Comparison of Gonadotropin-Releasing Hormone versus Estrogen-Based Fixed-Time Artificial Insemination Protocols in Grazing Bos taurus Suckled Beef Cows

Fixed-timed artificial insemination (FTAI) protocols for beef cattle in South America are primarily based on estradiol esters and intravaginal progesterone-releasing devices (IVPD). The objective of this study was to determine the optimal gonadotropin-releasing hormone (GnRH)-based protocol as an alternative to the use of estrogen-based protocols in grazing Bos taurus suckling beef cows. All cows received an IVPD on the day of protocol initiation and prostaglandin F2α (PG) plus equine chorionic gonadotropin (eCG) treatments at the time of IVPD removal. In Experiment 1, cows (n = 235) were randomly assigned to one of four treatments: (i) 7-day estradiol = 2 mg of estradiol benzoate (EB) at IVPD insertion on Day 9 and 1 mg of estradiol cypionate (ECP) at IVPD removal on Day 2; (ii) 7-day GnRH = 10 µg of GnRH at IVPD insertion on Day 10, IVPD removal on Day 3 and GnRH at FTAI; (iii) 7 & 7 estradiol = PG at IVPD insertion on Day 16, EB on Day 9 and ECP at IVPD removal on Day 2; (iv) 7 & 7 GnRH = PG at IVPD insertion on Day 17, GnRH on Day 10, IVPD removal on Day 3 and GnRH at FTAI. In Experiment 2, cows (n = 462) were randomly assigned to one of four treatments: (i) 6-day estradiol = EB at IVPD insertion on Day 9, IVPD removal on Day 3 and GnRH at FTAI; (ii) 7-day estradiol; (iii) 7-day GnRH; (iv) 7 & 7 GnRH. In Experiment 1, plasma progesterone concentrations and percentage of cows with a corpus luteum (CL) at IVPD removal, and pregnancy per AI (P/AI) were greater for cows subjected to GnRH-based protocols compared with cows subjected to estrogen-based protocols (p < 0.01). In Experiment 2, cows subjected to the 7 & 7 GnRH protocol had the greatest P/AI (p < 0.01). In summary, GnRH-based FTAI protocols resulted in similar or greater P/AI compared to estrogen-based FTAI protocols in grazing postpartum Bos taurus suckled beef cows. The greatest P/AI was attained with the 7 & 7 GnRH protocol.

Transvaginal ultrasound-guided oocyte retrieval in cattle: State-of-the-art and its impact on the in vitro fertilization embryo production outcome

Transvaginal ultrasound-guided oocyte retrieval (commonly called OPU) and in vitro embryo production (IVP) in cattle has shown significant progress in recent years, in part, as a result of a better understanding of the full potential of these tools by end users. The combination of OPU and IVP (OPU-IVP) has been successfully and widely commercially used worldwide. The main advantages are a greater number of embryos and pregnancies per unit of time, faster genetic progress due to donor quick turn around and more elite sires mating combinations, larger spectrum of female age (calves, prepuberal, heifer, cow) and condition (open, pregnant) from which to retrieve oocytes, a reduced number of sperm (even sexed) required to fertilize the oocytes, among other benefits. OPU-IVP requires significant less donor preparation in comparison to conventional embryo transfer (<50% of usual FSH injections needed) to the extent of no stimulating hormones (FSH) are necessary. Donor synchronization, stimulation, OPU technique, oocyte competence, embryo performance, and its impact on cryopreservation and pregnancy are discussed.

Effect of pterostilbene on development, equatorial lipid accumulation and reactive oxygen species production of in vitro-produced bovine embryos

The pterostilbene (PT) molecule is a phytoalexin with a reducing effect on reactive oxygen species (ROS) and with a capacity to block lipogenesis. However, the potential reducing effects of PT on equatorial lipid accumulation and ROS have not yet been elucidated for in vitro-derived bovine embryos. The present study evaluated the effects of concentrations of 3, 1, 0.33, 0.11 μM PT, and a vehicle group on the percentage of cleaved embryos, embryos with more than 6 cells, percentage of blastocyst on Day 7 and 8, percentage of transferable embryos on Day 7, the cell count and relative concentration of lipids. In the second experiment, the effects of 0.33 μM PT and a vehicle group within two different O₂ environments (5% and 20%) were evaluated for ROS generation and the percentage of Day 8 blastocysts. In the first experiment, no significant differences were found between the treatments with PT and the vehicle group (p > .05) concerning the percentage of cleaved embryos and embryos with more than 6 cells. Lipid reduction was observed in the groups treated with PT versus the vehicle group (p < .05). The vehicle group showed a higher rate of blastocyst production on Days 7 and 8 (p < .05) and an increase in the percentage of transferable embryos on Day 7 compared to the PT treatment groups (p < .05). Cell counts were not significantly different between treatments with PT and the vehicle group (p > .05). In the second experiment, the O₂ concentration did not significantly affect ROS generation (p > .05); however, the groups treated with PT (0.33 μM) had a reduction in ROS (p < .05). The O₂ concentration also did not significantly affect the rate of blastocyst production on Day 8 (p = .7696). Future research should be conducted to ascertain whether the reduction of lipids could enhance the cryopreservation and post-thaw viability of PT-treated embryos.

Recent progress in bovine in vitro-derived embryo cryotolerance: Impact of in vitro culture systems, advances in cryopreservation and future considerations

Cryopreservation of in vitro-derived bovine embryos is a crucial step for the widespread reproduction and conservation of valuable high-merit animals. Given the current popularity of bovine in vitro embryo production (IVP), there is a demand for a highly efficient ultra-low temperature storage method in order to maximize donor ovum pickup (OPU) turn-over, recipient availability/utilization and domestic/overseas commercial trading opportunities. However, IVP bovine embryos are still very sensitive to chilling and cryopreservation, and despite recent progress, a convenient (simple and robust) protocol has not yet been developed. At the moment, there are two methods for bovine IVP embryo cryopreservation: slow programmable freezing and vitrification. Both of the aforementioned techniques have pros and cons. While controlled-rate slow cooling can easily be adapted for direct transfer (DT), ice crystal formation remains an issue. On the other hand, vitrification solved this problem but the possibility of successful DT commercial incorporation remains to be determined. Moreover, simplification of the vitrification protocol (including warming) through the use of an in-straw dilution without the use of a microscope is a prerequisite for its use under farm conditions. This review summarizes the bovine IVP embryo cryopreservation achievements, strengths and limitations of both freezing systems and prospective improvements to enhance cryosurvival, as well as perspectives on future directions of this assisted reproductive technology.

Different as night and day: Behavioural and life history responses to varied photoperiods in Daphnia magna

Nearly all animal species have utilized photoperiod to cue seasonal behaviours and life history traits. We investigated photoperiod responses in keystone species, Daphnia magna, to identify molecular processes underlying ecologically important behaviours and traits using functional transcriptomic analyses. Daphnia magna were photoperiod‐entrained immediately posthatch to a standard control photoperiod of 16 light/ 8 dark hours (16L:8D) relative to shorter (4L:20D, 8L:16D, 12L:12L) and longer (20L:4D) day length photoperiods. Short‐day photoperiods induced significantly increased light‐avoidance behaviours relative to controls. Correspondingly, significant differential transcript expression for genes involved in glutamate signalling was observed, a critical signalling pathway in arthropod light‐avoidance behaviour. Additionally, period circadian protein and proteins coding F‐box/LRR‐repeat domains were differentially expressed which are recognized to establish circadian rhythms in arthropods. Indicators of metabolic rate increased in short‐day photoperiods which corresponded with broadscale changes in transcriptional expression across system‐level energy metabolism pathways. The most striking observations included significantly decreased neonate production at the shortest day length photoperiod (4L:20D) and significantly increased male production across short‐day and equinox photoperiods (4L:20D, 8L:16D and 12L:12D). Transcriptional expression consistent with putative mechanisms of male production was observed including photoperiod‐dependent expression of transformer‐2 sex‐determining protein and small nuclear ribonucleoprotein particles (snRNPs) which control splice variant expression for genes like transformer. Finally, increased transcriptional expression of glutamate has also been shown to induce male production in Daphnia pulex via photoperiod‐sensitive mechanisms. Overall, photoperiod entrainment affected molecular pathways that underpin critical behavioural and life history traits in D. magna providing fundamental insights into biological responses to this primary environmental cue.

Recent advances in bovine sperm cryopreservation techniques with a focus on sperm post-thaw quality optimization

Sperm cryopreservation facilitates the storage and transport of germplasm for its use in artificial insemination (AI) and other advanced reproductive technologies. The cryopreservation process can damage sperm and compromise functionality. Several cryobiological studies have found that the physical and biological factors that affect sperm survival at low temperatures during the cryopreservation process often involve the integrity of sperm membrane. In this review, the behaviour of the sperm membrane against cooling, cold shock, ice crystal formation, oxidative stress, osmotic changes, reorganization of the lipid bilayer and addition of cryoprotective agents (CPA) is discussed. In addition, the phenomenon of reactive oxygen species (ROS) and its relationship with the cryopreservation process is also described. Semen cryopreservation techniques have progressed slowly in past years, and the current performance, measured as post-thawed survival, is not very different compared to past decades. Recent advances in understanding the structure of the cell membrane, its function and metabolism have driven to new conservation systems, including lyophilization and vitrification. However, none of these technologies is commercially available, although its future appears very promising.

Improvement in pregnancy outcomes in couples with immunologically male infertility undergoing prednisolone treatment and conventional in vitro fertilization preceded by sperm penetration assay: a randomized controlled trial

PURPOSE

Anti-sperm antibodies (ASA) in men impair not only sperm motility but also fertilization and conception. However, utilization of corticosteroids to suppress ASA has shown variable pregnancy outcomes. This controversy is also extended to include the usefulness of conventional in vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) in treatments of men with ASA. This study was therefore designed to define factors contributing to these inconsistent results.

METHODS

Infertile men having ASA (n = 241) were randomly assigned for treatment with or without prednisolone for three cycles each of 21 days of their partner's menstrual cycles. Control and treated men underwent then human sperm penetration assay (SPA), of hamster oocytes, to diagnose men with impaired sperm fusogenic capacity. Men with positive or negative SPA results were admitted to conventional IVF or ICSI programs, respectively.

RESULTS

Treated patients had improved sperm motility and progressive motility when compared to control patients (P < 0.001). Fertilization (P = 0.04), embryo cleavage (P = 0.01), and chemical (P = 0.02) and clinical (P = 0.04) pregnancy rates were higher in treated patients than in control patients undergoing conventional IVF but not ICSI cycles.

CONCLUSIONS

Men with ASA may also have compromised sperm fusogenic capacity, which can mask the clinical significance of corticosteroids. Corticosteroid administration in men with ASA, but without compromised sperm fusogenic capacity, improves conventional IVF but not ICSI outcomes; the reason being that ICSI bypasses issues of compromised fusogenic capacity. Inclusion of SPA in infertility clinics that offer both conventional IVF and ICSI services may be useful to identify which patients with ASA benefit from corticosteroid treatments.

Effect of different mini-volume colloid centrifugation configurations on flow cytometrically sorted sperm recovery efficiency and quality using a computer-assisted semen analyzer

Straws of sex-sorted sperm are usually packaged at a low concentration (e.g., ~2.1 × 10⁶  sperm/ml) and cost significantly more than unsorted conventional semen from the same sire. In order to maximize the efficiency of using sex-sorted sperm under in vitro fertilization conditions, the selection of an appropriate sperm separation technique is essential. In this study, the effect of using different silane-coated silica colloid dilutions and layering configurations during centrifugation of sex-sorted sperm was examined over an extended period of incubation time. Sperm recovery and viability after centrifugation using the colloid separation technique were measured along with several sperm motility parameters using CASA. For this purpose, frozen and thawed sex-sorted sperm samples were centrifuged using mini-volume single-layer (40%, 60% and 80%) and mini-volume two-layer (45%/90%, 40%/80% and 30%/60%) separation configurations using PureSperm^® . A single layer of 40% PureSperm^® recovered significantly more sex-sorted sperm (78.07% ± 2.28%) followed by a single layer of 80% PureSperm^® (68.43% ± 2.33%). The lowest sperm recovery was obtained using a two-layer PureSperm^® dilution of 45%/90% (47.57% ± 2.33%). Single-layer centrifugation recovered more sorted sperm (68.67% ± 1.74%) than two layer (53.74% ± 1.74%) (p < .0001). A single layer of 80% PureSperm^® exhibited the highest sorted sperm viability (72.01% ± 2.90%) after centrifugation (p < .05). The mini-volume single layer of 80% PureSperm^® was determined to be an effective alternative to a two-layer centrifugation configuration for sex-sorted sperm selection. In addition, single-layer colloid dilution of 80% performed either as well as or significantly outperformed the other treatments, as well as the control, with regard to motility (MOT) for all time periods of analysis.

Effect of spermatozoa motility hyperactivation factors and gamete coincubation duration on in vitro bovine embryo development using flow cytometrically sorted spermatozoa

The aim of the present study was to evaluate the effects of sperm motility enhancers and different IVF times on cleavage, polyspermy, blastocyst formation, embryo quality and hatching ability. In Experiment 1, sex-sorted X chromosome-bearing Bos taurus spermatozoa were incubated for 30 min before 18 h fertilisation with hyperactivating factors, namely 10 mM caffeine (CA), 5 mM theophylline (TH), 10 mM caffeine and 5 mM theophylline (CA + TH); and untreated spermatozoa (control). In Experiment 2, matured B. taurus oocytes were fertilised using a short (8 h) or standard (18 h) fertilisation length, comparing two different fertilisation media, namely synthetic oviducal fluid (SOF) fertilisation medium (SOF-FERT) and M199 fertilisation medium (M199-FERT). Cleavage and blastocyst formation rates were significantly higher in the CA + TH group (77% and 27%, respectively) compared with the control group (71% and 21%, respectively). Cleavage rates and blastocyst formation were significantly lower for the shortest fertilisation time (8 h) in M199-FERT medium (42% and 12%, respectively). The SOF-FERT medium with an 8 h fertilisation time resulted in the highest cleavage rates and blastocyst formation (74% and 29%, respectively). The SOF-FERT medium produced the highest embryo quality (50% Grade 1) and hatching rate (66%). Motility enhancers did not affect polyspermy rates, whereas polyspermy was affected when fertilisation length was extended from 8 h (3%) to 18 h (9%) and in M199-FERT (14%) compared with SOF-FERT (6%). We conclude that adding the motility enhancers CA and TH to sex sorted spermatozoa and Tyrode’s albumin lactate pyruvate (TALP)-Sperm can improve cleavage and embryo development rates without increasing polyspermy. In addition, shortening the oocyte–sperm coincubation time (8 h) resulted in similar overall embryo performance rates compared with the prolonged (18 h) interval.

Pronuclear formation by ICSI using chemically activated ovine oocytes and zona pellucida bound sperm

Background

In order to improve ICSI, appropiate sperm selection and oocyte activation is necessary. The objective of the present study was to determine the efficiency of fertilization using ICSI with chemically activated ovine oocytes and sperm selected by swim up (SU) or swim up + zona pellucida (SU + ZP) binding.

Results

Experiment 1, 4–20 replicates with total 821 in vitro matured oocytes were chemically activated with ethanol, calcium ionophore or ionomycin, to determine oocyte activation (precense of one PN). Treatments showed similar results (54, 47, 42 %, respectively) but statistically differents (P < 0.05) than mechanical activated oocytes in sham, ICSI and sham injection (13, 25, 32 %, respectively) (10–17 replicates; n = 429).

Experiment 2: Twelve ejaculates and 28 straws of semen were used (11–19 replicates). Sperm were selected by SU in BSA-TCM 199-H medium. A total of 2,294 fresh sperm and 2,760 from frozen-thawed semen were analyzed after SU or SU + ZP binding. Fresh sperm selected by SU showed acrosome reaction (AR) of 59 %, the sperm selected by SU + ZP binding increased AR to 91 %. In comparison, the AR of frozen-thawed sperm using SU or SU + ZP binding was 77 and 86 %, respectively (P < 0.05).

Experiment 3: fertilization in 200 mechanical activativated oocytes (17 replicates) was 4 %, but fertilization increased in ethanol activated oocytes after ICSI (12-28 %) (5–6 replicates). When fresh sperm only selected by SU were injected to 123 oocytes, a fertilization rate (28 %) was achieved; in sperm selected by SU + ZP was 25 % (73 oocytes). In comparison, in frozen-thawed sperm selected by SU, fertilization was 13 % (70 oocytes), whereas sperm from SU + ZP binding displayed 12 % (51 oocytes) (P > 0.05).

Conclusions

Chemical activation induces higher ovine oocyte activation than mechanical activation. Ethanol slightly displays higher oocyte activation than calcium ionophore and ionomicine. Sperm selection with SU + ZP increased AR/A and AR/D rates in comparison with SU in fresh and frozen-thawed sperm. According to this, in terms of fertilization rates, chemical activation after ICSI increased oocyte PN formation compared to mechanical activation. Also, fresh sperm treated with SU and SU + ZP were significantly different than frozen-thawed sperm, but between sperm treatments no significant differences were obtained.

Comparison of different fertilisation media for an in vitro maturation?fertilisation?culture system using flow-cytometrically sorted X chromosome-bearing spermatozoa for bovine embryo production

High demand exists among commercial cattle producers for in vitro-derived bovine embryos fertilised with female sex-sorted spermatozoa from high-value breeding stock. The aim of this study was to evaluate three fertilisation media, namely M199, synthetic oviductal fluid (SOF) and Tyrode's albumin-lactate-pyruvate (TALP), on IVF performance using female sex-sorted spermatozoa. In all, 1143, 1220 and 1041 cumulus-oocyte complexes were fertilised in M199, SOF and TALP, respectively. There were significant differences among fertilisation media (P < 0.05) in cleavage rate (M199 = 57%, SOF = 71% and TALP = 72%), blastocyst formation (M199 = 9%, SOF = 20% and TALP = 19%), proportion of Grade 1 blastocysts (M199 = 15%, SOF = 52% and TALP = 51%), proportion of Grade 3 blastocysts (M199 = 58%, SOF = 21% and TALP = 20%) and hatching rates (M199 = 29%, SOF = 60% and TALP = 65%). The inner cell mass (ICM) and trophectoderm (TE) cells of Day 7 blastocysts were also affected by the fertilisation medium. Embryos derived from SOF and TALP fertilisation media had higher numbers of ICM, TE and total cells than those fertilised in M199. In conclusion, fertilisation media affected cleavage rate, as well as subsequent embryo development, quality and hatching ability. SOF and TALP fertilisation media produced significantly more embryos of higher quality than M199.

Gamete therapeutics: recombinant protein adsorption by sperm for increasing fertility via artificial insemination

A decrease in fertility can have a negative economic impact, both locally and over a broader geographical scope, and this is especially the case with regard to the cattle industry. Therefore, much interest exists in evaluating proteins that might be able to increase the fertility of sperm. Heparin binding proteins (HBPs), specifically the fertility associated antigen (FAA) and the Type-2 tissue inhibitor of metalloproteinase (TIMP-2), act to favor the capacitation and acrosome reaction and perhaps even modulate the immune system’s response toward the sperm. The objective of this research was to determine the effect on fertility of adding recombinant FAA (rFAA) and recombinant TIMP-2 (rTIMP-2) to bovine semen before cryopreservation for use in an artificial insemination (AI) program in a tropical environment. For this experiment, 100 crossbred (Bos taurus x Bos indicus) heifers were selected based on their estrus cycle, body condition score (BCS), of 4 to 6 on a scale of 1 to 9, and adequate anatomical conformation evaluated by pelvic and genital (normal) measurements. Heifers were synchronized using estradiol benzoate (EB), Celosil® (PGF2α) (Shering-Plough) and a controlled internal drug release (CIDR) device was inserted that contained progesterone. Inseminations were performed in two groups at random, 50 animals per group. The control group was inseminated with conventional semen. The treatment group was inseminated with semen containing rFAA (25 µg/mL) and rTIMP-2 (25 µg/mL). In the control group a 16% pregnancy rate was obtained versus a 40% pregnancy rate for the HBP treatment group, resulting in a significant difference (P = 0.0037). Given the results herein, one may conclude that the HBPs can increase fertility and could be an option for cattle in tropical conditions; however, one needs to consider the environment, nutrition, and the genetic interaction affecting the final result in whatever reproductive program that is implemented.

DNA fragmentation kinetics and postthaw motility of flow cytometric-sorted white-tailed deer sperm

This study examined DNA damage and postthaw motility of white-tailed deer sperm (n = 28) before and after sex selection and conventional sorting using MoFlo XDP SX flow cytometry. Semen samples from the same individuals were treated in 4 different ways: 1) chilled-extended sperm samples (without glycerol); 2) cryopreserved conventional samples, samples directly cryopreserved after the addition of extenders; 3) cryopreserved conventionally sorted samples, sorted samples to remove the dead sperm subpopulation; and 4) cryopreserved sex-sorted samples; sorted samples to remove the dead sperm subpopulation and separation of X- and Y-chromosome-bearing sperm. In all the cases (n = 6), conventional samples showed decreased postthaw motilities (43 ± 26%) when compared with X-sorted samples (59 ± 20%; P < 0.05) and Y-sorted samples (54 ± 20%; P > 0.05). The DNA fragmentation baseline was <5% for frozen-thawed conventional samples, but even less after sex sorting and conventional sorting: 2.4 and 1.7%, respectively. On the other hand, conventional samples showed greater (P < 0.05) DNA fragmentation than the sex-sorted sperm (n = 6) at 96 h (average of 4.8 ± 4.5% and 5.3 ± 4%, respectively). Conventionally sorted samples (n = 8) did not have greater (P > 0.05) DNA fragmentation when compared with the sex-sorted samples. Fragmentation of DNA on X-chromosome and Y-chromosome-bearing sorted sperm were not significantly different (n = 10, P > 0.05) after 96 h (2.6 ± 3.6% and 2.2 ± 0.5%, respectively). Future research should be implemented for examining the fertilizing potential of sex-sorted white-tailed deer sperm (e.g., AI fertility trials).

A comparison of bovine seminal quality assessments using different viewing chambers with a computer-assisted semen analyzer

Computer-assisted sperm analysis of fresh and frozen-thawed bovine sperm requires proper handling and preparation, and the type of slide used in the assessment is critical if the resultant data are to be useful quality control measurements. In the present study, 4 different slide viewing chambers, a Makler chamber, a clean slide-coverslip, or a 2- or 4-cell chamber Leja slide, were compared with assess their utility in providing reliable measurements of sperm motility variables. A Hamilton-Thorne IVOS Computer-Assisted Semen Analyzer (CASA) was the instrument used to determine sperm measurements utilizing the 4 different chambers. Fifty-eight different freeze batches of bovine semen that had been collected from 47 bulls at 7 sites that sex-sort sperm using Sexing Technologies sorting criteria were incorporated into the trial. Neither the percentage of motile sperm nor the percentage of progressively motile sperm differed for the Makler chamber vs. slide-coverslip comparisons. Similarly, total and progressively motile sperm did not differ between the 2- and 4-cell chambered Leja slides. However, total and progressive motility of sperm determined with the Makler chamber and slide-coverslip were greater (P < 0.0001) than motilities recorded by the 2- or 4-cell chambered Leja slides. Based on the results, the type of viewing chamber can affect the range of sperm motility values when CASA is used for quality control evaluations of thawed, cryopreserved sex-sorted sperm samples.

Bacteria in bovine semen can increase sperm DNA fragmentation rates: a kinetic experimental approach

Cryopreserved straws of semen (n=228) from Holstein bulls (n=47) were examined for bacterial presence and sperm DNA fragmentation (SDF) dynamics. Commercial semen doses (representing six ejaculates per individual) were randomly selected from a bull stud in Spain. The dynamics of SDF were assessed after thawing (T0) and at 4, 24, 48, 72 and 96h of incubation at 37°C, using the commercial variant of the sperm chromatin dispersion test for Bovine (Halomax®). One group of bulls showed a bacterial presence in semen samples between 0 and 96h of incubation (n=23, group A) while the other did not (n=24, group B). Immediate post-thaw differences in SDF were not observed when both groups were compared. However, the rate of increase in SDF (rSDF) over time, considered as an estimate of the kinetic behaviour of sperm DNA survival, was significantly higher (P<0.05) in semen samples from group A (0.7% per hour) versus group B (0.05% per hour). Polymerase Chain Reaction (PCR) assay was used for DNA amplification using primers designed for specific regions of the bacterial gene that codifies for 16S rRNA. Different species within the phyla Bacteroidetes, Firmicutes, Proteobacteria, Cyanobacteria, Fusobacteria and Actinobacteria were identified. The results show that (1) SDF at baseline (T0) may not be affected by the presence of bacteria but the rSDF can increase due to bacterial growth during incubation, (2) the increase in the rSDF is characteristic of some bulls but not for others, and (3) certain bacterial strains are repeatedly found in separate ejaculates from the same bull.

Factors related to spatial patterns of rural land fragmentation in Texas

Fragmentation of family-owned farms and ranches has been identified as the greatest single threat to wildlife habitat, water supply, and the long-term viability of agriculture in Texas. However, an integrative framework for insights into the pathways of land use change has been lacking. The specific objectives of the study are to test the hypotheses that the nonagricultural value (NAV) of rural land is a reliable indicator of trends in land fragmentation and that NAV in Texas is spatially correlated with population density, and to explore the idea that recent changes in property size patterns are better represented by a categorical model than by one that reflects incremental changes. We propose that the State-and-Transition model, developed to describe the dynamics of semi-arid ecosystems, provides an appropriate conceptual framework for characterizing categorical shifts in rural property patterns. Results suggest that changes in population density are spatially correlated with NAV and farm size, and that rural property size is spatially correlated with changes in NAV. With increasing NAV, the proportion of large properties tends to decrease while the area represented by small properties tends to increase. Although a correlation exists between NAV and population density, it is the trend in NAV that appears to be a stronger predictor of land fragmentation. The empirical relationships established herein, viewed within the conceptual framework of the State-and-Transition model, can provide a useful tool for evaluating land use policies for maintaining critical ecosystem services delivered from privately owned land in private land states, such as Texas.