Critical THI thresholds based on the physiological parameters of lactating dairy cows

The severity of heat stress conditions in high-yielding dairy cows is currently underestimated. The present study aimed to determine the heat load threshold of the temperature-humidity index (THI) on physiological parameters of lactating Holstein-Friesian cows under a continental climatic zone in Germany. Physiological parameter measurements, such as respiration rate (RR), measured hourly, and heart rate (HR) and rectal temperature (RT), both measured twice daily, were performed in a total of 139 multiparous cows on three randomly chosen measurement days per week. In addition, the ambient temperature and relative humidity of the barn were recorded every 5 min to calculate the current THI. The physiological parameter data were linked to the THI, and the heat load thresholds were determined using the broken-stick model. The heat load duration effect of each physiological parameter was obtained by regression analysis. Considering the increases in the physiological parameters, our study provided reliable data to determine heat load thresholds for lactating high-yielding dairy cows in a moderate climatic zone. The heat load threshold could be determined for RR in standing cows (THI = 70) and lying cows (THI = 65) and for HR (THI = 72) and RT (THI = 70) in standing cows. The heat load duration also demonstrated a significant effect on the increases in physiological parameters among dairy cows. In particular, the present study enabled a strategy to be devised to initiate heat mitigation in high-yielding dairy cows when they are exposed to THIs above 65.     

Impact of heat stress on conception rate of dairy cows in the moderate climate considering different temperature–humidity index thresholds,periods relative to breeding,and heat load indices

The objectives of this retrospective study were to investigate the relationship between temperature–humidity index (THI) and conception rate (CR) of lactating dairy cows, to estimate a threshold for this relationship, and to identify periods of exposure to heat stress relative to breeding in an area of moderate climate. In addition, we compared three different heat load indices related to CR: mean THI, maximum THI, and number of hours above the mean THI threshold. The THI threshold for the influence of heat stress on CR was 73. It was statistically chosen based on the observed relationship between the mean THI at the day of breeding and the resulting CR. Negative effects of heat stress, however, were already apparent at lower levels of THI, and 1 hour of mean THI of 73 or more decreased the CR significantly. The CR of lactating dairy cows was negatively affected by heat stress both before and after the day of breeding. The greatest negative impact of heat stress on CR was observed 21 to 1 day before breeding. When the mean THI was 73 or more in this period, CR decreased from 31% to 12%. Compared with the average maximum THI and the total number of hours above a threshold of more than or 9 hours, the mean THI was the most sensitive heat load index relating to CR. These results indicate that the CR of dairy cows raised in the moderate climates is highly affected by heat stress.     

Alterations in the relative abundance of Haptoglobin (Hp) transcripts in total milk somatic cells during different stages of lactation cycle in high yielding cross-bred cows

The expression profile of Haptoglobin (Hp) gene in total milk somatic cells (SCC) of high-yielding cross-bred Karan Fries (KF) was studied during early, mid, and late lactation cycle. Milk samples (200 ml/animals) were collected from 10 high-yielding and 10 low-yielding cows throughout the lactation cycle (from day 7 to day 300) with an interval of one month. Relative mRNA expression profiles of Hp by RT polymerase chain reaction was studied in high-yielding cows, whereas low-yielding cows were taken as control. The folds of induction of Hp was significantly (p < 0.001) downregulated by a mean factor of 0.207 in milk SCC during early lactating cows. Whereas, it was significantly (p < 0.01) upregulated by a mean factor of 20.888 during mid lactation. The expression was unaltered during the late lactation. The study demonstrates that Hp is synthesized within the mammary gland and significantly upregulated during mid-lactation period compared to other stages of lactation cycle.     

Microclimate modeling in naturally ventilated dairy barns during the hot season: Checking the accuracy of forecasts

Monitoring and predicting the microclimate in naturally ventilated barns (NVB) is important given the adverse effects of high summer temperatures on dairy cows in the context of global climate change. The aim of the work was to verify the accuracy of the microclimate forecast in a NVB using linear regression (LR). Our working hypothesis suggested that multiple periodic measurements of air temperature and relative humidity outside and inside the barns at the same time will allow us to build LR models for predicting the temperature-humidity index (THI). This was done not only for a specific dairy barn based on this indicator outside, but also in other dairy barns with a similar design, located in similar weather conditions. The results of the research indicate that the use of LR had a high accuracy of forecasting (93–96%) the THI in NVB of various designs during the summer heat. At the same time, differences were found between traits (air temperature, relative humidity as well as resulting THI) provided by meteorological weather stations and these data measured simultaneously next to the dairy barns. The proposed LR models can be used to predict THI in NVBs of different designs.     

Dairy cattle in a temperate climate: the effects of weather on milk yield and composition depend on management

A better understanding of how livestock respond to weather is essential to enable farming to adapt to a changing climate. Climate change is mainly expected to impact dairy cattle through heat stress and an increase in the frequency of extreme weather events. We investigated the effects of weather on milk yield and composition (fat and protein content) in an experimental dairy herd in Scotland over 21 years. Holstein Friesian cows were either housed indoors in winter and grazed over the summer or were continuously housed. Milk yield was measured daily, resulting in 762 786 test day records from 1369 individuals, and fat and protein percentage were sampled once a week, giving 89 331 records from 1220 cows/trait. The relative influence of 11 weather elements, measured from local outdoor weather stations, and two indices of temperature and humidity (THI), indicators of heat stress, were compared using separate maximum likelihood models for each element or index. Models containing a direct measure of temperature (dry bulb, wet bulb, grass or soil temperature) or a THI provided the best fits to milk yield and fat data; wind speed and the number of hours of sunshine were most important in explaining protein content. Weather elements summarised across a week’s timescale from the test day usually explained milk yield and fat content better than shorter-scale (3 day, test day, test day −1) metrics. Then, examining a subset of key weather variables using restricted maximum likelihood, we found that THI, wind speed and the number of hours of sunshine influenced milk yield and composition. The shape and magnitude of these effects depended on whether animals were inside or outside on the test day. The milk yield of cows outdoors was lower at the extremes of THI than at average values, and the highest yields were obtained when THI, recorded at 0900 h, was 55 units. Cows indoors decreased milk yield as THI increased. Fat content was lower at higher THIs than at intermediate THIs in both environments. Protein content decreased as THI increased in animals kept indoors and outdoors, and the rate of decrease was greater when animals were outside than when they were inside. Moderate wind speeds appeared to alleviate heat stress. These results show that milk yield and composition are impacted at the upper extreme of THI under conditions currently experienced in Scotland, where animals have so far experienced little pressure to adapt to heat stress.     

Genetics of heat tolerance for milk yield and quality in Holsteins

Tropical and sub-tropical climates are characterized by high temperature and humidity, during at least part of the year. Consequently, heat stress is common in Holstein cattle and productive and reproductive losses are frequent. Our objectives were as follows: (1) to quantify losses in production and quality of milk due to heat stress; (2) to estimate genetic correlations within and between milk yield (MY) and milk quality traits; and (3) to evaluate the trends of genetic components of tolerance to heat stress in multiple lactations of Brazilian Holstein cows. Thus, nine analyses using two-trait random regression animal models were carried out to estimate variance components and genetic parameters over temperature–humidity index (THI) values for MY and milk quality traits (three lactations: MY×fat percentage (F%), MY×protein percentage (P%) and MY×somatic cell score (SCS)) of Brazilian Holstein cattle. It was demonstrated that the effects of heat stress can be harmful for traits related to milk production and milk quality of Holstein cattle even though most herds were maintained in a modified environment, for example, with fans and sprinklers. For MY, the effect of heat stress was more detrimental in advanced lactations (−0.22 to −0.52 kg/day per increase of 1 THI unit). In general, the mean heritability estimates were higher for lower THI values and longer days in milk for all traits. In contrast, the heritability estimates for SCS increased with increasing THI values in the second and third lactation. For each trait studied, lower genetic correlations (different from unity) were observed between opposite extremes of THI (THI 47 v. THI 80) and in advanced lactations. The genetic correlations between MY and milk quality trait varied across the THI scale and lactations. The genotype×environment interaction due to heat stress was more important for MY and SCS, particularly in advanced lactations, and can affect the genetic relationship between MY and milk quality traits. Selection for higher MY, F% or P% may result in a poor response of the animals to heat stress, as a genetic antagonism was observed between the general production level and specific ability to respond to heat stress for these traits. Genetic trends confirm the adverse responses in the genetic components of heat stress over the years for milk production and quality. Consequently, the selection of Holstein cattle raised in modified environments in both tropical and sub-tropical regions should take into consideration the genetic variation in heat stress.     

Effect of high temperature-humidity conditions on milk production of dairy herds grazed on farms in a pasture-based feed system

The influence of stressful temperature-humidity conditions on output from dairy cows on farms near Wauchope (31°S Lat.), Australia, was examined by comparing weekly milk production and Temperature-Humidity Index (THI) values over a two-year period (1973 to 1975). Production during weeks with relatively high THI values (70 or over) was higher than production in weeks with lower temperature-humidity stress. In autumn and winter when THI values were low, the quantity and quality of pasture available was inadequate to sustain high levels of milk production. Short-term (weekly) responses of milk output to changes in temperature-humidity conditions above THI values of 70 were not consistent, either in terms of the direction or magnitude of production change. THI values may not have been high enough to adversely affect week-to-week production from predominantly Jersey herds, although some depression in lactation yields may have occurred. The reduction in digestibility and palatability of grasses during late summer appeared to be of greater importance in influencing production patterns than the direct effects of stressful temperature-humidity conditions on cows.     

Correction: Periconceptional Heat Stress of Holstein Dams Is Associated with Differences in Daughter Milk Production and Composition during Multiple Lactations

The fertility of lactating Holstein cows is severely reduced during periods of heat stress. Despite this reduction in fertility, however, some inseminations conducted during heat stress result in successful pregnancies from which heifer calves are born. Many of these heifer calves are retained and raised to enter the milking herd as replacement animals. Heat stress experienced by these females around the time they were conceived may confer long-lasting effects that alter subsequent milk production capacity. The objective of this study was to examine the relationship between periconceptional heat stress and subsequent milk production of primiparous cows. National Dairy Herd Improvement Association data was obtained from Dairy Records Management Systems. Records included Holstein cows that had completed at least one lactation in one of three states with large populations of dairy cattle and which are known for having hot, humid summers: Georgia, Florida or Texas. Dates of conception were calculated by subtracting 276 d from the recorded birth date of each individual cow. Records for cows conceived within the months of June, July, and August were retained as heat stress-conceived (HSC) cows (n = 94,440); cows conceived within the months of December, January, and February were retained as thermoneutral-conceived (TNC) contemporaries (n = 141,365). In order to account for the effects of environmental conditions on total milk production for a given lactation, cows were blocked by season of calving (winter, spring, summer or fall). Adjusted 305-day mature-equivalent milk production was evaluated with a mixed model ANOVA using SAS, in which random effects were used to account for variability between herds. Of the cows that calved in the summer, fall and winter, TNC cows had higher milk yield than the HSC cows in all states. Interestingly, the cows that calved in the spring presented a unique relationship, with HSC cows producing more milk. Overall however, heat stress at the time of conception is associated with lower milk production during the first lactation. While this association does not prove cause and effect, it does provide justification for additional investigation into whether heat stress around the time of conception results in long-term, detrimental consequences for the conceptus.     

Misting and fan cooling of the rest area in a dairy barn

This summer study aimed to evaluate the effect on dairy cows, kept in a free stall barn equipped with fans and sprinklers in the feeding area, of the delivery rate of misters in a cooling system in rest areas with different bedding materials. Thirty cows were divided into two homogenous groups according to milk yield and kept in two pens: one had beds with sand (SAMM) while the other had straw (STLM). Each pen was equipped with 2 fans (Ø 70 cm, 0.50 kW) and 2 misters (delivery rate of 11.2 and 22.5 L/h in STLM and SAMM, respectively) in the rest area. Microclimatic parameters, rectal temperature (RT), breathing rate (BR), milk yield, and some milk traits were recorded. Behavioural routines of the cows (standing and lying) were also continuously recorded during the hotter days. During the trial, two mild–moderate heat waves were observed. During these hotter periods, the daily maximum temperature recorded in the rest areas was 28.9 in SAMM and 31.2 in STLM, and the daily maximum THI was 78.2 in SAMM and 81.5 in STLM. In these periods, the cows in SAMM compared with those in STLM showed lower BR (P?相似文献   

Metabolic Heat Stress Adaption in Transition Cows: Differences in Macronutrient Oxidation between Late-Gestating and Early-Lactating German Holstein Dairy Cows

High ambient temperatures have severe adverse effects on biological functions of high-yielding dairy cows. The metabolic adaption to heat stress was examined in 14 German Holsteins transition cows assigned to two groups, one heat-stressed (HS) and one pair-fed (PF) at the level of HS. After 6 days of thermoneutrality and ad libitum feeding (P1), cows were challenged for 6 days (P2) by heat stress (temperature humidity index (THI) = 76) or thermoneutral pair-feeding in climatic chambers 3 weeks ante partum and again 3 weeks post-partum. On the sixth day of each period P1 or P2, oxidative metabolism was analyzed for 24 hours in open circuit respiration chambers. Water and feed intake, vital parameters and milk yield were recorded. Daily blood samples were analyzed for glucose, β-hydroxybutyric acid, non-esterified fatty acids, urea, creatinine, methyl histidine, adrenaline and noradrenaline. In general, heat stress caused marked effects on water homeorhesis with impairments of renal function and a strong adrenergic response accompanied with a prevalence of carbohydrate oxidation over fat catabolism. Heat-stressed cows extensively degraded tissue protein as reflected by the increase of plasma urea, creatinine and methyl histidine concentrations. However, the acute metabolic heat stress response in dry cows differed from early-lactating cows as the prepartal adipose tissue was not refractory to lipolytic, adrenergic stimuli, and the rate of amino acid oxidation was lower than in the postpartal stage. Together with the lower endogenous metabolic heat load, metabolic adaption in dry cows is indicative for a higher heat tolerance and the prioritization of the nutritional requirements of the fast-growing near-term fetus. These findings indicate that the development of future nutritional strategies for attenuating impairments of health and performance due to ambient heat requires the consideration of the physiological stage of dairy cows.     

Bovine platelet-activating factor acetylhydrolase (PAF-AH) activity related to fertility

Plasma platelet-activating factor acetylhydrolase (PAF-AH), the enzyme characterized by the association with plasma lipoproteins, degrades platelet-activating factor (PAF) as well as PAF-like oxidatively fragmented phospholipids produced during oxidative stress. Apart from pro-inflammatory properties, PAF is also related to reproductive processes and successful fertility. In order to get a better insight into the involvement of PAF-AH in the fertility of cows, the aim of the study was to determine the PAF-AH activity as well as the C-reactive protein, cholesterol and high density lipoprotein-cholesterol (HDL-C) in the serum of dairy cows throughout the pregnancy and lactation, as well as in infertile cows. The results showed that serum PAF-AH activity changes throughout pregnancy and lactation with a lower level during periparturient period. It is also found higher PAF-AH activity in lactating cows with reproductive disorders compared to high lactating cows without reproductive disorders. Strong correlation between PAF-AH activity and HDL-C concentration indicates that HDL could have considerable influence on PAF-AH activity in bovine plasma. CRP concentration was also lower during transition period suggesting that lactation might stimulate CRP synthesis in bovine. A higher CRP concentration in cows with reproductive disorders compared to fertile cows at the peak of lactation, demonstrates that milk production is not the only factor influencing CRP in cows. A significant correlation between PAF-AH activity and CRP level shows that both parameters could be influenced by reproductive status of dairy cows.     

Climatic effects in Central Europe on the frequency of medical treatments of dairy cows

In the present study, the relationship between the temperature–humidity index (THI) and the incidence of medical treatments in lactating dairy cows in Lower Saxony, Germany, was investigated. Records of all veterinary-treated cases over 2 years (2003 and 2005) from eight Holstein–Friesian dairy herds raised in loose-housing systems (55 to 170 cows per herd) were evaluated. After exclusion of management-dependent and climate-independent cases, a total of 5547 treatments were analyzed. Treatments were clustered into the following groups: metabolism, fertility, udder and foot/leg. Meteorological data were compiled from the nearest weather station (average distance ± s.d. 39 ± 13 km). Hourly temperatures and relative humidity values were used to calculate the THI, which was divided into classes. Out of the total number of treatments, 37.4%, 32.9%, 21.6% and 8.1% belonged to metabolism, udder, fertility and foot/leg, respectively. Data were analyzed with a mixed model that included THI class, season and year as fixed effects and farm as random effect. In general, incidences were neither affected by the year (P > 0.05) and season (P > 0.05) nor by THI classes (P > 0.05). In tendency, incidences of metabolic treatments increased with increasing THI and incidences of udder treatments increased with decreasing THI. In conclusion, indications of moderate heat stress during summer months in Central Europe were found in the present study, although THI and season did not affect the different disease complexes significantly.     

Modeling heat stress effects on dairy cattle milk production in a tropical environment using test-day records and random regression models

In tropical environments, dairy cattle production is constrained by several factors, including climate. The seasonal loss of milk due to heat stress is a recurring challenge for many dairy producers. The objective of this study was to detect heat stress thresholds, milk yield loss and individual animal variations using random regression models for dairy cattle from test-day milk records. Data were obtained from the Kenya Livestock Breeders Organization for the years 2000–2017 and merged with weather data. The weather parameters were grid-interpolated solar and meteorological data obtained from the National Aeronautics and Space Administration/Prediction Of Worldwide Energy Resources (NASA/POWER). After editing, the records comprised 49 993, 45 251 and 36 136 test-day records for first, second, and third lactations, respectively, for the four main dairy breeds: Friesian (68.0%), Ayrshire (21.1%), Jersey (7.6%) and Guernsey (3.3%). Variance components were estimated using Restricted Maximum Likelihood in ASReml software. Random regression models with third-order Legendre polynomials were fitted to the average and individual lactation curves and the reaction norms. An extended factor analytic variance structure for the random cow effects was used to estimate (co)variances between days in milk and thermal load. The daily average temperature (TA) and temperature humidity index (THI) were identified as the most suitable thermal load indicators for assessing milk yield losses. Considering a one day lag, the estimated heat stress thresholds were about 22 °C and 69 index units for TA and THI, respectively. Almost no differences were observed for estimated residual variances between the thermal load indicators, indicating there was no better model fit by TA or THI. The heat stress thresholds and milk loss patterns are important for management of dairy production systems in the tropics with climatic conditions similar to this study. Data recording should be improved as a tool to monitor the expected impacts of climate change and mitigation measures.     

Canola Oil in Lactating Dairy Cow Diets Reduces Milk Saturated Fatty Acids and Improves Its Omega-3 and Oleic Fatty Acid Content

To produce milk that is healthier for human consumption, the present study evaluated the effect of including canola oil in the diet of dairy cows on milk production and composition as well as the nutritional quality of this milk fat. Eighteen Holstein cows with an average daily milk yield of 22 (± 4) kg/d in the middle stage of lactation were used. The cows were distributed in 6 contemporary 3x3 Latin squares consisting of 3 periods and 3 treatments: control diet (without oil), 3% inclusion of canola oil in the diet and 6% inclusion of canola oil in the diet (dry matter basis). The inclusion of 6% canola oil in the diet of lactating cows linearly reduced the milk yield by 2.51 kg/d, short-chain fatty acids (FA) by 41.42%, medium chain FA by 27.32%, saturated FA by 20.24%, saturated/unsaturated FA ratio by 39.20%, omega-6/omega-3 ratio by 39.45%, and atherogenicity index by 48.36% compared with the control treatment. Moreover, with the 6% inclusion of canola oil in the diet of cows, there was an increase in the concentration of long chain FA by 45.91%, unsaturated FA by 34.08%, monounsaturated FA by 40.37%, polyunsaturated FA by 17.88%, milk concentration of omega-3 by 115%, rumenic acid (CLA) by 16.50%, oleic acid by 44.87% and h/H milk index by 94.44% compared with the control treatment. Thus, the inclusion of canola oil in the diet of lactating dairy cows makes the milk fatty acid profile nutritionally healthier for the human diet; however, the lactating performance of dairy cows is reduce.     

Impact of maternal heat stress at insemination on the subsequent reproductive performance of Holstein, Brown Swiss,and their crosses

Heat stress in hot environments is one of the major factors that can negatively affect milk production, reproduction, and the health of dairy cows. The aim of this study was to evaluate the impact of maternal heat stress at insemination on the subsequent reproductive performance of the pure Holstein (HO), Brown Swiss (BS), and their F₁ crossbred (BF) cows, under subtropical Egyptian conditions. The influence of temperature–humidity index (THI) on the pregnancy rate, fetal loss rate, calving traits, and reproductive indices were investigated. Fetal loss rate of pure HO was significantly increased from 17.1% at low THI to 24.9% at greater THI (odds ratio = 2.09; P = 0.032). Furthermore, abortion and stillbirth rates of pure HO were significantly increased from 3.6% and 3.8%, respectively, at low THI to 7.2% and 5.9%, respectively, at greater THI (odds ratio = 2.17 and 2.58; P = 0.037 and 0.031, respectively). In contrast, BS and BF cows can tolerate the heat stress, as there were no differences in the fetal loss, abortion, and calving difficulty rates at the different levels of THI. Pure HO cows had a significant longer calving interval and days open at high THI (449 and 173 days, respectively), compared with low THI (421 and 146 days, respectively). On the contrary, BS and BF cows had no difference in the calving interval at the different levels of THI. Our results indicate that pure BS and BF cows have a better adaptability and competent reproductive performance than pure HO under subtropical conditions.     

Short-term physiological responses to moderate heat stress in grazing dairy cows in temperate climate

Even in temperate climate regions, an increase in ambient temperature and exposure to solar radiation can cause heat stress in lactating dairy cows. We hypothesised that grazing dairy cows exhibit short-term physiological changes due to increasing heat load under moderate climate conditions. Over two consecutive summers, 38 lactating Holstein dairy cows were studied in a full-time grazing system. Data were collected in 10 experimental periods of up to three consecutive days with a moderate comprehensive climate index (CCI). The individual animals’ vaginal temperature (VT), heart rate, and locomotor activity data were automatically monitored with sensors. Blood samples and proportional whole milk samples were collected at afternoon milking. The concentrations of beta-hydroxybutyrate, glucose, non-esterified fatty acids, urea nitrogen, plasma thyroxine and triiodothyronine were analysed in blood plasma, and fat, protein, lactose, urea nitrogen, cortisol, Na⁺, K⁺, and Cl^? concentrations were analysed in milk. The daily distribution of VT recordings greater than 39 °C showed a circadian rhythm with a proportion of recordings of 2% and lower during the night and a percentage of 10% or higher in the afternoon. The cows’ maximal daily vaginal temperature (VT_MAX) between 0830 and 1430 h was positively related to the mean daily CCI in the same time period (CCI_MEAN; mean and SD 23.6 ± 5.4 °C). Cows with greater VT_MAX had an increased mean heart rate, plasma glucose and milk cortisol concentrations and decreased concentrations of plasma thyroxine and triiodothyronine. The concentration of Na⁺ in milk was lower, and the concentration of K⁺ in milk tended to be higher in cows with increased VT_MAX. For beta-hydroxybutyrate, non-esterified fatty acids and urea nitrogen concentrations in plasma and fat and lactose concentrations in milk no relationships were found in terms of increasing VT. For milk urea nitrogen and protein concentrations, the proportion of total variance explained by inter-individual or -period variance was high. In conclusion, changes observed in milk and blood likely reflected short-term physiological responses to moderate heat stress. In particular, milk cortisol and Na⁺ may be useful traits for timely monitoring of heat stress in individual cows because their inter-individual variances were relatively small and samples can be collected non-invasively.     

Seasonal variations in the composition of Holstein cow’s milk and temperature–humidity index relationship

A retrospective study on seasonal variations in the characteristics of cow’s milk and temperature–humidity index (THI) relationship was conducted on bulk milk data collected from 2003 to 2009. The THI relationship study was carried out on 508 613 bulk milk data items recorded in 3328 dairy farms form the Lombardy region, Italy. Temperature and relative humidity data from 40 weather stations were used to calculate THI. Milk characteristics data referred to somatic cell count (SCC), total bacterial count (TBC), fat percentage (FA%) and protein percentage (PR%). Annual, seasonal and monthly variations in milk composition were evaluated on 656 064 data items recorded in 3727 dairy farms. The model highlighted a significant association between the year, season and month, and the parameters analysed (SCC, TBC, FA%, PR%). The summer season emerged as the most critical season. Of the summer months, July presented the most critical conditions for TBC, FA% and PR%, (52 054±183 655, 3.73%±0.35% and 3.30%±0.15%, respectively), and August presented higher values of SCC (369 503±228 377). Each milk record was linked to THI data calculated at the nearest weather station. The analysis demonstrated a positive correlation between THI and SCC and TBC, and indicated a significant change in the slope at 57.3 and 72.8 maximum THI, respectively. The model demonstrated a negative correlation between THI and FA% and PR% and provided breakpoints in the pattern at 50.2 and 65.2 maximum THI, respectively. The results of this study indicate the presence of critical climatic thresholds for bulk tank milk composition in dairy cows. Such indications could facilitate the adoption of heat management strategies, which may ensure the health and production of dairy cows and limit related economic losses.     

Effect of feeding Rumen-protected capsule containing niacin,K2SO4, vitamin C,and gamma-aminobutyric acid on heat stress and performance of dairy cows

This study was conducted to evaluate the effects of supplemental rumen-protected capsule (RPC) on animal performance, serological indicators, and serum heat shock protein 70 (HSP70) of lactating Holstein cows under heat stress (HS). During summer months, 30 healthy multiparous lactating Holstein cows with a parity number of 3.1 ± 0.44, 70 ± 15 d in milk, an average body weight of 622 ± 62 kg, and an average milk yield of 32.28 ± 0.96 kg/d, were used. The cows were randomly allocated to two groups: a control group and an RPC-supplemented group (0.13373 kg K₂SO₄, 0.02488 kg vitamin C, 0.021148 kg niacin, and 0.044784 kg gamma-aminobutyric acid per cow). During the 42-d experiment, ambient air temperature and relative humidity inside and outside the barn were recorded hourly every day for the determination of temperature-humidity index (THI). Milk and blood samples were collected every week, and body weight and body condition scoring were measured on day 0. Based on the THI values, the animals had moderate HS. On day 42, the RPC group had lower HSP70, adrenocorticotropic hormone (P = 0.0001), lactate dehydrogenase (P = 0.0338), and IL-6 (P = 0.0724) levels than the control group, with no significant differences in creatine kinase, glucocorticoid, or IL-2 levels. Milk yield, energy-corrected milk, and dry matter intake were higher in RPC than in the control group (P = 0.0196). There were no significant differences in milk fat or daily protein levels between the two groups; however, daily protein and milk fat levels were higher in the RPC group than in the control group (P = 0.0114 and P = 0.0665, respectively). Somatic cell counts were no different between the two groups. In conclusion, RPC may alleviate HS and improve dairy cow performance.     

Identifying risk factors for poor hind limb cleanliness in Danish loose-housed dairy cows

The objective of this study was to identify possible risk factors for poor cow hind limb cleanliness in Danish loose-housed, lactating dairy cows. The study was conducted as a cross-sectional study of 1315 cows in 42 commercial Danish dairy herds with primarily Danish Holstein cows. The effect of four cow-level factors (parity, days in milk, daily lying time and lameness) and eight herd-level factors (herd size, milk production, milking system, floor type, access to pasture grazing, floor scraping frequency, hoof bathing frequency and hoof washing frequency) on the risk of having dirtier hind limbs were analysed using ordinal logistic regression fitting a proportional odds model. Cow hind limb cleanliness was scored using an ordinal score from 1 to 4: 1 being clean and 4 being covered in dirt. The odds ratios (ORs) estimated from the proportional odds model depict the effect of a risk factor on the odds of having a higher rather than a lower cleanliness score. First parity cows had an increased risk of being dirtier compared with third parity or older cows (OR=1.70). Compared with late lactation, early and mid lactation were associated with an increased risk of being dirtier (OR=2.07 and 1.33, respectively). Decreasing the daily time lying by 30 min was associated with an increased risk of being dirtier (OR=1.05). Furthermore, an increased risk of being dirtier was found in herds with no pasture access (OR=3.75).     

Influence of weather conditions on milk production and rectal temperature of Holsteins fed two levels of concentrate

Twelve lactating Holstein cows in 2nd lactation were allocated randomly, six each, to two feeding treatments: high concentrate (1 kg dairy concentrate to 2 kg milk produced) and low concentrate (1 kg dairy concentrate to 4 kg milk produced) from 7 to 106 days postcalving. Forage and water were provided adalibitum. Milk and butter fat yields and rectal temperatures were examined in relation to 9 weather variables (minimum, maximum and mean temperatures, relative humidity, temperature-humidity index (THI), radiation, wind velocity and mean temperature of the previous day). Averages for milk yield, fat yield and rectal temperature were respectively 20.4 kg, 0.7 kg and 38.9°C for the high concentrate treatment and 18.4 kg, 0.6 kg and 38.6°C for the low concentrate treatment. Weather conditions accounted for 5.6%, 0.8% and 10.8% of the day to day variation in milk yield, fat yield and rectal remperature, respectively, for the high concentrate group and 29.4%, 9.7% and 0.6%, respectively, for the low concentrate group. Only measures of ambient temperature, especially mean temperature, were closely associated with these traits.