Quantitative estimates of mammary growth during various physiological states: a review

Carryover effects of maternal late-gestation heat stress on granddaughters' growth and mammary gland development

Maternal (F0) exposure to late-gestation heat stress reduces their daughter's (F1) mammary gland fat pad (FP) mass, parenchyma (PAR) mass, and epithelial cell proliferation when evaluated at birth and weaning, and the daughters go on to produce less milk in their first lactation. Herein, we investigated the effect of maternal late-gestation heat stress on whole-body growth and mammary development of their granddaughters (F2). Multiparous F0 cows had access to heat abatement (n = 41, shade, and active cooling via fans and water soakers) or not (n = 41, shade only) for the last 56 d of gestation during a subtropical summer. Consequently, the F1 daughters, born to F0 cows, were heat-stressed (HTF1, n = 36) or cooled (CLF1, n = 37) in utero during the last 2 mo of gestation. All F1 heifers were raised as an identically managed cohort until first calving. The F2 granddaughters, born to HTF1 (HTF2, n = 12) or CLF1 (CLF2, n = 17), were raised as an identically managed cohort until 70 d of age. Dry matter intake, BW, hip height, wither height, chest girth, head circumference, mammary gland teat length, and left-right and front-rear teat distances were measured. Average daily gain was calculated for the preweaning period (0-49 d). Mammary ultrasounds were performed on d 21, 49, and 70 (n = 9/group) on the rear left and right quarters to quantify PAR and FP areas. Mammary biopsies were collected for histological evaluation of epithelial structures (hematoxylin and eosin staining), and to quantify cells positive for estrogen receptor, α subunit (ERα), cell proliferation (Ki67), and apoptosis (terminal deoxynucleotidyl transferase dUTP nick-end labeling, TUNEL). Heifer growth from birth to d 49 was similar between CLF2 and HTF2 for all parameters evaluated. Distances between teats and teat length were not different between groups. On d 70, CLF2 heifers tended to have a greater average PAR (right and left quarters) relative to HTF2 heifers. Although the left FP was smaller in HTF2 heifers relative to CLF2 heifers, the average FP was not different. The lumenal and nonlumenal epithelial structures in the PAR of HTF2 heifers were significantly smaller than those of CLF2 heifers. In addition, HTF2 heifers had a reduced percentage of proliferating cells in the epithelial and stromal compartments and a greater percentage of apoptotic cells, particularly in the stroma. The percentage of ERα positive cells was significantly reduced in HTF2 heifers. In summary, although HTF2 heifers' DMI was similar and they grew at the same rate as CLF2 heifers throughout the preweaning phase, their mammary glands had smaller PAR areas with fewer epithelial structures characterized by reduced cell turnover and lower ERα expression. These early changes in the microstructure and cellular turnover of the mammary gland may partly explain the reduction in lactation performance relative to CLF2 counterparts at maturity.

Feed efficiency in dairy sheep: An insight from the milk transcriptome

Introduction

As higher feed efficiency in dairy ruminants means a higher capability to transform feed nutrients into milk and milk components, differences in feed efficiency are expected to be partly linked to changes in the physiology of the mammary glands. Therefore, this study aimed to determine the biological functions and key regulatory genes associated with feed efficiency in dairy sheep using the milk somatic cell transcriptome.

Material and methods

RNA-Seq data from high (H-FE, n = 8) and low (L-FE, n = 8) feed efficiency ewes were compared through differential expression analysis (DEA) and sparse Partial Least Square-Discriminant analysis (sPLS-DA).

Results

In the DEA, 79 genes were identified as differentially expressed between both conditions, while the sPLS-DA identified 261 predictive genes [variable importance in projection (VIP) > 2] that discriminated H-FE and L-FE sheep.

Discussion

The DEA between sheep with divergent feed efficiency allowed the identification of genes associated with the immune system and stress in L-FE animals. In addition, the sPLS-DA approach revealed the importance of genes involved in cell division (e.g., KIF4A and PRC1) and cellular lipid metabolic process (e.g., LPL, SCD, GPAM, and ACOX3) for the H-FE sheep in the lactating mammary gland transcriptome. A set of discriminant genes, commonly identified by the two statistical approaches, was also detected, including some involved in cell proliferation (e.g., SESN2, KIF20A, or TOP2A) or encoding heat-shock proteins (HSPB1). These results provide novel insights into the biological basis of feed efficiency in dairy sheep, highlighting the informative potential of the mammary gland transcriptome as a target tissue and revealing the usefulness of combining univariate and multivariate analysis approaches to elucidate the molecular mechanisms controlling complex traits.

Histological tissue structure alterations resulting from Staphylococcus aureus intramammary infection in heifer mammary glands hormonally induced to rapidly grow and develop

Intramammary infections (IMI) are common in nonlactating dairy cattle and are expected to impair mammary growth and development and reduce future milk production. The objective of this study was to histologically evaluate how IMI alter tissue structure in growing and developing heifer mammary glands. A total of 18 nonpregnant, nonlactating heifers between 11 and 14 mo of age were used in the present study. Heifers received daily supraphysiological injections of estradiol and progesterone for 14 d to stimulate rapid mammary growth and development. One-quarter of each heifer was subsequently infused with Staphylococcus aureus (CHALL) while a second quarter served as an uninfected control (UNINF). Heifers were randomly selected and euthanized either the last day of hormonal injections to observe IMI effects on mammary gland growth (GRO), or 13 d post-injections, to observe IMI effects on mammary development (DEV). Mammary tissues were collected from the center and edge parenchymal regions of each mammary gland for morphometric tissue area evaluation. For GRO tissues, CHALL quarters had less epithelial tissue area and marginally more intralobular stroma tissue area than UNINF quarters. Tissue areas occupied by luminal space, extralobular stroma, adipose, and lobular tissue were similar. For DEV tissues, area occupied by epithelium, luminal space, intralobular stroma, and extralobular stroma did not differ between quarter treatments, but UNINF quarters had more adipose tissue area and marginally less lobular area than CHALL quarters. Results indicate that IMI in growing and developing mammary glands reduces mammary epithelial growth and alters mammary gland development by impairing epithelial branching into the mammary fat pad. Taken together, these tissue changes before calving may have adverse effects on milk production. Therefore, an important focus should be placed on improving udder health in replacement heifers through management strategies that mitigate the deleterious effects of IMI and promote the positive development of the mammary gland.

Determinants of delayed onset of lactogenesis II among women who delivered via Cesarean section at a tertiary hospital in China: a prospective cohort study

BACKGROUND

Cesarean birth is associated with a higher prevalence of delayed onset of lactogenesis II (DOLII) than vaginal birth. DOLII refers to the delayed initiation of copious milk production beyond 72 h after birth. This study aimed to determine the prevalence of, and factors associated with, DOLII among women who delivered via Cesarean section in China.

METHODS

This prospective longitudinal cohort study recruited 468 women who delivered via Cesarean section at a tertiary hospital in China from 9 October 2021 to 17 May 2022. Face-to-face interviews were conducted during their delivery hospital stay to obtain information about demographic, medical, and breastfeeding factors. We assessed the onset of lactogenesis on postpartum day four, based on the maternal perception of changes in breast fullness. The Edinburgh Postnatal Depression Scale (EPDS) was used to screen for postpartum depression. Women with DOLII were interviewed via telephone or WeChat daily for one week postpartum to determine the timing of the onset of lactogenesis II. Univariate and multivariable logistic regression analyses were used to identify the determinants of DOLII.

RESULTS

DOLII was experienced by 156 of 468 participants (33.3%). After adjusting for potential confounders, the odds of DOLII were 95% higher in primiparous women than multiparous women (adjusted odds ratio [aOR] 1.95; 95% confidence interval [CI] 1.29, 2.98), 75% higher in women with a serum albumin concentration < 35 g / L than women with normal serum albumin concentrations (aOR 1.78; 95% CI 1.09, 2.99), increased by 2.03-fold in women with an EPDS score ≥ 10 than women with an EPDS score < 10 (aOR 2.03; 95% CI 1.35, 3.07), and decreased in women with a higher number of breastfeeding sessions in the first 48 h postpartum (aOR 0.88; 95% CI 0.83, 0.93).

CONCLUSIONS

One-third of women with Cesarean section delivery experienced DOLII. DOLII was more likely in women who were primiparous, had a serum albumin concentration < 35 g / L, had a lower frequency of breastfeeding sessions, and had an EPDS score ≥ 10. Women with these risk factors who deliver via Cesarean section may need early breastfeeding support to ensure successful lactation.

Characteristics of mammary secretions collected from infected and uninfected primigravid dairy heifer mammary glands

Intramammary infections (IMI) in primigravid dairy heifers can affect mammary growth and development, which can reduce first-lactation milk yield. Detection of IMI in heifers most often involves the use of culture-based methods that are not often used in production dairy settings given their labor- and time-consuming nature. The objective of this study was to determine whether mammary secretion somatic cell count (SCC) and viscosity were associated with the infection status of primigravid heifer mammary glands. A total of 270 heifers from a single farm were used, selected based on the farmer's willingness to participate. The study was conducted from June to October 2020. Mammary secretion samples were aseptically collected from a randomly selected quarter of each heifer at 75 d prepartum (75PP), and another quarter of each heifer was sampled at 35 d prepartum (35PP). The remaining 2 quarters of each heifer were not examined. Mammary secretion samples underwent bacteriological examination to determine IMI status and quantitative SCC measurement and were also assessed for secretion viscosity based on visual observation. Prevalence of IMI was 26% (69/270) and 28% (71/255) at 75 and 35 d prepartum, respectively. Uninfected secretion samples had 133.2 [95% confidence interval (CI): 16.8 to >999.9] times greater odds to be thick compared with samples infected with a major pathogen, and 14.4 (95% CI: 8.5 to 24.1) times greater odds to be thick compared with samples infected with non-aureus staphylococci (NAS). The mean secretion SCC of uninfected quarters (6.04 ± 0.03 log₁₀ cells/mL) was significantly lower than that of secretions collected from quarters infected with Staphylococcus chromogenes (6.34 ± 0.04 log₁₀ cells/mL), other NAS species (6.28 ± 0.10 log₁₀ cells/mL), or a major pathogen (6.73 ± 0.08 log₁₀ cells/mL). These results indicate that mammary secretion viscosity and SCC measurement may be useful tools in identifying primigravid heifer quarters with IMI. The ability to evaluate viscosity at time of sampling may be a useful strategy that could be incorporated into interventions designed to diminish the negative effects of prepartum IMI on lactational performance.

Administration of internal teat sealant in primigravid dairy heifers at different times of gestation to prevent intramammary infections at calving

Intramammary infections (IMI) are common in primigravid dairy heifers and can negatively affect future milk production. Bismuth subnitrate-based internal teat sealants (ITS) have been used to prevent prepartum IMI in dairy heifers by creating a physical barrier within the teat, preventing pathogens from entering the gland, though determination of when to administer ITS in heifers has yet to be investigated. The objectives of this study were to determine if administration of ITS in primigravid heifers reduced the odds of IMI at calving and if administration of ITS at different stages of gestation (75 vs. 35 d prepartum) affected the odds of IMI at calving. A total of 270 heifers were used at a single farm. One quarter of each heifer was randomly chosen to be aseptically sampled and administered ITS 75 d prepartum (ITS75), another quarter of each heifer was sampled and received ITS 35 d prepartum (ITS35), whereas the remaining 2 quarters of each heifer served as control quarters (CON) and were not sampled before calving. Within 12 h of calving, aseptic colostrum samples were collected from all quarters to determine quarter infection status. When an IMI was caused by mastitis pathogens other than non-aureus staphylococci (NAS), CON quarters were 3 times [95% confidence interval (CI): 1.4-6.3] and 2.5 times (95% CI: 1.2-4.9) more likely to be infected at calving than ITS75 and ITS35 quarters, respectively. For IMI with NAS, CON quarters were 5.8 (95% CI: 3.2-10.5) and 6.4 (95% CI: 3.4-12.0) times more likely to be infected than ITS75 and ITS35 quarters, respectively. Odds of IMI at calving was similar between ITS75 and ITS35 quarters for both NAS (odds ratio = 0.9) and other pathogens (odds ratio = 1.2). Results indicate that ITS administration at either 75 and 35 d prepartum reduced IMI prevalence at calving in primigravid dairy heifers. Farm specific factors may influence prevalence and timing of heifer IMI and earlier administration of ITS provides an extended period of protection for the developing gland.

Effects of Staphylococcus aureus intramammary infection on the expression of estrogen receptor α and progesterone receptor in mammary glands of nonlactating cows administered estradiol and progesterone to stimulate mammary growth

Intramammary infections (IMI) are prevalent in nonlactating dairy cattle and are known to alter mammary structure and negatively affect the amount of mammary epithelium in the gland. Mechanisms responsible for the observed changes in mammary growth during an IMI are poorly understood, yet the importance of the key mammogenic hormones driving mammary growth is well recognized. This study's objective was to characterize the expression of estrogen receptor α (ESR1) and progesterone receptor (PGR) in mammary glands stimulated to grow and develop in the presence or absence of an IMI as well as preliminarily characterize myoepithelial cell response to IMI. Mammary growth was stimulated in 18 nonpregnant, nonlactating dairy cows using subcutaneous estradiol and progesterone injections, and 2 culture-negative quarters of each cow were subsequently infused with either saline (n = 18) or Staphylococcus aureus (n = 18). Mammary parenchyma tissues were collected 5 d (n = 9) or 10 d (n = 9) postchallenge and examined using immunofluorescence microscopy to quantify positive nuclei and characterize staining features. There tended to be a greater number of ESR1-positive nuclei observed across 8 random mammary parenchyma fields of view in saline quarters than in Staph. aureus quarters (201 vs. 163 ± 44 nuclei). Saline quarters also contained a greater number of PGR-positive nuclei (520 vs. 440 ± 45 nuclei) and myoepithelial cells (971 vs. 863 ± 48 nuclei) than Staph. aureus-challenged quarters. However, when ESR1, PGR, and myoepithelial nuclei counts were adjusted for Staph. aureus quarters containing less epithelium, differences between quarter treatments abated. The examined ESR1 and PGR staining characteristics were similar between saline and Staph. aureus quarters but were differentially affected by day of tissue collection. Additionally, nuclear staining area of myoepithelial cells was greater in Staph. aureus quarters than in saline quarters. These results indicate that IMI had little effect on the number or staining characteristics of ESR1- or PGR-positive nuclei relative to epithelial area, but myoepithelial cells appear to be affected by IMI and the associated inflammation in nonlactating mammary glands that were stimulated to grow rapidly using mammogenic hormones. Accordingly, reductions in mammary epithelium in affected glands are not suspected to be resultant of alterations in the number or staining characteristics of ESR1- or PGR-positive mammary epithelial cells.

Mammary cell proliferation and catabolism of adipose tissues in nutrition-restricted lactating sows were associated with extracellular high glutamate levels

Background

Persistent lactation, as the result of mammary cellular anabolism and secreting function, is dependent on substantial mobilization or catabolism of body reserves under nutritional deficiency. However, little is known about the biochemical mechanisms for nutrition-restricted lactating animals to simultaneously maintain the anabolism of mammary cells while catabolism of body reserves. In present study, lactating sows with restricted feed allowance (RFA) (n = 6), 24% feed restriction compared with the control (CON) group (n = 6), were used as the nutrition-restricted model. Microdialysis and mammary venous cannulas methods were used to monitor postprandial dynamic changes of metabolites in adipose and mammary tissues.

Results

At lactation d 28, the RFA group showed higher (P < 0.05) loss of body weight and backfat than the CON group. Compared with the CON group, the adipose tissue of the RFA group had higher (P < 0.05) extracellular glutamate and insulin levels, increased (P < 0.05) lipolysis related genes (HSL and ATGL) expression, and decreased (P < 0.05) glucose transport and metabolism related genes (VAMP8, PKLR and LDHB) expression. These results indicated that under nutritional restriction, reduced insulin-mediated glucose uptake and metabolism and increased lipolysis in adipose tissues was related to extracellular high glutamate concentration. As for mammary glands, compared with the CON group, the RFA group had up-regulated (P < 0.05) expression of Notch signaling ligand (DLL3) and receptors (NOTCH2 and NOTCH4), higher (P < 0.05) extracellular glutamate concentration, while expression of cell proliferation related genes and concentrations of most metabolites in mammary veins were not different (P > 0.05) between groups. Accordingly, piglet performance and milk yield did not differ (P > 0.05) between groups. It would appear that activation of Notch signaling and adequate supply of glutamate might assist mammogenesis.

Conclusions

Mammary cell proliferation and catabolism of adipose tissues in nutrition-restricted lactating sows were associated with extracellular high glutamate levels.

Electronic supplementary material

The online version of this article (10.1186/s40104-018-0293-6) contains supplementary material, which is available to authorized users.

Staphylococcus aureus intramammary challenge in non-lactating mammary glands stimulated to rapidly grow and develop with estradiol and progesterone

Intramammary infections (IMI) are prevalent in non-lactating dairy cattle and their occurrence during periods of significant mammary growth and development (i.e. pregnant heifers and dry cows) is believed to interfere with growth, development, and subsequent milk production. However, direct study of IMI impacts on non-lactating but developing mammary glands is lacking. The objectives of this study were to (1) define how IMI affected total and differential mammary secretion somatic cell counts in mammary glands stimulated to rapidly grow using estradiol and progesterone, and (2) characterize changes in mammary morphology in response to IMI. Mammary growth was stimulated in 19 non-pregnant, non-lactating cows and 2 quarters of each cow were subsequently infused with either saline (n = 19) or Staphylococcus aureus (n = 19). Mammary secretions were taken daily until mammary tissues were collected at either 5 or 10 days post-challenge. Staph. aureus quarter secretions yielded greater concentrations of somatic cells than saline quarters and contained a greater proportion of neutrophils. Staph. aureus mammary tissues exhibited higher degrees of immune cell infiltration in luminal and intralobular stroma compartments than saline quarters. Infected tissues also contained reduced areas of epithelium and tended to have greater amounts of intralobular stroma. Results indicate that IMI in non-lactating glands that were stimulated to grow, produced immune cell infiltration into mammary tissues and secretions, which was associated with changes in mammary tissue structure. The observed reduction of mammary epithelium indicates that IMI impair mammary development in rapidly growing mammary glands, which may reduce future reduced milk yields.

TRIENNIAL LACTATION SYMPOSIUM/BOLFA:Historical perspectives of lactation biology in the late 20th and early 21st centuries

The latter half of the 20th century and the early portion of the 21st century will be recognized as the "Golden Age" of lactation biology. This period corresponded with the rise of systemic, metabolomic, molecular, and genomic biology. It includes the discovery of the structure of DNA and ends with the sequencing of the complete genomes of humans and all major domestic animal species including the dairy cow. This included the ability to identify polymorphisms in the nucleic acid sequence, which can be tied to specific differences in cellular, tissue, and animal performance. Before this period, classical work using endocrine ablation and replacement studies identified the mammary gland as an endocrine-dependent organ. In the early 1960s, the development of RIA and radioreceptor assays permitted the study of the relationship between endocrine patterns and mammary function. The ability to measure nucleic acid content of tissues opened the door to study of the factors regulating mammary growth. The development of high-speed centrifugation in the 1960s allowed separation of specific cell organelles and their membranes. The development of transmission and scanning electron microscopy permitted the study of the relationship between structure and function in the mammary secretory cell. The availability of radiolabeled metabolites provided the opportunity to investigate the metabolic pathways and their regulation. The development of concepts regarding the coordination of metabolism to support lactation integrated our understanding of nutrient partitioning and homeostasis. The ability to produce recombinant molecules and organisms permitted enhancement of lactation in farm animal species and the production of milk containing proteins of value to human medicine. These discoveries and others contributed to vastly increased dairy farm productivity in the United States and worldwide. This review will include the discussion of the centers of excellence and scientists who labored in these fields to produce the harvest of knowledge we enjoy today.

Histological and Metabolic State of Dams Suckling Small Litter or MSG-Treated Pups

Lactation is an important function that is dependent on changes in the maternal homeostasis and sustained by histological maternal adjustments. We evaluated how offspring manipulations during the lactational phase can modulate maternal morphologic aspects in the mammary gland, adipose tissue, and pancreatic islets of lactating dams. Two different models of litter-manipulation-during-lactation were used: litter sizes, small litters (SL) or normal litters (NL) and subcutaneous injections in the puppies of monosodium glutamate (MSG), or saline (CON). SL Dams and MSG Dams presented an increase in WAT content and higher plasma levels of glucose, triglycerides, and insulin, in relation to NL Dams and CON Dams, respectively. The MG of SL Dams and MSG Dams presented a high adipocyte content and reduced alveoli development and the milk of the SL Dams presented a higher calorie and triglyceride content, compared to that of the NL Dams. SL Dams presented a reduction in islet size and greater lipid droplet accumulation in BAT, in relation to NL Dams. SL Dams and MSG Dams present similar responses to offspring manipulation during lactation, resulting in changes in metabolic parameters. These alterations were associated with higher fat accumulation in BAT and changes in milk composition only in SL Dams.

Nutrition-induced Changes of Growth from Birth to First Calving and Its Impact on Mammary Development and First-lactation Milk Yield in Dairy Heifers: A Review

This review focuses on the nutritional effects from birth until age at first calving on growth, mammary developmental changes, and first-lactation milk yield in heifer calves. The advancement in the genetic potential and the nutritional requirements of the animals has hastened the growth rate. Genetic selection for high milk yield has suggested higher growth capacity and hence increasing nutritional inputs are required. Rapid rearing by feeding high energy or high concentrate diets not only reduces the age of sexual maturity but also lowers the time period of attaining the age of first calving. However, high energy diets may cause undesirable fat deposition thereby affecting future milk yield potential. Discrepancies exist whether overfed or overweight heifers at puberty can influence the mammary development and future milk yield potential and performance. The data on post-pubertal nutritional management suggested that body weight at calving and post-pubertal growth rate is important in first lactation milk yield. There is a continuous research need for strategic feeding that accelerates growth of dairy heifers without reduction in subsequent production. Nutritional management from birth, across puberty and during pregnancy is critical for mammary growth and for producing a successful cow. This review will mostly highlight studies carried out on dairy breeds and possible available opportunities to manipulate nutritional status from birth until age at first calving.

Cellular proliferation rate and insulin-like growth factor binding protein (IGFBP)-2 and IGFBP-3 and estradiol receptor alpha expression in the mammary gland of dairy heifers naturally infected with gastrointestinal nematodes during development

Mammary ductal morphogenesis during prepuberty occurs mainly in response to insulin-like growth factor-1 (IGF-1) and estradiol stimulation. Dairy heifers infected with gastrointestinal nematodes have reduced IGF-1 levels, accompanied by reduced growth rate, delayed puberty onset, and lower parenchyma-stroma relationship in their mammary glands. Immunohistochemical studies were undertaken to determine variations in cell division rate, IGF-1 system components, and estradiol receptors (ESR) during peripubertal development in the mammary glands of antiparasitic-treated and untreated Holstein heifers naturally infected with gastrointestinal nematodes. Mammary biopsies were taken at 20, 30, 40, and 70 wk of age. Proliferating cell nuclear antigen immunolabeling, evident in nuclei, tended to be higher in the parenchyma of the glands from treated heifers than in those from untreated. Insulin-like growth factor binding proteins (IGFBP) type 2 and type 3 immunolabeling was cytoplasmic and was evident in stroma and parenchyma. The IGFBP2-labeled area was lower in treated than in untreated heifers. In the treated group, a maximal expression of this protein was seen at 40 wk of age, whereas in the untreated group the labeling remained constant. No differences were observed for IGFBP3 between treatment groups or during development. Immunolabeling for α ESR (ESR1) was evident in parenchymal nuclei and was higher in treated than in untreated heifers. In the treated group, ESR1 peaked at 30 wk of age and then decreased. These results demonstrate that the parasite burden in young heifers negatively influence mammary gland development, affecting cell division rate and parameters related to estradiol and IGF-1 signaling in the gland.

Invited review: Mastitis in dairy heifers: nature of the disease, potential impact, prevention, and control

Heifer mastitis is a disease that potentially threatens production and udder health in the first and subsequent lactations. In general, coagulase-negative staphylococci (CNS) are the predominant cause of intramammary infection and subclinical mastitis in heifers around parturition, whereas Staphylococcus aureus and environmental pathogens cause a minority of the cases. Clinical heifer mastitis is typically caused by the major pathogens. The variation in proportions of causative pathogens between studies, herds, and countries is considerable. The magnitude of the effect of heifer mastitis on an individual animal is influenced by the form of mastitis (clinical versus subclinical), the virulence of the causative pathogen(s) (major versus minor pathogens), the time of onset of infection relative to calving, cure or persistence of the infection when milk production has started, and the host's immunity. Intramammary infection in early lactation caused by CNS does not generally have a negative effect on subsequent productivity. At the herd level, the impact will depend on the prevalence and incidence of the disease, the nature of the problem (clinical, subclinical, nonfunctional quarters), the causative pathogens involved (major versus minor pathogens), the ability of the animals to cope with the disease, and the response of the dairy manager to control the disease through management changes. Specific recommendations to prevent and control mastitis in late gestation in periparturient heifers are not part of the current National Mastitis Council mastitis and prevention program. Control and prevention is currently based on avoidance of inter-sucking among young stock, fly control, optimal nutrition, and implementation of hygiene control and comfort measures, especially around calving. More risk factors for subclinical and clinical heifer mastitis have been identified (e.g., season, location of herd, stage of pregnancy) although they do not lend themselves to the development of specific intervention strategies designed to prevent the disease. Pathogen-specific risk factors and associated control measures need to be identified due to the pathogen-related variation in epidemiology and effect on future performance. Prepartum intramammary treatment with antibiotics has been proposed as a simple and effective way of controlling heifer mastitis but positive long-lasting effects on somatic cell count and milk yield do not always occur, ruling out universal recommendation of this practice. Moreover, use of antibiotics in this manner is off-label and results in an increased risk of antibiotic residues in milk. Prepartum treatment can be implemented only as a short-term measure to assist in the control of a significant heifer mastitis problem under supervision of the herd veterinarian. When CNS are the major cause of intramammary infection in heifers, productivity is not affected, making prepartum treatment redundant and even unwanted. In conclusion, heifer mastitis can affect the profitability of dairy farming because of a potential long-term negative effect on udder health and milk production and an associated culling risk, specifically when major pathogens are involved. Prevention and control is not easy but is possible through changes in young stock and heifer management. However, the pathogenesis and epidemiology of the disease remain largely unknown and more pathogen-specific risk factors should be identified to optimize current prevention programs.

Hypergravity disruption of homeorhetic adaptations to lactation in rat dams include changes in circadian clocks

Altered gravity load induced by spaceflight (microgravity) and centrifugation (hypergravity) is associated with changes in circadian, metabolic, and reproductive systems. Exposure to 2-g hypergravity (HG) during pregnancy and lactation decreased rate of mammary metabolic activity and increased pup mortality. We hypothesize HG disrupted maternal homeorhetic responses to pregnancy and lactation are due to changes in maternal metabolism, hormone concentrations, and maternal behavior related to gravity induced alterations in circadian clocks. Effect of HG exposure on mammary, liver and adipose tissue metabolism, plasma hormones and maternal behavior were analyzed in rat dams from mid-pregnancy (Gestational day [G]11) through early lactation (Postnatal day [P]3); comparisons were made across five time-points: G20, G21, P0 (labor and delivery), P1 and P3. Blood, mammary, liver, and adipose tissue were collected for analyzing plasma hormones, glucose oxidation to CO(2) and incorporation into lipids, or gene expression. Maternal behavioral phenotyping was conducted using time-lapse videographic analyses. Dam and fetal-pup body mass were significantly reduced in HG in all age groups. HG did not affect labor and delivery; however, HG pups experienced a greater rate of mortality. PRL, corticosterone, and insulin levels and receptor genes were altered by HG. Mammary, liver and adipose tissue metabolism and expression of genes that regulate lipid metabolism were altered by HG exposure. Exposure to HG significantly changed expression of core clock genes in mammary and liver and circadian rhythms of maternal behavior. Gravity load alterations in dam's circadian system may have impacted homeorhetic adaptations needed for a successful lactation.

Effect of heat stress during the dry period on mammary gland development

Heat stress during the dry period negatively affects hepatic metabolism and cellular immune function during the transition period, and milk production in the subsequent lactation. However, the cellular mechanisms involved in the depressed mammary gland function remain unknown. The objective of the present study was to determine the effect of heat stress during the dry period on various indices of mammary gland development of multiparous cows. Cows were dried off approximately 46 d before expected calving and randomly assigned to 2 treatments, heat stress (HT, n=15) or cooling (CL, n=14), based on mature equivalent milk production. Cows in the CL treatment were provided with sprinklers and fans that came on when ambient temperatures reached 21.1°C, whereas HT cows were housed in the same barn without fans and sprinklers. After parturition, all cows were housed in a freestall barn with cooling. Rectal temperatures were measured twice daily (0730 and 1430 h) and respiration rates recorded at 1500 h on a Monday-Wednesday-Friday schedule from dry off to calving. Milk yield and composition were recorded daily up to 280 d in milk. Daily dry matter intake was measured from dry off to 42 d relative to calving. Mammary biopsies were collected at dry off, -20, 2, and 20 d relative to calving from a subset of cows (HT, n=7; CL, n=7). Labeling with Ki67 antigen and terminal deoxynucleotidyl transferase deoxyuridine triphosphate nick-end labeling were used to evaluate mammary cell proliferation and apoptosis, respectively. The average temperature-humidity index during the dry period was 76.6 and not different between treatments. Heat-stressed cows had higher rectal temperatures in the morning (38.8 vs. 38.6°C) and afternoon (39.4 vs. 39.0°C), greater respiration rates (78.4 vs. 45.6 breath/min), and decreased dry matter intake (8.9 vs. 10.6 kg/d) when dry compared with CL cows. Relative to HT cows, CL cows had greater milk production (28.9 vs. 33.9 kg/d), lower milk protein concentration (3.01 vs. 2.87%), and tended to have lower somatic cell score (3.35 vs. 2.94) through 280 d in milk. Heat stress during the dry period decreased mammary cell proliferation rate (1.0 vs. 3.3%) at -20 d relative to calving compared with CL cows. Mammary cell apoptosis was not affected by prepartum heat stress. We conclude that heat stress during the dry period compromises mammary gland development before parturition, which decreases milk yield in the next lactation.

A simple analytical and experimental procedure for selection of reference genes for reverse-transcription quantitative PCR normalization data

Variation in cellular activity in a tissue induces changes in RNA concentration, which affects the validity of gene mRNA abundance analyzed by reverse transcription quantitative PCR (RT-qPCR). A common way of accounting for such variation consists of the use of reference genes for normalization. Programs such as geNorm may be used to select suitable reference genes, although a large set of genes that are not co-regulated must be analyzed to obtain accurate results. The objective of this study was to propose an alternative experimental and analytical protocol to assess the invariance of reference genes in porcine mammary tissue using mammary RNA and DNA concentrations as correction factors. Mammary glands were biopsied from 4 sows on d 110 of gestation (prepartum), on d 5 (early) and 17 (peak) of lactation, and on d 5 after weaning (postweaning). Relative expression of 7 potential reference genes, API5, MRPL39, VAPB, ACTB, GAPDH, RPS23, and MTG1, and one candidate gene, SLC7A1, was quantified by RT-qPCR using a relative standard curve approach. Variation in gene expression levels, measured as cycles to threshold at each stage of mammary physiological activity, was tested using a linear mixed model fitting RNA and DNA concentrations as covariates. Results were compared with those obtained with geNorm analysis, and genes selected by each method were used to normalize SLC7A1. Quantified relative mRNA abundance of GAPDH and MRPL39 remained unchanged across stages of mammary physiological activity after accounting for changes in tissue RNA and DNA concentration. In contrast, geNorm analysis selected MTG1, MRPL39, and VAPB as the best reference genes. However, when target gene SLC7A1 was normalized with genes selected either based on our proposed protocol or by geNorm, fold changes in mRNA abundance did not differ. In conclusion, the proposed analytical protocol assesses expression invariance of potential reference genes by accounting for variation in tissue RNA and DNA concentrations and thus represents an alternative method to select suitable reference genes for RT-qPCR analysis.

Mastitis and its impact on structure and function in the ruminant mammary gland

It is a given in biology that structure and function go hand-in-hand. At the level of the mammary alveoli, copious milk production depends on the proliferation of mammary epithelial cells and the biochemical and structural differentiation of these cells after parturition. For example, data from quantitative structural studies demonstrate that differences in milk production between beef and dairy cows correspond with a relative failure of alveolar cell differentiation in cattle not specifically selected for milk yield. It is likely, but not proven, that production differences within or between dairy breeds are also determined by differences in the capacity of alveolar cells to differentiate or to maintain an adequate state of differentiation. These observations strongly support the belief that insults from mastitis that lead to losses in mammary function are directly related to disruption of alveolar cell integrity, sloughing of cells, induced apoptosis, and increased appearance of poorly-differentiated cells. Ironically, reduced milk production in cases of subclinical mastitis, is also associated with increases in milk somatic cell count. Thus the elevated neutrophil migration evoked to fight inflammation can inadvertently rendered alveolar epithelial cells non-secretory. A challenge to future researchers will be to devise mastitis treatments and therapies that prevent and/or repair damage to alveolar structure and maximize subsequent secretory cell differentiation.

Effects of energy allowance and cimaterol feeding during the heifer rearing period on growth, puberty and milk production

Twenty-one 6-month-old Israeli Holstein heifers were used to determine the effect of three 6-month feeding regimes on growth, blood concentration of insulin, prolactin and insulin-like growth factor-1 (IGF-1), attainment of puberty and milk production during first lactation. Feeding regimes were as follows. (1) Restricted: the heifers were given food during months 1, 2 and 4, 5 of an experimental period, to support live-weight (LW) gain of 0·35 and 0·50 kg/day, respectively and during months 3 and 6 the heifers were given food to support compensatory growth. (2) Control: the heifers were given food to support LW gain of 1·0 kg/day. (3) Control + C: the heifers were given the same as the control, with a daily supplement of 0·05 mg/kg LW cimaterol (C) for 4 months. The total LW gain of the restricted heifers during the 6 months of the trial was significantly lower than that of the control heifers. Cimaterol improved growth rate only during the first 2 months of its application and its withdrawal was associated with severe LW gain retardation. The feeding regime employed in the restricted treatment was associated with a significant reduction in serum concentrations of insulin, prolactin and IGF-1 during the first restricted phase, followed by an elevation in the first compensatory phase. During the second restriction-compensation cycle, only the serum concentration of prolactin was significantly reduced. Cimaterol addition was also associated with a reduced blood concentration of the hormones. The animals in the restricted, control and control + C groups attained puberty at LW of 249·2, 277·6 and 304·9 kg (P<0·05), respectively. No effect of the treatments on milk yield was observed. The effect of the feeding regimes on skeletal growth and on metubolizable energy efficiency for growth is discussed.

Diverse and active roles for adipocytes during mammary gland growth and function

The mammary gland is unique in its requirement to develop in close association with a depot of adipose tissue that is commonly referred to as the mammary fat pad. As discussed throughout this issue, the mammary fat pad represents a complex stromal microenvironment that includes a variety of cell types. In this article we focus on adipocytes as local regulators of epithelial cell growth and their function during lactation. Several important considerations arise from such a discussion. There is a clear and close interrelationship between different stromal tissue types within the mammary fat pad and its adipocytes. Furthermore, these relationships are both stage- and species-dependent, although many questions remain unanswered regarding their roles in these different states. Several lines of evidence also suggest that adipocytes within the mammary fat pad may function differently from those in other fat depots. Finally, past and future technologies present a variety of opportunities to model these complexities in order to more precisely delineate the many potential functions of adipocytes within the mammary glands. A thorough understanding of the role for this cell type in the mammary glands could present numerous opportunities to modify both breast cancer risk and lactation performance.

Ultrasound imaging of mammary glands in dairy heifers at different stages of growth

To obtain B-mode ultrasound images of mammary glands in dairy heifers at different stages of growth, 25 clinically normal Holstein heifers were used. The heifers were divided into 5 groups (n=5/group) by stage of their growth: 2-month-old (group 1), 5-month-old (group 2), postpuberty (group 3), mid (group 4), and late (group 5) pregnancy. Furthermore, the sections of mammary glands were observed grossly at postmortem examination in one heifer in each group. Ultrasound images varied with the development of mammary glands. In group 1, the mammary glands had distinctive ultrasonographic findings: an oval to fusiform homogeneous hypoechoic structure. In all groups except group 1, mammary tissue consists of two major areas: a homogeneous, medium echogenic area and a poorly-defined, heterogeneous, hypoechoic area mostly in the superficial part. The superficial hypoechoic area spread more extensively and more irregularly with the development of mammary glands. Most pregnant heifers had irregular and extremely hypoechoic or anechoic areas like lactiferous sinus in the glands. The gross findings of mammary glands suggested that the hypoechoic areas of various shapes represented the lactiferous sinus and ducts. Thus, these results indicate that B-mode ultrasound imaging can visualize the internal structures of udders and could be a useful tool for evaluation of mammary glands in heifers.

Molecular signatures reveal circadian clocks may orchestrate the homeorhetic response to lactation

Genes associated with lactation evolved more slowly than other genes in the mammalian genome. Higher conservation of milk and mammary genes suggest that species variation in milk composition is due in part to the environment and that we must look deeper into the genome for regulation of lactation. At the onset of lactation, metabolic changes are coordinated among multiple tissues through the endocrine system to accommodate the increased demand for nutrients and energy while allowing the animal to remain in homeostasis. This process is known as homeorhesis. Homeorhetic adaptation to lactation has been extensively described; however how these adaptations are orchestrated among multiple tissues remains elusive. To develop a clearer picture of how gene expression is coordinated across multiple tissues during the pregnancy to lactation transition, total RNA was isolated from mammary, liver and adipose tissues collected from rat dams (n = 5) on day 20 of pregnancy and day 1 of lactation, and gene expression was measured using Affymetrix GeneChips. Two types of gene expression analysis were performed. Genes that were differentially expressed between days within a tissue were identified with linear regression, and univariate regression was used to identify genes commonly up-regulated and down-regulated across all tissues. Gene set enrichment analysis showed genes commonly up regulated among the three tissues enriched gene ontologies primary metabolic processes, macromolecular complex assembly and negative regulation of apoptosis ontologies. Genes enriched in transcription regulator activity showed the common up regulation of 2 core molecular clock genes, ARNTL and CLOCK. Commonly down regulated genes enriched Rhythmic process and included: NR1D1, DBP, BHLHB2, OPN4, and HTR7, which regulate intracellular circadian rhythms. Changes in mammary, liver and adipose transcriptomes at the onset of lactation illustrate the complexity of homeorhetic adaptations and suggest that these changes are coordinated through molecular clocks.

Characterization of mammary gland development in pregnant gilts

The purpose of this study was to quantify mammary gland (MG) growth during pregnancy in gilts and to determine the effect of anatomical location on gland growth. Size, composition, and histomorphology of MG were determined during gestation in 29 primigravid gilts. Gilts were allotted randomly to 6 slaughter groups: d 45 (n = 6), 60 (n = 4), 75 (n = 5), 90 (n = 4), 102 (n = 5), and 112 (n = 5) of gestation. Mammary glands were obtained at slaughter, and skin and extraneous fat pad were removed to obtain parenchymal MG tissue. Mammary glands were further separated into individual MG, and their locations were recorded. Individual MG were weighed and bisected in an approximate midsagittal section to measure cross-sectional area. Mammary glands were ground individually and pooled according to anatomical region: the first and second pairs of MG = anterior MG; the third, fourth, and fifth pairs of MG = middle MG; the sixth, seventh, and eighth pairs of MG = posterior MG. Contents of DM, CP, ether extract, and crude ash were measured. Wet weight, DM, CP, and ash content of total and individual MG increased (P < 0.01) between d 45 and 112 of gestation. Cross-sectional area of individual MG increased (P < 0.01) as gestation progressed. Percentage of CP and ash increased (P < 0.01), whereas percentage of ether extract decreased (P < 0.01) as gestation progressed. This inverse relationship between percentages of CP and ether extract (r = -0.999; P < 0.0001) was consistent with the histological shift from primarily an adipose tissue in early gestation to one containing extensive lobuloalveolar tissue in late gestation. Wet weight of middle MG was greater (P < 0.05) than that of posterior MG at d 102 and 112 of gestation, and amount of CP in middle MG was greater (P < 0.05) than that in anterior and posterior MG at d 102 and 112 of gestation, indicating that middle MG grow faster than other MG during late gestation. Rates of wet weight gain and protein accretion were accelerated (P < 0.01) after d 74 and 75 of gestation, respectively, indicating the importance of MG growth during the last trimester of gestation. The increase in rate of protein accretion after d 75 indicates a greater protein requirement for MG growth during later gestation.

The declining phase of lactation: peripheral or central, programmed or pathological?

In most species the functional activity of the mammary gland during lactation follows a biphasic developmental pattern. This pattern starts with a rapid increase in milk output that occurs with secretory activation and continues with a more gradual increase until the point of peak lactation is reached. Following this gain-of-function phase, the ability of the gland to produce milk decreases. This decrease occurs even if the lactation is prolonged by the presence of continued suckling stimulus and complete milk removal. This review describes the current state of our knowledge concerning the factors that regulate milk synthesis capacity by the mammary gland during the lactation cycle. The review describes four potential alternatives as mechanisms governing the process, which we refer to as secretory diminution. These alternatives are not presented as mutually exclusive of each other or other possible mechanisms, but are proposed as potential contributing mechanisms.

Meta-Analysis to Assess Effect of Prepubertal Average Daily Gain of Holstein Heifers on First-Lactation Production

Decreased mammary development has been observed as prepubertal average daily gain (ADG) is increased; however, responses in first-lactation milk production to alterations in prepubertal ADG have been inconsistent across several experiments. Due to the continuous nature of ADG, body weight at calving (BWC), milk production, and milk composition, designing an experiment that encompasses a large range of ADG while maintaining an adequate number of animals at each ADG becomes prohibitive. Therefore, the objective of the current analysis was to quantitatively and statistically assess effects of alterations in prepubertal ADG and BWC on first-lactation production of milk, fat-corrected milk, milk fat, and milk protein. Eight studies that included Holstein heifers and were published within the past 15 yr were included in this analysis. The mixed model procedure of SAS was used to assess effects of prepubertal ADG and BWC on milk production independent of genetic or management differences that were evident between trials. Linear and quadratic effects of prepubertal ADG and BWC and their combinations were modeled including a random classification variable for each trial. Milk yield responses were associated quadratically with increasing prepubertal ADG; first-lactation production increased as prepubertal gains increased up to 799 g/d, the point of maximal milk production, whereas further increases in prepubertal ADG were associated with lower milk production. Increasing BWC within the range of 477 to 550 kg tended to linearly increase first-lactation milk production, but BWC significantly affected milk production in a model that included the linear and quadratic effects of ADG as well as linear BWC. In that model, which accounted for differences in calving weight, milk production was maximal at prepubertal ADG of 836 g/d. Milk protein yield was quadratically affected by alterations in prepubertal ADG, and milk protein yield was maximized when prepubertal growth occurred at 836 g/d. This analysis also revealed that yield of milk fat remained relatively constant independent of alterations in prepubertal ADG, which occurred despite the significant quadratic effect on milk and milk protein yield.

Effect of bovine somatotropin and rumen-undegradable protein on mammary growth of prepubertal dairy heifers and subsequent milk production

Rapid body growth during the prepubertal period may be associated with reductions in mammary parenchymal growth and subsequent milk yield. The objective of this study was to test effects of dietary rumen-undegradable protein (RUP) and administration of recombinant bovine somatotropin (bST) during the prepubertal period on mammary growth and milk yield of dairy heifers. Seventy-two Holstein heifers were used in the experiment. At 90 d of age, 8 heifers were slaughtered before initiation of treatment. Remaining heifers were assigned randomly to 1 of 4 treatments. Treatments consisted of a control diet (5.9% RUP, 14.9% CP, DM basis) or RUP-supplemented diet (control diet plus 2% added RUP) with or without 0.1 mg of bST/kg of BW per day applied in a 2 x 2 factorial design. A total of 6 heifers per treatment (3 each at 5 and 10 mo of age) were slaughtered for mammary tissue analysis. Remaining heifers were bred to evaluate impact of treatment on subsequent milk yield and composition. Mammary parenchymal growth was not affected by RUP or bST treatment. Total parenchymal mass increased from 16 to 364 g, and parenchymal DNA from 58 to 1022 mg from 3 to 10 mo of age, respectively. Furthermore, number of mammary epithelial cells likely was not affected by diet or bST because the epithelial cell proliferation index, assessed by Ki-67 labeling, was not affected by treatment, nor was total parenchymal DNA and lipid content. Neither deleterious effects of increased rates of gain nor positive effects of bST were evident in prepubertal mammary growth. Subsequent milk production and composition was not different among treatments.

Bovine Somatotropin and Rumen-Undegradable Protein Effects in Prepubertal Dairy Heifers: Effects on Body Composition and Organ and Tissue Weights

The objectives of this study were to determine the effect of recombinant bovine somatotropin (bST) and added dietary rumen undegradable protein (RUP) on organ and tissue weights and body composition in growing dairy heifers. Thirty-two Holstein heifers were in the experiment, 8 killed initially at 3 mo of age, with the remaining 24 Holstein heifers randomly assigned to treatments (n = 6) consisting of 0.1 mg/kg of body weight per day of bST and 2% added dietary RUP (dry matter basis) applied in a 2 x2 factorial design. A total of 6 heifers per treatment group (3 each at 5 and 10 mo of age), were slaughtered to determine body composition and organ masses. Feed intake measured from group intakes were increased by 0.25 and 0.35 kg/d with bST and RUP, respectively. Administration of bST tended to increase the weights of visceral organs including heart, kidney, and spleen by 16, 16, and 38%, respectively. At 10 mo of age, there was a trend for increased empty body weights (EBW) and non-carcass components for heifers treated with bST, but there were no effects of RUP. Body components and organ weights, expressed as a percentage of BW were not affected by RUP or bST. Somatotropin increased ash weight at 10 mo without affecting amounts of protein, fat, and energy. Rates of ash deposition between 3 and 10 mo of age were increased 7 and 4 g/d by bST and RUP, respectively. There were no treatment effects on rates of body fat, protein, and energy deposition. Bovine somatotropin and RUP altered the metabolism of growing heifers in a manner that was consistent with increased rates of skeletal growth. This suggests that nutritional and endocrine manipulations could increase growth rates of skeletal tissues without increasing fat deposition in prepubertal dairy heifers.

Bovine Somatotropin and Rumen-Undegradable Protein Effects on Skeletal Growth in Prepubertal Dairy Heifers

The objectives of this study were to determine the effects of dietary rumen-undegradable protein (RUP) and bovine somatotropin (bST) during the period from weaning until puberty on body weight (BW) and skeletal growth rates and age at puberty. Fifty-one Holstein heifers at 90 d of age were randomly assigned to 4 treatment groups consisting of 0.1 mg/kg BW per day of bST and 2% added dietary RUP (dry matter basis) applied in a 2 x 2 factorial design (n = 13 per group, except bST with no RUP group, n = 12). From 90 to 314 d, bST increased average daily gain (ADG) by 0.07 kg/d and BW by 16.2 kg, while added RUP increased ADG by 0.10 kg/d and BW by 21.4 kg. Both bST and added RUP effects on BW and ADG were additive. Skeletal growth rates, as measured by withers height (WH) and hip height (HH) were increased by both bST and added RUP. Somatotropin and RUP increased WH by 1.8 and 2.7 cm and hip height by 2.5 and 4.0 cm, respectively, at 314 d of age. Growth curves showed that added RUP effects on rates of BW, WH, and HH growth were greatest from 90 to 150 d age and diminished thereafter, suggesting that protein was limiting during this time period. Conversely, bST effects tended to be greater as the heifers approached puberty, but only in the presence of added RUP. Age at puberty was not affected by treatment, averaging 314 d of age across treatments. From 314 to 644 d of age, rates of BW, WH, and HH growth were similar among treatment groups. However, treatment differences present at 314 d of age persisted through 644 d of age, more than 10 mo after treatments ceased. These results suggest that protein during the early postweaning period and bST during the 200 to 300 d of age period just prior to puberty could be used to accelerate simultaneous increases in both BW and skeletal growth rates in dairy heifers without reducing age at puberty.

Exogenous TGF-β1 Promotes Stromal Development in the Heifer Mammary Gland

The objectives of this study were to determine the local effects of transforming growth factor-beta1 (TGF-beta1) on mammary epithelial and stromal cell proliferation and expression of the TGF-beta1 responsive genes c-myc and fibronectin. A single slow-release plastic pellet containing 5 microg of TGF-beta1 and 20 mg of BSA was implanted in the parenchyma of the right rear quarter of the mammary gland of 9-mo-old prepubertal heifers. A control pellet containing 20 mg of BSA was implanted in the left rear quarter of each heifer. All heifers were treated with bromodeoxyuridine (BrdU) at 4, 12.5, and 22 h after the pellets were implanted to label proliferating cells. Two hours after the last BrdU injection, the animals were euthanatized, and their mammary glands were recovered. Proliferation of mammary stromal cells was significantly higher in TGF-beta1-treated quarters than in BSA-treated, control quarters (3.5 vs. 1.8% BrdU-positive cells). This result coincided with a lack of significant effect of TGF-beta1 on proliferation of mammary epithelial cells and apoptosis. By quantitative reverse transcriptase-polymerase chain reaction, we found that c-myc gene expression was unchanged after TGF-beta1 treatment, but fibronectin gene expression was increased 3-fold in TGF-beta1-treated quarters compared with BSA-treated, control quarters. Thus, we concluded that TGF-beta1 selectively acts on the stromal compartment of the bovine mammary gland by increasing cell proliferation and gene expression of the extracellular matrix protein fibronectin.

Modeling extended lactation curves of dairy cattle: a biological basis for the multiphasic approach

Objectives of this study are to describe the biological basis for multiphasic milk production and to propose a new empirical model for the lactation curve. To illustrate this model, we used data on 3573 first-lactation Holsteins having lactations of various lengths (285, 345, 405, 465, and 525 d) and with various days open (45, 105, 165, 225, and 285 d). The model describes an increasing first phase of milk yield and a series of decreasing phases of yield. The increasing phase, described by an increasing logistic function of time, is associated with increase in number of active mammary gland cells and increase in yield per cell. The decreasing phases, described by three decreasing logistic functions of time, are associated with decreases in cell number due to apoptosis and in yield per cell due to pregnancy. The new model is [equation: see text] where yDIM is milk yield at each day in milk (DIM), a1 is upper level for the increasing first phase, and p2, p3, and p4 = (1 - p2 - p3) are proportions of a1 for the decreasing second, third, and fourth phases; b's are proportional to duration of each phase; and c's are time of maximum increase or decrease. Nonlinear regression was used to fit average milk yield for each of nine datasets, four with 180 d carried calf and five with 240 d carried calf. Average results indicated that for the first phase, upper level of milk yield was about 22 kg. Duration was about 120 d, centered on time of maximum increase, which was about 11 d before calving. For the second phase (first phase of apoptosis), decrease in yield was relatively large (about 20%) and duration was relatively long (about 375 d). Time of maximum decrease was about 107 d after calving. For the third phase (pregnancy), decrease in yield was relatively small (about 6%) and duration was relatively short (about 200 d). Time of maximum decrease was about 300 d after calving. For each additional day open, time of maximum decrease increased about 1 d. For the fourth phase (second phase of apoptosis), decrease in yield was relatively large (about 74%) and duration was relatively long (about 765 d). Duration for the lactation length of 525 d was exceptionally long. Time of maximum decrease was about 382 d after calving. For each additional day of lactation, duration increased about 5.4 d and day of maximum decrease increased about 0.82 d. We believe that it is possible to model empirically standard and extended lactation curves of dairy cows, based on biological theory and predicated on the multiphasic approach. Further research to understand better the biology of extended lactations, using the proposed multiphasic model, should use planned extended lactations that are at least 525 d in milk and have at least 240 d carried calf.

Regulation of mammary gland growth and morphogenesis by the mammary fat pad: a species comparison

The growth and morphogenesis of mammary parenchyma varies substantially between species and is regulated by an array of systemic and local factors. Central to this regulation is the mammary fat pad, a matrix of adipose and connective tissue capable of mediating hormone action and synthesizing an array of growth regulatory molecules. In this article we highlight differences between the morphological development of the mammary parenchyma in rodents, humans, and ruminant dairy animals, placing emphasis on differences in the cellular composition and structure of the mammary fat pad. While a great deal remains to be understood about the ability of stroma to locally regulate mammary development, the significance of its contribution is becoming increasingly apparent. The actions of several steroid and peptide hormones appear to be mediated by an array of growth factors, proteases and extracellular matrix components synthesized by constituents of the mammary fat pad. Further, mammary adipose tissue represents a significant store of lipid which, by itself and through its derivatives, could influence the growth of mammary epithelium in diverse ways. This review describes the integral role of the mammary fat pad during mammogenesis, emphasizing the point that species differences must be addressed if local growth and morphogenic mechanisms within the mammary gland are to be resolved.

Milk production of Holstein heifers fed either alfalfa or corn silage diets at two rates of daily gain

Seventy-five prepubertal heifers were fed diets based on either alfalfa silage or corn silage plus soybean meal for daily gains of either 725 or 950 g/d in a 2 x 2 factorial. Heifers were fed from 175 to 325 kg of body weight (BW). The alfalfa diet contained more digestible protein and less digestible energy than did the diet containing corn silage plus soybean meal. Actual gains were preexperimental BW gain, 633 g/d; lowest experimental BW gain, 785 g/d; highest experimental BW gain, 994 g/d; lowest postexperimental BW gain, 494 g/d; and highest postexperimental BW gain, 546 g/d. Compensatory postexperimental BW gains of heifers fed a common diet allowed the heifers to calve at 732 d of age. The postcalving BW was 508 kg, and precalving height at withers was 134 cm. A total mixed diet containing 17.1% CP and digestible energy at 3.12 Mcal/kg of dry matter was fed during lactation. Feed intake, milk and milk component production, and milk composition were not affected by either experimental diet or growth rate. As covariates, milk production was related to age at calving and was more strongly related to BW after calving, but no differences were observed among growth diets. Differences in protein and energy concentrations in experimental growth diets did not affect lactation performance. About 75% of total BW gains during the treatment period occurred before puberty, but rate of gain did not affect milk production. This lack of an effect of prepubertal growth rates on the milk production of primiparous heifers is consistent with six other similar studies that were conducted recently.

A model to describe growth patterns of the mammary gland during pregnancy and lactation

Extensive proliferation and death of cells in the mammary gland occur during pregnancy and lactation. In this study, a mechanistic model was developed that yielded a single equation to describe the pattern of mammary growth of mammals throughout pregnancy and lactation. The model contains a single pool, which is the cell population of the mammary gland; one influx, representing cell proliferation; and one efflux, representing cell death. The parameters of the equation lend themselves to direct physiological interpretation. The model fitted data on mammary gland DNA adequately and can be related to current knowledge on factors and inhibitors of mammary gland growth. A unique definition of the parameters of the model can be difficult because of the high degree of variation among animals, an improper number of observations, or timing, as indicated by analyses of simulated data. The model can also be applied to the study of the entire lactation curve. The widely applied gamma equation and the equation that was developed in this study were compared using weekly production data from dairy cows. The new model performed well, particularly when a sharp peak in milk production occurred. The model has the advantage of providing, for the first time, a simple biological description of the lactation curve that can be used to discriminate changes in lactational performance that are associated with experimental treatments.

Increased weight gain and effects on production parameters of Holstein heifer calves that were allowed to suckle from birth to six weeks of age

Forty Holstein heifer calves were assigned to two treatments. Control calves (n = 20) were fed milk replacer in open buckets, and calves that were allowed to suckle (n = 20) were paired and suckled the same dam three times daily. Treatments were conducted during the first 6 wk following birth; thereafter, all calves received the same management, and weaning was at 60 d of age. During treatment, calves that were allowed to suckle had significantly higher average daily gains than did control calves. However, at 12 wk of age, calves that were allowed to suckle had significantly lower body weights (BW) than did control calves. Age at conception was significantly lower, and BW at conception and conception rate tended to be higher, for calves that were allowed to suckle. Calving age was significantly earlier for heifers that had been allowed to suckle as calves, and BW at calving also tended to be higher. Height at the withers after calving was also significantly higher for those heifers. Milk production during first lactation tended to be higher for the heifers that had been allowed to suckle as calves. Our results indicated that heifer calves that suckled milk during the first 42 d of age had higher average daily gains, higher height at the withers, an earlier age at calving, and a tendency for greater milk production than did calves fed milk replacer.

Expression of amphiregulin in the sheep mammary gland

The reverse transcription-polymerase chain reaction (RT-PCR) was used to amplify, from sheep mammary gland total RNA, a 280 bp sequence of amphiregulin cDNA. Cloned and sequenced, it corresponded to the 78 amino acids of the major secreted form of amphiregulin, showing 81, 70 and 69% identity with human, rat and mouse amphiregulin, respectively. Expression of amphiregulin was detected by RT-PCR in the mammary gland at several developmental stages (fetal, lamb, early and late pregnant and lactating ewes) and in isolated myoepithelial cells. By Western blotting with an antiserum to human amphiregulin, two molecular weight forms, 27 and 51 kDa were detected in sheep mammary gland microsomal preparations, in a mammary gland extract after heparin affinity chromatography and in a medium conditioned by mammary epithelial cells. By immunocytochemistry, amphiregulin was detected in the cytoplasm and nuclei of luminal epithelial cells, myoepithelial cells and in intralobular stroma. An autocrine/paracrine role in sheep mammary growth is indicated.

Mammary sensitivity to protein restriction and re-alimentation

The present study tested the influence of protein undernutrition and re-alimentation on mammary gland size and secretory cell activity in lactating rats. During gestation, female Sprague-Dawley rats were offered a high-protein diet (215 g crude protein (N x 6.25; CP)/kg DM; H); litters were standardized to twelve pups at parturition. During lactation, two diets were offered ad libitum, diet H and a low-protein diet (90 g CP/kg DM; L). Lactational dietary treatments were the supply ad libitum of either diet H (HHH) or diet L (LLL) for the first 12 d of lactation, or diet L transferring to diet H on either day 6 (LHH) or 9 (LLH) of lactation. On days 1, 6, 9 and 12 of lactation, rats from each group (n > or = 6) were used to estimate mammary dry mass, fat, protein, DNA and RNA; the activities of lactose synthetase (EC 2.4.1.22) enzyme and Na+,K(+)-ATPase (EC 3.6.1.37) were also measured. Rats offered a diet considered protein sufficient (H) from day 1 of lactation showed a decrease in mammary dry mass and fat but an increase in DNA, RNA and protein on day 6, after which there was no further change, except for mammary protein which continued to increase. However, rats offered diet L showed a steady loss in mammary mass and fat throughout the 12 d lactation period and no change in mammary DNA, RNA or protein. Rats previously protein restricted for either the first 6 or 9 d of lactation had their mammary dry mass and mammary fat loss halted and showed a rapid increase in mammary DNA, RNA and protein on re-alimentation. Lactose production in group HHH, as measured by lactose synthetase activity, was similar on days 1 and 6 of lactation, after which a significant increase was seen. Protein-restricted rats showed no change in lactose synthetase activity during the 12 d experimental period. Changing from diet L to diet H led to a significant increase in lactose synthetase activity to levels comparable with those offered diet H from day 1. These results show that rats offered a protein-restricted diet during lactation suffer mammary underdevelopment, but this may be rapidly reversed by re-alimentation with a high-protein diet.

Effect of season of birth on milk, fat, and protein production of Israeli Holsteins

The effects of birth month on production of milk, fat, and protein and percentages of fat and protein were analyzed based on production records of 101,653 first parity, 77,541 second parity, and 51,856 third parity Israeli Holstein cows. Each parity was analyzed separately. The analysis model also included the effects of herd-year, DIM, calving age, and calving month. First parity Type III sums of squares for birth month were nearly as large as those for calving month but decreased for later parities. Similar results were obtained using multiplicative models in which the dependent variables were the logarithms of the production traits. The effects of calving month and birth month were not similar, but birth month had similar effects for milk, fat, and protein production. Production was lowest by cows born in the early spring and highest by cows born in the fall. Analyses of the log-transformed traits showed that the F values for calving month were greater than, and the F values for birth month were nearly identical to, the F values for the untransformed trait analyses. The physiological basis for these trends was not clear.

Influence of prepubertal dietary regimen on mammary growth of Holstein heifers

One hundred-sixteen Holstein heifers (mean BW, 175 kg) were randomly assigned to diets of alfalfa silage or corn silage and were fed to gain approximately 725 or 950 g/d in order to study the influence of prepubertal diet and rate of gain on mammary growth and milk production. Blood was collected before puberty for hormone determination, and 8 heifers per group were killed at puberty for evaluation of tissue variables. Serum growth hormone was reduced, and IGF-I was increased, in the group of heifers reared at a high rate of gain on the corn silage diet. Accompanying the decline in growth hormone, total mammary parenchymal DNA and RNA was reduced in heifers reared at a high rate of gain on the corn silage diet. Mammary parenchyma in heifers of the latter group contained a greater volume of adipocytes and a lower volume of epithelial cells than did mammary parenchyma in heifers of other groups. Data are consistent with previous investigations that showed a deleterious effect of prepubertal rapid weight gain on mammogenesis when accompanied by excess body fat deposition. However, this effect did not cause a decline in subsequent milk production.

Mastitis in dairy heifers: initial studies on prevalence and control

Initial studies to determine the prevalence of mastitis in heifers of breeding age and in pregnant dairy heifers demonstrated that IMI were present in 97% of heifers and 75% of quarters. The most common isolates were Staphylococcus aureus, Staphylococcus hyicus, and Staphylococcus chromogenes; SCC ranged from 12.4 to 17.3 x 10(6)/ml. Approximately 29% of heifers and 15% of quarters exhibited clinical mastitis at breeding age, as evidenced by clots or flakes in mammary secretions. Histologic examination of mammary tissues demonstrated significant reductions in alveolar epithelial and luminal areas and increases in connective tissue stroma and leukocytosis, illustrating limited development and marked inflammation of infected tissues. A one-time infusion of antibiotic for nonlactating cows into infected quarters > or = 45 d prepartum reduced incidence of IMI by 59% at calving compared with the pretreatment level; the cure rate for Staph. aureus IMI was > 90%. Prophylactic treatment of uninfected quarters > or = 45 d prepartum reduced new Streptococcus sp. IMI by 93%. The mean SCC was 50% lower at calving for treated heifers, and milk yield over the first 2 mo of lactation was 10% greater than that of untreated controls. Heifers from herds using fly control had a lower prevalence of IMI than herds without fly control. Prevalences of IMI and SCC in dairy heifers were higher than previously realized, but mastitis at calving was controlled by use of therapeutic products for nonlactating cows during pregnancy.

Evidence of a direct role for growth hormone (GH) in mammary gland proliferation and lactation

A panel of monoclonal antibodies to the growth hormone (GH) receptor/binding protein was used to demonstrate the existence and detail the expression of GH receptors in ductal and alveolar epithelial cells from rat and rabbit mammary glands by immunohistochemistry. Intense immunoreactivity was present in membrane, cytoplasm and some nuclei of epithelial cells during proliferation and lactation. Receptor expression decreased during weaning and was absent or weak in regressive mammary glands. Immunoreactivity was weak in ductal epithelial cells from virgin adult animals. Pronounced expression of GH receptor/binding protein was observed with two monoclonal antibodies and lesser reactivity was seen with others, paralleling their affinities for the receptor. The cytoplasmic presence of this putatively plasma membrane located GH receptor is accounted for by the existence of a soluble form on the GH receptor, namely the growth hormone binding protein derived from the membrane receptor by cleavage. Primary localization of the receptor in proliferating and lactating epithelial cells suggests that the rat and rabbit mammary gland is a GH target tissue. This finding is in contradiction to both classical GH action and the somatomedin hypothesis and challenges the widely held view that GH has no direct influence on mammary growth and function.