Promoting Effect of L-tyrosine Supplement on New Zealand Rabbit Bucks' Performance and Reproduction Through Upregulation of Steroidogenic Markers.

ORIGINAL RESEARCH published: 14 October 2020 doi: 10.3389/fvets.2020.00605 Promoting Effect of L-tyrosine Supplement on New Zealand Rabbit Bucks’ Performance and Reproduction Through Upregulation of Steroidogenic Markers Shawky Mahmoud 1 , Michel Saad 1 , Ahmed M. El-Shehawi 2,3 , Foad Farrag 4 , Mahmoud M. Abo Ghanima 5 , Mahmoud A. O. Dawood 6* and Mustafa Shukry 1 1 Department of Physiology, Faculty of Veterinary Medicine, Kafrelsheikh University, Kafrelsheikh, Egypt, 2 Department of Biotechnology, College of Science, Taif University, Taif, Saudi Arabia, 3 Department of Genetics, Faculty of Agriculture, Alexandria University, Alexandria, Egypt, 4 Department of Anatomy, Faculty of Veterinary Medicine, Kafrelsheikh University, Kafrelsheikh, Egypt, 5 Animal Husbandry and Animal Wealth Development Department, Faculty of Veterinary Medicine, Damanhour University, Damanhour, Egypt, 6 Department of Animal Production, Faculty of Agriculture, Kafrelsheikh University, Kafrelsheikh, Egypt Edited by: Fulvia Bovera, University of Naples Federico II, Italy Reviewed by: Manuel Gonzalez Ronquillo, Universidad Autónoma del Estado de México, Mexico Vito Laudadio, University of Bari Aldo Moro, Italy *Correspondence: Mahmoud A. O. Dawood Specialty section: This article was submitted to Animal Nutrition and Metabolism, a section of the journal Frontiers in Veterinary Science Received: 11 April 2020 Accepted: 28 July 2020 Published: 14 October 2020 Citation: Mahmoud S, Saad M, El-Shehawi AM, Farrag F, Abo Ghanima MM, Dawood MAO and Shukry M (2020) Promoting Effect of L-tyrosine Supplement on New Zealand Rabbit Bucks’ Performance and Reproduction Through Upregulation of Steroidogenic Markers. Front. Vet. Sci. 7:605. doi: 10.3389/fvets.2020.00605 Delayed puberty and lower fertility are among the most challenging concerns in rabbit development during the summer season. This study was, therefore, aimed at enhancing male NZ rabbits’ performance by using L-tyrosine. Thirty male, New Zealand rabbits, were employed for this purpose at the age of 60 days. Rabbits were divided accidentally into two groups: a control group and another treated with L-tyrosine (100 mg/kg body weight). After 4 weeks, three bucks of each group were assassinated. A comparable oral dose of L-tyrosine was administered to half of the treated group left untreated during the second half. Weekly blood samples were assembled from each group for testosterone, T3, and T4 hormone testing. The results showed that body weight and serum testosterone, T3, and T4 increased exponentially with increasing age in both groups. L-tyrosine contributed to another vital rise in dose-dependence than control, in bodyweight, GSI, and testosterone, T3, and T4. At the end of the third month, tests fell in the scrotum, compared to 2 weeks before in the L-tyrosine group. In the middle of the fourth month, the semen evaluations were first carried out for the L-tyrosine group and 1 month after for the control group. L-tyrosine has contributed to a substantial upsurge in semen quality and motility, and abnormalities have reduced dramatically (P < 0.01). The L-tyrosine-treated group showed significantly increased mRNA expression of steroidogenesis markers STAR, CYP11A1, and 3B-HSD. Besides, free sperm in the seminiferous tubular lumen was discovered at the end of the third month. Nevertheless, it achieves only in control of the spermatocyte stage. The research suggests that L-tyrosine supplements promote puberty and improve male New Zealand rabbit fertility during high-temperature periods in the year. Keywords: L. tyrosine, New Zealand rabbits, testosterone, steroidogenesis markers, summer, fertility Frontiers in Veterinary Science | www.frontiersin.org 1 October 2020 | Volume 7 | Article 605 Mahmoud et al. Impact of L-tyrosine on Rabbit Bucks INTRODUCTION (Serva, Heidelberg, Germany) (18) at about 8 weeks of age. The following 4 weeks after L-tyrosine was orally administered, three male rabbit bucks from the standard control and treated group were killed. The testes were weighed and prepared for histopathological technique and transcriptomic analysis. Ltyrosine’s common oral dosage was given to half of the treated group (N = 8), while the other half remained untreated. After another 4 weeks, three bucks from each group were killed. Semen selection and assessment were applied to the remaining bucks (five in each group). The rabbits were fed a diet of 16.76% protein, 2.36% ether extract, 12.2% fiber, and 2,600 k digestible energy over the experimental period. Durable energy consumption calories/kg and vitamin and mineral nutritional needs were met (19). Sigma-Aldrich (St Louis, MO, USA) provided all the reagents. The testes are hidden inside the abdominal cavity when a young rabbit is born. They fall in the scrotum at around 3–4 months of age, abruptly before puberty (1). The male rabbit’s puberty is described as when it first shows the endocrine testicular function or the first time that a male can deliver sperm (2). Puberty was demonstrated a month before most rabbits reached puberty, and an age difference existed between rabbits of different races. White bucks in New Zealand reached puberty at the age of 5 months (3). Rabbit testicular growth follows a sigmoid curve that grows exponentially during puberty (4). It was reported that the weight of each testis in New Zealand white rabbits was 3.08 ± 0.1 g at ∼ 5 months of age (5). In New Zealand, spermatogonia mitosis first happened at 8 weeks of life, and the Leydig cell growth predated the initiation of spermatogenesis (6, 7). Sperm cells were between 9 and 12 weeks of age; sperm maturation was observed between 13 and 14 weeks, and at the end of the fourteenth week, sperm was found in the tubular lumen (8). Regular rhythms in amino acid metabolism have discovered a correlation between food intake and neurotransmission (4). L-tyrosine, an amino acid of catecholamine, affects thyroid hormones and protein (9, 10). Dopamine is one of the hypothalamic catecholamines regulating prolactin secretion and helps in growth hormone activation (11, 12). L-tyrosine is considered acceptable for all animal species when supplemented for non-food animals (13). The puberty age in rats was decreased by external L-tyrosine (10) and increased pulse frequency in growing lambs (11). It also accelerated maturity and improved the body weight gain of female New Zealand rabbits (14, 15). L-tyrosine also enhances testosterone levels and semen quality of bulls (16). Also, cows treated with one or two doses of Ltyrosine (50 gm/bull calves) induced an improvement in growth and yield (17). One of the issues faced in the rearing of rabbits is the reduced breeding success in the high-temperature season. The purpose of this report, consequently, was to analyze the influence of oral given L-tyrosine on the creation of thyroid and testosterone in puberty and hormonal levels, along with semen quality and steroidogenesis markers i (...truncated)