巴美肉羊发情期外周血E2和P4浓度变化规律与排卵数关系研究

绵羊在发情周期中各生殖激素浓度变化与卵泡发育、成熟和排卵有着密切的关系。为了研究巴美肉羊血清生殖激素的动态变化及其与排卵数关系,试验采用电化学法,测定了12只成年母羊发情期血清中2种类固醇激素(E₂和P₄)的浓度水平,分析其动态变化规律,并用SAS 9.0的方差分析程序分析激素浓度与排卵数的关系。结果表明,两种激素在排单卵组和排双卵组绵羊间变化规律不同,E₂在排单卵组表现为先下降后升高的变化趋势,在排双卵组表现为持续下降趋势;P₄在排单卵组表现为持续上升的趋势,在排双卵组为先上升后下降的变化趋势。排单卵和排双卵组绵羊在各时间点的E₂和P₄激素浓度差异均不显著(P＞0.05)。     

Influence of mare uterine tubal fluids on the metabolism of stallion sperm.

Three experiments were conducted on the metabolism of stallion sperm. In experiment 1, whole and washed sperm were incubated under aerobic and anaerobic enviroments and analyzed before and after controlled incubation for motility, pH, lactic acid, glucose, fructose, and O2 comsumption. In experiment 2, whole and washed sperm were incubated aerobically and anaerobically with and without uterine tubal fluids. Experiment 3 was the same as experiment 2, except added substrates of glucose and lactic acid were studied. The same examinations were made in experiments 2 and 3 as for experiment 1. Motility decreased significantly during incubation for all treatments, with the greatest decrease occurring for whole semen where only trace amounts of substrate (fructose) were present. Exogenous glucose plus uterine tubal fluid maintained sperm motility better than did added lactate. However, sperm respiration rates were highest when exogenous lactate was the only substrate in the incubation medium. The mean pH values for gel-free stallion semen at the start of controlled aerobic and anaerobic incubation were 7.08 and 7.34. Lactic acid accummulation for 1 hour increased from 0.05 mg to 0.09 mg/10(9) sperm when uterine tubal fluid was added to the incubation medium. Washed spermatozoa incubated in 0.03 M glucose plus uterine tubal fluid utilized less glucose than did sperm incubated in the glucose medium. These results, along with the increased oxygen utilization (ZO2) values produced by adding uterine tubal fluid to the incubation mediums, might indicate utilization of a uterine tubal substrate. Added uterine tubal fluid resulted in increased ZO2 values (expressed in mul of O2 utilized by 10(8) sperm in 1 hour at 37 C) for whole semen from 10.45 to 12.63. Washed spermatozoa also respired at a significantly greater rate than whole sperm. Respiration rates were greater for sperm incubated with 0.01 M lactic acid than for any other substrate or experiment.     

Conservation of Pattern and Process: Developing an Alternative Paradigm of Rangeland Management

This article examines the question of how well the rangeland management profession has served conservation of patterns and processes that support multiple ecosystem services. We examine the paradigms under which rangeland management operates and argue that our profession developed under the utilitarian paradigm with the primary goals of sustainable forage for livestock production. While optimization of multiple rangeland products and services has always been a consideration, a comprehensive set of principles have not be been developed to advance this concept. We argue that fire and grazing, often viewed as mere tools used for production goals, should rather be viewed as essential ecosystem processes. Rangeland management continues to operate under the utilitarian paradigm appropriate to societal values of the 20th century and by and large has failed to provide management guidance to reverse degradation of several highly valued ecosystem services. We support this argument with evidence that biodiversity has declined on rangelands in the past half century and that much of this decline is due to management goals that favor a narrow suite of species. The full suite of ecosystem services valued by society will only benefit by management for heterogeneity, which implies that there is no one goal for management and that landscape-level planning is crucial. Explicitly incorporating heterogeneity into state-and-transition models is an important advancement not yet achieved by our profession. We present new principles for rangeland management formed on the basis of conservation of pattern and process. While recognizing that many rangelands have significant deviations from historic plant communities and disturbance regimes, we suggest that management for conservation of pattern and process should focus on fire and grazing to the extent possible to promote a shifting mosaic across large landscapes that include patches that are highly variable in the amount of disturbance rather than the current goal of uniform moderate disturbance.     

Contrasting Preference for Grassland Landscapes Among Population Groups in the Central and Southern Great Plains

Recent opposition to the rangeland management paradigm of achieving uniform, moderate grazing across entire landscapes has emerged because heterogeneity is recognized as the foundation of biodiversity, ecosystem resilience, and multifunctionality of agricultural landscapes. Agriculture production goals appear to drive the traditional rangeland management focus on homogeneity and uniformity. To determine if preference for homogeneity is a broadly applicable social construct or one limited to agricultural producers, we determined preferences for heterogeneous grassland landscapes expressed by three study populations—managers of working lands (ranchers), natural resource professionals (grassland/rangeland specialists), and the general population living in rangeland regions within the US Great Plains. We distributed surveys that included photographs of landscapes and patterned images to assess preference. Preference for heterogeneous landscapes among ranchers, natural resource professionals, and the general population in our study area were generally consistent with the central paradigm of managing rangeland for homogeneity. However, we discovered that people, across geographic location and population group, clearly prefer heterogeneous patterned images to homogeneous patterned images. This suggests that preference for homogeneity is acquired.     

Effects of Ω-3 (n-3) Fatty Acid Supplementation on Insulin Sensitivity in Horses

The objective of this study was to examine the effects of dietary ω-3 fatty acid supplementation on insulin sensitivity (SI) in horses. Twenty-one mares were blocked by age, body weight (BW), and body condition score (BCS) and randomly assigned to one of three dietary treatments. Treatments consisted of (1) 38 g of n-3 fatty acids via fish and algae supplement and diet (MARINE), (2) 38 g of n-3 fatty acids via a flaxseed meal from the supplement and diet (FLAX), and (3) control (CON) no supplemental fatty acid. Treatments were supplemented for 90 days. Frequent sampling intravenous glucose tolerance tests were performed on days 0, 30, 60, and 90. Blood samples were analyzed for glucose and insulin. The minimal model was applied for the glucose and insulin curves using MinMod Millennium. SI increased 39% (P < .007) across all treatment groups. Acute insulin response to glucose decreased 22% (P < .006) between days 30 and 60 and increased (P = .040) again at day 90. Disposition index (combined SI and β pancreatic response) increased (P = .03) by 53% in the MARINE- and 48% in the FLAX-supplemented horses and did not change with time in the CON group. In insulin-resistant mares, MARINE- and FLAX-treated horses had an increase in SI (P = .09). It would be interesting to test this supplement in a larger group of insulin-resistant horses. If proven effective, supplementation with ω-3 fatty acids would help to reduce problems associated with insulin resistance in horses.     

Foodfish Production Strategies Using 13‐cm and 19‐cm Hybrid Catfish, ♀Ictalurus punctatus × ♂Ictalurus furcatus

Most hybrid catfish, ♀Ictalurus punctatus × ♂Ictalurus furcatus, producers stock 18‐ to 19‐cm fingerlings in single‐batch production. While stocking smaller fingerlings would be less expensive, the economic trade‐offs of using smaller fingerlings is unknown. Two sizes of hybrid catfish fingerlings (13‐cm and 19‐cm) were stocked in single‐size treatments at 9884 head/ha and a multi‐size treatment with each size stocked at 9884 head/ha (total 19,768 head/ha). In the 13‐cm and 19‐cm single‐size treatments, 87 and 98%, respectively, reached market size in one season. In the multi‐size treatment, 77% of all fish stocked reached market size, demonstrating that more than half of the 13‐cm fish reached market size in this treatment. Gross, net, and marketable yields were significantly greater in the multi‐size treatment when compared to the 13‐cm or 19‐cm single‐size treatments, but were not significantly different between the two single‐size treatments. The 19‐cm single‐size treatment resulted in greater break‐even prices and economic risk than the other two treatments. This study demonstrated that 13‐cm hybrid catfish fingerlings can be raised economically in both single‐ and multi‐size production systems in the southern USA.     

Effects of ractopamine supplementation and postmortem aging on longissimus muscle palatability of beef steers differing in biological type

Effects of ractopamine hydrochloride (RAC) supplementation and postmortem aging on palatability of beef from steers differing in biological type were evaluated using LM samples from British, Continental crossbred, and Brahman crossbred calf-fed steers (n = 98/type). Equal numbers of steers within each type were assigned to treatments of 0 or 200 mg.steer(-1).d(-1) of RAC fed during the final 28 d of the finishing period. Warner-Bratzler shear force (WBSF) was measured at 3, 7, 14, and 21 d postmortem, and trained sensory panel (TP) evaluation was conducted using LM samples aged for 14 d postmortem. A RAC x type interaction (P = 0.006) was detected for WBSF. Within each type, steers fed RAC produced steaks with greater (P < 0.05) WBSF values than steaks from control steers; however, the magnitude of the effect of RAC on WBSF was more pronounced among Brahman cross-breds (5.53 vs. 4.96 +/- 0.10 kg) than among Continental crossbred (4.16 vs. 3.96 +/- 0.10 kg) and British steers (4.10 vs. 3.75 +/- 0.10 kg). The effect of RAC on WBSF, though diminished slightly by aging (mean WBSF difference: 3 d = 0.49 kg; 21 d = 0.24 kg), was not completely mitigated by 21 d of postmortem storage (P(RAC x AGE) = 0.16). Steers fed RAC produced steaks that received lower (P < 0.05) TP ratings for tenderness (8.09 vs. 8.95 +/- 0.18) and juiciness (7.41 vs. 8.07 +/- 0.16 kg), along with slightly lower (P = 0.06) ratings for beef flavor (6.67 vs. 6.93 +/- 0.10 kg), compared with steaks from unsupplemented steers, regardless of biological type. Among the 3 biological types, Brahman crossbred cattle produced steaks with the greatest (P < 0.05) WBSF values at each aging period; WBSF values for steaks from British and Continental type steers did not differ (P > 0.05) at any aging time. Sensory panel ratings of tenderness, juiciness, and beef flavor were greatest (P < 0.05) for steaks from British steers, and least (P < 0.05) for steaks produced by Brahman-type steers. Results from this study suggest that RAC supplementation slightly decreases LM tenderness (WBSF and TP) of British, Continental crossbred, and Brahman cross-bred steers, and that the effect of RAC on WBSF may be more pronounced in steaks from Brahman crossbred cattle than among stenks from Continental type or British steers.     

The Expanding Role of Recombinant Gonadotropins in Assisted Reproduction

Using recombinant gonadotropins for assisted reproduction of domestic species is still in its infancy. Yet, the purity, potency and pathogen-free nature of recombinant gonadotropins make them attractive alternatives to tissue-derived gonadotropic agents. In this study, the authors summarize the work to date using recombinant gonadotropins to enhance the - fertility of domestic animals and they discussed their recent studies examining the biopotency of single chain analogues of human gonadotropins. In these studies, single chain analogues of follicle stimulating hormone (Fcα), chorionic gonadotropin (CGβα) or a gonadotropin construct with dual activity (FcCGβα) were administered to sheep pre-treated with antisera directed against GnRH. Ovulation was induced 3 days after analogue administration using hCG (1000 IU, iv). Although Fcα or CGβα alone induced only modest oestradiol production during the pre-hCG period, serum concentrations of oestradiol were markedly increased (p < 0.05) 3 days after administration of FcCGβα or the Fcα + CGβα combination. Final ovarian weight was significantly increased (p < 0.05) in animals receiving Fcα, Fcα + CGβα or FcCGβα. Collectively, these observations demonstrate that the single chain analogues of the human gonadotropins are active in sheep.     

Effects of heifer finishing implants on beef carcass traits and longissimus tenderness

Effects of finishing implants on heifer carcass characteristics and LM Warner-Bratzler shear force (WBSF) were investigated using commercially fed Continental x British heifers (n = 500). Heifers were blocked by initial BW (block 1, BW > or = 340 kg; block 2, BW < 340 kg) and assigned randomly to 12 treatments that utilized 0, 1, or 2 finishing implants to deliver cumulative dosages of trenbolone acetate (TBA) and estradiol 17-beta (E2) ranging from 0 to 400 mg of TBA and 0 to 40 mg of E2 during the finishing period. Heifers in blocks 1 and 2 were slaughtered after 135 and 149 d on feed, respectively. At these endpoints, the treatment groups did not differ (P > 0.05) in adjusted fat thickness or predicted percentage of empty body fat. Compared with a nonimplanted control, implanting heifers once during finishing increased (P = 0.025) HCW by an average of 7.9 kg without affecting the mean marbling score, the percentage of carcasses grading Choice and Prime, or LM WBSF values. Compared with the use of 1 implant, the use of 2 finishing implants resulted in an additional increase (P = 0.008) in HCW of 6.0 kg. Reimplanting also increased (P < 0.001) LM area, reduced (P = 0.024) the percentage of KPH, and improved (P = 0.004) mean yield grade. However, reimplanted heifers produced a lower (P = 0.044) percentage of carcasses grading Choice and Prime and LM steaks with greater (P < 0.05) WBSF values at all postmortem aging times compared with heifers that were implanted once. Among heifers receiving 2 implants, mean 14-d LM WBSF increased linearly (P < 0.05) as the cumulative, combined dosage of E2 plus TBA increased. Heifers implanted with a combination of E2 plus TBA had larger (P = 0.046) LM areas, lower (P = 0.004) mean marbling scores, and greater LM WBSF values after 3 d (P = 0.001), 7 d (P = 0.001), 14 d (P = 0.003), and 21 d (P = 0.045) of postmortem aging than did heifers implanted with TBA alone. Heifers that received combination implants containing both E2 and TBA also produced fewer (P = 0.005) carcasses with marbling scores of modest or greater compared with heifers that received single-ingredient implants containing TBA alone. Implant treatment effects on LM WBSF gradually diminished as the length of the postmortem aging period increased. Postmortem aging periods of 14 to 28 d were effective for mitigating the detrimental effects of mild or moderately aggressive heifer implant programs on the predicted consumer acceptability of LM steaks.     

A Comprehensive Genotype and Environment Assessment of Wheat Grain Ash Content in Oregon and Washington: Analysis of Variation

A comprehensive analysis of the variation in wheat grain ash content has not been previously conducted. This study assessed the relative contribution of genotype and environment to variation in ash content, with a particular aim of ascertaining the potential for manipulating the trait using contemporary adapted germplasm. A total of 2,240 samples were drawn from four years of multilocation field plots grown in the wheat production areas of Oregon and Washington states. Genotypes included commercial cultivars and advanced breeding lines of soft and hard winter, and soft and hard spring wheats with red and white kernel color, several soft white club wheats, and one soft white spring waxy wheat cultivar. In addition to ash, protein content, test weight, and Single Kernel Characterization System kernel hardness, weight and size were also measured. In total, 20 separate fully balanced ANOVA results were conducted. Whole model R² values were highly significant, 0.62–0.91. Nineteen of the 20 ANOVA results indicated significant genotype effects, but the effects were not large. In contrast, environment effects were always highly significant with F values often one to two orders of magnitude larger than the genotype F values. The grand mean for all samples was 1.368% ash. For individual data sets, genotype means across environments varied ≈0.1–0.3% ash. The genotypes judged noteworthy because they had the highest least squares mean ash content were OR9900553 and ClearFirst soft white winter, NuHills hard red winter, Waxy‐Pen and Cataldo soft white spring, and WA8010 and Lochsa hard spring wheats. Genotypes with lowest least squares mean ash were Edwin (club) soft white winter, OR2040073H hard red winter, WA7952 soft white spring, and WA8038 hard spring wheats. In conclusion, wheat grain ash is more greatly influenced by crop year and location than by genotype. However, sufficient genotype variation is present to plausibly manipulate this grain trait through traditional plant breeding.