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* Unitat de Producció Animal, Department of Animal and Food Sciences, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
Hannah Research Institute, Ayr, KA6 5HL, United Kingdom
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Key Words: milking frequency • cisternal size • udder health • ultrasonography
Abbreviation key: 2x = twice-daily milking
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Throughout the world, twice-daily milking (2x) is the most frequent milking schedule of dairy cattle. Although, in the last 30 yr, 12-h intervals have been widely recommended, the 12-h milking frequency is not common in practice. Due to economical and social conditions, the unequal 8–16-h, 9–15-h or 10–14-h milking interval is more suitable than the equal 12–12-h milking interval (Sahr and Ormiston, 1966; Labussière and Coindet, 1968; Knight et al., 1994). The accumulation of milk in the udder during extended milking intervals reduces the activity of mammary cells, which indicates that milk secretion is under local intramammary control (Peaker and Wilde, 1996; Stelwagen and Knight, 1997, Stelwagen, 2001). Omitting one milking weekly, which can be done with a 24- or 18-h milking interval, may reduce milk yield to a lesser extent than once daily milking.
There are few reported studies on the effect on milk yield in dairy animals of omitting one milking weekly, compared to twice a day milking. Yield losses ranged from 3 to 10% in cows (Labussière and Coindet, 1968; Radcliffe et al., 1973), 8 to 26% in ewes (Casu and Labussière, 1972; Labussière et al., 1974; Huidobro, 1988) and 3 to 5% in goats (Mocquot, 1978; Le Mens, 1978; Le Du, 1989). Yield losses seem to be related to the level of milk yield, breed, and udder morphology.
Recent studies suggest that udder anatomy (size of mammary cisterns) in terms of milk storage characteristics may be an important factor in determining reduced yield associated with extended milking intervals (Knight and Dewhurst, 1994; Stelwagen et al., 1996; Davis et al., 1998). A new approach using direct udder scanning for the study of udder cisterns in dairy cow milk production has been reported by Ayadi et al. (2003).
The objective was to evaluate the short term effects of omitting one milking weekly (Sunday afternoon) on milk yield and milk composition and the medium-term effects of the reduced milking frequency on milk yield and udder cistern size measured by ultrasonography.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Routine milking.
During the experiment, milking was conducted in the stalls by using a high pipeline Westfalia Landtechnik (Granollers, Barcelona, Spain) milking system at 50 kPa (Vacurex, Westfalia Landtechnik). Pulsation ratio and rate were set at 60:40 and 60 pulses/min by using a Metatron 12 (Westfalia Landtechnik). The milking routine for the regular daily milking (0800 and 1800) included teat cleaning, machine stripping and teat dipping (P3-cide plus, Henkel Hygiene S.A., Madrid, Spain). All cows were free from clinical mastitis at the start of the experiments.
Experimental procedures, calculations, and milk analysis.
For the first 5 wk period of the experiment, cows were milked twice a day at a 10–14-h milking interval (0800 and 1800). For the second 5 wk period, cows were milked twice a day at the 10–14-h milking interval from Monday p.m. to Saturday p.m. and on Sunday only one milking was performed at 1300. The Monday a.m. milking was brought forward by one hour to 0700 to match the long milking intervals (18 h). So, the milking pattern at the weekend was as follows: Saturday a.m., 0800; Saturday p.m., 1800; Sunday p.m., 1300; Monday a.m., 0700; and, Monday p.m., 1800.
Yield of each milking was recorded individually by using a Metatron 12 automatic milk recording and proportional milk sampling unit (Westfalia Landtechnik). Milk yield loss produced by the omission of one milking weekly was calculated as the difference between the extrapolated values from milk yield regression of each experimental period on the week in which the milking schedule was changed (wk 5). Lactation persistency was calculated on a 4 wk basis from the slope of the milk yield regressions.
Representative milk samples for milk composition analysis of each cow were taken weekly at Friday (a.m. and p.m.) and Saturday (a.m. and p.m.) milkings to avoid residual effects of the milking omission according to the procedures recommended by Labussière and Coindet (1968). The a.m. and p.m. samples were composited in a daily sample according to milk yield at each milking. Milk fat, milk protein and milk lactose content were analyzed by using CombiFoss 5000 equipment (Foss España, Barcelona, Spain) and somatic cell count (SCC) by Fossomatic equipment (Fosselectric, Hillerød, Denmark).
To evaluate the effect of milking omission on the morphological changes produced in the cow udders, cisternal scans were performed 8 h after the a.m. milking and in duplicate for each udder quarter according to the methodology proposed by Ayadi et al. (2003). Cows were randomly selected for scanning between Tuesday and Friday at the start and at the end of the experiment by using a real time B-mode ultrasonograph (Ultra Scan 900, Ami Medical Alliance Inc., Montreal, Canada) with a 5 MHz sectoral probe (2 dB power, 80° scanning angle, 0.5 mm axial and 1.5 mm lateral resolution). Prior to udder scanning, 10 µg/kg BW of an oxytocin receptor blocking agent (Atosiban, Ferring Lab., Malmö, Sweden) was injected into the epigastric vein to prevent the milk ejection reflex and to make possible the recording of cisternal and alveolar milk fractions separately (Knight et al., 1994; Bruckmaier et al., 1997; Wellnitz et al., 1999). Afterwards, duplicated udder scans in perpendicular planes were taken and the images were transmitted in groups of four to a portable computer and stored for processing. Image treatment software (MIP4 Advanced System, Microm España, Barcelona, Spain) was used to estimate by triplicate the cisternal area in the scans, and pixels converted to cm2 (1 cm2 = 1,024 pixels) for calculations as indicated by Ayadi et al. (2003).
After the scans, cisternal milk was milked from each udder quarter using a quartered claw and the values recorded. Alveolar milk was machine milked by using the quartered claw after a 20.0 x 10-3 IU/kg BW i.m. injection of oxytocin (Veterin Lobulor, Lab. Andreu, Barcelona, Spain). Milk fractions per quarter were weighed separately following collection to an accuracy of 10 g, and the weights recorded.
Experiment 2
Animals, feeding, and routine milking.
Five Holstein cows (3 multiparous and 2 primiparous) from the S1GCE of the Universitat Autònoma of Barcelona, different from the cows used in Experiment 1 and previously adapted to the omission of one milking weekly schedule from the start of the first lactation, were used during a 10-wk period to study the daily effects of the omission of one milking weekly. At the start of the experiment days in milk were 227 ± 67 d and milk yield was 21.0 ± 3.4 L/d (mean ± SEM). Cows were kept in tied stalls with a 6 h/d period of exercise in a paddock, as in Experiment 1, and fed ad libitum a total mixed ration (1.2 Mcal NEl/kg; 16.1% CP, dry matter basis) according to their requirements (Jarrige, 1989). The same milking routine and milking equipment as described in Experiment 1 were used.
Experimental Procedures and Milk Analysis.
For the 10 wks of the experiment, cows were milked twice a day at 0800 and 1800 but on Sunday one milking only was performed at 1200. Monday morning milking was done at the regular time (0800) due to labor organization reasons, resulting in unequal long milking intervals (Saturday p.m. to Sunday, 18-h; and, Sunday to Monday a.m., 20-h). Throughout the experiment, milk yield at each milking was recorded individually using a Metatron 12 (Westfalia Landtechnik). Milk samples of each cow at each milking were taken every day to analyze daily milk composition changes. Milk fat, protein and lactose content were analyzed by using NIRS equipment (Infra Alyser 450 D, Bran + Luebbe, Norderstedt, Germany), according to the methodology described by Albanell et al. (1999). Milk SCC were analyzed by using Fossomatic equipment (Fosselectric, Hillerød, Denmark). Average milk yield and composition for Friday and Saturday were used as reference values to evaluate the effect of changing the milking frequency on Sunday.
Statistical Analysis
Data were processed by the PROC MIXED procedure for repeated measurements of SAS (version 8.1). The model included general means and the effects of the treatment, animal, experimental week, and the respective interactions and residual error. Logarithmic transformation (log10) of SCC was previously carried out for statistical analysis. When the probability of the interaction term was non significant (P > 0.20), it was deleted from the model. Differences between Least Square Means were localized with the PDIFF test and significance was declared at P < 0.05. Linear regression analysis of milk yield for each experimental period was done by using the REPEATED statement in PROC MIXED using time as a regression variable. Pearson’s correlation coefficients between cisternal areas and cisternal milk were also calculated.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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). Persistency coefficient of milk yield was 95.9% on average during the experiment. Linear regression analysis of weekly milk yields for each experimental period, before and after the omission of one milking weekly, revealed non significant (P > 0.05) differences in the slope of lactation curves from wk 1 to 5 and 6 to 10 (Table 1). Interaction between the suppression of one milking on Sunday afternoon and the experimental week was not significant (P = 0.58) and milk yield persistency before and after the omission of one milking weekly (Table 1) was unaffected by the treatment.
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), the specific loss produced by the weekly omission was lower than calculated by mean of the milk yield regressions before and after the omission of one milking. Milk yield loss due to the weekly milking omission estimated by regression was 1.08 L/d, or 3.7%. Individual analysis per cow did not show significant differences in the milk yield slope between the before and after experimental periods.
Milk composition did not change significantly (P > 0.05) during the experimental period (Table 1). Moreover, the omission of one milking applied from wk 5 did not induce any important change in any milk component (Figure 2).
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. Omitting one milking weekly did not affect (P > 0.05) the mean value of log10 SCC x 1000 which was steadily constant (2.32) during the experiment. The SCC response was very variable among cows and was dependent on SCC at the start of the experiment. To investigate this possibility, cows were divided into two equal groups of animals according to the level of SCC: low (average 134.000 ± 40.000 cells/ml) and high (average 383.000 ± 59.000 cells/ml). Milking omission did not affect (P > 0.05) the SCC change in cows of the SCC low group but showed a tendency to increase in the cows of the SCC high group (+24%; P = 0.20).
Relationship between udder cisternal size and yield loss.
Average values of measured cisternal areas and evacuated cisternal milk volumes per quarter ranged from 4.1 to 55.0 cm2 and from 0.21 to 1.95 L, respectively. Cisternal size did not significantly change (P > 0.05) after the alteration in milking frequency; the scanning area values were 21.7 ± 2.91 cm2 for the complete milking schedule and 19.94 ± 1.92 cm2 for the Sunday afternoon milking omission schedule (Table 1). Milk partitioning in the udder 8 h after milking showed a decrease in alveolar milk volume (38%, P < 0.001) and a tendency to decrease in cisternal milk volume (15%, P < 0.07) and cisternal size (7%, P < 0.11) as a result of the joint effect of milking omission and advancing lactation (Table 1). Correlation between the scanning area and the volume of cisternal milk for each quarter 8 h after milking were significant and positive before (r = 0.82; P < 0.01) and after omitting one milking weekly (r = 0.80; P < 0.01), as well as when pooled data were used (r = 0.83; P < 0.01). No significant (P > 0.05) correlation was found between milk yield and the loss produced by omitting one milking weekly. Moreover, loss of milk yield was not significantly correlated with alveolar milk volume at 8-h. However, there was a significant negative relationship between the cisternal area measured at 8-h and the loss of total milk yield on omitting one milking weekly which can be described by the equation,
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Experiment 2
Milk yield, milk composition, and udder health.
Average milk yield and milk composition did not significantly vary (P > 0.05) during the experimental weeks, but SCC increased with lactation stage. The evolution of milk yield, milk composition and SCC for the different days of the week is shown in Figure 2. On Sundays, milk yield (15.6 L/d), fat content (3.38%) and log SCC x 1000 (2.59) decreased by 29, 21, and 27% (P < 0.05), respectively, as a result of the change in milking frequency. On Mondays, milk yield (23.9 L/d), fat content (4.84%) and log SCC x 1000 (3.02) increased by 9, 14, and 100% (P < 0.05) respectively. The increase in SCC was dependent on the previous measurement but decreased again after four milkings. All values reached the average level by Wednesday. Milk protein (3.47%) increased by 2% and lactose (4.37%) decreased by 2% (P < 0.05) on average during the week. Compared with estimated for 14 milkings/week, omitting one milking weekly decreased the weekly yields of milk (3%), fat (4%), protein (5%), and lactose (5%), but milk SCC increased by 25%. Loss of milk yield varied according to the cow’s yield but not to experimental week. Clinical mastitis was not observed in any cows at any time during the experiment.
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DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Moreover a reduction of 8 to 26% in milk yield in dairy ewes (Casu and Labussière, 1972; Labussière et al., 1974; Huidobro, 1988) and a reduction of 3 to 5% in milk yield in dairy goats (Mocquot, 1978; Le Mens, 1978; Le Du, 1989) by omitting one milking weekly has also been reported. This can be related to their respective cistern size. Pattern of milk yield change during the days of the week shown in our work agrees with the results obtained by Labussière and Coindet (1968) and Charron (1986) in which milk yield decreased during the day of the suppression and increased dramatically 24-h after. Nevertheless, milk yield values reached the average level 72-h after omitting the milking. In our experiments we observed that the loss of milk yield produced by omitting one milking weekly was not affected by milk yield (Experiment 1) or by the lactation wk of the cows (Experiment 2) although in both cases the cows were in late lactation (201 to 236 DIM in Experiment 1; and, 227 to 297 DIM in Experiment 2).
The size of the cistern plays a major role in the ability of the udder to accumulate 24-h worth of milk secretion, it is responsible for approximately half of the functional udder capacity in cows (Davis et al., 1998). However, the question arises as to whether a larger cistern is associated with increased tolerance of the extended milking interval in animals.
In relation to understanding the yield loss incurred when extended milking intervals are applied, Davis et al. (1998) and Stelwagen (2001) reported that, together with cisternal size, the freedom of alveoli to drain (actively or passively) to the cistern is an important factor to explain the loss of milk yield observed when the milking interval is extended to 24-h. Knight et al. (1994) and Ayadi et al. (2003) showed that correlation between cisternal milk and cisternal size was higher at 8-h after milking than longer intervals. Based on those data, cisternal measurements in the present study (Experiment 1) were made 8-h after the morning milking.
The average size of the cisterns observed in our work by scanning for 8-h milking intervals was similar before and after omitting one milking weekly. Moreover, the methodology of Ayadi et al. (2003) was adequate to obtain a repeatable image of the udder cistern, as indicated by the high correlation between cisternal milk and cisternal size in the two periods of the experiment. Correlation between the scanning area and the cisternal milk for each quarter at the 8-h milking interval were significant and positive. This result agrees with those previously reported by Bruckmaier et al. (1994) and Ayadi et al. (2003) in cows. Moreover, Knight and Dewhurst (1994) reported a significant relationship between udder volume and milk yield. In our result (Experiment 1) we showed a strong negative correlation between the reduction in milk yield attributable to omitting one milking weekly and cisternal size measured by ultrasonography. The same conclusion was obtained in previous studies comparing once versus twice daily milkings (Knight and Dewhurst, 1994; Stelwagen and Knight, 1997; Davis et al., 1998) with the large cisternal cows showing the smallest decrease in yield. The interpretation of these data was that the putative effect of the Feedback Inhibitor of Lactation (FIL), which is a milk protein and an autocrine inhibitor of milk secretion (Peaker and Wilde, 1996), would be concentration-dependent and inactive in the cisternal milk as reported by Knight and Dewhurst (1994) and Wilde et al. (1995). Therefore, udders with large cisterns produce more milk and are more tolerant of longer milking intervals in dairy cows (Knight and Dewhurst, 1994), dairy goats (Peaker and Blatchford, 1988; Salama et al., 2003) and dairy ewes (Labussière, 1988; Rovai et al., 2000). On the other hand, small cisterned cows, by virtue of being more affected by FIL, respond better to increased milking frequency (Knight and Dewhurst, 1994).
Omitting one milking weekly did not significantly affect the milk yield composition in Experiment 1. This result agrees with the recent short-term effects observed by Sheehy (2001) and O’Brien et al. (2002) but is not in accordance with data from all lactation. Labussière and Coindet (1968) obtained an overall reduction in milk composition of 6 to 7% when one milking was omitted. The results obtained in Experiment 2 about milk composition and SCC changes for the different days of the week were in accordance with Labussière and Coindet (1968) and all values reached the average level 72-h after omitting one milking weekly. All cows were free from clinical mastitis in both trials. Although SCC in milk after the omission of one milking weekly vary, previous studies confirmed our results in short and long term experiments in dairy cows (Labussière and Coindet, 1968; Sheehy, 2001; O’Brien et al., 2002), dairy ewes (Casu and Labussière, 1972; Labussière, 1974) and dairy goats (Mocquot, 1978; LeMens, 1978).
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CONCLUSIONS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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ACKNOWLEDGEMENTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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Corresponding author:
G. Caja; e-mail:
gerardo.caja{at}uab.es.
Received for publication October 28, 2002. Accepted for publication February 18, 2003.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONCONCLUSIONSACKNOWLEDGEMENTSREFERENCES |
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-adrenergic receptor stimulation and in unfamiliar surroundings. J. Dairy Res. 60:449–456.
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), protein (
), lactose (
) and log10 SCC (
) during the 10 wk of the experiment. Values are the total dairy milk yield measured for 8 cows. Vertical bars represent SEM.