Twice-daily Milking Research Articles

A comparison of the direct and residual response of dairy cows to once or twice-daily milking, in late lactation

Two experiments were undertaken to examine the direct and residual responses of late lactation (mean of 232 days calved) autumn calving dairy cows (Experiment 1), and late lactation (mean of 240 days calved) spring calving dairy cows (Experiment 2), to once-daily milking. Experiments 1 and 2 involved 50 and 44 Holstein–Friesian dairy cows respectively. In each of the two experiments, cows were milked either once daily (ODM) or twice daily (TDM), during the late lactation period (mean of 79 and 66 days in Experiments 1 and 2 respectively). Cows in Experiment 1 were managed within a grazing system, and were offered 3.0 kg of concentrate/day, while cows in Experiment 2 were housed, and offered grass silage supplemented with 6.0 kg concentrate/day. Forty-one cows from Experiment 1, and 32 cows from Experiment 2, completed the first eight weeks of the subsequent lactation on a twice-daily milking regime. Food intakes were not measured in Experiment 1, while treatment had no significant effect on dry matter intake in Experiment 2 ( P > 0.05). In each of Experiments 1 and 2, total milk output was increased with twice-daily milking ( P ≤ 0.05), while milk fat ( P ≤ 0.01) and protein ( P < 0.001) concentrations increased with once-daily milking. Somatic cell counts were higher with animals milked once daily in Experiment 1 ( P < 0.001), while not being significantly affected by milking frequency in Experiment 2 ( P > 0.05). Milking frequency had no significant effect on cow live weight or on cow condition score at the point of drying off in either Experiment ( P > 0.05). Milking time per cow during morning milking was unaffected by treatment in either experiment, while total daily milking time per cow (morning and evening combined) was significantly longer with the TDM treatment ( P < 0.001). In Experiment 1, milk flow rates during the morning milking were higher with animals on the ODM treatment, compared to those on TDM treatment ( P < 0.001), while being unaffected by treatment in Experiment 2 ( P > 0.05). Neither daily milk yield, milk fat content, milk protein content, or somatic cell count during the subsequent lactation, were affected by previous lactation milking frequency in either of Experiments 1 or 2 ( P > 0.05).

Effect of milking interval on milk yield and quality and rate of recovery during subsequent frequent milking

Forty mid-lactation, pasture-fed dairy cows were used to study the effects of milking interval on milk yield and quality and whether effects could be reversed during a short period of subsequent frequent milking. Following a 2-day pre-experimental period of normal twice-daily milking (TDM), cows were milked again after 6, 12, 18, 24 or 30 h, with each milking interval followed by 24 h of frequent milking (i.e., every 6 h). Milk yield increased linearly until 18 h and then started to plateau. Similarly, milk quality (serum albumin and proteolytic enzyme activity) became adversely affected after 18 h. These changes coincided with increased permeability of mammary tight junctions (TJ), starting after a milking interval of 18 h. A brief period of frequent milking helped restore milk yields to pre-experiment levels, even after the longest milking interval.

Once-daily milking of Holstein cows for one-week decreases milk yield by twenty-five percent without any carry-over effect

Abstract Short-term (i.e. several days) once-daily milking (ODM) of dairy cows could help to improve work organization or quality of life for dairy farmers. ODM implemented during three periods of one week in the descending phase of lactation led to an average 23.4% decrease in the milk yield of 9 Holstein cows compared to 9 other cows on twice-daily milking (TDM). Short-term ODM significantly increased fat content (by 4.5 g/kg on average) and somatic cell count (by 73,000 cells/mL) and decreased lactose content by 1.9 g/kg. Protein content increased (by 2.1 g/kg) only in the third period. When twice-daily milking was resumed, there were no longer between-group differences in daily yields of milk, fat, protein, and somatic cells.

A Systems Comparison of Once- Versus Twice-Daily Milking of Pastured Dairy Cows

The objective of this study was to compare the effect of milking frequency (once vs. twice-daily milking) and breed (Holstein-Friesians vs. Jerseys) on milk and milk solids (MS; milk fat + milk protein), yield per cow, milk composition, somatic cell count and lactation length; cow body weight, body condition score, and reproductive performance over a 4-yr period. Total cow numbers in each herd were 30, 35, 36, and 42 for Holstein-Friesians milked once or twice daily, and Jerseys milked once or twice daily, respectively. Forty hectares of pasture were subdivided into 4 smaller pastures of 10ha each. Stocking rates for the once-daily herds were 16.7% greater than the twice-daily herd in their respective breed. An increased stocking rate was chosen to achieve equal milk and MS per ha from the 2 milking frequencies. Annual milk, fat, protein, and lactose yields per cow were less for once-daily than for twice-daily milking. Interactions were detected between milking frequency and breed for annual milk, fat, protein, and lactose yields per cow, because Jerseys were relatively less affected by once-daily than by twice-daily milking than Holstein-Friesians. Holstein-Friesian cows milked once daily produced 31.2% less milk and 29.4% less MS per cow than their twice-daily counterparts. In contrast, Jersey cows milked once daily produced 22.1% less milk and 19.9% less MS per cow than their twice-daily counterparts. Milk per ha was 17.7 and 9% less for the once-daily Holstein-Friesians and once-daily Jersey herds, respectively, compared with their twice-daily counterparts, because the greater stocking rate for the once-daily herds did not fully compensate for the milk loss per cow. Milking once daily increased somatic cell count throughout the year in both breeds. Cows milked once daily conceived 3 d earlier, took 5 d less from calving to conception, and needed 11% fewer controlled internal drug release devices than those milked twice daily. Milking once daily is a viable milking option for New Zealand farmers who are prepared to trade-off loss of MS income for increased time to accomplish other non-milking activities.

Once-daily milking of dairy cows: a review of recent French experiments

Once-daily milking (ODM) implemented in the declining phase of lactation for up to at least 10 weeks reduced milk yield by 20-30%, according to the trial, from the first day. Milk loss (%) exhibited a high between-cow variability and was unrelated to the milk yield (kg) of the cows. When twice-daily milking (TDM) was resumed, milk yield recovered completely following implementation of ODM for a few days, but reached only about 90% of the yield of TDM cows following implementation of ODM for 8-10 weeks. When implemented from calving, ODM had a progressively higher negative impact (a decrease of between 30 and 50%), which was more pronounced in primiparous cows than in multiparous cows. The residual loss (%), once TDM resumed, was generally higher than in the declining phase. When ODM was implemented during three successive lactations, there was no between-lactation effect. ODM increased fat and protein content in milk and decreased lactose content by an average 2.8, 1.5 and 1.5 g*L-1, respectively. The casein/protein ratio was reduced (by 1.8% on average). Resumption of twice-daily milking cancelled these modifications within a few days. Protease activity in milk tended to increase, whereas lipase activity tended to decrease with ODM. Free fatty acid content was reduced significantly with ODM. Implementation of ODM did not significantly modify feed intake of the cows in the short term (up to 6-8 weeks), but tended to decrease it thereafter. The quality of cheese manufactured from TDM or ODM milks were similar. ODM implementation led to an improved nutritional status of the cows, as appreciated by changes of live weight, body condition score, or calculated energy balance. It also improved reproduction parameters. The cows adapted quickly to ODM (within a few days). ODM increased the somatic cell count in milk without impact on mastitis infection incidence in the short term. When implemented throughout lactation during which cows were partly in barn conditions, ODM increased mastitis infection incidence in 2 out of 3 trials.

Effects of Amino Acid Nutrition on the Responses of Dairy Cows to Milking More Frequently With or Without Injection of Growth Hormone

The influence of amino acid nutrition on the response to milking more frequently, with or without injection of growth hormone, was examined in eight dairy cows in two 4×4 Latin squares with 28-d periods. The four treatments were a diet adequate in amino acids with or without injection of growth hormone and a diet inadequate in amino acids with or without injection of growth hormone. For all four treatments, during the last 14 d of each period, one half of the mammary gland was milked three times a day (3×), while the other half remained on twice-daily milking (2×). Both diets were based on grass silage given ad libitum and 4kg/d of sugar beet pulp together with a supplement containing either fish meal (adequate diet) or feather meal (inadequate diet) as the only protein feeds. The diet containing feather meal is known to be deficient in His, Met, and Lys. On the fish meal diet, the cows responded positively to growth hormone and to milking more frequently and the responses to both treatments were additive. On the feather meal diet, however, even though injection of growth hormone increased the yield of milk protein by around 10%, milking more frequently did not affect milk production. It is concluded that milking more frequently has a weaker effect on the partitioning of amino acid use between body and udder than does growth hormone treatment.

The Yield and Composition of Milk in Sarda, Awassi, and Merino Sheep Milked Unilaterally at Different Frequencies

Sarda (n=8), Awassi (n=8), and Merino (n=8) ewes were subjected unilaterally to once-daily milking (ODM) or twice daily milking (TDM) to test the hypothesis that the two breeds highly selected for milk production (Sarda and Awassi) would not respond as much to a change in the frequency of milking as the Merino, a wool sheep that has not been selected for dairy production. Milk composition and somatic cell count (SCC) were also assessed to determine if the changes in milking frequency affected milk quality. Milk yield was 24% and 18% lower in ODM udder halves than TDM udder halves in Sarda and Awassi breeds, respectively. The yield loss due to ODM was similar to that observed in Merino ewes (23%) and did not support our hypothesis. Fat content did not differ significantly in any breeds between ODM and TDM udder halves. Protein content was higher in the milk of ODM than TDM udder halves in Sarda and Merino ewes. The SCC was influenced by milking treatment only in the Sarda ewes, with high values observed in the milk of ODM udder halves. The same trend was observed in the Awassi and Merino breeds, but the differences were not significant. The effects on milk yield, composition, and SCC caused by ODM were completely reversed when TDM was resumed. This suggests that in sheep flocks the milk yield losses due to short-time suppression of one daily milking, for example, on festive days, are low and temporary.

Effect of frequency of milking on yield, composition and processing quality of milk.

The objective was to determine the effect of once-daily milking (ODM) and omitting one evening milking each week (13TWM), in late lactation on milk production, composition and processability. Seventy-two cows were assigned to three treatments (ODM, 13TWM and twice-daily milking [TDM]) from 4 October to 12 December. Cows were on average 218 d into lactation at the start of the trial, and all cows were managed similarly throughout the trial. Milk yields and gross milk composition of cows on all treatments were measured, and milk samples for detailed compositional and processability analysis were collected from TDM and ODM treatments at two consecutive milkings and at one milking each week, respectively. Milk yield was significantly reduced (P < 0.001) and milk fat and protein concentrations were increased (P < 0.01) with ODM compared with TDM. Milk yield and fat and protein concentrations of milk from TDM and 13TWM herds were similar. Casein concentrations in ODM and TDM milks were similar, but ODM milk had a higher (P < 0.05) whey protein content. Somatic cell count of ODM and TDM milks was similar. Rennet coagulation time (RCT) and curd firmness (A60) of milk were not affected by milking frequency. However, rate of curd aggregation (K20) of ODM milk was reduced (P < 0.05) compared with that of TDM milk. Plasmin activity in ODM milk was numerically higher than in TDM milk, but the effect was not significant. ODM milk had higher NAGase activity than TDM milk (P < 0.01). In conclusion, once daily milking reduced milk yield by 29% and did not adversely affect the processability of milk. Moreover, one evening milking per week could be eliminated without adverse effects on milk yield or composition.

Effect of Milking Frequency on Mammary Functioning and Shape of the Lactation Curve

Milk yield is a function of the number of mammary secretory cells and their metabolic activity. Both are not static, but change during the course of lactation. The rate at which they change may be influenced by farm management practices, such as feeding, photoperiod, hormonal treatment (e.g., bovine somatotropin), and milking frequency. By applying such practices, or a combination thereof, at any time during lactation, the farmer has tools to alter the shape of the lactation curve. These practices could be applied after peak lactation to increase milk yield and perhaps slow down the rate of postpeak decline in milk yield, but can also be used to promote mammary involution near drying-off. The present review focuses on milking frequency. Compared with twicedaily milking, milking three times a day or more often (robotic milking) will increase milk yield by 18%, whereas once-daily milking decreases milk output by 20%. Although frequent milking is practiced more often than once daily, the once-daily milked gland provides an excellent model to study functional changes related to milking frequency. The effects of increasing and decreasing milking frequency on mammary functioning are discussed, with emphasis on functional changes in the once-daily milked gland with regard to processes such as changing cell number or activity, feedbackinhibition, tight junction leakiness, apoptosis, and cisternalalveolar milk storage.

Physiological levels of Stat5 DNA binding activity and protein in bovine mammary gland.

Signal transducer and activator of transcription (Stat)5 has been implicated in the signal transduction pathways of several factors that are lactogenic or galactopoeitic in mammary cells, including prolactin, GH, and IGF-I. Data from cell or explant culture support the concept that Stat5 may represent part of a common route by which different extracellular signals converge and are transduced into the cell. There are few data on Stat5 activity and level in vivo, and we set out to determine whether physiological stimuli of milk synthesis, including GH, GH-releasing factor, and milking frequency, would be associated with alterations in Stat5 activity or protein. We measured Stat5 DNA binding activity using electrophoretic mobility shift assay and Stat5 protein by Western blot in bovine mammary tissue obtained by biopsy or slaughter. Stat5 activity was absent in nonlactating, nonpregnant cows and was present in late pregnancy and throughout lactation. Stat5 activity varied considerably among cows at similar stages of lactation. Mammary Stat5 activity and protein were determined in hormone-treated lactating cows and mammary quarters of cows milked at different frequencies. Infusion of GH and GH-releasing factor for 2 mo significantly raised levels of milk production and depressed mammary Stat5 activity without influencing Stat5 protein abundance. Mammary Stat5 was also influenced by milking frequency; once-daily milking reduced milk production, Stat5 activity, and protein abundance compared with twice-daily milking. Analysis of mammary Stat5 in relation to milk protein concentration in pooled data from lactating cows indicated that Stat5 activity was correlated (r = 0.505, P < 0.05) with average milk protein concentration and not related to milk protein yield (P > 0.05). These results show that both Stat5 protein and Stat5 activity are modulated by different physiological signals in vivo and suggest that Stat5 lies within in the zone where signal transduction cascades from a variety of factors are convergent. Further work is required to clarify the role of Stat5 in relation to other factors in regulation of milk protein gene expression.

Effect of music on voluntary approach of dairy cows to an automatic milking system

The main objective of this experiment was to assess the effect of music on the voluntary approach of cows to an automatic milking system (AMS). A group of 19 mid- and late-lactating Holstein cows with 2 months prior experience of twice-daily milking in the AMS was used in this study. The cows were housed in a free stall barn with slatted floors and fed a complete mixed ration using an indoor feed bunk. They were also offered 1.5 kg per cow of grain pellets in the AMS during milking. Music was played during the milking period for 69 days prior to observation with amplifiers located within the milking compartments, approximately 1.2 m above the head of the milking cows and also on the long side of the barn. The sounds were activated at the start of each milking period and terminated after the last milking cow left the AMS. Behavioural observations were carried out during the afternoon milking for 20 days randomly fluctuating between days with music and days without music. The number of cows in the holding area was instantaneously recorded at 5 min before and 5 min after the onset of the milking period. On days with music, the number of cows in the holding area increased from 22.3 ± 15.1% to 45.0 ± 18.0% ( P < 0.01). On control days without music, this difference was less pronounced, increasing from 27.1 ± 13.7% to 35.1 ± 15.4% ( P = 0.150). Changes in the composition of behavioural states from 5 min before to 5 min after the onset of the milking period were significant on days with music ( P < 0.001) but not on control days ( P = 0.412). The results show a stimulatory effect of music, influencing behavioural readiness of cows to access the milking compartments of the AMS.

Welfare considerations in future selection and management strategies

AbstractThis paper considers the welfare implications of breeding, feeding and managing dairy cows for increased productivity. The physiological demands of lactation for the high genetic merit dairy cow are exceptional, less in their intensity and more in their duration. Most welfare problems can be attributed less to productivity per se than to systems of feeding, milking and management that are unsuitable to the genotype of the high yielding cow. These include the inadequacies of wet grass silage as a staple food and the abnormal restriction of cows to twice-daily milking. It is also necessary to consider welfare problems that may arise from the application of new technologies to increase milk yield or to increase the rate of genetic progress. These may be related to the process itself or to its consequences. It is proposed that the commercial exploitation of these new technologies should be controlled by legislation similar to that for the protection of animals used for scientific purposes which applies a cost-benefit analysis to determine whether the cost to the animal can be justified in terms of any potential benefit to society.

Relationship between milk storage characteristics and the short-term response of dairy cows to thrice-daily milking

AbstractTwenty lactating dairy cows were used to investigate the relationship between the site of milk storage in the udder and the short-term response to thrice-daily milking. Cisternal and alveolar milk volumes were measured 8 h after an ordinary morning milking by catheter drainage and machine milking with oxytocin respectively. The response to thrice-daily milking was assessed using a half-udder technique and the relative milk yields quotient (RMYQ). Over the first 7 days, both halves were milked twice daily (8/16 h intervals) and milk yields over the final 4 days of this period were higher for left fore/right hind (LF/RH) (12·4 (s.e. 0·85) kg/day) than for RF/LH (10·5 (s.e. 0·63) kg/day) which was milked after LF/RH throughout the experiment. Over the following week, LF/RH quarters were milked an additional time (8/8/8 h intervals) and yields over the final 4 days were increased (15•7 (s.e. 0·95) kg/day) compared with control quarters (9·8 (s.e. 0·73) kg/day). In a final 4-day period, animals were milked twice daily and half udder yields were 13·1 (s.e. 0·89) kg/day and 10•6 (s.e. 0·77) kg/day respectively. Differences between yields from the two halves of the udders were highly significant in all 3 weeks of the experiment (P &lt; 0·001). Cistern milk yield as a proportion of total milk yield at 8 h (cistern proportion) averaged 0·170 (s.e. = 0·0275; range 0·020 to 0·334) and tended to be greater for multiparous (0·215, s.e. 0·0279) than for primiparous animals (0·118, s.e. 0·0437; P = 0·076). During the periods of twice-daily milking, the proportion of milk yielded from LF/RH quarters was not significantly related to cistern proportion (P = 0·70 and 0·43 for weeks 1 and 3 respectively). However the response to thrice-daily milking, assessed as RMYQ, was significantly related to cistern proportion both when changing up to, and down from, thrice-daily milking (P &lt; 0·01). Animals with low cistern proportions showed larger responses to thrice-daily milking. There was a significant relationship (P &lt; 0·05) between the responses on changing up to, and down from, thrice-daily milking. Primiparous animals tended to exhibit smaller declines on returning to twice-daily milking than multiparous animals with equivalent responses to thrice-daily milking.

Milking frequency alters the milk yield and mammary blood flow response to intra-mammary infusion of insulin-like growth factor-I in the goat.

The milk yield and mammary blood flow responses to close-arterial, intra-mammary infusion of IGF-I were investigated in five Saanen goats milked frequently or normally the day before. Animals were infused for 6 h with recombinant human IGF-I (1.3 nmol/min) and milked hourly following i.v. injection of oxytocin beginning 2 h before infusion and then every 2 h. On one occasion animals were milked five times (after i.v. injection of oxytocin) on the day before infusion and on the other they were milked twice, without oxytocin. The ratio of milk yield from the infused to that from non-infused gland increased by 17 +/- 4% (mean +/- S.E.M.) in goats milked twice the day before infusion and by 6 +/- 2% when the infusion was preceded by frequent milking. Maximal responses were obtained 4 h after the start of the infusion and differed significantly (P < 0.05), according to pretreatment milking. Blood flow through the infused gland rose in parallel to the milk yield response. At 5 h, when maximal levels were achieved, blood flow was 182 +/- 23% of the pre-infusion flow rate following twice-daily milking and 139 +/- 3% of the pre-infusion flow rate following more frequent milk removal. Thus, more frequent milk removal on the day before close-arterial infusion of IGF-I attenuated both the milk yield and mammary blood-flow response to the infusion of IGF-I.

Milk yield and mammary function in goats during and after once-daily milking

Starting in week 5 of lactation, goats were milked unilaterally once daily for 4 1/2 weeks, then twice daily for 12 weeks and finally thrice daily for 2 weeks. The control gland was milked twice daily throughout. During less frequent milking, yield fell by 26%. There was a rapid and essentially complete recovery of milk yield on resumption of twice-daily milking, and five of the six goats subsequently responded to thrice-daily milking with a small increase in milk yield. Mammary function was assessed during each phase by determining enzyme activities and in vitro synthesis rates of lactose and casein in mammary biopsies. There was a trend towards reduced differentiation of secretory cells during infrequent milking, with very little recovery during twice-daily milking but complete recovery during thrice-daily milking. The differentiative state of the control gland remained unchanged throughout.

An initial economic assessment of fully automatic milking of dairy cows

A simulation model of a fully automatic on-demand milking system is described. It is used to determine the number of milking units needed for various herd sizes from twenty to two hundred cows. It can also be used to determine some operational parameters such as the required holding area capacity. The costs and benefits of changing from a conventional parlour to automatic milking are calculated using these numbers and increases in milk yield are predicted due to more frequent milking. Compared with conventional twice-daily milking, if labour costs are excluded, there is an annual saving for herds over 60 cows of £48 to £72 per cow without quotas or £1 to £25 per cow with quotas. If labour costs are included, the annual savings are £71 to £103 per cow without quotas or £24 to £62 per cow with quotas. Benefits in improved health and oestrus detection could save £17 per cow or more annually. Comment is also made on other benefits which may arise from automatic milking, but which cannot be given monetary values.

Feed-back control of milk secretion in the goat by a chemical in milk.

In order to investigate the nature of the inhibition of milk secretion during a long milking interval, goats were treated in three possible ways: (i) milked twice daily at 08.00 h and 16.00 h or (ii) milked thrice daily at 00.00 h, 08.00 h and 16.00 h, or (iii) milked thrice daily at 00.00 h, 08.00 h and 16.00 h, but at 00.00 h the milk removed was replaced with an equal volume of isosmotic sucrose solution. The latter treatment was carried out in order to subject the gland to a degree of physical distension equivalent to that on treatment (i). On either thrice-daily milking or thrice-daily milking with sucrose replacement, milk secretion rate over the 16.00-08.00 h period was significantly higher (by about 10% in both cases) than on twice-daily milking. Secretion rates of lactose, milk protein, citrate and calcium during the 00.00-08.00 h period were similar on either thrice-daily milking or thrice-daily milking with sucrose replacement; the secretion rate of fat was significantly higher on thrice-daily milking with sucrose replacement. Secretion rates of Na+, K+ and Cl- were significantly higher on thrice-daily milking with sucrose replacement. In the case of Na+, the increased Na+ secretion rate was sufficient to create a normal Na+ concentration in the milk/sucrose mixture removed at the next milking. In the cases of K+ and Cl-, their secretion rates were not sufficient to restore their concentrations to normal by the next milking.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of weaning age, milking frequency, and udder stimulation on dairy milk production and post-partum oestrus interval of Dorset ewes

Abstract The dairy milk production of Dorset ewes was measured in a 2 × 2 × 2 factorial experiment. Factors were: machine milking of ewes from parturition or following the weaning of lambs at 4 weeks of age; once- or twice-daily milking from Week 6 of lactation; and udder stimulation or no stimulation. Ewes milked from parturition had a mean total dairy yield of 147 litres compared with 76 litres for those which had suckled lambs for 4 weeks; both groups had a similar dairy lactation period of about 154 days. Milking ewes once daily from Week 6 of lactation caused a 14% (NS) reduction in total dairy yield compared with twice-daily milking. Udder stimulation in contrast to no stimulation resulted in a 21% increase in dairy yield. The mean post-partum oestrus interval (about 116 days) was unaffected by treatments.

The effect of equal and unequal intervals in twice-daily milking on the milk yield of ewes

SummaryThe effect of equal and unequal milking intervals (12 + 12, 10 + 14 and 8 + 16h) was investigated in milch ewes. The treatments were applied to 9 ewes using a double 3 × 3 Latin square. The daily production of milk and fat was unaffected by the changes in milking interval.

Lactation Studies. X. Total Daily Production as Affected by Number of Times Milked, Number of Times Stimulated, and Method of Stimulation1,2,3

An experiment was conducted to measure the milk production response to increased frequency of milking and to mammary gland stimulation per se. A total of 25 cows was employed in two trials. The treatments compared were twice-daily milking (2 ×), four-times-daily milking (4 ×), and either two-times-daily milking plus hand stimulation without milking (2×H) or two-times-daily milking plus oxytocin injection (2×I) midway between each milking interval. Treatments 2×H and 2×I compared to treatment 2×resulted in a 1.0 to 1.5% nonsignificant increase in production. Treatment 4×resulted in a milk production increase of 7.9% over treatment 2 ×. Further, this increase was attained by the second day on the increased milking frequency. The rapidity of the production response, plus the lack of response to additional stimulations per se, suggests that stimulation→oxytocin→prolactin→increased milk synthesis is not the explanation. Rather, that frequent milking→reduced intramammary pressure→increased secretion is probably the explanation.