Cisternal Milk Research Articles

The Influence of Selected Environmental Factors on the Number of Somatic Cells in Cistern and Alveolar Milk of Polish Holstein-Friesian Cows.

The aim of the study was to evaluate the influence of the milking phase on somatic cell count (SCC) in milk obtained from the cisternal and alveolar parts of udders of selected Polish Holstein-Friesian cows. The study also assessed the impact of other genetic and environmental factors on SCC variability in cisternal and alveolar milk, including: the individual cow, lactation stage, age of cow, production level, milking speed, fat-to-protein ratio, and milking type. The research included 15 cows of Polish Holstein-Friesian breed at different ages, lactation stages, and with varying daily milk yield. A total of 210 milk observations were conducted, including 105 for 1 min milking and 105 for 8 min milking. The results obtained in the study indicated that milk obtained during two different milking phases exhibited similar SCC levels (F for LOGSCC = 0.79). The average actual SCC in milk produced by 15 cows in 105 observations for 1 min milking was 219,000 cells/mL, while for 8 min milking it was 229,000 cells/mL. The results were inconclusive, suggesting that SCC in cisternal and alveolar milk must be influenced by factors other than the milking phase. The analysis of variance conducted for this purpose provided the basis for stating a highly statistically significant effect of the individual cow (F for LOGSCC = 147.9), lactation stage (F for LOGSCC = 54.64), age of cow (F for LOGSCC = 12.39), daily production level (F for LOGSCC = 34.49), milking speed (F for LOGSCC = 17.56), and fat-to-protein ratio (F for LOGSCC = 22.99) on the variability of characteristics defining SCC in milk. In summary, SCC is characterized by high variability, influenced by a range of environmental and genetic factors such as the individual cow, lactation stage, age of cow, milking speed, and dietary fat-to-protein ratio. The influence of milking phase (1 min or 8 min) and milking type (morning or evening) should be considered inconclusive based on the entire population studied. For half of the cows, SCC in cisternal milk was higher than in alveolar milk, while for the other half, the situation was reversed. Further observations are required to confirm the hypothesis regarding the extent to which cows' immunological response to bacterial infections is concentrated in the cisternal or alveolar part of the udder under national environmental conditions.

The impact of kit, environment, and sampling contamination on the observed microbiome of bovine milk.

In low-microbial biomass samples such as bovine milk, contaminants can outnumber endogenous bacteria. Because of this, milk microbiome research suffers from a critical knowledge gap, namely, does non-mastitis bovine milk contain a native microbiome? In this study, we sampled external and internal mammary epithelia and stripped and cisternal milk and used numerous negative controls, including air and sampling controls and extraction and library preparation blanks, to identify the potential sources of contamination. Two algorithms were used to mathematically remove contaminants and track the potential movement of microbes among samples. Results suggest that the majority (i.e., >75%) of sequence data generated from bovine milk and mammary epithelium samples represents contaminating DNA. Contaminants in milk samples were primarily sourced from DNA extraction kits and the internal and external skin of the teat, while teat canal and apex samples were mainly contaminated during the sampling process. After decontamination, the milk microbiome displayed a more dispersed, less diverse, and compositionally distinct bacterial profile compared with epithelial samples. Similar microbial compositions were observed between cisternal and stripped milk samples, as well as between teat apex and canal samples. Staphylococcus and Acinetobacter were the predominant genera detected in milk sample sequences, and bacterial culture showed growth of Staphylococcus and Corynebacterium spp. in 50% (7/14) of stripped milk samples and growth of Staphylococcus spp. in 7% (1/14) of cisternal milk samples. Our study suggests that microbiome data generated from milk samples obtained from clinically healthy bovine udders may be heavily biased by contaminants that enter the sample during sample collection and processing workflows.IMPORTANCEObtaining a non-contaminated sample of bovine milk is challenging due to the nature of the sampling environment and the route by which milk is typically extracted from the mammary gland. Furthermore, the very low bacterial biomass of bovine milk exacerbates the impacts of contaminant sequences in downstream analyses, which can lead to severe biases. Our finding showed that bovine milk contains very low bacterial biomass and each contamination event (including sampling procedure and DNA extraction process) introduces bacteria and/or DNA fragments that easily outnumber the native bacterial cells. This finding has important implications for our ability to draw robust conclusions from milk microbiome data, especially if the data have not been subjected to rigorous decontamination procedures. Based on these findings, we strongly urge researchers to include numerous negative controls into their sampling and sample processing workflows and to utilize several complementary methods for identifying potential contaminants within the resulting sequence data. These measures will improve the accuracy, reliability, reproducibility, and interpretability of milk microbiome data and research.

Decreased lactose percentage in milk associated with quarter health disorder and hyperketolactia, a proxy for negative energy balance, in dairy cows

Several studies have described variations in lactose content (LC) in dairy cows during udder quarter health disorder or negative energy balance (NEB). However, their joint effects on LC have never been described. This was the aim of a longitudinal observational study performed on 5 Quebec dairy farms using automatic milking systems. Quarter milk samples were collected every 14 d from 5 to 300 DIM. Quarter health status was described by combining SCC level (SCC- or SCC+: < or ≥100,000 cells/mL) and infectious status (Patho- or Patho+: presence or absence of pathogens on a milk culture). Cows with NEB in early lactation (DIM <70) were identified using milk β-hydroxybutyrate (BHB) content: 0.15 mM = BHB-; 0.15 - 0.19 mM = BHB+; > 0.19 mM = BHB++. A total of 14,505 quarter cisternal milk samples were collected from 380 lactating cows. The quarter LC was analyzed using a mixed linear regression model with the following fixed effects: quarter health status, parity, time interval between last milking and sampling, quarter milk yield (in kg/d), DIM, and herd. A random quarter intercept with a repeated measures correlation structure and a cow random intercept were also specified. The LC of SCC+ quarters was lower (-0.17 ± 0.013% pts) compared with LC of SCC- quarters for both primiparous and multiparous cows. Over the 162 bacterial species identified, only 8 species had a prevalence greater than 4.0%, and just 5 of them were associated with a reduction in LC: Staphylococcus aureus, Staph. chromogenes, Streptococcus dysgalactiae, Staph. epidermidis, and Staph. simulans. Cows identified as BHB+ and BHB++ in early lactation had a lower LC (-0.05 ± 0.019% and -0.13 ± 0.020% pts, respectively) compared with BHB- cows. For BHB++ cows, in both parity groups the decrease in LC (-0.20 ± 0.025% pts) was higher in SCC+ quarters compared with SCC- quarters. Moreover, the additive effect of the quarter health status and NEB on milk LC was greater with larger increases in BHB. Our findings highlight the necessity to jointly take into consideration both quarter health status and milk BHB concentration when using LC as a biomarker for NEB.

Milk production and anatomical udder capacity changes of udder halves subjected to increased milking frequency at two stages of lactation

This study aimed to characterize the effects of increased milking frequency (IMF) at early and mid-lactation on milk yield and its association with changes in cistern and alveolar capacity. Fourteen multiparous Holstein cows were subjected to IMF using the unilateral frequent milking method from 3 to 24 d in milk (DIM). At mid-lactation, cows were randomly assigned to 1 of 2 treatments: control or repeated. From 150 to 170 DIM, IMF treatment was reimposed in the repeated group. During IMF, left udder halves were milked 2× and right udder halves were milked 4× daily. To separate individual milk yields of udder halves, separate buckets were used to collect samples from each udder half. Milk samples and milk yield from right and left udder halves were collected on d 150, 170, 200, 230, 260, and 290 of lactation. Alveolar and cistern capacity were measured 26 h after the last milking at 140 and 172 DIM using an oxytocin inhibitor. Cistern and alveolar capacity were measured by evaluating the milk harvested after oxytocin inhibitor and oxytocin administration, respectively. Udder half difference yields were calculated by subtracting left half yield from right half yield. At 170 DIM, the udder half difference in repeated was 2.27 kg greater than the udder half difference in control. Udder halves milked 4× produced more milk and protein than 2× udder halves in the repeated group at 170, 200, 230, and 260 DIM. Cumulative (150 to 290 DIM) and carry over (200 to 290 DIM) udder half differences in milk yield were similar between the control and repeated treatments. Alveolar volume was similar between udder halves milked 2× or 4× at 140 DIM, while cistern volume was larger for udder halves milked 4× than 2× in early lactation. There was no difference between alveolar or cistern volume proportion in udder halves milked 2× or 4× before mid-lactation IMF. After 20 d IMF for the repeated group, alveolar volume was similar between control and repeated independent of udder half milking frequency. However, repeated held 4.9 kg more cistern milk than control. Control treatment udder halves had a greater alveolar proportion than repeated treatment udder halves. As expected, the cistern proportion was smaller in control and larger in repeated after mid-lactation IMF. IMF at early and mid-lactation enhances milk and protein yield largely during differential milking frequency regimens. The lack of enhancement in milk yield after IMF might be associated with a different response to IMF in the mammary gland at early versus mid-lactation. Based on our results, we conclude that udder halves subjected to early and mid-lactation IMF had increased cistern volume capacity.

Risk factors for delayed milk ejection in Holstein dairy cows milked 3 times per day

Delayed milk ejection, manifested most often as bimodal milk flow, occurs when the cisternal milk fraction is removed before the alveolar milk reaches the gland cistern. It is thought to be a consequence of not meeting cows' physiological needs, due to insufficient premilking teat stimulation, inadequate timing of milking unit attachment, or both. It has been associated with decreased milking efficiency, reduced milk yield, and impaired teat and udder health. Traditionally, portable electronic milk meters have been used to assess the presence of delayed milk ejection in dairy cows. By contrast, incremental milk flow rates from on-farm milk meters and their suitability as a measure to assess delayed milk ejection have not been studied by rigorous methods. The objectives were (1) to describe a protocol for identification of cows with chronically delayed milk ejection (CDME) and (2) to investigate risk factors for CDME using incremental milk flow rates obtained from automated on-farm milk meters. In a retrospective case control study, milk flow data from a 4,300-cow dairy with a thrice-daily milking schedule were obtained over a 1-wk period. Incremental milk flow rates (0-15 s, 15-30 s, 30-60 s, and 60-120 s) were used to identify cows with delayed milk ejection. Cases of CDME were defined as presence of delayed milk ejection at all 21 milking observations. Cows that had no delayed milk ejection at any of the same 21 milking observations were included as controls. A total of 171 cases and 393 controls were included in the study based on these criteria. A logistic regression model was used to evaluate associations of the following risk factors with CDME: parity (1, 2, ≥3), stage of lactation (<100, 101-200, >200 DIM), presence of a nonlactating quarter, milk somatic cell count, average daily milk production, and health and management events. Parity and CDME were associated such that compared with cows in their third or greater lactation, the odds (95% confidence intervals, 95% CI) of CDME were 1.27 (0.71-2.25) for cows in their first and 4.77 (2.47-9.22) for animals in their second lactation. The odds of CDME increased with increasing stage of lactation, with an odds ratio of 0.20 (0.11-0.36) for early and 0.28 (0.15-0.52) for mid-lactation animals, respectively, compared with late lactation cows. A 1-kg increase in average daily milk production was associated with decreased odds of CDME [odds ratio (95% CI): 0.89 (0.87-0.92)]. A lameness event during the study period increased the odds of CDME [odds ratio (95% CI): 8.04 (1.20-53.83)], as did a vaccination event 1 wk before the study period [odds ratio (95% CI): 4.07 (0.99-16.71)]. This study confirmed associations between CDME and previously reported risk factors and identified several previously less rigorously investigated health and management events that could be associated with CDME. Incremental milk flow rates from individual cows serve as an automated tool to evaluate milk flow dynamics. This information could be used to improve individual premilking udder preparation to meet the animal's physiological requirements, improve teat and udder health, and enhance parlor efficiency.

The effect of milking frequency on milk yield and milk composition in ewes

Milking frequency is the main factor regulating milk yield and milk quality if feeding, welfare, health, and environmental conditions are adequate. Milk yield and composition are substantially influenced by breed, and consequently the breed has an impact on both factors at a different frequency of milking. Further, the size of cisternal compartment plays an important role in accommodating secreted milk between milkings. Thus, ewes with large cisterns (i.e. large cisternal area, high cisternal milk percentage, and delayed tight junction opening during milk stasis) adapt themselves better to longer milking intervals than ewes with a small cistern. The increase of milking frequency from two to three times a day can lead to an increase of milk yield in the range of 3 to 36%. On the other hand, the reduction of milking frequency from twice to once a day can decrease milk yield from 9 to 67%. Two milkings per week could be omitted with no negative effects on milk yield, milk composition, and somatic cell count in ewes with large cisterns. However, besides the breed and cistern storage capacity, the results in literature show that the effects of milking frequency on milk yield and milk composition can vary according to the stage of lactation, individual animal, production level, practice of stripping, and duration of changed frequency. The right use of different milking frequency strategies can result in increased milk yield or in significant savings in labour and time spent in the milking parlour with negligible or no negative effects on milk yield and composition.

Understanding bovine mammary gland niches for staphylococci using different milk sampling techniques

Mastitis is usually caused by a bacterial intramammary infection (IMI) with Staphylococcus being the most commonly isolated genus. The standard method for diagnosing an IMI is to aseptically prepare the teat end and collect milk via the teat orifice into a sterile vial for bacterial culture. While this method has been advocated for decades, there has been debate about the importance of some bacteria isolated from such samples when the milk somatic cell count (SCC) in the mammary quarter is &lt; 200,000 cells/ml (threshold for a healthy mammary gland). Recently, Hiitio et al. (2016) showed that milk samples collected directly from the gland cistern were less likely to contain staphylococcal DNA when using a commercial PCR diagnostic test kit than milk samples that were collected via the teat orifice. Unfortunately, the PCR only differentiated staphylococci into Staphylococcus spp. and Staphylococcus aureus, and so it is unknown which of the nonaureus staphylococcal (NAS) species may be more likely to inhabit the teat canal than those that cause a true IMI. These data provide preliminary evidence that some staphylococci in milk may be teat canal inhabitants and not intramammary pathogens that cause mastitis. The objective of this study was to determine if some species of staphylococci isolated from milk are only isolated when the sample is collected through the teat orifice and absent in cisternal milk collected using the method described by Hiitio et al. (2016).

Oxytocin Induces Mammary Epithelium Disruption and Could Stimulate Epithelial Cell Exfoliation.

Mammary epithelial cells (MEC) are exfoliated from the epithelium into milk, influencing the number of MEC present in the udder. This process is associated with epithelium integrity. The release of oxytocin (OT) induced by milking causes myoepithelial cell contraction, which, in turn, may stimulate MEC exfoliation through mechanical forces. To investigate the role of OT in MEC exfoliation, we inhibited or induced myoepithelial cell contraction by injecting the OT receptor antagonist atosiban (Ato) or a supraphysiological dose of OT, respectively. Eight cows were assigned to 2 treatments during 2 milkings according to a crossover experimental design: Control+OT (cows were first milked to collect standard milk and then received 5IU of OT to collect residual milk through a second milking) and Ato + OT (cows were injected with Ato (50μg/kg of body weight) and milked to collect cisternal milk, then received 5IU of OT to collect alveolar milk through a second milking). Milk MEC were purified to determine their concentration and number in milk. Mammary epithelium integrity was assessed by measuring the kinetics of plasma lactose concentration. Inhibiting myoepithelial cell contraction by Ato injection decreased the number of exfoliated MEC in milk. In contrast, OT injection increased the concentration of MEC in the residual milk and the number of MEC in the alveolar milk. Ato injection reduced plasma lactose concentration, whereas, in both treatments, OT injections increased it. Our results suggested that myoepithelial cell contraction caused by OT could stimulate MEC exfoliation into milk and was associated with epithelium disruption.

Influence of sampling technique and bedding type on the milk microbiota: Results of a pilot study

The objective of this pilot study was to evaluate the influence of sampling technique and exposure to different bedding types on the milk microbiome of healthy primiparous cows. Primiparous Holstein cows (n = 20) with no history of clinical mastitis or monthly somatic cell counts >150,000 cells/mL were selected for this study. From each enrolled cow, a composite milk sample was aseptically collected from all 4 mammary quarters (individual quarter somatic cell counts <100,000 cells/mL), 1 individual quarter milk sample was collected using conventional aseptic technique, and 2 individual quarter milk samples were collected directly from the gland cistern using a needle and vacuum tube. All milk samples were cultured using standard milk microbiological techniques and DNA was extracted. Extracted DNA was subjected to PCR and next-generation sequencing for microbiota determination. All samples yielded relatively little total DNA. Amplification of PCR was successful in 45, 40, and 83% of composite, conventional, and cisternal samples, respectively. Bacteria were successfully cultured from 35% of composite milk samples but from none of the quarter milk samples collected using conventional or cisternal sampling techniques. Bacterial DNA sequences were assigned to operational taxonomic units (OTU) based on 97% sequence similarity, and bacterial richness and diversity were determined. Most samples were dominated by low-prevalence OTU and of the 4,051 identified OTU, only 14 were prevalent at more than 1% each. These included bacteria typically recovered from environmental sources. Chao richness was greatest in composite samples and was 636, 347, and 356 for composite, conventional quarter, and cisternal milk samples, respectively. Shannon diversity was similar among sample types and ranged from 3.88 (quarter) to 4.17 (composite). Richness and diversity did not differ by bedding type among cisternal samples, but the power of this pilot study was limited due to small sample size. Despite the small sample size, for milk samples collected from the gland cistern, overall bacterial community composition differed among bedding types. These results demonstrate that sampling technique and bedding type may be associated with the microbiota detected in bovine milk, and we suggest that these variables should be considered in designing and reporting studies about the milk microbiota.

Mammary epithelium disruption and mammary epithelial cell exfoliation during milking in dairy cows

The presence of mammary epithelial cells (MEC) in the milk of ruminants indicates that some MEC are shed from the mammary epithelium; however, the mechanisms that regulate the MEC exfoliation process are not known. Through the release of oxytocin, prolactin, and cortisol and through oxytocin-induced mechanical forces on the mammary epithelium, milking could participate in regulating the MEC exfoliation process. The aims of the present study were to determine the rate of MEC exfoliation throughout milking and to investigate its relationship to mammary epithelium integrity and milking-induced hormone release. Milk samples from 9 Holstein dairy cows producing 40.6 ± 1.36 kg of milk/d were collected at the beginning (after 1 and 2 min), in the middle, and at the end of milking. Milk MEC were purified using an immunomagnetic method. Blood samples were collected before, during, and after milking, and the oxytocin, prolactin, and cortisol concentrations in the samples were measured. Tight junction opening was assessed by plasma lactose concentration and the Na+:K+ ratio in milk. The somatic cell count in milk varied during the course of milking; it decreased at the beginning of milking and then increased, reaching the highest values at the end of milking. Exfoliated MEC were present in all milk samples collected. The presence of MEC in the milk sample collected during min 1 of milking, likely corresponding to the cisternal milk fraction, suggests that MEC were exfoliated between milkings. The observed increase in the Na+:K+ ratio in milk and in the plasma concentration of lactose indicated that disruption of mammary epithelium integrity occurred during milking. The MEC exfoliation rate at milking was not correlated with the variables describing milking-induced prolactin release but was negatively correlated with cortisol release, suggesting that cortisol may play a role in limiting exfoliation. In conclusion, milking induced a disruption of the mammary epithelial barrier. Mammary epithelial cells may be continuously exfoliated between milkings or exfoliated during milking as a consequence of the oxytocin-induced mechanical forces and the disruption of mammary epithelium integrity.

Influence of milk urea concentration on fractional urea disappearance rate from milk to blood plasma in dairy cows

The relationship between milk urea nitrogen (MUN; mg of N/dL) and urinary N excretion is affected, among others, by diurnal dynamics in MUN, which in turn is largely influenced by feed intake pattern and characteristics of urea transfer from blood plasma to milk and vice versa. This study aimed to obtain insight in urea transfer characteristics within the mammary gland and from the mammary gland to blood plasma in dairy cows at various concentrations of plasma urea nitrogen (PUN; mg of N/dL) and MUN. Urea transfer from milk to blood plasma and urea transfer within the mammary gland itself was evaluated in a 4×4 Latin square design using 4 lactating multiparous Holstein-Friesian cows (milk production of 39.8±4.70kg/d and 90±3.9 d in milk). Treatments consisted of 4 primed continuous intravenous urea infusions of 0, 5, 10, and 15g of urea/h. Boluses of [15N15N]urea were injected in cistern milk at 20, 60, and 100 min before the 1700h milking. Milk was collected in portions of approximately 2 L at the 1700h milking. Milk samples were analyzed for urea and enrichment of 15N-urea. Results from one cow were discarded because of leakage of milk from the teats after injection of boluses of [15N15N]urea. Increasing urea infusion rate linearly increased PUN from 11.4 (0g of urea/h) to 25.9mg/dL (15g of urea/h) and MUN from 10.3 (0g of urea/h) to 23.5 (15g of urea/h) mg of N/dL. The percentage of injected [15N15N]urea recovered from milk at the time of injection was not affected by urea infusion rate and varied between 65.1 and 73.0%, indicating that a substantial portion of injected [15N15N]urea was not accounted for by collected milk. The estimated fractional disappearance rate of 15N-urea from milk to blood (Kurea; per hour) linearly increased from 0.429 (0g of urea/h) to 0.641 per hour (15g of urea/h). Cistern injected [15N15N]urea diffused within 20 min after injection toward alveoli milk. Calculations with the average Kurea estimated in this study show that 89% of an initial difference between PUN and MUN will have disappeared after 4 h. In conclusion, urea disappearance from milk in the mammary gland is substantial, as well as the intramammary urea exchange between cistern, duct, and alveoli milk. However, results have to be interpreted with caution given the lack of full recovery of dosed 15N urea at time of injection. Information on Kurea is useful to quantify the effects of diurnal variation in PUN on MUN, which enhances the utility of MUN as an indicator for N excretion in urine.

Effect of milking interval on milk partitioning between udder compartments, milk yield and milk composition in Maghrebi dairy camels

Ten multiparous Maghrebi she-camels (Camelus dromedarius L.) were used to study the effects of 6 milking intervals (4, 8, 12, 16, 20 and 24h) at mid-late lactation (281±41 days in milk) on milk partitioning between udder compartments, milk yield and milk composition. Camels were kept in loose stalls, fed forage and concentrate, and hand milked twice-daily. Average milk yield during the experiment was 4.2±0.3l/day. Cisternal and alveolar milk were obtained by sequential milking, before and after inducing milk let-down with exogenous oxytocin, respectively. Udder cisterns volumes were measured by real-time ultrasonography before and after milk let-down. Backflow of milk from the cistern to the alveoli as consequence of udder elastic recoil was measured at 12-h milk interval by delaying milking for 90min after inducing milk let-down with oxytocin. On average, 44% of total milk volume was stored in the front udder quarters and 56% was stored in the rear udder quarters. Alveolar compartments accounted for 92% of milk volume and cisternal compartment for 8%. The volume of milk in the cistern (132±30ml) did not vary with increase in milking interval. Udder cisterns were visible by ultrasonography as small cavities that were dramatically engorged with milk after milk let-down. Milk secretion rate decreased linearly (ml/h=168.3−3.2 x; r2=0.90, P<0.05) upon increase of milking interval from 4 to 24h (from 168±28 to 105±10ml/h). Fat content in alveolar milk was 3.26±0.10% and protein content in alveolar milk was 3.39±0.08% .The content of fat and protein in the alveoli were greater across all milking intervals (P<0.05) than those measured in cisternal milk (2.22±0.10% for milk fat and 2.96±0.05% for milk protein). The concentration of fat and protein in milk decreased linearly with increase in milking interval (r2=0.98; P<0.05), except in the case of milk protein in cisternal milk, which did not change significantly with advancing milking intervals. Lactose concentration was steady across all milking intervals. A dramatic drop of milk secretion (62%) was observed when milking was delayed 90min after induced milk let-down, indicating the necessity of early milking after milk let-down. In conclusion, selection for large-cistern udders and twice-daily milking are recommended for improving the machine milking ability of this breed in order to increase its use for milk production.

Effects of manual udder stimulation on milk partitioning and flow traits during the machine milking in dairy camels (Camelus dromedarius)

A total of 9 multiparous dromedary camels in late stage of lactation (287±8 DIM; 3.8±0.8 kg/d) were used to study the effect of manual udder stimulation on machine milking efficiency of dairy camels under intensive management condition. Experimental design consisted of 3x3 Latin square with 9 animals allocated randomly and equally to 3 treatment (T1=60 s, T2=90 s and T3=120 s). All camels were machine milked twice daily. Milk yield and milk flow parameters were recorded by Lactocorder® milk meters. Udder health was evaluated by California mastitis test (CMT) and somatic cell counts (SCC). Cisternal milk was determined 14 h after milking using Atosiban®. Volumes of machine milk (MM), machine stripping milk (MSM) and residual milk (RM) were recorded in duplicate. No subclinical mastitis was detected during the experimental period as indicated by the CMT ( 25%). The increase of udder stimulation from T1 to T3 decreased (p<0.05) the lag time (LT) (3.83 to 2.24 sec) in camels of G1 and the MSM (26.6 to 14.8%) as well as RM (46.1 to 31.4%) in camels of G2. Bimodal curves tended (P=0.08) to decrease from 43.6% to 28.1% when duration of udder stimulation increased from T1 to T3 in camels of G2. In conclusion, increase duration of manual udder stimulation to 90–120 s ameliorate the machine milking efficiency in harder milked camels at late stage of lactation. (Resume d'auteur)

Evolution of udder morphology, alveolar and cisternal milk compartment during lactation and their relationship with milk yield in Najdi sheep

A total of 30 multiparous Najdi ewes were used to study the evolution of udder morphology traits and milk fractions in the udder during suckling (3rd, 6th, 9thwk) and milking (10th, 11th, 12thwk) periods. During suckling period, daily milk yield was estimated by using the double oxytocin injections method 4-h after milking. During milking period, ewes were hand-milked once daily. Udder and teat morphology traits for all ewes were measured 4-h after milking. Udder compartments were evaluated 8-h after milking by using atosiban and oxytocin; milk samples of each fraction were collected. Najdi ewes had a medium and healthy udders (CMT&lt;1), with medium sized teats (length, 3.2±0.1 cm and width, 1.7±0.1 cm) attached at 35.7 ± 11º angle. Milk yield averaged 1.88±0.18 and 0.44±0.12 L d-1 during suckling and milking periods, respectively. A drop in milk yield (-75%, p&lt;0.01) was found in the transition from suckling to milking. Udder traits, teats angle and width, and distance between teats declined (p&lt;0.05) throughout lactation, whereas teat lengths did not show any change. Positive correlations (p&lt;0.05) were observed between milk yield and udder depth (r=0.47-0.49), width (r=0.31-0.39) and distance between teats (r=0.26-0.39). The cisternal milk volumes decreased (p&lt;0.05) after weaning, whilst the corresponding percentages increased (p&lt;0.05). Cisternal milk accounted for 55% and 67% of the total udder milk during suckling and milking periods, respectively. Cisternal milk was positively correlated (r=0.93, p&lt;0.05) with total milk yield. The percentages of protein and total solids in alveolar and cisternal milk increased significantly (p&lt;0.05) after weaning, whilst fat percentages in cisternal milk did not change. In conclusion, the evaluated Najdi ewes showed medium sized cisterns and teats, which considered adequate for machine milking. Udder morphology traits had positive correlations with milk yield and hence, can be utilized in breeding programs.

Can vasopressin induce milk ejection in the dairy goat?

Suckling increases plasma levels of both oxytocin (OT) and vasopressin (AVP) and intravenous infusions of AVP increase milk flow and milk fat concentration in goats. We hypothesized that vasopressin can cause contraction of the myoepithelial cells and thereby milk ejection. Eight goats were used in each of two series. They were kept together with their kids and were both suckled and hand milked. At experiments, one teat was first emptied by hand and after 3min the same teat was milked again. On control days, cisternal milk (CM) was achieved at the first milking and at the second milking only a small volume of alveolar milk (AM) with modest fat content was received. On experimental days the goats were milked and immediately thereafter OT (10mg) or AVP at the low dose 125ng (AVPL) was injected intravenously followed by the second milking 3min after the first (series I). In series II saline (0.9% NaCl) or vasopressin at the high dose 250ng (AVPH) was injected. The plasma OT concentrations were unchanged after AVP injections. The CM volume did not differ between treatments within each series. Injections of AVPH or OT increased volume and fat content of AM. The proportion of AM to total milk volume was 15% in control experiments, 21% after saline and 29% after AVPL. However, after AVPH and OT the AM proportions were 56 and 57%, respectively, accompanied by an increased fat content. In conclusion, the high dose of AVP elicited a milk ejection reflex similar to that of OT.

Relationship between udder morphology traits, alveolar and cisternal milk compartments and machine milking performances of dairy camels (Camelus dromedarius)

A total of 22 dairy dromedary camels under intensive conditions in late lactation (275±24 days) were used to study the relationship between external and internal udder morphology and machine milking performances. Measurements of udder and teat morphology were obtained immediately before milking and in duplicate. Individual milk yield, lag time and total milking time were recorded during milking, and milk samples were collected and analyzed for milk composition thereafter. Cisternal and alveolar milk volumes and composition were evaluated at 9 h milking interval. Results revealed that dairy camels had well developed udders and milk veins, with medium sized teats. On average, milk yield as well as milk fat and protein contents were 4.80±0.50 L d-1, 2.61±0.16% and 3.08±0.05%, respectively. The low fat values observed indicated incomplete milk letdown during machine milking. Lag time, and total milking time were 3.0±0.3, and 120.0±8.9s, on average, respectively. Positive correlations (p&lt;0.05) were observed between milk yield and udder depth (r=0.37), distance between teats (r=0.57) and milk vein diameter (r=0.28), while a negative correlation was found with udder height (r=-0.25, p&lt;0.05). Cisternal milk accounted for 11% of the total udder milk. Positive correlations were observed between total milk yield and volume of alveolar milk (r=0.98; p&lt;0.001) as well as with volume of cisternal milk (r=0.63, p&lt;0.05). Despite the low udder milk storage capacity observed in dairy camels, our study concluded that the evaluated dromedary sample had adequate udder morphology for machine milking. Finally, positive relationships were detected between milk yield and udder morphology traits of dairy camels.

Short communication: Assessing urea transport from milk to blood in dairy cows

The concentration of urea in milk (MUC) has emerged as a potentially useful tool to predict urinary N excretion. Various factors may affect the relationship between MUC and urinary N excretion, including transport characteristics of urea from blood to milk and vice versa. The main objective of this study was to test whether substantial transport of urea from milk to blood exists in lactating dairy cattle. The subobjectives were (1) to assess the effects of various urea gradient levels between blood and milk on urea transport from milk to blood and (2) to test the occurrence of urea transport between different compartments of the mammary gland such as the cistern and the alveoli. Urea transport was studied in 2 multiparous lactating Holstein-Friesian cows (36.0±6.18kg of milk/d; mean ± SD). In 3 separate trials, boluses of [15N15N]urea were injected in the cisterns via the teat canals at 20, 60, and 120min before the 1700-h milking at various levels of MUC and of blood plasma urea concentration (PUC). In trial 1, a primed continuous infusion of urea (105g at the start, continuing with 20g/h) into the jugular vein started at 0500 h and stopped at 0, 1, 2, and 3h before the 1700-h milking on d 1, 2, 3, and 4, respectively. In trial 2, 5.5g of urea was injected into the cisterns at 20, 60, and 120min before the 1700-h milking on d 5, 6, and 7, respectively. In trial 3, urea fluxes were measured without an experimentally induced gradient between MUC and PUC on d 8, 9, and 10, respectively. During milking, successive milk samples were taken from first to last milk. Blood and milk were analyzed for 15N-urea enrichment. Levels of 15N-urea in blood increased after injection of a [15N15N]urea bolus in milk, indicating urea transport from milk to blood. Between 21.0 and 35.3% of injected [15N15N]urea in milk was recovered after 2h. The fractional [15N15N]urea decline rate in milk varied between 0.0076 and 0.0096/min. The level of MUC, rather than the concentration gradient between MUC and PUC, appeared to affect this fractional rate of decline. Enrichment levels of 15N-urea in milk samples within a single milking showed that urea was transported from cistern milk to alveoli milk. In conclusion, the results indicate that transport of urea from milk to blood in lactating dairy cattle occurs and that urea is transported from cistern milk to alveoli milk.

Relationship between mammary morphology traits and milk yield of Sicilo-Sarde dairy sheep in Tunisia

Sicilo-Sarde is a local breed from northern Tunisia resulting from crossing Sarda and Comisana dairy sheep and is traditionally used for cheese production after lamb weaning. A sample of 52 adult Sicilo-Sarde lactating ewes was used for studying their udder morphological traits and milk yield potential during weeks 4–8 (milking–suckling period) and 10 (milking period) of lactation. Daily milk yield was estimated on a daily basis by using the double oxytocin injection method 4 h after machine-milking at d 30 and 45. Udder and teat morphology were also measured at d 45 of lactation. Cisternal area (by ultrasonography) and udder compartments (cisternal and alveolar milk) were evaluated 8 h after milking by using atosiban and oxytocin on d 72 of lactation. Milk yield averaged 0.56 ± 0.10 L/d and ewes had small (volume, 496 ± 28 mL) and healthy udders (CMT, <1), with medium sized teats (length, 18.5 ± 4.9 mm; diameter, 10.0 ± 2.0 mm) attached at 45 ± 10°. A drop in milk production (49%) was found in the transition from suckling (day 30) to milking (week 10). Udder cisterns were multilocular and small sized (half udder area, 11.6 ± 4.5 cm 2), although cisternal milk accounted for 54% of the total milk in the udder. Correlation between cisternal milk and cisternal area was moderate ( R 2 = 0.48; P < 0.05). Lag time and total milking time were 1.9 ± 0.1 and 31 ± 5 s, respectively. In conclusion, the Sicilo-Sarde ewes evaluated showed medium sized cisterns and teats which were morphologically adequate for machine milking, although milk production needs to be improved.

The efficacy of milk ejection induced by luteal oxytocin as a method of early pregnancy diagnostics in cows

The aim of this research was to determine the accuracy and reliability of early diagnosis of pregnancy in cows using PGF2α analogue. Namely in the case of corpus luteum (CL) presence, the release of luteal oxytocin is induced by intravenous administration of a non luteolytic dose of PGF2α. The research was performed in 30 lactating cows, 18-22 days after insemination, and three hours prior to evening milking. A teat cannula is placed in the left fore-teat. When the cisternal milk flow ceased, Dinoprost (256 μg Dinolytic) was injected in the v. jugularis. If CL was present, the alveolar milk flow (559.4±83.7 mL) started 189±18 s later and early pregnancy could be presumed. If CL was no longer functional, the milk flow did not start again and the cow was considered not pregnant. Seventeen out of 30 cows were confirmed pregnant 35 days after insemination by ultrasound and 13 were found not pregnant. The accuracy of positive results is 100% and is identical to that obtained by ELISA of milk progesterone used as a reference method. The accuracy of negative results was lower (46.1% vs. 84.6%) (p<0.05), because seven out of 13 non pregnant cows has responded to the milk ejection test. In spite of this disadvantage, the test approved as being inexpensive, rapid, and easy to interpret and is therefore very applicable, especially under field conditions. It can be applied i.e. 20 days after insemination. Progesterone rapid test from milk or by milk ejection test can be used with similar accuracy.

Effects of milking interval and cisternal udder evaluation in Tunisian Maghrebi dairy dromedaries (Camelus dromedarius L.)

Effects of 4 different milking intervals (8, 12, 16, and 24h) on milk yield and milk composition were studied in Tunisian Maghrebi dairy dromedaries (n=6) at late lactation [240±14 days in milk (DIM), 5.84±1.62 L/d]. Camel-cows suckled their calves for 2 mo, were hand milked while suckling until mo 4 of lactation (calf weaning) and machine milked thereafter. Intravenous injection of oxytocin was administered before machine milking at each experimental milking to induce complete milk ejection and to avoid carryover effects of milking intervals. Cisternal and alveolar milk were measured at 380±16 DIM for a 24-h milking interval. Milk accumulated logarithmically (R2=0.95) in the udder from 8- to 24-h milking interval without reaching a plateau. Consequently, milk secretion rate decreased exponentially (R2=0.93) according to milking interval. Compared with 12-h milking interval (6.1 L/d), estimated daily milk yield was 113, 87, and 70% for 8-, 16-, and 24-h intervals, respectively. Total milk solids, milk fat content, and milk pH decreased with increasing milking interval, showing the greatest value at 8-h intervals (14.1±0.4%, 4.6±0.5%, and 6.66±0.05, respectively) and the lowest at 24-h intervals (12.3±0.9%, 2.9±0.6%, and 6.54±0.02, respectively). Milk protein (3.9±0.1%), lactose (4.5±0.2%), ash (0.84±0.01%) and density (1.028±0.01) remained constant for all milking intervals. Milk K, Ca, and Mg contents increased as milking interval increased, but Na content did not change (0.06±0.01%, on average). Milk Na:K ratio tended to decrease from 0.35 (1:2.9) to 0.22 (1:4.5) for the extreme milking intervals. Plasma lactose concentration steadied from 8- to 16-h (67±32 μmol) but increased dramatically at 24-h intervals (338±118 μmol), indicating that mammary tight junctions became permeable after 24h of milk accumulation. Camel udders showed small cisterns (19.3% of total milk in the udder at 24h) when compared with other dairy animals; we recommend the use of prestimulation for machine milking and selection for larger udder cisterns. Alveolar milk contained more fat (5.16 vs. 1.75%; SEM, 0.39%) and protein (3.23 vs. 2.73%; SEM, 0.15%) than cisternal milk. Despite the increase of plasma lactose during tight junction leakiness, the tendency for the Na:K ratio to decrease may be indicative of a camel's specific regulatory mechanism for controlling Na and K concentrations in milk and delaying the inhibitory effect of milk stasis on milk secretion rate. In conclusion, this short-term study proved the low storage capacity of the Tunisian Maghrebi camel udder but also showed their moderate ability to adapt to extended milking intervals at late lactation.