Relationships Between Gastrointestinal Permeability, Heat Stress, And Milk Production in Lactating Dairy Cows

Heat stress (HS) is a global issue that decreases farm profits and compromises animal welfare. To distinguish between the direct and indirect effects of HS, 16 multiparous Holstein cows approximately 100 d in milk were assigned to one of 2 treatments: pair fed to match HS cow intake, housed in thermoneutral conditions (PFTN, n = 8) or cyclical HS (n = 8). All cows were subjected to 2 experimental periods. P1 consisted of a 4 d thermoneutral period with ad libitum intake. During P2, the HS cows were housed in cyclical HS conditions with a temperature humidity index (THI) ranging from 76 to 80 and the PFTN cows were exposed to a constant THI of 64 for 4 d. DMI of the PFTN cow was intake matched to the HS cows. Milk yield, milk composition, rectal temperature, and respiration rate were recorded twice daily, blood was collected daily via a jugular catheter, and cows were fed twice daily. On d 3 of each period, Cr-EDTA and sucralose were orally administered and recovered via 24 h total urine collection to assess gastrointestinal permeability (GIP). All data were analyzed using the GLIMMIX procedure in SAS. The daily data collected in P1 was averaged and used as a covariate if deemed significant in the model. HS decreased voluntary intake by 35% and increased rectal temperature and respiration rate (38.4 vs 39.4°C and 40 vs 71 respirations/min, respectively). HS reduced dry matter intake (DMI) by 35% which accounted for 66% of the decrease in milk yield. The yield, and not concentration, of milk protein, fat, and other solids were lower in the HS cows on d 4 of P2. Milk urea nitrogen (MUN) was higher and plasma urea nitrogen (PUN) tended to be higher on d 3 and d 4 of HS. Glucose was 7% lower in the HS cows and insulin was 71% higher in the HS cows than the PFTN cows on d 4 of P2. No difference in lipopolysaccharide binding protein (LBP) was observed. HS cows produced 7 L/d more urine than PFTN cows. No differences were detected in the urine concentration or percentage of the oral dose recovered for Cr-EDTA or sucralose. In conclusion, HS was responsible for 34% of the reduction of milk yield. The elevated MUN and the tendency for elevated PUN indicate a whole-body shift in nitrogen metabolism. No differences in GIP or LBP were observed. These results indicate that, under conditions of this experiment, activation of the immune system by gut derived lipopolysaccharide was not responsible for the decreased milk yield observed during HS.

Form of calf diet and the rumen. I: Impact on growth and development

Preweaning diet is known to affect rumen tissue appearance at the gross level. The objectives of this experiment were to investigate effects of different preweaning diets on the growth and development of the rumen epithelium and on putative rumen epithelial stem and progenitor cell measurements at the gene and cell levels. Neonatal Holstein bull calves (n = 11) were individually housed and randomly assigned to 1 of 2 diets. The diets were milk replacer only (MRO; n = 5) or milk replacer with starter (MRS; n = 6). Diets were isoenergetic (3.87 ± 0.06 Mcal of metabolizable energy per day) and isonitrogenous (0.17 ± 0.003 kg/d of apparent digestible protein). Milk replacer was 22% crude protein, 21.5% fat (dry matter basis). The textured calf starter was 21.5% crude protein (dry matter basis). Water was available ad libitum and feed and water intake were recorded daily. Putative stem and progenitor cells were labeled by administering a thymidine analog (5-bromo-2'-deoxyuridine, BrdU; 5 mg/kg of body weight in sterile saline) for 5 consecutive days and allowed a 25-d washout period. Calves were killed at 43 ± 1 d after a 6 h exposure to a defined concentration of volatile fatty acids. We obtained rumen tissue from the ventral sac and used it for immunohistochemical analyses of BrdU (putative stem and progenitor cells) and Ki67 (cell proliferation), gene expression analysis, and morphological measurements via hematoxylin and eosin staining. Epithelial stem and progenitor cell gene markers of interest, analyzed by real-time quantitative PCR, were β1-integrin, keratin-14, notch-1, tumor protein p63, and leucine-rich repeat-containing G protein-coupled receptor 5. Body growth did not differ by diet, but empty reticulorumens were heavier in MRS calves (MRS: 0.67 ± 0.04 kg; MRO: 0.39 ± 0.04 kg). The percentage of label-retaining BrdU basale cells was higher in MRO calves than in MRS calves (2.0 ± 0.3% vs. 0.3 ± 0.2%, respectively). We observed a higher percentage of basale cells undergoing proliferation in MRS calves than in MRO calves (18.4 ± 2.6% vs. 10.8 ± 2.8%, respectively). Rumen epithelial gene expression was not affected by diet, but the submucosa was thicker in MRO calves and the epithelium and corneum/keratin layers were thicker in MRS calves. Presumptive stem and progenitor cells in the rumen epithelium were identifiable by their ability to retain labeled DNA in the long term, changed proliferative status in response to diet, and likely contributed to observed treatment differences in rumen tissue thickness.

Form of calf diet and the rumen. II: Impact on volatile fatty acid absorption

Diet is known to affect rumen growth and development. Calves fed an all-liquid diet have smaller and less developed rumens and a decreased ability to absorb volatile fatty acids (VFA) compared to calves fed both liquid and dry feed. However, it is unknown how rumens respond when challenged with a defined concentration of VFA. The objective of this study was to assess the effects of 2 different feeding programs on VFA absorption in preweaned calves. Neonatal Holstein bull calves were individually housed and randomly assigned to 1 of 2 diets. The diets were milk replacer only (MRO; n = 5) or milk replacer with starter (MRS; n = 6). Diets were isoenergetic (3.87 ± 0.06 Mcal of metabolizable energy per day) and isonitrogenous (0.17 ± 0.003 kg/d of apparent digestible protein). Milk replacer was 22% crude protein, 21.5% fat (dry matter basis). The textured calf starter was 21.5% crude protein (dry matter basis). Feed and ad libitum water intakes were recorded daily. Calves were exposed to a defined concentration of VFA buffer (acetate 143 mM, propionate 100 mM, butyrate 40.5 mM) 6 h before euthanasia on d 43 ± 1. Rumen fluid samples were obtained every 15 to 30 min for 6 h to measure the rate of VFA absorption. Rumen tissues were obtained from the ventral sac region and processed for morphological and immunohistochemical analyses of the VFA transporters monocarboxylate transporter 1 (MCT1) and 4 (MCT4). Body growth did not differ between diets, but empty reticulorumens were heavier in MRS than MRO calves (0.67 vs. 0.39 ± 0.04 kg) and MRS calves had larger papillae areas (0.76 vs. 15 ± 0.08 mm²). We observed no differences between diets in terms of the abundance of MCT1 and MCT4 per unit area. These results indicate that the extrapolated increase in total abundance of MCT1 or MCT4 in MRS calves was not due to increased transporter density per unit area. Modeled VFA absorption metrics (flux, mmol/h, or 6 h absorbed VFA in mmol) were not different across diets. These results demonstrate that the form of calfhood diet, whether solely MR or MR and starter, does not alter VFA absorption capacity when the rumen is exposed to a defined concentration of VFA at 6 wk of age.

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.

Excess deposition of collagen in mammary glands of tamoxifen-treated Holstein heifers is associated with impaired mammary growth

It is established that the ovary and estrogen are essential to bovine mammary development with the onset of puberty. Recent studies have shown that ovariectomy in the very early prepubertal period, well before onset of puberty, also dramatically impairs mammary growth. Similarly, prepubertal heifers treated with the antiestrogen tamoxifen (TAM) also exhibit markedly impaired mammary growth in correspondence with reduced estrogen receptor α (ESR1) expression. Our objective was to evaluate the effect of TAM on the mammary stroma and specifically to determine if the reported decrease in mammary development was related to changes in TAM-induced alterations in the stroma surrounding the mammary parenchyma. Briefly, 16 Holstein heifers calves were randomly assigned to one of 2 treatment groups: TAM-injected or control. Calves were administered TAM (0.3 mg kg¹ d¹) or placebo from 28 to 120 d of age. At day 120, calves were euthanized and udders removed. Mammary tissue from near the boundary between the parenchyma and surrounding mammary fat pad was collected for histology and morphometric analysis, expression of selected extracellular matrix-related genes, and quantitation of stromal collagen deposition by study of Sirius Red-stained tissue sections imaged with polarized light. Compared with tissue from control heifers, TAM heifers frequently exhibited areas with abundant fibroblasts and mesenchymal cells especially within the intralobular stroma, as well as less complex ductal structures. Among the array of extracellular matrix-related genes tested, only a small difference (P < 0.05) in expression of laminin was found between treatments. The relative tissue area occupied by stromal tissue was not impacted by treatment. However, the deposition of collagen within the stromal tissue was more than doubled (P < 0.0001) in TAM-treated heifers. These data suggest that blocking ESR1 expression with TAM allows for excessive collagen deposition in the stroma surrounding the developing epithelial structures and that this interferes with both the degree of overall mammary parenchymal development, as well as the pattern of normal ductal morphogenesis.

Technical note: p40 antibody as a replacement for p63 antibody in bovine mammary immunohistochemistry

Tumor protein 63 (p63) is a nuclear antigen found in basal epithelial cells. To date, 10 isoforms of p63 have been identified, falling into 2 major groups identified by presence or absence of an N-terminal transactivation domain (TAp63 and ΔNp63, respectively). Literature suggests that ΔNp63 is the predominant form expressed in basal epithelial cells and myoepithelial cells (MYEC). The mouse anti-p63 antibody, clone 4B1E12, has been used as a specific nuclear marker for bovine MYEC. Unfortunately, this antibody is no longer commercially available. A new mouse monoclonal antibody, clone BC28, specific to ΔNp63 (designated p40) has been developed. We hypothesized that the p40 antibody would be an appropriate substitution as a MYEC and epithelial basal cell marker. An array of archived formalin-fixed, paraffin-embedded bovine tissues were subjected to immunohistochemical staining for either p40 or p63, with a subset being dual stained for direct comparison. Positive staining for p40 and p63 was observed in serial sections of mammary, skin, rumen, salivary gland, ureter, and bladder. As predicted, negative staining for p40 and p63 was observed in testis and intestine. Dual staining for p40 and p63 in calf mammary (n = 4), lactating mammary (n = 4), rumen (n = 4), and skin (n = 4) showed nearly 100% agreement. Thus, we established that the mouse monoclonal antibody, clone BC28, is a suitable replacement for anti-p63, clone 4B1E12, as a marker of MYEC and basal epithelial cells in bovine tissues.

Short communication: Does early-life administration of a Megasphaera elsdenii probiotic affect long-term establishment of the organism in the rumen and alter rumen metabolism in the dairy calf?

Megasphaera elsdenii is a bacterial species of the rumen that can utilize lactate to produce butyrate, a key volatile fatty acid often implicated in driving calf rumen development. Because lactate is abundant in the rumen of young calves, administration of M. elsdenii to increase butyrate production and thus promote calf rumen development is an appealing possibility. The main objective of this study was to determine whether M. elsdenii administration to calves via oral drench at 14 d of age affected its long-term establishment at 70 d postadministration. Ruminal volatile fatty acid and lactate profiles and blood glucose and β-hydroxybutyrate concentrations were also examined to determine potential influence on rumen metabolism. Six neonatal Holstein heifer calves were blocked on d 1 by body weight (41.3 ± 1.8 kg) and total serum protein (5.23 ± 0.16 g/dL) and assigned to either the M. elsdenii (n = 3) or control (n = 3) treatment groups. On d 14, calves in the M. elsdenii group orally received 25 mL of a commercially available M. elsdenii suspension, whereas calves in the control group received 25 mL of the same product that had been autoclaved. Rumen contents and blood samples were collected weekly from each animal until 84 d of age. The oral administration of M. elsdenii at 14 d did not increase the abundance of M. elsdenii 70 d postdosing, alter rumen fermentation, or change blood metabolites associated with butyrate. These results suggest that a single administration of the M. elsdenii probiotic may not affect the rumen establishment of the organism.

Growth, intake, and health of Holstein heifer calves fed an enhanced preweaning diet with or without postweaning exogenous estrogen

Research has shown that changes in nutrition both before and after weaning can affect mammary development. Additionally, estrogen is known to be a potent mammogenic stimulant. Our objectives were to determine effects of altered preweaning feeding and exogenous estradiol postweaning on growth, intake, and health. Thirty-six Holstein heifer calves were reared on (1) a restricted milk replacer (MR) diet fed at 0.44kg powder dry matter (DM)/day [R; 20.9% crude protein (CP), 19.8% fat, DM basis], or (2) an enhanced MR fed at 1.08kg powder DM/d (EH; 28.9% CP, 26.2% fat, DM basis). The MR feeding was reduced 50% during wk 8 to prepare for weaning. Starter was offered after wk 4 but balanced between treatments. Body weight and frame were measured weekly with intakes and health monitored daily. At weaning, a subset of calves were slaughtered (n=6/diet). Enhanced-fed calves had greater carcass, thymus, liver, spleen, and mammary gland (parenchyma and mammary fat pad) weights. The EH calves also had greater average daily gain (ADG) starting during wk 1 (0.36 vs. -0.06kg/d) and lasting through wk 7 (1.00 vs. 0.41kg/d). Remaining calves received estrogen implants or placebo and were slaughtered at the end of wk 10, creating 4 treatments: (1) R, (2) R + estrogen (R-E2), (3) EH, and (4) EH + estrogen (EH-E2). Postweaning ADG was similar between R, EH, and EH-E2 calves, but greater in R-E2 calves than E calves. The EH-E2 calves had the heaviest mammary glands, and R-E2 calves had heavier mammary glands than R calves. The EH calves consumed more MR DM, CP, and fat preweaning. The R-fed calves consumed more starter DM preweaning. Fecal score was greater for EH calves (1.74 vs. 1.50) preweaning, but days medicated did not differ. Fecal scores were lower for R-E2 calves postweaning. Improved preweaning feeding of calves increased body weights and frame measures. Differences in body weights remained postweaning. Enhanced-fed calves showed greater ADG during the preweaning period but not postweaning. Exogenous estrogen may elicit diet-dependent growth responses. Analysis of collected samples will allow determination of cellular and molecular processes responsible for the marked differences in mammary development observed.

Tamoxifen impairs prepubertal mammary development and alters expression of estrogen receptor α (ESR1) and progesterone receptors (PGR)

Research has shown that prepubertal heifers experience allometric mammary growth that is influenced by the ovaries. Our purpose was to determine the role of estrogen in prepubertal mammary gland development. Sixteen Holstein calves were randomly assigned to 1 of 2 treatment groups: tamoxifen-injected (TAM) or control (CON). Calves were administered the antiestrogen tamoxifen (0.3 mg kg(1) d(1)) or placebo from 28 to 120 d of age. At 120 d, calves were euthanized and udders removed. Weight and DNA content of trimmed parenchymal tissue were halved (P ≤ 0.0001) in TAM compared with CON calves. Parenchymal samples from 3 zones of the left rear mammary gland (lower, middle, and outer regions) were processed for immunohistochemical staining for estrogen receptor α (ESR1) and progesterone receptor (PGR), Ki67-positive cells, and 5-bromo-2'-deoxyuridine label retaining cells (LRCs). Overall, neither the percentage nor location within the epithelial tissue layer of either ESR1- or PGR-positive cells was impacted by TAM treatment. However, image analysis indicated a 6.2-fold lower (P = 0.0001) level of ESR1 protein expression in TAM calves. Similarly, messenger RNA expression of ESR1 was also reduced (P = 0.0001) in TAM heifers. In contrast, expression of PGR protein was greater by 43% (P = 0.03) in TAM calves, but messenger RNA expression did not differ between treatments. Overall, TAM calves had a higher (P ≤ 0.03) percentage and density (cells per tissue area) of Ki67-positive cells. Irrespective of treatment, there were also more Ki67-labeled cells in the outer zones of the mammary gland (P ≤ 0.001). We were able to effectively use multispectral imaging to identify positive cells and quantify the expression of ESR1 and PGR protein. We also identified and counted the proportion of label retaining cells (LCR) (putative epithelial stem cells). We noted an overall 2.9-fold greater number of LRCs in TAM heifers and more LRCs in the outer sampling zones. This suggests that a cohort of LCR cells in TAM remained inactivated in comparison with CON heifers, which exhibited markedly increased growth of the mammary parenchymal tissue over the treatment period. These results suggest that the impacts of ovariectomy are partially explained by loss of ESR1 expression and/or estrogen receptor signaling in the prepubertal bovine mammary gland. The significance of mammary expression of PGR in control of prepubertal bovine mammary development remains unresolved.

Localization and quantitation of macrophages, mast cells, and eosinophils in the developing bovine mammary gland

Prepubertal mammary development involves elongation and branching of ducts and stromal tissue remodeling. This process is highly regulated and in mice is known to be affected by the presence of innate immune cells. Whether or not such immune cells are present or involved in bovine mammary development is unknown. For the first time, we determined the presence, location (relative to mammary ductal structures), and changes in numbers of eosinophils, mast cells, and macrophages in prepubertal bovine mammary tissue, and evaluated the effects of age, ovariectomy, and exogenous estrogen on numbers of each cell type. Chemical stains and immunofluorescence were used to identify the 3 cell types in formalin-fixed, paraffin-embedded mammary tissue from prepubertal female calves from 3 archived tissue sets. The ontogeny tissue set included samples of mammary tissue from female calves (n=4/wk) from birth to 6 wk of age. The ovary tissue set contained samples from ovary intact and ovariectomized heifers allowing us to investigate the influence of the ovaries on immune cells in the developing mammary gland in prepubertal heifers. Nineteen animals were intact or ovariectomized 30 d before sampling; they were 90, 120, or 150 d old at the time of sampling. A third tissue set, the estrogen set, allowed us to determine the effect of exogenous estrogen on innate immune cells in the gland. Eosinophils were identified via Luna staining, mast cells by May-Grunwald Giemsa staining, and macrophages with immunofluorescence. Key findings were that more eosinophils and mast cells were observed in near versus far stroma in the ontogeny and ovary tissue sets but not estrogen. More macrophages were observed in near versus far stroma in ontogeny animals. Eosinophils were more abundant in the younger animals, and fewer macrophages tended to be observed in ovariectomized heifers as compared with intact heifers and estrogen treatment resulted in a reduction in cell numbers. In summary, we show for the first time that innate immune cells are present in prepubertal bovine mammary tissue, localization varies by immune cell type, and abundance is related to proximity of epithelial structures and physiological state. We suggest a likely role for these cells in control of bovine mammary growth and ductal development.