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Reactive dairy cows are more susceptible to stress, and this may result in negative effects on milk yield and quality. The aims of this study were to investigate the relationships between temperament traits and concentration of milk cortisol and oxytocin, milk yield, milkability, and milk quality in Holstein-Gyr cows. Temperament traits were assessed in 76 Holstein-Gyr cows in the milking parlor (by scoring milking reactivity and recording the numbers of steps and kicks during pre-milking udder preparation and when fitting the milking cluster) and during handling in the corral (by measuring the time to enter in the squeeze chute, ET and flight speed, FS). Milk samples were collected for milk quality (% fat, % protein, % lactose, and somatic cell count, SCC), and milk cortisol and oxytocin. Milk yield, milking time, and average flow were also measured. The calmer cows during milking management (class 'low') produced milk with higher protein (p = 0.028) content and tendencies for lower fat (p = 0.056) and higher lactose (p = 0.055) contents. Regarding the hormones, the most reactive cows (class 'high') in the milking and handling corral produced milk with higher concentrations of cortisol (p<0.001) and oxytocin (p = 0.023). In addition, the temperament of the animals affected some of the productive measures evaluated. Cows with reactive temperament had lower milk flow and longer milking time than the intermediate ones and had higher fat and a tendency for lower protein percentage in milk compared to cows with intermediate temperaments. Calm and intermediate cows in the handling corral produced more milk and presented better milkability parameters, such as a shorter milking time and greater average milk flow. Our results suggest that the cows' behavioral reactivity can be related to the intensity of their response to stress during handling., Competing Interests: The authors have declared that no competing interests exist., (Copyright: © 2023 Marçal-Pedroza et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.)

The temperament of dairy cows interferes in milk yield and quality, but there is a lack of consensus throughout the literature. Thus, systematic review (SR) and meta-analysis (MA) methodologies were used to assess the effects of dairy cow temperament on milk yield. Our literature search included four electronic databases (CABI Abstracts, Web of Science, PubMed, and Scopus) and bibliographies of the publications included on MA. As inclusion criteria, we considered publications about the temperament of lactating cows and its effect on daily milk yield and total milk yield (whole lactation). A random effect-MA was carried out separately for daily milk yield and total milk yield related to each class of cows' temperament, 'low' (low reactivity, calm animals), 'intermediate' (intermediate reactivity), and 'high' (high reactivity, reactive animals). A total of eight publications reporting 75 trials were included in the analyses for daily milk yield, and three publications reporting nine trials for total milk yield. For daily and total milk yield the heterogeneity between publications was high (I2 = 99.9%). Cows of European breeds with intermediate temperament produced less milk daily than the calm (P = 0.020) and reactive ones (P < 0.001). In the case of primiparous cows, those with intermediate temperament produced less milk daily (P < 0.001) than the reactive ones, while for multiparous, the intermediate produced less than calm (P = 0.032) and reactive cows (P < 0.001). Regarding the stage of lactation, cows evaluated throughout lactation with a calm temperament tended (P = 0.081) to produce more milk than the intermediate ones, but less than the reactive ones (P < 0.001). For total milk yield, reactive cows tended to produce more than the calm (P = 0.082) and intermediate (P = 0.001) ones. Among European and primiparous cows, reactive cows produced more than the intermediate (P = 0.001). According to our results, we cannot confirm what we expected, that calmer cows would be the most productive for both daily and total yield., (© The Author(s) 2023. Published by Oxford University Press on behalf of the American Society of Animal Science. All rights reserved. For permissions, please e-mail: journals.permissions@oup.com.)

It remains unknown whether dairy cows with more reactive temperament produce more enteric methane (CH 4 ) and are less bioenergetically efficient than the calmer ones. The objectives of this study were (a) to evaluate the relationship between cattle temperament assessed by traditionally used tests with energetic metabolism and enteric CH 4 emissions by crossbred dairy cows; (b) to assess how cows' restlessness in respiration chambers affects energetic metabolism and enteric CH 4 emissions. Temperament indicators were evaluated for 28 primiparous F1 Holstein-Gyr cows tested singly in the handling corral (entrance time, crush score, flight speed, and flight distance) and during milking (steps, kicks, defecation, rumination, and kick the milking cluster off). Cows' behaviors within respiration chambers were also recorded for each individual kept singly. Digestibility and calorimetry trials were performed to obtain energy partitioning and CH 4 measures. Cows with more reactive temperament in milking (the ones that kicked the milking cluster off more frequently) spent 25.24% less net energy on lactation (P = 0.04) and emitted 36.77% more enteric CH 4 /kg of milk (P = 0.03). Furthermore, cows that showed a higher frequency of rumination at milking parlor allocated 57.93% more net energy for milk production (P < 0.01), spent 50.00% more metabolizable energy for milk production (P < 0.01) and 37.10% less CH 4 /kg of milk (P = 0.04). Regarding the handling temperament, most reactive cows according to flight speed, lost 29.16% less energy as urine (P = 0.05) and tended to have 14.30% more enteric CH 4 production (P = 0.08), as well as cows with a lower entrance time (most reactive) that also lost 13.29% more energy as enteric CH 4 (P = 0.04). Temperament and restless behavior of Holstein-Gyr cows were related to metabolic efficiency and enteric CH 4 emissions. Cows' reactivity and rumination in the milking parlor, in addition to flight speed and entrance time in the squeeze chute during handling in the corral, could be useful measures to predict animals more prone to metabolic inefficiency, which could negatively affect the sustainability of dairy systems., (Copyright © 2021 The Authors. Published by Elsevier B.V. All rights reserved.)