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An abrupt cessation of milking at the time of dry-off is a most common and a well-proven management procedure that was already established at the beginning of the 20th century. But whereas cows even in the 1970s rarely produced more than 9 kg milk per day at the time of dry-off, in recent years milk yield exceeding 30 kg and more is not uncommon. In addition to an increased udder firmness and udder swelling after an abrupt cessation of milking, cows frequently show certain behavioral changes, e.g., reduced feed intake and increased vocalization. These behavioral changes might be an indicator for stress, pain and discomfort. Considering these evidences, I hypothesized that there is a relationship between milk yield at the time of dry-off, udder pressure and elevated stress levels after dry-off. Thus, the overall objective of this thesis was, to evaluate stress caused by drying-off dairy cows and to relate milk yield at dry-off, udder pressure and stress levels after dry-off.
While udder pressure has been measured for multiple reasons, the equipment used in previous studies was cumbersome and had diverse technical limitations. Manual palpation, however, might be subjective. A new device, a dynamometer, developed to measure fruit crisp, facilitates an objective, non-invasive measurement of udder pressure. While these dynamometers have been already validated for the measurement of fruit crisp, there is a dearth of information about their applicability to measure udder pressure. Therefore, the objective of the first study of my thesis was to validate a dynamometer (Penefel DFT 14) for the measurement of udder pressure in dairy cows.
Two experiments were conducted in order to establish a measuring procedure that guarantees an excellent inter-investigator repeatability. In both experiments udder pressure was measured multiple times (n = 2838) by two independent investigators. According to operation procedures implemented for the measurement of fruit crisp, an initial protocol utilized in experiment 1 was developed. The basic handling of the device was determined, the penetration depth was roughly defined, and a general definition of the measuring location was given. Following this protocol, the agreement between investigators was mediocre and repeatability was not sufficient (i.e., r = 0.80, P < 0.001). Therefore, it was improved and experiment 2 was conducted. This protocol featured the usage of a spacer to define the penetration depth more precisely and the marking of the measuring point. In this experiment there was no disagreement between investigators (P > 0.05) and the coefficient of correlation exceeded the one calculated for experiment 1 clearly (i.e., r = 0.94, P < 0.001). Experiment 1 and 2 demonstrated that udder pressure measurements with a sufficient inter-investigator repeatability could be achieved with an exact measuring protocol.
A third experiment was conducted in order to quantify the effects of location within a given quarter and between quarters on udder pressure. Therefore, udder pressure was measured in 6 different locations – at the upper, middle, lower third of the left hind quarter (n = 198) and in the middle of each quarter at the same level (n = 56). Udder pressure differed significantly between the three locations within the left hind quarter. Between quarters udder pressure was lower in the front than in the hind quarters (P < 0.05). Based on these results, it was recommended to carry out udder pressure measurements at the same quarter and at the same level in order to achieve comparable results.
In the last experiment, the change of udder pressure before to after milking and its relationship to milk yield was investigated. Measurements were carried out 1 h ± 30 min before and directly after the evening milking. Udder pressure decreased after milking in 91.5% of the udders. In average, pressures after milking were 36.5% lower than before. The predictive value of udder pressure, however was limited (i.e., correlation udder pressure change – milk yield r = 0.42, P < 0.001). Nevertheless, this experiment showed the importance of measuring udder pressure every day at the same time before or after milking in order to allow an objective comparison of values.
The first study provided evidence that the dynamometer provides reliable results, given that a standardized protocol is followed in order to minimize confounding.
The second study determined the relationship between milk yield, udder pressure and stress levels before dry-off and in the early dry period. While the dynamometer presented an adequate method to measure udder pressure, the evaluation of stress in dairy cows was challenging. The blood cortisol concentration is a common, albeit highly sensitive indicator of stress that is not usable to determine chronic stress levels. 11,17-dioxoandrostane, a fecal cortisol metabolite is less susceptible to acute stress and provides a reliable alternative for the measurement of chronic stress. Therefore, the objectives of the second study were 1) to quantify changes of udder pressure and fecal 11,17-dioxoandrostane concentrations after a sudden dry-off, 2) to determine the effect of milk yield prior to dry-off on udder pressure and the fecal 11,17-dioxoandrostane concentration, and 3) to evaluate the relationship between udder pressure and fecal 11,17-dioxoandrostane concentration in the early dry period.
Seventy-six healthy, late-lactating Holstein-Friesian dairy cows were enrolled in the study 7 days before dry-off. They were grouped based on their average daily milk yield in low (< 15 kg/d, n = 25), medium (15-20 kg/d, n = 26) and high (> 20 kg/d, n = 25) yielding. Udder pressure was measured daily at the same time utilizing the Penefel DFT 14. Fecal samples were collected twice within the last week before dry-off and 2, 3, 5, 7 and 9 days after dry-off. An 11-oxo-etiocholanolone enzyme immunoassay was carried out to determine the 11,17-dioxoandrostane concentration.
For all cows, an effect of yield group (P = 0.001) and day (P < 0.001) on udder pressure could be proven. Udder pressure increased in all yield groups (P < 0.001) after dry-off, peaked on the second day after dry-off and declined afterwards. Considering different yield groups, udder pressure after dry-off was highest in high yielding cows. Values differed between high and low yielding and between medium and low yielding cows for 9 and 7 days after dry-off, respectively (P < 0.05). Milk leakage was recorded as one factor associated with udder pressure. While a total of 27 cows (33.8%) had milk leakage after dry-off, cows with high udder pressure were more likely to show milk leakage than cows with low pressure values (P = 0.021).
After dry-off, 11,17-dioxoandrostane concentrations were effected by day (P = 0.005) and udder pressure (P = 0.05). They increased after dry-off in medium and high yielding cows, peaked on day 3 after dry-off and remained at an elevated level afterwards (P < 0.05). In low yielding cows, however, only the 11,17-dioxoandrostane concentration on the third day after dry-off was higher than the baseline (P = 0.005). While 11,17-dioxoandrostane concentrations after dry-off did not differ between yield groups (P > 0.05), the increase of 11,17-dioxoandrostane compared to the baseline diverged clearly (P < 0.05). It was highest in high yielding cows (P < 0.001). The increase in low yielding cows, however, was negligible.
Interestingly, udder pressure and 11,17-dioxoandrostane concentrations after dry-off showed a similar profile, but a time lag of 1 day. Former studies evaluated a time lag of 8 to 16 h between an increase in blood cortisol coinciding with the triggering stressor and an elevated concentration of fecal 11,17-dioxoandrostane. Therefore, a causal relationship between udder pressure and 11,17-dioxoandrostane concentration could be suspected. This hypothesis is furthermore supported by the fact that high yielding cows had the highest udder pressure values and the highest increase in 11,17-dioxoandrostane.
Overall, the second study showed that an abrupt cessation of milking causes an increase in udder pressure and fecal stress hormone concentration. While high yielding cows showed higher udder pressure and a greater increase in their stress levels after dry-off, the effect of a sudden dry-off on low yielding cows was negligible.
The effect of a sudden dry-off on udder pressure and stress levels in high yielding cows was clearly demonstrated in the second study of this thesis, the relevance of these data for the dairy husbandry and animal welfare, however, remained unclear. In order to prove the importance of this research results, especially for German dairy farms and to substantiate the relevance of this thesis a third experiment was conducted. The objectives of this third study were 1) to evaluate current dry-off strategies on German dairy farms using a questionnaire, 2) to quantify behavior indicative of stress after dry-off, and 3) to compare dry-off strategies used on commercial dairy farms to recommendations given in the current literature.
A questionnaire was developed and distributed among participants in a continuing education event organized by a German cattle breeding organization. Two hundred questionnaires were distributed and data from 91 farms (35 to 1,000 lactating cows) with an average milk yield of 8,949 kg 305-day lactation were analyzed.
Farmers participating in the survey mentioned that cows were dried off approximately 7 weeks before the calculated calving date. Only 9.9% of the farms had a dry period length of 5 weeks or less. A continuous milking regime without dry period was not established on any farm participating in the survey.
The majority (73.0%) of the farmers performed a sudden dry-off without any previous preparation. Only 11.8% and 15.0% of the farms attempted to lower milk yield prior to dry-off by reducing the milking frequency and adjusting the feed ration, respectively.
Most farmers (94.1%) transferred cows after last milking to a separate dry cow pen. At the same time the feed ration was mostly (76.5%) changed to a low energy density roughage mix. Only 7.1% of the farmers reduced the feed quantity instead of changing the ration. A blanked antibiotic dry cow treatment was carried out on 79.6% of the farms, whereas 64.9% of all antibiotic dry cow treatments were conducted without preceding bacteriological examination. A selective dry cow treatment was not mentioned by any farmer.
Milk yield was an important factor considering the dry-off management. Most farmers (77.4%) preponed the dry-off date, if milk yield fell below an individual threshold, an altered dry-off procedure in high yielding dairy cows, however, was rare (9.7%). Besides milk yield, udder health was the most important factor to adjust the dry-off procedure. Reasons to forgo the dry-off were clinical (78.9%) and subclinical mastitis (16.7%).
All participating farmers monitored their dry cows, 92.1% by evaluating the general health status of the cow. Only 29.2% of the participating farmers, however, regularly touched the udder and checked for udder pain.
The last section of the questionnaire covered questions about behavioral changes associated with stress after dry-off. Each farmer participating in the study reported at least one stress related behavior like reduced feed intake and increased vocalization.
Regarding the overall hypothesis of my thesis, the results of the three studies demonstrated that the sudden dry-off is a stressful management procedure in high yielding dairy cows. Considering increasing milk yield, this finding is relevant as the sudden dry-off currently is one of the most common dry-off procedures. Therefore, a re-evaluation of present dry-off methods especially in high yielding cows is indicated. Strategies to reduce udder pressure and stress caused by an abrupt cessation of milking are necessary and further research is warranted in this field.