Research Article

Investigation of Litter Size in Awassi Sheep and their Correlation to Adipose Tissue Biomarkers

Suroor Hafedth Mohammed, Tahreer Mohammed Al-Thuwaini*

Department of Animal Production, College of Agriculture, Al-Qasim Green University, Al-Qasim, Babil, Iraq.

Received | March 18, 2024; Accepted | June 29, 2024; Published | September. 20, 2024

*Correspondence | Tahreer Mohammed Al-Thuwaini, Department of Animal Production, College of Agriculture, Al-Qasim Green University, Al-Qasim, Babil, Iraq; Email: tahrearmohammed@agre.uoqasim.edu.iq, tahreermohammed@ymail.com

Citation | Mohammed SH, Al-Thuwaini TM (2024). Investigation of litter size in Awassi Sheep and their correlation to adipose tissue biomarkers. J. Anim. Health Prod. 12(4): 481-485.

DOI | http://dx.doi.org/10.17582/journal.jahp/2024/12.4.481.485

ISSN (Online) | 2308-2801

 

 

Copyright: 2024 by the authors. Licensee ResearchersLinks Ltd, England, UK.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https://creativecommons.org/licenses/by/4.0/).

INTRODUCTION

Sheep are small ruminants that provide high levels of animal protein which contributes to human diet protein content worldwide (Goldansaz et al., 2022). Sheep producers benefit economically and biologically from increasing ewe productivity and reproduction (Habtegiorgis et al., 2022). Many factors affect reproductive performance, including litter size, season, photoperiod, age, nutrition, management, male behavior, and genetics (Ajafar et al., 2022; Al-Thuwaini and Kareem, 2022). The litter size is influenced by various factors, such as the rate of ovulation, the capacity of the uterus, the length of gestation, parity, the mortality of lambs before weaning, and the body fat of the ewe (Sarvinda et al., 2022; Alkhammas and Al-Thuwaini, 2023). Live weight and body fat reserves of ewes at mating affect their reproductive and productive behavior. Low body fat reserves and low live weight at mating affect sheep’s productivity and reproductive ability (Ptacek et al., 2014; McNamara and Huber, 2018). Multiple studies have been conducted to analyze fat’s impact on fat-tailed sheep productivity, reproductive traits, and physiological functions. Furthermore, these studies focus on adipose biomarkers that have a significant impact on productive traits. Notably, Xu et al. (2015), Yue et al. (2016), and Ibrahim (2021) have greatly contributed to our understanding of this area. Adipose biomarkers, including metabolites, proteins, hormones, and DNA can be used to measure or predict traits indirectly in livestock. As well, biomarkers are particularly useful when measuring traits in a short period, or if direct measurements of traits require lengthy trials, are labour-intensive, result in animal loss, or are expensive (Fontanesi, 2016; Goldansaz et al., 2017).

There are multiple adipokines produced and secreted by adipose tissue, such as leptin, visfatin, adiponectin, chemerin, and many others (Häussler et al., 2022; Al-Jumaili et al., 2023). Adipose tissue-secreted hormones, namely adipokines, could contribute to fertility regulation (Estienne et al., 2020; Mohammed et al., 2022). Leptin, produced by adipose tissue, regulates various physiological processes including energy balance, metabolism, fat oxidation, and reproductive processes (Kuźnicka et al., 2020). A second adipokine called Visfatin or (nicotinamide phosphoribosyl-transferase) is expressed in the uterus, ovary, and testis. There is evidence that visfatin increases the gonad expression of chickens and buffaloes, as well as is involved in the regulation of ovarian steroidogenesis in these species (Diot et al., 2015; Thakre et al., 2021). Kaminski et al. (2021) conducted a study that revealed the hypothalamus of porcine-expressed visfatin. This expression is found to be intricately linked to the hormonal environment associated with early pregnancy and the estrous cycle. According to these data, information regarding these biomarkers could be of considerable interest concerning potential associations between sheep breeds and reproductive traits. Middle Eastern countries are predominantly home to the Awassi sheep breed (Al-Thuwaini and Al-Hadi, 2022). While it is capable of surviving harsh conditions (Al-Thuwaini, 2021), it is generally regarded as having lower reproduction rates than Karakuls and Assaf (Ajafar et al., 2022). There is a lot of concern from Middle Eastern breeders about this breed’s low reproductive capacity, which drives efforts to enhance it. However, no publications have used adipose tissue biomarkers to characterize litter size in Awassi ewes. This study aimed to examine the relationship between the number of lambs born to ewe and biomarkers found in adipose tissue, emphasizing the significant role of the Awassi breed in sheep reproduction.

MATERIALS AND METHODS

Sheep population and phenotypic measurements

The study was performed between July 2022 and September 2023 at Al-Qasim Green University with approval from the ethics committee (Agri, No. 01, 7, 22). There were 100 ewes of the Awassi breed, aged 3 to 4 years, mature sexually, not pregnant or lactating, and healthy. A singleton ewe and a twin ewe were randomly selected from Babylon and Karbala stations and classified as 50 and 50, respectively, after parturition. The animals were given a concentrated feed consisting of barley, bran, and salt in the proportions of 59%, 40%, and 1%, respectively, equivalent to 2.5% of their body weight. Additionally, 3 kilograms of alfalfa and 1 kilogram of straw were given to the animals. Throughout the day, all animals had access to fresh water.

The sheep’s external jugular vein was punctured with a disposable needle of 18 gauge to collect blood (5 ml). An analysis of hormone levels was made by centrifuging blood for 15 minutes at 2,000 xg and storing the serum at -20°C. An ELISA kit provided by SunLong Biotech Co., LTD (Hangzhou, China) was used to measure leptin and visfatin levels in the adipose tissue (SL00009Sp and SL00147Sp, respectively). Leptin sensitivity was 8 pg/mL, and the intra- and inter-assay coefficients of variation were 10% and 12%, respectively. The assay range of leptin concentrations was 30 pg/mL to 2000 pg/mL. The sensitivity of the visfatin assay was 0.1 ng/ml, with intra-assay and inter-assay coefficients of variation of 10% and 12%, respectively. Assay visfatin concentrations ranged from 0.5 ng/mL to 40 ng/mL. A suspended spring balance was used in the morning to measure the weight of Awassi ewes (kg) (Kadhem and Al-Thuwaini, 2022).

Data analysis

An investigation was conducted to determine the effects of birth type on various animal traits. Based on the general linear model, SPSS version 23.0 was used to conduct this study:

Yijk= μ + Li + Pj + eijk

Where Yijk = characteristics phenotypically, μ = overall mean, Li = fixed effect of ith birth type (i = 1, 2), Pj = fixed effect of jth parity (j = 1, 2, 3), and eijk = random error associated with Yijk observation and assumed to be NID (0, σ2e). Bonferroni test with a significance level of 0.05 was used to compare means. The results of preliminary statistics showed that seasonal, station, and factor interactions did not significantly influence phenotypic traits. Thus, the general linear model excluded these variables.

RESULTS AND DISCUSSION

This study examined the associated progeny type with adipose tissue biomarkers in Awassi ewes. The least-square means of adipose tissue biomarkers affected by the progeny type are presented in Table 1. The live body weight, leptin, and visfatin levels were significantly higher (P ≤ 0.05) in Awassi ewes with twin births than in ewes with single births. However, the age of Awassi ewes did not show a significant difference (P ≥ 0.05). The correlation coefficient between progeny type and phenotypic characteristics of Awassi ewes is presented in Table 2. The highest and strongly positive correlations (P ≤ 0.05) were recorded between twin ewes with live body weight (r = 0.45, P = 0.001), leptin (r = 0.37, P = 0.001), and visfatin (r = 0.33, P = 0.02), respectively. Univariate regression analyses further explored the association of the progeny type with adipose tissue biomarkers (Table 3).

 

Table 1: The effect of progeny type on adipose tissue biomarkers in Awassi ewes.

Indices	Progeny type (LSM ± SE)		P value
	Single (52)	Twin (48)
Live body weight (Kg)	47.19 ± 0.85b	50.41± 0.92a	0.01
Age (year)	3.53 ± 0.09	3.50 ± 0.10	0.79
Leptin (pg/ml)	192.16±27.63b	286.41±30.51a	0.02
Visfatin (ng/ml)	3.56 ± 0.96b	6.51 ± 0.91a	0.03

LSM±SE, Least square means±Standard error. a,b Significant differences in means represent differences in the same row within each classification.

 

Table 2: Correlation between litter size and other variables in Awassi ewes.

Variables	Single		Twin
	r	P-value	r	P-value
Live body weight (Kg)	0.33	0.004	0.45	0.001
Age (year)	-0.03	0.75	-0.12	0.46
Leptin (pg/ml)	0.30	0.008	0.37	0.001
Visfatin (ng/ml)	0.29	0.01	0.33	0.02

P ≤ 0.05: Significant, P ≥ 0.05: Not significant.

 

Table 3: Logistic regression analysis of progeny type with phenotypic parameters in Awassi ewes.

Characteristic	Univariate logistic regression
	Estimate	Odds ratio (95% Cl)	P value
Live body weight (Kg)	0.43	1.53 (0.98-4.58)	0.04
Age (year)	0.12	1.12 (0.91-3.98)	0.43
Leptin (pg/ml)	0.93	2.53 (1.21-5.83)	0.003
Visfatin (ng/ml)	0.89	2.43 (1.01-5.67)	0.01

The P-value with statistical significance is indicated in bold numbers; CI: confidence interval.

The economic viability of livestock exploitation heavily relies on reproduction efficiency. Thus, a comprehensive understanding of the factors influencing livestock reproductive traits is essential for enhancing these traits (Ajafar et al., 2022; Al-Jaryan et al., 2023). Sheep litter size has been reported to be influenced by their live body weight. Twin ewes have a higher twinning ratio when their live body weight increases. The litter size of ewes can generally be predicted by their live weights, with heavier ewes bearing more lambs than ewes bearing a single lamb (Al-Thuwain and Al-Hadi, 2022). Furthermore, sheep reproductive traits are a complex combination of endocrine signals exchanged among the pituitary gland, ovary, and adipose tissues. The adipose tissue and its secreted adipokines play a crucial role in all aspects of reproduction (Al-Thuwaini, 2022). Adipokines regulate numerous physiological activities, serving as energy sensors and communicating body energy levels to hypothalamic neurons. For instance, ovarian functions are influenced by adipokines, impacting puberty, estrus behavior, follicular development, and ovulation, as well as the formation and functioning of the corpus luteum in livestock (Mishra et al., 2016).

Leptin is one of these adipokines that acts centrally in the hypothalamus to promote the release of gonadotropins, which are essential for initiating and maintaining the reproductive cycle, by increasing neuronal activity and secretion of gonadotropin-releasing hormones (GnRH) (Hausman et al., 2012; Kuźnicka et al., 2020). Neuropeptide Y, proopiomelanocortin, and kisspeptin are the pathways that interact with leptin to affect GnRH. Moreover, leptin affects follicular and luteal steroidogenesis in the ovary by altering the pituitary gland’s sensitivity to GnRH (Hausman et al., 2012). A study conducted in animals found that administering leptin stimulates the production of gonadotropins, specifically follicle-stimulating hormone (FSH) and luteinizing hormone (LH), and restores fertility (Priyadarshini et al., 2015). Additionally, leptin impacts the maturation of oocytes, the rupture of follicles, and the development of the corpus luteum (Kuźnicka et al., 2020). In sheep, leptin and leptin receptor proteins regulate oocyte maturation and embryo development across all stages of ovarian follicle development. Furthermore, sheep with high leptin levels exhibit improved antrum formation and oocyte production rates, and faster maturation of their oocytes (Ma et al., 2022). The results of this study revealed that ewes with single births had the lowest leptin concentrations, while ewes with twin births had the highest concentrations. This may be due to the inverse relationship between leptin and estradiol levels. Leptin may suppress estradiol synthesis, thereby promoting the development of additional vesicles in sheep (Bobowiec et al., 2001). Additionally, the results showed a positive relationship between litter size and leptin levels. Interestingly, leptin concentration has a positive correlation with litter size (P ≤ 0.01), as confirmed in the correlation studies by Kuźnicka et al. (2020). Another crucial adipokine is visfatin, which has been identified in the corpus luteum, ovarian follicles, cumulus cells, and oocytes of bovines, resulting in increased levels of progesterone and estradiol (Reverchon et al., 2016). Furthermore, vifatin stimulates the release of progesterone in the corpus luteum of water buffalo (Thakre et al., 2021). The hypothalamic-pituitary-gonadal axis (HPG), including the pituitary, could also be influenced by visfatin, in addition to its direct effect on the reproductive system. The HPG axis expresses visfatin in all of its structures (Szymanska et al., 2023a). Additionally, visfatin could influence LH and FSH secretion via the INSR, AKT/PI3K, MAPK/ERK1/2, and AMPK signaling pathways in porcine anterior pituitary cells, thereby contributing to the physiological integration of reproduction and energy balance (Szymanska et al., 2023b). However, no publications have examined the effects of visfatin on litter size in Awassi ewes.

CONCLUSIONs and Recommendations

There was an association between the litter size of Awassi ewes and adipose tissue biomarkers. Ewes with twin births had higher live body weights, leptin, and visfatin levels when compared to those with single births. Determining the association between litter size and adipose tissue biomarkers could improve various aspects of animal production and may provide further evidence that adipose tissue biomarkers are a key regulator of reproductive function.

Acknowledgement

The authors gratefully acknowledge the staff of two sheep stations,Babylon and Karbala, for their facilities that supported the Awassi ewe population.

NOVELTY STATEMENT

This study investigated the relationship between the number of lambs born to ewes and biomarkers found in adipose tissue for the first time. The Awassi ewes with twins exhibited elevated levels of leptin and visfatin, making them potential candidates for further research in sheep breeding and reproduction.

AUTHORS CONTRIBUTION

Tahreer M. AL-Thuwaini designed the idea and wrote the draft of the manuscript. Suroor H. Mohammed carried out the laboratory analysis. Both authors checked and approved the final version of the manuscript for publishing in the Journal of Animal and Health Production.

Conflict of interest

The authors have declared no conflict of interest.

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