Legumes are the major element of grassland ecosystem, on which the forage quality depends. Breeding of pasture varieties in perennial legumes firstly aims at achieving tolerance and persistence of the legume component in the pasture. In species having low natural grazing tolerance (lucerne and red clover) it is necessary to conduct breeding for biological, morphological and physiological characteristics, directly related to grazing tolerance. In the species having high grazing tolerance (white clover, birds foot trefoil, sainfoin), the pasture persistence is considered as a function of particular morphological characteristics, adaptive potential and stress tolerance. The indirect breeding for pasture persistence includes also breeding for competitive ability and co-adaptivity with grass pasture species adapted to the region and practices of cultivation, as well as breeding for improved nodulation and nitrogen fixation as an important element of the adaptive ability. The breeding for grazing tolerance and persistence is concentrated also on the mechanisms of self-maintenance of the legumes in the pasture-vegetative reproduction, spread and self-seeding. Many breeding programmes are concentrated also on morphology providing better intake by the animals, on main and specific quality characteristics, on anti-nutrient factors, on adaptation to systems and practices of pasture establishment and use. The breeding strategy using germplasm consolidated through the mechanisms of specific adaptation to unfavourable or specific agro-ecological conditions and influencesi.e. breeding through ecotypic selection is considered to be the most efficient for grazing purposes. The interactions in the system: pasture species-companion species in the pasture herbaceous community-grazing animals (kind, category, grazing style and behaviourial reactions) and the applied regime of use of the pasture are direct and strong. These interactions are of essential importance in genotypic differentiation of the pasture ecotypes. The adaptive variability of the pasture ecotypes is used directly, as well as in recombination breeding.

The effect of the intravenous injection of 100 mcg (2 ml) gonadotropin-releasing hormone (Ovarelin, Ceva) from the 1st to the 20th day after calving of beef cows was monitored in the article, in regard to the occurrence of the first oestrus and the possibilities for its controlling. It was established that in the first minutes of intravenous application of Ovarelin the concentration of luteinizing hormone (LH) increased. By increasing the number of days increased the amount of secreted LH. Maximum effect of the injection of 100 mcg GnRH occurred between the 10th and 15th day. The physiological dose (100 mcg) GnRH injected intravenously on the 1st day after birth of cows led to increased content of LH in blood circulation.

The experiment included 20 ewes of the Tsigai breed, allocated in two groups of 10 animals each. Inducing of oestrus synchronisation was performed during anoestral season (April-May) through vaginal sponges containing gestagens, and administration of Gravohormon (Vetbiopharm, Bulgaria)-500 UI in group 1 ewes and 1000 UI in group 2 ewes. Macromorphological study of the ovaries was carried out by means of laparoscopy after the adopted methods-on the 56 th hour, 72 nd hour and 5 th day following sponge withdrawal and injection of gonadotropin. The levels of the steroid hormones progesteron and 17ß-oestradiol were recorded in three ewes per each group at different times according to the experiment scheme. The histological structure of the ovaries was determined in seven animals subjected to ovariectomy.

Abstract:The experiment included 20 ewes of the Tsigai breed, allocated in two groups of 10 animals each. Inducing of oestrus synchronisation was performed during anoestral season (April -May) through vaginal sponges containing gestagens, and administration of Gravohormon (Vetbiopharm, Bulgaria) -500 UI in group 1 ewes and 1000 UI in group 2 ewes. Macromorphological study of the ovaries was carried out by means of laparoscopy after the adopted methods -on the 56 th hour, 72 nd hour and 5 th day following sponge withdrawal and injection of gonadotropin. The levels of the steroid hormones progesteron and 17ß-oestradiol were recorded in three ewes per each group at different times according to the experiment scheme. The histological structure of the ovaries was determined in seven animals subjected to ovariectomy.

Different schemes of PMSG treatment on some reproductive parameters in sheep were studied. Two groups of 6 sheep each at the end of the non breeding season were treated with vaginal sponges Chrono-gest (Intervet, Holland) containing 30 mg fluorogeston acetate (FGA). The sponges were removed 12 days after insertion. Sheep of the experimental group were injected with 500UI Folligon (Intervet, Holland) 48 hours before sponge removal whilst the corresponding control sheep were treated with the same dose Folligon at the day of of sponge withdrawal. The clinical signs of oestrus, plasma progesterone concentrations and changes in the ovarian morphology during the observation period were registered. The conception rate, fertility and twinning rate were also recorded. The results show that the earlier application of the gonadotropin influence positively the reproductive traits in ewes.