Necrotic enteritis (NE) is an important enteric disease in poultry production that has re-emerged as a major problem following an EU wide ban on the use of in-feed antimicrobials. Although the primary aetiological agent of disease is Clostridium perfringens type A, a commensal in the gastrointestinal tract (GIT) of chickens, numerous additional influential factors have been reported that can predispose chickens to NE. These precipitating factors mainly include diet, co-infection with other pathogens particularly coccidia, as well as environmental and management factors. Despite being first described almost more than 50 years ago, a reliable, consistently reproducible experimental model for NE induction is still lacking. Here, a series of experiments were conducted to investigate the importance of the various potential predisposing factors, in isolation and in combination, that are believed to play a role in sub-clinical NE development: feed withdrawal, dietary protein sources, co- infection with coccidia, C. perfringens dose and contact with reused litter. In addition, chicken breed sensitivity to NE was assessed, and last, but not least, blood and gut tissue samples were used to identify novel biochemical markers for sub-clinical NE. Chapter 3 reports an experiment showing that feed withdrawal up to 24 hrs in experimentally challenged birds did not result in NE specific lesions. Chapter 4 shows that replacing dietary soyabean meal with potato protein concentrate or canola meal or adding synthetic trypsin inhibitor to the soyabean meal control diet did not induce sub-clinical NE in birds housed on reused litter, a natural source of C. perfringens challenge. Chapter 5 describes that in vitro growth of C. perfringens on in vitro digested grower diets was prolonged following the addition of fishmeal, suggesting that the role of fish meal as a predisposing factor for in vivo sub-clinical NE cannot be excluded. All subsequent diets therefore contained high levels of fish meal. When this was used in combination with high dose of coccidial vaccine, a repeated in-feed challenge for three days at 102 colony forming units (cfu) C. perfringens per g feed did not result in sub-clinical NE, though at 109 cfu/g resulted in 10% of challenged birds (3 out of 30) showing NE-specific lesions (Chapter 6). Further study is needed to determine if the two Ross birds with gross NE lesions compared to the one Hubbard bird (out of 15 birds each) was due to a lower level of NE resistance. 3 The failure to significantly induce sub-clinical NE in the previous experiments suggests that challenging the birds with C. perfringens in the isolated presence of suspected predisposing factors may not provide a suitable experimental model. Indeed, when birds were dosed twice daily with 108 cfu C. perfringens for three days in the presence of high levels of fishmeal, canola meal as main protein source, coccidial and IBD vaccinations, and feed withdrawal prior to challenge, 40.6% of the challenged birds developed lesions of sub-clinical NE without inducing mortality (Chapter 7). This concurred with reduced growth performance relative to the sham-infected control birds, and thus is a successful model for induction of sub-clinical NE. Finally this work has, for the first time provided novel information on potential biomarkers (Chapter 8). Whilst challenge did not impact on the expression of genes previously shown to be differentially expressed upon C. perfringens toxin exposure, the serum ceruloplasmin concentration increased, suggesting that monitoring this acute phase protein may indicate the presence of C. perfringens infection in poultry. However, as such markers generally lack specificity, further research confirming its role in response to sub-clinical NE is needed to provide a fully effective diagnostic and prognostic marker for flock health and welfare, as well as ultimately helping to gain better understanding of the pathophysiology of sub-clinical NE. Improved knowledge of the effect of different dietary components on the growth of C. perfringens may help in the formulation of broiler diets to assist in further reducing the incidence of NE particularly in the absence of antimicrobial growth promoters. It is hoped that host responses in terms of acute phase proteins, and possibley gene expression, will also provide greater insight into the pathogenesis of NE. Provided that the developed experimental sub-clinical NE model is reproducible, this will benefit the understanding of this billion dollar disease and enable further investigation of various chemical and non-chemical interventions to reduce its severity and impact on poultry production.

Tannins are polyphenolic compounds which precipitate, or conjugate, with proteins to make them indigestible. Tannins appear to confer anti-herbivore defense in shrub live oak (Quercus turbinella), a common browse in the interior chaparral of Central Arizona. The results of the present study indicate that the rumen microflora in goats can adapt to tannin rich diets thereby increasing in vitro dry matter digestibility of shrub live oak leaves. Major digestion inhibitors of shrub live oak appear to be fiber content (NDF, ADF, and lignin) and presence of condensed tannins in the leaves. In vitro dry matter digestibility of oak leaves appears to be higher in rumen microflora from goats than in rumen microflora from cows, although further research is needed to determine digestive efficiency among these species.

Effects of weaning on metabolic profiles and hepatic IGF-1 mRNA of beef dams (Trial 1), and diet effects for early-weaned (EW) steers on response to an infectious bovine herpesvirus-1 (BHV-1) challenge (Trial 2) were investigated. Trial 1 treatments were arranged in a 2 x 2 factorial and included 14 heifers and 14 cows assigned randomly to one of two treatment regimens: EW (average age of 114 ± 13 d) or normal-weaned (NW, average age of 197 d). Heifers with calves EW experienced a greater increase (parity x weaning; P = 0.02) in BW over heifers with calves NW, but no change in BW due to weaning was observed for cows (P > 0.71). Early weaning (vs. NW) increased (P < 0.05) body condition (BC) and change in BC of all dams. No parity x weaning or parity x weaning x d interactions (P > 0.14) were observed for serum IGF-1, NEFA, or urea nitrogen (SUN). A parity x d interaction (P < 0.05) for hepatic IGF-1 mRNA, serum IGF-1, and SUN was observed, but no differences (P > 0.10) were detected between heifers and cows within d. For Trial 2, backgrounding treatments included a bermudagrass hay diet (CTRL); bermudagrass hay plus soybean meal (SBM) fed at 0.175% of BW (as-fed); bermudagrass hay plus SBM at 0.35% of BW; or a 70% concentrate (CONC) diet. During the receiving phase, all steers were fed CONC and intranasally challenged with BHV-1. Treatment x d interactions (P < 0.01) were observed for serum NEFA, total protein, SUN, glucose, immunoglobulin G (IgG), insulin, and rectal temperature. Three d after the BHV-1 challenge, IgG was greater (P < 0.05) for forage-fed steers vs. CONC. Three and 4 d after the challenge, rectal temperature was greater (P < 0.01) for protein supplemented steers vs. CTRL. Therefore, EW can increase BW and BC of first-calf heifers and decrease SUN in first-calf heifers and mature cows, and a higher quality diet fed to EW steers during a backgrounding phase enhances ADG and G:F, and increases febrile response (measured by rectal temperature) to an infectious BHV-1 respiratory challenge.

Objectives were to determine the effects of feeding dry-rolled (DR) vs steam-flaked (SF) sorghum grain and degree of processing (flake density, FD) of corn and sorghum grain on site and extent of starch digestion and post-absorptive metabolism of energy-yielding nutrients in steers fed 77% grain. The design for each trial was a randomized block. Seven steers (400 kg) with duodenal and ileal cannulas were used to determine corn and sorghum starch digestibilities (Cr ratio, 3-d collection). Steers fed SF versus DR sorghum increased starch digestibility in the rumen (23%; P < .01), total tract (2.3%; P < .01), and in the small intestine (6%; P < .01, as percentage of starch entering duodenum). Decreasing flake density of SF sorghum grain increased linearly (P < .05) starch digestion (percentage of intake) in the rumen and total tract, and diminished linearly (P < .05) starch digestibilities post-ruminally and in the small intestine. Similar responses in starch digestibilities occurred by lowering FD of SF corn. Percent dietary corn or sorghum starch digestibility in the large intestine was less than 2% of intake. Feeding SF compared to DR sorghum did not alter net absorption and uptake or release of energy-yielding nutrient across SPL tissues. As expected, net absorption of glucose across portal-drained viscera (PDV) was negative (-.60 mol/d). Incrementally decreasing FD of SF sorghum linearly increased net PDV absorption of lactate (P =.04), glucose synthesis by the liver (P =.03), and SPL output of glucose (P < .01) and L-lactate (P =.03). Net propionate PDV absorption (P =.18), hepatic uptake (P =.21), and SPL output (P =.15) tended to be increased with lower FD. Increasing degree of grain processing, by incrementally decreasing FD, linearly increased ruminal and total tract starch digestibilities and net absorption of glucose precursors (propionate and L-lactate), resulting in increased hepatic synthesis and greater output of glucose from the gut and liver to the rest of the body. Based on these changes, the optimum FD for SF sorghum grain was 283 g/L (SF22).

Two experiments were conducted to determine the effects of grain processing, grain sources, protein sources, and bST treatments on lactation performance, ovarian activity and nutrient digestion in early lactation dairy cows. In experiment 1, forty-eight dairy cows were divided into six groups and fed diets containing 37 to 39% grain as either steam-flaked sorghum (SFS, 360 g/L), steam-flaked corn (SFC, 360 g/L), or steam-rolled corn (SRC, 490 g/L) with one of two protein sources, soybean meal (SBM) or Prolak® for 70 days. Main effects for grain and protein source were not different for DMI, milk yield, 3.5% FCM yield or feed efficiency. Although efficiency of feed conversion into FCM did not differ among treatments, cows fed Prolak® required 10% less NEL for every Mcal of NEL converted into body weight or FCM. Milk protein yield was increased by both flaked gain and Prolak®. Feeding flaked grain increased milk production by 1.5 kg/d compared with rolled grain. Increasing the ratio of RDS/RDP to more than 2.4 increased milk yield by 2.7 kg/d (39.0 vs 36.3 kg/d). Plasma NEFA levels did not differ among treatments and grain and protein source had variable effects on PUN. Compared with other grains, SFC increased digestibilities of DM and OM, and flaked grains increased digestibility of starch. Cows fed SFS had the lowest crude protein digestibility, but was highest in NDF. In experiment 2, thirty-two postpartum (5 DIM)Holstein cows were assigned to one of four treatments in a 2 x 2 factorial design for 90 days. Treatments were: steam-flaked sorghum diet with bST (SFS-B); steam-flaked sorghum diet without bST (SFS-N); steam-rolled corn diet with bST (SRC-B); and steam-rolled corn diet without bST (SRC-N). Cows receiving bST during the first 45 days of treatment had lower DMI and DMI as % of BW. Milk yield was increased by bST 3.1 kg/d and 1.8 kg/d during the 45 d and 90 d periods, respectively, resulting in greater feed efficiency for bST-treated cows. Grain processing did not affect DMI, milk yield and FCM yield. Neither composition nor yields of milk components were influenced by treatments. Compared to the SRC diet, SFS increased plasma glucose 5% and plasma insulin 19%. Grain processing and bST had no effect on either BHBA or hepatic triglycerides. PUN was reduced by bST, but NEFA was increased. Compared with SRC, SFS increased progesterone during the first two postpartum estrous cycles and cows receiving bST had significantly larger CL. Flaked sorghum compared with SRC increased digestibility of DM, OM, and starch, and neither grain affected digestibilities of CP, NDF or ADF. Treatments with bST did not affect any nutrient digestibilities.

Three experiments were conducted to determine the effects of bST on lactational performance throughout several stages of lactation, emphasizing advanced lactation and summer heat stress conditions. In the first experiment, a preliminary trial was conducted using seven Holstein cows averaging 424 DIM. Injections of bST increased milk, fat and protein yields, but did not affect milk composition. In the second trial, 24 cows in advanced lactation (292 DIM) with breeding problems were assigned to one of the three treatments in a randomized block design. Treatments were: (1) CON; low energy diet, without bST injection; (2) LED; low energy diet, injected with bST; and (3) HED; high energy diet, injected with bST. Cows showed a large response to bST in yields of milk, FCM, fat and protein, as well as on efficiency of feed conversion to milk. Energy density in the diet of cows receiving bST did not significantly affect any measured variable. In the second experiment, 76 lactating Holstein cows were distributed in three trials according to stage of lactation. Six intervals of DIM were considered: very early, early, mid, late, advanced, and extended lactations. A favorable response in milk yield to bST injections was observed in mid, late, advanced and extended lactations, while only a tendency was observed in early, but not in very early lactation cows. In the third experiment, 32 Holstein cows averaging 195 DIM were placed on four treatments to determine the effect of bST and evaporative cooling on lactational performance during summer heat stress. Milk yield was significantly increased by bST injections and tended to be higher for cooled cows. Fat and protein yields were increased by bST, but not by cooling. Non-esterified fatty acids in blood serum were higher in cows injected with bST, suggesting greater fat mobilization to support the increased milk production. Rectal temperatures and respiration rates were decreased by evaporative cooling, but not affected by bST injections.

To evaluate the effect of two different cooling systems on production, physiological, and hormonal responses, 37 Holstein and 26 Brown Swiss dairy cows were allotted to three treatments. A control group of cows had access to only shade (C). A second group was cooled with spray and fan (S/F) and the third group was under an evaporative cooling system called Korral Kool&circR; (KK). The trial lasted from May to September with a daily maximum temperature-humidity index from 73 to 85. Milk production differences in Holstein cows were significantly increased by KK and S/F. No treatment differences in milk production were observed in Brown Swiss cows. Protein percentages were higher in C group compared to Korral Kool group only in Brown Swiss cows, while fat percentage were similar among treatments in Holstein cows. Rectal temperatures and respiration rates of the C group were higher than S/F and KK in both Holstein and Brown Swiss cows. Triiodothyronine levels in milk were significantly higher in KK group compared to S/F and C groups, while cortisol levels were lower in C group than S/F and KK. Similar differences were observed in body weight and body condition score changes between treatments in Holstein or Brown Swiss cows. Pregnancy rate was increased in the groups under the cooling systems in Holstein cows, however this effect was not observed in Brown Swiss cows where C group had a higher pregnancy rate than cooled groups. The cows under cooling systems spend more time eating and outside of the shade in the early afternoon (12:00 to 15:00) than control group. Cows injected with bST (bovine somatotropin) increased milk yield significantly only in Brown Swiss cows, whereas respiration rates were increased in both breeds by bST but rectal temperatures were similar between bST and non-bST cows. These results demonstrate that both cooling systems are an alternative to increase productive and reproductive performance and comfort of Holstein cows during summer in hot-dry climates. The physiological responses of Brown Swiss cows indicated a better adaptation to a hot climate, however their milk production was lower than in Holstein cows.

Experiments were conducted to determine effects of feeding whole cottonseed (WCS), expander solvent cottonseed meal (CSM), or a combination of these, as well as other factors on blood gossypol concentrations in cattle. In an 84 d trial, lactating cows were fed zero, 900 or 1800 ppm total gossypol (TG) in diets from WCS and/or CSM. Plasma gossypol (PG) in cows receiving 1800 ppm TG plateaued at 3.28 μg/ml after 28 d. However, by 28 d, erythrocyte fragility increased for cows receiving WCS diets. Plasma chemistry, vitamin A, body temperatures, and respiration rates were within normal ranges. Serum vitamin E levels increased with cottonseed in diets. Milk yield and FCM higher (P < 0.05) for cows fed 13.5% WCS and 7% CSM diet than controls. Feed efficiency and milk fat and protein percentages were not influenced by diets. In another study, young Holstein steers were fed diets during five consecutive treatment periods of 28 d each. The following was shown: (1) A basal diet with 15% Upland WCS resulted in average TG intakes of 9.08 g/d. (2) When varying concentrations of dietary iron (5 treatments) were fed with 15% WCS, PG and plasma total gossypol response (PG/TG intake) decreased as iron in diets increased. (3) Five diets with 15% cottonseed in the whole, cracked, roasted, roasted and cracked, or extruded forms showed that roasting or excluding WCS reduced FG in seed up to 86%. The PG concentration was higher (P < 0.05) for the whole and cracked diets, but plasma total gossypol response (PTGR) increased over controls for the cracked and roasted treatments. (4) When varying amounts of WCS and CSM (6 treatments) were fed up to 14 and 9% of the diet, respectively, PG concentration was higher (P for diets with 14% than 7% WCS. The PTGR was not affected by CSM supplementation for the 7% WCS treatments. (5) When feeding of four diets with 15% cottonseed as whole Upland, cracked Upland, whole Pima, or cracked Pima seed, PG and PTGR were higher for the Pima than Upland diets. Performance for the 28 d periods was not altered by treatments.

Recent declines in the availability of large marine shrimp reinvigorated the market for the freshwater prawn Macrobrachium rosenbergii. Simultaneously, pressures to find more lucrative and water efficient crops are increasing in arid regions. The integration of a highly valuable crop such as Macrobrachium with irrigated agriculture could be of benefit to arid land farmers. Using a specific farming region in Arizona as a model of arid land systems, the objectives of my research were to: (1) Determine if the physical conditions for prawn culture occur in Arizona. (2) Investigate the feasibility of inland larvae culture. (3) Raise to maturity and spawn M. rosenbergii. (4) Assess the utility of a new species evaluation protocol. To meet these objectives, I reviewed physical conditions in Central Arizona and compared them to known requirements for culture of M. rosenbergii, developed a model larvae culture method and stocked postlarvae from the larvae culture experiments into ponds where they could grow to maturity and spawn. After spawning, the larvae were collected and the fecundity of the adult females determined. My results suggest M. rosenbergii likely can be cultured seasonally in ponds filled with surface water within the representative region. Constraints to culture include high source water pH, hardness, alkalinity, contaminants and low winter water temperatures. Larvae culture is possible within the representative region. However, successful mass culture will require refinement of techniques used in my study. Constraints to culture include high ambient pH of surface waters, periodic high hardness and alkalinity levels and low winter temperatures. Improved filtration techniques in the incubator and a consistent availability of Artemia for food are also issues of concern. Prawns hatched and grown in Arizona spawned readily, were as fecund as other cultured stocks and produced viable larvae up through stage 2. The protocol I used was appropriate for evaluating a species for aquaculture at a new location. Overall, M. rosenbergii shows potential as a candidate for integration with irrigated agriculture systems within arid farming regions.

Growing beef steers were used in completely randomized block designs to evaluate effect of processing method, dry-rolled (DR) versus steam-flaked (SF) sorghum, and degree of processing (flaking density) of corn and sorghum grain on nitrogen (N) digestion and post-absorptive N metabolism. In experiments (Exp.) 1 and 2, seven duodenally and ileally cannulated steers were used to investigate N digestibilities. Experimental diets contained 77% grain: Exp. 1, DR or SF sorghum at densities of 437, 360 and 283 g/L (SF34, SF28, SF22); Exp. 2, corn at two flake densities (SF34 and SF22). Nitrogen intakes by steers fed sorghum (142 g/d) and corn (149 g/d) diets were similar among treatments. Steers fed SF compared to DR, increased ruminal (P =.04) DM digestibility. Microbial protein flow to the duodenum averaged 10% greater for SF vs DR. Reducing flaking density of sorghum grain linearly increased (P .05) ruminal DM and tended to increase linearly ruminal feed N (P =.11), total tract DM and N digestibilities and microbial efficiency (P .08). Unexpectedly, flake density did not affect DM or N digestibilities of SF corn diets by steers. In Exp. 3, eight steers implanted with indwelling catheters were used to measure blood flow, net absorption and uptake of ammonia-N, urea-N (UN) and alpha-amino N (AAN) across portal-drained viscera (PDV), hepatic and total splanchnic tissues. Experimental diets were the same as those in Exp. 1. Six arterial, portal and hepatic blood samples were collected per day at 2 h intervals for each diet and steer. Daily DM and N intakes averaged 7.0 kg and 142 g, respectively. Decreasing flake density of SF sorghum linearly increased net absorption of AAN (P =.04) and UN recycling to the gut (P =.02). Net UN recycling to the gut averaged 38% of N intake across treatments. Steers fed SF compared to DR decreased (P =.03) net splanchnic UN output (33 vs 50 g/d). The improved N retention and lower splanchnic UN output, contingent with greater ruminal microbial protein synthesis and flow to intestines may explain in part the observed higher performance of cattle fed SF compared to DR sorghum. Based on improved total tract N digestibilities and greater net absorption of AAN and UN recycling to the gut, optimum flake density for SF sorghum grain was 283 g/L (SF22).