<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>

<p dir="ltr">Porcine reproductive and respiratory syndrome virus (PRRSV) is a devastating virus that is endemic to the swine industry. This virus has little direct effect on the dam but results in abortions, stillborn, and delivery of viremic piglets. PRRSV is unable to cross the swine placenta in early gestation but as gestation progresses, the placenta becomes permissible during late gestation. The mechanisms that allow the virus to cross the late gestation placenta are not well understood, but several theories have been presented regarding changes in placental morphology or enzymatic changes. Additionally, piglets who experience IUGR due to uterine crowding have been found to be more resistant to PRRSV infection, having lower viral levels than their normal litter mates. When vertical transmission from the dam to fetus occurs not only can the effects previously mentioned occur, but PRRSV is also known to cause suppression of maternal and fetal thyroid hormone. Thyroid hormone plays numerous roles in fetal development such as accretion of fetal mass, appetite regulation, and coincidently follows a similar increase trajectory to that of fetal growth during mid- to late-gestation. Consequently, any dysregulation of thyroid hormone has the potential to cause severe side-effects and may alter fetal growth. The relationship between thyroid hormone and fetal growth and development is not well understood. Chapter 2 investigates the potential cause-and-effect relationship between fetal growth and thyroid hormone through the induction of fetal hypothyroidism. Pregnant gilts (n=24) were given a sham treatment (CON; n=12) or treated with methimazole (MMI; n=12), a goitrogen capable of crossing the placenta. These gilts were then further subdivided across four gestational timepoints spanning mid- to late-gestation, these being days 55, 66, 76, and 86. Treatment started 21 days prior to these desired dates. Upon completion of treatment the gilts were humanely euthanized, and fetuses were extracted (resulting populations of n=174 MMI and n=166 CON) and fetal body and organ weights were recorded. Collected tissues included heart, liver, lung, kidneys, spleen, brain and thyroid. Fetuses were imaged in the left and right lateral recumbency for phenotypic analysis, including novel head measurements. Placental sample were also taken. Additionally fore- and hind limbs were taken from the centermost male and female from each litter so that radiographs could be taken to analyze bone growth. Statistical analysis of all phenotypic differences was carried out using a linear mixed effect model including gestational age and treatment as fixed effects and gilt as a random effect. The data revealed that the left and right phenotypic parameters are highly correlated (R2>0.9). Upon extraction, goiters were present in the MMI fetuses and there was a significant increase in both absolute and relative thyroid weights. Thus, the use of MMI during this period of gestation was successful in inducing hypothyroidism. Additionally, the MMI treated thyroids had a significant treatment by time interaction with 0.014g and 0.21g increase at day 55 and 66 respectively indicating reduced compensatory action within the fetal hypothalamic-pituitary-thyroid axis during this earliest period. Liver weight as a percentage of body weight decreased from 6.06% to 2.56% between days 55 and 86 in the CON group but, was significantly increased at all time points in response to MMI induced hypothyroidism (P<0.01). Thus, the in brain to liver weight ratio decreases over time, in MMI fetuses (P<0.05). While all other phenotypic parameters were significantly altered by gestation age, there was no significant impact of fetal hypothyroidism. This indicates that fetal thyroid hormone is not the driving factor for the exponential fetal growth seen in mid- to late-gestation. PRRSV virus is a complex and devastating virus to the swine industry, especially when it infects pregnant gilts and sows. PRRSV is unable to cross the swine placenta during mid-gestation but as gestation progresses the virus readily crosses the placenta and is able to infect piglets during this late gestation period. The mechanisms by which PRRSV crosses the highly restrictive porcine placenta are not clear. Additionally, piglets who experience intrauterine growth retardation experience lower virus levels than their normal counterparts. Chapter 3 investigates the changes in three genes of interest that we hypothesized, had the potential to fluctuate throughout gestation and facilitate PRRSV transfer, as well as the morphological changes that occur in the maternal-fetal interface through mid- to late-gestation and how these aspects may vary between IUGR and normal piglets. Placental samples were collected from pregnant gilts (n=12) equally divided across days 55, 66, 76, and 86 of gestation. Samples were taken of each fetus’s placenta adjacent to the umbilical cord. A portion of the sample was cut into 1 cm2 and placed into a mold with optimal cutting temperature media (OCT) for later cryo-sectioning and histology. The remaining portion had the fetal placenta peeled from the endometrium and flash frozen in liquid nitrogen for RNA extraction. A subset of samples was chosen based on fetus’s brain to liver weight ratios (n=96). From each litter two males and two females with the most extreme case of IUGR, based on z-scores, were chosen and the same was done for the two males and females with lowest brain to liver weight ratios, the later were classified as large for gestational age (LGA). 56 of the original 64 had acceptable levels of placental RNA for analysis. A total of 3 genes were chosen for analysis based on their function and previous literature. These included CD163, SIGLEC1 and IL-10. No significant up or down regulation was seen in any of the selected genes and there was no variation between IUGR and LGA fetuses. Additionally, placenta histology was conducted to evaluate populations of CD163 positive macrophages throughout the maternal fetal interface across mid- to late-gestation. Populations of CD163 positive macrophages were found on both the maternal and fetal sides of the maternal fetal interface at all timepoints. Collectively these results show there is no fluctuation in CD163, SIGLEC1, or IL-10 among timepoints or between IUGR and LGA fetuses. Additionally, the histology samples confirm the presence of resident populations of CD163 positive macrophages on maternal and fetal sides of the MFI. Collectively these results indicate that more research needs to be done to determine the underlying mechanisms of PRRSV transmission during late gestation.</p>

Prolificacy in sheep, under most types of flock management, may exert an overwhelming influence on profitability. Three major classes of sheep farming are found in New Zealand, namely Extensive farming, on high country and droughty areas where wool is the chief product, Store sheep farming, on harder hill country, where income is derived from sales of both wool and surplus stock, and Fat lamb farming, in the easier and improved areas, where sales of fat stock almost exclusively dictate the size of the income. In all three types, ewe fertility is of paramount importance. This investigation was undertaken as a pilot attempt to demonstrate, with more accuracy, the source of, or reason for, the additional lambs which result from flushing ewes, in as far as this practice may increase both ovulation rate and subsequent mortality or merely reduce mortality in developing ova at some as yet underdefined stage of early pregnancy. The nature of the experiment was such that a study of the time-relationships of ovum loss and embryo mortality at various stages in early pregnancy could be made. Thus the matings of 225 ewes in two separate mobs were observed and slaughter dates were measured for individual ewes from mating times. By this means a considerable collection of both field and laboratory data was made available for a study of comparative individual and group reactions to the flushing treatment applied.