Growth and body composition of dairy calves fed only milk replacer at 3 intakes.

Determination of energy requirements for growth depends on measuring the composition of body weight (BW) gain. Previous studies have shown that the composition of gain can be altered in young dairy calves by composition of the milk replacer diet. Here, our objective was to determine body composition and the composition of empty body gain in young calves fed increasing amounts of a milk replacer containing adequate CP. Male Holstein calves underwent an adjustment period of 14 d after birth in which they were fed whole waste milk at 10% of BW. Calves were then stratified by BW and randomly assigned to either an initial harvest group (n = 11) or to groups fed 1 of 3 milk replacer amounts and harvested after 35 d of growth. All treatments consumed the same milk replacer containing 24.8% CP (dry matter [DM] basis; from all milk proteins) and 18.9% fat, reconstituted to 12.5% solids. Treatments were milk replacer fed at 1.25% of BW (DM basis; n = 6), 1.75% of BW (n = 6), or 2.25% of BW (n = 8), adjusted weekly as calves grew. Calves fed at 1.25% or 1.75% of BW were fed twice daily and those fed 2.25% of BW were fed 3 times daily. No starter was offered. Post harvest, the bodies of calves were separated into 4 fractions: carcass; total viscera minus digesta; head, hide, feet, and tail; and blood. The sum of those 4 fractions was empty BW, which increased linearly as amount of milk replacer increased. Final heart girth and body length, but not withers height, increased linearly as intake increased. Gain:feed increased linearly with increasing milk replacer. Feeding more milk replacer increased the amounts of lean tissue and fat in the body. The percentages of water and protein in the final body decreased linearly, whereas fat percentage and energy content increased linearly as intake increased. As gain increased, the percentage of protein in gain decreased and the percentage of fat increased, resulting in an increase of energy content of EBW gain. Efficiency of energy use (retained energy:gross energy intake) increased linearly but retained energy:metabolizable energy available for growth was not different among treatments. Efficiency of protein use increased quadratically as feeding rate increased; there was no further increase at 2.25% of BW. Plasma insulin-like growth factor 1, insulin, and glucose increased linearly, whereas urea-N decreased linearly, as milk replacer intake increased. Our data document changes in body composition that affect estimates of retained energy in the bodies of calves harvested at a common age. These data are important for calculations of energy requirements for young calves.

Association between prepartum body condition score and prepartum and postpartum dry matter intake and energy balance in multiparous Holstein cows.

The objectives of this retrospective observational study were to investigate the association between body condition score (BCS) at 21 d before calving with prepartum and postpartum dry matter intake (DMI), energy balance (EB), and milk yield. Data from 427 multigravid cows from 11 different experiments conducted at the University of Florida were used. Cows were classified according to their BCS at 21 d before calving as FAT (BCS ≥4.00; n = 83), MOD (BCS 3.25 to 3.75; n = 287), and THIN (BCS ≤3.00; n = 57). Daily DMI from -21 to -1 and from +1 to +28 DIM was individually recorded. Energy balance was calculated as the difference between net energy for lactation consumed and required. Dry matter intake in FAT cows was lesser than in MOD and THIN cows both prepartum (FAT = 9.97 ± 0.21, MOD = 11.15 ± 0.14, THIN = 11.92 ± 0.22 kg/d) and postpartum (FAT = 14.35 ± 0.49, MOD = 15.47 ± 0.38, THIN = 16.09 ± 0.47 kg/d). Dry matter intake was also lesser for MOD cows compared with THIN cows prepartum, but not postpartum. Energy balance in FAT cows was lesser than in MOD and THIN cows both prepartum (FAT = -4.16 ± 0.61, MOD = -1.20 ± 0.56, THIN = 0.88 ± 0.62 Mcal/d) and postpartum (FAT = -12.77 ± 0.50, MOD = -10.13 ± 0.29, THIN = -6.14 ± 0.51 Mcal/d). Energy balance was also lesser for MOD cows compared with THIN cows both prepartum and postpartum. There was a quadratic association between BCS at 21 d before calving and milk yield. Increasing BCS from 2.5 to 3.5 was associated with an increase in daily milk yield of 6.0 kg and 28 d cumulative milk of 147 kg. Increasing BCS from 3.5 to 4.5 was associated with a decrease in daily milk yield of 4.4 kg and 28 d cumulative milk of 116 kg. In summary, a moderated BCS at 21 d before calving was associated with intermediate DMI and EB pre- and postpartum but greater milk yield compared with thinner and fatter cows. Our findings indicate that a moderated BCS is ideal for ensuring a successful lactation.

Impact of nutrient restriction at dry-off on performance and metabolism.

Thanks to improvements in genetics, nutrition, and management, modern dairy cows can still produce large amounts of milk at the end of lactation, with possible negative effects on health and welfare, particularly when milking is stopped abruptly. To limit yield at dry-off, strategies involving different types of dietary restriction have been used worldwide. Thus, we aimed to investigate the effects of a reduced nutrient density at dry-off on milk production, metabolism, the pattern of rumen fermentation, and milk fatty acid profile around dry-off and in the ensuing periparturient period. During the last week before dry-off, 26 Holstein cows were enrolled in pairs according to the expected calving date and either fed ad libitum ryegrass hay (nutrient restricted, NR; 13 cows) or continued to receive lactation diet (control group, CTR, 13 cows). After dry-off, both groups received only grass hay for 7 d, and free access to water was always provided. Blood, milk, and rumen fluid samples were collected from 7 d before dry-off to 28 d in milk. Milk production, DMI (during the periparturient period), and rumination times were recorded daily. At dry-off, compared with CTR, NR decreased milk yield (- 62%) and milk lactose but had higher fat and protein contents. In the subsequent lactation, no significant differences were observed in milk yield and composition. The BCS did not differ between groups during the transition period, but it decreased in NR after dry-off. Before dry-off, NR had decreased glucose, urea, and insulin, but higher creatinine, ß-hydroxybutyrate, and nonesterified fatty acids (NEFA). The day after dry-off, NEFA were lower in NR, but they were higher 7 d after calving. At dry-off, NR had higher rumen pH, lower lactate, urea, and total volatile fatty acid concentrations. Considering volatile fatty acid molar proportions, NR had increased acetate but decreased propionate and butyrate at dry-off. Rumination time dropped 6 d before dry-off in NR and after dry-off in CTR, but no differences were observed in the periparturient period. Milk fatty acid profile revealed a remarkably lower proportion of short-chain fatty acids in NR at dry-off and a higher proportion of medium- and long-chain ones. These results confirmed that decreasing nutrient density reduce milk yield before dry-off. However, metabolism around dry-off was significantly impacted, as suggested by plasma, rumen fluid, and milk analyses. Further research is required to investigate the impact of the metabolic effects on the inflammatory response, liver function, and immune system, particularly concerning the mammary gland.

Graduate Student Literature Review: The challenge of drying-off high-yielding dairy cows.

The cessation of lactation (i.e., dry-off) in dairy cattle is an area of research that has received much focus in recent years. The dry period is necessary to optimize tissue remodeling of the mammary gland, but represents a stressful event, incorporating several changes in daily routine, diet, and metabolism. Moreover, the high milk yields achieved by modern cows in late gestation exacerbate the need for relevant manipulations in the days around dry-off, as excessive accumulation of milk might jeopardize the success of the dry period, with potential negative effects on future lactation. Production levels over 15 kg/d are an additional risk factor for udder health, delay mammary involution, and worsen metabolic stress and inflammatory responses. Furthermore, the pressure to reduce antibiotic usage in farm animals has resulted in increased attention on the dry period, given that historically most dairy cattle were provided prophylactic intramammary antibiotic treatment at dry-off as a means to reduce the risk of intramammary infections in the subsequent lactation. Several strategies have been proposed over the years to cope with these challenges, aiming to gradually reduce milk yield before dry-off, promoting at the same time the start of mammary involution. Among them, the most common are based on feed or nutrient restriction, a decrease in milking frequency, or administration of prolactin inhibitors. These practices have different capacities to reduce milk yield through different mechanisms and entail several implications for udder health, animal welfare, behavior, endocrine status, metabolism, and inflammatory conditions. The present review aims to provide a comprehensive overview of the dry-off phase in high-yielding cows and of the impact of high milk production at dry-off, and to describe possible strategies that might be implemented by farmers and veterinarians to optimize this critical phase in an integrated way.

Effect of in utero exposure to hyperthermia on postnatal hair length, skin morphology, and thermoregulatory responses.

Skin and hair coat play important functions in maintaining homeostasis and thermoregulation for cattle, which can affect all modes of heat loss. Our objective was to investigate the effect of hyperthermia experienced in utero during late gestation on postnatal hair length, skin properties, and thermoregulation. Pregnant dams were heat stressed (n = 41) or actively cooled (n = 41) for the last ∼56 d of gestation and gave birth to heifers that were in utero heat stressed (IUHT) or in utero cooled (IUCL), respectively. Hair samples and skin tissue biopsies were collected from neck and rump locations at birth (d 0), 1 wk after weaning (d 63), and at 12 mo. Hair samples were also obtained at 4 and 8 mo. Skin tissue was stained with hematoxylin and eosin to visualize morphology. Hair length (short and long hairs, undercoat and topcoat, respectively), stratum corneum (SC) area, SC thickness, epidermis thickness, sweat gland (SWT) number, SWT cross-sectional area, SWT average size, sebaceous gland (SEB) number, SEB cross-sectional area, SEB average size, and sweat gland depth were assessed. Respiration rate, skin temperature, sweating rate, and rectal temperature was measured weekly from d 7 to 63. Additionally, thermoregulatory patterns were measured every 4 h over a 36-h interval beginning 4 d after weaning. Data were analyzed using PROC MIXED in SAS with a main effect of in utero treatment with location and time points analyzed separately. No difference in hair parameters were detected at d 0 or 12 mo. At d 63, IUHT heifers had longer average hair length (14.8 vs. 13.8 ± 0.2 mm, standard error), shorter undercoats (9.3 vs. 10.4 ± 0.3 mm), longer topcoats (19.6 vs. 17.1 ± 0.3 mm), and a greater difference between topcoat and undercoat (10.1 vs. 7.0 ± 0.4 mm). At 4 mo, IUHT heifers had longer average hair lengths (26.1 vs. 22.2 ± 1.0 mm) and longer topcoats (36.9 vs. 33.9 ± 1.1 mm), and at 8 mo, IUHT had longer average hair lengths (17.9 vs. 16.2 ± 0.6 mm), relative to IUCL. At d 0, IUHT heifers had more (13 vs. 9 ± 2 glands) but smaller average sized SEB (neck: 1,636 vs. 2,238 ± 243 µm2; rump: 2,100 vs. 3,352 ± 379 µm2) and reduced SC area (79,243 vs. 169,419 ± 13,071 µm2). At d 63, IUHT had fewer SEB (11 vs. 15 ± 2 glands), smaller SWT (0.16 vs. 0.23 ± 0.02 mm2), fewer SWT (16 vs. 23 ± 4 glands), and deeper SWT (0.5 vs. 0.4 ± 0.03 mm). At 12 mo, IUHT had greater distance from the skin surface to the most superficial SWT (0.016 vs. 0.015 ± 0.0004 mm), shorter distance to the deepest SWT (0.031 vs. 0.033 ± 0.001 mm), and smaller SWT (81.1 vs. 108.9 ± 10.8 µm2), relative to IUCL. When measured both weekly and hourly, IUHT heifers had higher rectal temperature and sweating rate. Overall, in utero hyperthermia triggers long-lasting hair and skin adaptations, possibly leading to differences in postnatal thermoregulation.

Symposium review: Environmental effects on mammary immunity and health.

Environmental effects on pathogen abundance and access are precursors to mastitis. Indeed, high heat and humidity, and unsanitary housing and equipment, are associated with greater pathogen load and exposure. Although less is known about effects of environment on a cow's ability to resist infection, several indicators suggest that it can affect pathogen responses. Mastitis incidence and bulk tank somatic cell count vary with season, typically peaking in summer. Recent controlled studies have revealed that heat stress exposure results in changes in the microbiome of the cow and her environment, which may relate to negative effects on milk quality and cow health. Alternatively, specific pathogen loads may vary based on housing dynamics rather than associations with physical environment. Indeed, housing-related stressors, such as overcrowding and social group challenge, influence secretion of glucocorticoids, thus affecting pathogen resistance in the cow. Two key seasonal variables are photoperiod and temperature, specifically the heat stress consequent to elevated temperature and humidity. Shifts in light duration regulate immune function in other species, but apparently have limited effect on udder health of lactating cows. In contrast, in dry cows, short days increase peripheral blood mononuclear cell number and are associated with lower somatic cell count in the next lactation, compared with long days. With heat stress, elevated body temperature directly affects expression of immune-related genes in mammary tissue. Responses depend on duration of exposure and feature acute upregulation of immune-signaling pathways, followed by enrichment of other immune-related pathways after prolonged exposure. Most responses are transient and recover within 1 wk. Functionally, heat stress impairs some aspects of acquired immunity in dry cows, including antigen responses and lymphocyte proliferation, but apparently not innate immune function. However, heat stress in late gestation reduces neutrophil phagocytosis and killing in vitro, and neutrophils in circulation are reduced in vivo as are responses to pathogen challenge in the subsequent lactation. A holistic understanding of the complex interplay of environment, pathogens, and host is needed to inform advances in this area.

Oral administration of nucleotides in calves: Effects on oxidative status, immune response, and intestinal mucosa development.

The present work aimed to investigate the effects of nucleotide oral administration on oxidative stress biomarkers, immune responses, gut morphology, serum biochemical parameters, and growth performance in calves from birth to 25 d of life. A total of 40 male Holstein Friesian calves were randomly divided in 2 groups. All the calves were born and reared on the same commercial dairy farm. They were fed the same colostrum, milk replacer, and calf starter. Five grams/head of an additive were orally administered with a syringe directly in the mouth to calves of the nucleotide group (NG). The additive contained 74.12 g/100 g of nucleic acids from hydrolyzed yeast, and 75.38% was free nucleotide sodium salt. The other group represented the negative control (CG). At 25 d of life all of the calves were slaughtered. Calves supplemented with nucleotides had a higher final live weight and improved average daily gain, which was associated with better efficiency of nutrient use. Oral nucleotide administration did not affect IgG absorption efficiency; however, NG calves showed greater duodenum villi length and higher crypt depth compared with CG. Oral nucleotide administration increased the activity of antioxidant enzymes (superoxide dismutase, catalase and glutathione peroxidase) and the antioxidant capacity [ferric reducing antioxidant power and 2,2'-azino-bis (3-ethylbenzothiazoline-6-sulphonic acid) scavenging activity] both in plasma and in liver. An enhanced ability of cells to counter reactive oxygen species- and reactive nitrogen species-mediated damage was also observed in peripheral blood mononuclear cells from NG. The findings highlight the effectiveness of oral nucleotide administration, and potentially dietary supplementation of nucleotides, in boosting oxidative and immune status in newborn calves.

Programming effects of late gestation heat stress in dairy cattle.

The final weeks of gestation represent a critical period for dairy cows that can determine the success of the subsequent lactation. Many physiological changes take place and additional exogenous stressors can alter the success of the transition into lactation. Moreover, this phase is pivotal for the final stage of intrauterine development of the fetus, which can have negative long-lasting postnatal effects. Heat stress is widely recognised as a threat to dairy cattle welfare, health, and productivity. Specifically, late gestation heat stress impairs the dam's productivity by undermining mammary gland remodelling during the dry period and altering metabolic and immune responses in early lactation. Heat stress also affects placental development and function, with relevant consequences on fetal development and programming. In utero heat stressed newborns have reduced birth weight, growth, and compromised passive immune transfer. Moreover, the liver and mammary DNA of in utero heat stressed calves show a clear divergence in the pattern of methylation relative to that of in utero cooled calves. These alterations in gene regulation might result in depressed immune function, as well as altered thermoregulation, hepatic metabolism, and mammary development jeopardising their survival in the herd and productivity. Furthermore, late gestation heat stress appears to exert multigenerational effects, influencing milk yield and survival up to the third generation.

Maternal heat stress reduces body and organ growth in calves: Relationship to immune status.

Late-gestation heat stress of dairy cows reduces fetal growth and influences postnatal performance and immune status of the offspring. Our first objective was to evaluate the effect of in utero heat stress on overall fetal and organ growth, particularly organs associated with immune function. The second objective was to examine the cellular mechanism of altered passive immunity in neonatal bull calves after in utero heat stress. Specifically, we examined the rate of apoptosis of intestinal cells early in life, as it is associated with gut closure. Dams were dried off approximately 45 d before expected calving and randomly assigned to 1 of 2 treatments: heat stress (HT) or cooling (CL). During the dry period all cows were housed under shade in a freestall barn, where the pen for CL cows was equipped with active cooling, including water soakers and fans, whereas the pen for HT cows had no soakers or fans. Using rectal temperature and respiration rate as indicators, heat stress was severe. Average rectal temperature in HT cows was 39.3°C compared with 39.0°C in CL cows, and HT cows had a respiration rate of 66.7 breaths/min compared with 43.2 breaths/min for CL cows. Bull calves (n = 30) were immediately separated from their dams at birth, weighed, and then killed before colostrum feeding (n = 5/treatment; d 0) or at 1 or 2 d of age following colostrum feeding (n = 5/treatment per day). After slaughter, the small intestine was removed and weighed, and samples from the jejunum were fixed for immunohistochemistry. Birth weight of bulls from HT dams was 1.1 kg lower than that of bulls from CL dams. Thymus, spleen, and heart weights of HT bulls were lower relative to those of CL bulls, whereas liver weight of HT bulls tended to be lower relative to that of CL bulls. Jejunal cell apoptosis decreased with age in both HT and CL calves after birth, mirroring gut closure. However, in utero heat stress increased the apoptotic rate in the jejunum, particularly at birth. We conclude that the chronic exposure to heat strain of HT compared with CL dams in late gestation significantly affected fetal growth and immune tissue development, which may be associated with reduced immune function in early life. Also, late-gestation heat stress increased calves' intestinal apoptosis in the first 2 d of life, which might explain the decreased IgG uptake and limited passive immune competence observed in previous studies.

Effect of late-gestation heat stress in nulliparous heifers on postnatal growth, passive transfer of immunoglobulin G, and thermoregulation of their calves.

Youngstock such as nulliparous pregnant dairy heifers are not typically considered for active cooling, as they are thought to be more heat tolerant than mature cows. Recently, the benefits of heat stress abatement in pregnant heifers were studied, but the effect of in utero hyperthermia on the calf is still unknown. Herein, we aimed to investigate the effects of late-gestation heat stress in nulliparous heifers on the growth, immune, and thermoregulatory responses of their calves. Pregnant nulliparous dams were randomly selected for either active cooling (CL; fans and soakers; n = 15) or heat stress (HT; n = 16) 60 d before expected calving. After birth, respiration rate, rectal temperature, skin temperature, and sweating rate were obtained from their heifer calves at 24 h and on d 14, 28, 42, and 56. Blood samples and body weights were both collected for measurement of total protein and hematocrit and calculation of average daily gains, respectively. Gestation length was shorter in HT heifers (272 vs. 276 ± 1.28 d) relative to CL heifers. Birth weights, weaning weights, body weights up to d 56, and average daily gain from birth to weaning were not different between in utero HT (IUHT; n = 13) and in utero CL (IUCL; n = 12) calves. Apparent efficiency of absorption of immunoglobulin G tended to be lower in IUHT calves (26.3 vs. 42.7 ± 9.0%), and serum IgG concentrations from birth to d 56 were significantly lower in IUHT calves relative to IUCL calves (22.0 vs. 32.4 ± 4.47 g/L). Postnatal respiration rate, rectal temperature, sweating rate, total protein, and hematocrit were not different between in utero treatments. There was a tendency for IUHT calves to have lower skin temperature at 24 h (34.9 vs. 36.9 ± 1.05°C), and skin temperature tended to be elevated in IUHT calves at d 56 (29.6 vs. 27.9 ± 1.05°C). In summary, the lack of heat stress abatement during late gestation reduces gestation length of nulliparous heifers. Additionally, providing active cooling to nulliparous heifers during the prepartum period confers immune benefits to their offspring, although it does not translate to growth improvements.

Late-gestation heat stress abatement in dairy heifers promotes thermoregulation and improves productivity.

Multiparous, nonlactating pregnant cows are negatively affected by heat stress, but the effect of heat stress on more thermotolerant pregnant heifers has received less attention. Our objective was to characterize the effect of late-gestation heat abatement on thermoregulatory responses and subsequent milk production of nulliparous Holstein heifers. Pregnant heifers, blocked by body condition score (BCS) and predicted transmitting ability (PTA) for milk, were enrolled in either heat stress (HT, shade of freestall barn; n = 16) or cooling (CL, shade of freestall barn, water soakers, and fans; n = 15) environments during the last 60 d of pregnancy (~8 weeks). Rectal temperature (RT; thermometer), respiration rate (RR; breaths/min), sweating rate (SR; VapoMeter, Delfin Technologies, Kuopio, Finland), and skin temperature (ST; infrared thermometer) were measured thrice weekly from enrollment to calving. Vaginal temperature (VT; i-button intravaginal device) was measured every 10 min for 7 consecutive days at wk -8, -6, -4, and -2 relative to calving and averaged hourly. Daily thermoregulatory patterns assessed by SR and ST, were measured every 4 h over a 36-h time interval at wk -6, -4, and -2 relative to calving. Upon calving, milk, protein, and fat yields were recorded twice daily for 15 wk. The average temperature-humidity index (Hobo Pro temperature probe, Onset Computer Corporation, Pocasset, MA) in the barn during the precalving period was 77 (minimum of 72, maximum of 82). Only heifers that gave birth to a female calf (CL = 12, HT = 14) were included in the statistical analysis. In the precalving period, CL heifers had lower RR (44.3 vs. 60.0 ± 1.6 breaths/min), RT (38.7 vs. 38.8 ± 0.04°C), unshaved ST (34.7 vs. 35.3 ± 0.17°C), and unshaved SR (19.0 vs. 35.2 ± 1.9 g/m2h), relative to HT heifers. Additionally, VT was lower in CL heifers during wk -4, and -2, specifically during early morning and early afternoon hours. When measured over a 36-h time interval, ST and SR were lower in CL heifers, when compared with HT heifers for all weeks. Notably, ST was reduced overnight and SR was reduced during the daytime. Cooled heifers had higher milk yield (35.8 vs. 31.9 ± 1.4 kg/d), when compared with HT heifers. Similar to multiparous cows, our data indicate that actively cooling heifers in late pregnancy is effective in promoting thermoregulation and results in elevated milk production postcalving.

MILK Symposium review: Improving the productivity, quality, and safety of milk in Rwanda and Nepal.

Dairy production plays an important role in the lives of many people in Rwanda and Nepal. The aim of the Feed the Future Innovation Lab for Livestock Systems (LSIL; Gainesville, FL) is to introduce new location-appropriate technologies and to improve management practices, skills, knowledge, capacity, and access to inputs across livestock value chains in developing countries such as Rwanda and Nepal. To assist LSIL, our first aim was to describe gaps in the management of cows and in milk processing that constrain milk quality and quantity in Rwanda and Nepal. Our second aim was to describe training-of-trainers workshops in both countries as an initial response to the findings from the first objective. We conducted literature reviews and did rapid needs assessments in both countries. The literature reviews revealed similar aspects of the challenges of smallholder crop-livestock mixed farming systems in both countries. Many farms are struggling with feed quality, reproduction, and health of dairy cows. Milk production per cow and quality is often low. Fresh milk is collected by milk collection and cooling centers. Hygiene and milk processing capability and shelf life of products can be improved. Local rapid needs assessments were conducted in 2016 (Rwanda) and 2017 (Nepal) through visits to farms, milk collection and chilling centers, and processing plants, and through discussions with local dairy officials. The assessments supplemented and completed our understanding of stakeholders' needs in management and processing of milk. Limiting factors to improving the productivity, quality, and safety of milk in Rwanda and Nepal were a combination of sometimes limited knowledge in areas such as feeding, mastitis control, and hygiene, and a lack of access to resources such as quality feeds, transportation, and cooling that hindered implementation of existing knowledge. Training-of-trainers workshops in milk processing and hygiene were developed and given in Rwanda and Nepal based on the rapid needs assessments, and these were well received. We concluded that Rwanda and Nepal both have smallholder dairy farms that often face similar challenges such as lack of quality feeds, needs for basic dairy management education, low cattle productivity, and undesirable milk quality. Training-of-trainers programs to address these basic issues may be successful. Continued improvements in the dairy value chain depend on available resources for education.

Estimation of maximum thermo-hygrometric index thresholds affecting milk production in Italian Brown Swiss cattle.

It is known that heat stress affects dairy cow performance in multiple ways: physiological, behavioral, reproductive, and productive. The aim of the present study was to determine if a threshold of temperature-humidity index (THI) exists for multiple milk production traits (milk yield, fat-corrected milk, protein and fat yield and percentage, energy-corrected milk, cheese production, and cheese yield) in Italian Brown Swiss dairy cows from the period 15 d before the day of the Italian Breeders Association test-day sampling. A 10-yr data set (2009-2018) containing 202,776 test-day records of 23,296 Brown Swiss cows was matched with the maximum THI. In all parities considered, no THI thresholds were observed for milk yield in Brown Swiss. In contrast, a THI threshold of 75 was identified for fat-corrected milk. No THI threshold was found for fat percentage, but fat yield showed the highest THI thresholds in cows of first and second parity. Protein yield and cheese production were affected by heat stress with average THI threshold of 74. The THI thresholds identified indicate that the Brown Swiss breed has higher thermal tolerance versus literature values reported for Holstein cows. As THI rises, Brown Swiss cows tend to produce the same volume of milk, but with a decreasing quality with regard to components. Further study is necessary to estimate the genetic component of heat tolerance, in Brown Swiss cattle, considering that the correct estimation of THI thresholds represents the first step to identify components that could be included in selection procedures.

Methods for assessing heat stress in preweaned dairy calves exposed to chronic heat stress or continuous cooling.

Although dairy calves are more thermotolerant relative to mature cows, they are still susceptible to heat stress, as demonstrated by elevated physiological responses and reduced feed intake under high ambient temperature and relative humidity. However, indicators of heat stress have not been well-characterized in calves. Herein, we evaluated associations between environmental and thermoregulatory and productive animal-based indicators of heat stress in dairy calves exposed to chronic heat stress or continuous cooling in a subtropical climate. Holstein calves were exposed to heat stress (HT; shade of barn, n = 24) or continuous cooling (CL; shade of barn plus 2 fans, n = 24) from 2 to 42 d of age. Environmental indices, including ambient temperature, relative humidity, temperature-humidity index (THI), and wind speed, and animal-based indices, including respiration (RR), heart rate (HR), rectal (RT), and skin temperature (ST) were recorded thrice daily (0900, 1300, and 1900 h). Milk replacer (MI) and grain intakes were recorded daily from 15 to 42 d of age. Using segmented regression models, we then estimated THI thresholds for significant changes in physiological responses. We found a strong, positive correlation between animal-based indicators (except for HR, MI, and grain intakes) and ambient temperature and THI, with the highest correlation obtained with ST and THI (r ≥ 0.72). Ambient temperature and ST and ambient temperature or THI and MI were the only correlations that differed between treatments. The coefficient of determination (R2) obtained from regression analyses to model animal-based indicators was substantially improved by the inclusion of environmental indicators, with the greatest improvement achieved with THI. Overall, continuous cooling by fans promoted calf heat loss as CL calves had lower RR, RT, ST, and higher feed intake compared with HT calves. Temperature-humidity index breakpoints could be determined for RT (THI = 67), RR (THI = 65), and MI (THI = 82) in HT calves, and only for RR (THI = 69) in CL calves. Skin temperature variables had no detectable breakpoints in either treatment due to the strong linear relationship to THI. Collectively, our results suggest that ST is appropriate to estimate chronic heat stress and that THI is the best environmental indicator of heat stress in dairy calves raised in a shaded, subtropical environment. At a practical level, calves should be closely monitored when THI reaches 65 to 69 to minimize the risk of heat stress-related impairments.

Late-gestation heat stress impairs daughter and granddaughter lifetime performance.

Records of late-gestation heat stress studies conducted over 10 consecutive years in Florida were pooled and analyzed to test the hypothesis that maternal hyperthermia during late gestation impairs performance of the offspring across multiple generations and lactations, ultimately impeding the profitability of the US dairy sector. Dry-pregnant multiparous dams were actively cooled (CL; shade of a freestall barn, fans and water soakers, n = 196) or not (HT; shade only, n = 198) during the last 46 d of gestation, concurrent with the entire dry period. After data mining, records of 156 daughters (F1) that were born either to CL (CLF1, n = 77) or HT dams (HTF1, n = 79) and 45 granddaughters (F2) that were born either to CLF1 (CLF2, n = 24) or HTF1 (HTF2, n = 21) were used in the analysis. Life events and daily milk yield for 3 lactations of daughters and granddaughters were obtained. Milk yield, reproductive performance, and productive life data were analyzed using MIXED and GLIMMIX procedures, and lifespan was analyzed using PHREG and LIFETEST procedures of SAS (SAS Institute Inc., Cary, NC). Milk production of HTF1 was reduced in their first (2.2 kg/d), second (2.3 kg/d), and third lactations (6.5 kg/d) compared with CLF1. More HTF1 were culled before first calving, and the productive life and lifespan of HTF1 were reduced relative to CLF1 (4.9 and 11.7 mo, respectively). The granddaughters (HTF2) born to HTF1 produced less milk in their first lactation (1.3 kg/d) relative to granddaughters (CLF2) born to CLF1. More HTF2 were culled before first breeding relative to CLF2; however, productive life and lifespan were not different between HTF2 and CLF2 animals. An economic analysis was then performed based on the number of heat stress days, dry cows per state, and the aforementioned impairments on daughters' lifespans and milk production. Collectively in the United States, the economic losses for additional heifer rearing cost, reduced productive life, and reduced milk yield of the F1 offspring were estimated at $134, $90, and $371 million per year, respectively. In summary, late-gestation heat stress exerts carryover effects on at least 2 generations. Providing heat abatement to dry-pregnant dams is important to rescue milk loss of the dam and to prevent losses in their progeny.

Carry over effects of late-gestational heat stress on dairy cattle progeny.

The impacts of late gestation heat stress on the dam and her subsequent lactation are well-recognized. However, more recent research has demonstrated the long-lasting and severe negative consequences on the in-utero heat-stressed progeny. Dairy calves born to late gestation heat-stressed dams weigh less at birth and up to one year of age and have compromised metabolism and immune function. In-utero programming of these offspring may coordinate alterations in thermoregulation, mammary development, and milk synthetic capacity at different developmental windows. Thus, prenatally heat-stressed dairy heifers will produce less milk across multiple lactations and have a lower herd survival rate, potentially negatively impacting the U.S. dairy economy. Dry period heat stress abatement strategies should be considered not only for the productivity and welfare of the pregnant dam but also for the developing calf.

Late gestation heat stress in dairy cows: Effects on dam and daughter.

In dairy cattle, the final weeks before parturition are physiologically challenging and an important determinant of subsequent production performance. External stressors should be carefully managed during this period to avoid adding strain on the animals. Late-gestation heat stress impairs productivity in the dam and exerts transgenerational effects on progeny. Physiological responses are complex and detriments to performance are multifaceted. Late-gestation heat stress blunts mammary gland involution in the first half of the dry period and impairs cell proliferation as calving approaches. Moreover, cows that were exposed to prepartum heat-stress exhibit reduced adipose tissue mobilization and a lower degree of insulin resistance during early lactation. Prepartum heat exposure also depresses immune function and evidence links this decrease to altered prolactin signaling under heat stress. Placental functions are also impaired as reflected in a higher cotyledon mass but lower maternal circulating estrone sulfate concentrations, potentially resulting in lower nutrient supply and reduced calf birth weight. In addition, calves born to heat-stressed dams show impaired immune function and therefore higher disease susceptibly. Novel evidence reported that intrauterine heat stress alters the methylation profile of liver and mammary DNA, which may also contribute to the poorer performance during adulthood of calves exposed to heat stress in utero. Understanding the contribution of all altered biological systems during late-gestation heat stress can be used as a basis for improving cow management during the dry period. This article provides a review of the impacts of late-gestation heat stress and of the emerging understanding of the biological mechanisms that underlie the observed impairments of performance.

Pre- and postnatal heat stress abatement affects dairy calf thermoregulation and performance.

Prenatal heat stress during late gestation exerts long-term effects on growth and productivity of the dairy calf. Further, direct exposure to heat stress during the preweaning period impairs calf thermoregulation and performance. We examined the effects of heat stress abatement during the prenatal period, postnatal period, or both on calf performance. We hypothesized that calves exposed to pre- and postnatal heat stress abatement would perform most optimally in terms of thermoregulation, growth, and health responses when compared with calves that are heat-stressed at any time in the pre- or postnatal periods. Holstein calves born to heat-stressed (HT) or cooled (CL) dams during late gestation (44 ± 5 d; prenatal HT or CL) were exposed to heat stress or cooling postnatally for 56 d (postnatal HT or CL), resulting in 4 treatments: HT-HT, HT-CL, CL-HT, and CL-CL; n = 12/treatment. Calves were administered 4 L of pooled colostrum and after 2 d of age allotted 10 L/d milk replacer and up to 3 kg/d concentrate in automatic feeder group pens (n = 6/pen). Postnatal cooling was achieved by 2 fans (average wind speed 2 m/s). Thermoregulatory responses (respiration rate and heart rate; rectal, body, and skin temperature), feed intake, growth parameters including average daily gain and medication events were recorded, and blood samples were collected weekly. Thermoregulatory responses were lower in postnatal CL calves compared with postnatal HT. In the afternoon, HT-HT calves had the highest respiration rate and rectal temperature, HT-CL calves had the lowest respiration rate, and CL-HT calves had the lowest heart rate compared with the other treatment groups. Prenatal CL calves weighed more at birth and weaning with a tendency for greater average daily gain compared with prenatal HT calves, whereas postnatal CL calves had increased milk replacer and concentrate intake and a tendency for reduced fever, infection, and total medication events relative to postnatal HT. Prenatal HT calves were esophageal tube fed more often than prenatal CL. Blood hematocrit and 24-h serum IgG concentration were greater in prenatal CL calves relative to prenatal HT. Prenatal heat stress abatement improves weight gain, hematocrit, and immunoglobulin transfer, whereas postnatal heat stress abatement modulates thermoregulatory responses, feed intake, and calf health. This study is the first to characterize the combined effects of pre- and postnatal heat stress or active cooling on the dairy calf.

When do dry cows get heat stressed? Correlations of rectal temperature, respiration rate, and performance.

Previous studies have documented the negative effects of heat stress during the dry period on dairy cow performance during the next lactation, but an easy method to assess heat stress for dry cow management is lacking. In an effort to determine a threshold for heat stress based on the physiological response of respiration rate, an easily measured variable, an analysis including data collected from 6 different studies (n = 144 cows) was performed to summarize the correlations among rectal temperature (RT) and respiration rate (RR) during the dry period, milk production during the first 8 wk of lactation (MK), calf birth weight (CW), body weight at calving (BW), gestation length (GL), and dry matter intake (DMI) pre- and postpartum. Studies were conducted in Florida during the summer, and dry cows were assigned to 2 treatments: heat stress (only shade; HT, n = 75 cows) and cooling (shade, fans, and soakers; CL, n = 69 cows). Average RT (0.3°C) and RR [26 breaths per min (bpm)] of HT cows increased compared with CL. In addition, the CL group produced more milk (2.8 kg/d) during the first 8 wk of the subsequent lactation relative to HT. Correlation analysis indicated that RR of HT was negatively correlated with MK and GL. Within HT, RT was also negatively correlated with MK and GL and tended to be negatively correlated with CW. In addition to being negatively correlated with RT and RR, HT MK was positively correlated with CW, GL, and DMI postpartum. In CL, no correlations were observed for RR, but RT was positively correlated with BW, and MK was positively correlated with DMI postpartum and tended to be positively correlated with GL. Moreover, the overall RT was 39.1 ± 0.48°C and RR was 61 ± 19.5 bpm, which indicates that RR over 61 bpm is an indicator of heat stress in cows during the dry period and can be easily assessed at the cow level. In summary, the more heat load a cow carries in the dry period, the greater the negative effects are on subsequent milk production, which may suggest a threshold for the effects of heat stress. Also, variation among cows within the HT group indicates that cows with longer gestation length have heavier calves, eat more postpartum, and produce more milk, but not as much as CL cows.

Short communication: Effects of mammary biopsy in the dry period on activity and feeding behavior of dairy cows.

In dairy cattle, mammary biopsies are commonly used to study development and function of the mammary gland. The objective of this study was to investigate changes in activity and feeding patterns following the mammary biopsy procedure. Pregnant, nonlactating Holstein dairy cows (20 d before expected calving date) were exposed to either (1) a biopsy procedure, in which a mammary tissue sample (60 × 4 mm in diameter) was obtained from cows (n = 9) using a biopsy tool from the rear left quarter, following administration of a sedative (xylazine, 20 µg/kg of body weight) and local anesthetic (3 mL of lidocaine), or (2) a sham procedure, in which cows (n = 8) were removed from the pen and restrained for a similar duration of time as for the biopsy procedure. Behavior of cows was monitored for 5 d, beginning on the day following biopsy (approximately 14 h after the procedure). Cows were fitted with accelerometers to record daily lying time, lying bout frequency, and lying side. Daily individual feed intake was recorded using the Calan Broadbent feeding system, and feeding time and meal characteristics were determined from a subset of cows (n = 6 per treatment) using a change-of-state data logger to record the times the cows were accessing the feed bunk. Total daily lying time did not differ between treatments [13.9 h/d; standard error (SE) = 0.56], but biopsied cows had more frequent, shorter lying bouts on the biopsied side on d 1 following the procedure (6.67 vs. 4.25 bouts/d, SE = 1.03, and 70.0 vs. 97.0 min/bout, SE = 8.6; left vs. right side), whereas control cows had no side preference. We found no effects of treatment on feed intake and feeding time but, on the first day after treatment, biopsied cows had meals that were more frequent (7.2 vs. 4.6 meals/d; SE = 0.93) and tended to be shorter (28.2 vs. 60.9 min/meal; SE = 11.8) than control cows. In conclusion, we did not detect effects of mammary biopsy on feed intake or lying time during our time frame of observation, but activity patterns were altered, which could be indicative of increased overall restlessness and specific pain in the biopsied quarter.