Data from 34 yearling Hereford or Angus bulls were used to investigate relationships of testicular size, quantitative rates of sperm production, Sertoli cell numbers, numbers of germ cells supported per Sertoli cell, and the efficiency of spermatogenesis to daily sperm output and seminal quality. Two ejaculates were collected by electroejaculation from each bull on each of 2 days/week throughout the study. The percentage of progressively motile sperm and the percentage of morphologically normal sperm were determined from aliquots of fresh semen. Additional aliquots of semen were frozen in glass ampules or plastic straws and subsequently evaluated for postthaw motility and percentage of sperm with intact acrosomes. Sertoli cell numbers, the numbers of germcells per Sertoli cell, and the efficiency of spermatogenesis were unrelated to the quality of fresh or frozen semen (P greater than 0.05). In first ejaculates, the numbers of sperm and motile sperm were related (P less than 0.05) to testicular parenchymal weight (r = 0.38, and 0.50), daily sperm production (r = 0.45 and 0.53), and spermatids per gram of testicular parenchyma (r = 0.35 and 0.34). Testicular parenchymal weight and daily sperm production also were related to daily sperm output and to the average daily motile sperm output of these bulls (P less than 0.05), but could account for less than 25% of the variability in these end points among bulls.

The effect of two thawing temperatures (37°Cfor30 sec. and 60°Cfor 7 sec.)on sperm survivability and conception rate in buffaloes with frozen semen of Murrah bulls was compared. Thawing at 60°C resulted in statistically significant increase (P0.05) in sperm survivability (motility,live spermatozoa and intact acrosomes) compared with thawing at 37°c. In all, 161 buffaloes were inseminated with frozen semen thawed at 37°Cand 159buffaloeswith semen thawed at 60°Cbetween 2006-07 and 2009-10. Conception rate of 64.15% and 50.31% was obtained with semen thawed at 60°C and 37°C, respectively, and the difference was significant (P0.05). Artificial insemination of buffaloes with frozen semen thawed at 60°C for 7 sec. could be safely used to improve both sperm survivability and conception rate in buffaloes.

The objective of this experiment was to study wheather the administration of GnRH plus PGF2 alpha synchronizes the estrus in anestrus crossbred cows exposed to bull urine (BU) during the winter season (Nov to Feb). The results indicated that a greater proportion of BU-exposed cows (n=20) showed estrus as compared to control (n=8) (90 vs 37.5 % P0.05). The mean plasma progesterone concentration remained below 1ng/ml in all animals of each group during the treatment period. The overall conception rate was double in BU-exposed cows (66.7 vs 33.3 % P0.05). From this experiment it can be concluded that oro-nasal application of BU synchronizes the estrus in a greater proportion of anestrus cows treated with GnRH plus PGF2 alpha during winter season.

Firfty serum and fifty semen samples collected from cattle and buffalo bulls were subjected to ELISA and gB gene based PCR, respectively to detect antibodies in serum and viral DNA in the semen against BHV 1. Out of 50 bulls, 15 (30%) serum samples were detected positive by ELISA while 21 (42%) semen samples were positive by gB gene based PCR. While correlating the results of ELISA and PCR, some seronegative bulls revealed presence of viral genome in semen whereas few seropositive bulls could not reveal viral genome in semen, thus, suggesting application of combined serological assay and PCR assay to detect the presence of BHV-1 infection in bulls.

In the conditions of the Republic of Belarus there were analyzed indices of impregnating ability and efficiency of stud bull mothers of various genotypes on a kappa-casein gene (CSN3). As a result of genotyping of kappa-casein gene by DNA-diagnostics method it is revealed three genotypes - CSN3АА, CSN3AB, CSN3BB. Frequency of occurrence of homozygous genotype CSN3AA at stud bulls - 87,3%; heterozygotic CSN3AB - 20,5%; homozygous CSN3BB - 1,2%. Statistically authentic difference between these indices depending on a genotype it is not established. Thus, authentic connection between indices of impregnating ability and efficiency of stud bull mothers and their genotype on a locus of a kappa-casein gene that specifies in absence of influence of the last on the given indices is not established and gives the chance to conduct selection on gene CSN3 without decrease in breeding value of stud bulls on reproductive qualities.

In the conditions of the Republic of Belarus there was analyzed the efficiency of application of organic form of selenium Sel-plex in feeding of producer bulls. In course of the study there was showed the dynamics of live weight and average daily weight gain of producer bulls; blood indexes of analimals by the end of the experiment; sperm quality of experimental bulls. As a result of research it was established, that application of organic form of selenium Sel-plex in feeding of breeding bulls during the summer and winter periods in a dose of 0,4 mg/kg of dry matter of a ration promoted the increasing of daily average live weight gain on 6,4-8,1%, improvement of morphological and biochemical blood structure, increasing of indices of natural resistance on 0,5-6,1% and sperm production quality - on 7,3-28,0%.