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Disease-related milk losses directly affect dairy herds' profitability and the production efficiency of the dairy industry. Therefore, this study aimed to quantify phenotypic variability in milk fluctuation periods related to diseases and to explore milk fluctuation traits as indicators of disease resilience. By combining high-frequency daily milk yield data with disease records of cows that were treated and recovered from the disease, we estimated milk variability trends within a fixed period around the treatment day of each record for 5 diseases: udder health, reproductive disorders, metabolic disorders, digestive disorders, and hoof health. The average milk yield decreased rapidly from 6 to 8 d before the treatment day for all diseases, with the largest milk reduction observed on the treatment day. Additionally, we assessed the significance of milk fluctuation periods highly related to diseases by defining milk fluctuations as a period of at least 10 consecutive days in which milk yield fell below 90% of the expected milk production values at least once. We defined the development and recovery phases of milk fluctuations using 3,847 milk fluctuation periods related to disease incidences, and estimated genetic parameters of milk fluctuation traits, including milk losses, duration of the fluctuation, variation rate in daily milk yield, and standard deviation of milk deviations for each phase and their genetic correlation with several important traits. In general, the disease-related milk fluctuation periods lasted 21.19 ± 10.36 d with a milk loss of 115.54 ± 92.49 kg per lactation. Compared with the development phase, the recovery phase lasted an average of 3.3 d longer, in which cows produced 11.04 kg less milk and exhibited a slower variation rate in daily milk yield of 0.35 kg/d. There were notable differences in milk fluctuation traits depending on the disease, and greater milk losses were observed when multiple diseases occurred simultaneously. All milk fluctuation traits evaluated were heritable with heritability estimates ranging from 0.01 to 0.10, and moderate to high genetic correlations with milk yield (0.34 to 0.64), milk loss throughout the lactation (0.22 to 0.97), and resilience indicator (0.39 to 0.95). These results indicate that cows with lower milk losses and higher resilience tend to have more stable milk fluctuations, which supports the potential for breeding for more disease-resilient cows based on milk fluctuation traits. Overall, this study confirms the high effect of diseases on milk yield variability and provides insightful information about their relationship with relevant traits in Holstein cattle. Furthermore, this study shows the potential of using high-frequency automatic monitoring of milk yield to assist on breeding practices and health management in dairy cows.

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The ability of a dairy cow to perform reliably over time is an interesting trait to include in dairy cattle breeding programs aimed at improving dairy cow resilience. Consistency, defined as the quality of performing as expected each day of the lactation, could be highly associated with resilience, defined as animal's ability to maintain health and performance in the presence of environmental challenges, including pathogens, heat waves, and nutritional changes. A total of 51,415,022 daily milk weights collected from 2018 to 2023 were provided for 255,191 multiparous Holstein cows milked 3 times daily in conventional parlor systems on farms in 32 states. The temporal variance (TEMPVAR) of milk yield from 5 to 305 d postpartum was computed as the log-transformed variance of daily deviations between observed and expected individual milk weights. Lower values of TEMPVAR imply smaller day-to-day deviations from expectations, indicating consistent performance, whereas larger values indicate inconsistent performance. Expected daily milk weights were computed using 3 nonparametric and parametric regression models: (1) loceally estimated scatterplot smoothing regression with a 0.75 span; (2) polynomial quantile regression using the median (0.5 quantile), and (3) polynomial quantile regression using a 0.7 quantile. The univariate statistical model included age at first calving and herd-year-season as fixed effects and cow as a random effect. Heritability estimates (standard errors) of TEMPVAR phenotypes calculated over the entire lactation ranged between 0.227 (0.011) and 0.237 (0.011), demonstrating that cows are genetically predisposed to display consistent or inconsistent performance. Estimated genetic correlations calculated using a multiple-trait model between TEMPVAR traits and between lactations were high (>0.95), indicating TEMPVAR is repeatable across lactations and robust to the model used to compute expected daily milk yield. Higher TEMPVAR phenotypes reflect more variation in performance, hence greater inconsistency, which is undesirable. Therefore, correlations between predicted transmitting abilities (PTA) for TEMPVAR and milk yield of 0.57 indicate that high-producing cows exhibit more day-to-day variation in performance. Correlations with productive life and livability were -0.38 and -0.48, respectively. Correlations between PTA for TEMPVAR and those of postpartum health traits were also negative, ranging from -0.41 to -0.08. Given that health traits are derived from disease resistance measurements, and higher health trait PTA are preferred, our results indicate that more consistent cows tend to have fewer health problems and greater longevity. Overall, our findings suggest that temporal variation in daily milk weights can be used to identify consistent animals that maintain expected performance throughout the lactation, which will enable selection for greater resilience to management and environmental perturbations.

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The current research focused on the effects of parity, season, and lactation stage on the milk yield of indigenous dairy cows in selected districts of the Kaffa Zone of southern Ethiopia. The districts of Gesha and Chena were purposefully chosen. The study design for the 384 household surveys was a cross-sectional survey with a simple random sample approach as the sampling method. Following the survey, 192 lactating cows were chosen for a monitored investigation to track nighttime and morning milk supply. In addition to key informants and focus group discussions, primary and secondary data were obtained via a semi-structured questionnaire, interview, and field observation. The most favored features functioning as selection criteria were those favored for production, reproduction, physical appearance, physiological function, and temperament, in that order. Evening milk yield (EMY), mornning milk yield (MMY), daily milk yield (DMY), lactation length (LL) and lactation milk yield (LMY) were 0.91 ± 0.033 L, 1.22 ± 0.037 L, 2.125 ± 0.07 L, 6.36 ± 0.116 months, and 427.10 ± 20.678 L, respectively, with significant difference (p < 0.01) amongst districts, parity, and season. However, there was no significant variation between studies in EMY, MMY and DMY. Significantly higher values of production performances were recorded for interaction among districts, parity, and season. The study also revealed that interaction between district (Gesha) and parity (third), which were signficantlly higher for EMY, MME, DMY, LL, and LMY 1.50 L, 2.00 L, 3.50 L, 8.10 months, and 850.50 L, respectively. The same trend also observed for interaction among district (Gesha), season (wet), and parity (third), which were obtained to be highly significant values of EMY, MMY, DMY, LL, and LMY were 1.35 L, 1.75 L, 3.10 L, 7.65 months, and 716.80 L, respectively. The study region has a large population of indigenous dairy cows and produces higher yields than the national average. However, it falls short of the worldwide production benchmarks, and the trait preferences used as a selection criterion were based on the farmers' indigenous knowledge. Measures to enhance production abilities must be incorporated and selection criteria must be modernized.

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Genetic selection for resilience is essential to improve the long-term sustainability of the dairy cattle industry, especially the ability of cows to maintain their level of production when exposed to environmental disturbances. Recording of daily milk yield provides an opportunity to develop resilience indicators based on milk losses and fluctuations in daily milk yield caused by environmental disturbances. In this context, our study aimed to explore milk loss traits and measures of variability in daily milk yield, including log-transformed standard deviation of milk deviations (Lnsd), lag-1 autocorrelation (Ra), and skewness of the deviations (Ske), as indicators of general resilience in dairy cows. The unperturbed dynamics of milk yield as well as milk loss were predicted using an iterative procedure of lactation curve modeling. Milk fluctuations were defined as a period of at least 10 successive days of negative deviations in which milk yield dropped at least once below 90% of the expected values. Genetic parameters of these indicators and their genetic correlation with economically important traits were estimated using single-trait and bivariate animal models and 8,935 lactations (after quality control) from 6,816 Chinese Holstein cows. In general, cows experienced an average of 3.73 environmental disturbances with a milk loss of 267 kg of milk per lactation. Each fluctuation lasted for 19.80 ± 11.46 days. Milk loss traits are heritable with heritability estimates ranging from 0.004 to 0.061. The heritabilities differed between Lnsd (0.135-0.250), Ra (0.008-0.058), and Ske (0.001-0.075), with the highest heritability estimate of 0.250 ± 0.020 for Lnsd when removing the first and last 10 days in milk in a lactation (Lnsd2). Based on moderate to high genetic correlations, lower Lnsd2 is associated with less milk losses, better reproductive performance, and lower disease incidence. These findings indicate that among the variables evaluated, Lnsd2 is the most promising indicator for breeding for improved resilience in Holstein cattle.

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The objective of the present study was to determine heat stress zones (HSZ) in a year for daily milk yield (DMY) of Murrah buffaloes. Data for the study included 2,67,599 daily milk yield records of 445 Murrah buffaloes sired by 171 bulls as well as climatic parameters, viz. dry bulb temperature (Tdb) and wet bulb (Twb) temperatures spanning over 16 years (2001-2016). The regression analysis of DMY on carryover heat effect indicated that the decline in DMY was significant above the carryover heat effect (CHE) 70. April-November were critical for daily milk yield, and maximum decline in daily milk yield was observed during the month of August in Murrah buffaloes. Therefore, two zones in a year were classified as non-heat stress zone (NHSZ) with CHE < 70 for months December-March and heat stress zone (HSZ) with CHE > 70 during April-November.

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The objective of this study was to evaluate the different lactation stages of F1 Holstein x Zebu cows on intake and digestibility of nutrients, nitrogen use efficiency, feeding behavior and performance. Thirty-six F1 Holstein × Zebu cows with initial body weight (BW) of 482±43kg were used. The early, mid and late lactation stages were characterized after 50±13, 111.5±11.75 and 183.0±17.5 days in milk, respectively. A completely randomized design with three lactation stages and 12 cows in each treatment group was used. Dry matter intake (P=0.01) was higher in late lactation. Milk yield (P<0.01) was 24.17% higher in early lactation than in other stages. Body weight was lowest in mid-lactation cows (465.63kg; P<0.01). The feed efficiency was 23.36% higher in early lactation than in other stages (0.82kg of milk/kg of DM). F1 Holstein x Zebu cows have increased dry matter intake in late lactation. Milk yield and feed efficiency in early lactation were benefited by changes in feeding behavior, such as increased rumination time.(AU)

O objetivo deste estudo foi avaliar os diferentes estágios de lactação de vacas F1 Holandês x Zebu quanto ao consumo e à digestibilidade de nutrientes, à eficiência no uso de nitrogênio, ao comportamento ingestivo e ao desempenho. Trinta e seis vacas F1 Holandês × Zebu, com peso corporal inicial (PC) de 482±43kg, foram utilizadas. Os estágios inicial, médio e final da lactação foram caracterizados após 50±13, 111,5±11,75 e 183,0±17,5 dias de lactação, respectivamente. O arranjo experimental adotado foi o delineamento inteiramente ao acaso, com três fases de lactação e 12 vacas em cada grupo de tratamento. O consumo de matéria seca (P=0,01) foi maior no período final da lactação. Na fase inicial da lactação, a produção de leite (P<0,01) foi maior em 24,17% em comparação às demais fases. Na fase intermediária da lactação, as vacas apresentaram menor peso corporal (465,63kg; P<0,01) em relação às demais fases. A eficiência alimentar foi maior em 23,36% na fase inicial da lactação (0,82kg de leite/kg de MS). Vacas F1 Holandês x Zebu aumentam o consumo de matéria seca no período final da lactação. A produção de leite e a eficiência alimentar no início da lactação foram favorecidas por mudanças no comportamento ingestivo, como o aumento do tempo de ruminação.(AU)

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The present study was undertaken to estimate effect of various genetic and non-genetic factors on persistency of milk production and to identify the most appropriate persistency method that fits best in our environment. In the present study, effects of different non-genetic factors, viz. year, season, days to attain peak yield, and genetic group based on the level of exotic inheritance on persistency of milk yield in crossbred cattle were studied. Data comprised of 686 first lactation daily milk yield records of crossbred cattle that were maintained at GADVASU dairy farm over a period of 25 years from 1991 to 2015 were utilized to calculate persistency coefficients by four methods, viz., Ludwick and Peterson method (P1), Mahadevan method (P2), ratio method (P3), and Prasad et al. method (P4). Overall least squares means for persistency by Ludwick and Peterson method (P1), Mahadevan method (P2), ratio method (P3), and Prasad et al. method (P4) were 0.896 ± 0.096, 1.385 ± 0.224, 187.207 ± 26.398, and 0.621 ± 0.098, respectively. Effect of sires was significant (P < 0.05) on P2 and P4 methods. Effect of genetic group on all four methods was non-significant. Period of calving had significant (P < 0.01) effect on persistency of milk yield (P2, P3, and P4 methods). Effect of season of calving on persistency of milk yield was found to be significant in all estimates obtained by the four methods. Summer and autumn calvers were most persistent whereas spring and winter calvers were least persistent for (P2, P3, and P4 methods). Persistency of milk yield was significantly (P < 0.05) affected by days to attain peak yield in P1 and P2 methods. Maximum persistency was obtained in animals attaining peak at 41-57 days of lactation and minimum in < 41 days for Mahadevan method and ratio method. The highest heritability of persistency and minimum value of standard error was estimated as 0.275 ± 0.11 for the Mahadevan method followed by the Prasad method (0.197 ± 0.10) by half sib correlation method. The maximum coefficient of variation which indicates available variability was estimated as 20.788% for persistency by the Mahadevan method followed by 18.969% for the Prasad method. The highest correlation was also observed between P1 and P3 methods by Spearman's and Pearson's correlation for least squares breeding value of the sires. On the basis of heritability, standard error of heritability, and coefficient of variation, it can be concluded that the Mahadevan method followed by the Prasad method suits best to our environment for animals in first lactation as well as they can be utilized for effective selection for higher persistency in crossbred animals of Punjab.

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Different breeding systems associated with specific bovine genetic resources have coexisted in Burundi. To prepare for the development of a national action plan for the improvement of bovine genetic resources in Burundi, we aimed at performing genetic characterization of Ankole and Ankole × European crossbred individuals and assessing the effect of European ancestry on milk productivity of cows kept under the mixed crops livestock system. To that end, we genotyped 37 Ankole and 138 crossbred individuals on 42 636 SNPs and combined these genotypes with those from 21 cattle breeds, representative of the bovine genetic diversity. We also measured milk yield not suckled and estimated suckled milk. Given the results, we confirmed the indicine × African taurine admixed origin of the Ankole in Burundi and showed that crossbred individuals present a high proportion of European ancestry (i.e. 57% on average). As the proportion of European ancestry increased, milk yield increased by 0.03 ± 0.01 l/day, at a lower extent than expected. We also observed that breeders were unable to correctly evaluate the European proportion in their livestock. Our results may provide useful information for objective dairy breeding in Burundi. As an example, an ex-situ conservation program of Ankole within the framework of value chains is proposed as an accompanying strategy to improve the sustainability of the crossbreeding program.

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The climatic conditions in Croatia are deteriorating which significantly increases the frequency of heat stress. This creates a need for an adequate dairy farming strategy. The impact of heat stress can be reduced in many ways, but the best long-term solution includes the genetic evaluation and selection for heat stress resistance. In order to create the basis for genetic evaluation, this research determined the variation in daily milk yield (DMY) and somatic cell count (SCC) as well as the differences in resistance to heat stress due to production level (high, low) and breed (Holstein, Simmental) of dairy cattle breed in Croatia. For statistical analysis, 1,070,554 test-day records from 70,135 Holsteins reared on 5679 farms and 1,300,683 test-day records from 86,013 Simmentals reared on 8827 farms in Croatia provided by the Croatian Agricultural Agency were used. The results of this research indicate that the high-producing cows are much more susceptible to heat stress than low-producing especially Holsteins. Also, the results of this research indicate that Simmental breed, in terms of daily milk production and somatic cell count, could be more resistant to heat stress than Holstein. The following research should determine whether Simmentals are genetically more appropriate for the challenges that are in store for the future milk production in this region. Furthermore, could an adequate production level be achieved with Simmentals by maintaining the heat resistance?

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Aerococcus viridians (A. viridans), an environmental Gram-positive bacterium, has been documented to be associated with bovine mastitis. However, its exact role in bovine mastitis and the changes it brings about in milk characteristics are not yet known. The objectives of the current study were to describe the antibiotic resistance of A. viridans from bovine mastitis as well as the correlation between existence of this pathogen in udders and the somatic cell counts (SCC), daily milk yield, and composition of individual cow. One-year sampling for subclinical mastitis composite milk was conducted based on monthly DHI data from September 2013 to August 2014, in a commercial herd located in Beijing, China. All samples were cultured and pathogens were identified using microbiology method. A. viridians isolates were further identified by API identification system and 16S ribosomal RNA (rRNA) sequencing method. Kirby-Bauer disk diffusion method was used to test the antibiotic resistance of A. viridians against kinds of antimicrobial substance. SCC, milk yield, and milk composition data were from monthly Dairy Herd Improvement (DHI) results. Results showed that a total of 279 (16.67%) A. viridans isolates were identified from among 1674 bacterial isolates cultured from milk samples with high SCC. The incidence of mastitis caused by A. viridans was the highest (48-53%) during the summer season. Majority of the isolates were susceptible to most of antimicrobial compounds tested, especially to ß-lactams, but were found to be resistant (50-90%) to aminoglycosides, sulfonamides, and tetracycline. The average SCC of the A. viridans infected cows was significantly higher (1000.0 × 103 cells/mL) (P < 0.01) as compared to healthy cows (72.4 × 103 cells/mL) and daily milk yield decreased (P > 0.05) by 1.86 kg/day. Reductions were also observed in fat content (P > 0.05), lactose (P < 0.01), and total solids (P > 0.05), whereas protein content increased significantly (P < 0.01) in milk samples of cows infected with A. viridans. The results of this study suggest that A. viridans could be considered as an emerging aetiological agent of bovine subclinical mastitis wherein it exerts an effect on SCC, milk yield, and composition.

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The milk production of a dairy cow is characterized by lactation production, which is calculated from daily milk yields (DMY) during lactation. The DMY is calculated from one or more milkings a day collected at the farm. Various milking systems are in use today, resulting in one or many recorded milk yields a day, from which different calculations are used to determine DMY. The primary objective of this study was to develop a mathematical function that described milk production of a dairy cow in relation to the interval between 2 milkings. The function was partly based on the biology of the milk production process. This function, called the 3K-function, was able to predict milk production over an interval of 12h, so DMY was twice this estimate. No external information is needed to incorporate this function in methods to predict DMY. Application of the function on data from different milking systems showed a good fit. This function could be a universal tool to predict DMY for a variety of milking systems, and it seems especially useful for data from robotic milking systems. Further study is needed to evaluate the function under a wide range of circumstances, and to see how it can be incorporated in existing milk recording systems. A secondary objective of using the 3K-function was to compare how much DMY based on different milking systems differed from that based on a twice-a-day milking. Differences were consistent with findings in the literature.

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