Hydroxy Selenomethionine Can Rescue Broiler Growth Performance and Meat Quality Under Heat Stress Through Enhanced Antioxidative Capacity

Poultry meat is the second-largest meat source with excellent quality of proteins and essential micronutrients for human nutrition globally (Pawar et al., 2016). However, the pursuit of increased meat yield, lean mass ratio and large breast muscle has had significant impacts on meat quality in broilers. Moreover, in modern commercial broiler rearing systems, high stocking density and various stress factors also inevitably lead to impaired growth performance and meat quality (Liu et al., 2020). As well as being a serious animal welfare issue, HS in broiler production can cause significant economic losses due to its negative impact on growth performance and health conditions (Liu et al., 2020). During HS, the high environmental temperature exposure has been shown to induce severe oxidative stress in key metabolic organs including muscle, liver, and intestine. It is well documented that post-mortem (PM) meat quality traits, such as pH, meat colour, water-holding capacity, and tenderness are closely related to the oxidation status in the muscles (Zhang et al., 2020). Enhancing the muscular anti-oxidative capacity can therefore maintain the PM meat quality by reducing oxidation of phospholipid of cell membranes and myoglobin, resulting in less drip loss and more favourable meat colour (Zhang et al., 2020). In past decades, many molecules were tested to protect poultry against HS, including minerals, plant polyphenols, and probiotics. Among these solutions, selenium (Se) has been shown to increase Se deposition and provide defence against oxidative stress in animals, especially broilers (Vieira et al., 2022). Basically, Se exerts its biological function by interacting with a large set (25) of selenoproteins, and consequently increase the activity of some anti-oxidative enzymes, including glutathione peroxidases and melanoproteins. In the present study, OH-SeMet, an organic Se resource, was used to validate its impact on meat quality and growth performance in commercial broilers under chronic HS.

A total of 600,000 broilers (ROSS 308) were allocated into two groups. All animals were reared for 42 days in a commercial broiler farm. The diets for the two group were a. Control group (CTR) fed with broiler basal feed; b. Treated group (TRT) fed with basal diet supplemented with Hydroxy selenomethionine (Selisseo 0.2%, Adisseo France SAS) 150 gram/ton of feed (0.3 ppm). The selenium supplements were added to the diet via premix, and both the CTR and TRT feeds were measured for the actual Se content (Table 1). The basal diet was supplemented with a mineralvitamin premix without selenium. The feeding trial was carried out as planned for 6 weeks from March to May 2022 in Lopburi area (central area of Thailand) to take advantage of the high temperature and high humidity environment, which is normally recorded in this region during summertime over the past few decades. Therefore, the birds used in this trial were exposed to natural HS. The barn temperature and humidity were measured by automatic temperature and humidity detector on a daily basis. Throughout the trial, the birds were exposed to at least 28.5 °C and 81.5% humidity for minimal 6 hours per day.

The final body weight, feed conversion ratio (FCR), average daily gain (ADG), performance index (PI) and mortality of broilers were measured and calculated at D42 as per the procedure in the previous report by Zhao et al. (2017).

One side of the breast muscle was collected from 10 randomly selected birds in each group. Concentration of Se in the breast was measured as previously described (Zhao et al., 2017). These samples were also used to measure meat quality parameters.

In this trial, pH, meat colour, drip loss, thawing loss and cooking loss of breast samples as key meat quality traits were measured at different time points after slaughter. The pH was measured at 1h and 24 h post-mortem (PM) using a portable pH meter (HI9025, HANNA, Co. Italy). The meat colour, drip loss, thawing loss and cooking loss were measured in triplicate for each breast samples and the results were obtained to determine an average value at different time points (Table 4).

2-thiobarbituric acid (TBA) levels were measured by the method adapted from previous report (Rahman et al., 2015) and a UV-VIS spectrophotometer (UV-1200, Shimadzu, Japan) at 532nm wavelength. The TBA values were calculated from a standard curve and expressed as mg malonaldehyde per kilogram (MA/kg) for both fresh and dried samples on D1 and D7 PM.

As shown in Table 2, humid and hot whether led to a significant drop in overall growth performance, especially for FCR in both CTR and TRT groups, demonstrating the reliability of the HS model that was set up in Thailand. However, OH-SeMet brought significant improvements for FCR (P = 0.04), ADG (P < 0.01) and PI (P < 0.01) in TRT compared with CTR, although we only observed an improved trend on BW (P=0.08) and no difference for mortality between the two groups. This is consistent with the previous report that organic selenium can rescue broiler performance under HS in both experimental and commercial rearing systems (Surai et al., 2018).

As shown in Figure 1, there was a significant increase (P< 0.01) in selenium deposition in breast muscle from TRT compared with CTR , which is in line with the previous findings (Surai et al., 2018).

As the key molecule of 25 selenoproteins, selenium with enhanced content in breast muscle can establish a stronger antioxidative capacity, and hence improve PM meat quality traits. Similarly, the loss of muscle protein caused by oxidation and over-hydrolysis during HS can also be considerably prevented by OH-SeMet, leading to better growth performance. The elevated antioxidative capacity brought by higher Se content in breast muscle was partially demonstrated by the significant lower TBARS values (P value ranging from < 0.01 to 0.04) in both fresh and dry meat samples in PM D1 and D7 (Table 3).

Impaired meat quality traits were also caused by HS. Observing the dramatically affected L value (meat lightness), 24h PM pH and drip loss (Table 4), it is clear that breast muscle in both groups had the properties to be defined as pale, soft, exudative (PSE) like meat. Together with the decreased growth performance, HS in the commercial broiler farm, even if it was relatively moderate, can lead to significant economic loss due to the reduced proportion of marketable meat, or overall value of the carcass (Zhang et al., 2020). In the current trial, OH-SeMet treatment can improve the meat quality traits as shown in Table 4. The significantly improved L value (P < 0.01), drip loss (P < 0.01), thawing loss (P < 0.01) and cooking loss (P < 0.01) can help maintain a reasonable retail price for the meat cut or broiler carcass.

In conclusion, growth performance and meat quality of broilers reared in an extensive commercial feeding system under HS were inevitably affected. Using OH-SeMet can reduce the oxidative stress triggered by HS, thereby improving the profitability of commercial broiler producers significantly.