Ameliorative effects of L-glutamine on haematological parameters in heat-stressed Red Sokoto goats

Highlights

• The hot-dry season in the Northern Guinea Savanna zone of Nigeria imposes heat stress on livestock.

• Heat stress negatively impacts the haematological parameters of Red Sokoto goats.

• L-glutamine ameliorates environmental heat stress-induced changes in haematological parameters in Red Sokoto goats.

Abstract

The aim of the study was to evaluate haematological responses in Red Sokoto goats (RSGs) administered with L-glutamine during the hot-dry season. Experimental animals included 28 clinically healthy RSGs divided into treated group (n = 14); each administered L-glutamine at 0.2 g/kg body weight, dissolved in 10 mL distilled water, and control group (n = 14); each administered 10 mL distilled water, per os once daily for 21 days. The ambient temperature and relative humidity recorded daily for 4 weeks were used to calculate the temperature-humidity index. Three millilitres of blood sample was collected from each goat by jugular venipuncture for haematology, while rectal temperature (RT), heart rate (HR) and respiratory rate (RR) were also measured once weekly at weeks 0 (before), 1, 2, 3 (during) and 4 (after L-glutamine administration). The haematological, RT, HR and RR data obtained weekly were analysed using repeated-measures one-way ANOVA, followed by Tukey's post-hoc test to evaluate differences between periods, and between treated and control groups. The PCV, haemoglobin concentration and RBC count were higher (P < 0.05) in the treated group compared to the control group during the period of L-glutamine administration. These differences were sustained till week 4. Beginning from week 1 of the study, the total leucocyte count in treated group (10.10 ± 0.25 × 10³/μL) was higher (P < 0.05) than the count in control group (7.23 ± 0.41 × 10³/μL), this trend was also maintained throughout the study. The neutrophil:lymphocyte ratio during weeks 3 and 4 of the experiment was lower (P < 0.05) in the treated compared to the control group. RT was lower (P < 0.05) in treated group than the control group. In conclusion, L-glutamine administration ameliorated the adverse effects of heat stress on the haematological parameters in RSGs during the hot-dry season.

Introduction

In Nigeria goats represent a veritable resource for economic development and livelihood security in addition to major cultural importance (Ibrahim et al., 2014). Red Sokoto goats (RSGs) account for over 65% of the goat population in Nigeria and is the usual village goat in the Northern two-thirds (Savannah zones) of Nigeria (Ngere et al., 1984). Goat production in Nigeria is essentially a traditional management system, involving mainly household units (Ajala, 2004) where they are allowed to roam freely in search of pasture to graze. The environmental conditions during the dry season (cold- and hot-dry) of the Northern Guinea Savannah zone of Nigeria are thermally stressful to goats; hot-dry season being more stressful (Dzenda et al., 2011). The high ambient temperature and a relatively high relative humidity (RH), characteristic of the hot-dry season (Minka and Ayo, 2010), induce heat stress on goats when they are left to graze for long hours during the day. Heat stress is a major constraint of animal production in the tropical and subtropical regions (Marai et al., 2007; Nardone et al., 2010; Ribeiro et al., 2018). It is the perceived discomfort and physiological strain associated with exposure to the uttermost hot temperature. Heat stress stimulates a sort of complex responses which are fundamental in the preservation of cell survival (Altan et al., 2003; Hetem et al., 2011). Heat stress challenges the hypothalamus to activate neuroendocrine changes that induce alterations in plasma fluid and blood cellular parameters.

Blood is an important and reliable medium for assessing the health status of individual animals. Values of haematological parameters are of great importance in evaluating livestock adaptation and monitoring genetic selection (Zakari et al., 2014; Shi et al., 2018). Blood being an important indicator of physiological responses to heat stress in goats is particularly sensitive to changes in the environmental temperature (Okoruwa, 2014; Ribeiro et al., 2018). During heat stress, plasma fluid serves as an efficient thermoregulatory medium to reduce hyperthermia, but with negative consequences on the immune system as well as alteration in erythrocytic and leucocytic variables (Habibu et al., 2018). It is well known that heat stress disturbs the steady state concentrations of free radicals, resulting in both cellular and mitochondrial oxidative damage (BelhadjSlimen et al., 2016). Changes in haematological parameters of livestock due to heat stress occur partly as a result of heat stress-induced oxidative damages, mediated through reactive oxygen species (ROS) generated in excess of the body antioxidant system (Rahal et al., 2014; BelhadjSlimen et al., 2016). Antioxidant supplementation is one of the strategies employed to ameliorate the adverse effects of heat stress in livestock (Minka and Ayo, 2012). L-glutamine is an abundant amino acid in physiological fluids and proteins and a key regulator of gene expression (Wu et al., 2011). It is synthesized in the body from glutamic acid and ammonia in an energy requiring reaction. L-glutamine possesses antioxidant properties (El-Sheikh and Khalil, 2011) and plays a role in the metabolism of carbohydrates, fatty acids, and proteins, proliferation and differentiation of fibroblasts, lymphocytes and enterocytes, and phagocytosis of pathogens by activated macrophages (Li et al., 2007; Wu, 2009; Xi et al., 2011). It has been reported to be beneficial in humans (Hoffman et al., 2012), pigs (Hsu et al., 2012; Hanczakowska and Niwińska, 2013; Wu et al., 2013), horses (Lindinger and Anderson, 2014) and poultry (Jazideh et al., 2014; Shakeri et al., 2014; Hu et al., 2015). Although nonessential in health, glutamine is conditionally essential in stress and illness. This is because during these conditions, the requirement for L-glutamine cannot be satisfied by endogenous synthesis (Newsholme, 2001) and therefore the need for exogenous supplementation. Soltan (2009) reported that L-glutamine improves blood picture of broiler chickens supplemented with 1% L-glutamine. There is a dearth of information on the effect of L-glutamine on the haematological parameters of goats. The aim of this research was to investigate the ameliorative effects of L-glutamine on haematological parameters in heat stressed RSGs during the hot-dry season.