Browsing by Subject "reproduction"
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Item Demographic and trophic dynamics of fishes in relation to hydrologic variation in channel and floodplain habitats of the Brazos River, Texas.(2009-06-02) Zeug, Steven ChristopherLarge rivers in North America have been subjected to a variety of hydrologic alterations that have negatively impacted aquatic fauna. These impacts have triggered restoration efforts, including management of flows, to restore or maintain ecological integrity. Ecological data relevant to flow management and habitat restoration is scarce, and conceptual models of ecosystem function have been widely applied to large rivers despite a lack of quantitative evaluation of these models. Here, I examine demographic and trophic dynamics of fishes with divergent life histories and trophic guilds in relation to habitat heterogeneity and flow variability in a relatively unaltered floodplain system: the Brazos River, Texas. Reproductive activity of fishes with three divergent life history strategies was positively associated with long-term river hydrology, although species with alternate strategies exploited different portions of the hydrograph (peak flow versus increasing flow). Despite the positive association with hydrology, low-flow periods were favorable for recruitment, and food resources for larvae and juveniles were denser during these periods. Some species used both oxbow and channel habitats during some point in their life cycle, whereas other species appeared to be almost entirely restricted to one habitat type. Terrestrial C3 macrophytes accounted for a significant fraction of the biomass of most consumer species examined. Small-bodied species in oxbow lakes assimilated large fractions of biomass from benthic algae, whereas this pattern was not observed in the river channel. Frequent flow variations in the river channel may reduce algal standing stocks, and significant contributions from autochthonous algal sources may only occur during low-flow periods. Trophic positions of detritivores indicated that terrestrial carbon sources were assimilated, for the most part, via invertebrates rather than by direct consumption. My results indicate that current conceptual models are too vague to provide accurate predictions for restoration strategies in rivers with variable flow regimes. Flow and habitat management strategies that focus on reproducing key features of historical fluvial dynamics are likely to be more successful than strategies that focus on single indicator species or flow dynamics that differ from the historical hydrograph.Item Effects of exercise or oocyte heat shock on embryo development and gene expression in the horse(2009-05-15) Mortensen, Christopher JohnHorse owners commonly maintain their broodmares in training and competition during the breeding season. The effect this has on mare reproductive efficiency has received limited attention. Heat stress has shown to be detrimental to oocyte competence in other species and heat shock protein 70 has been shown to be an important gene in regulating cellular response to heat. Mares were exercised in a hot humid environment to determine the effects on reproductive efficiency. Embryos were collected at d 7 after ovulation from exercised and control mares. Oocyte developmental competence was measured after oocytes were subjected to a one time heat shock, 42 ?C for 2 or 4 h, at the onset or near completion of in vitro maturation. Embryos from both previous experiments were examined for HSP70 gene expression by real time RT-PCR. Exercised mares ovulated significantly smaller follicles, 39.8 vs. 41.5 mm diameter, and ovulated later after being given PGF2?, 8.5 vs. 9.2 d. Twenty-two embryos (22/35) were recovered from control mares, recovery rate of 63%. Significantly fewer embryos were recovered in exercised mares (11/32), recovery rate of 34%. A lower proportion of grade 1 embryos were recovered from exercised versus control mares (4/11 vs.16/22,respectively). No effect was observed on oocyte nuclear maturation or embryonic development after ICSI when oocytes were exposed to heat shock at the onset of IVM. A heat shock of 42 ?C for 2 or 4 h on oocytes during late IVM resulted, however, in a significantly lower rate of nuclear maturation, and a significant decrease in advanced embryo development (morulae plus blastocysts). Heat shock protein 70 gene expression was shown to be related to quality score of in vivo-recovered embryos, with lower quality embryos recording a significantly higher relative expression. Heat shock of late stage IVM oocytes for 4 h resulted in significantly higher blastocyst HSP70 expression. Results of this study indicate that exercise in a hot humid environment is detrimental to mare reproductive efficiency, late-stage maturing oocytes are sensitive to heat, and HSP70 expression in equine embryos is related to embryo quality score and oocyte quality.Item Evaluation of Postpartum Reproductive Performance in Brahman Females with Divergent Residual Feed Intake(2011-10-21) Poovey, Anna KathrynThese studies were designed to evaluate the relationships that exist between residual feed intake, parity, rate of return to estrous cyclicity and nonesterified fatty acid (NEFA) concentrations, as well as changes in both body weight (BW) and body condition score (BCS) during the prepartum and postpartum time periods in Brahman females. Residual feed intake classification was evaluated for all females during the course of 70-d trials conducted prior to these experiments. Heifers (n = 30) and cows (n = 63) were evaluated for BW and BCS, as well as by collection of weekly blood samples beginning five weeks prior to calving. Blood serum samples were utilized to assay for NEFA concentrations by enzymatic colorimetry both pre- and postpartum. Multiparous females (n = 44) were sampled weekly for five weeks following parturition. Beginning 28d postpartum, weekly blood samples were collected and assayed for progesterone concentrations by radioimmunoassay to determine return to estrous cyclicity. Following calving, females were exposed to epididymectomized bulls fitted with chin-ball markers to aid in estrus detection. After detection, estrus females were evaluated for presence of a corpus luteum by trans-rectal ultrasonography. Prepartum, it was found that inefficient females had a greater BCS than efficient females (P < 0.05), significant BW changes occurred during the sampling period (P < 0.05) and moderate to low correlations existed between BW and BCS. Additionally, it was found that the interaction between RFI x parity had a significant affect upon NEFA concentrations, BW and BCS (P < 0.05). During the postpartum period it was found that efficient females were lower in both BW and BCS (P < 0.05), no change occurred over time in NEFA concentrations (P > 0.1) and a greater pregnancy rate was achieved in efficient females, as well as in females that returned to estrous cyclicity rapidly (< 90d) following calving.Item Evaluation of udder and teat characteristics, calf growth, and reproduction in young Bos indicus-Bos taurus cows(Texas A&M University, 2008-10-10) Gladney, Cody JackSire and family effects were evaluated for calf growth, udder and teat conformation, and reproduction traits in 2- to 4- yr-old cows from the McGregor Genomics Project. Cows were produced by embryo transfer (ET) and natural service (NS) from the same 4 F1 Nellore-Angus sires, and were analyzed separately. Sire of cow was significant for calf birth weight (P = 0.014) among ET cows, but not NS cows. Among NS families, calves from cows out of Brahman-Hereford dams were 2.0 kg heavier (P = 0.064) at birth than calves from cows out of Brahman-Angus dams. Sire of cow accounted for variation in weaning weight (P = 0.006) and preweaning ADG (P = 0.005) of calves from ET dams, but not NS dams. Family nested within sire also accounted for variation (P = 0.061) in weaning weights of calves from ET dams. Sire of cow was significant for average teat length in ET (P < 0.001) and NS (P = 0.013) cows. Sire of cow was significant for average teat diameter (P = 0.022) among NS cows. Sire of cow also affected udder support score (P = 0.002), cow disposition at calf birth (P = 0.002), and cow weight at weaning (P = 0.045) in ET cows. Family and cow age also accounted for variation in cow disposition at calf birth (P = 0.015, P = 0.041, respectively) and cow weight at weaning (P = 0.001, P < .001, respectively) among ET cows. Calf year of birth also affected (P < .001) cow weight at weaning among ET cows. For NS dams, calf year of birth (P = 0.012), cow age (P < .001), and parity nested within cow age (P = 0.005) affected cow weight at weaning. Although reproduction data were not formally analyzed, there appear to be substantial differences for calving rate and average calving date among these cow families. Data from this project will be used for identification of genetic markers for these cow productivity traits.Item Influence of Bull Traits and Bull to Female Ratio on Reproductive Perfromance in Beef Females and of Nutrition During Gestation on Calving Difficulty in Primiparous Beef Females(2011-08-08) Bloomberg, Blake DavidThe current study involved two experiments that were conducted at the Texas A&M AgriLife Research and Extension Center in Uvalde, TX (semi-arid environment) from 2006 to 2008. In experiment one, Bonsmara bulls ( n = 39; 20-24 mo of age) were joined with multiparous Bonsmara and Bonsmara-influenced females (n = 1013) during a 90-day breeding season in 2006, 2007, and 2008 to quantify the effects of a reduction in bull to female ratio on reproductive performance. Bulls were also placed with primiparous beef females ( n = 142). Bulls were allotted by selected physical traits, social rank, serving capacity, and seminal traits to one of two bull to female (BFR) treatments: Low (1:30-1:45; n = 10 pastures) or Conventional (1:16-1:26; n = 12 pastures) BFR. Pregnancy rate (P = 0.36), calving date (P = 0.24), and calving rate (P = 0.25) did not differ between Conventional and Low BFR treatments. The current experiment demonstrates that Low BFR can be utilized in breeding pastures of up to 2,090 ha without negatively affecting reproductive performance. In experiment two, Bonsmara heifers (3/4, 7/8, and full bloods) were exposed to Bonsmara bulls from April 15 to July 15 during each of the two years. Heifers were weighed, rectally palpated for pregnancy, and scored for BCS (1 thin - 9 fat) and frame score (1 short - 9 tall) in December (end of second trimester) during years 1 and 2. Heifers were stratified on expected calving date and randomly allotted to one of two levels of nutrition for the remainder of gestation. In year 1, heifers were allotted to range forage (n=31, low nutrition, LN) or to non-irrigated oat pasture (n=31, high nutrition, HN). In year 2, heifers were placed onto the same range environment as in year 1 (n=31, LN) or onto irrigated ryegrass pasture (n=31,HN). Heifers in the LN groups were supplemented with 20% CP cubes at the rate of 0.9 kg/heifer/day from January 2 until calving while HN heifers were not supplemented. Within 4 hr of birth, calves were weighed, and calf vigor and calving difficulty scores were recorded. Heifers were weighed within 72 hours of parturition. From treatment initiation through calving, HN heifers gained 48.6 kg whereas the LN females lost 15 kg. Twice as many HN heifers required major assistance at calving as compared to LN heifers. Calves born to the HN females weighed 3.7 kg more at birth than those born to LN females. These differences resulted in HN heifers having (P = 0.005) more calving difficulty than LN heifers (mean calving difficutly of 2.3 for HN and 1.6 for LN). The calves of the HN females were also less vigorous (P = 0.005) after birth than the calves from LN females (calf vigor score of 2.2 for HN and 3.3 for LN). Consequently, the level of nutrition during the third trimester of gestation can affect calving difficulty, calf vigor, and female weight.Item Interactive Roles of Gonadotropin-Releasing Hormone and RF-Amide Related Peptide 3 in Adenohypophyseal Physiology and Reporduction in the Mare(2013-01-28) Thorson, Jennifer FrancesThe seasonal termination of ovarian cycles in mares initiated near the time of the autumnal equinox is a significant managerial issue for horse breeders world-wide. Studies presented herein had two over-arching aims. In Aim I, objectives were to develop the principals needed to apply gonadotropin-releasing hormone (GnRH) therapeutics for routinely establishing pregnancies in the winter anovulatory mare. We first tested the hypothesis that continuous administration of native GnRH, beginning in either early February or March, would induce ovulation without reversion to an anovulatory state following treatment withdrawal. Continuous 28-d treatments elevated circulating luteinizing hormone (LH) and stimulated spontaneous ovulation much earlier than controls. However, mares treated only in February ceased ovarian cycles at termination of treatment. In contrast, mares administered GnRH in March continued to exhibit estrous cycles. Thus, we concluded that GnRH treatment must continue through March to ensure continued escape from winter anovulation. We then tested the hypothesis that the Julian day of conception could be accelerated in winter anovulatory mares treated continuously with native GnRH for 56 d beginning on February 1. Indeed, GnRH treatment caused a marked increase in the frequency of pregnancy compared to controls. Data illustrated that continuous administration of native GnRH is a practical and highly efficient option for managing seasonal anovulation. In Aim II, we examined hypothalamic distribution, adenohyphyseal receptor gene expression, and ligand functionality of RFRP3 in the mare during the breeding and non-breeding seasons. Hypothalamic RFRP3 mRNA was detected in the mare; however, neither hypothalamic expression of RFRP3 nor its anterior pituitary receptor differed between reproductive states. We then used equine adenohypophyseal cell culture to test the hypothesis that RFRP3 reduces the responsiveness of the equine gonadotrope to GnRH. Addition of RFRP3 to cell culture failed to counter the effects of GnRH. Finally, the effects of a RFRP3 receptor-signaling antagonist (RF9) were examined in winter anovulatory mares. A robust increase in circulating concentrations of LH relative to controls was observed in response to RF9 treatments, but treatments had no effect on adenohypophyseal responsiveness to GnRH. Data provide indirect evidence that antagonism of the RFRP3 system by RF9 may be at the GnRH neuronal level.Item Plasma Concentrations of Testosterone, Luteinizing Hormone, and Estrone Sulfate in Stallions Following Hemicastration(2013-11-25) Valdez, RaulHemicastration is a veterinary surgical procedure in stallions and may be needed for removal of a diseased testicle. The effects of hemicastration on the neuroendocrine system and the hormonal response of the remaining testicle are unclear. In this study, blood plasma concentrations of testosterone, luteinizing hormone, and estrone sulfate were assessed following hemicastration. Miniature stallions (n=8) were used in this study and blood was drawn 7 d prior to hemicastration, and 12 h, 48 h, 14 d, 30 d, and 90 d post hemicastration. Blood samples from all stallions were drawn every 15 min (0, 15, 30, 45, 60 min) for 1 h each sampling period. Plasma was analyzed by RIA for concentrations of testosterone, luteinizing hormone, and estrone sulfate. Compared to pre-surgerical concentrations, plasma luteinizing hormone at 12 h, 48 h, 14 d and 60 d were greater (P < 0.05). Compared to 12 h, plasma testosterone values at 48 h, 14 d, and 60 d were higher (P < 0.05). Compared to pre-hemicastration values, plasma concentrations of estrone sulfate were lower (P < 0.05) at all time periods, but tended to increase up to 60 d. After 30 d, stallions were housed together rather than individually creating a harem group. Luteinizing hormone and testosterone values increased dramatically compared to previous time periods following the housing modification. These results provide insight to better understand the hormonal profiles and compensatory response of the remaining testicle following hemicastration.Item The influence of tropical adaptation and breedtype on adrenal and testicular function in beef bulls(Texas A&M University, 2005-08-29) Koch, Jeffrey WilliamBulls of various breedtypes including Angus (Bos taurus), Bonsmara (Sanga X Bos taurus), Brahman (Bos indicus), Romosinuano (Criollo), Tuli (Sanga) and Wagyu (Japanese Bos taurus) were utilized to evaluate the influence of tropical adaptation on adrenal and testicular function. The objectives were to determine if tropical adaptation influenced: a) response to management stressors, b) organ and gland weights, adrenal and testis StAR and P450 content and total adrenal, medullary and cortical areas, c) basal and hCG-induced testosterone and d) testis and epididymal sperm concentrations. Blood samples were obtained within 5 min before and after transportation and during restraint every 15 min for 6 h to evaluate cortical response. Angus, Brahman and Romosinuano bulls were slaughtered following sexual maturity. Cortical responses to transportation and restraint were not influenced by tropical adaptation. Response to these stressors could be categorized into high responders (Angus, Brahman), intermediate responders (Romosinuano, Tuli) and low responders (Wagyu, Bonsmara). Tropically-adapted breedtypes were not categorized into a single group; therefore, cortical responses to management stressors were influenced by breedtype, but not by tropical adaptation. Most organ and gland weights (actual weight and weight corrected for BW) and the steroid precursors, StAR and P450, were not influenced by tropical adaptation, but were by breedtype. Paired adrenal gland weight, total adrenal area, medullary and cortical areas were influenced by tropical adaptation. Tropically-adapted breedtypes had lighter glands and smaller areas than the temperate Bos taurus breedtypes. All breedtypes except Wagyu had similar basal concentrations of plasma testosterone prior to hCG administration; therefore, basal testosterone was not influenced by tropical adaptation, but only by breedtype. Wagyu had greater basal concentrations of testosterone than other breedtypes. Testosterone concentrations following hCG administration was similar between adaptation groups and breedtypes. As expected, testis and epididymal sperm concentrations were influenced by tropical adaptation. Tropically-adapted breedtypes had greater testicular and epididymal sperm concentrations than the temperate Bos taurus breedtypes during the summer months. In summary, adrenal weight and area and testicular and epididymal sperm concentrations were influenced by tropical adaptation. Cortical response to management stressors, basal testosterone and StAR and P450 content were influenced by breedtype, not tropical adaptation.