (P <0.05). The concentration of Ammonia-N and protozoa population were significantly decreased by experimental treatments (P <0.05). The reducing effect of conocarpus-containing treatments on ammonia-N and protozoa populations may be due to more phenolic compounds in these treatments (Yanez Ruiz et al 2004). Total concentrations of volatile fatty acids, propionate, valerate, isobutyrate and isovalerate were not affected by experimental treatments (P <0.05). The concentration of acetate significantly increased by BA6 and BA8 treatments (P <0.05). Also, the highest concentration of butyrate was observed in WB treatment (P <0.05). The increase in acetate concentration in BA6 and BA8 treatments may be due to the increased digestibility of cell wall in these treatments. Blood glucose concentration and BUN were significantly decreased by experimental treatments (P <0.05). The high concentration of propionate and glucose was observed in the control treatment. Hosseini (2018) similar to our results reported that the use of conocarpus silage and dried conocarpus had no significant effect on triglyceride, cholesterol, HDL and LDL concentrations compared to the control. The concentration of liver enzymes in this study was not significant but was numerically higher than the control, which agreed with the results of Rezaeinia et al. (2012).

The results of this study showed that due to the positive effects of the conocarpus treated with tannin-degrading bacteria than the untreated conocarpus on some measured parameter, and also due to the lack of a negative impact on animal health, it can be said that the treated of this plant to reduce tannin that is a suitable solution for the use of conocarpus in the ration of lambs.Keywords: Tannin-degrading bacteria, Feeding behavior, Blood and ruminal parameters, conocarpus, Arabi lambs