The experiments described herein were designed to answer questions that arose from initially attempting to determine whether treatment with dexamethasone increased concentrations of leptin in geldings. Dexamethasone treatment did in fact increase leptin concentrations in mares, geldings, and stallions. Additional experiments were designed to determine leptin's interaction, not only with the adrenal axis, but with the thyroid axis, the growth hormone/insulin-like growth factor-1 axis, as well as glucose and insulin metabolism in geldings, mares, and stallions. During the course of these experiments, differences in leptin concentrations in the horse were attributed to degree of body condition, gender, and feeding time. Additionally, it was found that horses with high body condition fell into two distinct groups based solely on circulating concentrations of leptin (high vs low). The obese, hyperleptinemic horses were found to be hyperglycemic and hyperinsulinemic and had elevated concentrations of triiodothyronine and decreased concentrations of growth hormone, a hormonal profile similar to that of a type II diabetic human. Indeed, this obesity-related hyperleptinemia was associated with a degree of insulin insensitivity evidenced by the increased insulin response to glucose in these horses. Thus, further experiments were conducted to determine the degree to which these horses were insensitive to insulin, as well as whether diet supplementation or feed restriction might alleviate this insulin insensitivity. Chromium propionate supplementation did not decrease plasma insulin or leptin; however, restricted nutrient intake (6 h of grazing per day) was successful in decreasing concentrations of leptin. It was concluded that leptin in the horse is affected by adrenal and thyroid hormones as well as by glucose/insulin metabolism, and that a syndrome of obesity-related hyperleptinemia, hyperglycemia, and hyperinsulinemia exists in the horse that is similar to type II diabetes in humans.

The purpose of this research was to compare dietary inorganic and organic Se sources in poultry. An experiment was conducted to assess daily egg production and Se deposition in eggs of hens fed diets supplemented with inorganic or organic Se. The results from this experiment indicated that hen production was not affected by Se source, and organic Se increased egg Se concentrations more than inorganic Se. Two experiments then were conducted with broilers to compare dietary organic and inorganic Se on growth performance, carcass traits, breast and plasma Se concentrations, and plasma glutathione peroxidase activity. The results from these experiments indicate that organic Se increases tissue Se concentration more than inorganic Se, but plasma glutathione peroxidase activity, growth performance, and carcass traits were not affected by source. Finally, three experiments were conducted to develop a Se-deficient diet, and then to compare plasma glutathione peroxidase and plasma and tissue Se concentrations in broilers fed a Se-deficient diet after they had been fed diets supplemented with either inorganic or organic Se. The results from these experiments indicate that organic Se increases tissue Se concentration compared with inorganic Se, but plasma glutathione peroxidase activity and growth performance were not affected by source. However, when broilers were placed on the Se deficient diet, organic Se maintained plasma glutathione peroxidase activity longer and at a higher level than inorganic Se. Overall, the results from these experiments indicate that dietary inorganic and organic Se result in similar growth performance and plasma glutathione peroxidase activity in broilers and layers, but organic Se increases tissue and egg Se concentrations more than inorganic Se.

Four experiments were conducted to evaluate the effects of diets with reduced Ca or nonphytate P (nPP) levels with supplemental virginiamycin (Vm) on growth performance and bone response variables in chicks. All diets were corn-soybean meal based and all treatments were replicated six or eight times with five or six chicks each. Reducing dietary nPP from 0.45 to 0.15, 0.25, or 0.35% decreased most growth and bone response variables. The addition of Vm to diets containing 0.35% nPP and above increased both growth and bone response variables. The addition of Vm to diets containing 0.25% nPP and below had no affect or decreased growth and bone response variables. Reducing dietary Ca levels from 1.0 to 0.80 or 0.70% decreased bone response variables, and the addition of Vm increased these response variables at 0.70% Ca but not at 0.80% Ca. Another experiment was conducted to determine the effect of supplemental Zn, Mn, and Cu in the inorganic or organic forms (metal-amino acid complexes) on egg production and egg quality during the post-molt production period. Nine hundred and sixty post-molt layers, were randomly assigned to five treatments with 12 replications of 16 layers each. The study lasted 32 wk and was divided into eight periods of 28 d each. The treatments consisted of: 1) Control (C) supplemented with inorganic trace minerals; 2) C + organic Zn (40 ppm), Mn (40 ppm), and Cu (7 ppm); 3) C + organic Zn (40 ppm); 4) C + inorganic Zn, Mn, and Cu to equal Diet 2; 5) C + inorganic Zn equal to Diet 3. The addition of trace minerals had variable effects on the egg production and quality during different periods. However, in the overall data, none of the forms of trace mineral supplementation affected any response criteria.

There has been great controversy involving progesterone (P₄) levels during early pregnancy in cattle. The objectives of these experiments were to determine the effect of an early low dose administration of P₄ or altrenogest (ALT) on pregnancy rates in repeat breeder (RPB) females, if an increase in pregnancy rates could result from a direct effect of P₄ on the embryo and if ALT could support pregnancy in the absence of a functional CL. Firstly, ALT was evaluated for use as a progestin in cattle by synchronizing estrus in beef heifers. There were no differences in the number of females displaying behavioral estrus or in pregnancy rates when synchronized with ALT or MGA. A second experiment was designed to determine the effect of P₄ or ALT supplementation during days 3 to 5 on pregnancy rate in RPB cattle. It was determined that 15 mg of P₄ or ALT during days 3 to 5 increased pregnancy rates compared with nontreated breeding periods. A third experiment was designed to determine if P₄ exerted a direct effect on the embryo. In vitro produced (IVP) embryos were cultured in the absence of a co-culture system. At day 3, post-insemination, embryos were cultured in the presence of P₄ and evaluated on days 6 to 9. On day 7 post-insemination, there were significantly more grade 1 blastocysts from the P₄ group compared with other treatment groups. Also, embryo developmental rates were increased when cultured in the presence of P₄ and more of these embryos developed to the hatched blastocyst stage compared with other treatment groups. After a direct effect of P₄ on developing IVP bovine embryos existed, it was determined that these embryos did not possess P₄ receptors. Finally, it was demonstrated that ALT could support pregnancy in the absence of a functional CL. These experiments demonstrated that ALT could serve as a progestin in cattle and when administered in low doses during early pregnancy could improve pregnancy rates in RPB cows. These results are likely due to a direct effect of P₄ on the embryo; however, this mechanism is by means other than binding the PR.

Calving rates are significantly reduced following in vitro production of embryos. Thus, if a technique could be developed that would increase calving rates by as little as one viable offspring, significant research advances could be made. Therefore, in a series of experiments, the efficiency and quality of culturing IVP bovine embryos in the amnion of a domestic chicken egg was tested. In Experiment I, by culturing IVP bovine embryos in the chick amnion (day 4 to 7 of incubation) it was discovered that there was no significant difference in blastocyst rates compared with controls. In Experiment II, it was shown that nuclear transfer bovine embryos cultured in the chick amnion reached the blastocyst stage at rates equal to controls and were capable of producing pregnancies following transplantation into recipient females. In a subsequent experiment, a method of naturally improving the chick embryo co-culture (CEC) system was explored by treating the developing chick embryo with prostaglandin E₂ (PGE₂) or prostaglandin F_2α (PGF_2α). It was determined that treatment with PGE₂ increased angiogenesis within the developing chicken egg, while treatment with PGF_2α decreased angiogenesis. When bovine embryos were cultured in PGE₂-treated chicks, developmental rates were not increased. In Experiment IV, chick amniotic fluid (CAF) was evaluated as a media supplement to the control culture system. Although replacing fetal bovine serum (FBS) with CAF resulted in significantly fewer blastocysts on day 7 of culture, there were no significant differences in the number of grade 1 embryos between the two treatments. This finding was important because it demonstrated an ability to culture IVP bovine embryos in the absence of FBS, a medium component that has been implicated in numerous fetal and calf abnormalities. Another experiment was designed to develop a method of culturing cells derived from the chick embryo and surrounding amniotic membrane for later use as a co-culture system for bovine IVP embryos. In the final experiment, using a novel method to detect apoptotic cells, it was determined that CEC did not alter the number of apoptotic cells in the embryo when compared with in vivo-derived or in vitro-cultured bovine embryos.

Cryopreservation of animal oocytes will permit germplasm of valuable or unique females to be preserved for extended times. The objective of this research was to derive a procedure to cryopreserve bovine oocytes by vitrification to be used as recipients for somatic cell nuclear transfer (SCNT). Caprine oocytes vitrified by the same procedure were assayed by cytological examination of microtubules. In the first two of three experiments, bovine oocytes matured in vitro were vitrified in a mixture of ethylene glycol (EG), dimethylsulfoxide (Me2SO) and trehalose, and then subjected to in vitro fertilization (IVF) or SCNT. For vitrification, oocytes were first exposed to increasing concentrations of EG + Me2SO, placed into the vitrification solution composed of 2.8 M Me2SO + 3.6 M EG + 0.65 M trehalose for 20 sec, immediately loaded onto 20-ìm cryoloops, and finally plunged directly into liquid nitrogen (LN2). Vitrified oocytes were warmed by direct immersion of cryoloops into 0.25 M trehalose prepared in TCM-199 medium at 37°C, rinsed briefly, and then assayed. In Experiment I, of 327 bovine oocytes subjected to IVF after being vitrified, 267 cleaved and 32 (9.8%) formed blastocysts, compared to 32.1% blastocysts for control oocytes. In Experiment II, of 266 bovine oocytes enucleated after vitrification and subjected to SCNT, 248 formed couplets, 152 of which cleaved and 31 (12.5%) developed into blastocysts, compared to 33.0% blastocysts for controls. During the course of Experiment II, 20 of 31 blastocysts derived by SCNT of somatic cells from a Brahman cow into vitrified oocytes were transferred into recipients, resulting in three pregnancies and the birth of one Braham calf that has survived to adulthood. In Experiment III, cytological analysis of caprine oocytes vitrified by the same procedure used for bovine oocytes demonstrated that their microtubules were normal, suggesting that this same procedure can also be used for the former species. The results demonstrate that bovine oocytes can be successfully vitrified and warmed, yielding normal embryos after fertilization or SCNT. Additional research is needed to verify that caprine oocytes vitrified by this method can also develop into kids.

The purpose of this research was to determine requirements for amino acids that limit the use of crystalline amino acids, to determine the effects of reducing crude protein, and to evaluate the problems associated with low crude protein diets for swine and poultry. Four experiments were conducted to determine the Lys and sulfur amino acid requirements for 5- to 10-kg pigs. The results of these experiments suggest pigs in this weight range require a diet containing 1.40% true digestible (TD) Lys and the ratio of sulfur amino acids to Lys is not greater than 0.54. Two experiments were conducted to determine the requirement of Lys and sulfur amino acids in 90-kg barrows using plasma urea nitrogen as the response. These experiments indicate a TD Lys requirement of 0.57% and there was no response to TD sulfur amino acid concentrations above 0.27%. Six experiments were conducted to evaluate the Ile requirement of 80- to 120-kg barrows. These experiments indicate a requirement of 0.34% TD Ile in a corn-blood cell diet; however, the requirement may not be greater than 0.24% in barrows fed a corn-soybean meal diet. Two experiments were conducted to evaluate the effects of soybean meal and lowering crude protein in diets for late-finishing barrows. Results suggest that reductions in soybean meal are not the cause of increased carcass fat in pigs fed low crude protein diets. Furthermore, the fortification of a corn diet with crystalline Lys, Trp, and Thr will not support optimal growth or carcass composition. Five experiments were conducted to determine the effects of lowering crude protein in diets for broilers and to evaluate limiting essential and nonessential amino acids. Results indicate that low crude protein diets can support optimal growth of broilers when surfeit Gly is supplied in the diet. The requirement of Gly + Ser appears to be not less than 2.14% from d 0 to 17 posthatching.

The influence of donor animal sex or age on in vitro bovine cell culture was evaluated to provide foundation information for the selection of donor tissue for nuclear transfer. Skin biopsies were taken from each of sixteen individuals including four bulls (B), four cows (C), four male calves (MC), four female calves (FC). At passage 2, cells from in vitro culture of cell lines were influenced not by gender but by age in the mean cell generation time (MGT). When evaluating familial lineage, comparison between related and unrelated groups showed that most comparisons do not show significant differences in lag time, stationary phase viable cell counts (SPCC) and MGT. In each cell line, there was high cell viability throughout the growth curves, indicating stable cell maintenance and proper cell harvest was conducted in this study. At passage 4, MGT of each cell line was not influenced by age but by sex at passage 2, however, at a later cell passage (by passage 4), the MGT of each cell line was not affected by either sex or age of the donor. By passage 4, the MGT of each cell line was not affected by either sex or age. As passages continued, the extrinsic environmental factors likely influenced the MGT. Cell cycle analysis at passage 4 on day 0 of this study showed that > 90% of cells were in G0/G1 portion in each cell line of all groups. Cell lines from younger donors were more frequently at higher G0/G1 percentages, or synchronized than those derived from older donors. Thus, age of donor animal could be a factor in selecting cell line for NT, especially when G0/G1 nuclei are intended for use. Male groups (B and MC) showed higher stationary phase viable cell counts than female groups (C and FC). Most comparisons showed no significant differences in lag time, SPCC and MGT between related and unrelated familial lineage groups. Each cell line showed constant viability (94.36 to 97.98%) at passage 4 throughout the growth curves.

Paternal half-sib groups of Brahman bull calves were purchased at weaning from purebred Brahman producers in Louisiana. Following backgrounding and grazing on ryegrass the steers shipped to a commercial feedlot in south Texas. Steers were slaughtered in groups when they reached an approximate average endpoint weight of 535 kg and 10mm backfat. After a 24 hr chill, carcasses were ribbed, data collected, and a longissimus muscle sample taken for calpastatin assay. Two 2.54 cm thick steaks were randomly removed from the large end of the strip loin, vacuum packaged, and randomly selected for 7 and 14 days of aging. Genetic correlations and heritabilities were calculated with an animal model using MTDFREML. The means were 1.49 kg/d for ADG, 336.4kg for USDA yield grade, 58.7 cm2 for ribeye area, 0.87 cm for fat thickness, 2.12 for percent kph, 2.34 for USDA yield grade, and 390.3 for marbling score which equals a high select USDA quality grade. Other means were 10.60 and 10.59 for purge loss after 7 and 14 days aging, 21.07 and 21.56 for percent cooking loss, 4.57 and 3.85 kg for shear force after 7 and 14 days aging. Factors influencing shear force were marbling score, purge loss after 7 day aging, purge loss after 14 day aging, cook loss after 7 day aging, cook loss after 14 day aging, and calpastatin. Heritablilities for growth and carcass traits were similar to those of non-Brahman cattle. Heritabilities for cooking traits were low. Tenderness as affected by moisture loss during the thawing and cooking process needs to be studied further.

Two experiments were performed to discover what, if any, reproductive differences exist in high body condition (BCS) mares with varying concentrations of leptin. Previous research showed that mares with high body condition scores can have a range of leptin levels, from very low (<5 ng/mL) to very high (>10 ng/mL). Earlier results indicated that most mares with high body condition scores maintain estrous cycles or show significant follicular activity during the winter. Among these high BCS mares, about 30% of them exhibit hyperleptinemia and hyperinsulinemia. The first experiment was designed to compare the reproductive characteristics of high BCS mares with high versus low leptin levels during vernal transition and the first estrous cycle. Also, an IVGTT, insulin challenge, and two sulpiride challenges were performed to characterize endocrine profiles of these mares. Results of these challenges were similar to previous work, in that hyperleptinemic mares had greater insulin responses to glucose and greater clearance rates of infused glucose compared to low leptin mares. These mares also showed a slightly greater prolactin response to sulpiride than their low leptin counterparts. When analyzing the reproductive traits of these mares, no differences between groups existed for follicular sizes or distributions, gonadotropin levels, or date of first ovulation. The second experiment was designed to assess what differences may exist between high BCS mares with high versus low leptin levels with regard to their gonadotropin and ovarian responses to several analogs of gonadotropin releasing hormone (GnRH). Histrelin and deslorelin appeared to be the most potent of the analogs, followed by buserelin and then GnRH. Leptin status did not appear to affect the gonadotropin response or time to ovulation for any of the analogs used in this trial. In conclusion, although hyperleptinemic mares showed altered insulin and glucose characteristics, no significant reproductive differences were observed between these mares and their normal counterparts in terms of ovarian function or the hypothalamic- pituitary axis during vernal transition or the estrous cycle.