بررسی اثر مصرف بافر پوشش‌دار بر قابلیت هضم خوراک وفراسنجه‌های سلامت انتهای دستگاه گوارش در اسب‌های بالغ مصرف کننده کنسانتره زیاد

Abstract
This experiment aimed to Investigating the effect of using coated buffer compared to raw buffer in horses consuming high levels of concentrate.Nutrient digestibility, blood parameters, fecal pH and volatile fatty acids concentration in horses were measured. This study was conducted on 18 adult horses divided into three groups with six repetitions. Each group was allocated to an experimental treatment in the form of a completely randomized modified design. The experimental period lasted 28 days (seven days adaptation period and 21 days sampling). The rutin daily diet of the stable club, with increased levels of non-structural carbohydrates, was selected as the basal diet, and the treatments included: 1- Basal diet (control), 2- Basal diet with 100 grams of raw buffer, 3- Basal diet with 240 grams of coated buffer. Samples of feed, blood, and feces were collected for analysis of the desired parameters during the sampling period and then sent to the laboratory for chemical analysis and digestibility calculation. According to the results, it was found that the use of coated buffer has a significant effect (P < 0.05) on protein digestibility, digestibility of neutral detergent fiber (NDF), fecal pH, blood urea nitrogen concentration, and total concentration of volatile fatty acids (VDAs). However, the amount of dry matter intake was not affected by the use of experimental treatments. Finally, based on the results of this experiment, it was revealed that the use of coated buffer can prevent the occurrence of hindgut acidosis, resulting in a reduction in the occurrence of other abnormalities such as lameness, which is considered the main factor in reducing performance in sport horses.


Introduction
Horses are monogastric herbivores, meaning they do not have a multi-compartment stomach like cows, and digestion in their gastrointestinal system is unique compared to the other mammals. Their digestive system is primarily divided into two major parts: the foregut and hindgut, with the cecum and colon forming the major part of it (Rowe, 1995). The consumed feed undergoes enzymatic digestion initially and then is fermented by microorganisms residing in the hindgut. The ability of horses to digest foregut carbohydrates is lower compared to other mammals (Johnson et al., 2019). Furthermore, breed modification and genetic advancements in performance horses have increased their daily energy and nutritional requirements. The consumption of forage alone cannot meet the needs of these horses, necessitating the addition of energy sources to increase the feed concentration. Grains are considered major energy sources, and excessive grain consumption with improper management can lead to various abnormalities (Figure 1) (Seabra, 2021; Hanis, 2023; NRC, 2007; Shirazi-Beechey, 2008).
Multiple solutions have been proposed for the management of grain consumption and control of hindgut acidosis in horses, including increasing access to feed, increasing the number of meals, enhancing access to forage, consuming high levels of buffer, prebiotic addition, and adding various commercial enzymes to the diet. In this study, the effect of coated buffer consumption on digestibility, blood metabolites, fecal pH and lactic acid concentration in horses consuming high levels of starch (at least two grams of starch per kilogram of body weight per feeding) was investigated (Salem et al., 2015; D. Józefiak et al., 2020).

Materials and Method
This research was conducted at an equestrian club located in the west of Tehran. Eighteen adult horses (weighing between 482 and 573 kilograms) were divided into 3 groups with 6 repetitions and were fed with 3 experimental treatments. The experimental period lasted 28 days (including a 7 days adaptation period and 21 days of sampling). The club’s common daily diet was selected as the basal feed, and the treatments included: 1- Basal feed (devoid of additional buffer), 2- Basal feed + raw buffer, 3- Basal feed + coated buffer (Table 1). Individual nutrition and daily feed intake were recorded. The buffer formulation in both treatments was prepared as a 2:1 ratio of sodium bicarbonate to sodium carbonate.


Resulrs and Discution
The dry matter intake and nutrient digestibility were measured (Table 3). The experimental treatments did not have a significant effect on the amount of feed intake. The digestibility of dry matter and NSC did not show significant differences among horses consuming different experimental treatments. However, NDF digestibility was significantly higher in animals that consumed added buffer compared to the control treatment. Additionally, the protein digestibility in control group was significantly lower. According to various sources, the lower level of protein digestibility might be due to an increase in fermentation in the hindgut with the consumption of easily fermentable carbohydrates by bacteria and an increase in the percentage of microbial protein in feces (Abeyta et al., 2023).
The fecal pH level in the control group was significantly lower compared to the group consuming coated buffer, but there was no significant difference between the control group and the group consuming raw buffer. It has also been confirmed in various studies that fecal pH is influenced by the amount of non-structural carbohydrates (from 2.2 to 4.3 grams per kilogram of body weight) (Medina B. et al., 2002; de Fombelle et al., 2001). Furthermore, an increase in the consumption of NSC (primarily starch) leads to an increase in the population of anaerobic bacteria and lactic acid consumers in the cecum and large intestine, while the population of cellulolytic bacteria in the cecum decreases. This could confirm the observed result regarding the decrease in the percentage of NDF digestibility (Table 3) (Chaucheyras-Durand, F. et al., 2022).
The results regarding the concentration of blood metabolites are presented in Table 4. The levels of glucose, urea nitrogen, phosphorus, calcium, and lactic acid in the plasma of different animals were statistically similar. Similar studies have also indicated that the concentration of urea nitrogen is affected by the amount of daily protein intake in horses (Muhonen, S. 2008). Nevertheless, the total blood protein level in the group that consumed coated buffer was significantly higher, which may be attributed to the higher protein digestibility in this group.