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1.
Changes in tissue composition associated with mammary gland growth during lactation in sows. 总被引：2，自引：0，他引：2
Twenty-four primiparous sows were used to determine the extent of mammary gland growth during lactation. Litter size was set to nine or 10 pigs immediately after birth. Sows were slaughtered in groups representing d 0 (within 12 h after farrowing), 5, 10, 14, 21, and 28 of lactation. Sows were provided 17.5 Mcal ME and 65 g of lysine per day during lactation. Mammary glands were collected at slaughter and trimmed of skin and extraneous fat pad. Each gland was weighed, cut in half to measure cross-sectional area, and ground for chemical analysis. Dry matter content, dry fat-free tissue (DFFT) content, protein content, amino acids composition, ash content, and DNA content were measured. Only glands known to have been suckled were included in these data. Wet and dry tissue weight; cross-sectional area; and the amount of DFFT, tissue protein, and amino acids in each suckled mammary gland increased (P < .05) during lactation to a peak on d 21. Fat percentage of each suckled gland declined (P < .05) and the percentage of protein and DFFT increased (P < .05) as lactation progressed. These results suggest that hypertrophy occurred in the tissue during lactation. There was a linear increase in the amount and percentage of DNA during lactation (P < .05), suggesting hyperplasia of the mammary tissue. Mammary tissue growth continues in suckled glands during lactation in sows, with gland wet weight increased by 55% and total gland DNA increased by 100% between d 5 and 21 of lactation. 相似文献
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Sixty-one primiparous sows were used to determine the response of mammary gland growth to different energy and protein intakes during lactation. After birth, litter size was set to 9 or 10 pigs. Sows were slaughtered at selected times up to 30 d of lactation. Individual sows were fed one of four diets that were combinations of different amounts of energy and protein (3.0 Mcal ME and 8.0 g lysine/kg diet; 3.0 Mcal ME and 16.2 g lysine/kg diet; 3.5 Mcal ME and 6.4 g lysine/kg diet; or 3.5 Mcal ME and 13.0 g lysine/kg diet). Mammary glands were collected at slaughter and trimmed of skin and the extraneous fat pad. Each gland was weighed, cut in half to measure cross-sectional area, ground, and stored at -20 degrees C for chemical analysis. Frozen, ground tissue was used to determine dry matter, dry fat-free tissue (DFFT), total tissue protein, ash, and DNA content. Only glands known to have been suckled were included in this data set. Response surface regression was used for statistical analysis. The percentage of protein, fat, ash, and DNA in each suckled mammary gland was affected only by total energy intake (P<.05). The percentage of dry tissue and fat decreased as the total energy consumed during lactation increased, whereas the percentage of protein and DFFT increased as total energy intake increased. There were quadratic effects (P<.05) of both total energy and protein intake on wet weight, dry weight, protein amount, DFFT amount, and DNA amount of each suckled mammary gland during lactation. This study shows that mammary gland growth is affected by nutrient intake during lactation. The weight of suckled mammary glands and the amount of mammary tissue protein, DFFT, and total DNA were maximal on d 27.5 of lactation when sows had consumed an average of 16.9 Mcal of ME and 55 g of lysine per day during lactation. Provision of adequate amounts of nutrients to sows during lactation is important for achieving maximal growth of mammary glands and maximal milk production. 相似文献
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Mammary gland involution was morphologically evaluated 21 or 42 d after prevention of suckling of one udder half in 10 crossbred beef cows. Parenchymal tissue was taken from lower, middle and upper zones of each quarter from the teat to the ventral body wall. Udder halves, trimmed of extraparenchymal tissue, were weighed and used for DNA determination. DNA content was reduced 50 and 64% after 21 and 42 d of involution. However, the percentage of tissue occupied by epithelium was similar in suckled and nonsuckled glands. Well-differentiated cells, typical of suckled glands, were rarely observed in nonsuckled glands. Alveolar structure was evident in nonsuckled glands, but the number of cells per alveolar cross-section was reduced (30 vs 22). Unlike in suckled glands, there was a marked gradation in classification of epithelial cells across zones in involuting glands. For example, nearly 10% of the epithelium was well-differentiated in the tissue from the upper zone, whereas no well-differentiated cells were found in the lower zones. Regression of the mammary parenchyma does not occur uniformly through the udder, so use of single biopsy to study involution should be avoided. Presence of alveoli after 42 d indicates that redevelopment of the udder with subsequent lactations is less dramatic than suggested from study of other species. 相似文献
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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. 相似文献
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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. 相似文献
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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. 相似文献
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Kuller WI Soede NM van Beers-Schreurs HM Langendijk P Taverne MA Verheijden JH Kemp B 《Journal of animal science》2004,82(2):405-413
An experiment was conducted to study effects of intermittent suckling on creep feed intake and weight gain of litters. Loss of weight and backfat during lactation, as well as reproductive performance, were also measured. Batches of multiparous sows (Parity 1 to 12, 4.1 on average) were either suckled intermittently (IS, eight batches; n = 50) or continuously (control, eight batches; n = 62). Litters were weaned at 27 +/- 2 d of age, on average. Litter size (11.1 +/- 0.2 piglets, on average) was standardized within a batch within 3 d of birth. All litters had free access to creep feed and water from 1 wk of age onward. In the IS group, litters were separated from the sow for a period of 12 h/d (0930 to 2130), starting 11 d before weaning. Rectal ultrasonography was applied at d 3 after weaning to check the ovaries for follicle development or presence of corpora lutea. Creep feed intake by the litters during lactation was higher in IS litters than in control litters (686 +/- 57 vs. 314 +/- 42 g/piglet, P < 0.01). The distribution of creep feed intake shifted from a skewed one, with a majority of litters consuming less than 250 g/piglet in control litters, to a normal distribution, with an average creep feed intake of 500 to 750 g/piglet in IS litters. During the 7 d after weaning, creep feed intake in IS litters was also higher (281 +/- 15 vs. 204 +/- 9 g-piglet(-1) x d(-1), P < 0.01). The ADG of piglets during lactation was negatively affected by IS, resulting in lower weight at weaning (7,229 +/- 140 vs. 7,893 +/- 145 g/piglet, P < 0.05). During the 7 d after weaning, however, ADG was higher in IS litters (255 +/- 10 vs. 177 +/- 8 g-piglet-1 x d(-1), P < 0.01), and 7 d after weaning, the weights of the litters were similar (9,011 +/- 167 vs. 9,132 +/- 164 g/ piglet, P = 0.81). The IS litters that consumed little or no feed during lactation had an ADG after lactation that was higher than in control litters, with comparable creep feed intake during lactation: 204 vs. 136 g/d. Body weight loss by the sows during lactation was lower in IS sows (-10 +/- 2 vs. -16 +/- 1 kg, P < 0.05). A higher percentage of IS sows ovulated during lactation (22 vs. 3%, P < 0.01), and weaning-to-ovulation interval (excluding sows with lactational ovulation) was shorter in IS sows (4.7 +/- 0.2 vs. 5.3 +/- 0.2 d, P < 0.05). We conclude that IS increased creep feed intake during lactation, and that IS increased ADG after weaning, despite lower weaning weights. Ovulation during lactation was induced in 22% of the IS sows. 相似文献
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U Magnusson 《American journal of veterinary research》1999,60(5):546-548
OBJECTIVE: To determine whether there is variation attributable to reproductive stage in lymphocyte subsets and major histocompatibility complex (MHC) class II expressing cells in mammary glands of sows. ANIMALS: 8 healthy primiparous crossbred sows that had been nursing piglets for 30 to 35 days. PROCEDURE: Needle biopsy of the mammary gland was performed after parturition, at midlactation, and after weaning. Various lymphocyte subsets and MHC class II expressing cells were detected immunohistochemically, using monoclonal antibodies. RESULTS: The number of CD8+ cells was significantly lower after parturition than after weaning but not significantly lower than at midlactation. The number of IgA-bearing cells was lower after parturition and after weaning than at midlactation. There were more B cells at midlactation than after weaning. There was no change over time in the number of CD4+ cells or MHC class II expressing cells. Immunohistochemically positive cells were detected only in interalveolar tissue. CONCLUSIONS AND CLINICAL RELEVANCE: Certain lymphocyte subsets in mammary glands of sows are affected by reproductive stage. The data do not support the hypothesis that development of postparturient coliform mastitis may be the result of impaired mammary immune defenses at parturition. 相似文献
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Suckling both, or only one contralateral mammary gland during 15 days postpartum was utilized to study lactogenic hormone binding to mammary microsomal membranes and quantitative mammary morphology in ewes. Binding of radiolabeled human growth hormone was specific for lactogenic hormones. Non-radiolabeled human growth hormone, ovine and bovine prolactin and human placental lactogen effectively competed with radiolabeled human growth hormone for binding sites but ovine and bovine growth hormone were completely ineffective. Specific binding of radiolabeled human growth hormone to 600 μg of membrane protein averaged 23 ± 3% in all lactating glands. Neither days postpartum nor treatment of contralateral mammary glands substantially altered hormone binding in lactating glands. Specific human growth hormone binding (6 ± 0.5%) in non-suckled glands (15 days postpartum both udder halves) was significantly lower (P<0.01) than in lactating tissue but only a moderate and variable reduction in specific binding was measured in membranes from glands non-suckled for 15 days but contralateral to a suckled gland (14 ± 4%). Specific binding was approximately doubled in assays with 600 compared with 300 μg of membrane protein and the pattern of binding among variously suckled glands was not changed by treatment of membranes with 4 M MgCl2 prior to assay. Most secretory cells from all lactating glands had rounded, basally displaced nuclei, apical fat globules, secretory vesicles and abundant densely stained basal cytoplasm (ergastoplasm). Alveolar lumenal area was maximal (50% of tissue area) and stromal tissue area was minimal. After 15 days of non-suckling (both udder halves) mammary cells were engorged with lipid, ergastoplasm was reduced and nuclei were irregularly shaped and randomly displaced compared with lactating tissue. In addition, lumenal area was reduced and stromal tissue more evident. Lack of suckling for 5 days had little apparent effect on mammary cytology. Like lactogenic hormone binding, mammary tissue morphology was only moderately altered by 15 days of non-suckling when the remaining gland was suckled. RNA concentration was lowest (2.1 ± 0.3 mg/g) in mammary tissue from ewes in which neither gland was suckled for 15 days postpartum but non-suckling interval had no significant effect when contralateral glands were suckled. DNA concentration was not significantly influenced by suckling treatments. Relative lactogenic hormone binding closely corresponded to changes in cytological and biochemical indices of secretory cell function. 相似文献
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The aim of this study was to determine the density of MHC class II, CD4 and CD8 positive cells in mammary glands of sows around parturition, and whether the densities were altered following intramammary inoculation with Escherichia coli prior to parturition. Also, animals developing clinical disease after inoculation were compared with animals not developing clinical disease. Fourteen cross-bred primiparous sows were subject to intramammary inoculation with E. coli bacteria 24h before estimated parturition. Mammary gland biopsies were collected and clinical observations were made. Four sows were categorised as clinically ill based on general condition, body temperature and gross mammary affection. There were no changes in density of MHC class II, CD4 and CD8 positive cells in non-inoculated glands around parturition, while significant changes in densities were shown in inoculated glands. Here, the density of MHC class II, CD4 and CD8 positive cells reached a peak at 72 h post-inoculation (p<0.01). In sows developing clinical disease, there was a tendency to an over all lower density (p=0.07) of MHC class II positive cells in inoculated glands compared with sows not developing clinical disease. When comparing the categories with respect to the density of CD4 and CD8 positive cells, the sows developing clinical disease showed a higher density (p=0.03) of CD4 and CD8 positive cells in inoculated glands than sows not developing disease. No differences were shown between categories in non-inoculated glands. It is concluded that the density of MHC class II, CD4 and CD8 positive cells seems to be unaltered around parturition. However, there is a rapid increase in density of these cells following intramammary inoculation with E. coli. Also, the data suggest that there is a difference between sows developing and sows not developing clinical disease after inoculation with respect to the increase in density of MHC class II, CD4 and CD8 positive cells in the mammary gland. 相似文献
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Mammary secretions from 12 Holstein dairy cows were collected to evaluate growth inhibition of Escherichia coli and Klebsiella pneumoniae during involution and during physiologic transitions of the mammary gland. Mammary secretions obtained during late lactation poorly inhibited growth of E coli and K pneumoniae. However, as involution progressed, mammary secretions increasingly inhibited growth of both coliform mastitis pathogens. Greatest inhibition of E coli and K pneumoniae growth was observed when mammary glands were fully involuted. Growth inhibition remained high until 7 days before parturition, and then it decreased significantly (P less than 0.05) to that observed during late lactation. Inhibition of coliform mastitis pathogen growth was associated with high concentrations of lactoferrin and immunoglobulin G, decreased citrate concentration, and a low citrate to lactoferrin molar ratio. These data suggested that differences in susceptibility or resistance to new intramammary infection with coliform mastitis pathogens during the nonlactating period may be attributable, in part, to marked changes in mammary secretion composition that develop during physiologic transitions of the mammary gland. Resistance of the fully involuted mammary gland to coliform infection may be associated with high concentrations of natural protective factors. 相似文献
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Third-parity sows received s.c. injections of sterile water (CTL, n = 12) or 15 mg of recombinant porcine prolactin (pPRL, n = 12) at 0730, 1530, and 2330 from d 2 to 23 of lactation. Litters were standardized to 11 or 12 pigs and were weighed weekly until weaning (d 24). On d 22 of lactation, milk production was estimated, and a milk sample was obtained the next day. Jugular blood samples were collected from sows on d 2, 7, 14, and 21 of lactation. Sows were slaughtered and mammary glands collected at d 24. Injections of pPRL doubled the serum concentrations of prolactin (P < .001) on d 7, 14, and 21 of lactation and decreased IGF-I concentrations on d 14 (P = .07) and 21 (P < .01). Weight, backfat, and milk yield of sows and mean pig weights were not affected by pPRL (P > . 1), yet the mean duration of intervals between nursings was reduced by 4.2 min (P = .06) in pPRL litters (45.9 vs 41.7 min). Dry matter and fat percentages in milk were lower in pPRL sows (P < .01). Weights of parenchymal and extraparenchymal tissues were not altered by pPRL treatment (P > .1). Number of prolactin receptors in parenchymal tissue as well as receptor affinity were similar in both groups (P > .1). Results indicate that virtually all prolactin receptors were saturated in CTL sows. This is probably the reason why additional exogenous prolactin had negligible effects. 相似文献
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Nutrient mobilization from body tissues as influenced by litter size in lactating sows 总被引：1，自引：0，他引：1
Twenty-eight primiparous sows were used to study nutrient mobilization among body tissues as influenced by litter size in lactating sows. Litter size was set to 6, 7, 8, 9, 10, 11, or 12 pigs within 48 h postpartum by cross-fostering. Four sows were allotted to each litter size group. Sows had 11.5 +/- 1.3 Mcal of ME and 39.3 +/- 4.4 g of lysine per day and were killed on d 20.6 +/- 1.1 of lactation. Liver, gastrointestinal tract (GIT, composed of the empty stomach, empty small and large intestines, cecum and rectum), reproductive tract, and other organs (excluding liver, GIT, reproductive tract, and mammary gland) were separated from the carcass. Gastrointestinal tracts were manually stripped of contents and flushed with water to remove digesta. Hot carcasses were split longitudinally at the midline after removing mammary glands and internal organs. Individual organs and carcasses were weighed then ground for chemical analysis. Dry matter, crude protein, fat, and ash contents were measured. As litter size increased, protein mobilization was linearly increased (P < 0.05) in carcass, GIT, and reproductive tract. Protein mobilization in liver was quadratically affected by litter size (P < 0.05). Fat mobilization was not affected by litter size. The amount of protein mobilized from carcass, GIT, liver, and reproductive tract in sows increased by 641 g as litter size increased by one pig from 6 to 12 pigs after a 21-d lactation. Carcass contributed the largest amount of protein (600 g for an additional pig) among body tissues, whereas the reproductive tract contributed the highest percentage (26%) of its protein among body tissues. Protein efficiency from milk to litter weight gain was 72% as litter size increased during a 21-d lactation. In feeding lactating sows, effect of litter size on nutrient mobilization from various tissues should be considered for minimizing the excess tissue mobilization during lactation. 相似文献
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Mammary gland is a kind of exocrine glands and a dynamic organ.Structure of mammary gland changes throughout the female reproductive cycles.Development of mammary gland occurs in the defined stages that are closely linted to sexual development and reproduction, namely embryonic, prepubertal and pubertal stages, pregnancy, lactation and involution.In this review, the roles of epithelial-stromal (mesenchymal) interactions in embryonic and postnatal mammary development were summarized, elaborated the regulations of different kinds of hormones on the mammary development after pubertal stage, and described the discovery of mammary stem cell populations (MaSC) and selection markers of mice and human.The objective of this work was to learn the basic processes and potential regulation mechanisms of the mammary development to provide some help for the researchers in the field of mammary gland. 相似文献
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Mammary uptake of nutrients is dependent on their availability in the circulation but the role of hormones in that process is not known. Arteriovenous differences (AVD) of glucose and key hormones across the mammary glands were therefore determined in sows fed varying levels of protein. Sixteen lactating sows (four/dietary treatment) were fed a 7.8, 13.0, 18.2 or 23.5% crude protein (CP) isocaloric diet throughout lactation and their litters were standardized to 11 pigs within 48 h of birth. The anterior main mammary vein and a carotid artery were cannulated on day 4+/-1 of lactation and blood samples were collected every 30 min over 6h on days 10, 14, 18 and 22 of lactation to measure glucose, insulin, IGF-I, and prolactin (PRL) concentrations. Amino acid data from these sows were previously published and used here to determine residual correlations. Dietary treatments had no effect on any of the insulin or PRL variables measured (P>0.1) and, on day 18 only, IGF-I AVD was greater (P=0.05) for sows on the 23.5% compared to the 18.2% diet. On days 18 and 22, sows fed the 13% CP diet had greater arterial, venous and AVD glucose concentrations than sows fed other diets (P<0.05). Total arterial amino acid concentrations were correlated to arterial insulin (P<0.001) and PRL (P<0.05) concentrations, but not to those of IGF-I (P>0.1). Mammary AVD for total (P<0.001) and essential amino acids (P<0.05) were correlated to arterial concentrations of insulin, but not to those of IGF-I (P>0.1) or PRL (P>0.1). Mammary AVD of both total (P<0.01) and essential (P<0.05) amino acids were also correlated to mammary PRL AVD. In conclusion, dietary protein level did not affect mammary AVD and circulating lactogenic hormone concentrations. Yet, amino acid utilization by the sow mammary gland seems to be regulated via both circulating insulin concentrations and PRL binding to and uptake by porcine mammary cells. 相似文献
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Two replicates of three multiparous crossbred Large White x Landrace lactating sows were used to develop a technique for the continuous direct measurement of the blood flow through the mammary gland using transit time ultrasound. Four to six days after farrowing, an ultrasonic transit time flow probe was implanted around the right external pudic artery in order to measure the short-term variations of mammary blood flow through this vessel in response to postural change (standing vs lying), meal distribution, hand-milking, and weaning. After surgery, all sows were fed 3.8 kg/d of a lactation diet and housed either at 20 or 28 degrees C. The implantation of the ultrasonic blood flow probe was successful in all six operated sows. Postmortem examination did not indicate the presence of infection, any collateral bypassing the flow probe, or a reduction of artery diameter. The right pudic artery mammary blood flow (PMBF) was measured for 8.5 h over two periods of three days (d 11 to d 13 and d 18 to d 20 of lactation). The PMBF averaged 910 +/- 238 mL/min but was variable within 1 d. Compared with the lying position, PMBF was decreased (- 6%, P < 0.05) when sows were standing. Between 0 to 15 and 16 to 30 min after oxytocin injection (t = 0) and hand-milking, PMBF remained constant (P = 0.05; 801 vs 767 mL/ min) and increased (P = 0.02), respectively, in comparison with the mean calculated over the preceding 30-min period (982 vs 784 mL/min). The PMBF increased (P < 0.05) after meal distribution and reached a peak 65 min later (i.e., 980 mL/min). The PMBF decreased regularly after separation of piglets at weaning; at 8 and 16 h after weaning, PMBF was 60 and 40% of the value recorded before weaning, respectively. Assuming that PMBF drains one-quarter of the whole mammary gland, it can be calculated that blood flow through the entire mammary gland averages 3.6 L/min and that about 470 L of blood are required to produce 1 kg of milk. The proposed methodology constitutes a new technique to measure direct mammary blood flow and its short-term factors of variation. 相似文献