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Animal welfare issues of food-producing animals are of increasing significance both in research and to the general public. As a result, there is a pressing need for the evaluation of non-invasive, practical, cow-based and standardized parameters to objectively measure animal welfare and stress in dairy cows on-farm. Data regarding validity and reliability of these measures is crucial. A high level of standardization in parameter measurement also leads to a more specific and optimized treatment of a disease.
The focus of this work was to evaluate non-invasive cow-side parameters to objectively verify clinical mastitis (CM) via udder firmness and heat stress via fecal glucocorticoid metabolites (11,17-dioxoandrostanes; 11,17-DOA). Both CM and heat stress negatively affect the welfare of dairy cows, result in behavioral changes such as lowered lying time and impair the reproductive performance. Furthermore, both cause substantial economic losses. Therefore, these topics are highly important for the dairy industry and intensively investigated.
Assessment of udder firmness is an essential part of a sound clinical examination of a dairy cow and a practical tool to detect CM promptly. Therefore, validity and reliability of estimates of udder firmness generated by palpation and by using a validated dynamometer in healthy lactating dairy cows was evaluated in the first study. Specifically, this study set out to determine within-observer repeatability and between-observer repeatability expressed as the intraclass correlation (ICC) in two specific experiments. Additionally, a 4-point palpation scoring system was compared with estimates obtained with a dynamometer.
First, the range of udder firmness of 25 cows was determined and an in-vitro model for udder firmness was developed in a pilot trial. This model enabled training of the observers and allowed investigating a 4-point palpation scoring system. In vivo, udder firmness was determined before and after milking by palpation and by using a dynamometer.
In experiment 1, within-observer repeatability based on estimates of udder firmness of 25 cows obtained by three observers on a single day (n = 500) by palpation was 0.968 [95% confidence interval (CI): 0.960 to 0.975]. Within-observer repeatability of these estimates of udder firmness obtained with the dynamometer was 0.997 (95% CI: 0.996 to 0.998) with a coefficient of variation of 9.1% (mean + SD: 1.176 + 0.107 kg). To determine between-observer repeatability, udder firmness of 100 cows was measured on four different days by nine observers in experiment 2. Considering all measurements (n = 1,800), between-observer repeatability of estimates of udder firmness obtained by palpation and the dynamometer was 0.932 (95% CI: 0.917 to 0.945) and 0.898 (95% CI: 0.867 to 0.925), respectively. Thus, udder firmness in dairy cows could be measured repeatably with both methods, especially when performed by a single observer. Estimates of udder firmness generated by palpation and with the dynamometer were moderately related (correlation coefficient: 0.54; n = 3,600; P < 0.001). Training of observers through the pilot trial or practical experience in the four days of the study in experiment 2 did not improve the correlation. As only healthy cows were included in this first study, further research was warranted to understand how udder firmness develops in infected udders. Therefore, a follow-up study (additional unpublished work, second study) focused on udder firmness in cows suffering from CM.
Swelling and an increased firmness of the mammary gland is an important sign to detect mastitis in dairy cows. The overall objective of this study was to evaluate if udder firmness can be used as a cow-side indicator for CM. The dynamometer was used to objectively determine udder firmness before and after milking in 45 cows with CM and 95 healthy cows. Udder firmness of both hind quarters was measured daily on three locations (upper, middle, lower measuring point) from the day of mastitis diagnosis till day 7 and again on day 14. Firmness of the middle measuring point was highest before and after milking in all cows (P < 0.001). Udder firmness before milking was similar (P = 0.675) in quarters without [1.867 kg, interquartile range (IQR): 1.243 to 2.671 kg; n = 6,340] and with CM (1.948 kg, IQR: 1.213 to 2.819 kg; n = 1,220). Subsequently, we concentrated on firmness measured on the middle point after milking. After milking, quarters with CM were firmer than healthy quarters (P < 0.001). An increase of firmness in a quarter with CM did not affect firmness in the healthy neighbor quarter (P = 0.419) nor did firmness of all healthy quarters differ (P = 0.349 to 0.931). To reduce grouping of data (data clustering), one firmness value per cow i.e., Δ firmness (difference in udder firmness between both hind quarters), was used for all further calculations. In all cows, CM affected Δ firmness significantly. More precisely, Δ firmness differed between cows without (0.098 kg, IQR: 0.030 to 0.216 kg) and with CM (0.756 kg, IQR: 0.170 to 1.914 kg; P < 0.001). In cows in their second and greater parity, Δ firmness was also significantly affected by milk yield per day and DIM.
The threshold for detection of CM using Δ firmness was 0.282 kg (area under the curve: 0.722; sensitivity: 64.3%, specificity: 89.7%) and 0.425 kg (area under the curve: 0.817; sensitivity: 62.5%, specificity: 96.7%) in cows in their first parity and older cows, respectively.
Cows with CM had a higher Δ firmness compared to cows without CM throughout the 14 days after the mastitis diagnoses (P < 0.001). Parity had an effect on Δ firmness (P = 0.016). Depending on the absence or presence of systemic signs of sickness, cows with CM were classified into cows with mild to moderate (n = 21) or severe CM (n = 24). Bacteriological and clinical cure was defined based on two bacteriological negative milk samples taken at day 7 and 14 after enrollment and normal appearance of milk on the same days. Cows with severe CM suffered from a firmer udder on all measuring days (P < 0.001). An effect of parity (P = 0.140) and bacteriological cure (P = 0.262) on Δ firmness did not exist. Cows not clinically cured showed an increased Δ firmness of 0.560 kg compared to cured cows (P < 0.001).
In conclusion, udder firmness can be a useful indicator for CM in hind quarters. Further research is warranted to evaluate if firmness estimated by palpation and firmness in front udders could also be used as an indicator for CM. It also remains unclear if udder firmness can be used as a predictor for the prognosis of a CM.
Measurement of fecal cortisol metabolites in fecal samples is a scientifically established and practical method to determine stress levels in animals. In dairy cows, fecal cortisol metabolites have already been used as an indicator for stress during the transition period, dry-off, handling and transport. In this thesis, the focus is on a new field of application of measurement of fecal cortisol metabolites i.e., measurement of heat stress. The negative impact of heat stress on health and productivity of dairy cows is well known. Heat stress can be quantified with the temperature-humidity-index (THI) and is defined as a THI > 72. For aforementioned reasons, finding a way to quantify heat stress in dairy cows has been of increasing interest over the past decades. Therefore, the objective of the third study of this thesis was to evaluate concentrations of fecal glucocorticoid metabolites (i.e., 11,17-dioxoandrostanes; 11,17-DOA) as an indirect stress parameter in dairy cows without heat stress (DOA 0), with heat stress on a single day (acute heat stress; DOA 1) or with more than a single day of heat stress (chronic heat stress; DOA 2).
Cows were housed on five farms under moderate European climates. Two statistical approaches (approach 1 and 2) were assessed. Using approach 1, concentrations of fecal 11,17-DOA were compared among DOA 0, DOA 1 and DOA 2 samples regardless of their origin (i.e., cow) using an unpaired test. Using approach 2, a cow was considered as its own control i.e., 11,17-DOA were treated as a cow-specific factor and only paired samples were included in the analysis for this approach (paired tests). In approach 1 (P = 0.006) and approach 2 (P = 0.038) 11,17-DOA values of cows under acute heat stress were higher compared to those of cows without heat stress. Therefore, the hypothesis could be confirmed that acute heat stress is associated with higher fecal 11,17-DOA concentration. This was, however, not the case in cows under chronic heat stress as concentrations of fecal 11,17-DOA in cows without and with chronic heat stress did not differ. Results of this study indicate that acute heat stress has to be considered as a confounder in studies measuring fecal glucocorticoid metabolites in cows to evaluate other stressful situations.
Regarding the overall hypothesis of my thesis, validity of both parameters was verified. Udder firmness can be measured repeatably and provides a feasible and easy-to-use indicator for CM. To optimally diagnose CM, udder of cows should be examined after milking in the middle or lower part of a given udder quarter. Furthermore, different udder firmness thresholds should be used to diagnose CM in first-parity or older cows. Concentrations of fecal glucocorticoid metabolites were proven to be affected by acute heat stress. Overall, results of the three studies add one part to the improvement of objective cow-side tests to detect important conditions negatively affecting animal welfare of dairy cows.