<p>    </p> <p>In honey bees, male fertility is directly involved in colony fitness. Males not only provide fifty percent of colony genetics, but they also provide material benefits involved with female fertility. Recent evidence suggests there is tremendous variation in drone fertility. Of drones which are sexually mature, as few as one in ten may be able to produce enough sperm to successfully inseminate a queen. If drones are not producing healthy sperm, their mates will not produce healthy colonies. Despite this, we have very little understanding of precisely how variation in drone reproductive quality is generated. Specifically, we know comparatively little about the role genetics plays in shaping drone reproductive traits. This standing genetic variation can contribute to phenotypic variation observed among honey bee stocks and contribute to the success (or failure) of colonies. <strong>The major goal of this thesis is to identify the major mechanisms and genes driving genotypic and phenotypic variation in honey bee males. </strong>First, we used a population genetics approach to estimate the evolutionary impact of haploid selection <strong>(Chapter 2) </strong>and variation in sexual selection <strong>(Chapter 3) </strong>on male genes. In <strong>Chapter 2</strong>, we found genes expressed by males had an increased genetic diversity, rate of adaptation, and more efficient purifying selection than non-haploid selected female-expression genes. This suggests haploid and sexually- expressed genes experience increases in the rate of molecular evolution. In <strong>Chapter 3</strong>, we found selection on sperm length shifted over evolutionary time within corbiculate bees, resulting in different strengths of sexual selection. As selection for sperm length intensified in male bees, there was rapid evolution of expression patterns and gene sequences associated with male-biased genes. Second, we used a quantitative genetics approach to connect genetic variation to the trait components of fitness <strong>(Chapter 4)</strong>. We identified key genes connected to honey bee male sperm and maturity traits. These genes also appear to have different rates of evolution. Overall, we combined both population and quantitative genetic approaches to provide comprehensive insights into the evolution of honey bee male genotypes and phenotypes. This powerful approach allowed me to identify the genetic and mechanistic underpinnings driving variation in fitness-related traits. This information can be used to identify candidate genes associated with honey bee male fitness. </p>

<p dir="ltr">The White Pekin duck (<i>Anas platyrhynchos domesticus</i>) is the most widely consumed duck protein in the world. Total duck meat production had a global annual increase of 2.1% per year from 2010 to 2019. The increase in duck meat production can be credited to improved management strategies, nutritional programs, and genetic improvement made to the Pekin ducks by structured breeding programs. Regardless of the advancements already achieved by Pekin duck breeding programs, improvements can still be made. One such improvement that can be made in Pekin duck populations is reducing the frequency of the emerging welfare concern known as flip-over (FO). We hypothesize that egg quality traits, wingspan, back length, and hip width are genetically influenced and their inclusion into Pekin duck breeding programs can be used to improve the Pekin duck. Egg quality traits were collected at weeks of age 30, 32, 35 and 40 on two generations of Pekin duck hens. All heritability estimates and Genetic correlations were calculated using BLUPF90 software, the Restricted Maximum Likelihood (REML) method, and 9,418 individuals in the pedigree. All egg quality traits evaluated are moderate to highly heritable ranging from 0.23 for egg shape to 0.70 for shell ratio. Two hatches of 1,200 Pekin duck hens were assessed at day of age 23 and 30 for wingspan, hip width, and back length using image analysis. Wingspan, hip width, and back length were found to be heritable ranging from 0.04 ± 0.013 to 0.27 ± 0.025 for hip width and back length respectfully. This thesis will discuss approaches to evaluating genetic parameters of egg quality traits in hatching eggs and the possibility of reducing FO through the selection of increased wingspan length.</p>

<p dir="ltr">Boars in the swine industry are one of the select animals subject to limit feeding. Limit feeding boars occurs once boars are selected to enter the boar stud. Before selection boars are <i>ad libitum</i> fed like a nursery or grow finishing pig. Research involving boar nutrition and the impact it has on growth, development, and semen characteristics are limited compared to the rest of the swine industry. The objective of these studies conducted at Purdue University were to determine how varying nutritional feeding strategies impact semen quality and quantity as well as growth and development of artificial insemination boars.</p><p dir="ltr">Feeding fiber is a commonly used strategy in gestating sow nutrition to mitigate some of the negative side effects of limit feeding animals. A variety of fiber sources are available to the swine industry, however most of the common sources used are wheat bran, alfalfa meal, sugar beet pulp, and soybean hulls. Soyhulls are one of the more easily accessible sources of fiber in Indiana and the Midwest U.S. due to large amounts of soybean production and processing which will continue to grow with bi-energy demands. Boars fed the fiber diet (14.3% soyhulls) had increased bodyweight and body condition changes over the twelve-week period. Additionally, fiber inclusion in the diet had no impact on semen characteristics but semen was impacted by the age and breed of the boar. Salivary cortisol levels were reduced in boars fed fiber as well as some changes in behavior were observed.</p><p dir="ltr">The addition of fiber had impacts on growth and development but no impacts on semen. Since boars are limit-fed for so long from selection after the grow-finish period until they are culled this drew up the question if feeding boars different levels after selection (1.8 kg/d or 2.7 kg/d) impacted trainability, first time semen collection characteristics, growth and development of young boars. No differences were observed for feeding level impacting trainability with 92% of all boars regardless of treatment being successfully trained. Semen volume was increased in boars fed 2.72 kg/d by approximately 50% but no other semen characteristics were impacted. Boars fed 2.72 kg/d also had increased bodyweight and body condition score measures.</p><p dir="ltr">The boars subject to the training study unknowingly arrived at the farm naturally infected with porcine circovirus three (PCV3). Research has been conducted on the ability of viruses (PRRSv, PEDv) to be detected and transmitted through semen. Porcine circovirus three is a relatively new variant of circovirus so the opportunity to evaluate the question of if this virus was able to be detected in seminal plasma and the impacts it has on semen characteristics was presented. Serum and semen samples were collected for polymerase chain reaction analysis of detection of PCV3 conducted at Purdue Animal Disease Diagnostic Laboratory. Porcine circovirus three was able to be detected in the serum of positive boars however no positive detection occurred for seminal plasma samples. Morphological abnormalities such as distal midpiece reflex, distal droplets, and head and tail differed between infected and non-infected boars. Young boars sero-positive for PCV3 had decreased total sperm, total normal sperm motility, and head and tail abnormalities but had decreased distal midpiece reflex abnormalities when compared to PCV3 negative young boars. Young boars were also able to maintain the virus for 98+ days, while some old boars were able to clear the virus withing 14 weeks of becoming positive.</p><p dir="ltr">The next chapter evaluated maintenance energy equation listed in the swine NRC 2012 and if it was still accurate for sexually active boars and if weight management through the use of this equation impacted boar performance. Boars were subject to three treatments (150%, 100%, 80%) of maintenance energy for the first nine-week period and 150% and 80% diets were switched for second nine-week period while 100% stayed the same the entire time in a cross-over design. Semen, bodyweight, and body condition parameters were analyzed throughout the two nine-week periods. Boars fed 80% of maintenance had the largest reduction in semen parameters compared to 150% and 100% maintenance fed boars. Additionally, switching 80% feed intake boars to 150% maintenance feed intake, boars were able to recover some of the negative impacts, however they were not able to fully recover in the second nine-week period. Boars fed 100% and 80% maintenance energy lost weight regardless of age. The loss of body weight of the 100% maintenance fed boars indicates the swine NRC 2012 equation is underestimating the modern AI boar maintenance needs. Old boars were able to handle changes in weight and body condition better than young boars as there was reduced variation in serum metabolites analyzed with old boars compared to young boars.</p><p dir="ltr">The last chapter of this thesis focused on a big data project from commercial sow farms. The objective of this study was to determine if breeding gilts at first signs of estrus or after has an impact on sow performance and economic value to parity three. A regression model was developed from on farm data to determine the difference in total born piglets to parity 3 between gilts bred on their first estrus or after. Gilts bred on their first estrus had six fewer total piglets to parity three compared to gilts who were bred after the first estrus. Also, gilts bred after their first estrus had a larger percentage of sows being profitable compared to gilts bred on first estrus. This model data was compared to actual data for comparison between the two. The model with the limited variables inputted and compared to the actual data was fairly accurate with economic profitability and with more refinement the accuracy can be increased.</p><p dir="ltr">Overall, nutrition of the boar needs to be an area of interest in the swine industry to continue improving efficiency of production. Feeding fiber to boars has minimal impact on semen characteristics but can be used to reduce stress in boars that are limit-fed for weight and body condition management. Limit feeding boars beginning at selection reduces growth and development and had negative impacts on first time semen collection volume. Porcine circovirus 3 was not found in the seminal plasma of naturally infected boars when serum analysis was positive. Boars fed below maintenance levels listed in the swine NRC 2012 have negative impacts on semen, bodyweight, and body condition parameters. Once diets were changed boars were able to recover from the feed restriction but not meet baseline measures prior to feed restriction. Young boars are more sensitive to feeding changes than old boars, this could be due to the young animal still growing while the older animal is closer to mature size. Big data projects can aid producers in making production changes decisions to estimate the economic impact it can have to an individual farm or the entire production system.</p>

<p dir="ltr">In this dissertation, we investigated the genetic background of milk consumption, feeding behavior, disease resistance, and calf resilience in North American Holstein dairy calves using precision livestock farming (PLF) technologies and genetic modeling. Genomic and phenotypic information obtained from automatic milk feeding machines were obtained from 10,072 pre-weaned Holstein calves and used to derive and genetically evaluate novel traits such as daily milk consumption, calf resilience, and incidence of bovine respiratory disease (BRD). Heritability estimates for milk consumption and feeding behavior traits were found to be low but improved with specific statistical models, suggesting potential for genetic improvement if included in selection schemes. Random regression models captured greater amounts of genetic variability among calves for longitudinal milk feeding and behavior traits, with moderate negative (favorable) genetic correlations between milk consumption and BRD, indicating potential for genetic selection to enhance calf health outcomes and performance based on milk intake data. Various quantitative trait loci (QTL) for milk consumption, drinking duration traits, feeding behavior, and disease susceptibility were identified, linking key genes involved in metabolic processes, growth, and overall health. The same datasets were used to derive resilience indicators based on cumulative milk consumption. Genetic parameters for resilience traits, including amplitude, perturbation time, and recovery time, were estimated, highlighting substantial phenotypic and genetic variability. Significant genomic regions for six resilience traits were identified, with key genes such as <i>ABCB8</i>,<i> ABCF2</i>, and <i>AGAP3</i> linked to resilience traits, impacting mitochondrial function, cellular stress responses, and homeostasis. Pathway analyses revealed critical biological processes for stress response, including nucleotide binding and hormone activity. Genes such as <i>EPC1</i>, <i>ASB10</i>, and <i>ASIC3</i> were associated with recovery time, while <i>DPP6</i>, <i>GBX1</i>, and <i>GIMAP5</i> were linked to other resilience traits. These findings underscore the importance of genetic tools and breeding strategies in enhancing health, resilience, and productivity, offering potential new traits to genetically improve health and resilience in dairy cattle, and consequently, improve the sustainability of the dairy cattle industry.</p>

<p>  </p> <p>Microbiome studies are varied and involve the examination of microorganisms at different levels: individual cells to determine individual functions, populations of specific microorganisms to determine interactions between organisms, and/or communities of microorganisms for a broader investigation of interactions between organism and environment. These studies are typically done within the context of a particular niche or environment. There are two parts to this dissertation, separated by the types of research involved. First, the analysis of bacterial communities using 16S rRNA sequencing and analysis. In this first part the bacterial communities of the reproductive tract of bulls and the gastrointestinal tract of weanling pigs were studied. The reproductive organs of the male, domestic species had not been studied from an ecological perspective prior to the study. As such, the research was mainly focused on characterizing the bacterial communities found within the prepuce of bulls that were considered to be healthy, or that the breeding soundness exam was satisfactory and the bulls had no clinical disease in the urogenital tract. Through this study two distinct types of bacterial communities were found based on the diversity of the observed taxa; the groups were split into a low diversity group identified by the presence of <em>Bradyrhizobium</em> and a high diversity group distinguished by the abundance of mucosal-associated bacteria found in oral, respiratory, and vaginal communities of cattle. Second, the effects of supplementary, soluble fiber on the intestinal bacterial communities of piglets pre- and/or post-weaning were studied. The rationale behind this study was to determine if pre-weaning fiber could alter the microbiome prior to weaning and the change of diet from liquid to solid. Pre-weaning, supplementary, soluble fiber was found to increase short-chain fatty acid concentrations and bacterial taxa potentially involved in their production. Additionally, bacterial taxa implicated in an increased inflammatory response were reduced in groups fed supplementary fiber. Taken together, the two bacterial community studies highlight the gaps in knowledge for reproductive communities in male animals as well as the potential for reducing weaning stress in pigs. Part two of this dissertation focuses on whole genome sequence analysis as a way to study bacterial populations associated with bovine respiratory disease (BRD), a common and potentially fatal disease in cattle. Identification of BRD has low accuracy and the presence of antibiotic resistant bacteria increases the chance of treatment failure. Using machine learning, the prediction of antibiotic resistance in bacterial isolates from animals with BRD was performed to find potential sequences for use in future molecular assays. While using known resistance genes was helpful for some antibiotics, several of the antibiotics used in treating BRD were better predicted using the machine learning models. Model output sequences should be further tested using molecular methods to determine function and importance before using as an assay target. Put together, the contents of this dissertation should serve as an introduction to bacterial ecology as well as how the concepts can be applied to food animal production systems.</p>

<p>Thyroid hormone is essential for regulating adult metabolism and proper fetal development. Under normal conditions, maternal and fetal thyroid hormones are subject to metabolism at the placenta and within fetal tissues through deiodination and sulfation to regulate fetal exposure to the bioactive hormone. Disruptions of the thyroid hormone system can result in non-thyroidal illness syndrome (NTIS), which is classified as the dysregulation of thyroid hormone homeostasis. The exact cause of the alterations in circulating thyroid hormone levels during NTIS is not well- known. In comparison, hypothyroidism results from the absence of thyroid hormone production and presents as low thyroid hormone levels.</p> <p>Porcine reproductive and respiratory syndrome virus (PRRSV) crosses the late gestation placenta and causes suppression of circulating maternal and fetal thyroid hormone. Chapter 2 investigates the potential role of thyroid hormone metabolism in this disruption. Pregnant gilts were challenged with PRRSV2 (n=22) or sham inoculated (n=5) at gestation day 85. Samples were collected on day 106, and viral load was assessed in fetal serum and thymus. From the entire fetal population, three distinct subsets of fetuses representing biological extremes were identified, including uninfected with no detectable viral load (UNIF), high viral load viable (HV-VIA), or high viral load with severe meconium staining (HV-MEC). In addition, control fetuses from sham inoculated gilts (CON) were used as a reference group. Samples of fetal liver, kidney, and the corresponding fetal placenta and maternal endometrium for n=10 fetuses per group were then used to evaluate gene expression. A total of 11 genes associated with thyroid hormone metabolism including deiodinases (DIO1,2,3), sulfotransferases (SULT1A3,1B1,1C2,1E1,2A1), sulfatase (STS), and solute carriers (SLC16A2,16A10) were quantified using absolute quantification qPCR. Evidence of fetal decompensation was observed within the high viral fetuses in the form of decreased DIO1 expression within the fetal liver and increased DIO3 expression in both components of the placenta. Circulating levels of T4 and inactive thyroid hormone metabolites, reverse-triiodothyronine (rT3) and two diiodothyronines (3,5-T2 and 3,3’-T2), were measured in fetal serum. While T4 was depressed, no change was observed in circulating rT3 levels, and neither T2 metabolite reached the lower detection limit. This may suggest that alterations in thyroid hormone metabolism generate a localized effect on hormone metabolites in the respective tissues.</p> <p>Alternatively, the low levels of available T3 and T4 limit the production of downstream metabolites to be found in serum.</p> <p>The cause-and-effect relationship between PRRSV infection, fetal thyroid disruption, and the effects on fetal thyroid hormone metabolism are unclear. Therefore, Chapter 3 developed a non-pathogenic model using methimazole (MMI) to induce hypothyroidism in the late gestation fetus and evaluate the impact on fetal development and thyroid hormone metabolism. Pregnant gilts were either treated with oral methimazole or equivalent sham from gestation day 85-106 (n=4/group), followed by classification of all fetuses as live, live but meconium stained, or dead. Fetuses exposed to MMI in-utero were notably hypothyroid with significantly suppressed serum T3 and T4 and histological evidence of goiter. Surprisingly, fetuses from MMI-treated dams were substantially larger but appeared to exhibit non-allometric growth with an increase in girth but not length. The liver, kidney, and the corresponding fetal placenta and maternal endometrium were collected from a subset of 16 fetuses per group to evaluate the relative expression of five genes associated with thyroid hormone metabolism, including three deiodinases and two solute carriers known to transport thyroid hormone. Compensatory transcription of DIO3 was observed in all tissues evaluated, suggesting increased vertical transfer of maternal thyroid hormone at the placenta and decreased breakdown of thyroid hormone within fetal organs.</p> <p>The evaluation of thyroid hormone metabolism within the fetus and within the placenta has allowed us to differentiate suppressed thyroid hormone levels of the pig fetus under pathogenic and non-pathogenic conditions. In the context of PRRSV infection, the observed decompensation of thyroid hormone metabolism would further exacerbate the hypothyroid state and is therefore consistent with NTIS. In contrast, fetuses with induced thyroid hormone suppression following maternal exposure to MMI showed compensatory thyroid hormone metabolism in the same tissues. This indicates true hypothyroidism and clearly demonstrates a fetal capacity to respond to such endocrine disruption.</p>

<p dir="ltr">Heat stress is one of the leading welfare concerns for modern swine production globally. Swine are especially susceptible as the species has inactive sudoriferous glands and, as a result, these animals thermoregulate mainly through behaviors such as wallowing and rooting up cooler patches of ground. In commercial settings, access to open ground or wallowing pits would present a threat to the animals’ health in the form of a vector for diseases and parasites. This puts aspects of swine welfare in direct conflict with one another, while public legislature and consumer pressures increasingly call for approaches to animal welfare that encompass all aspects of welfare to be considered. Efforts towards improved welfare are also crucial to the environmental and economical sustainability for producers and consumers. Previous genetic selection tactics used in swine herds focused intensely on a few traits and have led to modern animals being highly productive but also more environmentally sensitive. Intensely selected animals have energy margins that are narrower and more devoted to higher production leaving less accommodations for resilience in moments of stress. Since swine behaviorally thermoregulate, the use of behavior studies combined with those of genetics is one possible way to effectively identify heritable aspects of climatic resilience into future herds while still improving production traits. The primary objectives of this thesis were to develop an ethogram that can be used to base phenotypes of behavior; calculate the variance components of the behavior traits; correlate these components with those of maternal productivity and heat tolerance; and finally explore the genetic background of the behavior traits based on the identification of genomic markers significantly associated with them. Data was collected on 1,678 Landrace × Large White sows from a commercial swine herd in North Carolina. The data comprised information on climatic factors, litter performance, and behavior during a standardized human handling procedure in the summer of 2021. These animals were genotyped using the PorcineSNP50K Bead Chip (Illumina, San Diego, CA, USA). These studies describe the development of an ethogram for use on lactating sows in a commercial setting in order to create the novel behavior traits of Responsiveness Score (RS), Vocalization Score (VS), and Shave Time (ST). The genetic variance components were then estimated, and heritabilities found to be 0.17 ± 0.05 for RS, 0.15 ± 0.05 for VS, and 0.10 ± 0.05. These novel behavior traits had low genetic correlations with traits of maternal performance and heat stress resilience. Genome-wide association studies were then performed, and 19 genomic markers were significantly associated with the three behavior traits. However, only one region located on chromosome 3 harbors a candidate gene that may play a role in heat stress resilience. Although the novel behavior traits explored in this study are heritable, they were not found to be viable indicator traits for heat stress resilience due to their low genetic correlations with direct indicators of heat tolerance in lactating sows. It is important that additional phenotypic records of behaviors related to welfare are generated in the future to better map their polygenic nature. </p>

<p dir="ltr">Nulliparous replacement beef heifers represent an opportunity to improve both genetic potential and lifetime production within the herd. However, advances in reproductive efficiency and synchrony in the herd require heifers to conceive earlier than multiparous cows in order to account for the extended postpartum interval following first-time parturition. Further, those heifers that achieve early calving dates continue to calve early throughout their lifetime. This early calving results in increased weaning weights and better synchrony in subsequent years. One obstacle producers face when breeding nulliparous heifers is the ability to identify which animals have reached puberty at the initiation of the breeding season. This results in the variation observed in synchronization success within a group of heifers. In Chapter 2 our laboratory formulated a study to analyze the efficacy of the 7-d CO-synch + CIDR protocol when utilizing short-term exposure to a progestin (melengestrol acetate, MGA) as a pre-synchronization protocol. Our hypothesis was that the heifers may respond more efficiently to an orally fed progestin as the increase in serum progesterone is less pronounced, when compared to the CIDR. This first study resulted in a protocol application error, in which MGA was fed an extra day (8 vs. 7). This additional day of treatment with MGA following the administration of a prostaglandin eliminated our laboratory’s opportunity to collect meaningful data from this first attempt. Thus, it was pertinent to restart the experiment in an attempt to obtain data for analysis. In order to avoid confounding data, half of the heifers in each treatment received a new treatment, while the other half remained on the treatment assigned during the first attempt. After completing the second round of experiments it was observed that at the first pregnancy check (study day 30), the heifers that were originally assigned to MGA, but were switched to a CIDR for the second attempt numerically outperformed their counterparts in the other three formulated treatment groups. In an attempt to replicate these results, a second study was formulated (Chapter 3), to mimic the timeline from the preliminary study. This resulted in a pre-synchronization treatment protocol prior to the initiation of the breeding season synchronization protocol. Previous studies that have been conducted with similar protocols were designed to provide heifers with a pre-synchronization period that would aid in the attainment of puberty prior to their first attempt at breeding through exposure to progesterone. The purpose of the Chapter 3 experiment was to evaluate the effects of feeding melengestrol acetate (MGA®) as a pre-synchronization for 10 days immediately prior to estrous synchronization and fixed-timed artificial insemination (FTAI). The ten days were chosen as this was a novel protocol that was the result of the preliminary study and the subsequent restart. Ninety-three crossbred heifers (395.67 ± 5.37 kg) were blocked by BW, genetics, and reproductive tract scores and allotted to 3 treatments. The 3 treatment groups were: 7-day CO-synch + CIDR without pre-synchronization (CON, n=31); 25 mg PGF2α (Lutalyse®) followed immediately by MGA feeding for 7 d prior to the start of the 7-day CO-synch + CIDR program (PRE, n=31); and 25 mg PGF2α followed immediately by MGA feeding for 7d followed 10 d later by the start of the 7-day CO-synch + CIDR program (PRE+10, n=31). The 7-day Co-synch + CIDR protocol in all three treatments was initiated on d 0 by administering a 2 cc IM injection of GnRH (Cystorelin®) and placing a CIDR into the vagina. The CIDRs were removed 7 days later and accompanied by 25 mg IM injection of PGF2α. An injection of GnRH occurred 60-66 hours following PGF2α at FTAI with frozen semen from a single bull. Ten days after FTAI, heifers were exposed to a bull. Estrotect® patches were applied throughout the study to assess estrous behavior. Ovaries were visualized by transrectal ultrasonography 24 hours post-FTAI to determine whether ovulation occurred. Pregnancy was determined on days 40, 64, and 109 post-FTAI via transrectal ultrasonography. Blood was collected via jugular venipuncture (d -19 and -12, MGA initiation and termination, days 0, 7, and 9) and serum progesterone determined. Performance data were analyzed using the MIXED procedure and conception data were analyzed using the GLIMMIX procedure of SAS. Heifers in the PRE+10 treatment group had higher levels of progesterone (P=0.04) at d 0 compared to PRE heifers. At d 7 (CIDR removal) there was a tendency (P=0.07) for PRE+10 heifers to have higher levels of progesterone than PRE, but did not differ by d 9 (FTAI, P=0.36). FTAI conception rates in heifers in the PRE treatment group (63%) tended (P = 0.09) to be higher compared to the controls (35%), but not different from PRE+10 (43%), with no differences in season-long pregnancy rates (P > 0.15). Pre-synchronization with MGA immediately prior to FTAI synchronization appears to increase conception rates early in the breeding season in beef heifers. In Chapter 4, our laboratory analyzed the efficacy of supplementation strategies post-insemination. Unlike the first two experiments, the third study focused on reproductive failure that occurs after insemination. The overarching goal remained the same, increasing the reproductive efficiency within our nulliparous heifer herd. A common practice for beef producers in the United States is to use estrous synchronization, and immediately turn heifers out to lush spring pasture immediately following FTAI. The fresh forage is high in water content which lowers dry matter intake (DMI) and creates a negative energy balance. Ultimately, this reduced energy intake can result in a reduction in reproductive performance. In the Chapter 4 our laboratory formulated a supplementation strategy utilizing the SmartFeed™ technology to deliver soybean hulls to our treatment group following insemination for 45 days. The utilization of the SmartFeed® technology provided the opportunity to analyze the efficacy of the supplementation strategy using each individual animal as an experimental unit. Sixty-two nulliparous crossbred heifers were fed in drylot to obtain moderate body condition prior to breeding at d 0 via FTAI and trained to utilize the SmartFeed™ system.Heifers were blocked by weight and body condition score to either the soybean hull supplementation group (SOY) or the non-supplemented control group (CON). . Heifers in the treatment group received their supplementation by entering the SmartFeed™ system, allowing for RFID controlled release of 2.27 kg. per head each day for 45 days. Scales located beneath each feed pan sent real time weight data for regulation and analysis on individual animal feeding behavior. On study d 6, a subset of the nulliparous crossbred heifers (n = 12; n = 6/ treatment) were transported by trailer from the Feldun Purdue Agricultural Center to Purdue West Lafayette main campus (approximately 217.74 km.). The subset of heifers had embryos flushed and evaluated for embryo quality and number of live/dead cells. Ultrasonography was utilized to monitor ovarian activity throughout the duration of the study and to determine pregnancy status 30 days after FTAI and 30 days after the 45-day breeding season. Though conception rates were not statistically (P=0.17) different (SOY 16/25; 64% vs. CON 11/25; 44%) when comparing treatment groups, the numerical differences suggest there is potential in pursuing a similar supplementation strategy following breeding in nulliparous beef heifers. The supplementation of SBH resulted in greater weight gain over time (P = 0.04), potentially explaining the numeric improvement in conception rate. The two pre-synchronization studies from Chapters 2 and 3 resulted in numerical improvements in conception rate as a result of exposing replacement heifers to a source of progestin prior to the initiation of their synchronization protocol. The implementation of progesterone priming mitigates the occurrence of short cycles and immature oocyte maturation at the time of ovulation. Based on results from previous studies conducted by our laboratory, the source of progestin greatly determines the timing and concentration of P4 circulating in replacement heifers immediately following treatment. Additionally, the 7 & 7 estrous synchronization protocol has grown in popularity and implementation. This protocol when broken down is very similar to the pre-synchronization protocol our laboratory utilized for the first two studies. Several studies have been conducted to analyze the efficacy of the 7 & 7 and the conception data was comparable to the MGA derived protocol. Thus, one potential direction for the future would be to formulate a research study that compares the two protocols. Since the conception rates were similar, it may be hypothesized that the MGA protocol could be more widely accepted as there is a reduction number of times animals are handled.</p>