Document Type

Dissertation - Open Access

Award Date

2023

Degree Name

Doctor of Philosophy (PhD)

Department / School

Animal Science

First Advisor

Crystal Levesque

Abstract

The best-known predictor of reproductive success in gilts is the age at puberty. Early puberty (i.e., d170 – d180 of age) is associated with improved long-term reproductive performance and more full value offspring for market. The ability to predict, in the prepubertal stage, the age that a replacement gilt would be expected to achieve puberty has great reproductive and economic advantages. This work focuses on identifying biological markers that are potentially predictive of age at puberty. Study 1 identified changes in the vaginal epithelium during gilt reproductive development. Pre-pubertal gilts (n =13) were followed from d70 of age until first estrus or d213-215 of age. Blood, vaginal epithelia, and anogenital distance were collected at five timepoints during reproductive development [d70/77 (on-farm arrival), d100/110 (mid-folliculogenesis), d130 (post-folliculogenesis), d160 (start of boar exposure) and first estrus or end of trial (d214 of age)]. Total RNA was isolated from vaginal epithelia and relative gene expression of two toll-like receptors (TLR-4 and TLR-5), tacykinin precursor-3 (TAC-3), insulin-like growth factor-1 (IGF-1), and estrogen receptor-alpha (ER-α) was quantified by real time q-PCR, relative to expression of ribosomal protein lateral stalk subunit P0 (RPLP0). Expression of IGF-1 and TAC-3 were up-regulated 9- and 7-fold, respectively at d160 (P < 0.05). Expression of ERα tended to be upregulated 3-fold at d100 (P = 0.08) and expression of TLR-4 and TLR-5 was lowly detected prior to first estrus. Anogenital distance was positively correlated to age at first estrus and negatively correlated to daily gain (P < 0.01; r = 0.83). In experiment 2, pre-pubertal gilts (n = 29) were followed from d70 of age until first estrus or d215 of age. Vaginal swabs were collected at similar timepoints as described in experiment 1. By d215 of age, 19 females were classified as expressing estrus ‘early’ (d160 to d181), 4 were ‘average’ (d181- d202), and 6 were ‘late’ or ‘anestrus’ (d202 to d215). A subset of 5 gilts that expressed estrus early and 5 gilts that expressed estrus ‘late’ or ‘anestrus’ were used for vaginal transcriptome analysis using RNAseq and vaginal samples at d100, d130, and d160 of age. Data normalization used the reads per kilobase million (RPKM) method. Fold change differences were calculated across genes, within each estrus grouping (early or late). Differences in gene expression between ‘early’ and ‘late’ gilts were calculated using a Welch two-sample t-test in R (v 4.0.2). A gene selection process was used based on differential expression at each time point, between estrus groups, and across multiple time points to identify target biomarker genes. The process reduced total differentially expressed genes from > 2,000 to 6 genes of interest, with genes Lin28 homolog A (LIN28A), Anoctamin 2 (ANO2), and Lysl oxidase homolog 2 (LOXL2) more highly expressed in early estrus females. Genes of interest relative to late estrus females were Glycogen synthase 2 (GYS-2), Growth regulating estrogen receptor binding 1 (GREB-1), and Interferon alpha 16 (IFN-Alpha-16). Gene LIN28A had higher expression in early estrus gilts (P < 0.05). There was no significance between early and late estrus gilts for gene ANO2 but was expressed at least 10-fold greater in early estrus gilts at d130 of age. Gene LOXL2 tended to be expressed at higher levels in early estrus gilts across all time points than their late estrus counterparts (P =0.06). For the late estrus gilts, GYS-2 was 35 and 15-fold greater at both d100 and d130 of age (P = 0.04). Gene GREB-1 was expressed more than 10-fold greater in late estrus gilts, with a tendency at d160 of age (P = 0.09). Lastly, IFN-Alpha-16 tended to be more expressed at d100 of age (P = 0.06) in late females. Overall, there are distinct differences in vaginal gene expression at a given day of age for replacement gilts that may be used to predict age at puberty. Within this dataset, 100, 130, and 160 days of age may be ideal timepoints for identification of early estrus in pre-pubertal gilts; however, a more robust dataset analysis is necessary to pinpoint the ideal day of age in reproductive development to serve as a marker for identification of early estrus. The goal of the third chapter of this dissertation was to collect descriptive data of gilt rearing practices in the Midwest. A successful gilt development program is critical to the success of a production system because it has a direct effect on reproductive performance. While there have been reviews of literature for current industry practices employed for reproductive management (Kraeling and Webel, 2015), and performance data collected and reported by Metafarms, there is little to no data that includes both gilt management practices and decisions throughout reproductive development and a sow’s first parity within a breeding herd. Therefore, the objective of this survey was to obtain an understanding of gilt development practices across the Midwest to ensure that the next phases of research have high practical application and relevance. A total of 10 respondents participated, with farms located in Nebraska, South Dakota, Iowa, and Minnesota. These farms collectively manage approximately 43,000 sows. Data was collected and analyzed for descriptive statistics within Microsoft Excel. The herd parity 3 after gilt acclimation, with a minimum parity of 2.1 and the highest parity average of a 5. With such a young herd parity average range, it means animal removal is occurring at a young production age and warrants further investigation into reasons for removal. Based on this survey, more detailed information on gilt rearing, diet composition, and space per pig needs to be obtained. In conclusion, vaginal gene expression appears to change in concert with circulating reproductive hormones, with significant changes in IGF-1 and TAC-3 occurring at the start of boar exposure (d160 of age). Anogenital distance was positively correlated to age at first estrus and negatively correlated to daily gain, but due to inconsistencies in measurement collection, caused by events like gilt restlessness and vulva clenching makes this unapplicable for on-farm application. There are distinct differences in vaginal transcriptome between gilts deemed ‘early’ and ‘late’ estrus. Within this dataset, there were three genes of interest that have greater expression in ‘early’ gilts, and three genes of interest that have greater expression in ‘late’ estrus gilts. Currently, d100, d130 and d160 may be ideal timepoints for identification of early estrus in pre-pubertal gilts, but a larger sample size is necessary to pinpoint the ideal deal in reproductive development. Identification of the ideal age for pubertal detection, paired with an understanding of common gilt rearing practices and diet regimes can provide swine producers with information to maximize their gilt development program and reduce the number of replacement females needed within a herd each year.

Library of Congress Subject Headings

Sows.
Sows -- Reproduction.
Sows -- Productivity.
Gene expression.
Puberty.

Publisher

South Dakota State University

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Rights Statement

In Copyright