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Cryopreservation of bull semen is a common biotechnology procedure in cattle breeding. However, when the ejaculate is obtained by electroejaculation, wide variation is observed in the sperm/seminal plasma (SP) ratio that can affect the freezability of semen in this species. The removal of SP may improve the quality of frozen bull semen. The objective of this study was to evaluate the effect of SP removal from the ejaculate on the cryopreservation of semen from 38 Nellore bulls collected by electroejaculation. After collection, the ejaculate was divided into three aliquots: (1) control (N) diluted to a concentration of 60 × 10 spermatozoa/mL and frozen with SP; (2) centrifugation (C) at ×600g for 10 minutes and the pellet resuspended and frozen at the same concentration as N; and (3) filtration (F) through SpermFilter and sperm recovered and frozen at the same concentration as N. After thawing, sperm kinetics, plasma and acrosome membrane integrity, mitochondrial membrane potential, oxidative stress, and in vitro fertility were evaluated. Statistical analysis was performed using the SAS 9.2 package, and differences were considered significant when P < 0.05. Higher average path velocity and straight-line velocity were observed in the groups submitted to SP removal compared to the control group (P < 0.01). In contrast, filtered samples exhibited higher beat cross frequency, straightness, and linearity compared to the other groups. Plasma membrane integrity was reduced when SP was removed, but lower oxidative stress was observed in groups C and F (34.91 ± 2.95% and 31.63 ± 2.95%, respectively) compared to group N (57.39 ± 2.95%). However, the percentage of hatched blastocysts was similar in the N and F groups (21.22 ± 1.05% and 24.00 ± 1.05%, respectively) and higher compared to group C (18.83 ± 1.05%). In conclusion, removal of SP by centrifugation for bull semen freezing reduced the rate of in vitro-produced embryos, whereas filtration of prefrozen semen was found to be an efficient alternative in terms of semen freezability and in vitro production of bovine embryos.

Semen cryopreservation comprises different steps, among them are the cooling and freezing rates which significantly influence the quality of thawed sperm. Different systems with variable freezing rates are used for freezing bull semen in the field, with a consequence of variable success rates. The objective of this study was to compare different systems for freezing bull semen in the field. Five cooling methods of semen and two methods for the subsequent freezing phase (5 × 2 factorial scheme) were used. Two to four ejaculates were collected from 12 bulls with an electroejaculator. The ejaculates were diluted in BotuBov® to a concentration of 50 × 10 6 spermatozoa/mL in 0.5-mL straws. After dilution, the straws were cooled to 5°C in five cooling systems: TK 4000® at a cooling rate of −0.25°C/min (R1); TK 4000® at a rate of −0.5°C/min (R2); Minitube® refrigerator at a rate of −2.8°C/min (R3); Botutainer® at a rate of −0.65°C (R4), and domestic refrigerator at a rate of −2.0°C/min (R5). After stabilization at 5°C for 4 h, these straws were then submitted to two freezing systems: TK 4000® at a freezing rate of −15°C/min (C1) and Styrofoam box with liquid nitrogen at a rate of −19°C/min (C2). Sperm kinetics were evaluated by computer-assisted sperm analysis at four time points: in fresh semen, after cooling, post-thawing, and after the rapid thermal resistance test (TRT). In addition, plasma and acrosomal membrane integrity, mitochondrial potential and intracellular H 2 O 2 were analyzed after thawing by flow cytometry. The R1, R2 and R4 cooling systems were the most efficient in preserving sperm viability, membrane integrity and intracellular H 2 O 2. Samples frozen in the C1 system exhibited better post-thaw and post-TRT kinetics than C2 samples. In conclusion, slower cooling curves in conjunction with a constant freezing rate obtained with the programmable unit were more efficient for freezing bull semen in the field.

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RESUMO: A taxa de prenhez é de extrema importância para a eficiência produtiva de bovinos de corte, e a fertilidade dos touros pode influenciar na taxa de prenhez das matrizes em monta natural. O objetivo deste trabalho foi avaliar a relação entre as características do exame andrológico, especialmente a circunferência escrotal (CE), de touros da raça Nelore (Bos indicus), selecionados para reprodução com base em maior ganho de peso pós-desmama, com a taxa de prenhez de vacas Nelore em estação de monta natural de 90 dias de duração. Foram avaliados registros de 7171 entradas na monta de 1923 vacas submetidas a 216 touros em 368 lotes de estação de monta a campo (touro único), durante os anos de 1995 a 2014, e a CE dos touros. A CE foi pré-ajustada para idade do touro (2,67±0,62 anos) na entrada da estação de monta, em modelo de regressão linear, sendo posteriormente expressa em 3 classes: classe 1: CE < 35 cm; classe 2: 35 ≥ CE < 37 cm; classe 3: CE ≥ 37. Mais da metade das observações de CE ficaram na classe 2, e 74,52% das exposições aos touros resultaram em prenhez, com mínimo de 0% e máximo de 100% de sucesso de prenhez nos 368 lotes de monta. Parte (n=33) dos 216 touros tinham registros de características obtidas em exame andrológico parcial [CE, volume, motilidade, vigor, concentração e morfologia espermática (defeitos maiores e menores)]. Verificou-se que a classe de valores intermediários de CE (classe 2: 35 ≥ CE < 37 cm) foi a de maior risco relativo para sucesso na prenhez. Na amostra dos 33 touros, a taxa de prenhez apresentou correlação moderada e positiva (r = 0,66) somente com a concentração espermática. A fraca relação entre as características do andrológico os touros e taxa de prenhez das vacas pode ser devido ao fato da amostra dos touros avaliados neste tipo de trabalho ser sempre viesada. Ou seja, só são considerados os touros que entraram em monta, que é uma pequena porcentagem dos machos nascidos e, portanto, a variação observada nesses não representa a variação em CE, nas características seminais, e possivelmente na aptidão reprodutiva, de todos os machos nascidos. Além disso, a taxa de prenhez é o resultado da expressão de muitos fatores que incidem distintamente nas vacas e nos touros, e que devem ter influência individual sutil neste resultado.Palavras-chaves: Bos indicus, perímetro escrotal, prenhez, sêmen. RELATIONSHIP BETWEEN SCROTAL CIRCUMFERENCE OF NELLORE BULLS AND COW PREGNANCY RATE IN NATURAL MATINGABSTRACT: The pregnancy rate is extremely important for the productive efficiency of beef cattle and bull fertility can influence the pregnancy rate of cows in natural mating. The objective of this study was to evaluate the relationship of andrological traits, especially scrotal circumference (SC), of Nellore bulls (Bos indicus) selected for breeding based on greater postweaning weight gain with the pregnancy rate of naturally mated Nellore cows in a 90-day breeding season. Records of 7,171 entries into the breeding season of 1,923 cows exposed to 216 bulls in 368 mating batches in the ...