Review: Milking routines and cluster detachment levels in small ruminants.

Small ruminants not only differ on mammary gland anatomy, milk's properties and the amount of milk yielded comparable to those of dairy cattle, but also on the milking routine strategies and machine milking settings to maximize daily milk secretion. The udder compartment is proportionally larger in dairy sheep and goats, which requires modifications in the milking machine settings, milking procedures and allows the use of different milking strategies as they better tolerate extension of milking intervals. Depending on the breed, cisternal milk in goats varies from 70% to 90%, whereas in dairy sheep it varies from 50% to 78% of the total gland capacity. This explains why these species are commonly milked without pre-milking teat preparation, while in goats it is applied only in cases of high prevalence of intramammary infection in the herd. Recent French researchers observed that 40% of the goats presented an unbalanced udder as well as unbalanced morphology (21% to 30%) and functional milk flow (around 10% to 20% more) which could induce overmilking. In dairy sheep, selection for higher milk production increases teat angle insertion. Thus, to increase machine milk fraction, it is recommended to use either the 'Sagi hook' as an alternative for lifting up the 'pendulous' udder during milking or to perform machine stripping. There are three cluster removal strategies for small ruminants: manual, timed and milk flow driven automatic cluster removal (ACR). Automatic cluster removal reduces overmilking, improves teat condition, enables labour saving and provides a consistent milking routine in small ruminants. There are three to five main milk flow profiles in ewes and goats, which result in curves with one or two peaks (or plateau) and different patterns of the milk flow decreasing phase due to the degree of mammary gland imbalance and teat characteristics. When taking into account our current knowledge, ACR recommended take-off settings for goats are: 200 g/min+10 s delay time (DT) for a long decreasing phase or two plateau curves and 500 g/min+5 s DT for a short decreasing phase and one plateau curve. The ACR take-off settings for ewes are: 150 g/min +10 s DT for long decreasing phase and 200 g /min+5 s DT for a short decreasing phase. This review is intended to be useful for scientists and producers seeking basic knowledge of milking routines and cluster detachment settings for parlour performance and milk quality.

Adaptation of dairy cows to increasing degrees of incomplete milk removal during a single milking interval.

Milk accumulation in the udder decreases milk secretion and this effect is explained as well by the effects of the quantity of milk stored in the udder as by the duration and repetition of periods of milk stasis. This experiment aimed to better understand the underlying mechanisms of decreased milk yield in response to the specific effects of the quantity of milk stored in the udder, independent from storage duration, on milk yield and composition. Sixteen Holstein cows were assigned to 4 blocks of 4 cows in a 4 × 4 Latin square design using 7-d periods, with a 4-d sampling period and a 3-d washout period. Cows were milked twice daily at approximately 0700 and 1630 h throughout the trial. Treatments consisted of 4 degrees of milk removal (100, 70, 40, and 0%) applied at one morning milking, designated M0. Effects of the quantity accumulated were studied in relation to udder distension, via measurements of the total distance between the ends of the 4 teats, and cisternal capacity, via the evaluation of cisternal area by ultrasonographic scan at 1 and 9 h after M0. The effect of the quantity accumulated was also evaluated in relation to mammary epithelium permeability by determining plasma lactose concentrations 1 h before and 4, 7, and 10 h after M0. Leaving milk in the udder at M0 decreased milk production during the M0-M1 interval in a negative curvilinear manner. As a result, M0+M1 milk yield decreased or tended to decrease significantly by -1.3, -5.3, and -12.8 kg for the 70, 40, and 0% treatments compared with the 100% treatment (41.7 ± 1.26 kg/d), respectively. Negative carry-over effects on milk yield were observed until the M3 milking only for the 40 and 0% treatments, and no differences were observed between the effects of these treatments. The total distance between teats increased significantly but to decreasing degrees during the M0-M1 interval. For the 40 and 0% treatments, cisternal area, which was increased 1 h after M0 milking, exhibited no further increase during the M0-M1 interval, suggesting cisternal distension was close to maximum. Simultaneously, lactose concentrations increased in blood plasma for only these 2 treatments, and this increase occurred earlier for the 0% treatment. It was also observed that cows presenting the earliest increases in plasma lactose concentrations during milk accumulation lost more milk in response to extended milking intervals.

Role of ovarian secretions in mammary gland development and function in ruminants.

The mammary gland is a dynamic organ that undergoes cyclic developmental and regressive changes during the lifetime of a female mammal. Mammogenesis begins during embryonic life with the development of the first mammary gland rudiments and ductal system. After birth, during the pre-pubertal period, the ductal growth of the mammary parenchyma occurs through the fat pad. In most of the ruminant species allometric mammary parenchyma development begins with the onset of cyclic ovarian secretions activity. The two main hormones secreted during an ovarian cycle are estradiol and progesterone. These steroid hormones are derived from cholesterol and are synthesized by theca and granulosa cells in ovaries. During puberty, the mammary parenchyma develops in a compact, highly arborescent parenchymal mass surrounded by a dense connective matrix. Ductal elongation and lobulo-alveolar development are accomplished during growth and pregnancy to prepare for future milk production. At the end of lactation, the mammary gland undergoes involution, which corresponds to a regression of the secretory tissue, a reduction in the alveolar size and a loss of mammary epithelial cells (MECs). Ovarian steroids (estradiol and progesterone) appear to be key regulators of the different stages of mammogenesis and mammary function. Through this review, the role and the importance of ovarian steroids on mammary gland and on MECs is described.

Changes in mammary secretory tissue during lactation in ovariectomized dairy cows.

In dairy animals, the milk yield (MY) changes during a lactation and is influenced by several physiological, livestock management and environmental factors. The MY produced by a mammary gland depends on synthetic activity of mammary epithelial cells (MECs) as well as MEC number and mammary secretory tissue organization. It has been suggested that ovarian steroids (estradiol and progesterone) have a negative effect on MY in lactating cows. In a previous study, we showed that the suppression of ovarian secretions by an ovariectomy improved lactation persistency in dairy cows. Here we were interested in the effects of ovariectomy on plasma estradiol and progesterone concentrations and on changes that occur in mammary secretory tissue during lactation. We demonstrated that the ovariectomy of lactating cows at the time of the lactation peak induced a rapid and dramatic drop in plasma progesterone and a smaller reduction in plasma estradiol. Interestingly, the study of the changes in mammary secretory tissue over time revealed that the improvement of MY measured in the ovariectomized cows was associated with a limited increase in estradiol receptivity in MECs, a reduced mammary tissue remodeling and reduced blood protein concentration in milk, in late lactation. These results suggest that ovarian secretions, particularly estradiol and progesterone, act to enhance processes for mammary gland involution in late-lactating dairy cows.

The decrease in milk yield during once daily milking is due to regulation of synthetic activity rather than apoptosis of mammary epithelial cells in goats.

Once daily milking (ODM) is a management practice that can improve working conditions and reduce production costs in dairy farming compared with twice daily milking (TDM). However, ODM is associated with a decrease in milk yield. Previous research indicated that disruption of tight junctions in the mammary gland may be one of the regulatory factors involved in the milk yield decrease observed during ODM. The aim of this study was to investigate the involvement of mammary epithelium disruption in the regulation of the activity and dynamics of mammary epithelial cells (MEC) during 5 weeks of ODM in goats. Twelve alpine goats (producing 3.67 ± 0.64 kg/day and 47 ± 1.6 days in milk) were assigned to two groups that were milked once or twice a day during 5 weeks and then switched back to TDM. Mammary biopsies were collected before and on days 2 and 16 of both ODM and TDM switchback periods. Milk purified epithelial cells were collected before and on days 1, 7, 21 and 28 during ODM as well on days 1 and 7 of the TDM switchback period. The mRNA levels of genes involved in the regulation of synthetic activity and apoptosis were analysed by RT-PCR in milk MEC and mammary biopsies. ODM decreased yields of milk (-23%), lactose (-23%) and casein (-16%). Lactose synthesis was regulated at the transcriptional level by downregulation of α-lactalbumin mRNA levels in both biopsy samples (-30%) and milk MEC (-74%). TUNEL (terminal deoxynucleotidyl transferase-mediated dUTP-biotin nick end labelling) staining of mammary gland biopsies did not show any increase in cell apoptosis after 2 and 16 days of ODM (0.8% and 1%, respectively) despite upregulation of Bax mRNA levels in milk MEC. This suggests that the decrease in milk yield observed during ODM is attributable to a decrease in synthetic activity rather than to induction of MEC cell death. ODM induced the disruption of tight junctions in the mammary gland only on the first day of the treatment as indicated by increased blood lactose concentration. This indicates that the decrease in MEC activity observed over the 5 weeks of ODM was not due to disruption of the mammary gland tight junctions. There was no carryover effect of 5 weeks of ODM on milk production. Therefore, it appears that the decrease in milk yield that occurs during ODM in goats is due to regulation of synthetic activity rather than to apoptosis of MEC.

Ovariectomy improves lactation persistency in dairy cows.

A current trend in the dairy industry is to reduce milk yield at the peak of lactation and improve lactation persistency. Lactation persistency is influenced by livestock management factors, such as feeding level or milking frequency, or by physiological status, including reproductive status or calving period. These factors modulate mammary gland apoptosis and tissue remodeling, which determine the rate of decline of milk yield after the lactation peak. Previous studies on lactating cows suggested that ovarian steroids have a negative effect on milk yield after the peak of lactation. In the present study, 4 Holstein × Normande crossbred multiparous cows were ovariectomized at the time of the lactation peak, and 5 cows underwent sham operations. All of the cows were maintained in lactation for 14 mo and milk yield was recorded daily. At slaughter, mammary epithelial cell apoptosis and mammary tissue remodeling were assessed. Ovariectomized cows had improved lactation persistency and presented an average daily milk gain of 2.5 kg compared with the sham-operated cows between mo 6 and 14 of lactation. The ovariectomy appears to have limited the decline in the milk yield after the peak of lactation by reducing mammary epithelial cell apoptosis [by reducing poly(adenosine diphosphate-ribose) polymerase expression] and mammary-tissue remodeling (by reducing matrix metalloproteinase activity). In conclusion, removal of ovarian secretion via ovariectomy improved the cows' lactation persistency.

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.

Disruption of cell junctions induces apoptosis and reduces synthetic activity in lactating goat mammary gland.

Although it is known that disruption of the cell junctions in the mammary gland induces a decrease in milk yield, the cellular mechanisms involved in milk secretion reduction during mammary cell junction disruption are not well understood. The aim of this study was to investigate the cellular regulations taking place after cell junction disruption in the mammary gland of goats. We performed intramammary infusions of Ca chelators to induce cell junction disruption. In a first group of 5 goats, intramammary infusions of ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid (EGTA) in the right gland halves and saline as a control in the left gland halves were performed after 4 consecutive milkings. A second group of 4 goats received 4 intramammary infusions of citrate solution in the right gland halves and lactose solution as a control in the left halves. Intramammary infusion of EGTA and lactose induced a disruption of cell junctions, whereas citrate infusions failed to modify mammary epithelium integrity. The effect of the infused solutions was also tested in vitro via the measurement of transepithelial resistance, confirming mammary epithelium disruption by the EGTA, lactose, and citrate solutions at high concentrations. The disruption of mammary epithelium integrity by EGTA induced a decrease in the expression of the cell junction protein E-cadherin. Both the EGTA and lactose infusions induced a decrease in milk secretion that was accompanied by cellular modifications. We observed a decrease in milk casein, which was associated with a decrease in the mRNA level of kappa-casein in the lactose-infused glands, and a decrease in milk lactose, which was associated with a downregulation of alpha-lactalbumin transcripts in both the EGTA- and lactose-treated glands. Both the EGTA and lactose infusions increased terminal deoxynucleotidyl transferase-mediated 2'-deoxyuridine 5'-triphosphate nick-end labeling (TUNEL) in the mammary tissue, indicating an induction of apoptosis. Lactose infusion increased the mRNA level of Bax, suggesting that apoptosis was regulated at the transcriptional level. The results obtained in these experiments suggest that disruption of mammary epithelium integrity was associated with both reduced synthetic activity and apoptosis induction in the mammary gland.

Nocturnal melatonin concentrations vary dramatically between the two jugular veins in most individual sheep maintained under mimicked or natural photoperiod.

Two experiments were designed to determine if melatonin concentrations differ between jugular veins. In a first experiment, blood was collected continuously every 30 min from each jugular during 12-h from 6 ewes. In a second experiment, 100 ewes were sampled twice at night simultaneously from the two jugular veins. In both experiments, mean melatonin concentrations were similar between right and left jugulars. However, within individuals, large differences were observed between the two sides (p<0.001). This difference was stable over time and the higher side varies among individuals. The concentrations of prolactin and oxytocin, measured in the same samples did not show such differences. This observation raises the question of the origin of this phenomenon. Moreover, it has important implications for studies in which melatonin concentrations need to be assessed accurately. Indeed, a reliable quantitative assessment of melatonin production by the pineal gland requires sampling from both jugular veins.

Cell junction disruption after 36 h milk accumulation was associated with changes in mammary secretory tissue activity and dynamics in lactating dairy goats.

Milk stasis in the mammary gland is a situation that induces a reduction in milk yield and a change in its composition. Theses changes could be related to a decrease in the number and/or activity of secretory cells. Previous observations showed that a disruption of cell junctions is one of the early phenomena accompanying milk accumulation in the mammary gland. The aim of the present study was to investigate the local effect of 36 h milk accumulation on mammary cells activity, apoptosis and proliferation. We also studied the expression of cell junction proteins after 36 h of milk stasis. We observed a decrease in the quantity of milk produced after 36 h of milk stasis in goat. Lower milk lactose and protein yields were also observed, which was associated with a decrease in the transcripts of genes involved in synthesis of these constituents, such as alpha-lactalbumin and kappa-casein. Mammary gland apoptosis was more intensive than mammary cell proliferation after 36 h of milk accumulation. All these changes were associated with an up-regulation of E-cadherin protein and increase of its transcripts levels. It could suggest that these adjustments are made in order to limit losses of secretory cell number and activity.

Once-daily milking effects in high-yielding Alpine dairy goats.

Two experiments were conducted to determine the milk loss of high-yielding Alpine goats resulting from once-daily milking (ODM) and its relationship to udder cisternal size. We investigated the effects of application of this management strategy on milk yield, composition, and technological parameters: lipolysis, fat globule size, and cheese yield. In a second experiment, we investigated the effect of repeated periods of ODM management during lactation. Goats at the beginning of both experiments were at 25 d in milk on average and were previously milked twice daily (twice-daily milking; TDM). In experiment 1, which was conducted for 2 periods (P) of 9 wk (P1, P2), 48 goats were grouped (1, 2, 3, and 4) according to milk yield, parity, and somatic cell count (SCC). Over the 2 periods, goats from group 1 were managed with TDM and those from group 2 were managed with ODM. In group 3, goats were assigned to TDM during P1 and ODM during P2, conversely, those in group 4 were assigned to ODM in P1 and TDM in P2. During P1, the 12 goats from group 3 underwent 2 distinct morning machine milkings to measure milk repartition (cisternal and alveolar) in the udder based on the "atosiban method." On P1 plus the P2 period of 18 wk, milk loss caused by ODM (compared with TDM) was 16%. In our condition of 24-h milk accumulation, there was no correlation between milk loss and udder cisternal size. Milk fat content, fat globule size, or apparent laboratory cheese yield was not modified by ODM, but milk protein content (+2.7 g/kg), casein (+1.8 g/kg), milk soluble protein concentration (+1.0 g/kg), and SCC increased, whereas lipolysis decreased (-0.3 mEq/100 g of oleic acid). In experiment 2, which was conducted for 4 periods (P1, P2, P3, P4) of 5 wk each, 8 goats, blocked into 2 homogenous groups (5 and 6), were used to study the effects of a double inversion of milking frequency (TDM or ODM) for 20 wk of lactation. Milk loss was 17% and ODM did not modify milk fat or protein contents, SCC, casein, or milk soluble protein concentration, but lipolysis was decreased (-0.3 mEq/100 g of oleic acid). Neither experiment showed the effects of period of ODM management on milk yield, milk fat or protein content, SCC, fat globule size, lipolysis, casein, milk soluble protein concentration, or apparent laboratory cheese yield.

Effects of twice-daily nursing on milk ejection and milk yield during nursing and milking in dairy cows.

Milk production and hormonal responses to milking in Holstein cows that were milked twice daily, and that either also nursed calves twice daily 2 h after milking for 9 wk after calving (n = 10) or that served as nonnursing controls (n = 8) were examined to assess how nursing affected responses to machine milking. Milk yield at milking during the 9 wk of nursing was lower in nursing cows compared with control cows (26.1 +/- 1.0 vs. 35.5 +/- 1.1 kg) that were only machine milked. During nursing, the amount drunk by calves increased from 6.5 +/- 0.7 kg/d on wk 1 to 12.5 +/- 1.4 kg/d on wk 9. When this was added to the amount of milk obtained at milking, nursing cows did not differ from control cows in total milk produced (35.5 +/- 1.0 vs. 35.5 +/- 1.0 kg). Residual milk yield, after i.v. injection of oxytocin after milking, was higher in nursing cows than in control cows (8.7 +/- 0.8 vs. 3.2 +/- 0.8 kg). During the 6 wk after weaning, milk production was the same for the nursing and control cows (34.0 +/- 1.35 vs. 34.7 +/- 1.42 kg). Plasma oxytocin levels during milking were greater for control cows than for nursing cows (31.7 +/- 5.4 vs. 18.0 +/- 2.8 pg/mL), but were equivalent to concentrations in nursing cows during nursing (35.5 +/- 7.5 pg/mL). Plasma concentrations of prolactin and cortisol increased after both milking (control vs. nursing: prolactin: 40.2 +/- 6.8 vs. 32.9 +/- 6.1 ng/mL; cortisol: 6.4 +/- 1.23 vs. 7.4 +/- 1.10 ng/mL) and nursing (control vs. nursing: prolactin: 18.6 +/- 7.3 vs. 38.9 +/- 6.6 ng/mL; cortisol: 2.34 +/- 1.15 vs. 7.37 +/- 1.04 ng/mL). In contrast to previous studies, there was no obvious advantage for milk production by keeping a calf with the cow. This appears to result from the reduced oxytocin secretion during milking for the nursing cows.

Management systems with extended milking intervals in ruminants: regulation of production and quality of milk.

This paper aims to compare different adaptive responses of the mammary gland of cows, ewes, and goats submitted to extended milking intervals in different systems of management. Depending on the species, these extended milking intervals can be characterized by the following milk removal approaches; 3 milkings every 2 d, elimination of 1 milking per week (i.e., 13 vs. 14 milkings per week), and once-daily milking with additional suckling (i.e., dual purpose system of suckling and milking) or without suckling (exclusive once-daily milking). All the high-yielding animals and breeds adapted without problems to being submitted to intervals between milking less than 20 to 21 h. Under these conditions, all ruminant species demonstrated only low and transitory variations in milk production and quality. Thus, management systems using such an interval are good tools for the dairy producer who wants to save time without important adverse economic impact. When animals have good mammary gland health, these management systems can be applied without preliminary adaptation. However, goats and some breeds of dairy ewes seem to adapt to once-daily milking better than cows. Additionally, goats and ewes with higher production levels demonstrate a lower reduction in milk yield. With goats, there is only a limited variation in milk quality and cheese-making capacity of the milk produced, but ewes and cows show a significant enrichment of milk constituents, especially in fat. This indicates some differences in the regulation of lactose, protein, and fat synthesis depending on the duration of the milking interval and provides interesting models for physiological studies on milk secretion and synthesis regulation. Anatomical and physiological characteristics of lactating cows and ewes, in terms of cisternal vs. alveolar volumes within the mammary glands, could contribute to different abilities in adaptation to different milking systems. In goats, however, other mechanisms, such as compliancy of the mammary gland and regulation of tight junction impermeability, could be involved in milk secretion regulation and, thus, could become new targets for genetic selection of animals better adapted to accept extended milking intervals.

Composition of milk fat from cows selected for milk fat globule size and offered either fresh pasture or a corn silage-based diet.

The objective of this study was to examine the synthesis and composition of milk produced by dairy cows that secrete either small milk fat globules (SMFG) or large milk fat globules (LMFG), and to study their response to diets known to alter milk composition. Four groups of 3 multiparous dairy cows were assigned to 2 isoenergetic feeding treatments: a corn silage treatment supplemented with soybean meal, and fresh pasture supplemented with cereal concentrate. The 4 groups comprised 2 groups of 3 dairy cows that produced SMFG (3.44 microm) and 2 groups of 3 dairy cows that produced LMFG (4.53 microm). The SMFG dairy cows produced higher yields of milk, protein, and calcium. Nevertheless, their milk had lower fat and protein contents. Both SMFG and LMFG cows secreted similar amounts of milk fat; therefore, higher globule membrane contents in milk fat were observed in SMFG cows. Higher calcium mineralization of the casein micelles in SMFG cows suggests that it may be possible to improve cheese-making properties even if the lower protein content may lead to lower cheese yields. The SMFG cows secrete milk fat with a higher concentration of monounsaturated fatty acids and a lower concentration of short-chain fatty acids. They also have a higher C18:1/C18:0 ratio than LMFG cows. This suggests that SMFG cows have more significant fatty acid elongation and desaturation. The pasture treatment led to an increase in milk and protein yields because of increased energy intake. It also resulted in lower milk fat yield and fat and protein contents. The pasture treatment led to a decrease in milk fat globule size and, as expected, an increase in monounsaturated and polyunsaturated fatty acid contents. However, it induced a decrease in the protein content, and in calcium mineralization of casein micelles, which suggests that this type of milk would be less suitable for making cheese. This study also shows that there is no correlation between the cows, based on milk fat globule size and diet. These results open up possibilities for improving milk fat quality based on milk fat globule size, and composition. The mechanisms involved in milk fat globule secretion are still to be determined.

Effects of restricted nursing on milk production and collection, kid growth and plasma prolactin and growth hormone concentrations in dairy goats.

The milk production of dairy goats under various regimes of mother-young contact from day 4 post partum were studied during the first 2 months of lactation, together with the prolactin (PRL) and growth hormone (GH) responses to udder stimulation. In the control group, 13 goats and their kids were left in permanent contact and did not undergo milking. In two additional groups, goats were machine milked once a day in the morning (at 0800 h) and kids were allowed 10 hours (from 1000 to 2000 h; 10H group, n = 11) or 5 h (from 1000 to 2000 h; 5H group, n = 11) of mother-young interaction per day. In the last group (MO, n = 10), mothers were permanently separated from their kids on day 4 post partum and milked once a day. Milk production during a 24-h period at 37 days post partum performed by controlled nursing and weighing of the kids (groups with kids) or by two machine milking 12 h apart (milking only group) revealed a higher production in the three groups with some mother-young contact than in the MO group. Total milk collected by milking over the 2 months of the study did not differ between the three groups that underwent milking. Kid weights at 2 months were 3.4 to 4.8 kg. lighter in the groups that underwent milking than in the control group. Hormonal profiles were significantly affected by restricted mother-young contact, with highest pre-stimulation concentrations of PRL and GH in the 5H group. Restricting mother-young contact from the first week postpartum can permit an early collection of milk without major effects on kid growth, when compared with one daily milking in goats totally separated from their young.

Effect of weaning system on milk composition and distribution of milk fat within the udder of East Friesian dairy ewes.

We investigated whether the inhibition of milk ejection during and/or between machine milkings is responsible for the low milk fat observed in commercial milk obtained from dairy ewes managed with a mixed system (MIX) of partial daily suckling (10 h) and once daily machine milking (after 14 h of udder filling). East Friesian crossbred dairy ewes were randomly allocated postpartum to the MIX system (n = 9) or to exclusive twice-daily machine milking (DY1, n = 8). Following wk 4, MIX ewes were permanently weaned from their lambs and milked twice daily. All ewes were injected with saline, oxytocin, or an oxytocin-receptor antagonist prior to three morning milkings during wk 2,4, and 6 of lactation to study cisternal and alveolar milk distribution. Overall milk yield (cisternal + alveolar) for MIX ewes was 42% greater than for DY1 ewes during wk 2 and 4, which demonstrates the beneficial effect of lamb suckling on milk production of dairy ewes. However, during normal machine milking, only the cisternal fraction was obtained from MIX ewes, confirming that milk ejection did not occur for as long as these ewes remained in partial daily contact with their lambs. Although the volume of milk stored within the cistern, and its concentration of milk protein was similar for the two weaning systems, milk of MIX ewes was significantly inferior in cisternal milk fat concentration and yield compared to DY1 ewes. This provides evidence that not only is there inhibition of milk ejection during machine milking of MIX ewes, there is additional inhibition of transfer of milk fat, but not milk protein, from the alveoli to the cistern during the evening when MIX ewes a reseparated from their lambs. Following weaning of MIX ewes, the majority of lactation traits studied were similar compared to DY1 ewes.

Effect of milking interval on alveolar versus cisternal milk accumulation and milk production and composition in dairy ewes.

Cisternal and alveolar milk fractions were measured in East Friesian crossbred dairy ewes (n = 32) after 4, 8, 12, 16, 20, or 24 h of milk accumulation in a 6 x 6 Latin square design by administration of an oxytocin receptor antagonist for recuperation of cisternal milk followed by injection of oxytocin to remove the alveolar fraction. Less than half (38 to 47%) of the total milk yield was stored within the cistern for the first 12 h of udder filling compared with up to 57% after 24 h of udder filling. Subsequent milk yield was significantly reduced following the 16-, 20-, and 24-h treatments. Cisternal milk fat percentage, but not milk protein percentage, was lower than in alveolar milk (4.49 vs. 7.92% milk fat, respectively), indicating that casein micelles pass more freely from the alveoli to the cistern between milkings compared with fat globules. Alveolar compared to cisternal somatic cell count was higher for the 16-, 20-, and 24-h treatments. Significant increases in cisternal milk yield and milk composition observed for the 24-h compared with the 20-h treatment demonstrated the importance of the cistern as a storage space when the alveoli and small intramammary ducts became full. The main difference between cisternal and alveolar milk fractions is the poor fat content of cisternal milk, which is an important reason for the milk ejection reflex to be present during machine milking of dairy ewes. In a second experiment, milking every 16 h compared with every 12 h during mid- to late-lactation did not effect milk yield, milk composition, and quality, or lactation length; however, a 25% savings in labor was achieved with the longer milking interval.

Effect of presence or absence of corpora lutea on milk production in East Friesian dairy ewes.

The potential luteal effects on milk production were examined in dairy ewes that were not superovulated in contrast to studies using superovulated ewes. Lactating East Friesian crossbred ewes (n = 24) were synchronized using intravaginal progesterone (controlled intravaginal drug-releasing device), PGF2alpha, and gonadotropins. After ovulation, corpora lutea (CL) were counted via laparoscopy on d 4 and 11. On d 5, ewes received either saline (CLYES, n = 12) or PGF2alpha (CLNO, n = 12) to allow CL persistence (2.4 +/- 0.3 CL on d 11) or regression (0 CL on d 11), respectively. Each ewe received two CIDR d 5 to 18 to maintain high concentrations of plasma progesterone (P4) and to suppress estradiol (E2). Each ewe received PGF2alpha on d 18. Data were collected during three periods (pretreatment: d 0 to 5; treatment: d 6 to 18; posttreatment: d 19 to 25). Milk yield and milking time were recorded daily, milk samples were obtained for analyses of fat and protein, and blood samples were collected for P4 and E2 immunoassay. During treatment, CLYES ewes had higher milk yield (1.56 vs. 1.44 +/- 0.01 kg/d), milk fat (92.2 vs. 81.1 +/- 1.3 g/d), and milk protein (83.7 vs. 77.5 +/- 0.8 g/d) compared with CLNO ewes, respectively. Differences were maintained posttreatment, despite luteolysis in CLYES ewes. Estradiol concentrations did not differ between treatments and were low after d 5. Milk production was increased in East Friesian ewes in the presence of an average of 2.4 corpora lutea, an effect independent of estradiol.

Human contact and the effects of acute stress on cows at milking.

We examined the effects of novelty/isolation stress on cows at milking and whether human contact reduced the stress. Holstein cows (n=18) were observed during three experimental milkings following a balanced order: (1) control (C) - milked in usual place; (2) novelty/isolation stress (S) - milked alone in an unfamiliar room; (3) human contact (HC) - milked in unfamiliar room and brushed by a familiar person. Behavior and heart rate during milking, milk yield and residual milk following oxytocin injections were recorded, and blood samples assayed for oxytocin and cortisol. Cows defecated/urinated and vocalized more and made more steps during milking in the unfamiliar room and human contact prevented this increase. Cows kicked and lifted their legs less in the unfamiliar room, but human contact did not affect this. Both plasma cortisol concentrations and heart rates were higher when cows were milked in the unfamiliar room. Although human contact reduced heart rates during the initial period of isolation, heart rates during milking and cortisol concentrations were not affected by human contact. Milk yield was lower, residual milk higher, and oxytocin during milking was lower in the unfamiliar room but this was not changed by human contact. Cows milked alone in an unfamiliar room showed signs of acute stress and gave less milk due to higher residual milk and reduced oxytocin secretion. Human contact reduced some behavioral signs of agitation and heart rate, but had no effect on milk yield or hormonal responses. For dairy cows, human contact may not be sufficiently comforting to be able to reduce the endocrine response to novelty/isolation stress.

Effect of milking frequency on oxytocin release and milk production in dairy ewes.

The experiment was conducted to investigate the effectiveness of milking stimulus on oxytocin release and to compare the effect of milking frequency on plasma levels of oxytocin and milk parameters. Twelve Lacaune ewes were subjected to six treatments (T1, T2, T3, T4, T5 and T7 daily milkings) during 6 days. At each milking, blood was sampled and plasma oxytocin levels were determined by enzyme immunoassay. Baseline levels of oxytocin were similar for all milking frequencies. The start of milking was followed by a significant increase in oxytocin levels for all milking frequencies. One daily milking induced significantly higher oxytocin levels than 2, 3, 4, 5 and 7 daily milkings. Milk yield was significantly increased between 4 (1787.0+/-141.5ml) and 7 (1780.0+/-53.6ml) daily milkings compared to 1 (1104.0+/-81.2ml) daily milking. Total concentration of milk protein did not change, but the total milk fat yield for 5 (73.0+/-2.0g/l) and 7 (72.8+/-1.4g/l) daily milkings were significantly higher than for 1 (58.1+/-4.3g/l) daily milking. This study confirmed milk yield gains caused by frequent milk ejection and also showed that oxytocin release was not a limiting factor for milk yield gain when daily milking frequency was increased.