A new field of research in reproductive biology was heralded by the discovery of melatonin in 1958. The concentration of melatonin follows light-dark cycles with significantly higher concentrations during darkness. The authors present the importance of the melatonin protein hormone by focusing on the reproductive processes in domestic sheep. In their literature review, they report that sheep melatonin levels show daily and seasonal rhythms. In sheep as a seasonal breeder and short-day animal species, seasonal increases in melatonin production stimulate sexual activity. The authors describe innovative possibilities for regulating melatonin levels in sheep production. The use of exogenous melatonin brings forward the expression of the sexual cycle. It increases the fertility rate, the number of lambs born, and the chances of survival of twin lambs. Melatonin is a neuroprotection compound against cerebral hypoxia and the development of inflammatory processes in the growing foetus and the newborn lamb.

The preservation of endangered domestic animal breeds is a specific area of sustainable livestock farming. In the southern part of the Carpathians, a variant of Zaupel-type (Racka) sheep, which was small in size and resistant to the cold mountain weather, developed at the beginning of the 19th century. In order to preserve this historical variant, it was introduced in Hungary in the early 1990s. The aim of this work is to study the pedigree of the repatriated population of the Gyimes Racka to understand its population structure and to support its future breeding work. The pedigree data (2005-2020) show that the number of founding individuals (Nf) was 3,838, within which the number of maternal lineages was 2,255. The effective number of founders (fe) and the effective number of significant ancestors (fa) in the total pedigree population were higher than in the reference population (n=2,591; 67 and 56 vs. 20 and 14, respectively). The pedigree traced back to a maximum of 2.51 generations with an average of 1.34 complete generations and 1.78 equivalent complete generations on average (in the reference population: 6.05, 2.73 and 3.82, respectively). Of the 16,947 animals registered in the herd book (with an average normalised COI of 1.43 % obtained by log transformation), 3,828 were inbred (6.30 %). As regards the maternal generations, it can be observed that the inbred stage increases steadily and significantly from the beginning to the present eighth generation (from 0.00 % to 9.54 %). The average generation interval between breeding animals was 3.29 years (obtained by log transformation). The sire-progeny paths had shorter (2.92-3.02) and the dam-progeny paths had longer (3.62-3.70) intervals. The Gyimes Racka population is already showing signs of genetic narrowing during its short conservation period, which calls for attention to stop undesirable trends.