Three experiments were conducted to further study the use of intravenous insulin injection to measure insulin sensitivity in horses. In the first experiment, glucose responses to multiple doses of recombinant human insulin were compared in insulin sensitive and insensitive mares. Regression lines describing the responses in insensitive mares had less (P = 0.003) steep slopes and greater (P = 0.006) effective doses at 50% response (ED50) compared to sensitive mares. Curvilinear regression models provided a good fit (R2 = 0.95) for the prediction of ED50 from the individual responses to 50 mU/kg BW insulin. The second experiment estimated the repeatability of the glucose responses to a fixed dose of insulin in 41 horses (mares and geldings) injected twice, between 7 and 14 days apart. Overall agreement between the responses was significant (P < 0.001) but not high enough to be predictive (R2 value = 0.384). Intra-horse coefficients of variation (CV) ranged from 0 to 68.7%, and averaged 23%. Mares and geldings were similar in their repeatabilities. Horses in the bottom half of the sensitivity rankings had a greater (P = 0.03) average intra-horse CV (28.7 ± 4.6%) than horses in the top half (16.7 ± 2.2%). In the third experiment (single switch-back design), glucose responses to a fixed dose of insulin were compared after an overnight (about 12 hours) versus a 24-hour period of feed deprivation in geldings previously determined to be insulin sensitive (n = 4) versus insensitive (n = 4). The longer period of feed deprivation decreased (P = 0.06) the percentage decrease in blood glucose concentrations, indicating a lesser sensitivity relative to the 12-hour period of deprivation. Insulin sensitivity also affected (P = 0.0003) the glucose response, with sensitive geldings exhibiting the greater response. It was concluded that the response to a single dose of insulin is often a good predictor of a horse's insulin sensitivity, but that the lack of repeatability in some horses could lead to errors in diagnosis. The decrease in glucose response seen after 24 hours of feed deprivation is likely due to the elevation of fatty acid concentrations in the blood.

Different antimicrobials are added in the manufacturing of dairy products such as flavored yogurts and processed cheese. Potassium Metabisulfite (PM) and Potassium Nitrite (PN) have been reported to have antimicrobial effect on pathogenic microorganisms such as Clostridium botulinum and Listeria monocytogenes. Yogurt is known for its health benefits, due to the presence of cultured bacteria. PM and PN are not commonly used in the dairy industry hence it would be interesting to study their influence in yogurt culture bacteria. The objectives of this study were: 1. to elucidate the influence of PM and PN at various concentrations, on the growth of yogurt culture and 2. to determine the possible acquisition of resistance after prior exposure to low doses of these antimicrobials. For the first objective different concentrations of PM and PN (100, 1,000, 10,000, 100,000 and 1,000,000ppm) were separately added to broth previously inoculated with Lactobacillus bulgaricus LB-12 and Streptococcus thermophilus ST-M5. Control samples did not receive any antimicrobial. Growth was determined by plating at 0, 24, 48 and 72 hours of incubation. For the second objective, treatments consisted of separately exposing cultures to 100 and 1,000ppm of both antimicrobials and after 24, 48 and 72 hours, transferring them into 10,000 and 100,000ppm, of both antimicrobials. Growth was measured at 0, 24, 48 and 72 hours of incubation. Data were analyzed using Proc Mixed and Repeated Measures model of the Statistical Analysis System SAS®. Differences of Least Square Means where used to determine significant differences. Neither PM nor PN had an antimicrobial effect on yogurt culture Lactobacillus bulgaricus LB-12 or Streptococcus thermophilus ST-M5. Both antimicrobials at 1,000,000ppm significantly increased counts of Streptococcus thermophilus ST-M5 6 log CFU/mL compared to control. Prior exposure of Streptococcus thermophilus ST-M5 to both antimicrobials at 100 and 1,000ppm for 72 hours showed resistance to 10,000 and 100,000ppm of both PM and PN with a significant increase of 6 log CFU/mL compared to control. Commercial applications of this study would be to incorporate PM and PN in yogurt manufacture for inhibition of spoilage and pathogenic bacteria to ensure good preservation of the product and improved shelf life.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (leaves 232-242).

The first objective of the two studies presented herein evaluated on farm sources of variation and correlated effects contributing to BRD incidence in a population of crossbred steers sent to the feedlot from 2010-2013. Analyses revealed that incidence of BRD was lowly positively correlated to birth weight (BW) and lowly negatively correlated to weaning weight (WW), hip height (HH), sire breed, site, and birth year. These results indicate that the traits analyzed herein are not precursors for BRD in the current population. However, since little is still known about the correlation between genetic predisposition to BRD and animal performance, further studies should be conducted in the future. The second study presented herein evaluated single nucleotide polymorphisms (SNP) located on previously described QTL regions of Bos Taurus Autosome 6 and Bos Taurus Autosome 20 for potential associations with growth traits, carcass traits, and incidence of BRD in crossbred steers. Growth traits analyzed included birth weight (BW), weaning weight (WW), and hip height (HH). Carcass traits evaluated included hot carcass weight (HCW), yield grade (YG), marbling score (MS), ribeye area (REA), and back fat thickness (BF). Along with growth and carcass traits, incidence of BRD was also evaluated in the current population. Genotyping analyses identified fourteen unique SNP located on BTA 6 and eleven unique SNP located on BTA 20 that were significantly (P < 0.05) associated with the aforementioned traits. However, no markers on either BTA 6 or BTA 20 were identified as significantly associated with BF. These results indicate that there may be a higher genetic predisposition to BRD than previously thought. However, before their incorporation into MAS programs, additional SNP located on BTA 6 and BTA 20 should be genotyped, along with other QTL regions spanning the genome. Additionally, a larger population of crossbred steers should be utilized to further validate the results herein.

The first objective of the current study was to evaluate genetic trends from 10 years of the American Brahman Breeders Association Carcass Evaluation Program from 2004 to 2013. Changes of performance in growth, carcass composition, and carcass quality traits were evaluated. Overall means were calculated to report the total average for each trait along with an average rate of change per year. Growth traits evaluated included feedlot entrance weight (INWT), harvest weight (HRVWT), and average daily gain (ADG). Carcass composition and quality traits evaluated included hot carcass weight (HCW), rib eye area (REA), marbling score (MARB), dressing percent (DP), quality grade (QG), yield grade (YG), and Warner-Bratzler shear force score (WBS). Trends indicated that over the 10 year period of improved sire selection, Brahman cattle began entering the feedlot lighter, exited heavier, and improved average daily gain. Furthermore, all carcass composition and quality traits showed overall improvement with the exception of shear force scores. Further investigation of shear force score showed WBS had in fact been experiencing a favorable downward trend since 2009. The second objective of this study was to evaluate SNP located on six candidate genes and their potential association with growth, carcass composition, and carcass quality traits in a population of Brahman and Brahman-influenced steers that participated in the ABBA carcass evaluation program. Traits analyzed included birth weight (BW), weaning weight (WW), hip height (HH), days on feed (DOF), and the previously mentioned feedlot and carcass traits INWT, HRVWT, ADG, HCW, REA, MARB, DP, QG, YG, and WBS. Single nucleotide polymorphisms (SNP) were chosen for analysis within six candidate genes including Thyroglobulin (TG, Adiponectin (ADIPOQ), Calpastatin (CAST), Calpain-3 (CAPN3), Insulin like growth factor-1 (IGF1), and Growth Hormone gene (GH1). Analysis revealed representation of all six candidate genes in the 41 SNP found to have 58 significant associations (p<.05) with growth and feedlot traits BW, WW, HH, INWT, HRVWT, DOF, and ADG. Furthermore, all six candidate genes were represented in the 32 SNP found to have 49 significant associations with carcass composition and quality traits HCW, REA, YG, MARB, QG, and WBS. No markers showed association with DP.

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).

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.

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).