Level of nutrient intake affects mammary gland gene expression profiles in preweaned Holstein heifers.

Bovine mammary parenchyma (PAR) and fat pad (MFP) development are responsive to preweaning level of nutrient intake. We studied transcriptome alterations in PAR and MFP from Holstein heifer calves (n=6/treatment) fed different nutrient intakes from birth to ca. 65 d age. Conventional nutrient intake received 441 g of dry matter (DM)/d of a control milk replacer (MR) [CON; 20% crude protein (CP), 20% fat, DM basis]. Calves in the accelerated nutrition groups received 951 g/d of high-protein/low-fat MR (HPLF; 28% CP, 20% fat, DM basis), 951 g/d of high-protein/high-fat MR (HPHF; 28% CP, 28% fat, DM basis), or 1,431 g/d of HPHF (HPHF+) MR. Out of 13,000 genes evaluated, over 1,500 differentially expressed genes (DEG) were affected (false discovery rate <0.10) by level of nutrient intake in PAR or MFP. Feeding HPLF versus CON resulted in the most dramatic changes in gene expression, with 278 and 588 DEG having ≥1.5-fold change in PAR and MFP. In PAR, the most-altered molecular functions were associated with metabolism of the cell (molecular transport and lipid metabolism) with most of the genes downregulated in HPLF versus CON. In MFP, DEG also were primarily associated with metabolism but changes also occurred in genes linked to cell morphology, cell-to-cell signaling, and immune response. Compared with CON, feeding HPHF or HPHF+ did not result in substantial additional effects on DEG beyond those observed with HPLF. The pentose phosphate, mitochondrial dysfunction, and ubiquinone biosynthesis pathways were among the most enriched due to HPLF versus CON in PAR and were inhibited, whereas glycosphingolipid biosynthesis, arachidonic acid metabolism, and eicosanoid synthesis pathways were among the most enriched due to HPLF versus CON in MFP and were inhibited. These responses suggest that, in PAR, doubling nutrient intake from standard feeding rates inhibited energy metabolism and activity of oxidative pathways that partly serve to protect cells against oxidative stress. The MFP in those heifers appeared to decrease production of lipid-derived metabolites that may play roles in signaling pathways within the adipocyte. Overall, results indicated that prepubertal/preweaned mammary transcriptome is responsive to long-term enhanced nutrient supply to achieve greater growth rates before weaning. The biological significance of these results to future milk production remains to be elucidated.

Effect of milk fraction on concentrations of cephapirin and desacetylcephapirin in bovine milk after intramammary infusion of cephapirin sodium.

Clinical mastitis in dairy cows is commonly treated with intramammary (IMM) antimicrobial agents. Pharmacokinetic data are used to design treatment regimens and determine withholding times. In some pharmacokinetic studies, investigators measure antimicrobial concentrations in foremilk, whereas in others, they use bucket milk or do not specify the milk fraction sampled. Our objective was to compare antimicrobial concentrations in foremilk, bucket milk, and strippings after IMM treatment of six healthy Holsteins. One mammary gland/cow was infused with 200 mg of cephapirin (CEPH) after each of the two milkings, using different milking frequencies and treatment intervals in a randomized crossover design. Treated glands were sampled at the first milking following each infusion. Antimicrobial concentrations in milk were measured using HPLC/MS/MS. CEPH concentration was higher in foremilk (geometric mean 44.2 microg/mL) than in bucket milk (15.7 microg/mL) or strippings (18.5 microg/mL), as it was true for desacetylcephapirin (DAC) (59.5, 23.0, and 30.2 microg/mL, respectively). This finding, which was based on milk samples collected at the first milking after IMM infusion, suggests that pharmacokinetic data based on drug concentrations in foremilk may be misleading. Strippings were more representative of bucket milk than foremilk. The relationship between milk fraction and antimicrobial concentration should be investigated for other IMM antimicrobial agents. Meanwhile, it is essential that pharmacokinetic and residue studies report the fraction of milk that was analyzed.

Review: Mammary gland development in swine: embryo to early lactation.

Milk production by the sow is a major factor limiting the growth and survival of her litter. Understanding the process of morphogenesis of the sow's mammary gland and the factors that regulate mammary development are important for designing successful management tools that may enhance milk production. Primordia of the mammary glands are first observable in the porcine embryo at approximately 23 days of gestation. The glands then progress through a series of morphologically distinct developmental stages such that, at birth, each mammary gland is composed of the teat, an organized fat pad and two separate lactiferous ducts each with a few ducts branching into the fat pad. The glands continue to grow slowly until about 90 days of age when the rate of growth increases significantly. The increased rate of mammary gland growth coincides with the appearance of large ovarian follicles and an increase in circulating estrogen. After puberty, the continued growth of the gland and elongation and branching of the duct system into the fat pad takes place in response to the elevated levels of estrogen occurring as part of the estrous cycles. After conception, parenchymal mass of each gland increases slowly during early pregnancy and then grows increasingly rapidly during the final trimester. This growth is in response to estrogen, progesterone, prolactin and relaxin. Lobuloalveolar development occurs primarily during late pregnancy. By parturition, the fat pad of the mammary gland has been replaced by colostrum-secreting epithelial cells that line the lumen of the alveoli, lobules and small ducts. All mammary glands develop during pregnancy, however, the extent of development is dependent on the location of the mammary gland on the sow's underline. The mammary glands undergo significant functional differentiation immediately before and after farrowing with the formation of colostrum and the transition through the stages of lactogenesis. Further growth of the glands during lactation is stimulated by milk removal. Individual glands may grow or transiently regress in response to the intensity of suckling during the initial days postpartum. Attempts to enhance milk production by manipulation of mammary development at stages before lactation generally have met with limited success. A more in depth understanding of the processes regulating porcine mammary gland morphogenesis at all stages of development is needed to make further progress.

Internal controls for quantitative polymerase chain reaction of swine mammary glands during pregnancy and lactation.

High-throughput microarray analysis is an efficient means of obtaining a genome-wide view of transcript profiles across physiological states. However, quantitative PCR (qPCR) remains the chosen method for high-precision mRNA abundance analysis. Essential for reliability of qPCR data is normalization using appropriate internal control genes (ICG), which is now, more than ever before, a fundamental step for accurate gene expression profiling. We mined mammary tissue microarray data on >13,000 genes at -34, -14, 0, 7, 14, 21, and 28 d relative to parturition in 27 crossbred primiparous gilts to identify suitable ICG. Initial analysis revealed TBK1, PCSK2, PTBP1, API5, VAPB, QTRT1, TRIM41, TMEM24, PPP2R5B, and AP1S1 as the most stable genes (sample/reference = 1 +/- 0.2). We also included 9 genes previously identified as ICG in bovine mammary tissue. Gene network analysis of the 19 genes identified AP1S1, API5, MTG1, VAPB, TRIM41, MRPL39, and RPS15A as having no known co-regulation. In addition, UXT and ACTB were added to this list, and mRNA abundance of these 9 genes was measured by qPCR. Expression of all 9 of these genes was decreased markedly during lactation. In a previous study with bovine mammary tissue, mRNA of stably expressed genes decreased during lactation due to a dilution effect brought about by large increases in expression of highly abundant genes. To verify this effect, highly abundant mammary genes such as CSN1S2, SCD, FABP3, and LTF were evaluated by qPCR. The tested ICG had a negative correlation with these genes, demonstrating a dilution effect in the porcine mammary tissue. Gene stability analysis identified API5, VABP, and MRPL39 as the most stable ICG in porcine mammary tissue and indicated that the use of those 3 genes was most appropriate for calculating a normalization factor. Overall, results underscore the importance of proper validation of internal controls for qPCR and highlight the limitations of using absence of time effects as the criteria for selection of appropriate ICG. Further, we showed that use of the same ICG from one organism might not be suitable for qPCR normalization in other species.

Effect of relaxin on mammary development in ovariectomized pregnant gilts.

The role of relaxin in mammary development was studied between days 80-110 of pregnancy in ovariectomized gilts given progesterone to maintain pregnancy. To obtain an objective measurement of lobulo-alveolar (parenchymal) composition, mammary glands were cut in cross-section through the teat, and the area of parenchymal tissue on the exposed face of the gland was determined. Ovariectomy on day 80 or 100 followed by progesterone replacement therapy resulted in a dramatic reduction in the rate of growth of mammary parenchymal cross-section area on days 100 and 110 of gestation, respectively, compared to that in controls. In contrast, progesterone plus relaxin therapy, with highly purified porcine relaxin, restored the mammary parenchymal cross-section area to control values in ovariectomized gilts. Morphometric analysis of mammary tissue on day 110 of pregnancy indicated that both the absence of relaxin after ovariectomy and replacement therapy with porcine relaxin in ovariectomized gilts had little if any effect on the percentages of the lumen, stroma, or epithelial that comprised the mammary parenchyma. It is concluded that relaxin has a stimulatory effect on the growth of mammary parenchymal tissue during late gestation in the pig.

Molecular cloning and nucleotide sequence of a bovine alpha-lactalbumin cDNA.

A cDNA clone for the bovine milk protein, alpha-lactalbumin (alpha LA), has been identified using a rat cDNA probe. The bovine cDNA clone is 703 nucleotides (nt) long, contains 8 nt of 5'-untranslated sequence and 269 nt of 3'-untranslated sequence. When compared with previously reported sequences, the bovine alpha LA mRNA sequence has 74% similarity with rat alpha LA mRNA, 79% similarity with human mRNA and 74% similarity with guinea pig mRNA.

Identification of surface proteins on bovine leukocytes by a biotin-avidin protein blotting technique.

A method has been developed which covalently attaches biotin to proteins on the outer surface of leukocytes. These proteins are separated by polyacrylamide gel electrophoresis and transferred to nitrocellulose by protein blotting. Labeled proteins are detected using an avidin-peroxidase conjugate and color indicator. The method has been used to identify surface proteins specific to either polymorphonuclear leukocytes or mononuclear leukocytes prepared from bovine peripheral blood. The method provides a highly sensitive, non-radioactive means of examining alterations of surface proteins on leukocytes under differing functional and physiological conditions. Cell viability is not altered by this labeling method and labeled cells can be used to examine functions of surface proteins.

In vitro inhibition of mammary cell growth by lactoferrin: a comparative study.

The effect of lactoferrin (Lf) on mammary epithelial cell growth in culture was tested in a comparative study of bovine and human Lf. Bovine Lf was inhibitory to growth of a bovine mammary epithelial cell line, both in the presence and absence of fetal bovine serum in the medium. The growth inhibition activity of bovine Lf was not affected by iron-saturation status of the protein. In contrast with bovine Lf, human Lf had minimal inhibitory activity on bovine cell growth in the presence of serum, and cell growth was stimulated by human Lf in the absence of serum. In the latter case, human Lf may have acted as an iron-transport protein for the cells. Bovine Lf and human Lf had no effect on growth of MCF-7 human breast tumor cells and only minimal inhibitory activity toward the MDA-MB 231 human breast tumor cell line. The effect of bovine Lf on bovine mammary epithelial cells could be prevented by immunoneutralization of the Lf. These results indicate that Lf can be inhibitory to growth of mammary epithelial cells in culture, but this response to specific for the species origin of the Lf and of the mammary cell.

Assays and activities of glycosidic enzymes in bovine peripheral blood leukocytes.

Methods are described for the quantitative measurement of N-acetyl-beta-D-glucosaminidase, alpha-mannosidase and beta-glucuronidase in peripheral blood leukocytes of the bovine. Enzyme kinetics and stability were determined. Activities of the glycosidases in polymorphonuclear leukocytes and mononuclear leukocytes were determined using the optimized assays. Polymorphonuclear leukocytes had greater activities of N-acetyl-beta-D-glucosaminidase and alpha-mannosidase, and similar levels of beta-glucuronidase, when compared to mononuclear leukocytes.

Sequence and expression of the FcRn in the porcine mammary gland.

Transport of immunoglobulin G across epithelial cell barriers is thought to occur by a system involving the Fcgamma receptor called the neonatal Fc receptor (FcRn). The FcRn may also play a role in IgG transport in the mammary gland. To determine the presence of FcRn in the porcine mammary gland, biopsies were taken from glands 3 days prepartum and on the day of farrowing. The full length porcine FcRn cDNA sequence was obtained by rapid amplification of cDNA ends and determined to be 1557 base pairs in length that codes for a 359 amino acid peptide. Expression of FcRn mRNA in the porcine mammary gland was determined by reverse transcriptase-PCR and revealed that the mRNA is present prepartum and on the day of farrowing. These results indicate that the FcRn is expressed in porcine mammary tissue and are consistent with the hypothesis that FcRn may have a role in mammary gland immunoglobulin transport during colostrogenesis.

Lysosomal enzymes in bovine mammary leukocytes during the nonlactating period.

Leukocytes from mammary secretions in dairy cows were collected during the nonlactating and postpartum periods. Differential cell counts, viability and activity of peroxidase, N-acetyl-beta-D-glucosaminidase (NAGase, beta-glucuronidase and alpha-mannosidase in cells were determined. Cell viability (trypan blue exclusion) was 75-80% during most of the nonlactating period, but declined to 45-50% by parturition. Polymorphonuclear neutrophils (PMN) predominated during the first week of involution, after which macrophages were the predominant cell type. Peroxidase activity in leukocytes from mammary secretions was high in early involution, probably reflecting the predominant peroxidase-containing PMN. Peroxidase activity declined through the remaining nonlactating and postpartum periods. The activity of NAGase was variable in early involution, then increased to a peak during the mid-nonlactating period, before declining prior to parturition. Activity of beta-glucuronidase generally was unchanged during the nonlactating period, although NAGase and beta-glucuronidase activities were significantly and positively correlated throughout the period studied. Activity of alpha-mannosidase changed in a manner similar to peroxidase activity.

Extracellular matrix and mouse mammary cell function: comparison of substrata in culture.

Cultured mammary cells depend on interaction with a substratum for functional differentiation, even in the presence of lactogenic hormones. Protein synthesis and secretion by mouse mammary epithelial cells on floating collagen gels and (EHS) matrix were compared. Cells were prepared by collagenase digestion of tissue from mid-pregnant mice. Protein synthesis was consistently greater in cells attached to EHS matrix, and was associated with proportionately higher rates of protein secretion into culture medium. Cells on EHS secreted protein into a luminal space formed within multicellular alveolus-like structures. Luminal secreted protein, extracted by EGTA treatment of cells in situ, constituted up to 40% of total secreted radiolabeled protein for cells on EHS matrix. The EGTA extract contained a higher proportion of casein and lactoferrin, whereas transferrin was predominantly in the medium. This indicated that cells on EHS matrix had become polarized and were secreting proteins vectorially. In contrast, EGTA treatment of cells on floating collagen gels released virtually no radiolabeled protein, showing that mammosphere formation was a property of cells on EHS. These biochemical observations were supported by ultrastructural evidence. In EHS cultures, the proportion of secreted protein in the luminal fraction, but not the distribution of secreted proteins, changed with time. This suggests that there may be leakage out of the lumen, or intraluminal degradation of protein after secretion. Nevertheless, the results suggest that cellular organization into mammospheres on EHS matrix promotes synthetic and secretory activity. This system provides a useful model for investigation of the regulation of milk secretion.

Extracellular matrix and mouse mammary cell function: Comparison of substrata in culture.

Cultured mammary cells depend on interaction with a substratum for functional differentiation, even in the presence of lactogenic hormones. Protein synthesis and secretion by mouse mammary epithelial cells on floating collagen gels and (EHS) matrix were compared. Cells were prepared by collagenase digestion of tissue from mid-pregnant mice. Protein synthesis was consistently greater in cells attached to EHS matrix, and was associated with proportionately higher rates of protein secretion into culture medium. Cells on EHS secreted protein into a luminal space formed within multicellular alveoluslike structures. Luminal secreted protein, extracted by EGTA treatment of cells in situ, constituted up to 40% of total secreted radiolabeled protein for cells on EHS matrix. The EGTA extract contained a higher proportion of casein and lactoferrin, whereas transferrin was predominately in the medium. This indicated that cells on EHS matrix had become polarized and were secreting proteins vectorially. In contrast, EGTA treatment of cells on floating collagen gels released virtually no radiolabeled protein, showing that mammosphere formation was a property of cells on EHS. These biochemical observations were supported by ultrastructural evidence. In EHS cultures, the proportion of secreted protein in the luminal fraction, but not the distribution of secreted proteins, changed with time. This suggests that there may be leakage out of the lumen, or intraluminal degradation of protein after secretion. Nevertheless, the results suggest that cellular organization into mammospheres on EHS matrix promotes synthetic and secretory activity. This system provides a useful model for investigation of the regulation of milk secretion.

Cellular uptake of taurine by lactating porcine mammary tissue.

Milk taurine plays a critical role in neonatal development. Taurine uptake in lactating sow mammary tissue has not been characterized previously. The kinetic properties, ion dependence and substrate specificity of taurine uptake were characterized in mammary tissue collected from lactating sows at slaughter. Tissue explants were incubated in an isosmotic physiologic buffer with [3H]taurine tracer to measure taurine uptake. Taurine uptake was dependent upon the presence of extracellular sodium and chloride ions, which is consistent with the co-transport of sodium and chloride with taurine. Uptake was not dependent upon ion exchange mechanisms or upon furosemide-sensitive ion co-transport. Taurine uptake was saturable and exhibited an apparent Km of 20 microM and a V(max) of 386 micromol/kg cell water/30 min. Substrate specificity studies indicated a strong interaction of beta-amino acids with the taurine transport system. Taurine transport in lactating sow mammary tissue is therefore a high affinity, sodium-dependent mechanism specific for beta-amino acids, and is analogous to sodium-dependent taurine uptake in other tissues. The high affinity and high specificity of the taurine uptake system allows for concentration of taurine within the mammary cell and is ultimately responsible for provision of taurine required for neonatal development.

The effect of immunization against somatostatin on growth and concentration of somatotropin in plasma of Holstein calves.

Holstein calves were used to investigate the effects of immunization procedures against somatostatin (SRIF) on growth and concentrations of somatotropin in plasma. In Trial 1, eight heifers 37 weeks of age were inoculated with cyclic-SRIF conjugated to human alpha-globulin. Final body weight, average daily gain, and measurements of body size were not significantly different between control and SRIF-immunized calves. Apparent total tract nutrient digestibilities and efficiency of feed utilization also were not significantly different between treatments. Plasma concentrations of somatotropin were increased and plasma concentrations of urea nitrogen were decreased in calves immunized against SRIF compared to controls, but these mean differences were not significant. In Trial 2, eleven bull calves seven weeks of age were inoculated with cyclic-SRIF conjugated to keyhole limpet hemocyanin. Calves immunized against SRIF had larger average daily gains (P less than .06) than did control calves. Body size, efficiency of feed utilization, and concentrations of somatotropin in plasma were not significantly different for SRIF immunized calves and control calves. Urea nitrogen in plasma was lower (P less than .04) for calves immunized against somatostatin than for control calves. Data indicate that Holstein calves can produce auto-antibodies against SRIF; however, additional research will be required before such immunization techniques can be effectively used to improve weight gains in cattle.

Mammary gland growth as influenced by litter size in lactating sows: impact on lysine requirement.

Twenty-eight primiparous sows were used to determine the effect of litter size on the growth of mammary glands and nursing pigs during lactation. Litter size was set to 6, 7, 8, 9, 10, 11, or 12 pigs by cross-fostering immediately after birth. Four sows were allotted to each litter-size group. Sows were allowed to consume a daily maximum of 13.6 Mcal ME and 46.3 g of lysine during lactation. Sows were slaughtered on d 21 (20.6+/-1.1) of lactation. Mammary glands were collected at slaughter and trimmed of skin and the extraneous fat pad. Each gland was separated, weighed, and ground for chemical analysis. Dry matter, dry fat-free tissue (DFFT), crude protein, ash, and DNA contents were measured. Only glands known to have been nursed were included in the data set. Wet and dry weights and the amounts of DFFT, protein, DNA, ash, and fat in individual nursed mammary glands linearly decreased (P<.05) as litter size increased. Percentages of DFFT, protein, and DNA were quadratically affected (P<.05) by litter size on d 21 of lactation. Total mammary wet and dry weights and total DFFT, protein, DNA, fat, and ash amount of all nursed mammary glands of each sow were increased as litter size increased (P<.05). Changing litter size from 6 to 12 pigs resulted in 2,098, 432, 253, 227, 4.4, 178, and 20 g increases in the amounts of total mammary wet weight, dry weight, DFFT, protein, DNA, fat, and ash, respectively, on d 21 of lactation. Litter weight gain was 18.1 kg greater in sows with 12 pigs than in sows with 6 pigs. Sows with a larger litter size had a greater increase in total mass of mammary gland tissue and litter weight but had lower growth of individual nursed mammary glands and individual pigs than sows with the smaller litter size. The need for nutrients to support additional mammary gland and litter growth as litter size increases should be considered when estimating nutrient requirements for lactating sows. Sows need an additional .96 g lysine per day to account for mammary gland growth for each pig added to a litter.

The regression of unsuckled mammary glands during lactation in sows: the influence of lactation stage, dietary nutrients, and litter size.

During lactation in the sow, mammary glands that are not regularly suckled undergo regression. This study characterizes the regression of unsuckled mammary glands and how that regression is affected by dietary nutrients and litter size. Sixty-nine primiparous sows were fed one of four diets containing combinations of two protein levels (32 or 65 g lysine/d) and two energy levels (12 or 17.5 Mcal ME/d) during lactation. Litter size was adjusted to 10. Sows were killed on d 0, 5, 10, 14, 21, or 28 of lactation. In another experiment, twenty-eight primiparous sows were allotted to have different litter sizes and were killed on d 21 of lactation. The day before slaughter, teat order of each litter was observed. After death, mammary glands were removed and dissected. Skin and extraneous fat pads were removed from the mammary glands and individual glands were separated. Each gland was weighed, cut in half to measure cross-sectional area, and ground for chemical analysis. The amounts of dry tissue, protein, fat, ash, and DNA were measured. Only glands observed to be unsuckled were included in the results. Regression of unsuckled mammary glands occurred rapidly during the first 7 to 10 d of lactation, as indicated by a decline in wet weight, dry weight, protein, fat, DNA, and cross-sectional area. The rate of regression was slowed after the early lactation period. The rate of regression of unsuckled glands was affected by dietary nutrient levels. Dietary energy level affected (P < 0.05) the decline in wet and dry weights, protein, fat and DNA content, and cross-sectional area, whereas dietary protein level affected (P < 0.05) the decline in dry weight and fat content. At d 5 of lactation, the wet weight of unsuckled mammary glands in sows fed the high-energy high-protein diet was 91% greater (P < 0.05) than in sows fed the low-energy low-protein diet. Effects of litter size on size and composition of unsuckled glands were not significant by d 21 of lactation. Unsuckled mammary glands regress rapidly during early lactation, and the rate of regression is affected by dietary nutrient intake.

Lysine uptake by mammary gland tissue from lactating sows.

Kinetic properties and substrate specificity of the lysine transport system in porcine mammary gland were studied using mammary tissue explants from nine lactating sows. Sodium dependence of lysine uptake was determined by replacing sodium in the medium with choline. Kinetic parameters of lysine uptake were determined using lysine concentrations from 5 microM to 5.12 mM. Competition of lysine uptake by other amino acids was determined using the cationic amino acids, arginine and ornithine, and using other essential amino acids. Transport of lysine was time-dependent and was unaffected by replacing sodium with choline. Lysine uptake occurred by a transport mechanism with a Km of approximately 1.4 mM and a Vmax of 7.9 mmol x kg cell water(-1) x 30 min(-1). Lysine uptake was inhibited by arginine and ornithine and by high concentrations of L-alanine, L-methionine, L-leucine, cycloleucine, and D-lysine, but not by 2-(methylamino)-isobutyric acid. This transport mechanism is the primary system responsible for uptake of cationic amino acids in lactating sow mammary tissue. The relatively high Km, compared with physiological blood concentrations of lysine, indicates that the kinetic properties of the lysine transport system should not be limiting to milk protein synthesis. Transmembrane transport of lysine by lactating sow mammary tissue should be a direct function of plasma concentrations. However, interactions of other amino acids with the uptake system may affect lysine uptake.

Cellular uptake of valine by lactating porcine mammary tissue.

The cellular uptake of branched-chain amino acids in mammary tissue is important for understanding their role in milk synthesis in the sow. This study characterized the kinetic properties and substrate specificity of the valine uptake system in the porcine mammary gland. Mammary tissue was collected from lactating sows at slaughter and tissue explants were incubated in media containing isosmotic salt and amino acids of interest, plus [3H]valine tracer. Valine uptake was time-dependent and was dependent on the presence of sodium, as indicated by a reduction in uptake when sodium in the medium was replaced by choline. The valine transport system in porcine mammary tissue had a Km of 0.64 mM, a Vmax of 1.84 mmol-kg cell water(-1) 30 min(-l), and a Kd (diffusion constant) of 1.16 L x kg cell water(-1) x 30 min(-1). Valine uptake was inhibited by leucine and alpha-aminoisobutyric acid and by high concentrations of L-alanine, L-lysine, cycloleucine, L-glutamine, and L-methionine, but not by 2-(methyl-amino)-isobutyric acid. This transport system is the primary system responsible for uptake of valine, and probably other branched-chain amino acids, in lactating sow mammary tissue. Physiological concentrations of valine in the blood are below the Km of the specific valine transport system and well below the diffusion uptake capabilities. The kinetic parameters of this valine transport system should not be limiting to valine uptake for milk protein synthesis. However, competition of valine uptake with branched-chain amino acids, as well as with other amino acids, may affect valine uptake in lactating tissue.

Growth of nursing pigs related to the characteristics of nursed mammary glands.

The purpose of this study was to determine growth performance of nursing pigs in relationship to teat order and to observe teat preference by pigs. In the first experiment, litter size of 13 primiparous sows was adjusted to 9 (8.7 +/- 1.5) pigs and teat order of each litter was observed on the day before slaughter. Another group of eight sows was killed on d 0 (within 12 h after farrowing). In the second experiment, litter size was adjusted to 9 (8.9 +/- 1.4) pigs for 20 primiparous sows and teat order for each litter was observed 1 d before slaughter. The weights of sows and individual pigs were recorded at farrowing, weekly, and on the day before slaughter. Mammary glands were collected at slaughter on d 21 of lactation and trimmed of skin and the extraneous fat pad. Individual glands were separated, weighed, and ground for measurement of dry matter, dry fat-free tissue, protein, fat, ash, and DNA contents. Middle mammary glands had the greatest wet weight among glands obtained within 12 h after weaning (P < .05). For sows completing the 21 d lactation, only glands known to have been nursed were included in the data sets. Greater than 60% of the first four pairs of mammary glands were nursed, and less than 40% of the seventh and eighth glands were nursed by pigs during lactation. Pigs that nursed the first five pairs of anterior glands gained faster than pigs nursing the remaining glands. The first five pairs of anterior glands had greater wet and dry weights, and greater protein and DNA contents compared with the remaining glands. Pigs that nursed heavier glands gained weight faster (r = .68, P = .0001), and those heavier glands contained greater amounts of protein (r = .98, P = .0001) and DNA (r = .66, P = .0001). Variation in weight gain of pigs nursing the anterior and middle glands was not statistically significant. The functional superiority of anterior and middle glands was positively correlated with body weight gain of nursing pigs.