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Simple Summary: Reproductive loss is a major constraint to efficient swine production. Our goal is to better understand the biology of reproduction in female swine. Gonadotropin-releasing hormone II and its receptor are proteins produced by the pig ovary, but their function is not fully understood. To further explore their role in female reproduction, we measured reproductive hormones in the circulating blood of genetically modified pigs that produce less gonadotropin-releasing hormone II receptor throughout the body, and their littermate control siblings during the estrous (reproductive) cycle. Additionally, we compared the morphological characteristics of the ovary and hormone production by the Corpora lutea (ovarian structures that produce the critical pregnancy hormone, progesterone). Ovaries from females with reduced gonadotropin-releasing hormone II receptor levels ovulated 17% fewer oocytes (eggs), contained Corpora lutea with smaller steroidogenic cells, containing 23% less progesterone, with 18% less progesterone into circulation compared with littermate controls. These data suggest that GnRH-II and its receptor play a role in regulating the number of oocytes ovulated, Corpora lutea development, and progesterone production in pigs. A better understanding of female reproduction will lead to novel interventions to enhance the reproductive efficiency of pigs, increasing the productivity and sustainability of the swine industry. Reproduction is classically controlled by gonadotropin-releasing hormone (GnRH-I) and its receptor (GnRHR-I) within the brain. In pigs, a second form (GnRH-II) and its specific receptor (GnRHR-II) are also produced, with greater abundance in peripheral vs. central reproductive tissues. The binding of GnRH-II to GnRHR-II has been implicated in the autocrine/paracrine regulation of gonadal steroidogenesis rather than gonadotropin secretion. Blood samples were collected from transgenic gilts, with the ubiquitous knockdown of GnRHR-II (GnRHR-II KD; n = 8) and littermate controls (n = 7) at the onset of estrus (follicular) and 10 days later (luteal); serum concentrations of 16 steroid hormones were quantified by high-performance liquid chromatography tandem mass spectrometry (HPLC-MS/MS). Upon euthanasia, ovarian weight (OWT), ovulation rate (OR), and the weight of each excised Corpus luteum (CLWT) were recorded; HPLC-MS/MS was performed on CL homogenates. During the luteal phase, serum progesterone concentration was reduced by 18% in GnRHR-II KD versus control gilts (p = 0.0329). Age and weight at puberty, estrous cycle length, and OWT were similar between lines (p > 0.05). Interestingly, OR was reduced (p = 0.0123), and total CLWT tended to be reduced (p = 0.0958) in GnRHR-II KD compared with control females. Luteal cells in CL sections from GnRHR-II KD gilts were hypotrophic (p < 0.0001). Therefore, GnRH-II and its receptor may help regulate OR, CL development, and progesterone production in gilts. [ABSTRACT FROM AUTHOR]

Neonatal piglets can experience both a decrease in body temperature and hypoxia, increasing risks for pre-weaning mortality. This research evaluated the effects of drying and providing supplemental oxygen to newborn piglets on rectal temperature (RT) over the first 24 h after birth. The study used a CRD with three Intervention Treatments (IT; applied at birth): Control (no intervention), Drying (dried using a desiccant), Oxygen [dried using a desiccant and placed in a chamber (at 40% oxygen concentration) for 20 min]. A total of 42 litters (485 piglets) were randomly allotted to treatments at the start of farrowing. At birth, each piglet was given a numbered ear tag, weighed, and the treatment was applied; RT was measured at 0, 20, 30, 45, 60, 120, and 1440 min after birth. Blood was collected from one piglet from each birth weight quartile within each litter at 24 h after birth to measure plasma immunocrit concentration. There was no effect (P  > 0.05) of IT on piglet RT at 0 or 1440 min after birth. Between 20 and 60 min after birth, piglet RT was lower (P  ≤ 0.05) for the Control than the Drying treatment, with the Oxygen treatment being intermediate and different (P  ≤ 0.05) from the other two IT. The effect of piglet birth weight on responses to IT were evaluated by classifying piglets into Birth Weight Categories (BWC): Light (<1.0 kg), Medium (1.0 to 1.5 kg), or Heavy (>1.5 kg). There were IT by BWC interactions (P  ≤ 0.05) for piglet RT at all measurement times between 20 and 120 min after birth. Relative to the Control, the effects of the Drying and Oxygen treatments on RT were greater (P  ≤ 0.05) for Light than heavier piglets. Plasma immunocrit concentrations tended (P  = 0.07) to be greater for piglets on the Control treatment compared to the other two IT and were lower (P  ≤ 0.05) for Light than Heavy piglets, with Medium piglets being intermediate and different (P  ≤ 0.05) to the other BWC. In conclusion, drying piglets at birth reduced the extent and duration of RT decline in piglets in the early postnatal period compared to undried piglets, especially for those of low birth weight. However, the combination of drying and placing piglets in an oxygen-rich environment provided no additional benefit over drying alone. [ABSTRACT FROM AUTHOR]

Piglets experience a decline in body temperature immediately after birth, and both drying and warming piglets at birth reduce this. However, these interventions may be less effective at higher farrowing room temperatures. This study was carried out at a commercial facility to compare the effect of drying and/or warming piglets at birth on postnatal rectal temperature (RT) under relatively warm farrowing room temperatures (26.6 ± 2.09 °C). Forty-five sows/litters were used in a completely randomized design to compare three Intervention Treatments (applied at birth): Control (no treatment); Warming (piglets placed in a plastic box under a heat lamp for 30 min); and Drying+Warming (piglets dried with desiccant and warmed as above). Temperatures in the warming boxes over the study period averaged 37.7 ± 2.75 °C. At birth, piglets were weighed; RT temperature was measured at 0, 10, 20, 30, 45, 60, 120, and 1,440 min after birth. Blood samples were collected at 24 h after birth from a subsample of one piglet from each birth weight quartile within each litter to measure plasma immunocrit concentration. Data were analyzed using PROC MIXED of SAS with litter as the experimental unit, and piglet as a subsample of litter. The model for analysis of piglet rectal temperature included fixed effects of Intervention Treatment, measurement time (repeated measure), the interaction, and the random effect of sow. Compared with the Control, piglet RT were higher (P ≤ 0.05) for the Warming treatment between 10 and 60 min, and higher (P ≤ 0.05) for the Drying+Warming treatment between 10 and 120 min after birth. Rectal temperatures were higher (P ≤ 0.05) for the Drying+Warming than the Warming treatment between 20 and 120 min. Responses to drying and/or warming were greater for low-birth-weight piglets (<1.0 kg) than heavier littermates, but were generally less than observed in previous experiments with similar treatments carried out under cooler temperatures. Piglet immunocrit values were lower (P ≤ 0.05) for the Drying+Warming treatment compared to the other Intervention Treatments, which were similar (P > 0.05). Immunocrit values tended (P = 0.10) to be lower for light (<1.0 kg) compared with heavier birth weight piglets. In conclusion, drying and warming piglets at birth was more effective for reducing piglet RT decline after birth than warming alone, though the effect was less than observed in previous studies carried out under cooler farrowing room temperatures. [ABSTRACT FROM AUTHOR]

In swine production, boars are castrated to prevent boar taint from testicular androgens and skatole accumulation in fat. Kisspeptin (KISS1) regulates secretion of gonadotropins and gonadal steroids. We used boars from our line of KISS1-/-pigs (10.3389/fgene.2022.1078991) to understand how loss of KISS1 function affects compounds causing boar taint. Boars were fed ad libitum during development. Body weights and testicular volume (TV) were collected at weaning, 40, 70, 100, 130, 160, and 190 d of age using TV = 4/3*π *a*b2*2 and subtracting scrotal skin thickness measured by a Harpenden skinfold caliper. Average daily gain (ADG) was calculated by subtracting the beginning from ending body weight at each age range and dividing by the number of days. At each age, a blood serum sample was collected by jugular venipuncture to quantify changes in hormones during development. Serum concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH) and testosterone were quantified with radioimmunoassay and analyzed as repeated measures with genotype (KISS1+/+; KISS1+/-; KISS1-/-; n = 8 - 20 animals per genotype) and age as the fixed effects. Concentrations of androstenone and skatole in backfat (quantified using ELISA and HPLC, respectively) were log transformed and analyzed with ANOVA. Body weight did not differ among KISS1 genotypes but increased normally with age (P < 0.0001). During development, KISS1+/+ and KISS1+/- boars grew at similar rates. Although the ADG of KISS1-/-boars was similar to other genotypes up to 160 d of age, ADG was reduced at 190 d of age (age x genotype; P < 0.05). Mean concentrations of LH and FSH in KISS1+/+ and KISS1+/- boars were similar throughout development (LH, 1.16 ±0.11 and 1.34 ± 0.17 ng/mL; FSH, 0.88 ± 0.06 and 0.89 ± 0.05 ng/mL, respectively), and were greater than KISS1-/- boars (LH, 0.38 ± 0.23 ng/mL; FSH, 0.56 ± 0.07 ng/mL; P < 0.05). TV of KISS1+/+ and KISS1+/- boars did not differ during development and was greater than KISS1-/- boars (P < 0.05), for which testes could not be palpated after 100 d of age. Testosterone concentrations in KISS1+/+ and KISS1+/- increased 40-fold during development but were below detectable limits in KISS1-/- boars (age x genotype; P = 0.06). Androstenone and skatole in KISS1-/- boars (0.30 ± 1.24 μg/g and 12.6 ± 1.6 ng/g, respectively) at 190 d of age was less (P < 0.0001) than in KISS1+/+ and KISS1+/- boars (androstenone, 4.33 ± 1.16 μg/g; skatole, 69.2 ± 1.2 ng/g), which did not differ from one another. Thus, a single functional allele of KISS1 is sufficient to confer normal secretion of reproductive hormones, testicular growth, and skatole in boars. Moreover, knocking out the KISS1 gene will prevent boar taint, but might slightly reduce growth in later stages of development. [ABSTRACT FROM AUTHOR]

The biological role of kisspeptin in the reproduction of swine has been far less studied than in other species. In the porcine hypothalamus, kisspeptin is coexpressed with neurokinin B and dynorphin in KNDy neurons. Although kisspeptin-stimulated secretion of gonadotropin hormones in gilts was established early, increased expression of hypothalamic KISS1 was only recently confirmed to be associated with puberty and cyclicity in pigs. Gene knockout (KO) models to study kisspeptin in livestock did not exist until TALEN gene editing technology was used to knockout KISS1R in pigs, resulting in a hypogonadotropic-hypogonadal (HH) phenotype that caused pubertal failure. Little is known about the reproductive physiology of KISS1R KO pigs, except that exogenous follicle-stimulating hormone and gonadotropin-releasing hormone only partially restored gonadal development in boars. To further explore the biological function of kisspeptin and its receptor in swine, we recently used CRISPR/cas9-ribonucleoproteins to knockout KISS1 in pigs (10.3389/fgene.2022.1078991). A total of 684 zygotes were injected resulting in 69 piglets with 58% bearing KISS1 KO alleles (KISS1-/-). The proportion of KISS1-/-alleles did not affect BW or ADG in these mosaic founder pigs. Two boars and 2 gilts with complete KISS1 KO exhibited HH and failed to become pubertal. Germ and Sertoli cells were disorganized in small seminiferous tubules. Mating mosaic F0 pigs (frequency of KISS1-/-, 35 to 88%) resulted in 170 F1 piglets with KISS1-/- alleles observed in a Mendelian frequency. These KISS1-/- pigs displayed normal BW growth during development but were also HH. Ovarian development of KISS1-/- gilts was arrested at a juvenile state, although antral follicles were present. The KISS1-/- boars lacked testicular development and had dramatically reduced concentrations of androgens and skatole, suggesting the lack of boar taint in their meat. Importantly, KISS1 and KISS1R are expressed in ovarian, uterine and testicular tissue; however, the direct role of kisspeptin in these reproductive organs remains unknown in livestock. These KISS1-/- pigs provide a unique animal model that opens new avenues for understanding the role of kisspeptin and gonadotropin hormones in regulation of reproductive development and function in pigs as well as livestock in general. These animals facilitate our ability to explore questions such as: 1) how KNDy neurons function and control gonadotropin pulses or 2) what role does KISS1 play in the development and function of the ovary, uterus and testis in domestic animals. Some of these questions have heretofore only been addressable with difficult surgical modifications, and therefore, KISS1-/- pigs represent an alternative to painful procedures in livestock research. Pursuing these fundamental studies is expected to lead to methods that restore fertility in KISS1-/- pigs. This, in turn, could provide new possibilities for the elimination of surgical castration from pork production. The USDA is an equal opportunity provider and employer. [ABSTRACT FROM AUTHOR]