The objective of this study was to determine the relationship between the traits of average daily gain, backfat, loin muscle depth, feed intake and feed conversion measured in growing gilts and their subsequent feed intake (as estimated by feed delivery) in lactation, and to estimate the effects of lactation feed intake on subsequent maternal productivity and sow longevity. Phenotypic performance measurements and estimated breeding values (EBV) were compared with first and second parity lactation feed delivery in a group of selected nucleus gilts of 3 genetic lines. The effects of lactation feed delivery on weaning to conception interval, total piglets born in the subsequent litter and lifetime productivity measures were investigated. Genetic parameters for the growing period traits of average daily gain, backfat, loin muscle depth, daily feed intake and feed conversion, as well as maternal productivity traits of litter size (number alive at day 2), weaning to conception interval and litter weaning weight were estimated and EBV were computed. Phenotypes of growth rate, feed intake, backfat and loin muscle depth recorded in the growing period were not good predictors of lactation feed delivery. However, one genetic line (YO-A) showed significant correlations between second parity lactation feed delivery and growth rate and loin muscle depth measured in the growing period. EBV calculated for the growing period traits of growth rate, feed intake and feed conversion showed much stronger relationships with lactation feed delivery than the growing period phenotypes, particularly for parity 2. Parity 2 lactation feed delivery showed favorable correlations with EBV for growth rate and feed conversion and an unfavorable correlation with the growing period daily feed intake EBV. Lactation feed delivery in the first and second parity had significant effects on the odds of occurrence of the next litter, next litter total born, stayability to parity 3 or parity 4 and sow longevity. Since lactation feed intake is very important to subsequent productivity and longevity of sows and has a positive (unfavorable) genetic correlation with growth period feed intake, it is recommended that lactation feed intake be measured directly and included in the selection goal. The correlation between lactation feed delivery in parity 1 and parity 2 was low at 0.28 across genetic lines, leading to the conclusion that lactation feed delivery in the first and second parities appear to be different traits under different control mechanisms. It is concluded that a balanced selection program for maternal lines that includes selection for reduced feed intake, feed conversion or residual feed intake measured in the growing period, should also include selection for increased lactation feed intake (probably in combination with changes in sow body weight or backfat during lactation in order to prevent negative consequences for sow longevity or productivity). It is also recommended that lactation feed intake in the first and later parities be evaluated as separate traits.

The American black bear (ABB) (Ursus americanus) exhibits physiological strategies highly synchronized with the environment. Such strategies enable bears to exploit food resources when available and survive the winter months by hibernating without ingesting food or water. However, there are multiple aspects of ABB hibernation physiology that remain unknown. For instance, there is conflicting evidence on the occurrence of ABB pseudopregnancy (a physiological state in which a non-pregnant bear exhibits progesterone levels similar to gravid bears in the absence of an actual pregnancy). Also, there is little known about postnatal development of cubs or the influence of maternal traits on embryonic implantation and cub growth. Finally, the role of satellite cells (SCs – stem cells able to regenerate muscle fibers) play in maintaining muscle functionality during hibernating remains understudied. Therefore, I aimed to assess these four aforementioned aspects using wild ABBs held temporarily captive at Virginia Tech's Black Bear Research Center (VT-BBRC). The major findings of this dissertation are: 1) I suggest that wild ABBs do not experience pseudopregnancy as a reproductive strategy; 2) interactions between litter size and cub age best described postnatal cub weight dynamics and organ development. Twin cubs were heavier than single and triplet cubs, yet cubs from all litter sizes reached similar weights after mothers began consuming food post hibernation. Single cubs experienced delayed timing in ear, eye, and teeth development compared to other litter sizes; 3) maternal traits such as higher body weight and higher ability to gain weight in the fall are closely associated with earlier timing of embryonic implantation than in leaner females, which gained less weight per day in the fall; and 4) SC ability to generate muscle fibers is increased during ABB hibernation. I propose that maintaining the SCs are an important potential pathway for limiting muscle atrophy during bear hibernation. Understanding pre and postnatal development of ABBs is important for exploring factors related to climate, maternal characteristics, which possibly affect birthing phenology, and fitness of bears experiencing rapid anthropogenic environmental change. Functional aspects of bear muscle conservation are interesting for potentially for elucidating avenues to improve treatments for human metabolic disorders such as muscular dystrophy, sarcopenia, and disuse atrophy. / Ph. D. / The American black bear (ABB) (Ursus americanus) exhibits physiological strategies highly synchronized with the environment. Such strategies enable bears to exploit food resources when available and survive the winter months by hibernating without ingesting food or water. However, there are multiple aspects of ABB hibernation physiology that remain unknown. For instance, there is conflicting evidence on the occurrence of false pregnancies in the ABB. Also, there is little known about postnatal development of cubs or the influence of maternal traits at the beginning of active gestation and cub growth. Finally, the role of satellite cells (SCs – stem cells able to regenerate muscle fibers) play in maintaining muscle functionality during hibernating remains understudied. Therefore, I aimed to assess these four aforementioned aspects using wild ABBs held temporarily captive at Virginia Tech’s Black Bear Research Center (VT - BBRC). The major findings of this dissertation are: 1) I suggest that wild ABBs do not experience false pregnancy as a reproductive strategy; 2) interactions between litter size and age best described postnatal cub weight dynamics and organ development. Twin cubs were heavier than single and triplet cubs, yet cubs from all litter sizes reached similar weights after mothers began consuming food post hibernation. Single cubs experienced delayed timing in ear, eye, and teeth development compared to other litter sizes; 3) maternal characteristics such as higher body weight and higher ability to gain weight in the fall are closely associated with earlier timing of embryonic implantation than in leaner females, which gained less weight per day in the fall; and 4) SC ability to generate muscle fibers is increased during ABB hibernation. I propose that maintaining the SCs are an important potential pathway for limiting muscle atrophy during bear hibernation. Understanding pre and postnatal development of ABBs is important for exploring factors related to climate, maternal characteristics, which possibly affect birthing phenology, and fitness of bears experiencing environmental change. Functional aspects of bear muscle conservation are interesting for potentially for elucidating avenues to improve treatments for human metabolic disorders such as muscular dystrophy, sarcopenia, and disuse atrophy.