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Ovulation synchronization protocols are well established and are routinely used in beef livestock systems. In addition to the genetic gain provided using fixed-time artificial insemination (TAI), there is an optimization in production in bovine females that are submitted to this reproduction biotechnique. In Bos indicus cows created in extensive system, a long period of postpartum anestrus is observed due to factors inherent to the presence of the calf and the negative energy balance. Therefore, the main advantage of using hormonal treatments after calving is to anticipate the first ovulation and the return to cyclicity. However, the final response to the TAI protocol based on estrogen (E2) and progesterone (P4) is approximately 80% in suckled Bos indicus beef cows. Hormonal strategies, such as the use of P4 and energy/protein supplementation prior to the TAI protocol, are used to increase the reproductive efficiency of these females. Furthermore, the correct time to start the TAI protocol after calving to optimize productivity and the duration of exposure to P4 during the TAI protocol directly impacts bovine fertility and will be discussed. [ABSTRACT FROM AUTHOR]

Objective: The objective of this study was to evaluate the effect of pre-synchronization with progesterone (P4) for 3 and 6 days in Nelore cows in postpartum anestrus period, submitted to a fixed-time artificial insemination program (FTAI). Materials and methods: Seventy-four multiparous Nelore cows with a body condition of 2.5 were used. The cows were submitted to three experimental groups, control group and groups pre-synchronized with P4 for a period of 3 and 6 days. For the determination of postpartum anestrus status, ultrasound scans and blood samples were taken to verify the absence of endogenous P4. Forty-five days after AI, gestation was diagnosed. Data were obtained by descriptive analysis and in the case of presentation of significant differences the Chi-square test was used, considering a frequency of P < 0.05. Results: A higher gestation rate was observed for the group that was pre-synchronized for three days with P4 (40 %), in relation to the groups of six days of pre-synchronization and control (25 % and 32 %, respectively). Conclusion: It is possible to conclude that the pre-synchronization with P4 for three days improved the gestation rate of Nelore cows in the postpartum anestrus period. [ABSTRACT FROM AUTHOR]

Objective. To compare the reproductive performance of postpartum and open Bos indicus cows and to study the cost effectiveness of retaining non-pregnant animals after a short breeding season in tropical region of Mexico. Material and Methods. A total of 128 Bos indicus were included, 87 postpartum cows (PP) with ≤90 days after calving and 41 open cows (OC) with >90 days open. The study was divided into three phases: 1) Estrus synchronization followed by FTAI (day 0-10), 2) Estrus detection and AI (day 11-45) and 3) Natural mating (day 46-90). For the first phase, all animals were synchronized and AI at fixed time (day 10). Cows displaying overt signs of estrus (day 11-45) were AI. Open cows during the previous two phases were exposed to the bull. Results. Pregnancy in phase 1 was different (p<0.01) for PP and OC groups, 58.6% and 34.1%, respectively. Overall pregnancy percentage over the second service was 42.5% (p>0.05). No differences (p>0.05) were observed at phase 3, average 44.2%. By the end of the breeding season, the cost of OC, was 3 times more expensive than PP cows. Conclusions. Pregnancy rate at first phase was higher in PP cows than OC cows. At the end of breeding season, a pregnancy rate of 80% was found. Incorporation of open cows from previous breeding season was more expensive than PP cows in all phases of the breeding program. Retaining an open cow for rebreeding one year or more could not be economically feasible. [ABSTRACT FROM AUTHOR]

Antecedentes: los niveles de expresión de los genes de las proteínas de choque térmico (HSP) y de supervivencia se han empleado para monitorear el crecimiento y la maduración del cigoto, dado que codifican proteínas cruciales para el desarrollo embrionario. Objetivo: evaluar la expresión génica de HSP y genes de viabilidad en blastocistos de cinco cruces bovinos. Metodología: los embriones se produjeron in vitro hasta el estadio de blastocisto de los cruces bovinos ♀ Gir × ♂ Holstein (♀ G × ♂ H), ♀ Holstein × ♂ Gir (♀ H × ♂ G), ♀ Brahman × ♂ Holstein (♀ B × ♂ H), ♀ Holstein × ♂ Brahman (♀ H × ♂ B) y ♀ Romosinuano × ♂ Holstein ( ♀ R × ♂ H). La expresión relativa de ARNm de HSPs y 14 genes de supervivencia fueron evaluadas mediante PCR en tiempo real y el método 2-ΔΔCt. Los datos fueron analizados con la prueba Shapiro-Wilk, Krustal-Wallis seguidos del post hoc Benjamini, Krieger and Yekutieli. Las diferencias fueron consideradas estadísticamente significativas cuando p < 0‚05. Resultados: los transcriptos de genes relacionados al estrés térmico fueron detectados en todos los embriones bovinos. La expresión de HSP40 (p = 0‚003; SD = 0‚4), HSP60 (p = 0‚003;SD = 0‚8), HSP70 (p = 0‚018; SD = 0‚7) y AKR72a (p = 0‚03; SD = 1‚2) son significativamente inferiores para ♀ R × ♂ H. Los transcriptos de HSF1 son significativamente más bajos en ♀ R × ♂ H en comparación con ♀ H × ♂ B (p = 0‚01; SD = 1). Los niveles de mRNA de TXNIP (p = 0‚014; SD = 0‚1), y BAX (p = 0‚022;SD = 0‚3) y CASP3 (p = 0‚008; SD = 12‚9) son significativamente más altos cuando Holstein y Gir son las razas donadoras, respectivamente. Además, el gen NOS2 (p = 0‚005) tuvo una expresión significativamente baja en ♀ H × ♂ G. Adicionalmente, el gen ROCK2 se halló únicamente en los blastocistos de los cruces ♀ B × ♂ H, ♀ H × ♂ B y ♀ R × ♂ H, siendo significativamente más bajo en ♀ B × ♂ H (p = 0‚025; SD = 3‚1). Los genes DNMT1 y DNMT3B no se expresaron en la etapa de blastocisto en los cinco cruces bovinos. Conclusión: el presente estudio confirma la susceptibilidad térmica de B. taurus en comparación con B. indicus a partir de la expresión del gen HSP. A conocimiento de los autores, este estudio es el primer reporte de expresión de genes involucrados en la supervivencia embrionaria en cruces ♀ G × ♂ H, ♀ H × ♂ G, ♀ B × ♂ H, ♀ H × ♂ B y ♀ R × ♂ H. [ABSTRACT FROM AUTHOR]

The objective of this work was to evaluate the effect of pre-exposure of progesterone (P4) in Nelore breed cows in the postpartum period, undergoing a fixed-time artificial insemination program (FTAI). 74 multiparous cows with 2,5 body condition, acyclic, were used. For the determination of the state of anestrus, ultrasound scans were performed evaluating the absence of the corpus luteum and taking blood samples in order to verify endogenous P4 levels < 1 ng / mL. The cows were submitted to three experimental groups, being an untreated group and two groups with previous P4 exposure for 3 and 6 days before the start of the estrus synchronization protocol. Animals underwent synchronization protocol based on progesterone, estradiol benzoate, prostaglandin and equine chorionic gonadotropin. 45 days after the IA, the pregnancy diagnosis was made. No differences (P > 0.05) were observed between the gestation rates of the experimental groups. In conclusion, pre-synchronization with P4 in Nelore cows in the postpartum anestrus period did not improve pregnancy rates after artificial insemination. [ABSTRACT FROM AUTHOR]

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Leucaena leucocephala is a shrub rich in proteins and mimosine. This high-density crop is cultivated to increase protein intake in cattle production systems. Mimosine is an antimitotic and its effect on the endometrium is still unknown. It is presumed that it could accumulate in the endometrial tissue, inhibiting the development of the endometrial glands, which are in charge of nurturing the embryo. The objective of this study was to determine mimosine accumulation in the endometrial tissue as a result of the consumption of L. leucocephala and to observe its effect in the development of the endometrial glands of early postpartum cows in a silvopastoral system. Twenty-four Bos indicus-Bos taurus cows were divided in two treatments: grazing in a silvopastoral system (SSP, n-12), formed by the association of Cynodon nlemfuensis and L. leucocephala, var. Cunningham; and grazing in a monoculture system (SM, n-12) of C. nlemfuensis. Mimosine consumption per kilogram of live weight was estimated based on the daily consumption of mimosine per cow. Mimosine concentration in the uterine tissue was determined using HPLC. A Student's t test (p≤0.05) was applied to contrast the differences between the mimosine concentration in the endometrial tissue of functional and non-functional glands. Mimosine accumulated in the endometrial tissue of SSP cows. Its concentration ranged from 51.02 to 63.45 -g g-1 of endometrial tissue (TE). The endometrial glands had a normal development, with -53.73 μg g-1 mimosine concentration in TE. By contrast, with 60.81 μg g-1, or higher, TE concentrations, endometrial glands showed signs of atrophy. Daily mimosine consumption in the SSP was 0.019 g kg-1 live weight. Mimosine from L. leucocephala consumption accumulates in the endometrial tissue and can cause endometrial glands atrophy in early postpartum cows. [ABSTRACT FROM AUTHOR]

The objective of the present study was to determine the milk yield of Simmental-Zebu and Brown Swiss-Zebu cows with different proportions of Bos taurus genes. The study was carried out from 1985 to 2007 at the the Instituto Nacional de Investigaciones Forestales, Agrícolas y Pecuarias, Playa Vicente research station (Veracruz, Mexico). The site presents a humid tropical climate. Milk yield records of Simmental x Zebu and Brown Swiss x Zebu cows with different proportions of Bos taurus genes (50, 62.5 or 75%) were analyzed. The cows were maintained in rotational grazing of the introduced pastures: Star grass (Cynodon plectostachyus) and Guinea (Panicum maximum), and were milked twice a day, after a restricted suckling by their calves. Calves were weaned at 210 days of age. The statistical model included the fixed effects of breed group, year of calving, season of calving, lactation number, and lactation length as a linear covariate; in addition, the model included sire of the cow within breed group as a random effect. The lactation length of Brown Swiss x Zebu cows was greater (P<0.05) than that of Simmental x Zebu cows. Milk yield per lactation, per day and per calving interval of Simmental x Zebu and Brown Swiss x Zebu cows were similar. Third-parity cows yielded more milk (P<0.001) per lactation, per day and per calving interval than first- and second-parity cows. Second-parity cows yielded more milk (P<0.001) per lactation, per day and per calving interval than first-parity cows. [ABSTRACT FROM AUTHOR]

Objective: To investigate the association between scrotal circumference size and sperm characteristics in 194 males of Guzerat breed. Methods: The bulls were divided by age groups from 12 to 36 months of age. The length and width of the testicle and scrotal circumference were measured. Semen was collected from the animals that showed a circumference ⩾ 19 cm through transrectal electrostimulation in order to induce ejaculation. The characteristics assessed in the semen were motility, speed, sperm concentration and presence of rounded cells. Results: the correlation between the scrotal circumference with the sperm motility by group of age was positive (r = 0.94; p < 0.005). The present study showed that the presence of proximal cytoplasmic droplet, the rounded cells in the semen and the defects on the head of the spermatozoids are objective evaluation features, which can be used for early selection of sperm production in Guzerat males. Conclusions: The production of sperm with normal rates in the Guzerat breed is achieved when males reach the age of 28 months and a scrotal circumference close to 30 cm. [ABSTRACT FROM AUTHOR]