Estimates of calf starter energy affected by consumption of nutrients. 2. Effect of changing digestion on energy content in calf starters.

Apparent total-tract digestibility data from 3 published studies with calves from 0 to 4 mo of age were used to evaluate National Research Council (NRC; 2001) estimates of digestible energy (DE) and metabolizable energy (ME) in calf starters (CS). Calves (n = 83) or pens of calves (n = 24) were used in model development. In each study, 48 Holstein bull calves (2-3 d of age at initiation of each study) were fed varying amounts of milk replacer with CS and water for ad libitum consumption. Calf starters varied in nutrient composition and physical form (pelleted, textured, or mixed with 5% grass hay and fed as a total mixed ration). Apparent total-tract digestibility was measured at various ages. Feed and feces were collected from 20 calves per trial during 5-d collection periods during the first 56 d of each trial. In 2 studies, calves were grouped in pens (4 calves/pen) for a second 56-d measurement period. Fecal collections were repeated occasionally during the second period. Total-tract digestibilities (n = 207) of neutral detergent fiber, nonfiber carbohydrates (NFC), crude protein (CP), and fat were used to calculate ME in CS using equations from the 2001 Dairy NRC. Contributions of digestible CP and fat from milk replacer before weaning were estimated using nonlinear regression and removed from estimates of fat and CP digestibility in CS. Digestion of most nutrients in CS and calculated DE and ME in CS were low early in life and increased with increasing cumulative NFC intake. The natural logarithm of cumulative NFC intake, measured from d 0 to the end of each digestibility period, accounted for more variation in CS nutrient digestibilities, DE and ME estimates compared with daily NFC intake or intake of other nutrients, intake of milk replacer, or age of calf. Calculated ME values in CS were similar to those predicted by NRC after calves consumed approximately 15 kg of cumulative NFC or 28 kg of cumulative dry matter intake (assuming 53% NFC in CS). Current estimates of energy in CS fed to 4 mo of age may overestimate contribution of dry feed to overall energy metabolism in young calves.

Estimates of calf starter energy affected by consumption of nutrients. 1. Evaluation of models to predict changing digestion on energy content in calf starters.

Apparent total-tract digestibility data from 3 published studies with calves from 0 to 4 mo of age were used to evaluate National Research Council (2001) estimates of metabolizable energy (ME) in calf starters (CS). Calves (n = 83) or pens of calves (n = 24) were used in model development. In each study, 48 Holstein bull calves (2 to 3 d of age at initiation of each study) were fed varying amounts of milk replacer with CS and water for ad libitum consumption. Calf starters varied in nutrient content and form (pelleted, texturized, or mixed with 5% grass hay and fed as a total mixed ration). Apparent total-tract digestibility was measured at various ages from 3 to 16 wk. Feed and feces were collected from 20 calves per trial during 5-d collection periods during the first 56 d of each trial. In 2 studies, calves were grouped in pens (4 calves/pen) for a second 56-d measurement period. Fecal collections were repeated occasionally during the second period. Total-tract digestibilities (n = 207) of neutral detergent fiber, nonfiber carbohydrates, crude protein, and fat were used to calculate digestible energy (DE) and ME in CS using equations from the 2001 Dairy National Research Council. Three modeling approaches were constructed to evaluate changing digestion of nutrients, DE, and ME in CS, including linear mixed models, broken-line regression, and exponential models. Linear mixed models provided best model fit statistics for digestion of crude protein, ether extract, neutral detergent fiber, and ME. Exponential models were optimal for digestion of dry matter and nonfiber carbohydrates. Linear mixed models were selected for evaluation of effects of intake on changing nutrient digestion from CS and amount of DE and ME available at various ages.

Relationships between starch concentration of dry feed, diet digestibility, and growth of dairy calves up to 16 weeks of age.

Our objective was to examine the potential relationship between starch concentration of dry feed and growth performance of young dairy calves via mixed-effects model analyses. A database was developed from 6 published studies conducted at the Nurture Research Center, Provimi (Brookville, OH), from 2008 to 2017 that included 18 dietary treatments and 372 calves at 0 to 8 wk of age in 5 nursery trials and 26 dietary treatments and 660 calves at 8 to 16 wk of age in 8 grower trials. The dry feeds ranged from 10.1 to 53.3% starch, 12.1 to 45.3% neutral detergent fiber, and 2.7 to 3.0 Mcal/kg of metabolizable energy [dry matter (DM) basis]. In all nursery trials, with increasing starch concentration in starter, average daily gain (ADG), hip width change, and starter intake linearly increased. In all grower trials, as starch concentration of dry feed increased, ADG, hip width change, and ADG/DM intake linearly increased; DM intake and DM intake/body weight were unaffected. In addition, the calves at 6 to 16 wk of age had greater digestibility of DM and crude protein with increasing starch concentration of dry feed. As indicated by meta-regression analysis, growth responses to starch concentration were influenced by metabolizable energy concentration in dry feed fed to the calves up to 16 wk of age. Changing starch from 23 to 43% on a DM basis (a typical range in the US industry) was predicted to increase ADG and hip width change by 5.8 and 5.0%, respectively, for calves at 0 to 8 wk of age and by 9.6 and 11.2%, respectively, for calves at 8 to 16 wk of age. Positive linear relationships between starch concentration of dry feed with DM digestibility, ADG, and hip width change reflect the importance of starch in the diets of young dairy calves.

Invited review: Current representation and future trends of predicting amino acid utilization in the lactating dairy cow.

In current dairy production systems, an average of 25% of dietary N is captured in milk, with the remainder being excreted in urine and feces. About 60% of total N losses occur postabsorption. Splanchnic tissues extract a fixed proportion of total inflow of each essential AA (EAA). Those EAA removed by splanchnic tissues and not incorporated into protein are subjected to catabolism, with the resulting N converted to urea. Splanchnic affinity varies among individual EAA, from several fold lower than mammary glands' affinity for the branched-chain AA to similar or higher affinity for Phe, Met, His, and Arg. On average, 85% of absorbed EAA appear in peripheral circulation, indicating that first-pass removal is not the main source of loss. Essential AA in excess of the needs of the mammary glands return to general circulation. High splanchnic blood flow dictates that a large proportion of EAA that return to general circulation flow through splanchnic tissues. In association with this constant recycling, EAA are removed and catabolized by splanchnic tissues. This results in splanchnic catabolism equaling or surpassing the use of many EAA for milk protein synthesis. Recent studies have demonstrated that EAA, energy substrates, and hormones activate signaling pathways that in turn regulate local blood flow, tissue extraction of EAA, and rates of milk protein synthesis. These recent findings would allow manipulation of dairy diets to maximize mammary uptake of EAA and reduce catabolism by splanchnic tissues. Dairy cattle nutrient requirement systems consider EAA requirements in aggregate as metabolizable protein (MP) and assume a fixed efficiency of MP use for milk protein. Lysine and Met sufficiency is only considered after MP requirements have been met. By doing so, requirement systems limit the scope of diet manipulation to achieve improved gross N efficiency. Therefore, this review focuses on understanding the dynamics of EAA metabolism in mammary and splanchnic tissues that would lead to improved requirement prediction systems. Inclusion of variable individual EAA efficiencies derived from splanchnic and mammary responses to nutrient and hormonal signals should help reduce dietary protein levels. Supplementing reduced crude protein diets with individual EAA should increase gross N efficiency to more than 30%, reducing N excretion by the US dairy industry by 92,000 t annually.

Invited review: Enteric methane in dairy cattle production: quantifying the opportunities and impact of reducing emissions.

Many opportunities exist to reduce enteric methane (CH4) and other greenhouse gas (GHG) emissions per unit of product from ruminant livestock. Research over the past century in genetics, animal health, microbiology, nutrition, and physiology has led to improvements in dairy production where intensively managed farms have GHG emissions as low as 1 kg of CO2 equivalents (CO2e)/kg of energy-corrected milk (ECM), compared with >7 kg of CO2 e/kg of ECM in extensive systems. The objectives of this review are to evaluate options that have been demonstrated to mitigate enteric CH4 emissions per unit of ECM (CH4/ECM) from dairy cattle on a quantitative basis and in a sustained manner and to integrate approaches in genetics, feeding and nutrition, physiology, and health to emphasize why herd productivity, not individual animal productivity, is important to environmental sustainability. A nutrition model based on carbohydrate digestion was used to evaluate the effect of feeding and nutrition strategies on CH4/ECM, and a meta-analysis was conducted to quantify the effects of lipid supplementation on CH4/ECM. A second model combining herd structure dynamics and production level was used to estimate the effect of genetic and management strategies that increase milk yield and reduce culling on CH4/ECM. Some of these approaches discussed require further research, but many could be implemented now. Past efforts in CH4 mitigation have largely focused on identifying and evaluating CH4 mitigation approaches based on nutrition, feeding, and modifications of rumen function. Nutrition and feeding approaches may be able to reduce CH4/ECM by 2.5 to 15%, whereas rumen modifiers have had very little success in terms of sustained CH4 reductions without compromising milk production. More significant reductions of 15 to 30% CH4/ECM can be achieved by combinations of genetic and management approaches, including improvements in heat abatement, disease and fertility management, performance-enhancing technologies, and facility design to increase feed efficiency and life-time productivity of individual animals and herds. Many of the approaches discussed are only partially additive, and all approaches to reducing enteric CH4 emissions should consider the economic impacts on farm profitability and the relationships between enteric CH4 and other GHG.

Effects of wortmannin, sodium nitroprusside, insulin, genistein, and guanosine triphosphate on chemotaxis and cell growth of Entodinium caudatum, Epidinium caudatum, and mixed ruminal protozoa.

The mechanisms by which ruminal protozoa sense and migrate toward nutrients are not fully understood. Chemotaxis by many diverse eukaryotic cells is mediated by phosphatidylinositol-3-kinase, which is highly conserved in receptor tyrosine kinase (RTK) signaling pathways and consistently inhibited by wortmannin. In experiment 1a, increasing the concentration of wortmannin inhibited cell growth nonlinearly at 24h of a culture of the rumen protozoan Entodinium caudatum, but high variability prevented growth inhibition of Epidinium caudatum from reaching significance. In experiment 1b, increasing the insulin concentration recovered 24-h cell counts for both cultures, depending on wortmannin concentration. In experiment 2, addition of sodium nitroprusside (Snp; activator of protein kinase G for cilial beat reversal in nonrumen ciliate models) at 500µM or wortmannin at 200µM in beakers containing rumen fluid decreased random swimming by mixed entodiniomorphids into capillary tubes (inserted into beakers) containing saline. Both Snp and wortmannin increased chemotaxis into tubes containing glucose compared with the beaker control. For isotrichids, beaker treatments had no response. Glucose increased chemotaxis, but peptides decreased chemotaxis even when combined with glucose. In experiment 3, we assessed preincubation of genistein (a purported RTK blocker in nonrumen ciliate models) at 40 or 400µM in beakers and guanosine triphosphate (GTP; a universal chemorepellent in nonrumen ciliate models, perhaps mediated through an RTK) at 10 or 100µM combined with glucose in capillary tubes. Neither genistein nor GTP affected chemotaxis toward glucose for entodiniomorphids. However, GTP at 100µM reduced chemotaxis toward glucose for isotrichids. After the animal is fed, isotrichids that are depleted in glycogen migrate to the dorsal area of the rumen, and the rapid uptake of sugars is enhanced through strong chemotaxis but can be reversed by peptides or GTP. In contrast, entodiniomorphids are less intensely chemoattracted to glucose than isotrichids but are chemoattracted to peptides. Entodiniomorphids' chemoattraction appears to be integrated with slower but prolonged availability of energy from digesting starch and fiber.

Effects of jugular-infused lysine, methionine, and branched-chain amino acids on milk protein synthesis in high-producing dairy cows.

In addition to lysine and methionine, current ration-balancing programs suggest that branched-chain amino acid (BCAA) supply may also be limiting in dairy cows. The objective of this study was to investigate whether BCAA, leucine, isoleucine, and valine become limiting for milk protein synthesis when methionine and lysine supply were not limiting. Nine multiparous Holstein cows with an average milk production of 53.5±7.1 kg/d were randomly assigned to 7-d continuous jugular infusions of saline (CTL), methionine and lysine (ML; 12 g and 21 g/d, respectively), or ML plus leucine, isoleucine, and valine (ML+BCAA; 35 g, 15 g, and 15 g/d, respectively) in a 3×3 Latin square design with 3 infusion periods separated by 7-d noninfusion periods. The basal diet consisted of 40% corn silage, 14% alfalfa hay, and a concentrate mix, and respectively supplied lysine, methionine, isoleucine, leucine, and valine as 6.1, 1.8, 4.7, 8.9, and 5.3% of metabolizable protein. Dry matter intake (23.9 kg/d), milk yield (52.8 kg/d), fat content (2.55%), fat yield (1.33 kg/d), lactose content (4.77%), lactose yield (2.51 kg/d), and milk protein efficiency (0.38) were similar across treatments. Protein yield and protein content were not significantly different between ML (1.52 kg/d and 2.88%, respectively) and ML+BCAA (1.51 kg/d and 2.83%, respectively), but they were significantly greater than that of CTL (1.39 kg/d and 2.71%). Cows that received ML+BCAA had less milk urea nitrogen content (10.9 mg/dL) compared with milk of CTL cows (12.4 mg/dL) and ML cows (11.8 mg/dL). Whereas high-producing cows responded positively to methionine and lysine supplementation, no apparent benefits of BCAA supplementation in milk protein synthesis were found. Infusion of BCAA may have stimulated synthesis of other body proteins, probably muscle proteins, as evidenced by decreased milk urea nitrogen.

Effects of a polymer-coated urea product on nitrogen metabolism in lactating Holstein dairy cattle.

The purpose of this study was to evaluate the impact of polymer-coated urea on nitrogen retention, rumen microbial growth, and milk production and composition. Coated urea (CU) that is more slowly hydrolyzed to ammonia than unprotected urea could potentially be used more efficiently by rumen microorganisms. Eight cows were offered each of three diets in a randomized crossover design. Each treatment period consisted of a 14-d adjustment period and a 5-d collection period. Diets were formulated to maintain milk production while reducing plasma urea nitrogen concentrations and urinary nitrogen excretion. Diets consisted of corn silage, mixed grass/legume haylage, chopped alfalfa hay, corn meal, protein, vitamin and mineral supplements, in a total mixed ration and fed ad libitum. The diets contained 17.9%, 18.1%, and 16.4% CP and 0, 0.77%, and 0.77% CU (dry matter basis) and are denoted as CP18-CU, CP18+CU, and CP16+CU, respectively. Individual feed intakes were measured, and total fecal, and urine collections were conducted. Cows were milked twice daily at 0500 and 1700 h, and the milk sampled for composition and milk urea N analysis. Dry matter intake averaged 23.5 +/- 0.2 kg/d and was not altered by diet. Also, milk fat and true protein were not altered by diet and averaged 3.72 and 3.07%, respectively. Milk yield was highest for diets CP18-CU and CP18+CU. Significant differences were observed in N intake and excretion in urine, feces, and milk between dietary treatments. Cows fed CP16+CU consumed 11% less N than in CP18-CU. Cows fed CP18+CU showed the highest excretion of N in urine, and together with CP16+CU, the lowest N excretion in feces. Nitrogen excretion in milk was lower for cows fed CP16+CU. Calculated N balance was not significantly different between diets nor was it significantly different from zero. Efficiency of N capture in milk protein as a function of N intake was higher for animals on CP16+CU. Urinary excretion of purine derivatives was not different between diets, and estimated microbial CP was also similar. Coated urea was not effective at reducing nitrogen excretion by dairy cattle.

Physical and mechanical characteristics of tibias from transgenic mice expressing mutant bovine growth hormone genes.

Physical and mechanical characteristics of tibia from mice expressing either the M4, M11, or G119K mutant bovine growth hormone (bGH) gene and displaying large, near-normal, or small-size phenotypes, respectively, were compared to those of non-transgenic, control mice (NTC). Three animals of each strain were euthanized at 28, 38, 48, 58, and 68 days of age. Variables were regressed against age to establish the pattern of change throughout the experiment, and the regression results are presented. Tibias from G119K were shorter (13.1 mm) and lighter (37.3 mg) than those from other strains, and M4 tibias were heavier (87.9 mg) and longer (16.6 mm) at 70 days of age. The ratio of tibia length to body weight suggests longitudinal bone growth was not reduced as much as overall growth in G119K mice. The external and internal dimensions of the G119K tibias were smaller than the other strains whereas the M4 tibias were somewhat larger. Differences in physical dimensions between the NTC and M11 mice did not greatly affect bone mechanical characteristics. Tibias from M4 mice resisted more load at both flexure and breaking compared to the other strains. At 50 days of age, stress at flexure was greater at all ages for G119K mice (12.4 kg/mm2) and was decreased in M4 mice (8.5 kg/mm2). The bGH mutations produce different effects on bone growth and its mechanical characteristics. There also may be differential tissue responsiveness to the mutant bGH analogs, as longitudinal growth was not as affected as empty body growth in the G119K mice. These transgenic mouse strains provide valuable models to study bone growth, formation, and reformation in response to GH regulation, and more importantly, the M4 and G119K mice may serve as a model in which the priorities for GH action on bone vs muscle may be determined.

Growth hormone (GH) receptors, binding proteins and IGF-I concentrations in the serum of transgenic mice expressing bovine GH agonist or antagonist.

We have examined the regulation of hepatic growth hormone receptors (GH-R) and serum GH binding proteins (GHBP) in transgenic mice expressing an antagonist of bovine growth hormone (bGH), G119K-bGH, and consequently exhibiting a growth suppressed dwarf phenotype. Specific GHBP could be measured in transgenic dwarf mouse serum only by immunological methods (RIA), because these mice have a very high concentration of mutated bGH in circulation (> 1 microgram/ml) and, therefore, almost all GHBP is bound to G119K-bGH and cannot be quantitated in binding assays. The concentrations of GHBP were 0.6 +/- 0.4 nM and 1.7 +/- 0.4 nM for normal and dwarf mice respectively. The concentrations of free GHBP in normal mice and in transgenic mice expressing wild-type GH can be calculated using chromatographic techniques as the dissociation constant (Kd) and the ratio of bound 125I-GH to free 125I-GH in the serum ([GHBP]free = B/F.Kd). In agreement with the assumption that GHBP reflects GH-R status, liver uptake of injected labeled bGH was greatly reduced in transgenic dwarfs in comparison with normal mice or with transgenic mice expressing wild-type bGH (liver/blood ratio of 0.48 +/- 0.21, 2.7 +/- 0.2, and 1.3 +/- 0.3 respectively) indicating that the high concentration of the mutated bGH (G119K-bGH) prevents labeled bGH uptake, as was expected from the dwarf phenotype. 125I-bGH taken up by the liver of transgenic dwarf mice was found in a smaller molecular species than in normal mice, compatible with the presence of 1:1 [(GH-R):GH] complexes instead of the 2:1 [(GH-R)2:GH] or 2:2 [(GHBP)2:(GH)2] complexes found in normal mice. The concentration of IGF-I, the principal mediator of GH activity, in the G119K-bGH transgenic mice was correlated with the concentration of free GHBP. This allowed us to use free GHBP concentration as a marker of the effects of the active endogenous hormone (mGH) on liver receptors in the presence of different concentrations of the antagonist of GH. The levels of GHBP in serum, as well as the concentration of GH-R in liver microsomes from mice expressing the bGH antagonist, are up-regulated by the high concentration of G119K-bGH (85%), but significantly less so than that which could be expected for the same concentration of native GH (220-275%). This up-regulation suggests that the G119K-bGH antagonist is internalized and induces synthesis of the receptor and of the binding protein.

Expression of mutant bovine growth hormone genes in mice perturbs age-related nutrient utilization patterns.

Three lines of transgenic mice expressing mutant bovine growth hormone (bGH) genes and displaying small (G119K), near normal (M11) or large (M4) phenotypes and nontransgenic control (NTC) mice were used to determine GH-associated, age-specific changes in empty body composition. The single amino acid substitution in G119K mice reduced the quantities (P < 0.001) and early rates (P < 0.05) of deposition for water, protein and ash but resulted in similar quantities of fat as the NTC mice. The change in relative quantities of empty body components indicated the G119K analogue altered nutrient partitioning, basal metabolism and (or) nutrient availability to effect the differential observed in body composition. The two amino acid substitutions in the bGH gene expressed by the M11 mice caused only a small change in phenotype, but age-related changes in the accretion of protein, fat and ash indicated these mice were not mature by 68 d of age. The bGH analogue produced by the M4 mice resulted in a doubling (P < 0.001) of body weight in comparison with the NTC mice, a result of the increasing (P < 0.001) rate of weight gain. Empty body component gain of the M4 mice also indicated they had not yet matured by 68 d of age. The G119K and M4 mutant forms of bGH altered rates and composition of growth, possibly through redirection of tissue nutrient utilization, modification of nutrient metabolism, and(or) nutrient availability.

Consequences of overexpression of growth hormone in transgenic mice on liver cytochrome P450 enzymes.

The effect of growth hormone (GH) on cytochrome P450 (CYP) and P450-dependent monooxygenases was studied in 4-, 6-, 8-, and 10-month-old female bovine growth hormone (bGH) transgenic mice that overexpress GH. Nontransgenic female mice (C57/SJL) littermates were used for baseline determinations. The body weights of the bGH mice were approximately 35% greater than those of the controls. The liver weights were 2-fold higher than those of the controls, resulting in a 25-60% increase in liver/body weight ratio during the life span of the bGH mice when compared with the controls. Similar increases in heart and kidney weights were observed. Since the GH transgene was transcriptionally regulated by a metallothionein-I gene promoter, metallothionein concentrations in livers of transgenic and nontransgenic mice were measured. No significant differences were observed. In marked contrast to increases in liver weights, hepatic cytochrome P450 content, benzphetamine N-demethylase, and benzo [a] pyrene hydroxylase activities were decreased by 36, 42 and 75%, respectively. No age-related changes in the decrease of the monooxygenases were observed. Microsomal heme oxygenase (HO) in the liver was induced 44% above the control values. Immunoblot analysis also showed a marked increase in HO-1 in the bGH mice. These results indicate that GH suppresses the carcinogen-metabolizing enzyme benzo [a] pyrene hydroxylase and the drug-metabolizing enzyme benzphetamine N-demethylase. This suppression was accompanied by an induction of HO activity in bGH transgenic mice. The consequences of prolonged exposure to supraphysiological levels of this hormone cannot always be predicted from the known physiological actions of GH.

Effects of bovine growth hormone analogs on mouse skeletal muscle structure.

Skeletal muscles of transgenic mice expressing altered bovine growth hormones (bGH) have been compared with those of nontransgenic mice to determine whether muscle fiber type-specific responses or histopathologies are associated with the altered gene. The slow soleus and predominantly fast gastrocnemius muscles were prepared for myofibrillar ATPase activity (to determine muscle fiber type) and histological examination from mice that were either giant (M4 line), larger than normal (M11 line), dwarf (G119K line), or nontransgenic (NTC). No histopathology was observed in any of the muscles. Although body weights were significantly different between all four lines of mice, only the giant M4 mice had significantly larger muscle fibers than the other lines of mice, while neither the G119K nor M11 lines were significantly different from the NTC for either muscle. No fiber type-specific differences were noted. These results suggest that the different muscles are the product of differences in numbers of muscle fibers expressed in the G119K and M11 lines of mice; the increase in body mass matched the fiber size growth only in the giant M4 line. Therefore, the altered bGH genes may be acting on fetal liver and myoblast/myotube GH receptors to change the GH and IGF-I regulated pattern of muscle development, and eventually, to determine the adult muscle fiber numbers.

Growth patterns and body composition of transgenic mice expressing mutated bovine somatotropin genes.

The objectives of this study were to determine growth rates, feed intakes, feed efficiencies, and chemical composition of mice from three transgenic lines in 10-d periods from weaning to near maturity. Lines M4, M11, and G119K express bovine somatotropin (bST) mutations E117L, L121P-E126G, and G119K and display phenotypes of large, near normal, and small body size, respectively. M4 mice were 28% larger at 28 d and 84% larger at 68 d than non-transgenic control (NTC) mice. M11 mice were the same size at 28 d as NTC but were 25% larger at 68 d. G119K mice were 34% and 25% smaller than NTC at 28 and 68 d, respectively. Growth rates of G119K mice and NTC were similar, whereas growth rates of M11 and M4 mice were increased (P < .05). Feed intakes of M4 and M11 mice were greater than those of NTC mice (P < .05), whereas feed intakes of G119K mice were lower than those of NTC mice (P < .05). Feed efficiency (gain/feed) was improved in M4 and M11 mice (P < .05) and not altered in G119K mice compared to that of NTC mice (P > .05). Chemical composition was also altered by expression of bST analogs in transgenic mice. G119K and M4 mice had increased body fat percentages and decreased body protein percentages in comparison to M11 and NTC mice (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

The use of transgenic mice in nutrition research.

The ability to generate transgenic mice that express exogenous genes, express genes in a tissue specific manner, or do not express an endogenous gene will dramatically impact nutritional studies. Use of transgenic animals will greatly expand the types of experiments that can be performed, for example, by permitting researchers to examine specific mechanisms underlying nutritional relationships. These studies can be viewed from two perspectives; the effect of nutrition in general or nutrients in specific on the regulation of gene expression; and conversely, the effects of gene expression upon nutrient utilization or other aspects of metabolism. In addition, transgenic animal models have been and can be established to characterize human pathologies, e.g., pituitary gigantism or atherosclerosis, and the roles and interactions of nutrition in these and other metabolic diseases may then be evaluated. The use of transgenic animals in nutrition research is new and quite fertile, and exciting results will continue to surface.

In vitro and in vivo development of bovine embryos from zygotes and 2-cell embryos microinjected with exogenous DNA.

The objectives of these experiments were: 1) to determine an effective culture method for production of transferable bovine embryos following exogenous DNA microinjection; 2) to determine the effect of these methods on the ability of the injected zygotes and 2-cell embryos to develop in vivo; and, 3) to compare development of embryos microinjected as zygotes or 2-cell embryos. DNA fragments encoding bovine growth hormone (bGH), bGH-10Delta6, and a bGH antagonist, bGH-M8 (5) were used. A total of 639 zygotes and 153 2-cell embryos were injected. Zygotes and 2-cell embryos microinjected with bGH-M8 were incubated for 6 days in oviducts of intermediate recipients (rabbits or sheep) or co-cultured in vitro with bovine oviduct epithelial cells. Zygotes and 2-cell embryos microinjected with bGH-10Delta6 were co-cultured in vitro only. The most effective method for the production of transferable bovine embryos following exogenous DNA microinjection was via in vitro co-culturing with bovine epithelial cells. For example, 32.3% of the bGH-M8 and 33.5% of the bGH-10Delta6 microinjected zygotes reached the morula/blastocyst stage while 48.4% and 63.0% of the 2-cell embryos injected with bGH-M8 and bGH-10Delta6, respectively, developed to the morula/blastocyst stage. The percentage of blastocysts obtained for control, non-injected zygotes and 2-cell embryos was 34.5% and 69.6%, respectively. The developmental rate to the morula/blastocyst stage was approximately 20% greater for embryos obtained from microinjected 2-cell embryos relative to microinjected zygotes. However, there was no significant difference in pregnancy rates following transfer of these blastocysts to cow uteri.

Recombinant bovine somatotropin's effects on patterns of nutrient utilization in lactating dairy cows.

The discussion of effects of recombinant bovine somatotropin (rbST) administration on the metabolism of lactating dairy cows presented is divided into two parts: short term and long term. Short-term effects are evident during the initial period of treatment when milk production is increased but feed intake has not yet increased. During this period body reserves are mobilized to support the higher rates of milk production. This phase is very similar to the early lactation condition, when energy requirements for milk production also exceed energy intake. Two notable exceptions to this analogy are that glucose and beta-hydroxybutyrate concentrations are not altered during rbST treatment but are influenced by stage of lactation. After the initial phase of rbST treatment, feed intake increases to compensate for the increase in milk production. During this phase the metabolism of cows treated with rbST essentially mirrors the metabolism of untreated cows producing comparable amounts of milk.

Effects of somatotropin and substrates on patterns of liver metabolism in lactating dairy cattle.

Objectives of this study were to quantitate metabolite fluxes in ruminant liver and to delineate effects of recombinant bST on patterns of nutrient metabolism by liver. Nineteen multiparous cows ranging in previous lactational performance from 6400 to 13,500 kg per 305-d lactation were treated with either placebo or bST (40 mg/d) from wk 11 to 18 of lactation. Liver tissue was collected at slaughter. Tissue slices were incubated with various 14C-labeled substrates, and rates of conversion of label to CO2 and metabolites were measured. In vivo recombinant bST treatment increased in vitro conversion of [1-14C]propionate and [2-14C]acetate to glucose more than twofold. At 2.5 mM propionate, bST-treated cows converted propionate to glucose at 90% efficiency. Recombinant bST increased [14C]bicarbonate incorporation into glucose five-fold. Overall, bST treatment resulted in greater C flow from propionate and acetate through the TCA cycle. Acetate had only small effects on propionate metabolism and no effects on lactate plus pyruvate metabolism. Unexpectedly, propionate decreased acetate conversion to ketone bodies. Suggested mechanisms for this observation include depletion of coenzyme A and allosteric regulation of carnitine palmitoyltransferase I by methylmalonyl-coenzyme A formed from propionate. In summary, bST treatment resulted in increased rates of gluconeogenesis and oxidation in liver in support of lactation.

Physical attractiveness, physical effectiveness, and self-concept in late adolescents.

The differential role of various body attitudes in predicting the self-concepts of late adolescents (124 males and 218 females), enrolled in introductory psychology courses, was assessed. Subjects rated 24 body characteristics in terms of 1) how physically attractive they assumed these parts of their bodies were, and 2) how physically effective they assumed them to be; subjects also responded to a short self-concept scale. In accordance with the theory of Erikson (1968) and of McCandless (1970), it was expected that attractiveness attitudes should contribute more to the self-concepts of females than should effectiveness attitudes, while a reverse pattern of interrelatedness was expected for males. Results indicated a higher correspondence between what are seen as attractive body parts and what are viewed as effective body components for males than for females. Moreover, findings from step-wise multiple regression analyses of each sex group's ratings of the body parts for attractiveness and effectiveness, respectively, each with the criterion variable constituting mean self-concept score, were consistent with expectations. For females, the multiple correlation between attractiveness ratings and self-concept was greater than the multiple correlation between effectiveness ratings and self-concept, and more attractiveness variables than effectiveness variables were significant predictors of self-concept. The converse of these findings were obtained with the males' data. The relevance of these results for theories of personality development were discussed.

Structure of racial attitudes in white middle adolescents.

Middle adolescent White children (N=101, mean age 17.0 years) were subjects in a study assessing the comparability of racial attitudes as measured through the use of various response formats. Attitudes toward White and Black racial stimuli, respectively, were assessed through responses to (1) a traditional, forced-choice format; (2) a dimensionalized, bipolar item format requiring placement of ten Whites and ten Blacks, respectively, along each of ten 7-point dimensions; (3) a format identical to (2) except in the requirement of only one racial stimulus attribution per dimension; and (4) a format requiring the estimation of the percentage of time a White and a Black stimulus, respectively, manifested each item characteristic. Although mean responses derived from the latter three response-latitude methods were directionally consistent with corresponding forced-choice, frequency data, neither the multidimensional locations of these means nor their intradimensional separations were very disparate. Moreover, although correlational analyses indicated relatively low forced-choice /response-latitude method consistency, and even lower, and essentially nonsignificant, intramethod consistency when intra-item Black-White ratings from the response-latitude methods were considered, moderate and significant consistencies existed in the intermethod comparisons among the response-latitude methods. This finding was taken as evidence of convergent and discriminant validation. It was concluded that inferences drawn about the structure of racial attitudes based on data derived from forced-choice formats are not supported by data derived from response-latitude methods and that, alternatively, these latter methods provide evidence for the existence of other attitude structures.