The effect of varying the interval between milkings on milk secretion

Abstract

The effect of 6-, 12-, 18-, 24-, 30-and 36-h milking intervals on milk secretion has been investigated. The effect of the previous milking intervals was eliminated by interposing a recovery period consisting of 12-h milking intervals between the experimental intervals. Bias due to the carry-over of residual milk was reduced by removing the residual milk at the end of each milking, after an injection of oxytocin.The rate of secretion of milk and of the individual constituents decreased curvilinearly, with duration of the interval, but the degree of curvilinearity differed between constituents. The rates of decrease were in the following increasing order: sodium, chloride, fat, whey proteins, casein N, water, non-protein N, lactose and potassium. The effects of the treatments persisted for some time after the end of the experimental intervals, but the original rates of secretion were regained by the end of the recovery period. The differing effects on the secretion of individual constituents resulted in increases in the concentrations of sodium, chloride and whey proteins in the milk and decreases in those of lactose and potassium.The earliest work on the rate of secretion of milk was carried out by Ragsdale, Turner & Brody (1924), who concluded that there was a progressive decline in the rate of milk secretion with increase in the length of milking interval, and that there was an even more marked effect on the secretion of fat. In the interpretation of the results the authors assumed that the milk obtained at a milking was that which had been secreted in the previous interval. Johansson (1940) demonstrated, however, that there is a considerable carry-over of milk and of fat from one milking interval to the next. He found that the carry-over of residual fat was in direct proportion to the amount of milk in the udder before milking. This was confirmed by Bailey, Clough & Dodd (1955), and Turner (1953, 1955 showed that it was true also for residual milk. In the type of experiment devised by Ragsdale et al. (1924) the carryover would therefore bias the results so that the quantity of milk removed from the udder after short intervals would be greater than that secreted during the interval and, conversely, after a long milking interval the quantity removed would be less than the amount secreted. The effects would be even more marked for fat than for milk yield.• Present address: Department of Agriculture, The University, Leeds.

Performance of dairy cows milked twice daily at contrasting intervals

“…The daily milk yield reduction for the 5 : 19 h milking schedule was modest (4.1%) in experiments 1 and 2, in agreement with the 2.4% recorded for 6.5 : 17.5 h intervals by Ichikawa and Fujishima (1982). It results from the slow decrease in the hourly milk secretion rate up to a milking interval of about 19 h (Figure 4), which seems less marked than the losses recorded in analytical conditions (8% to 12% for milking interval of 16 h to 20 h; Schmidt, 1960;Wheelock et al, 1966;Delamaire and Guinard-Flament, 2006). In our TDM groups, long milking intervals alternated with short ones, which may have tempered their detrimental effects on milk secretion rate (Turner, 1955;Wheelock et al, 1966).…”

“…As the milking interval increased from 2.5-3 h to 12-15 h, the first fraction decreased, while the second one increased, the two effects jointly lowering the fat content in the harvested milk (Figure 2). This trend should have continued up to the longest milking intervals (19 to 21.5 h, according to the experiment), but it was increasingly thwarted by the earlier slowdown of the lactose secretion rate compared with the fat secretion rate, beyond a milking interval of 15 to 18 h (Wheelock et al, 1966). Consequently, milk fat content ceased to decrease and even increased, as previously described by Wheelock et al (1966).…”

“…It results from the slow decrease in the hourly milk secretion rate up to a milking interval of about 19 h (Figure 4), which seems less marked than the losses recorded in analytical conditions (8% to 12% for milking interval of 16 h to 20 h; Schmidt, 1960;Wheelock et al, 1966;Delamaire and Guinard-Flament, 2006). In our TDM groups, long milking intervals alternated with short ones, which may have tempered their detrimental effects on milk secretion rate (Turner, 1955;Wheelock et al, 1966). This alternation of long and short milking intervals might also explain the higher milk yield (1.9 kg for the three experiments pooled; P 5 0.08) recorded after the longest milking intervals in the TDM groups (19 h to 21.5 h) compared with the 24 h interval in ODM.…”

“…The declining coefficient of correlation between the pre-and experimental milk yields for groups 10 : 14 h, 5 : 19 h and ODM (r 5 0.79, 0.69 and 0.37, respectively) in experiment 3 suggests that as the milking intervals become more unequal, the milk yield of the cows depends less and less on their milk yield capacity (appraised by the milk yield on a conventional milking regime) and more and more on their tolerance to long milking intervals. This tolerance (appraised by percentage loss of milk) is not related to their milk yield capacity (Hansson et al, 1958;Wheelock et al, 1966) and shows a wide between-cow variability (coefficient of variation of 29%, for a mean loss of milk of 27%, in a set of 237 cows switched from a conventional TDM regime to ODM; Ré mond and Pomiè s, 2005). This explains the non-significant relation between the pre-and experimental milk yields in the ODM group of experiment 3.…”

“…The consequences of short (,8 h) or long (.16 h) milking intervals on milk secretion have essentially been determined in analytical experiments using specific designs: intervals tested once (Stelwagen et al, 2008), or applied several times consecutively, which modifies the daily milking frequency (Schmidt, 1960;Ayadi et al, 2004;Delamaire and Guinard-Flament, 2006); complete milk removal from the udder through oxytocin administration before the experimental interval in order to empty the mammary reservoirs (Schmidt, 1960;Wheelock et al, 1966); a standard 12 h milking interval preceding all the experimental intervals (Wheelock et al, 1966;Fernando and Spahr, 1983), and generally a short duration of experimentation (1 day to a few days), though not always (60 days for Villiers de and Smith (1976)). These experimental conditions differ from those met in practice and cannot provide reliable information on the effect of widely contrasting milking intervals on milk production in commercial TDM herds.…”