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Ergot alkaloids in endophyte-infected grasses inhibit prolactin secretion and reduce milk production in lactating cows. However, we previously showed that prepartum consumption of infected seed throughout the dry period did not inhibit subsequent milk production and prior exposure to bromocriptine (ergot peptide) actually increased production in the next lactation. To identify changes in the transcriptome and molecular pathways mediating the mammary gland's response to ergot alkaloids in the diet, RNA sequencing (RNA-seq) was performed on mammary tissues obtained from 22 multiparous Holstein cows exposed to 1 of 3 treatments. Starting at 90 ± 4 d prepartum, cows were fed endophyte-free fescue seed (control; CON), endophyte-free fescue seed plus 3×/wk subcutaneous injections of bromocriptine (BROMO; 0.1 mg/kg of BW), or endophyte-infected fescue seed (INF) as 10% of the diet. Cows were dried off 60 ± 2 d prepartum. Mammary biopsies from 4 (BROMO, INF) or 5 (CON) cows/treatment at each of the 3 phases were obtained: 7 d before dry off during the initial lactation (L1), mid-dry period (D), and 10 d postpartum (L2). Although tissue from the same cow was preferentially used at 3 phases (L1, D, L2), tissue from additional cows were used to as necessary to provide RNA of sufficient quality. Individual samples were used to generate individual RNA-seq libraries. Normalized reads of the RNA-seq data were organized into technical and biological replicates before processing with the RSEM software package. Each lactation phase was processed separately and genes that differed between any of 3 treatments were identified. A large proportion of genes differentially expressed in at least 1 treatment (n = 866) were found to be similarly expressed in BROMO and INF treatments, but differentially expressed from CON (n = 575, total for 3 phases). Of genes differentially expressed compared with CON, 104 genes were common to the L1 and L2 phases. Consistent with the production findings, networks most affected by treatments in L1 and L2 included lipid metabolism, small molecule biochemistry, and molecular transport, whereas networks related more to developmental and cellular functions and maintenance were evident during D phase. Similar patterns of expression in BROMO and INF during late and early lactation suggest involvement of similar cell signaling pathways or mechanisms of action for BROMO and INF and the importance of prolactin messaging pathways., (Copyright © 2018 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Glucagon-like peptide 2 (GLP-2) therapy was shown previously to reduce inflammation-related gut damage from coccidiosis in dairy calves, and feeding of artificial sweetener stimulates GLP-2 secretion from intestinal L cells. The purpose of this study was to determine whether GLP-2 treatment or artificial sweetener feeding beginning 1 wk before an experimental inoculation with the coccidian parasite Cryptosporidium parvum can reduce infection-related intestinal damage in Holstein bull calves. Newborn calves were assigned to 1 of 4 treatment groups of 6 calves each, including noninfected control calves injected s.c. every 12 h with control buffer (CON), infected control calves injected s.c. every 12 h with control buffer (INF), infected calves injected s.c. every 12 h with 50 µg/kg of body weight of GLP-2 (GLP2), and infected calves injected s.c. every 12 h with control buffer and supplemented in the diet with Sucram (Pancosma, Geneva, Switzerland) at 400 mg/kg of dry matter of milk replacer (SUC). Treatments were initiated on d 1, and calves in INF, GLP2, and SUC were orally dosed on d 8 with 12,500 C. parvum oocysts. Fecal scores were recorded daily, plasma was collected on d 1, 8, 12, 15, and 18 to evaluate markers of inflammation, and fecal samples were collected on d 1, 8, and every other day thereafter to determine the presence of oocysts. Calves were euthanized on d 18 for collection of intestinal tissues and histological and gene expression analyses. Relative to CON, calves in INF exhibited an increase in diarrhea severity, increased plasma serum amyloid A concentration on d 15 and 18, reduced intestinal villus height, increased villus apoptosis and crypt cell proliferation, and increased intestinal mRNA expression of MARVELD2 and GPX2. However, calves in SUC and GLP2 had reduced diarrhea severity and fecal C. parvum oocyst shedding, reduced plasma serum amyloid A concentration on d 15 and 18, and, depending on the intestinal segment, increased villus height, reduced crypt cell proliferation, and reduced mRNA expression of MARVELD2, GPX2, and other tight junction proteins relative to INF. Lastly, GLP2 and SUC exhibited increased intestinal mass-to-length ratio and decreased length-to-empty body weight ratio relative to INF. Our findings suggest that GLP-2 and Sucram treatments administered before a low-level C. parvum exposure may contribute to fewer effects on intestinal integrity, morphology, and inflammation in response to infection, and shorter, denser intestines., (Copyright © 2017 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Ergot alkaloids in endophyte-infected grasses inhibit prolactin (PRL) secretion and may reduce milk production of cows consuming these grasses. We investigated the effects of consuming endophyte-infected fescue seed during late lactation and the dry period on mammary growth, differentiation, and milk production. Twenty-four multiparous Holstein cows were randomly assigned to 3 treatment groups. Starting at 90±4 d prepartum, cows were fed endophyte-free fescue seed (control; CON), endophyte-free fescue seed plus 3×/wk subcutaneous injections of bromocriptine (0.1mg/kg of body weight, positive control; BROMO), or endophyte-infected fescue seed (INF) as 10% of the diet on an as fed basis. Although milk yield of groups did not differ before treatment, at dry off (-60 d prepartum) INF and BROMO cows produced less milk than CON. Throughout the treatment period, basal concentrations of PRL and the prepartum increase in plasma PRL were reduced in INF and BROMO cows compared with CON cows. Three weeks after the end of treatment, circulating concentrations of PRL were equivalent across groups. In the subsequent lactation milk yield was not decreased; in fact, BROMO cows exhibited a 9% increase in milk yield relative to CON. Evaluation of mammary tissue during the dry period and the subsequent lactation, by quantitative histology and immunohistochemical analysis of proliferation markers and putative mammary stem or progenitor cell markers, indicated that feeding endophyte-infected fescue seed did not significantly affect mammary growth and development. Feeding endophyte-infected grasses during the dry period may permit effective utilization of feed resources without compromising milk production in the next lactation., (Copyright © 2016 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Numerous endocrine cell subtypes exist within the intestinal mucosa and produce peptides contributing to the regulation of critical physiological processes including appetite, energy metabolism, gut function, and gut health. The mechanisms of action and the extent of the physiological effects of these enteric peptides are only beginning to be uncovered. One peptide in particular, glucagon-like peptide 2 (GLP-2) produced by enteroendocrine L cells, has been fairly well characterized in rodent and swine models in terms of its ability to improve nutrient absorption and healing of the gut after injury. In fact, a long-acting form of GLP-2 recently has been approved for the management and treatment of human conditions like inflammatory bowel disease and short bowel syndrome. However, novel functions of GLP-2 within the gut continue to be demonstrated, including its beneficial effects on intestinal barrier function and reducing intestinal inflammation. As knowledge continues to grow about GLP-2's effects on the gut and its mechanisms of release, the potential to use GLP-2 to improve gut function and health of food animals becomes increasingly more apparent. Thus, the purpose of this review is to summarize: (1) the current understanding of GLP-2's functions and mechanisms of action within the gut; (2) novel applications of GLP-2 (or stimulators of its release) to improve general health and production performance of food animals; and (3) recent findings, using dairy calves as a model, that suggest the therapeutic potential of GLP-2 to reduce the pathogenesis of intestinal protozoan infections., (Published by Elsevier Inc.)

Tight junction (TJ) proteins are integral factors involved in gut barrier function, and therapy with glucagon-like peptide-2 (GLP-2) enhances gut integrity. Our aim was to assess effects of GLP-2 treatment on mRNA expression of 8 TJ complex proteins in the intestine of dairy calves not infected or infected with Eimeria bovis at 11±3d of age. Mucosal epithelium from jejunum, ileum, and cecum was collected at slaughter from Holstein bull calves assigned to 4 groups: noninfected, buffer-treated (n=5); noninfected, GLP-2 treated (n=4); E. bovis-infected, buffer-treated (n=5); and E. bovis-infected, GLP-2-treated (n=4). Infected calves were orally dosed with 100,000 to 200,000 sporulated E. bovis oocysts on d 0; GLP-2-treated calves received 50 µg of GLP-2/kg of body weight subcutaneously twice daily for 10d beginning on d 18; and buffer-treated calves received an equal injection volume of 0.01 M Na bicarbonate buffer. All calves were killed on d 28. The mRNA expression of coxsackie and adenovirus receptor (CXADR), claudins 1, 2, and 4 (CLDN1, CLDN2, and CLDN4), F11 receptor (F11R), junction adhesion molecule 2 (JAM2), occludin (OCLN), and tight junction protein ZO-1 (TJP1) was determined by real-time quantitative PCR. In jejunum and ileum, an interaction of E. bovis infection and GLP-2 treatment on gene expression was noted. In jejunum of noninfected calves, GLP-2 increased CXADR, CLDN2, OCLN, and TJP1 mRNA expression but had no effect on mRNA expression in infected calves. Treatment with GLP-2 also increased tight junction protein ZO-1 protein expression in jejunum of noninfected calves as determined by immunohistochemistry. In ileum, E. bovis decreased expression of JAM2, OCLN, and TJP1 in buffer-treated calves, and GLP-2 increased TJP1 expression in infected calves. In cecum, E. bovis infection reduced expression of CXADR, CLDN4, F11R, and OCLN, and GLP-2 therapy increased expression of CLDN4, F11R, OCLN, and TJP1. Results are consistent with studies in nonruminants showing decreased expression of TJ complex proteins in the intestinal tract during pathogen-induced diarrhea and increased TJ protein expression in intestinal tissues in response to GLP-2 treatment. In conclusion, E. bovis reduces gene expression of TJ proteins primarily in cecum of calves 28d postinfection, and GLP-2 increases expression of selected TJ genes in intestinal tissues. Use of GLP-2 to improve gut barrier function in ruminants during pathogen-induced diarrhea warrants additional study., (Copyright © 2015 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Glucagon-like peptide-2 (GLP-2) is a 33-amino acid peptide derived from proteolytic cleavage of proglucagon by prohormone convertase 1/3 in enteroendocrine L cells. Studies conducted in humans, in rodent models, and in vitro indicate that GLP-2 is secreted in response to the presence of molecules in the intestinal lumen, including fatty acids, carbohydrates, amino acids, and bile acids, which are detected by luminal chemosensors. The physiological actions of GLP-2 are mediated by its G protein-coupled receptor expressed primarily in the intestinal tract on enteric neurons, enteroendocrine cells, and myofibroblasts. The biological activity of GLP-2 is further regulated by dipeptidyl peptidase IV, which rapidly cleaves the N-terminus of GLP-2 that is responsible for GLP-2 receptor activation. Within the gut, GLP-2 increases nutrient absorption, crypt cell proliferation, and mesenteric blood flow and decreases gut permeability and motility, epithelial cell apoptosis, and inflammation. Outside the gut, GLP-2 reduces bone resorption, can suppress appetite, and is cytoprotective in the lung. Thus, GLP-2 has been studied intensively as a therapeutic to improve intestinal function of humans during parenteral nutrition and following small bowel resection and, more recently, as a treatment for osteoporosis and obesity-related disorders and to reduce cellular damage associated with inflammation of the gut and lungs. Recent studies demonstrate that many biological actions and properties of GLP-2 in ruminants are similar to those in nonruminants, including the potential to reduce intestinal nitro-oxidative stress in calves caused by parasitic diseases such as coccidiosis. Because of its beneficial impacts on nutrient absorption, gut healing, and normal gut development, GLP-2 therapy offers significant opportunities to improve calf health and production efficiency. However, GLP-2 therapies require an extended time course to achieve desired physiological responses, as well as daily administration because of the hormone's short half-life. Thus, practical means of administration and alternative strategies to enhance basal GLP-2 secretion (e.g., through specific feed additives), which are more likely to achieve consumer acceptance, are needed. Opportunities to address these challenges are discussed.

Damage to the intestinal epithelium reduces nutrient absorption and animal growth, and can have negative long-term health effects on livestock. Because the intestinotropic hormone glucagon-like peptide 2 (GLP-2) has been shown to contribute to gut integrity, reduce inflammation, and improve nutrient absorption, the present study was designed to determine whether administration of GLP-2 to calves with coccidiosis in the first month of life affects intestinal growth and mediates negative effects of the proinflammatory response. Holstein bull calves (n=19) were assigned to 4 treatment groups of 4 to 5 calves each: (1) infected with Eimeria bovis, GLP-2 treated; (2) noninfected, GLP-2 treated; (3) infected with E. bovis, buffer treated; and (4) noninfected, buffer treated. Infected calves received 100,000 to 200,000 sporulated E. bovis oocysts suspended in milk replacer on d 0 of the study. On d 18, calves in the GLP-2 groups received a subcutaneous injection of 50 μg of bovine GLP-2/kg of body weight twice daily for 10 d, and calves in the buffer-treated groups received an equivalent volume of sodium bicarbonate buffer only. On d 28, calves were slaughtered 2h after injection of 5-bromo-2'-deoxyuridine (BrdU). Intestinal tissues were measured and villus height, crypt depth, and BrdU immunostaining were evaluated in segments of the small intestine. Nitrotyrosine immunostaining, a measure of nitro-oxidative damage, was evaluated in the ileum and cecum. No GLP-2 treatment by E. bovis infection interaction was observed for any parameter measured, with the exception of nitrotyrosine immunostaining in the cecum. Large intestinal weight was greater in infected than noninfected calves and with GLP-2 treatment relative to buffer treatment. Calves that received GLP-2 also had greater small intestinal weight but no difference in cell proliferation, as assessed by BrdU labeling, relative to buffer-treated calves. No treatment effects were detected for villus height, crypt depth, or villus height:crypt depth ratio in segments of the small intestine. Protein tyrosine nitration was over 3-fold greater in the ileum and cecum of infected calves relative to noninfected calves, and GLP-2 therapy reduced tyrosine nitration in infected calves by 47% in the ileum and 69% in the cecum relative to buffer-treated calves. Treatment with GLP-2 promotes intestinal growth in neonatal calves and reduces the detrimental effects of nitro-oxidative stress in the ileocecum of calves with coccidiosis., (Copyright © 2013 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Background: Previous molecular characterizations of mammary stem cells (MaSC) have utilized fluorescence-activated cell sorting or in vitro cultivation of cells from enzymatically dissociated tissue to enrich for MaSC. These approaches result in the loss of all histological information pertaining to the in vivo locale of MaSC and progenitor cells. Instead, we used laser microdissection to excise putative progenitor cells and control cells from their in situ locations in cryosections and characterized the molecular properties of these cells. MaSC/progenitor cells were identified based on their ability to retain bromodeoxyuridine for an extended period., Results: We isolated four categories of cells from mammary epithelium of female calves: bromodeoxyuridine label retaining epithelial cells (LREC) from basal (LRECb) and embedded layers (LRECe), and epithelial control cells from basal and embedded layers. Enriched expression of genes in LRECb was associated with stem cell attributes and identified WNT, TGF-β, and MAPK pathways of self renewal and proliferation. Genes expressed in LRECe revealed retention of some stem-like properties along with up-regulation of differentiation factors., Conclusion: Our data suggest that LREC in the basal epithelial layer are enriched for MaSC, as these cells showed increased expression of genes that reflect stem cell attributes; whereas LREC in suprabasal epithelial layers are enriched for more committed progenitor cells, expressing some genes that are associated with stem cell attributes along with those indicative of cell differentiation. Our results support the use of DNA label retention to identify MaSC and also provide a molecular profile and novel candidate markers for these cells. Insights into the biology of stem cells will be gained by confirmation and characterization of candidate MaSC markers identified in this study.

Mammary stem cells (MaSC) provide for net growth, renewal and turnover of mammary epithelial cells, and are therefore potential targets for strategies to increase production efficiency. Appropriate regulation of MaSC can potentially benefit milk yield, persistency, dry period management and tissue repair. Accordingly, we and others have attempted to characterize and alter the function of bovine MaSC. In this review, we provide an overview of current knowledge of MaSC gained from studies using mouse and human model systems and present research on bovine MaSC within that context. Recent data indicate that MaSC retain labeled DNA for extended periods because of their selective segregation of template DNA strands during mitosis. Relying on this long-term retention of bromodeoxyuridine-labeled DNA, we identified putative bovine MaSC. These label-retaining epithelial cells (LREC) are in low abundance within mammary epithelium (<1%). They are predominantly estrogen receptor (ER)-negative and localized in a basal or suprabasal layer of the epithelium throughout the gland. Thus, the response of MaSC to estrogen, the major mitogen in mammary gland, is likely mediated by paracrine factors released by cells that are ER-positive. This is consistent with considerable evidence for cross-talk within and between epithelial cells and surrounding stromal cells. Excision of classes of cells by laser microdissection and subsequent microarray analysis will hopefully provide markers for MaSC and insights into their regulation. Preliminary analyses of gene expression in laser-microdissected LREC and non-LREC are consistent with the concept that LREC represent populations of stem cells and progenitor cells that differ with regard to their properties and location within the epithelial layer. We have attempted to modulate the MaSC number by infusing a solution of xanthosine through the teat canal and into the ductal network of the mammary glands of prepubertal heifers. This treatment increased the number of putative stem cells, as evidenced by an increase in the percentage of LREC and increased telomerase activity within the tissue. The exciting possibility that stem cell expansion can influence milk production is currently under investigation.

Glucagon-like peptide 2 (GLP-2), secreted by enteroendocrine cells, has several physiological effects on the intestine of monogastric species, including promotion of growth of intestinal epithelium, reduction of epithelial cell apoptosis, and enhancement of intestinal blood flow, nutrient absorption, and epithelial barrier function. The regulatory functions of GLP-2 in the ruminant gastrointestinal tract (GIT) have not been well studied. The objectives of this investigation were to characterize the mRNA expression of 4 members of the GLP-2 pathway throughout the bovine GIT, including (1) proglucagon (GCG), the parent peptide from which GLP-2 is derived through cleavage by prohormone convertase; (2) prohormone convertase (PCSK1); (3) GLP-2 receptor (GLP2R); and (4) dipeptidyl peptidase IV (DPP4), the enzyme that inactivates GLP-2. Gene expression was evaluated in rumen, reticulum, omasum, abomasum, duodenum, jejunum, ileum, cecum, and rectum collected at slaughter from prepubertal heifers, mature cows in early, mid, and late lactation, and nonlactating cows (n=3 per stage) by a gene expression profiling assay. In addition, mRNA expression of 14 genes involved in nutrient transport, enzyme activity, blood flow, apoptosis, and proliferation were evaluated in the 9 GIT tissues for their association with GCG and GLP2R mRNA expression. Immunohistochemistry was used to localize GLP2R protein in tissues of the lower GIT. Results indicated that mRNA expression of GCG, PCSK1, GLP2R, and DPP4 varies across the 9 GIT tissues, with greatest expression in small and large intestines, and generally nondetectable levels in forestomachs. Expression of DPP4 and GLP2R mRNA varied by developmental stage or lactational state in intestinal tissues. Expression of GCG or GLP2R mRNA was correlated with molecular markers of proliferation, apoptosis, blood flow, enzyme activity, and urea transport, depending on the tissue examined, which suggests a potential for involvement of GLP-2 in these physiological processes in the ruminant GIT. The GLP2R protein was expressed in intestinal crypts of the bovine GIT, which is consistent with the distribution in monogastric species. Our findings support a functional role of the GLP-2 pathway in bovine GIT and the potential for use of GLP-2 as a therapy to improve intestinal function and nutrient absorption in ruminants., (Copyright © 2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

A rapid method of 5-bromo-2'-deoxyuridine (BrdU) immunostaining was developed in cryosections of bovine mammary tissue while preserving RNA quality of the stained section. A thymidine analog that is incorporated into DNA of proliferating cells, BrdU serves as a proliferation marker. Immunostaining of BrdU-labeled cells within a histological section requires heat, enzymatic or chemical-mediated antigen retrieval to open double-stranded DNA, and exposure to the BrdU antigen. Although these established treatments permit staining, they preclude use of cells within the tissue section for further gene expression experiments. Additionally, long antibody incubations and washing steps lead to extensive RNA degradation and elution. A protocol was developed for immunolocalization of BrdU-labeled cells in cryosections of bovine mammary tissue, which does not require harsh DNA denaturation and preserved RNA integrity and quantity. This protocol used an initial acetone:polyethylene glycol 300 [9:1 (vol/vol)] fixation (2 min) followed by staining with methyl green (0.5% aqueous; 2 min) to stabilize macromolecules, antigen retrieval with deionized formamide (70% in nuclease-free phosphate buffered saline; 4 min incubation), antibody incubation in the presence of RNase inhibitors (5 min), and minimal washing to facilitate recovery of RNA from cells from the stained sections. Applicability of this protocol to other nuclear antigens was evaluated by testing its suitability for staining estrogen receptor alpha and Ki-67 antigen. In both cases, use of the protocol provided good immunostaining and tissue morphology. The RNA quality of estrogen receptor alpha- and Ki-67-stained sections was not evaluated. Quality of the isolated RNA from BrdU-stained sections was evaluated by micro-fluidic electrophoresis and its utility was confirmed using quantitative reverse transcription-PCR. Staining intensity obtained with this labeling protocol was similar to that obtained using conventional immunohistochemistry protocols. When coupled with laser microdissection and RNA or cDNA amplification, this immunostaining protocol provided a means for future transcriptome analysis of BrdU-labeled cells within a complex tissue., (2010 American Dairy Science Association. Published by Elsevier Inc. All rights reserved.)

Mammary stem cells provide for growth and maintenance of the mammary gland and are therefore of considerable interest as determinants of productivity and efficiency of dairy animals and as targets of carcinogenesis in humans. Xanthosine treatment was previously shown to promote expansion of hepatic stem cells in vitro. The objective of this study was to determine if in vivo treatment with xanthosine can increase the mammary stem cell population. Xanthosine was infused into the right mammary glands of four female Holstein calves for 5 consecutive days. Immediately after each xanthosine treatment, calves were injected intravenously with 5-bromo-2-deoxyuridine (BrdU). Forty days after the final treatment, calves were euthanized and mammary tissue harvested. BrdU-label retaining epithelial cells (LREC) were detected immunohistochemically and quantified. Retention of BrdU was used as a marker for putative bovine mammary stem cells. Infusion of xanthosine into the bovine mammary gland significantly increased the number of LREC in treated glands compared to contralateral control glands (P < 0.05). LREC averaged 0.4% of epithelial cells in control glands and 0.8% in xanthosine-treated glands. The increase in LREC in xanthosine-treated glands was supported by a concomitant increase in telomerase activity (P < 0.01) and a correlation between LREC and telomerase (P < 0.05; r (2) = 0.7). Data indicate that in vivo treatment with xanthosine can be used to increase the number of mammary stem cells. This is the first demonstration of an in vivo treatment to increase the endogenous population of mammary stem cells, with utility for biomedical research and dairy management.

Background: Previous research has demonstrated that increased milking frequency of dairy cattle during the first few weeks of lactation enhances milk yield, and that the effect persists throughout the entire lactation period. The specific mechanisms controlling this increase in milk production are unknown, but suggested pathways include increased mammary epithelial cell number, secretory capacity, and sensitivity to lactogenic hormones. We used serial analysis of gene expression (SAGE) and microarray analysis to identify changes in gene expression in the bovine mammary gland in response to 4x daily milking beginning at d 4 of lactation (IMF4) relative to glands milked 2x daily (Control) to gain insight into physiological changes occurring within the gland during more frequent milking., Results: Results indicated changes in gene expression related to cell proliferation and differentiation, extracellular matrix (ECM) remodeling, metabolism, nutrient transport, and immune function in IMF4 versus Control cows. In addition, pathways expected to promote neovascularization within the gland appeared to be up regulated in IMF4 cows. To validate this finding, immunolocalization of Von Willebrandt's factor (VWF), an endothelial cell marker, and its co-localization with the nuclear proliferation antigen Ki67 were evaluated in mammary tissue sections at approximately d 7 and d 14 of lactation in cows milked 4x daily versus Controls to estimate endothelial cell abundance and proliferation within the gland. Consistent with expression of genes related to neovascularization, both abundance of VWF and its co-localization with Ki67 appeared to be elevated in cows milked 4x daily, suggesting persistent increased milk yield in response to increased milking frequency may be mediated or complemented by enhanced mammary ECM remodeling and neovascularization within the gland., Conclusion: Additional study is needed to determine whether changes in ECM remodeling and neovascularization of the mammary gland result in increased milk yield during increased milking frequency, or occur in response to an increased demand for milk production. Gene pathways identified by the current study will provide a basis for future investigations to identify factors mediating the effects of milking frequency on milk yield.

The current study is a comprehensive genome analysis to detect QTL affecting metabolic traits in chickens. Two unique F(2) crosses generated from a commercial broiler male line and 2 genetically distinct inbred lines (Leghorn and Fayoumi) were used in the present study. The plasma glucagon, insulin, lactate, glucose, tri-iodothyronine, thyroxine, insulin-like growth factor I, and insulin-like growth factor II concentrations at 8 wk were measured in the 2 F(2) crosses. Birds were genotyped for 269 microsatellite markers across the entire genome. The program QTL Express was used for QTL detection. Significance levels were obtained using the permutation test. For the 10 traits, a total of 6 and 9 significant QTL were detected at a 1% chromosome-wise significance level, of which 1 and 6 were significant at the 5% genome-wise level for the broiler-Leghorn cross and broiler-Fayoumi cross, respectively. Most QTL for metabolic traits in the present study were detected in Gga 2, 6, 8, 9, 13, and Z for the broiler-Leghorn cross and Gga 1, 2, 4, 7, 8, 13, 17, and E47 for the broiler-Fayoumi cross. Phenotypic variation for each trait explained by all QTL across genome ranged from 2.73 to 14.08% in the broiler-Leghorn cross and from 6.93 to 21.15% in the broiler-Fayoumi cross. Several positional candidate genes within the QTL region for metabolic traits at the 1% chromosome-wise significance level are biologically associated with the regulation of metabolic pathways of insulin, triiodothyronine, and thyroxine.

Two unique chicken F(2) populations generated from a broiler breeder male line and 2 genetically distinct inbred (>99%) chicken lines (Leghorn and Fayoumi) were used for whole genome QTL analysis. Twelve phenotypic skeletal integrity traits (6 absolute and 6 relative traits) were measured or calculated, including bone mineral content, bone mineral density, tibia length, shank length, shank weight, and shank length:shank weight. All traits were also expressed as a percentage of BW at 8 wk of age. Birds were genotyped for 269 microsatellite markers across the entire genome. The QTL affecting bone traits in chickens were detected by the QTL express program. Significance levels were obtained using the permutation test. For the 12 traits, a total of 56 significant QTL were detected at the 5% chromosome-wise significance level, of which 14 and 10 were significant at the 5% genome-wise level for the broiler-Leghorn cross and broiler-Fayoumi cross, respectively. Phenotypic variation for each trait explained by all detected QTL across the genome ranged from 12.0 to 35.6% in the broiler-Leghorn cross and 2.9 to 31.3% in the broiler-Fayoumi cross. Different QTL profiles identified between the 2 related F(2) crosses for most traits suggested that genetic background is an important factor for QTL analysis. Study of associations of biological candidate genes with skeletal integrity traits in chickens will reveal new knowledge of understanding biological process of skeletal homeostasis. The results of the current study have identified markers for bone strength traits, which may be used to genetically improve skeletal integrity in chickens by MAS, and to identify the causal genes for these traits.

A genome scan was used to detect chromosomal regions and QTL that control quantitative traits of economic importance in chickens. Two unique F(2) crosses generated from a commercial broiler male line and 2 genetically distinct inbred lines (Leghorn and Fayoumi) were used to identify QTL affecting BW and daily average gain traits in chickens. Body weight at 2, 4, 6, and 8 wk was measured in the 2 F(2) crosses. Birds were genotyped for 269 microsatellite markers across the entire genome. Linkage distance among microsatellite markers was estimated by the CRIMAP program. The program QTL Express was used for QTL detection. Significance levels were obtained using the permutation test. For the 8 traits, a total of 18 and 13 significant QTL were detected at a 1% chromosome-wise significance level, of which 17 and 10 were significant at the 5% genome-wise level for the broiler-Leghorn cross and broiler-Fayoumi cross, respectively. Highly correlated growth traits showed similar QTL profiles within each cross but different QTL profiles between the 2 crosses. Most QTL for growth traits in the current study were detected in Gga 1, 2, 4, 7, and 14 for the broiler-Leghorn cross and Gga 1, 2, 4, 5, 8, and 13 for the broiler-Fayoumi cross. Potential candidate genes within the QTL region for growth traits at 1% chromosome-wise significance level were discussed. The results in the current study lay the foundations for fine mapping these traits in the advanced intercross lines and provide a start point for identification causative genes responsible for growth traits in chickens.

Two informative chicken F(2) populations based on crosses between a broiler breeder male line and dams from genetically distinct, highly inbred (>99%) chicken lines, the Leghorn G-B2 and Fayoumi M15.2, have been used for genome-wide linkage and QTL analysis. Phenotypic data on 12 body composition traits (breast muscle weight, breast muscle weight percentage, abdominal fat weight, abdominal fat weight percentage, heart weight, heart weight percentage, liver weight, liver weight percentage, spleen weight, spleen weight percentage, and drumstick weight, and drumstick weight percentage) were collected. Birds were genotyped for 269 microsatellite markers across the genome. The QTL Express program was used to detect QTL for body composition traits. Significant levels were obtained using the permutation test. For the twelve traits, a total of 61 (Gga 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 18, 24, and Z) and 45 (Gga 1, 2, 3, 4, 6, 7, 8, 9, 10, 12, 15, 17, and E46) significant QTL were detected at the 5% chromosome-wise significance level, of which 19 and 11 were significant at the 5% genome-wise level for the broiler-Leghorn cross and broiler-Fayoumi cross, respectively. Phenotypic variation for each trait explained by all QTL across the genome ranged from 3.22 to 33.31% in the broiler-Leghorn cross and 4.83 to 47.12% in broiler-Fayoumi cross. Distinct QTL profiles between the 2 crosses were observed for most traits. Cryptic alleles were detected for each trait. Potential candidate genes within the QTL region for body composition traits at the 1% chromosome-wise significance level were identified from databases for future association study. The results of the current study will increase the knowledge of genetic markers associated with body composition traits and aid the process of identifying causative genes. Knowledge of beneficial genetic variation can be incorporated in breeding programs to enhance genetic improvement through marker-assisted selection in chickens.

The effect of multiple lipopolysaccharide (LPS) challenges in swine undergoing long-term treatment with porcine somatotropin (PST) was determined. Changes in aspartate serine transaminase (AST) occurred only at 24h following the first LPS challenge dose (P<0.05), while PST treatment moderated any change from occurring. Nonesterified free fatty acid (NEFA) levels were elevated in PST treated animals for the first 3 days following daily LPS treatment (P<0.05), while LPS treatment alone had no effect on plasma NEFA levels. Plasma urea nitrogen (PUN) levels were unchanged by LPS following the initial LPS challenge, but were decreased following the second challenge dose (P=0.014). These changes were long lasting, with a return to normal PUN levels not evident until Day 6. The PST treatment mitigated changes in PUN (P<0.05) when LPS was administered. Haptoglobin plasma levels, along with lipid peroxide production were not affected by LPS challenge or PST administration. LPS challenge reduced the levels of immunoreactive heat shock protein 70 (HSP70) throughout the entire challenge period (P<0.001). PST-LPS animals had normal levels of this protein. The results of the present study demonstrate that long-term PST treatment mitigates the adverse effects of subchronic LPS administration.

An avian uncoupling protein (UCP) gene homolog was recently sequenced from skeletal muscle and was proposed to have a role in thermogenesis in chickens, ducks and hummingbirds. Since mammalian UCP 2 and UCP 3 also appear to have functions associated with energy and substrate partitioning and body weight regulation, the purpose of this study was to further characterize chicken UCP under conditions of nutritional stress and/or leptin administration. Male 3-week-old chickens were starved for 24 or 48 h and then half of each group was refed for an additional 24 h. In a follow-up experiment, chickens were fed or starved for 48 h with or without leptin administration. Feed deprivation increased UCP mRNA expression in skeletal muscle by up to 260% (P<0.001), and in a time-dependent manner in pectoralis muscle. Refeeding for 24 h normalized muscle UCP mRNA levels. Leptin administration had no effect on muscle UCP. Chicken muscle UCP mRNA levels were highly correlated with plasma triglyceride and non-esterified fatty acid (NEFA) concentrations, and with circulating levels of insulin, insulin-like growth factor (IGF)-I and IGF-II. These results suggest that, as in mammals, avian UCP is up-regulated during feed deprivation and is highly correlated with increased fatty acid oxidation and flux into skeletal muscle.

The dietary dose responsiveness of conjugated linoleic acid (CLA) addition relative to the fatty acid profile of edible lean tissue was examined in grower pigs treated with or without porcine somatotropin (pST). Gilts and barrows were fed CLA at 0, 0.25, 0.5, 1.0, or 2.0% of diet by weight from 20 to 55 kg BW. Additional pigs were administered (pST) at 0 or 100 microg x kg BW x d(-1) and fed either 0.5 or 2.0% CLA. Animals were fed diets containing 18% CP, 1.2% lysine, and 3.5 Mcal of DE/kg at 110% of ad libitum intake. The fatty acid profile in latissimus dorsi and dorsal s.c. adipose tissue samples was determined by gas chromatography. Dietary CLA replacement of corn oil increased the percentage of total fatty acids as stearic acid, whereas the percentages as oleic and linolenic acids were reduced in lattisimus muscle. Treatment with CLA + pST increased the percentages of linoleic and arachidonic acids while reducing the percentages of palmitic and oleic acids in lattisimus muscle. Dietary CLA increased the percentages of palmitic and stearic acids in s.c. adipose tissue while reducing the percentages of oleic, linoleic, linolenic, and arachidonic acids. The percentage of palmitic acid was reduced in s.c. adipose tissue, whereas linoleic acid was increased with CLA + pST. No synergistic effect was detected between CLA and pST for reducing carcass lipid content in grower pigs. However, pST increased the percentage of polyunsaturated fatty acids in lattisimus muscle and s.c. adipose tissue while reducing the percentages of saturated fatty acids in swine fed CLA.

Growing (35 kg body weight) and finishing (85 kg body weight) swine challenged with endotoxin (Escherichia coli O55:B5) at a dose of either 2 or 20 microg/kg produced tumor necrosis factor (TNF)alpha in a dose-response relationship as measured by bioassay. Peak TNFalpha plasma levels were observed 1-2 hr post-challenge, returning to basal values 4 hr post-challenge. However, both an enzyme-linked immunosorbent assay specific for swine TNFalpha and total human TNFalpha demonstrated no dose-response relationship; peak plasma levels of immunoreactive TNFalpha were also observed 1-2 hr post-challenge. Maximal plasma interleukin-6 levels occurred 1-2 hr post-challenge and remained elevated through 8 hr post-challenge; there was no effect of lipopolysaccharide dose or metabolic status. Although the metabolic status of the animals also affected glucose levels, with growing animals exhibiting greater sensitivity compared with finishing animals, endotoxin-induced decreases in blood glucose levels were primarily dose-dependent. In contrast, changes in plasma urea nitrogen and free fatty acid (FFA) levels were strictly related to the metabolic status. Urea nitrogen levels were unchanged in growing swine, whereas they were increased in finishing swine and remained elevated 24 hr post-challenge. FFA levels in growing and finishing swine increased 3-6 hr post-challenge. FFA levels returned to basal values for finishing swine 24 hr post challenge, but in growing swine remained elevated 24 hr post-challenge. Plasma aspartate transaminase levels were increased through 24 hr post-challenge; animals given a dose of 20 microg/kg exhibited the greatest increase. Similarly, swine challenged with a dose of 20 microg/kg also exhibited the greatest increase in levels of conjugated bilirubin; there was no effect on unconjugated (free) bilirubin. These results demonstrate that endotoxin challenge of swine result in a pattern of changes that are dependent on both the dose of endotoxin used and the metabolic status of the animal examined.

Dual-energy x-ray absorptiometry (DXA) was used as a noninvasive method to measure the composition of pig carcasses. A total of 181 half-carcasses (10 to 51 kg, from pigs slaughtered at approximately 30, 60, 90, and 120 kg) were scanned using a Lunar (Madison, WI) DPX-L densitometer. The DXA measurements of fat, lean, bone mineral, and total tissue mass were compared with chemical analysis for fat, water, protein, total ash, and scale weight. The mean value for total tissue mass by DXA was slightly less than the mean carcass weight (32.3 kg vs 33.6 kg, P > .05, R2 = .998). Although highly correlated (R2 = .81), the DXA measurement of the percentage of fat in the half-carcass was less (P < .001) than the chemical measurement (19.5 vs 24.9%). The DXA measurement of lean tissue mass (total mass less fat and bone mineral) was correlated with carcass protein (R2 = .97) and water (R2 = .99) content. The correlation (R2) between DXA bone mineral content and carcass ash content was only .68; however, DXA bone mineral content was more highly correlated with carcass weight (R2 = .93) than was carcass ash content (R2 = .70). When we used the DXA R value (ratio of the attenuation coefficients for fat and lean) to predict percentage of fat in the carcass, the mean value for predicted carcass fat was 25.9% (P > .05). Similarly, carcass protein and water content were predicted from DXA lean. Using DXA region of interest analysis, estimates of the fat content of the shoulder and ham regions were close to chemical values; however, DXA underestimated the fat content of the loin and side regions by 20 and 28%, respectively. When prediction equations were used to evaluate DXA measurements of the half-carcasses of 28 gilts and 37 boars slaughtered at approximately 120 kg, the half-carcasses of gilts contained more fat (33.9 vs 27.8%, P < .001), less protein (14.1 vs 16.1%, P < .001), and less water (45.9 vs 52.1%, P < .001) than those of boars. These results indicate that DXA could be a valuable research tool for measuring the composition of pig carcasses. On the basis of the results of this study, prediction equations were revised for the DXA estimation of fat, protein, and water content of the half-carcass: Fat (%) = 450 - (315 x DXA R value), Protein (g) = -145 + (.23 x DXA lean), and Water (g) = 150 + (.73 x DXA lean). Furthermore, it seems that separate prediction equations are needed for regional analysis.

Growth rate and body composition of livestock can be optimized to meet consumer needs for a leaner product and to improve the efficiency of meat-animal production. Optimization strategies have traditionally focused on genetic selection and cost-effective ration formulation to achieve the genetic potential. Advances in understanding the mechanisms of growth and its control have led to additional opportunities for its manipulation. These include nutritional manipulation,the use of growth promotants, and, more recently, the ability to change the genetic potential through genetic engineering. Selection of appropriate candidate genes for manipulation depends on understanding the mechanisms underlying differentiation and growth of embryonic muscle cells. Recent advances in genetic engineering techniques, including gene therapy and germline transgenesis, will likely hasten the genetic progress toward a leaner carcass in domestic livestock. Such strategies may prove to be more beneficial then the controlled enhancement of somatotropin expression.

Barrows were restrictively fed starting at 20 kg BW to determine the effects of endotoxin on growth performance of control and somatotropin-treated pigs. The following treatments were used: 1) daily i.m. vehicle injection until 55 kg BW; 2) daily i.m. injections of 100 micrograms of recombinant porcine somatotropin (pST)/kg BW, until 55 kg; 3) i.v. saline injections for 7 d consecutively starting at 60 kg BW; 4) i.v. injections of 1 microgram of bacterial lipopolysaccharide (LPS)/kg BW for 7 d starting at 60 kg BW; and 5) the combined LPS+pST treatment, with pST injections from 20 kg through the 7 d of LPS treatment. Pigs evaluated for LPS effects were fed to 60 kg anticipating a weight loss. Pigs were bled at 0800 and 1100 at 55 kg and on d 7 of LPS treatment. Rectal temperatures were taken on d 7. Treatment with pST increased ADG by 13 to 20% and improved feed:gain by 17 to 23% before LPS treatment. During the 7 d of LPS injections, ADG and feed:gain did not differ, although feed efficiency was impaired and variable. Rectal temperatures at 1100 were progressively increased: control < LPS < LPS-pST (P < .01). Protein accretion was improved 27% by pST treatment, and lipid accretion was decreased 45% before LPS. Lipid stores decreased (P < .01) after LPS treatment in the pST-treated pigs. Lipopolysaccharide treatment and(or) decreased feed intake reduced the hyperinsulinemia and hyperglycemia (P < .01) associated with pST treatment. These results indicate that LPS induced a simulated septicemia and that the effects were not negated by pST treatment. The observed hyperthermia was additive, possibly due to increased lean body mass induced by pST combined with the pyrogenic effect of LPS.

Objective: To determine whether recombinant porcine somatotropin (PST) or chromium picolinate (CrP) affected cytokine production and metabolism in swine after endotoxin challenge exposure., Animals: 20 Poland China X Landrace pigs, 5/group., Procedure: Pigs were given CrP-supplemented feed at body weight of 20 kg; PST treatment began at 60 kg, and both treatments continued through body weight of 90 kg. At 90 kg, pigs were challenge exposed with 20 micrograms of lipopolysaccharide (LPS)/kg of body weight. Blood samples were obtained at various times through 24 hours after LPS challenge exposure., Results: In all pigs not given PST, glucose concentration decreased 2 to 4 hours after LPS. In PST-treated pigs, blood glucose concentration was decreased at 6 to 8 hours after LPS. Plasma insulin concentration paralleled changes in glucose concentration. Nonesterified fatty acid concentration was high 2 to 24 hours after LPS in pigs not given PST and at 6 to 24 h in PST-treated pigs. Plasma urea nitrogen concentration was high at 6 to 24 hours after LPS in pigs not given PST. The urea nitrogen values in PST-treated pigs were lower at all times. Serum aspartate transaminase activity was high 6 to 24 hours after LPS in pigs not given PST, whereas PST treatment prevented the increase in this enzyme activity. In untreated (PST) pigs, plasma bilirubin (total and direct) concentrations were high 4 to 8 hours after LPS and returned to normal at 24 hours. The PST- and CrP-treated pigs maintained normal plasma bilirubin concentrations. Interleukin 6 activity was unaffected by CrP and PST treatments. Treatment with CrP and PST decreased the tumor necrosis factor alpha response to LPS, compared with that in control pigs., Conclusions: PST, and to a lesser extent CrP, provide protection against the adverse metabolic effects of LPS-induced septic shock.

Chromium (Cr) and somatotropin have been shown to increase lean body mass in pigs but by independent mechanisms. Somatotropin and Cr also affect blood glucose, lipids, and tissue trace metal concentrations. Twenty-four castrated male pigs were divided into four groups: 1) control basal diet; 2) basal diet + 300 micrograms of Cr/kg of diet as Cr picolinate; 3) basal diet + pituitary porcine somatotropin (ppST; 100 micrograms/kg live weight injected daily); and 4) basal diet + Cr + ppST. Pigs were fed the diets from 30 to 60 kg body weight and then killed. Supplemental Cr led to increased total Cr in kidney (1.1 vs 2.3 micrograms) and liver (5.9 vs 8.8 micrograms) but not in the heart independent of ppST treatment. Chromium concentrations in longissimus muscle were less than 1.5 ng/g in all samples, and any increases due to supplemental Cr were not detected. Somatotropin treatment led to decreased hepatic Cr, Cu, Fe, and Zn concentrations and increased total renal Cu, Fe, and Zn. These data demonstrate that supplemental Cr causes increased tissue Cr in the liver and kidney but not in the heart or muscle in control and somatotropin treated pigs. Somatotropin treatment caused decreased kidney and liver Cr concentrations that were offset by increased tissue weights. Somatotropin effects on tissue Cr, Cu, Zn, and Fe were variable and difficult to evaluate due in part to growth hormone-induced changes in organ weights.

The present study was conducted to determine whether porcine somatotropin (pST) differentially regulates expression of the GLUT4 and fatty acid synthase (FAS) genes in pig adipose tissue. Three different experiments were conducted in which pigs were treated daily with different doses of pST for different time periods (7 or 14 d and from 60 to 90 kg of body wt). In these experiments, pST significantly and consistently decreased FAS mRNA levels (80%, 66% and 85%, respectively); however, GLUT4 mRNA was not affected by pST in two of the three experiments, and in the one showing an effect (Experiment 2), the decrease was less than observed for FAS (44%). Because of these results, we conducted subsequent experiments to see if the effects of pST on glucose metabolism in cultured pig adipose tissue (48 h) differed when glucose concentrations were changed from 1 to 5 mmol/L. These studies revealed that the antagonistic effect of pST on insulin action was more potent when glucose transport was saturated (5 mmol/L) than when glucose concentration limited glucose entry into the cell (1 mmol/L). In summary, these results suggest that the effects of pST on glucose transport in pig adipocytes are secondary to changes elicited by the hormone on intracellular glucose use for lipogenesis. When considered in the context of the decrease previously observed in glucose transport in pig adipocytes, the findings reported herein suggest that pST acts to decrease GLUT4 protein activity and/or distribution between the plasma membrane and the intracellular pool with little alteration in GLUT4 gene expression or total cell GLUT4 protein.

This research was conducted to evaluate the characteristics of muscle fiber growth and the effects of porcine somatotropin (pST; 100 micrograms.kg-1 BW.d-1) administration on the morphology of 12 muscles located in different regions of the body in barrows growing from 20 to 90 kg BW. In the course of the growth of control pigs, the percentage distribution of beta R fibers did not show any changes in all 12 muscles, whereas the percentage of alpha R and alpha W fibers changed in different patterns in different muscles. The administration of pST had no effect on fiber type distribution. The cross-sectional area of alpha W fibers was the largest of the three fiber types, and beta R and alpha R fibers were of similar size in all muscles. All fiber types in all muscles increased in cross-sectional area by an average of 120% from 20 to 60 kg BW. After 60 kg BW, the growth of alpha W fibers in seven (early maturing) muscles and alpha R fibers in one muscle out of the 12 muscles was not apparent. The increase of their cross-sectional area was an average of 12%, but the area of the other muscle fibers continued to increase by an average of 38% until 90 kg BW. The administration of pST increased the area of alpha W fibers in four out of seven of these early-maturing muscles by an average of 25%, suggesting some possible relationships between pST effects and the rate of muscle fiber maturation. Most of the muscles that responded to pST treatment were located in hindlimb region.

The effect of dietary chromium picolinate (CrP) and recombinant porcine growth hormone, somatotropin (rPST) administration on growth performance and cytokine production in Landrace-Poland China gilts was determined using a 2 by 2 treatment array. Treatments were: (1) control (basal diet), (2) CrP-supplemented diet (basal diet + 300 micrograms Cr3+/kg diet as CrP), (3) rPST (100 pg/kg body weight/day), and (4) rPST+CrP. CrP-supplemented diets were fed beginning at 20 kg body weight through 90 kg. Administration of rPST was begun at 60 kg weight and continued through 90 kg. All rPST treated pigs demonstrated improvements in growth performance versus controls. Pigs given CrP-supplemented diets showed no differences in growth performance. At 90 kg, pigs were challenged with endotoxin (lipopolysaccharide, 0.2 microgram/kg i.v.). Blood samples were collected at 0, 1, and 3 h postchallenge. Plasma IL-6 levels increased from 23 U/ml at time 0 to 1,927 U/ml at 3 h for control swine. Swine from the CrP treatment group had IL-6 levels of 8,130 U/ml at 3 h post-LPS. There were no differences in plasma IL-6 from pigs in the rPST and rPST+CrP treatment groups compared to the controls. Endotoxin challenge had no effect on either blood glucose levels or induction of TNF-alpha in any treatment group. PBMC from CrP-treated animals produced more IL-2 than peripheral blood mononuclear cells from all other groups.

Twenty-four castrated male pigs were used in a 2 x 2 treatment array to determine the main effects of and interactions between dietary chromium supplementation and pituitary porcine somatotropin (ppST) administration on growth performance and serum hormone and metabolite concentrations. The treatments were 1) control (basal diet); 2) chromium (basal diet+300 micrograms/kg diet added trivalent chromium as chromium picolinate); 3) ppST (100 micrograms/(kg body wt.d); and 4) chromium+ppST. Treatments were administered when pigs weighed between 30 and 60 kg. Blood was collected when pigs weighted 45 and 60 kg. All pigs treated with ppST exhibited improvements in growth performance (P < 0.05). Pigs given chromium showed no improvements in growth rate, feed efficiency or composition of gain. Measurements at 60 kg body weight revealed that ppST increased the cholesterol:HDL cholesterol ratio (P < 0.05). Chromium lowered serum insulin and glucose concentrations relative to controls (P < 0.05) and normalized the increase in glucose and insulin resulting from ppST treatment. No ppST x chromium interactions were noted, suggesting these changes in glucose and insulin metabolism are exerted through different mechanisms. These results indicate that chromium does not affect growth performance of young growing pigs. Chromium does normalize altered hormone and metabolite concentrations resulting from ppST treatment.

Three groups of eight gilts weighing 20, 40, or 60 kg were fitted with indwelling venous catheters to determine daily integrated circulating levels (DICL, serum concentration above baseline x time) of insulin, growth hormone (GH), glucagon, glucose, urea, and nonesterified fatty acids (NEFA) in response to acute challenge with porcine pituitary GH (pGH). Pigs were fed a common diet containing 18% CP and 3.5 Mcal of DE/kg between 0800 and 1200 (85% of ad libitum). Blood and urine were collected at 2- or 4-h intervals for 4 d. On d 2, 3, and 4, four pigs in each group were injected i.m. at 0800 with pGH (.1 mg/kg) and four pigs (controls) were injected with buffer. In control pigs DICL of GH was 20.4, 14.1, and 10.2 ng pGH.h.mL-1 in 20-, 40-, and 60-kg pigs, respectively. The DICL of GH in pGH-treated pigs was 4.2-, 7.0-, and 10.7-fold greater in 20-, 40-, and 60-kg pigs, respectively, than in controls. The DICL of insulin in control pigs was 7.9, 9.7, and 9.4 ng.h.mL-1 and was increased (P < .001) in pGH-treated pigs by 118, 213, and 276% in 20-, 40-, and 60-kg pigs, respectively. Although serum levels of glucose were increased (P < .001) by pGH treatment, the acute elevation observed in 60-kg pigs was more consistent relative to 20- and 40-kg pigs. In contrast, the acute reduction in blood urea upon pGH injection was more apparent in 20-kg gilts.(ABSTRACT TRUNCATED AT 250 WORDS)

Thirty-two crossbred barrows were used to determine the effects of frequency of administration of equivalent total dosages of recombinant porcine somatotropin (rpST) on growth performance, tissue accretion rates, and hormone and metabolite status of pigs. Treatments were control (buffer-injected daily), 60 micrograms/kg BW daily (4 injections/4 d), 120 micrograms/kg BW injected every other day (2 injections/4 d), or 240 micrograms/kg BW given every 4th d (1 injection/4 d). Treatments were initiated at 35 BW and continued until each pig had consumed a total of 440 Mcal of DE intake. Pigs were fed a diet that contained 16% CP, 1.2% lysine, and 3.5 Mcal of DE/kg at 85% of calculated ad libitum intake. Feed intake and rpST dose were adjusted at 8-d intervals. The 240 micrograms/kg BW treatment did not decrease appetite beyond the 15% restriction already imposed in the experimental design. Treatment groups responded to rpST in a frequency-dependent manner. Average daily gain was improved by 10, 23, and 36%, respectively, as injection frequency was increased from 1/4 to 2/4 to 4/4 d. Muscle weights were increased uniformly (15% on average) on a BW basis by all rpST treatments. Carcass (21, 42, and 63%), visceral (43, 65, and 112%), and empty body (22, 43, and 65%) protein accretion rates were increased by rpST treatment in a frequency-dependent fashion, respectively. Lipid accretion also was reduced in carcass and empty body (31% on average) by all rpST injection schemes relative to controls; however, visceral lipid accretion was increased by 59% by rpST. Protein utilization efficiency increased linearly by 24, 45, and 65% as the frequency of injection of rpST was increased from 1/4 to 2/4 to 4/4 d. Hormones and metabolites exhibited frequency-related profiles as well. These results suggest that frequency of administration greatly influences the magnitude of responsiveness to rpST and that optimal benefit would be realized by a delivery system that mimicked a daily surge, at minimum, of rpST.