Influence of sperm post-thaw subpopulations of angus and nelore bulls on pregnancy rates by fixed-time artificial insemination.

Background: The heterogeneity of ejaculate indicates that fertility is still variable among bulls and that more stringent evaluation methods are needed to identify the ejaculates suitable for AI.

Objective: To identify and characterize the sperm subpopulations (SP) in thawed semen doses of Nelore and Angus bulls and to evaluate the influence of these sperm subpopulations on pregnancy rate in cows submitted to fixed-time AI (FTAI).

Materials And Methods: A dose of post-thawed semen from each bull (n=18; consisting of Angus n = 9 and Nelore n = 9) was analyzed for: sperm kinetics; morphology and plasma membrane integrity; and the determination of the sperm subpopulations.

Sperm subpopulations influence the pregnancy rates in cattle.

This study aimed to study the characteristics and subpopulations of spermatozoa from bulls with low and high reproductive performance based on pregnancy rates. Based on historical records of pregnancy rate from four farms, 24 bulls were selected. Two groups were established, with low pregnancy rates (n = 12; LOW), including bulls that presented pregnancy rates <52.

Syntheses and Biological Activities of the LMNO, ent-LMNO, and NOPQR(S) Ring Systems of Maitotoxin.

Structure-activity relationship studies of maitotoxin (MTX), a marine natural product produced by an epiphytic dinoflagellate, were conducted using chemically synthesized model compounds corresponding to the partial structures of MTX. Both enantiomers of the LMNO ring system were synthesized via aldol reaction of the LM ring aldehyde and the NO ring ketone. These fragments were derived from a common cis-fused pyranopyran intermediate prepared through a sequence involving Nozaki-Hiyama-Kishi reaction, intramolecular oxa-Michael addition, and Pummerer rearrangement.