Doctor of Philosophy / Department of Animal Sciences and Industry / Robert D. Goodband / Michael D. Tokach / The dissertation consisted of 6 chapters involving studies in heavy weight market pig production, dietary Ca and P requirements for nursery pigs, antimicrobial resistance development in finishing pig microbiota, seasonal growth variability in commercial pig production, and leftover feed management in wean-to-finish pig productions. The first chapter presents a thorough review of published studies involving genetic selection, nutritional requirements, health, welfare, and pork quality of finishing pigs with marketing weight greater than 130 kg and assessed future research needs. Chapter 2 describes 2 experiments that evaluated the growth performance and percentage bone ash of early nursery pigs fed various combinations of Ca and P provided by inorganic sources or phytase. Feeding more than 0.90% dietary Ca decreased average daily gain (ADG), average daily feed intake (ADFI), gain:feed ratio (G:F), and percentage bone ash when diets were at or below NRC (2012) requirement for standardized total tract digestible (STTD) P. However, adding inorganic P or phytase to P deficient diets improved pig performance and alleviated the negative impacts of high dietary Ca concentration on growth performance. The experiment presented in chapter 3 characterized the dose-response to increasing digestible P in diets without or with 2,000 units of phytase for 6- to 13-kg pigs. Increasing STTD P from 80 to 140% of NRC (2012) requirement estimates in diets without phytase, and from 100 to 170% of NRC (2012) in diets with phytase, improved ADG, G:F, and percentage of bone ash. Estimated STTD P requirements varied depending on the response criteria and statistical models and ranged from 91 to >140% of NRC (2012) in diets without phytase, and from 116 to >170% of NRC (2012) for diets containing phytase. In addition, phytase exerted an extra-phosphoric effect on promoting pig growth and improved the P dose responses for ADG and G:F. In chapter 4, a study was conducted to determine the effects of tylosin administration route (through feed, drinking water, or intramuscular injection) on the growth performance and the development of antimicrobial resistance in fecal enterococci of finishing pigs. Pigs that received tylosin injection had decreased ADG and G:F compared with control pigs that did not receive any antibiotic treatment, which may be due to a stress response to the handling during injection administration. Moreover, tylosin administration via injection and feed resulted in a higher probability of enterococcal resistance to erythromycin and tylosin compared with drinking water treatment. Chapter 5 presents a retrospective analysis on the seasonal growth patterns of nursery and finishing pigs in 3 commercial production systems located in the Midwest US. Nursery ADG and ADFI expressed prominent seasonal variations and were similar among systems, whereas nursery G:F was not affected by season. Finisher ADG, ADFI, and G:F varied over seasons, but the magnitudes and patterns of change were system dependent. This chapter also presents the concepts underlying the implementation of a multi-level linear mixed model of production records to analyze seasonality and potentially other decision factors in commercial systems. Finally, in chapter 6, 2 experiments were conducted regarding the strategy of managing leftover finisher feed in a wean-to-finish production system. Experiment 1 evaluated the timing (phase) of feeding 2.5 kg/pig of finisher feed in a 5-phase nursery program. All growth responses decreased immediately when the finisher feed was blended into nursery diets; however, pigs greater than 11 kg (phase 3) had improved ability to compensate for the negative effects of finisher feed on overall growth performance. Experiment 2 was then carried out to investigate the maximum amount of finisher feed can be fed to 11-kg pigs. Increasing the finisher feed budget from 0 to 3.75 kg/pig resulted in a linear decrease in ADG and ADFI. However, the economic analysis indicated no change in income-over-feed-cost due to the timing and dose of blending finisher feed into nursery diets.

<p>Two experimentswere  conducted  using  pigs  at different  life stages to  determine  the  effects  of dietary  tryptophan  and  water  delivered  oregano  essential  oil  on growth performance, rectal temperature, water use,intestinal integrity and gene expression of biomarkers in the face heat or transport stress. In the first experiment, 192 grow-finish pigs were used to investigate the effects of  water  supplementation  of  oregano  essential  oil  (OEO)  on  growth  performance,  water  intake, rectal temperature, intestinal integrity, and expression of genetic biomarkers during an acute heat challenge. Pigs were randomly allotted to 2 X 2 factorial arrangement of treatments with pigs being heat  stressed  or  not  and  being  supplemented  with  OEO  or  not with 8  replicate  pens  of  each treatment  with  6  pigs/pen  (4  barrows,  2  gilts  per  pen).  Water  treatments  were administered immediately, with  dosing at  47 μL/L of OEO. One-half  of  the  pigs  on  each  water  treatment remained under thermoneutral conditions (TN; 21.1C), while the other half was subjected to a 3 d diurnal, acute heat stress (HS) with 12 hours at 33.3 oC (7AM-7PM) and 12 hours at 26.7oC (7PM-7AM). Three days post-HS, temperatures were reduced back to TN for the rest of the study, and pigs remained on their water treatments. Rectal temperatures were collected in the morning and evening  of  the  heat  stress  period  on  one  barrow  and  one  gilt  in  each  pen. Jejunal  tissue was collected for subsequent histological examination and determination of gene expression. All data were  analyzed  using  the  GLM  procedure  of  SAS  (ver.  9.4).  Pigs  subjected  to  heat  stress  had reduced ADG (P < 0.003) and G:F (P < 0.008) during the 3d heat stress compared to pigs reared under thermoneutral conditions. However, post-heatstress, heat stressed pigs had compensatory gain resulting in increased ADG (P < 0.001) and G:F (P < 0.001) compared to thermoneutral reared pigs.   Overall,  there  was an  interaction  (P  <  0.006)  observed  between  water  and  heat  treatment with  OEO  increasing  ADG  in  thermoneutral  pigs  but  not  in  heat  stressed  pigs.  Similarly, interactions  between  water  and  heat  treatment  were  observed  for  ADFI  during  heat  stress  (P  < 0.004),  post  heat  stress  (P  <  0.01),  and  overall  (P  <  0.004)  from  increasing  OEO  intake  in thermoneutral pigs but not in heat stressed pigs. Rectal temperatures were higher (P < 0.001) for heat stressed pigs at the end of d 1 and 2 of the acute heat challenge compared to TN housed pigs. Pigs exposed to HS also used more water than pigs housed in a thermoneutral environment (P < 0.002). There were no differences between villi height, crypt depth or VH:CD between treatment groups  (P  >0.05).  There  was  also  no  difference  in  TP53  and  CDKNA1  gene  expression  among treatments (P > 0.10). In the second experiment, 36 barrows were used in an 18d experiment to investigate the effects of pre-weaning tryptophan supplementation on performance and intestinal integrity following  weaning  with  or  without  transport  stress  at  weaning.  Pigs  were  randomly allotted to 2 X 2 factorial arrangement of treatments of pre-weaning tryptophan supplementation or not and weaning transport or not. Pigs on the tryptophan treatment received 0.35, 0.45, and 0.55 g Trp/d in 5 day intervals, beginning 15 d prior to weaning.Tryptophan was dissolved in chocolate milk and administered by oral gavage with control pigs receiving milk only. At weaning, 4 pigs from each pre-weaning treatmentwere euthanized for collection of jejunal tissue.  Of the remaining pigs, half the pigs oneach treatment were transported for 12 h, and half were moved into individual pens  with  no  transport.  Following  transport,  all  pigs  were  individually  housed  and  provided  ad libitum  access  towater  andfeed  from  a  common  diet.  On  d  3  post-weaning,  all  pigswere euthanized for collection of jejunal tissue. Jejunal tissue was used for histological examination and for determination of gene expression. All data were analyzed using the GLM procedure of SAS (9.4).  No  effects  of  Trp  supplementation  were  observed  on  pre-weaning  (P  >  0.10)  growth. Pig BW and ADFI were unaffected (P > 0.10) by Trp supplementation and transport at weaning. Post-weaning, there was a tendency (P < 0.06) for an effect of transport on ADG as transported pigs lost weight in the 3 d post-weaning period while non-transported pigs gained slightly. Gain:Feed post-weaning  was  lower  (P  <  0.04)  for  transported  pigs  compared  to  non-transported  pigs.  No differences  were  observed  for villus base  and  mid  width,  villus  height,  crypt  depth  or  villus height:crypt   depth.   There   was   a   tendency   for   an   interaction   of   transportation   and   Trp supplementation  (P  <  0.06)  on  villi  base  width  driven  by  an  increased  villus  width  in  non-transported pigs given supplemental Trp but a decrease in villus width in transported pigs given supplemental Trp.These results conclude that these alleviating agents had minimal effects when pigs  were  stressed, however TN grow-finish pigs  benefitted  from  OEO  water  supplementation among growth performance.</p>