Culture Models to Investigate Mechanisms of Milk Production and Blood-Milk Barrier in Mammary Epithelial Cells: a Review and a Protocol

Mammary epithelial cells (MECs) are the only cell type that produces milk during lactation. MECs also form less-permeable tight junctions (TJs) to prevent the leakage of milk and blood components through the paracellular pathway (blood-milk barrier). Multiple factors that include hormones, cytokines, nutrition, and temperature regulate milk production and TJ formation in MECs. Multiple intracellular signaling pathways that positively and negatively regulate milk production and TJ formation have been reported. However, their regulatory mechanisms have not been fully elucidated. In addition, unidentified components that regulate milk production in MECs likely exist in foods, for example plants. Culture models of functional MECs that recapitulate milk production and TJs are useful tools for their study. Such models enable the elimination of indirect effects via cells other than MECs and allows for more detailed experimental conditions. However, culture models of MECs with inappropriate functionality may result in unphysiological reactions that never occur in lactating mammary glands in vivo. Here, I briefly review the physiological functions of alveolar MECs during lactation in vivo and culture models of MECs that feature milk production and less-permeable TJs, together with a protocol for establishment of MEC culture with functional TJ barrier and milk production capability using cell culture inserts.

Amiata donkey body conformation, udder characteristics, and their relationship with milk yield and quality

To date, no selective actions have been taken to improve milk traits in dairy donkeys, and the characteristics of the udder are not well defined in relation to the productive characteristics. This study aimed at increasing knowledge on Amiata dairy donkey body conformation, udder traits, and their relationship with milk yield and quality. Morphological, udder, and teat measurements and milk evaluations of 45 pluriparous jennies were carried out. The average wither height of the jennies was 126 cm and the chest girth was 148 cm; a large standard deviation of some body measurements was found. Forty-nine percent of the animals showed a moderately developed udder, while most of the jennies had symmetrical half-udders (96%) and the intermammary cleft was clearly visible in 53% of subjects. Correlation analysis indicated that bigger animals tend to have bigger udders, higher teat diameter, and greater distance between teat tips. A positive correlation between the teat length and the milk fat was found ( p < 0.01), which suggests that jennies with longer teats have a better ability to release milk fat. The results of this paper may be useful to define the characteristics of the milking device and address selective choices of the animals.

Effects of short and long milking intervals on milking characteristics and changes of milk constituents during the course of milking in crossbred Istrian × Awassi × East-Friesian ewes

The main objective of this experiment was to evaluate the effects of two milking intervals (8 and 16 h) on milk constituents (fat, protein, lactose, dry matter, and log10 SCC) of nineteen Istrian × Awassi × East-Friesian crossbred ewes in different milk fractions (0-25, 25-50, 50-75 and 75-100%) during the course of milking and in machine stripping (MS) milk. Furthermore, we sought to determine the effect of the two milking intervals on milking characteristics (average milk flow rate, peak milk flow rate, machine-on time, total milk yield, and milk production rate) and whether each milk constituent within each milking interval is best described by a linear, quadratic, or cubic function. Average milk flow rate and milk yield per milking decreased in the 8 h milking interval compared to the 16 h milking interval (P < 0.05). Peak milk flow rate, machine-on time, and milk production rate were not different between the two milking intervals. Overall, milk fat content, dry matter content, and log10 SCC increased in the 8 h milking interval compared to the 16 h milking interval (P < 0.05). Milk protein content did not change through the main milk fractions at either milking interval. Milk lactose content did not change through the milk fractions at the 8 h milking interval, whereas it decreased in the 75-100% and stripping milk fractions at the 16 h milking interval (P < 0.05). The 0-25% and stripping milk fractions contained the highest log10 SCC compared to all other milk fractions (P < 0.05). Changes of milk fat and dry matter content throughout milking were best described by quadratic functions, whereas milk protein content, milk lactose content, and log10 SCC were best described by different functions depending on the milking interval. These results demonstrate that milking interval influenced all milk constituents in various milk fractions during the course of ewe milking. Moreover, milking characteristics such as average milk flow and total milk yield, and the appropriate mathematical function to characterize milk constituents throughout a milking, were affected by milking interval.

Uneven milking intervals are adequate to achieve the benefits of increased milking frequency in early lactation

Increasing milking frequency (MF) increases milk yield (MY) and farm profit, and optimal milking intervals (MI) prevent milk production decline. The objective of this experiment was to compare the MY effect of even and uneven 4 times daily (4×) MI in early lactation under increased MF. Fourteen multiparous and 6 primiparous cows were milked using unilateral frequent milking, with right udder halves milked 4× and left udder halves milked 2 times daily (2×) for 20 d in early lactation starting on d 5 postpartum. Ten (7 multiparous and 3 primiparous) cows were allocated evenly based on parity and assigned to either the even or the uneven MI groups distinguished by intervals of 9:3:9:3 h or 6:6:6:6 h. The left and right udder halves were milked at 0100 and 1300 h. The right udder glands were additionally milked at 0400 and 1600 h for the uneven MI group and at 0700 and 1900 h for the even MI group. Milk from each udder half was weighed and sampled for components on the final day of treatment and at 60, 120, 180, 240, and 300 d in milk. The overall effect of 4× milking on the right udder halves was a 5.96 ± 0.70 kg/d increase in MY on d 21 of unilateral frequent milking compared with the 2× udder halves. This elevated MY continued through 300 d in milk and averaged 1.56 ± 0.70 kg/d. Increased MF in early lactation increased the udder half difference in total yield throughout a 300-d lactation by 508 kg for milk, 25 kg for milk fat, and 15 kg for milk protein. Increased MF in early lactation increased milk component yields, but there were no differences between MI groups. The lack of treatment difference may be beneficial to farmers. The ability to achieve the same increased MY effect with uneven MI may optimize labor efficiency because early-lactation cows could be milked at the beginning and end of milking sessions. Farmers would not have to add additional milking sessions to achieve the enhanced MY response regardless of normal milking session length.

Suppression of prolactin and reduction of milk secretion by effect of cabergoline in lactating dairy ewes

The effects of cabergoline, an ergot derivative and dopamine receptor agonist, were investigated in 30 ewes of 2 dairy breeds (Manchega; MN, n = 15; Lacaune; LC, n = 15). Ewes were in a similar late-lactation stage, but differed in milk yield according to breed (MN vs. LC, 1.02 ± 0.03 vs. 2.27 ± 0.05 kg/d). Treatments consisted of a single intramuscular injection of cabergoline at different doses per ewe. Cabergoline doses (per ewe) were: low (0.56 mg), high (1.12 mg), and control (CON; 0 mg; 1 mL of saline). Milk yield was recorded daily (d -14 to 25), milk and blood were sampled, and udder traits were measured from d -2 to 14 after injection. No local reaction at the injection site, nor behavior and metabolic indicators of the ewes were detected after the cabergoline injection, but milk yield fell rapidly in both breeds (MN vs. LC, -54% vs. -27%) when compared with CON ewes. Cabergoline effects progressively disappeared after d 5, and no milk yield differences between treatments were detected from d 8 to 25 after injection. Milk fat and protein contents increased similarly (22% and 23%; respectively) in both breeds and at both cabergoline doses until d 5, and the effects disappeared thereafter. Plasma prolactin (PRL) decreased dramatically in the low- and high-treated ewes the day after injection when compared with the CON ewes, and reached values below the detection limit of the assay between d 1 and 5, increasing similarly thereafter. On d 14, PRL values were 58% greater in the low- and high-treated than in the CON ewes, showing that PRL concentrations rebounded when the cabergoline effects ceased. Total udder volume correlated with milk accumulated in the udder (r = 0.77) of all groups of ewes throughout the experiment, suggesting its use as a noninvasive method for the estimation of milk stored in the udder. Udder volume was similar for the low and high ewes, but both values were lower than those of the CON ewes from d 1 to 14 after injection. No other effects on udder size were detected. Cabergoline dramatically inhibited PRL secretion and decreased milk yield and udder volume of lactating dairy ewes. The low dose of cabergoline was as effective as the high dose in the 2 breeds of dairy ewes. These results suggest the use of cabergoline to facilitate the decrease of milk production in dairy ewes (e.g., dry-off, illness care), although further research in pregnant dairy ewes and during the following lactation is still needed.

Invited review: Accelerating mammary gland involution after drying-off in dairy cattle

Bovine mammary gland involution, as a part of the reproductive cycle in dairy cows, is a very important remodeling transformation of the mammary gland for the subsequent lactation. There is considerable incentive to accelerate mammary gland involution to improve udder health, shorten the dry period, and simplify the management process by reducing dietary changes. The complex process of mammary involution is characterized by morphological changes in the epithelial cells and mammary tissue, changes in the composition of mammary secretions, and changes in the integrity of tight junctions. Involution is facilitated by elements of the immune system and several types of proteases and is coordinated by various types of hormones. This review first describes the involution process and then argues for the need to accelerate it. Last, this review focuses on various intervention methods for accelerating involution. Our aim is to provide a comprehensive overview of bovine mammary gland involution as well as potential techniques and new opinions for dry cow management.

Effect of milking frequency and α-tocopherol plus selenium supplementation on sheep milk lipid composition and oxidative stability

The aim of this research was to study the effect of milking frequency [once-daily milking (ODM) vs. twice-daily milking (TDM)] and antioxidant (AOX) supplementation on fatty acid (FA) profile and oxidative stability in sheep milk. Sixteen Assaf ewes were used; 8 did not receive any vitamin-mineral supplement (control), and the other 8 received an oral dose of 1,000 IU of α-tocopherol and 0.4 mg of Se daily. The experiment consisted of 2 consecutive periods; the first was 3 wk with TDM of both mammary glands. The second period was 8 wk and consisted of ODM of one mammary gland and TDM of the other gland. All ewes were fed ad libitum the same total mixed ration from lambing and throughout the experiment. There were no differences in plasma or milk Se concentrations between control and AOX ewes. However, plasma and milk α-tocopherol concentrations and AOX capacity were increased in ewes receiving the AOX supplement. Milk FA profile was practically unaffected after 21 d of AOX supplementation. However, after 77 d, AOX supplementation increased the relative percentage of C16:0 and cis-9 C18:1 and reduced the proportions of some saturated FA with less than 16 carbons and cis-9 C12:1. Antioxidant supplementation had no effect on the proportions of conjugated linoleic acid or total polyunsaturated FA (PUFA) but decreased the proportion of trans-7,cis-9 C18:2 and increased that of n-6 C20:3. Once-daily milking did not affect α-tocopherol, Se, or fat resistance to oxidation in milk. Total monounsaturated FA, cis-9 C16:1, and several cis and trans isomers of C18:1 were increased and total saturated FA were decreased in milk from ODM glands. Compared with TDM, ODM increased the proportions of cis-9,cis-12 C18:2 and several isomers of C18:2 and reduced those of cis-9,cis-12,cis-15 C18:3 and some PUFA of 20 and 22 carbons, but total proportion of PUFA was unaffected. Once-daily milking and AOX supplementation modified milk FA profile, but the effects of ODM could be considered of little biological relevance for consumer health. Supplementing ewes with α-tocopherol plus Se could be considered an effective strategy to improve plasma AOX status and reduce milk fat oxidation without substantial changes in the milk FA profile.

The effect of extended milking intervals (24, 48 and 72 h) on milk yield, milk composition, mammary physiology and welfare traits in dairy ewes

The majority of the work today regarding the effects of extended milking intervals has focused on dairy cattle and only to a limited extent on dairy goats and sheep. The aim of this study was to investigate the effect of different non-milking intervals on milk yield and composition, mammary physiology and welfare indices in dairy ewes. Thirty-six multiparous ewes in late lactation were allocated to one of four groups of nine and subjected to 24, 48 or 72 h of non-milking or normal milking interval (12 h) (group A, B, C and D, respectively). Data showed that there were no significant differences in milk yield among the experimental groups during the third day after re-milking. Furthermore, no significant differences in milk lactose, protein and fat concentration among the experimental groups were observed after 7, 14 and 21 d of re-milking, respectively. Non-milking for 72 h resulted in a temporary increase of sodium concentration, Na + /K + ratio and enzymatic activities of plasmin (PL), plasminogen (PG) and plasminogen activator (PA) in milk. However, these parameters had similar values among the experimental groups on day 5 after re-milking. The concentration of lactose in blood was also significantly increased as a result of the 72 h non-milking interval and returned to its initial levels the second day after re-milking. These data, taken together, suggest that early involution events that occurred as an effect of non-milking were fully reversible within a short period of time. Finally, no significant signs of welfare impairment were observed in ewes due to extended milking intervals. In conclusion, non-milking up to 72 h had no negative effects on milk yield and composition, mammary physiology and welfare parameters in dairy ewes.

Relationship of mammary gland health status and other noninfectious factors with electrical conductivity of milk in Manchega ewes

Measuring the electrical conductivity (EC) of milk during milking has been extensively studied in cattle as a low-cost mastitis detection method that can be easily automated. The aim of this work was to study the effect of the health status of the glands and several noninfectious factors (lactation stage, milking session, and lactation number) that affect the use of EC measurement of milk to detect mastitis in dairy sheep livestock. Likewise, we studied the relation between EC and milk composition (macrocomposition and mineral content) and between EC and somatic cell count (SCC). Finally, we evaluated the use of EC thresholds as a mastitis detection method. To this end, we monitored the glandular milk EC throughout 2 consecutive lactations, during which 42 and 40 ewes were controlled, respectively. We carried out 7 biweekly checks, analyzing the EC, SCC, composition, and mineral content of glandular milk at morning and evening milkings. Before the morning milking, samples were aseptically collected for bacteriological analysis, and the results along with the SCC were used to classify the glands according to their sanitary status (healthy, latently infected, or infected). Lactation stage, parity, milking (morning or evening), health status, and the interactions of parity with health status, lactation stage with health status, and parity with lactation stage all had a significant effect on SCC and EC of the milk. The correlation between EC and SCC was only significant when all the data were analyzed jointly (r = 0.33) and for SCC ≥ 600.000 cells/mL (r = 0.25). The changes in milk composition, mainly in fat content, largely explained the variation in EC (R² = 0.69). For the same EC threshold, the specificity and sensitivity varied depending on the parity or the milking, with the negative predictive value obtained being higher than the positive predictive value at all times. We concluded that developing methods of detecting mastitis in sheep by milk EC readings would require consideration of noninfectious factors that also affect the gauging of EC. One option to consider would be individualized daily monitoring of the glands, as demonstrated in other species such as cattle and goat.

The effect of lactational mastitis on the macronutrient content of breast milk

AIMS

Mastitis in lactating mothers reduces milk production and alters the cellular composition of milk. Changes occurring in the mammary gland during the inflammatory response are believed to increase the permeability of the blood-milk barrier. This study examined the effect of mastitis during lactation on the macronutrient content of breast milk.

METHODS

The study was conducted at Zekai Tahir Burak Maternity Teaching Hospital. Transitional breast milk samples were obtained from term lactating mothers with or without mastitis. Milk protein, fat, carbohydrate, and energy levels were measured using a mid-infrared human milk analyzer.

RESULTS

The study recruited 30 term lactating mothers: 15 mothers diagnosed with mastitis and 15 healthy mothers. The characteristics of the mothers in both groups were similar. Fat, carbohydrate, and energy levels were statistically lower in the milk samples of mothers with mastitis compared with the mothers without mastitis.

CONCLUSION

Lactational mastitis was associated with lower breast milk fat, carbohydrate, and energy levels. The local inflammatory response induced by cytokines and increased blood-milk barrier permeability might account for the changes in the fat, carbohydrate, and energy levels of human milk.

The effects of parity, litter size, physiological state, and milking frequency on the metabolic profile of Lacaune dairy ewes

Effects of parity (primiparous, PRIM vs multiparous, MULT) and litter size (singletons, SING vs twins, TWIN) on metabolic profiles from 1 wk before lambing to the end of lactation were studied in 48 Lacaune dairy ewes reared in confinement during most of the year and grazed on improved pastures at the end of lactation (summer). Another group of 48 ewes was incorporated during the milking period (ie, from 1 wk after weaning), to measure the effects of milking frequency (1 vs 2 milkings per day) on intake, milk production and composition, and body energy usage. Thus, in a 2 × 2 × 2 factorial design, ewes (n = 96) were allocated to homogeneous groups according to body weight (BW) and body condition score (BCS) and were monitored from late pregnancy to late lactation as a function of parity (PRIM, n = 48; MULT, n = 48), litter size (LSi) (SING, n = 40; TWIN, n = 56) and daily milking frequency (FREQ; milked once, ONE; n = 48; or twice, TWO; n = 48). Individual BW, BCS, plasma metabolites, and metabolic hormones were measured regularly (ie, 9 consecutive sampling dates). The BW was higher in MULT but no differences because of LSi or FREQ were detected at the intra-parity group level. The BCS was higher in MULT and in ewes with SING throughout the experiment. The latter was related to the demands for body reserves mobilization, as expressed by higher nonesterified fatty acids and β-hydroxybutyrate concentrations in ewes with TWIN from late pregnancy to weaning (35 d postpartum) in both PRIM and MULT ewes. This was consistent with higher insulin in MULT and higher triiodothyronine, leptin and insulin-like growth factor 1 in ewes with SING during this period. Differences in energy balance because of FREQ were evident after interpretation of plasma nonesterified fatty acids, glucose, insulin, and leptin concentration during the milking period. At similar feed intakes, ewes in ONE were in positive balance with regard to TWO. Overall, clear effects of parity, LSi, physiological states, and FREQ on metabolic profiles were found because of differences in nutrient partitioning when combining these experimental factors. Without considering FREQ, changes in metabolic measures in milking period were marginal compared with the periparturient adjustments performed until weaning to compensate energy deficiencies.

How does the milk removal method affect teat tissue and teat recovery in dairy ewes?

The aim of this work was to study how machine milking (MM) carried out in suitable conditions affects teat wall thickness and teat canal length and their return after milking to pre-milking conditions, in comparison with other milk extraction methods considered biological referents: lamb suckling (LS), milk removal by catheter (RC) and hand milking (HM). Three Latin square experiments were designed, using 11 ewes in the first experiment (LS), 13 in the second (RC) and 12 in the third (HM). Each of the Latin squares was divided into two periods: in the first, the left gland of each animal was machine milked and the corresponding treatment (LS, RC and HM) was applied to the right gland. Subsequently, in the second period the extraction methods were interchanged. During the experimental period, 4 sampling days were carried out (2 in each experimental period), where ultrasound scans were taken before (B) and immediately after milking (A) and at 1 (1 h), 2 (2 h), 3 (3 h), 4 (4 h), 6 (6 h), 8 (8 h) and 10 (10 h) hours after milking finished. Teat wall thickness (TWT), teat wall area (TWA), teat end area (TEWA) and teat canal length (TCL) were measured in all the ultrasound images. MM increased TWT after milking compared with RC. TWT, TWA, TEWA and TCL were lower (P<0.05) in HM than in MM. No significant differences (P>0.05) were found between LS and MM for any variable. The extraction method affected the recovery time of the variables, with total teat recovery at 6 h after RC and 4 h after HM. In the case of LS, the TEWA and TCL values were recovered sooner, as of 3 h. Teat recovery time after MM was similar to the extraction method with which it was compared in each experiment. Thus, considering the similar increase in wall thickness and their recovery time compared with the reference methods, it was concluded that machine milking, carried out in optimum conditions and respecting the time interval between milkings usually applied on sheep farms (8-12 h), would not affect teat integrity. Moreover, given the variability observed in teat thickness recovery time between the different experiments, further research should be carried out to study which factors intrinsic and extrinsic to the animal may affect the teat wall thickness and recovery time after machine milking.

Effect of sunflower oil supplementation and milking frequency reduction on sheep milk production and composition

The aim of this study was to investigate the effects of milking frequency reduction and dietary lipid supplementation on intake, BW, and milk yield and composition in high yielding dairy ewes. Ten lactating Assaf ewes were allocated into 2 experimental groups (n=5). Ewes were fed alfalfa hay ad libitum and 34 g·kg(-1) of BW of a concentrate feed with either 0 (Control group) or 43 g of sunflower oil·kg(-1) of DM (SO group). The experiment lasted 63 d and consisted of 3 periods. During Period 1 (from d 1 to 21), ewes were milked twice a day. During Period 2 (from d 22 to 49), ewes were unilaterally milked, so that each gland of each ewe was milked either once or twice daily. During Period 3 (from d 50 to the end of the experiment), both udder halves were again milked twice daily. Intake, BW, and milk composition were controlled weekly and milk production from each half udder was recorded twice a week. Total DM intake, BW, and milk yield in Period 1 were not significantly (P>0.10) affected by dietary treatments. Milk yield tended to be increased in the ewes fed the SO diet in periods 2 (P=0.093) and 3 (P=0.067). Oil supplementation (SO diet) significantly (P<0.05) decreased milk protein and total solids concentrations in the 3 experimental periods and fat content in Period 3, and tended (P=0.077) to decline fat content in Period 2. Lactose content and somatic cell count (SCC) were unaffected (P>0.10) by dietary lipid supplementation in any of the experimental periods. There were no significant (P>0.10) differences between half udders in milk yield and composition in Period 1, and in SCC in any of the experimental periods. Fat and total solids contents were unaffected (P>0.10) by reducing milking frequency. Nevertheless, milk protein content was increased (P<0.001) when glands were milked only once daily whereas milk yield and lactose content were decreased (P=0.001). The interaction between gland and diet was significant for lactose in Period 2, suggesting a greater effect of milking frequency reduction on tight junctions in Control ewes. In fact, the ratio between glands for milk yield was significantly (P<0.05) greater in SO (0.82) than in Control (0.72) ewes. In Period 3, this ratio increased but it was still lower in Control ewes (0.92 vs. 0.78, P<0.05). Thus, milking frequency reduction and SO supplementation seem to have counteracting effects on milk production and composition. Our results suggest that SO-supplemented ewes have a better capacity of adaptation to changes in milking frequency, probably due to processes induced in the mammary gland.

Use of milk epithelial cells to study regulation of cell activity and apoptosis during once-daily milking in goats

Generally, once-daily milking (ODM) decreases milk yield. This effect may be the consequence of a decrease in mammary epithelial cell (MEC) activity or a reduction in their number. The aim of this study was to determine the effect of ODM on the synthetic activity and rate of apoptosis of MEC using a non-invasive method. Eight Alpine goats were subjected to ODM or twice-daily milking for two 5-week periods. MECs were purified by centrifugation and immunocytochemical binding in milk after 1 and 5 weeks of each period. mRNA levels of some proteins involved in lactose and milk protein synthesis and in apoptosis were evaluated using real-time PCR. Isolation of MEC from milk was a useful method to investigate transcriptional regulation in a timeline study. ODM induced greater decreases in milk, lactose and protein yields after 1 week than after 5 weeks. This suggests an adaptation of the mammary gland to ODM, which reduces the inhibitory effect of this practice. Reductions in milk component yields were associated with lower α-lactalbumin transcripts, suggesting a transcriptional decrease of lactose synthesis during ODM. Glucose transporter GLUT1 transcripts were downregulated under ODM, suggesting that lactose precursor uptake by MEC might be involved in the regulation of lactose synthesis. κ-Casein mRNA levels tended to be lower during ODM. ODM increased levels of the pro-apoptotic transcript Bax after both 1 and 5 weeks, but no variation was observed in the Bax/Bcl-2 ratio. ODM affected cell synthetic activity through transcriptional regulation and may have induced apoptosis. The reduction of the negative effect of ODM on milk yield suggests that Alpine goats are able to adapt to ODM. Further studies are needed to investigate the effect of ODM on MEC turnover.

Effect of reduction of milking frequency and supplementation of vitamin E and selenium above requirements on milk yield and composition in Assaf ewes

The aim of this research was to study the effect of milking frequency and supplementation with a vitamin-mineral complex above requirements on intake, body weight (BW), and milk yield and composition in high-yielding Assaf ewes. Sixteen lactating Assaf ewes were used in this study, separated into 4 groups of 4 ewes each. Animals in 2 of the groups (control groups) did not receive any extra vitamin-mineral supplement, whereas animals in the other 2 groups (supplement groups) received daily an oral dose of 1g of vitamin E (1,000 IU, DL-α-tocopherol acetate) and 0.4 mg of selenium (sodium selenite anhydrous). The experiment consisted of 2 consecutive periods of 3 wk (twice-daily milking in both mammary glands) and 8 wk (once-daily milking in one mammary gland and twice-daily milking in the other gland). Intake, BW, and milk composition were controlled weekly, and milk production was recorded 3 times a week. Administration of the vitamin-mineral supplement had no effect on dry matter intake, BW, or milk production and composition. The reduction of milking from twice to once a day caused a decrease in milk production and lactose concentration and a significant increase in protein concentration, total solids, and somatic cell count, without affecting the fat content. Administration of a vitamin E and Se supplement at the doses used in the present study does not seem to exert, in the short term, a noticeable effect on the mammary gland when milking frequency is reduced.

Lactation curve and effects of milking regimen on milk yield and quality, and udder health in Martina Franca jennies (Equus asinus)

Three experiments were conducted on Martina Franca jennies. Experiment 1 tested Wood's model for evaluating the lactation curve. Data from the entire lactation period of 12 jennies were used. The results showed that Wood's model was able to recognize the shape of the lactation curve from pooled data (r(2) = 0.11; P < 0.01), with the lactation peak occurring at 48 d. Individual curves showed wide variability. Experiment 2 aimed to evaluate the effects of the daily number of milkings (1, 3, or 6) and the interval between the separation of foals from dams and milking (2 or 3 h) on milk yield and udder health. Four groups of jennies (n = 5) were considered: 1 × 3H, milked once per day (1×) with a 3-h interval from the time of foal removal (3H) from the dams to mechanical milking (3-h interval); 3 × 3H, milked 3 times per day with 3-h intervals; 3 × 2H, milked 3 times per day with 2-h intervals; and 6 × 2H, milked 6 times per day with 2-h intervals. The milk somatic cell count (SCC) was monitored. Better efficiency was observed for 3 vs. 1 milking per day and for 3-h vs. 2-h intervals. The regimen of 6 daily milkings at 2-h intervals did not increase milk yield and was related to an increase in the SCC compared with 3 daily milkings. In Exp. 3, the effects of the interval from foal removal to milking (3, 5, or 8 h) on yield, gross chemical composition, organoleptic characteristics of the milk, and udder health of the jennies were evaluated. The effects of milking time were also evaluated. Twenty jennies milked twice daily (2×) were subdivided into 4 groups (n = 5): 2 × 3H, with milkings at 1200 h and 1900 h and an interval of 3 h; 2 × 5H, milked at 1200 h and 1900 h with a 5-h interval; 2 × 8H(1), milked at 1200 h and 2200 h with an 8-h interval; and 2 × 8H(2), milked at 0700 h and 1900 h with an 8-h interval. Milk yield was greater by 28.4% when an 8-h interval was used compared with a 3-h interval and at the morning vs. the evening milking. The milk yield per milking was greatest at 0700 h, indicating the existence of a circadian rhythm in milk secretion processes. Intervals of 5 and 8 h caused significant decreases in the fat and lactose content and organoleptic characteristics of the milk, whereas an 8-h interval led to an increase in the SCC. In conclusion, a milking regimen of twice-daily milking at 0700 h and 1900 h with an 8-h interval provided the maximum yield per day. In terms of milk quality, a 3-h interval yielded the best results.

Short communication: Effect of estrogen supplemented at dry-off on temporal changes in concentrations of lactose in blood plasma of Holstein cows

The objective was to determine the effect of supplemental estrogen (estradiol cypionate, ECP) at dry-off on temporal changes in concentrations of lactose in blood plasma of Holstein cows as an indicator of rate of mammary involution. Thirty-two Holstein cows (8/group) were assigned randomly to 4 treatment groups: 30-d dry, 30-d dry + ECP, 60-d dry, and 60-d dry + ECP. A single injection (7.5 mL) of cottonseed oil (30- and 60-d dry) or ECP (15 mg) in oil (30- and 60-d dry + ECP) was administered intramuscularly at dry-off. Blood samples were collected from the coccygeal vein of all cows 24 h before dry-off and at dry-off, and then 8 samples were collected throughout the subsequent 48 h to monitor concentrations of lactose in blood plasma. No significant effects of ECP on the overall mean concentrations of lactose were detected. Concentrations of lactose increased and were greatest in blood collected 20 h (520.4 +/- 54.1, 268.1 +/- 48.2, 345.0 +/- 52.3, 418.4 +/- 49.8 microM, for the 4 treatment groups respective to the order listed above) after supplemental ECP and final milk removal. At 40 h, concentrations approached those observed 24 h before dry-off (140.5 +/- 52.1, 57.6 +/- 47.1, 90.1 +/- 51.4, 61.2 +/- 48.4 microM, respectively). Concentrations of lactose at 20 h were positively correlated with milk yield of cows at dry-off. Similar temporal profiles of lactose in blood plasma of cows supplemented or not with ECP indicated that ECP at dry-off did not markedly alter the course of tight junction leakage that typically occurs in mammary epithelial tissue during progressive early involution when milk removal is discontinued.

Long- and short-term effects of omitting two weekend milkings on the lactational performance and mammary tight junction permeability of dairy ewes

The long- and the short-term effects of omitting 2 milkings weekly in early (wk 8 to 14) and mid lactation (wk 15 to 22) were investigated in an experiment conducted with a total of 58 dairy ewes (40 Manchega and 18 Lacaune). Ewes submitted to 2 milking omissions were milked twice daily from Monday to Friday (0800 and 1800 h), and once daily on Saturday and Sunday (1600 and 1400 h, respectively). Individual data were collected for milk yield (weekly), milk composition (biweekly), and somatic cell count (SCC; monthly). Omitting 2 milkings per week in early lactation tended to decrease milk yield in Manchega ewes (-15%), whereas no effects were observed in Lacaune ewes. Averaged milk composition was not modified by milking omissions in either breed. Milking omissions in late lactation did not affect milk yield and milk composition in either breed. The SCC were unaffected by milking omissions in both breeds and in both stages of lactation. A sample of 22 Manchega and 11 Lacaune ewes were used to evaluate the short-term (daily) effects of the 2 milking omissions per week on milk yield and composition, udder health, and tight junction permeability, both in early lactation (wk 12) and in mid lactation (wk 20). Milking omission decreased milk yield, milk fat, and milk lactose contents on the first omission day in both breeds, with losses being more noticeable in early lactation than in mid lactation. Milk protein content and SCC did not vary by effect of the weekend milking omissions. After restoring the twice-daily milking routine on Monday, milk yield showed a compensatory increase that was greater in the large-cisterned than in the small-cisterned ewes, which allowed milk yield to return to Friday values in both breeds. Milk fat content increased during Sunday and Monday, reestablishing Friday values thereafter in both breeds. Weekend milking omissions in early lactation caused tight junction leakiness in both breeds, but mammary epithelia adapted to extended milking intervals when applied successively, recovering their tight state after milking. In mid lactation, the mammary tight junction showed leakiness only in Manchega ewes. In conclusion, 2 milkings per week could be omitted with no negative effects on milk yield, milk composition, and milk SCC values in large-cisterned dairy ewes, as observed in Lacaune and large-cisterned Manchega ewes. Losses in milk yield could be reduced if milking omissions were done from mid lactation in small-cisterned ewes.

Evaluation of udder cisterns and effects on milk yield of dairy ewes

Nine Manchega (0.94 L/d) and 10 Lacaune (2.07 L/d) ewes at the same stage of lactation (90 d in milk) were used to study the interbreed differences in milk yield, mammary morphological traits, and machine-milking ability. Udder traits were measured after 6 h of udder filling before the start of the experiment. Cisternal area (by ultrasonography), cisternal milk (by teat cannula drainage), and alveolar milk (by machine milking after an intravenous oxytocin injection) were randomly measured 8 h after milking for 2 wk consecutively either with an intravenous injection of an oxytocin receptor blocking agent (atosiban, AT) or without (control, C) to avoid the occurrence of milk letdown before milking. Lacaune ewes had greater udder depth (22.5 +/- 0.9 vs. 19.6 +/- 0.9 cm) and cistern height (27.1 +/- 3.8 vs. 15.6 +/- 3.5 mm), whereas Manchega ewes had longer (42.7 +/- 1.5 vs. 32.7 +/- 1.5 mm) and wider teats (17.4 +/- 0.5 vs. 13.9 +/- 0.5 mm). Values per half udder for Manchega and Lacaune ewes differed in cisternal area (12.8 +/- 0.7 and 23.7 +/- 0.6 cm(2)) and cisternal milk (120 +/- 0.6 and 269 +/- 0.5 mL), but not in alveolar milk (95 +/- 0.5 and 102 +/- 0.4 mL), respectively. Cisternal area and cisternal milk were positively correlated (r = 0.79). Ratios between cisternal and alveolar milk were 56:44 and 73:27 for Manchega and Lacaune ewes, respectively. Cisternal milk volumes obtained with the AT or C treatment were similar in Manchega (111 +/- 10 vs. 122 +/- 8 mL) but differed in Lacaune ewes (239 +/- 8 vs. 299 +/- 8 mL), respectively. Consequently, alveolar milk with AT vs. C was similar in Manchega (104 +/- 8 vs. 86 +/- 7 mL) but different in Lacaune ewes (115 +/- 7 vs. 89 +/- 7 mL). Results of this experiment confirm the need for the use of an oxytocin-blocking agent for accurate evaluation of milk contained in the udder of dairy ewes. Moreover, despite the differences in daily milk yield, alveolar milk did not vary between breeds, emphasizing the role of the cisternal more than the alveolar compartment for maximizing daily milk secretion in dairy sheep.

Changes in alveolar and cisternal compartments induced by milking interval in the udder of dairy ewes

The aim of this work was to evaluate the effects of milking interval (4, 8, 12, 16, 20, and 24 h) on cisternal size and milk partitioning (cisternal and alveolar) in the udders of dairy ewes. Twenty-four dairy ewes (Manchega, n = 12; Lacaune, n = 12) were used in a 2-wk experiment during mid-lactation. Cisternal and alveolar milk yields were measured and milk samples from each udder fraction were collected for analysis. Cisternal milk was obtained after i.v. injection of an oxytocin receptor antagonist, and alveolar milk was obtained after i.v. injection of oxytocin. Enlargement of the cisternal compartment due to milking intervals was measured by ultrasonography for each half udder. Volumes of cisternal and alveolar milk differed according to breed, being greater in Lacaune (888 +/- 43 and 338 +/- 25 mL, respectively) than in Manchega ewes (316 +/- 43 and 218 +/- 25 mL, respectively). Alveolar milk increased linearly to 16 h in Manchega and 20 h in Lacaune and remained constant thereafter. Cisternal milk accumulated linearly to 24-h milking intervals in both breeds. Cisternal area (values per udder half) increased as milking interval increased, reaching a plateau at 20 h in Manchega (21 +/- 1 cm(2)) and 16 h in Lacaune (37 +/- 1 cm(2)). Correlation between cisternal area and cisternal milk was the greatest at 8 h (Manchega: r = 0.70 and Lacaune: r = 0.56). Cisternal area correlated with total milk (r = 0.80). Milk fat content varied markedly with milking intervals, increasing in alveolar milk (until 12 h in Manchega, 8.90 +/- 0.18%; and 20 h in Lacaune, 8.67 +/- 0.19%) and decreasing until 24 h in cisternal milk (5.74 +/- 0.29% and 4.85 +/- 0.29%, respectively). Milk protein content increased in alveolar milk until 24 h (Manchega, 6.46 +/- 0.11%; Lacaune, 5.95 +/- 0.11%), but did not vary in cisternal milk. Milk lactose content only decreased at the 24-h milking interval in the cisternal milk of Manchega ewes (4.60 +/- 0.04%). In conclusion, our results suggest that cisterns play an important role in accommodating secreted milk during extended milking intervals. Thus, long milking intervals could be a recommended strategy for large-cisterned dairy sheep. Evidence indicates that ultrasonography provides accurate estimations of udder cistern size and could be used as an indicator for selecting large-cisterned dairy ewes.