Overall Performance, Carcass Yield, Meat Safety Potentials and Economic Value of Heat-Stressed Broilers Fed Diets with Balanced Electrolytes

Tropical regions across the globe are characterized by an annually prolonged hot weather conditions that showcase limiting production efficiency in livestock industry, as domesticated animals leave the zone of maximum comfort, under heat stress, with death and reduced carcass yield accompanying the subsequent alteration in body chemistry and behavior. However, pen house orientation, cooling systems, genetic modification and different dietary manipulations have been employed in poultry industry, but many of such did not account for the body’s acid-base equilibrium and the potentials of aggregate levels of dietary electrolytes in enhancing carcass yield of broilers under severe heat stress conditions. Therefore, this study was conducted to investigate the effects of different electrolyte-balanced diets on overall performance, carcass yield, meat safety potentials and economic value of heat-stressed broilers reared for five weeks. Arbor Acre broiler chicks (n = 300) were randomly allotted to diets with aggregate electrolyte balance of 210 (T1), 240 (T2), 270 (T3), 300 (T4), 330 (T5) and 360 (T6) mEq/Kg, in a completely randomised design. On day 35, birds whose weights were closest to the mean class weight were selected from each replicate pen for carcass yield assessment. Also, data on performance and cost-benefit analysis were analysed using descriptive statistics and ANOVA at α = 0.05. Electrolyte-balanced diets though contained salts that presumably could have improved satiety, yet they do not enhance appetite in heat-stressed broilers. However, dietary protein efficiency was enhanced at an electrolyte balance levels of 240 and 270 mEq/kg, which translated into increased body weight gain. Weights of primal parts of birds on 270 mEq/kg DEB were highest at 35 days. Feed cost values (per kiloHow to cite this paper: Popoola, I.O., Popoola, O.R., Adeyemi, A.A., Ojeniyi, O.M., Olaleru, I.F., Oluwadele, F.J. and Akinwumi, E.O. (2020) Overall Performance, Carcass Yield, Meat Safety Potentials and Economic Value of Heat-Stressed Broilers Fed Diets with Balanced Electrolytes. Food and Nutrition Sciences, 11, 615-628. https://doi.org/10.4236/fns.2020.117044 Received: June 9, 2020 Accepted: July 6, 2020 Published: July 9, 2020 Copyright © 2020 by author(s) and Scientific Research Publishing Inc. This work is licensed under the Creative Commons Attribution International License (CC BY 4.0). http://creativecommons.org/licenses/by/4.0/ Open Access I. O. Popoola et al. DOI: 10.4236/fns.2020.117044 616 Food and Nutrition Sciences gram weight gain) of rations with 240 mEq/kg and 270 mEq/kg DEB were lower and showcased promising economic buoyancy to both rural and commercial poultry farmers, while ensuring a high food safety standard under tropical conditions.


Introduction
The fast growth of the poultry industry has been attributed to poultry's good converting ability of feeds into useable protein in meat and eggs coupled with the relatively high return on investment as the production cycle is relatively short, and an undue tie up of capital over a long period is prevented [1] (Ojo, 2003). Also, poultry meat is very tender and has gained consumers' acceptability world-wide. However, it has been shown that feed cost constitutes about 80% of the total operating cost in the poultry industry, as there has been, in recent years, a rapid increase in the prices of feed ingredients that have affected net return from poultry industry (Ohajianya et al., 2013) [2]. According to Muriu et al. (2002) [3], the economization of feed cost using cheaper, but highly nutritive unconventional feed resources and additives is an important aspect of commercial livestock production. Oyewole et al. (2013) [4] opined that one of the ways of reducing the cost of poultry feeds and improving its efficiency is by preparing vitamin-mineral premix from materials sourced locally. However, St-Pierre et al. (2003) [5] reported that heat stress resulted in estimated total annual economic loss to the US livestock production industry of $1.69 to $2.36 billion; and from this total, $128 to $165 million occurs in the poultry industry. Rostagno (2009) [6] noted that there is increasing evidence to demonstrate that heat stress has a significant deleterious effect on food safety through a variety of potential mechanisms. However, while there is evidence linking heat stress with pathogen carriage and shedding in farm animals, the mechanisms underlying this effect have not been fully elucidated. Environmental stress has been shown to be a factor that can lead to colonization of farm animals by pathogens, increased fecal shedding and horizontal transmission, and consequently, increased contamination risk of animal products (Verbrugghe et al., 2012) [7]. Sohail et al. (2012) [8] reported that broilers subjected to chronic heat stress had significantly reduced feed intake, lower body weight, and higher feed conversion ratio at 42 days of age. The body weight changes were explained by Geraert et al. (1996) [9] who indicated that endocrinological changes caused by chronic heat stress in broilers stimulate lipid accumulation through increased de novo lipogenesis, reduced lipolysis, and enhanced amino acid catabolism. However, chronic heat stress negatively affects fat deposition and meat quality in broi-  [11] demonstrated that heat stress is associated with depression of meat chemical composition and quality in broilers. Zhang et al. (2012) [12] demonstrated that chronic heat stress decreased the proportion of breast muscle, while increasing the proportion of thigh muscle in broilers.
Animal infections have been attributed to effects of stress-associated hormones and mediators on the immune system. However, Lyte (2004) [13]

Materials and Methods
The study of evaluating the carcass and economic yield of heat-stressed broilers was carried out at the Teaching and Research Farm, University of Ibadan, Nigeria, after the experimental protocol was reviewed and approved by the Institu-  (2) where ∑DEB = Aggregate DEB; ιDEB = Inherent DEB in rations and εDEB = DEB in Electrolyte sources. Data on feed intake was determined by giving a known quantity of feed to the birds and subtracting the left over for a given period from the quantity supplied. This difference was divided by the number of birds in a replicate group to estimate the feed intake per bird. Body weight gain of birds was determined by subtracting the initial weight for each week from the final weights with the aid of sensitive weighing scale. The feed conversion ratio was calculated by dividing the mean feed intake with the mean body weight gain. Drinking water was supplied to broilers as described by Popoola et al. (2019) [21]. On day 35, birds were selected from each replicate pen whose weights were closest to the mean class weight for carcass yield assessment. Weights of internal organs were harvested same day that the carcasses were obtained. Prices of experimental diets were calculated according to the prices available for ingredients in local markets in Nigeria during the year 2019. Assay was conducted for sodium and potassium (Flame spectrophotometer), and chloride (titration) in diets fed to broiler chickens at different phases of growth (Lacroix et al., 1970) [22]. Microbial load in meat and faecal samples were determined by the agar well diffusion method. The analysis was run using the Bismuth sulfite agar which is a type of agar media used to isolate Salmonella species. The agar was prepared for Salmnella growth according to the instructions of the manufacturer. A 1 g faecal sample from each treatment was weighed and mashed in 9 ml of distilled water to give a uniform mixture. Serial dilution method was used in which 10 ml of 10 3 and 10 5 of each sample was pipette onto a sterile petri dish and the already prepared agar at 45˚C was poured into it. It was swirled gently for even distribution; the plates were inverted and incubated in an incubator at 38˚C for 24 hours after which the colonies formed on each media were counted using the visual aid. Data obtained were subjected to descriptive statistics and analysis of variance using SAS package (2012) [23]. Means for treatments in the analysis of variance were compared using Duncan Multiple range test and all statement of significance were based on probability level of 0.05.

Overall Performance of Heat-Stressed Broilers on Diets with
Balanced Electrolytes Table 1 shows the chemical composition of dietary treatments fed to heat-stressed broiler chickens for a period of 35 days at starter and finisher phases. Table 2 shows the overall performance of broiler chickens fed diets with different electrolyte balance. Feed intake of heat-stressed birds at 0 to 35 days was not significantly    Table 4 shows the organ weights and abdominal fat content of heat-stressed broiler chickens fed diets with varying electrolyte balance. The lungs, kidney, spleen and heart of broiler chickens were not significantly (P > 0.05) affected by varying DEB, and values ranged from 5.80 to 8.00 g; 7.20 to 9.00 g; 1.40 to 2.00 g; and 8.20 to 10.80 g, respectively. However, birds on T3 (36.60) and T6 (34.40 g) had the lowest (P < 0.05) liver weight compared to other dietary treatments. Birds on T1 (41.60 g) had significantly (P < 0.05) higher eviscerated gizzard weight compared to T2 (32.60), T3 (35.60), T5 (33.60) and T6 (34.20 g). Higher (P < 0.05) abdominal fat content was observed in birds on T3 (11.60) and T4 (11.40) compared to other dietary treatments. Figure 1 shows the relationship of varying dietary electrolyte balance with protein efficiency ratio of broiler chickens under severe heat stress condition. An optimum dietary protein efficiency was observed at a DEB range of 270 to 280 mEq/kg. The R 2 value (0.65) indicated that about 65% of the observed changes in dietary protein efficiency were as a result of dietary electrolyte balance.  Means for treatments within a column with no common superscript showed significant (P < 0.05) differences using DMRT. SEM-Standard error of mean, P Value-Probability, DEB-Dietary electrolyte balance. Means for treatments within a column with no common superscript showed significant (P < 0.05) differences using DMRT. One US Dollar at the trial period was equivalent to ₦360.00, SEM-Standard error of mean, P Value-Probability, DEB-Dietary electrolyte balance.

Discussion
A viable nutritional approach to solving heat stress in poultry industry is that which critically considers the birds' health, overall performance, meat safety and economical carcass yield. The results of present study on mortality are consistent with the report of Borges et al. (2003) [24] who observed no significant effects of DEB treatments (0, 120, 240, 360 mEq/Kg) on mortality in broilers reared under moderately high ambient temperature and relative humidity. Contrastingly, the authors also noted non-significant effects of DEB on carcass yield, breast, thigh  Mitchell and Kettlewell (1998) [25] reported that heat stress during transport has been associated with higher mortality rate, decreased meat quality, and reduced welfare status. Warriss et al. (2005) [26] demonstrated a seasonal impact with peak mortality rates of broilers occurring in the summer months with relatively higher environmental temperatures. The results of present study on differences in protein utilization could have been as a result of excessive increase in metabolic cations and anions from electrolytes and amino acids, with resultant effect of blood ionic disorder (alkalosis or acidosis) (Popoola et al., 2020) [20] and increased body temperature (Popoola et al., 2020) [15]. Ahmad et al. (2005) [18] reported that different sources of DEB rations increased significantly, the carcass weights; and supported the findings of current study. Ahmad et al. (2005) [18] also noted larger sizes of the proventriculus and gizzard which may have improved the digestive capacity and higher dressing percentage, breast meat and thigh of birds on electrolyte-supplemented diets. However, contrasting results from some researches might be due to differences in experimental periods, feed formulation, and severity of heat stress. Pourreza and Edriss (1992) [30] noted that gizzard weight was increased linearly with increasing levels of dietary sodium (Na) and this increase reflects the increasing digestive or metabolic capacity of birds. Kidney weight was almost double the lowest level of dietary Na in the case of NaHCO 3 when compared with the lowest level of Na 2 SO 4 . According to the author, bicarbonate buffer system mainly determines blood acid-base balance for optimal production performance and functions under regulatory control of the kidneys.

Conclusion
Electrolyte-balanced diets though contained salts that presumably could have improved satiety, yet they do not enhance appetite in heat-stressed broilers.
However, dietary protein efficiency was enhanced at an electrolyte balance levels of 240 and 270 mEq/kg, which translated into increased body weight gain.
Weights of primal cut of birds on 270 mEq/kg DEB were highest at 35 days. Feed cost values per kilogram weight gain in diets with 240 mEq/kg and 270 mEq/kg DEB were lower and showcased promising economic buoyancy to poultry farmers, while ensuring a high food safety standard under tropical conditions.