RESUMO

Pesticides are used worldwide to control arthropod parasites in cattle herds. The indiscriminate and/or inappropriate use of pesticides without veterinary guidance is a reality in several countries of South America. Improper pesticide use increases the chances of contamination of food and the environment with chemical pesticides and their metabolites. Reduction of these contamination events is an increasing challenge for those involved in livestock production. The horn fly, Haematobia irritans (Linnaeus) (Diptera: Muscidae), is one of the most economically important parasites affecting cattle herds around the world. As such, horn fly control efforts are often required to promote the best productive performance of herds. Pesticide susceptibility bioassays revealed that pyrethroid resistance was widespread and reached high levels in horn fly populations in the Brazilian state of Rondônia. The knockdown resistance (kdr) sodium channel gene mutation was detected in all horn fly populations studied (n = 48), and the super kdr sodium channel gene mutation was found in all homozygous resistant kdr individuals (n = 204). Organophosphate resistance was not identified in any of the fly populations evaluated.

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The aim of this study was to determine the effects of the cumulative gain in expertise in carrying out handmade cloning (HMC) procedures on embryo yield and pregnancy outcome in cattle. Results from in vitro and in vivo embryo development after HMC during three periods of 7 months, separated by 3-month intervals, were compiled and designated as P1, P2 and P3. Blastocyst yield, morphological quality and stage of development, and pregnancy per embryo transfer (ET) on Day 30 of gestation were compared. Zona-intact oocytes were activated chemically in each experiment replicate, and development of parthenogenetic blastocysts was used as a control measurement of oocyte quality and in vitro culture conditions. A total of 21,231 cumulus-oocyte complexes (COCs) were in vitro-matured, with 5,432, 10,721 and 5078 COCs used in 16, 18 and 10 replicates for P1, P2 and P3, respectively. Cloned blastocyst yields on Day 7 increased from 15.5% (124/798) in P1 to 21.6% (309/1428) and 36.6% (280/764) in P2 and P3, respectively. No differences were observed in blastocyst development of parthenogenetic embryos, which average 30.0, 37.6, and 36.4% in P1, P2, and P3, respectively. A 10-fold higher probability of obtaining cloned blastocysts at more advanced stages of development and of higher morphological grade was seen during P3 compared with P1. Pregnancy per ET on Day 30 also increased with gain in expertise, being 6.7% (2/30), 20.8% (10/48) and 40.0% (24/60) for P1, P2 and P3, respectively. The relative efficiency for the establishment of pregnancies (per total COC) increased from 0.04% (1:2716) in P1 to 0.22% (1:460) in P2, reaching 0.47% (1:212) in P3. Results demonstrated a gradual improvement in in vitro and in vivo embryo development over time after establishment of HMC procedures in the laboratory, highlighting the importance of gaining experience and technical skills on the overall cloning efficiency.

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Cloning procedures often interfere with conceptus growth and life ex utero, in a set of symptoms known as abnormal offspring syndrome (AOS). The aim of the present study was to compare the developmental pattern of in vivo-derived (IVD), IVF-derived and handmade cloning-derived (NT-HMC) Day 225 bovine concepti using established procedures. Pregnancy diagnosis was performed on Day 30 following blastocyst transfer on Day 7. Conceptus morphometry was assessed by ultrasonography on Day 51, and on Day 225 pregnant cows were killed for morphological examination of concepti. Pregnancy outcome was similar between groups, with greater pregnancy losses in the first trimester (70.6%) and smaller fetuses on Day 51 in the NT-HMC group than in the IVD (14.3%) and IVF (20.0%) groups. However, NT-HMC-derived concepti were twofold larger on Day 225 of gestation than controls. A higher frequency (63.5%) of placentomes larger than the largest in the IVD group was observed in the NT-HMC group, which may be relevant to placental function. Conceptus traits in the IVF group were similar to the IVD controls, with only slight changes in placentome types. Morphological changes in cloned concepti likely affected placental function and metabolism, disrupting the placental constraining mechanism on fetal growth in mid- to late pregnancy.

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Postpartum anovulation is a natural process that is observed in most mammals, including women. In lactating dairy cows, the interval from calving to first ovulation typically averages 4 to 5 weeks, but a substantial proportion of cows have not resumed estrous cyclicity by 60 days postpartum. Extended delay in resumption of first postpartum ovulation is known to exert long-lasting detrimental effects on fertility in dairy cows including the lack of spontaneous estrus and subsequent timely insemination postpartum, but when anovular cows have the estrous cycle synchronized for artificial insemination (AI), still pregnancy per AI is reduced and the risk of pregnancy loss increased. Many risk factors exist for extended postpartum anovulatory periods such as negative nutrient balance and diseases, and these risk factors are also known to depress fertility by themselves. A key feature in anovular cows when inseminated is that they develop the ovulatory follicle under subluteal or low concentrations of progesterone. Progesterone from the corpus luteum is pivotal for follicle development, oocyte competence, embryo growth, and endometrial function; however, many of these effects exerted by progesterone are mediated either by secretion of gonadotropins influencing follicular function and oocyte competence or by endometrial histotroph secretion influencing embryo/conceptus growth and developmental biology

Assuntos

RESUMO

Postpartum anovulation is a natural process that is observed in most mammals, including women. In lactating dairy cows, the interval from calving to first ovulation typically averages 4 to 5 weeks, but a substantial proportion of cows have not resumed estrous cyclicity by 60 days postpartum. Extended delay in resumption of first postpartum ovulation is known to exert long-lasting detrimental effects on fertility in dairy cows including the lack of spontaneous estrus and subsequent timely insemination postpartum, but when anovular cows have the estrous cycle synchronized for artificial insemination (AI), still pregnancy per AI is reduced and the risk of pregnancy loss increased. Many risk factors exist for extended postpartum anovulatory periods such as negative nutrient balance and diseases, and these risk factors are also known to depress fertility by themselves. A key feature in anovular cows when inseminated is that they develop the ovulatory follicle under subluteal or low concentrations of progesterone. Progesterone from the corpus luteum is pivotal for follicle development, oocyte competence, embryo growth, and endometrial function; however, many of these effects exerted by progesterone are mediated either by secretion of gonadotropins influencing follicular function and oocyte competence or by endometrial histotroph secretion influencing embryo/conceptus growth and developmental biology…(AU)

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The objective was to evaluate the individual and combined effect of anovulation and cytological endometritis (CTE) on the reproductive performance of dairy cows. A total of 1,569 cows from 3 data sets were used. In data set 1, 403 Holstein cows from 5 dairies in New York were used. In data set 2, 750 Holstein cows from 2 dairies, one in Florida and one in California were used. In data set 3, 416 dairy cows, 165 Holsteins, 36 Jerseys, and 215 Holstein-Jersey crossbreeds from a grazing dairy in Florida were used. Cyclicity and CTE was determined at 35±3 (data set 2) or 49±3 d in milk (data sets 1 and 3). A variable (VarCycCTE) containing all 4 possible permutations between cyclicity (cyclic = Cyc; anovular = Anov) and CTE (present = CTE; absent = Healthy) was created. In the combined data set (sets 1, 2, and 3), pregnancy per artificial insemination (P/AI) diagnosed at 30 to 38 d after first AI was affected by VarCycCTE, with AnovCTE cows having decreased P/AI compared with CycHealthy cows (21.3 vs. 46.7%), whereas AnovHealthy (37.9%) and CycCTE cows (36.0%) had intermediate P/AI. Pregnancy per artificial insemination for the individual data sets and for pregnancy diagnosed at 63 to 74 d after artificial insemination followed a similar pattern. Pregnancy loss was not affected by VarCycCTE. Hazard of pregnancy up to 300 d in milk was affected by VarCycCTE in the combined data sets 1 and 2, with AnovCTE [hazard ratio (HR)=0.55], AnovHealthy cows (HR=0.71), and CycCTE (HR=0.8) having decreased hazard of pregnancy compared with CycHealthy cows. Median days open were 200, 159, 145, and 121 for AnovCTE, AnovHealthy, CycCTE, and CycHealthy, respectively. Hazard of pregnancy for the individual data sets followed a similar pattern. In summary, both anovulation and CTE were negatively associated with reproductive performance and, when combined, they had an additive negative effect.

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[...] A wealth of information in the scientific literature is available linking diseases with depressed reproduction in dairy cows. Unfortunately, only few studies have established a causal relationship between a specific disease and fertility, and little is known about the mechanisms that underlie the decrease in pregnancy in dairy cows that had disease in early lactation. It is clear that dairy cows that suffer from disease processes have impaired resumption of postpartum ovulation, compromised fertilization and pre-and peri-implantation conceptus development, altered conceptus gene expression, increased pregnancy loss and, ultimately reduced pregnancy per insemination that causes an extension in time to pregnancy. Because mechanisms are poorly understood, no target intervention is available at this time to reverse the poor reproduction in cows that develop periparturient diseases, except methods to induce cyclicity in anovular cows or to improve insemination rate in cows not detected in estrus. Regardless of a better understanding of the underlying biology of poor fertility in diseased cows, a pivotal approach is to implement strategies that mitigate the risk factors that predispose cows to disease. Such interventions include, but are not limited to, improving transition cow management and grouping, proper dietary formulation to prevent periparturient diseases associated with intermediary and mineral metabolism, strategies for reducing calving-related disorders, and methods to prevent mastitis and lameness. Future developments in target strategies to improve reproduction of cows suffering from peripartum diseases will require a better understanding of the impaired biological processes that compromise establishment and maintenance of pregnancy in this subfertile population of cows. (AU)

Assuntos

RESUMO

[...] A wealth of information in the scientific literature is available linking diseases with depressed reproduction in dairy cows. Unfortunately, only few studies have established a causal relationship between a specific disease and fertility, and little is known about the mechanisms that underlie the decrease in pregnancy in dairy cows that had disease in early lactation. It is clear that dairy cows that suffer from disease processes have impaired resumption of postpartum ovulation, compromised fertilization and pre-and peri-implantation conceptus development, altered conceptus gene expression, increased pregnancy loss and, ultimately reduced pregnancy per insemination that causes an extension in time to pregnancy. Because mechanisms are poorly understood, no target intervention is available at this time to reverse the poor reproduction in cows that develop periparturient diseases, except methods to induce cyclicity in anovular cows or to improve insemination rate in cows not detected in estrus. Regardless of a better understanding of the underlying biology of poor fertility in diseased cows, a pivotal approach is to implement strategies that mitigate the risk factors that predispose cows to disease. Such interventions include, but are not limited to, improving transition cow management and grouping, proper dietary formulation to prevent periparturient diseases associated with intermediary and mineral metabolism, strategies for reducing calving-related disorders, and methods to prevent mastitis and lameness. Future developments in target strategies to improve reproduction of cows suffering from peripartum diseases will require a better understanding of the impaired biological processes that compromise establishment and maintenance of pregnancy in this subfertile population of cows.

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Re-suspension of frozen-thawed ram sperm with ovine and bovine whole seminal plasma (SP) is beneficial for its post-thawing viability. However, neither the influence of SP incubation duration nor the re-suspension with equine SP has been tested. In the first experiment, frozen-thawed ram sperm were incubated with SP from bovine (BSP), equine (ESP) or ovine (OSP) or without SP (-SP) for short (5 min) or long (6 h) periods. Viability parameters such as sperm progressive motility, percentage of live cells and membrane functionality were assessed every 2 h for 6 h. All SP treatments showed higher spermatozoa viability than the -SP treatment in most evaluations. Incubation time did not affect sperm viability for BSP treatment, however, ESP and OSP induced a transitory benefic effect in the short incubation period and detrimental effect in the longer period. In the second experiment, frozen-thawed sperm, with or without short incubation with SP, were selected by swim-up, and their DNA fragmentation rate was assessed using comet assay immediately after swim-up completion and after 5 h of incubation. BSP, ESP and OSP protein profiles were determined by SDS-PAGE. Only ESP was associated with sperm DNA stabilization capacity and SP from rams and bulls showed protein profiles different from that of stallions. These experiments indicate that equine or ovine, but not bovine whole SP supplementation to post-thawing incubation medium of frozen-thawed ram sperm affects its viability in a time dependent manner. The beneficial effect of ESP on stabilizing DNA integrity, even after sperm washing with swim-up method and incubation for 5 h, can be determined by SPP or by antioxidant components from SP.

Assuntos

RESUMO

Re-suspension of frozen-thawed ram sperm with ovine and bovine whole seminal plasma (SP) is beneficial for its post-thawing viability. However, neither the influence of SP incubation duration nor the re-suspension with equine SP has been tested. In the first experiment, frozen-thawed ram sperm were incubated with SP from bovine (BSP), equine (ESP) or ovine (OSP) or without SP (-SP) for short (5 min) or long (6 h) periods. Viability parameters such as sperm progressive motility, percentage of live cells and membrane functionality were assessed every 2 h for 6 h. All SP treatments showed higher spermatozoa viability than the -SP treatment in most evaluations. Incubation time did not affect sperm viability for BSP treatment, however, ESP and OSP induced a transitory benefic effect in the short incubation period and detrimental effect in the longer period. In the second experiment, frozen-thawed sperm, with or without short incubation with SP, were selected by swim-up, and their DNA fragmentation rate was assessed using comet assay immediately after swim-up completion and after 5 h of incubation. BSP, ESP and OSP protein profiles were determined by SDS-PAGE. Only ESP was associated with sperm DNA stabilization capacity and SP from rams and bulls showed protein profiles different from that of stallions. These experiments indicate that equine or ovine, but not bovine whole SP supplementation to post-thawing incubation medium of frozen-thawed ram sperm affects its viability in a time dependent manner. The beneficial effect of ESP on stabilizing DNA integrity, even after sperm washing with swim-up method and incubation for 5 h, can be determined by SPP or by antioxidant components from SP.(AU)

Assuntos

RESUMO

Reproduction continues to be a critical component to maintain a dairy farm economically viable. For every farm and for every cow, there is an optimum time for pregnancy, which is mostly influenced by level of production, persistency of lactation, and parity. In general, as production decreases, lactation number increases, and persistency of lactation decreases, cows should be bred sooner postpartum and pregnancy obtained early in lactation. The voluntary waiting period is determined based on the desired interval postpartum to pregnancy and the pregnancy rate of the farm. As pregnancy rates increase, the voluntary waiting period can be delayed, particularly when milk production is high. Studies in the literature have compared several breeding strategies to obtain a pregnant cow. In general, pregnancies obtained by artificial insemination are cheaper than those originated by natural service. The major reason is that AI programs result in similar or better reproductive performance and are cheaper to implement than natural service programs because of the high costs of acquiring and feeding bulls. Within the AI program, those that incorporate timed AI for first insemination followed by detection of estrus result in lowest median days open and more profit per cow, and the benefits of improving reproduction are greater when milk prices ar e low. The use of embryo technologies as a breeding program for lactating dairy cows, with the aim to improve reproductive performance, is only attractive when the differential in fertility relative to AI is large. In most cases, AI programs have to result in very poor fertility (<15%) for the typical results from embryo transfer (40-45% pregnancy) to be economically attractive at current costs. For dairy heifers, there is littl e justification to incorporate timed AI programs when detection of estrus is excellent, above 70%; however, for farms with detection of estrus below 60%, either timed AI for first AI followed by detection of estrus or timed AI alone improve reproductive performance and reduce the cost per pregnancy.(AU)

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RESUMO

During early postpartum, high-producing dairy cows undergo a period of extensive tissue catabolism because of negative nutrien t balance. Homeorrhetic controls assure that nutrients are partitioned to favor lactation at the same time that homeostasis secures survival. However, unrestrained metabolic disturbances often lead to diseases which, in turn, dramatically decrease both productive and reproductive performance. Negative nutrient balance ha s been associated with compromised immune and reproductive functions in dairy cows. Low circulating concentrations of glucose and insulin associated with elevated concentrations of non-esterified fatty acids and ketone bodies postpartum have disruptive and detrimental effects on the oocyte, granulosa and immune cells. Negative nutrient balance is associated with changes in the pattern of ovarian follicle growth which can indirectly affect oocyte quality. Some of this disruption seems to be the result of endocrine and biochemical changes that alter the micro- environment of the growing and maturing oocyte. In addition, cows under negative nutrient balance have extended periods of anovulation. Postpartum anestrus, as well as infertility, is magnified by losses of body condition during the early postpartum period. The underlying mechanism for resumption of ovulatory cycles seems to be associated with metabolic signals and regulatory hormones primarily insulin and insulin- like growth factor (IGF)-1, which link nutritional status with gonadotropin secretion, recoupling of the growth hormone-IGF system, and follicle maturation and ovulation. Feeding diets th at promote increases in plasma glucose and insulin may improve the metabolic and endocrine status of cows in early lactation. Furthermore, fertility in postpartum cows is also determined by uterine health. Reductions in circulating concentrations of Ca and antioxidant vitamins around parturition are also linked with impaired immune competence and result in greater risk of uterine diseases that impair reproduction. Specific nutrients and dietary ingredients have been implicated to affect reproduction in cattle. Excess intake of dietary protein has been suggested as detrimental to fertility, although feeding excess of dietary protein can no longer be justified. Addition of moderate amounts of supplemental fat to the diet improves caloric intake, modulates prostaglandin F2  secretion by the uterus, affects ovarian dynamics, enhances luteal function and embryo quality, and has moderate positive effects on fertility. More specifically, some fatty acids might impact fertilization rate and embryo quality in dairy cows. On the contrary, some dietary ingredients, such as gossypol, when ingested in large quantities decrease fertility of dairy cows because of its negative effects on embryo quality and pregnancy maintenance.(AU)

Assuntos

RESUMO

During early postpartum, high-producing dairy cows undergo a period of extensive tissue catabolism because of negative nutrien t balance. Homeorrhetic controls assure that nutrients are partitioned to favor lactation at the same time that homeostasis secures survival. However, unrestrained metabolic disturbances often lead to diseases which, in turn, dramatically decrease both productive and reproductive performance. Negative nutrient balance ha s been associated with compromised immune and reproductive functions in dairy cows. Low circulating concentrations of glucose and insulin associated with elevated concentrations of non-esterified fatty acids and ketone bodies postpartum have disruptive and detrimental effects on the oocyte, granulosa and immune cells. Negative nutrient balance is associated with changes in the pattern of ovarian follicle growth which can indirectly affect oocyte quality. Some of this disruption seems to be the result of endocrine and biochemical changes that alter the micro- environment of the growing and maturing oocyte. In addition, cows under negative nutrient balance have extended periods of anovulation. Postpartum anestrus, as well as infertility, is magnified by losses of body condition during the early postpartum period. The underlying mechanism for resumption of ovulatory cycles seems to be associated with metabolic signals and regulatory hormones primarily insulin and insulin- like growth factor (IGF)-1, which link nutritional status with gonadotropin secretion, recoupling of the growth hormone-IGF system, and follicle maturation and ovulation. Feeding diets th at promote increases in plasma glucose and insulin may improve the metabolic and endocrine status of cows in early lactation. Furthermore, fertility in postpartum cows is also determined by uterine health. Reductions in circulating concentrations of Ca and antioxidant vitamins around parturition are also linked with impaired immune competence and result in greater risk of uterine diseases that impair reproduction. Specific nutrients and dietary ingredients have been implicated to affect reproduction in cattle. Excess intake of dietary protein has been suggested as detrimental to fertility, although feeding excess of dietary protein can no longer be justified. Addition of moderate amounts of supplemental fat to the diet improves caloric intake, modulates prostaglandin F2  secretion by the uterus, affects ovarian dynamics, enhances luteal function and embryo quality, and has moderate positive effects on fertility. More specifically, some fatty acids might impact fertilization rate and embryo quality in dairy cows. On the contrary, some dietary ingredients, such as gossypol, when ingested in large quantities decrease fertility of dairy cows because of its negative effects on embryo quality and pregnancy maintenance.

Assuntos

RESUMO

Reproduction continues to be a critical component to maintain a dairy farm economically viable. For every farm and for every cow, there is an optimum time for pregnancy, which is mostly influenced by level of production, persistency of lactation, and parity. In general, as production decreases, lactation number increases, and persistency of lactation decreases, cows should be bred sooner postpartum and pregnancy obtained early in lactation. The voluntary waiting period is determined based on the desired interval postpartum to pregnancy and the pregnancy rate of the farm. As pregnancy rates increase, the voluntary waiting period can be delayed, particularly when milk production is high. Studies in the literature have compared several breeding strategies to obtain a pregnant cow. In general, pregnancies obtained by artificial insemination are cheaper than those originated by natural service. The major reason is that AI programs result in similar or better reproductive performance and are cheaper to implement than natural service programs because of the high costs of acquiring and feeding bulls. Within the AI program, those that incorporate timed AI for first insemination followed by detection of estrus result in lowest median days open and more profit per cow, and the benefits of improving reproduction are greater when milk prices ar e low. The use of embryo technologies as a breeding program for lactating dairy cows, with the aim to improve reproductive performance, is only attractive when the differential in fertility relative to AI is large. In most cases, AI programs have to result in very poor fertility (<15%) for the typical results from embryo transfer (40-45% pregnancy) to be economically attractive at current costs. For dairy heifers, there is littl e justification to incorporate timed AI programs when detection of estrus is excellent, above 70%; however, for farms with detection of estrus below 60%, either timed AI for first AI followed by detection of estrus or timed AI alone improve reproductive performance and reduce the cost per pregnancy.

Assuntos

RESUMO

The relationship between the level of cell confluence near the plateau phase of growth and blastocyst yield following somatic cell cloning is not well understood. We examined the effect of distinct cell culture confluence levels on in vitro development of cloned bovine embryos. In vitro-matured bovine oocytes were manually bisected and selected by DNA staining. One or two enucleated hemi-cytoplasts were paired and fused with an adult skin somatic cell. Cultured skin cells from an adult Nellore cow harvested at three distinct culture confluence levels (70-80, 80-90, and >95%) were used for construction of embryos and hemi-embryos. After activation, structures were cultured in vitro as one embryo (1 x 100%) or as aggregates of two hemi-embryos (2 x 50%) per microwell. Fusion, cleavage and blastocyst rates were compared using the chi(2) test. The fusion rate for hemi-embryos (51.4%) was lower than for embryos (67.6%), with no influence of degree of cell confluence. However, blastocyst rates improved linearly (7.0, 17.5, and 29.4%) with increases in cell confluence. We conclude that degree of cell culture confluence significantly influences subsequent embryo development; use of a cell population in high confluence (>90%) for nuclear transfer significantly improved blastocyst yield after cloning.

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