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Increased colostrum lactose concentration is also associated with greater colostrum yield and reduced protein and Brix% in dairy cattle ([83]), supporting the concept that colostrum yield may dilute component concentrations. Imposing mid to late-gestation nutrient restriction reduced first-milking colostrum yield (within 1 h postcalving) in beef cattle ([56]; [72]) without altering colostrum IgG concentration ([56]; [72]) but compromised total IgG yield ([72]). Colostrum IgG yield is often not reported in dairy and beef cattle, although one study noted that there was no difference in colostrum IgG output between treatments, despite colostrum IgG concentration being decreased ([84]). By contrast to cattle, colostrum yield in sheep appears more sensitive to protein supplementation during late gestation, with most studies indicating that increased protein intake (at times, in conjunction with greater RUP intake) increases colostrum yield ([38]; [3]). Keywords: cattle; colostrum; immunoglobulin G; prepartum; nutrition; sheep EN cattle colostrum immunoglobulin G prepartum nutrition sheep 24 36 13 06/20/23 20230601 NES 230601 Implications Many cattle and sheep do not produce enough colostrum for their offspring. [Extracted from the article]

Production of protein by the lactating mammary gland is stimulated by intake of dietary energy and protein. Mass-action effects of essential amino acids (EAA) cannot explain all of the nutritional response. Protein synthesis in tissues of growing animals is regulated by nutrients through the mammalian target of rapamycin (mTOR) and integrated stress response (ISR) networks. To explore if nutrients signal through the mTOR and ISR networks in the mammary gland in vivo, lactating cows were feed-deprived for 22 h and then infused i.v. for 9 h with EAA+ glucose (Glc), Glc only, L-Met+L-Lys, L-His, or L-Leu. Milk protein yield was increased 33 and 27% by EAA+Glc and Glc infusions, respectively. Infusions of Met+Lys and His generated 35 and 41%, respectively, of the EAA+GIc response. Infusion of EAA+Glc reduced phosphorylation of the ISR target, eukaryotic initiation factor(elF) 2, in mammary tissue and increased phosphorylation of the mTOR targets, ribosomal S6 kinase 1 (S6K1) and S6. Both responses are stimulatory to protein synthesis. Glucose did not significantly increase mammary S6K1 phosphorylation but reduced elF2 phosphorylation by 62%, which implicates the ISR network in the stimulation of milk protein yield. In contrast, the EAA infusions increased (P < 0.05) or tended to increase (P < 0.1) mammary mTOR activity and only His, like Glc, decreased elF2 phosphorylation by 62%. Despite activation of these protein synthesis signals to between 83 and 127% of the EAA+Glc response, EAA infusions produced less than one-half of the milk protein yield response generated by EAA+Glc, indicating that ISR and mTOR networks exert only a portion of the control over protein yield. J. Nutr. 140: 285-292, 2010. doi: 10.3945/jn.109.114033.

Although amino acids (AA) synthesized by enteric microbiota in the upper gut of nonruminants can be absorbed, they do not necessarily make a net contribution to the host's AA supply. That depends on whether protein or nonprotein nitrogen sources are used for microbial protein production. We determined the contributions of urea, endogenous protein (EP), and dietary protein (DP) to microbial valine (MVAL) at the distal ileum of growing pigs, based on isotope dilutions after a 4-d continuous infusion of L-[1-[sup.13]C]valine to label EP and of [[sup.15]N [sup.15]N]urea. Eight barrows were assigned to either a cornstarch and soybean meal-based diet with or without 12% added fermentable fiber from pectin. Dietary pectin did not affect (P > 0.10) the contributions of the endogenous and DP to M.VAL. More than 92% of valine in microbial protein in the upper gut was derived from preformed AA from endogenous and DP, suggesting that de novo synthesis makes only a small contribution to microbial AA.

Our objectives were to examine the effect of an i.p. injection of a flooding dose of L-phenylalanine (Phe) containing L-[[ring-.sup.2][H.sub.5]Phe on time courses of physiologic responses, the tracer Phe enrichments, and fractional protein synthesis rates (FSR) in plasma, visceral organs, and muscles. In a randomized complete block design, 5 blocks of 5 littermate piglets were weaned at 16 d of age and injected i.p. with a flooding dose of L-Phe (1.5 mmol/kg body weight) on d 8 postweaning under fed conditions. Tissues were collected at 15, 30, 45, 60, and 75 min postinjection. Plasma glucose concentration increased (cubic effect, P < 0.05) from 4.8 preinjection to 5.8 mmol/L 15 min postinjection and returned to preinjection levels thereafter. Plasma insulin concentration did not change (P > 0.05) over time. Plasma Phe concentration increased logarithmically (P < 0.05) from 85 to 711 [micro]mol/L and reached 95% of the maximum concentration 48 min postinjection, but no changes (P > 0.05) in tissue contents of other free amino acids were observed. The Phe free pools in plasma, visceral organs, and muscles were evenly enriched (32.3 [+ or -] 1.4 mol%) with [L-[.sup.2][H.sup.5]]Phe 15 min after the i.p. injection. The FSR in visceral organs did not change (P > 0.05), whereas plasma and muscle protein FSR decreased (P < 0.05) over time. We conclude that the i.p. injected tracer Phe rapidly distributed into plasma and intra- and extracellular spaces, and was effective for measuring FSR in visceral organs, but not in plasma and muscles of pigs. KEY WORDS: * route of tracer delivery * stable isotopes * isotopic enrichment * piglets

Xiao, Changting, V. Margaret Quinton, and John P. Cant. Description of glucose transport in isolated bovine mammary epithelial cells by a three-compartment model. Am J Physiol Cell Physiol 286:C792-C797, 2004. First published November 26, 2003; 10.1152/ ajpcell.00356.2003.--Initial rates of glucose entry into isolated bovine mammary epithelial cells display moderate degrees of asymmetry and cooperative interactions between export and import sites. The present study examined the hypothesis that these kinetic features are due to compartmentalization of intracellular glucose. Net uptake of 3-O-methyl-D-[l-[.sup.3H]glucose (3-OMG) by isolated bovine mammary epithelial cells was measured at 37 [degrees] C. The time course of 3-OMG net uptake was better fitted by a double-exponential equation than by a single- or triple-exponential equation. Compartmental analysis of the time course curve suggested that translocated 3-OMG is distributed into two compartments with fractional volumes of 32.6 [+ or -] 5.7% and 67.4 [+ or -] 5.7%, respectively. The results support the view that glucose transport in bovine mammary epithelial cells is a multistep process consisting of two serial steps: fast, carrier-mediated, symmetric translocation of sugar across the cell plasma membrane into a small compartment and subsequent slow exchange of posttranslocated sugar between two intracellular compartments. A three-compartment model of this system successfully simulated the observed time course of 3-OMG net uptake and the observed dependence of unidirectional entry rates on intra- and extracellular 3-OMG concentrations. Simulations indicated that backflux of radiolabeled sugar from the small compartment to extracellular space during 15 s of incubation gives rise to the apparent asymmetry, trans-stimulation, and cooperativity of mammary glucose transport kinetics. The fixed-site carrier model overestimated the rate of glucose accumulation in cells, and its features can be accounted for by the compartmentalization of intracellular sugar. compartmentalization; milk synthesis

Xiao, Changting, and John P. Cant. Glucose transporter in bovine mammary epithelial cells is an asymmetric carrier that exhibits cooperativity and trans-stimulation. Am J Physiol Cell Physiol 285: C1226-C1234, 2003. First published July 16, 2003; 10.1152/ajpcell.00190.2003.--Glucose transport kinetics were quantified in isolated bovine mammary epithelial cells using 3-O-methyl-D-glucose. Isolated cells retained satisfactory viability and glucose uptake activity, which was inhibited by cytochalasin B, phloretin, [HgCl.sub.12], and low temperature. Initial rates of entry were measured over a 15-s interval at 37[degrees]C under zero-trans, equilibrium-exchange, high-cis, and high-trans concentrations of 3-0-methyl-D-glucose between 0 and 20 mM. The combined set of rate measurements from all experimental conditions was fit to the fixed-site carrier model by nonlinear regression to estimate parameters of transport. For the regression between predicted and observed initial rates, [r.sup.2] was 0.97. Forward [V.sub.max] was estimated at 18.2 [nmo*min.sup.-1] * mg [protein.sup.-1], and the Michaelis constant was 8.29 mM. The cooperativity parameter was 1.63, trans-stimulation was 2.13-fold, and asymmetry was 2.06-fold. On the basis of the kinetic parameters, variations in intracellular glucose concentrations are not responsible for the range of glucose uptakes by bovine mammary glands observed in vivo. model; cow; mammary epithelial cell