The research projects covered in this dissertation were carried out under organic certified dairy management systems and were intended to provide basic information on the implementation of strategies for nutritional management, prevention and early detection of disease on dairy cows. Organic dairy systems provide unique settings to perform research on animal health and productivity, since certified organic dairy farms are regulated by fixed requirements that must be met at all times. Conversely to conventional dairy farms, the standardization of the regulations by the national organic program causes that all organic certified dairy farms have similar challenges regarding animal health, reproductive and productive performance. Therefore, significant evidence generated in studies carried out on organic dairy animals could be transversally applied into certified organic and conventional dairy farms in the USA, as production restrictions are increasing for both systems. Another relevant reason for implementing research studies for improving animal health and productivity for organic dairy systems is the growth of organic food sales in the USA, where organic dairy products represent the 15% of the organic food market. Due to this growth, the number of organic dairy cows per herd has consistently increased during the last 10 years, which will require more research to understand the relationship between dairy animals’ performance and intensive organic systems. This dissertation presents five research studies performed in young heifers and in lactating dairy cows, with emphasis 0n supplementation of energy dense feeds, cow’s conditioning behaviors, and in the development of methods of data analysis for improving welfare assessment and disease detection, based on behavioral multivariable correlations. The study presented in Chapter I evaluates the effects of supplemental rumen-protected fats (RPF), specifically developed for certified organic dairy farms in the USA. A randomized controlled trial was performed using 202 Holstein cows supplemented once a day with 0.45 kg/head of RPF (n = 101) or a control diet (n = 101) from calving day until 150 days in milk (DIM). The evaluated outcomes included daily milk yield, milk components, reproductive performance, metabolic markers, culling and mortality. A significant effect after the inclusion of RPF was found in daily milk yield among multiparous (MP) cows, where supplemented cows had greater milk yield (1.5 kg/d) compared to MP control cows by 150 DIM. No effect was found in primiparous (PP) cows. Reproduction performance was not improved or impaired by RPF in the diets. The inclusion of RPF tended to increase serum concentrations of β-Hydroxybutirate and non-esterified fatty acids especially at 7 and 21 DIM, which agreed with published studies on RPF supplementation in conventional dairy farms. Cows supplemented with RPF tended to have lower culling risk but mortality risk did not differ among supplemented and control cows. The research presented in Chapter II has direct relationship with the previous study, as manual sorting of the two treatment groups was used to separate the study cows for the RPF supplementation. A case report of the self-sorting behavior acquired by the study cows and the investigation of the conditioning factor for such behavior is presented. To test the effectiveness of human sorting on separating subgroups of lactating dairy cows and to assess the level of conditioning to this activity, we compared three sorting methods applied to the same cows: 1) human active sorting (AS) at the pen gate; 2) human presence as passive sorting (PS); and 3) non-human gate sorting (GS). We hypothesized that after a training period cows become conditioned to human sorting. Holstein cows (N = 176; parity = 2.5 ± 1.3), housed within the same lactating group were randomly assigned into two subgroups (A = 91 animals and B = 85 animals) to be sequentially separated by three sorting methods (AS; PS; and GS). Each sorting method was applied once per day after morning milking during 5 days. When AS was applied, the total proportion of animals correctly sorted was of 99.8%, whereas PS had 94.8% of sorting accuracy (P <0.0001). Non-human GS could not be accurately assessed because the cows lost their self-sorting behavior overcrowding one side of the pen making impossible the data collection. During the RPF study and during the evaluation of sorting methods, we observed a clear self-sorting behavior in response to human sorting, regardless the use of AS or PS. Therefore, after a period of training, lactating dairy cows became operant conditioned to human sorting, which represents an opportunity for animal separation without intense human labor or practices that result in increased animal stress. The studies presented in chapters III and IV develop exploratory methodologies for analyzing behavioral data recorded by remote sensor devices (RSD) in individual dairy cows. Such data include the assessment of active time, rumination, and eating time, and locomotion and lying behavior. In chapter III, temporal relationships between two behavioral variables were evaluated considering culling status in a subset of cows classified as cases (n =12, culled cows) and healthy controls (n=30). The analysis suggested to investigate temporal relationship based on time series and cross-correlation analysis. The data presented in chapter III suggest that there are differential patterns in animals that will be culled due to health reasons and animals that remained healthy and in good productive and reproductive standing by mid-lactation. These differential patterns in cross-correlations were observed before and after calving and predicting behavior variables for fluctuations observed in other behavior variables were determined by culling status. Additionally, in Chapter III, a relationship between production levels in the previous and current lactation and the lying time was determined. In general terms, high producing cows spent more time lying down compared to low producing cows during the first 21 d of lactation. Moreover, increments in lying times during that period were associated with increments in milk yield during the current lactation. Chapter IV covers the development of welfare indicators based on behavioral parameters continuously evaluated by RSD. To evaluate the association between welfare status and differences in behavior, we developed a welfare status criterion based on the absence of clinical disease during the observation period (calving to 150 DIM), cyclicity, and productive performance. Animals having absence of clinical disease, cycling before 60 DIM and in or above the average from group’s milk yield had significantly higher rumination and eating time, especially during the first 21 DIM compared with animals without the aforementioned conditions. Active time was not associated with the proposed welfare status. Additionally, it was determined that 5 min increments in rumination and eating time were associated with increased odds of being classified as animals in good welfare standing by 150 DIM. These findings open new research perspectives to develop welfare indicators for real-time welfare assessments without human error and in normal productive settings. Finally, in Chapter V, we evaluated the use of sunlight reflection technology to reduce temperature in the polyethylene hutched used to raise pre-weaned dairy calves. This evaluation was performed to provide scientific evidence on the usefulness of aluminized covers already in the market; therefore, farmers can have a more informed investment decision in this type of products. The objective was to evaluate the effect of aluminized reflective hutch covers on health and performance of pre-weaned Holstein heifers during summer. Health, behavior, rectal temperature, and respiratory rate were assessed twice per week from 1 to 60 d of life on calves housed in covered or uncovered control polyethylene hutches. No differences between treatments were found in presentation of clinical dehydration, nasal and eye discharge, rectal temperature, respiratory rate, and weight gain. However, calves in covered hutches had greater occurrence of diarrhea and abnormal ear scores. The use of reflective covers was only able to reduce the temperature of the hutch wall in intimate contact with the cover. Nonetheless, no differences were found in the center of the hutch or in the sand used for the bedding. As the body of knowledge on organic certified dairy systems advances, new opportunities for researching the effects of novel management strategies on animal health and, productive and reproductive performance appear. Additionally, the development of new therapeutic and preventative strategies for infectious, metabolic, and obstetric diseases, as well as the implementation of innovative management especially created for organic dairy cattle, bring a new prospective in veterinary medicine and livestock science research, that will follow the line of this dissertation.PFCHA-BecasPFCHA-Becas