Thermogenesis and some rearing strategies of dairy calves at low temperature – a review

A retrospective study of thermal events on the mortality rate of hutch-reared dairy calves

Introduction

Heat stress in hutch-reared dairy calves (Bos taurus) is highly relevant due to its adverse effects on animal welfare, health, growth, and economic outcomes. This study aimed to provide arguments for protecting calves against heat stress. It was hypothesized that the thermal stress caused by high ambient temperature in summer months negatively affects the survival rate in preweaning calves.

Methods

In a retrospective study, we investigated how calf mortality varied by calendar month and between thermoneutral and heat stress periods on a large-scale Hungarian dairy farm (data of 46,899 calves between 1991 and 2015).

Results

The daily mortality rate was higher in the summer (8.7-11.9 deaths per 10,000 calf days) and winter months (10.7-12.5 deaths per 10,000 calf-days) than in the spring (6.8-9.2 deaths per 10,000 calf-days) and autumn months (7.1-9.5 deaths per 10,000 calf-days). The distribution of calf deaths per calendar month differed between the 0-14-day and 15-60-day age groups. The mortality risk ratio was highest in July (6.92). The mortality risk in the 0-14-day age group was twice as high in periods with a daily mean temperature above 22°C than in periods with a daily mean of 5-18°C.

Conclusions

Heat stress abatement is advised in outdoor calf rearing when the mean daily temperature reaches 22°C, which, due to global warming, will be a common characteristic of summer weather in a continental region.

A review of thermal stress in cattle

Cattle control body temperature in a narrow range over varying climatic conditions. Endogenous body heat is generated by metabolism, digestion and activity. Radiation is the primary external source of heat transfer into the body of cattle. Cattle homeothermy uses behavioural and physiological controls to manage radiation, convection, conduction, and evaporative exchange of heat between the body and the environment, noting that evaporative mechanisms almost exclusively transfer body heat to the environment. Cattle control radiation by shade seeking (hot) and shelter (cold) and by huddling or standing further apart, noting there are intrinsic breed and age differences in radiative transfer potential. The temperature gradient between the skin and the external environment and wind speed (convection) determines heat transfer by these means. Cattle control these mechanisms by managing blood flow to the periphery (physiology), by shelter-seeking and standing/lying activity in the short term (behaviourally) and by modifying their coats and adjusting their metabolic rates in the longer term (acclimatisation). Evaporative heat loss in cattle is primarily from sweating, with some respiratory contribution, and is the primary mechanism for dissipating excess heat when environmental temperatures exceed skin temperature (~36°C). Cattle tend to be better adapted to cooler rather than hotter external conditions, with Bos indicus breeds more adapted to hotter conditions than Bos taurus. Management can minimise the risk of thermal stress by ensuring appropriate breeds of suitably acclimatised cattle, at appropriate stocking densities, fed appropriate diets (and water), and with access to suitable shelter and ventilation are better suited to their expected farm environment.

Association between transfer of passive immunity, health, and performance of female dairy calves from birth to weaning

The objective of this observational study was to compare calf health, average daily weight gain, and calf mortality considering the proposed categories of transfer of passive immunity (TPI) by the consensus report of Lombard et al. (2020). The consensus report defines 4 categories of passive immunity (excellent, good, fair, and poor) of calves obtained after colostrum ingestion. The association between the 4 TPI categories was analyzed on calf health (i.e., hazards for morbidity and mortality), and average daily weight gain (ADG) of female Holstein Friesian calves during the first 90 d of age. A further aim of this study was to examine the effects of calving-related factors, such as dystocia or winter season, on TPI status. We hypothesized that calves with excellent TPI have greater ADG, lower risks for infectious diseases such as neonatal diarrhea, pneumonia, and omphalitis, and lower mortality rates. This observational study was conducted from December 2017 to March 2021. Blood was collected from 3,434 female Holstein Friesian dairy calves from 1 commercial dairy farm. All female calves aged 2 to 7 d were assessed for TPI status by determination of total solids (TS) in serum via Brix refractometry by the farm personnel once a week. Passive immunity was categorized according to Lombard et al. (2020) with excellent (≥9.4% Brix), good (8.9-9.3% Brix), fair (8.1-8.8% Brix), or poor TPI (<8.1% Brix). For the analysis of ADG and calving ease 492 or 35 calves had to be excluded due to missing data. The distribution of calves according to TPI categories was as follows: 4.8% poor (n = 166), 29.5% fair (n = 1,012), 28.3% good (n = 971), and 37.4% excellent (n = 1,285). From the calving-related factors, parity of the dam, calving ease, birth month, calving assistance by different farm personnel, and day of life for TPI assessment were significantly associated with TS concentration. Out of 3,434 calves, 216 (6.3%) had diarrhea, and 31 (0.9%) and 957 (27.9%) suffered from omphalitis and pneumonia during the first 90 d of life, respectively. Overall, the morbidity during the preweaning period was 32.6% (n = 1,118), and the mortality was 3.1% (n = 107). The ADG was 0.90 ± 0.15 kg with a range of 0.32 to 1.52 kg. The Cox regression model showed that calves suffering from poor TPI tended toward a greater hazard risk (HR) for diarrhea (HR = 1.57, 95% CI: 0.92-2.69) compared with calves with excellent TPI. Calves suffering from TPI had a greater HR for pneumonia (HR = 2.00, CI: 1.53-2-61), overall morbidity (HR = 1.99, CI: 1.56-2.55), and mortality (HR = 2.47, CI: 1.25-4.86) in contrast to excellent TPI. Furthermore, calves with good and fair TPI had significantly greater HR for pneumonia (good TPI: HR = 1.35, CI: 1.15-1.59; fair TPI: HR = 1.41, CI: 1.20-1.65) and overall morbidity (good TPI: HR = 1.26, CI: 1.09-1.47; fair TPI: HR = 1.32, CI: 1.14-1.53) compared with the excellent TPI category. Average daily weight gain during the first 60 d of life was associated with TPI categories. Calves with excellent and good TPI status had ADG of 0.90 ± 0.01 kg/d and 0.92 ± 0.01 kg/d (mean ± SE), respectively. The ADG of calves with fair TPI status was 0.89 ± 0.01 kg/d, and calves suffering from poor TPI had 0.86 ± 0.01 kg/d. Average daily weight gain differed in calves with poor TPI compared with the other categories. Fair and excellent TPI differed additionally from good TPI. We found no statistical difference between the TPI categories fair and excellent. In conclusion, poor TPI was associated with higher morbidity and mortality during the first 90 d of life. Furthermore, calves with fair, good or excellent TPI had greater ADG.

Graduate Student Literature Review: The problem of calf mortality on dairy farms

Calf mortality can be used as an indicator of animal health and welfare on dairy farms. However, several challenges surround the estimation and reporting of this metric, specifically: (1) lack of records or reliable data, (2) methods of data collection, and (3) inconsistencies in calculation and definitions used. Therefore, despite its importance, the lack of consensus on a definition of calf mortality makes it difficult to compare mortality rates between dairy farms or studies. Monitoring factors associated with calf mortality is vital to create preventative strategies. Although common strategies have been set about how to raise dairy calves and manage dairy calves, discrepancies among studies evaluating factors associated with calf mortality still exist. This review summarizes research on the evaluation of calf mortality and associated risk factors, specifically, the lack of reliable data and standardization of the definition of calf mortality. In addition, current strategies to monitor and prevent calf mortality will be presented in this review.

The Role of Brown Adipose Tissue and Energy Metabolism in Mammalian Thermoregulation during the Perinatal Period

Hypothermia is one of the most common causes of mortality in neonates, and it could be developed after birth because the uterus temperature is more elevated than the extrauterine temperature. Neonates use diverse mechanisms to thermoregulate, such as shivering and non-shivering thermogenesis. These strategies can be more efficient in some species, but not in others, i.e., altricials, which have the greatest difficulty with achieving thermoneutrality. In addition, there are anatomical and neurological differences in mammals, which may present different distributions and amounts of brown fat. This article aims to discuss the neuromodulation mechanisms of thermoregulation and the importance of brown fat in the thermogenesis of newborn mammals, emphasizing the analysis of the biochemical, physiological, and genetic factors that determine the distribution, amount, and efficiency of this energy resource in newborns of different species. It has been concluded that is vital to understand and minimize hypothermia causes in newborns, which is one of the main causes of mortality in neonates. This would be beneficial for both animals and producers.

Thermoregulatory capacity of goat kids from birth to weaning in a dry hot climate

This study aimed to evaluate the thermoregulatory capacity and performance of Saanen goat kids from birth to weaning in a hot climate. Twelve newborn males and female goat kids with an initial body weight of 4.17 ± 0.81 kg were used. Physiological responses, climatic variables, and biometric traits data were collected. Univariate and multivariate analysis techniques were used. Heart rate (H_R) was high up to the 6th week of life, with a reduction from the 7th week on (P < 0.001). Rectal temperature (R_T) was lower in the first 2 weeks (P < 0.001), with an increase and stabilization occurring in the 7th and 8th weeks. Coat surface temperature (S_T) was more activated from the 5th week onwards (P < 0.001). Body weight (B_W) and withers height (W_H) were higher in later weeks of the calving phase with a linear effect (P < 0.001). The first principal component demonstrated the relationship of sensible heat dissipation × body area of the goat kids; the second component shows the relationship of meteorological data with R_T, having a positive relationship between R_T with R_H and negative with A_T, and the third component points to the association of R_R and H_R. Of the animals, 81.3% were correctly classified in their group of origin in discriminant canonical analysis, with emphasis on the classification of the kids in the 1st-2nd and 3rd-4th weeks (classification percentage Ʃ = 95.8%). It is concluded that (i) newborn kids activate latent mechanisms to maintain their homoeothermic during the first 2 weeks of life, and as they grow, they use sensitive heat loss processes, especially from the 5th week of life onwards and (ii) male and female goats do not show sexual dimorphism effect on body performance and body morphometric measurements up to 60 days of life.

Vitality in Newborn Farm Animals: Adverse Factors, Physiological Responses, Pharmacological Therapies, and Physical Methods to Increase Neonate Vigor

Vitality is the vigor newborn animals exhibit during the first hours of life. It can be assessed by a numerical score, in which variables, such as heart rate, respiratory rate, mucous membranes' coloration, time the offspring took to stand up, and meconium staining, are monitored. Vitality can be affected by several factors, and therapies are used to increase it. This manuscript aims to review and analyze pharmacological and physical therapies used to increase vitality in newborn farm animals, as well as to understand the factors affecting this vitality, such as hypoxia, depletion of glycogen, birth weight, dystocia, neurodevelopment, hypothermia, and finally, the physiological mechanism to achieve thermostability. It has been concluded that assessing vitality immediately after birth is essential to determine the newborn's health and identify those that need medical intervention to minimize the deleterious effect of intrapartum asphyxia. Vitality assessment should be conducted by trained personnel and adequate equipment. Evaluating vitality could reduce long-term neonatal morbidity and mortality in domestic animals, even if it is sometimes difficult with the current organization of some farms. This review highlights the importance of increasing the number of stock people during the expected days of parturitions to reduce long-term neonatal morbidity and mortality, and thus, improve the farm's performance.

The effect of birth weight and time of day on the thermal response of newborn water buffalo calves

During the 1st days of life, water buffalo calves, especially those with low birth weight, are susceptible to hypothermic mortality due to scarce energy reserves provided by fats. This means that monitoring the thermal state of newborns is essential. The objectives of the present study were to apply infrared thermography (IRT) in 109 buffalo calves to detect differences in the surface temperatures of six thermal windows -lacrimal gland, lacrimal caruncle, periocular region, nostrils, ear canal, pelvic limbs-, and determine their association to birth weight during the first 6 days of life. The calves were divided into four categories according to their weight (Q₁, 37.8-41.25 kg; Q₂, 41.3-46.3 kg; Q₃, 46.4-56.3 kg; Q₄, 56.4-60.3 kg). The thermographic images were recorded in the morning and afternoon. Results showed that the animals in Q₄ registered the highest temperatures in all the thermal windows, and that these were higher in the afternoon (p < 0.0001). When considering the thermal windows, those located in the facial region recorded the highest temperatures; in contrast, the temperatures at the pelvic limbs remained below the average values of the other windows (33.41 and 33.76°C in the morning and afternoon, respectively). According to these results, the birth weight of water buffaloes is a factor that alters their thermoregulation during the 1st days of life, a condition that can be partially compensated by colostrum intake to promote development of an efficient thermoregulatory mechanism in water buffalo calves.

Neonatal infrared thermography images in the hypothermic ruminant model: Anatomical-morphological-physiological aspects and mechanisms for thermoregulation

Hypothermia is one factor associated with mortality in newborn ruminants due to the drastic temperature change upon exposure to the extrauterine environment in the first hours after birth. Ruminants are precocial whose mechanisms for generating heat or preventing heat loss involve genetic characteristics, the degree of neurodevelopment at birth and environmental aspects. These elements combine to form a more efficient mechanism than those found in altricial species. Although the degree of neurodevelopment is an important advantage for these species, their greater mobility helps them to search for the udder and consume colostrum after birth. However, anatomical differences such as the distribution of adipose tissue or the presence of type II muscle fibers could lead to the understanding that these species use their energy resources more efficiently for heat production. The introduction of unconventional ruminant species, such as the water buffalo, has led to rethinking other characteristics like the skin thickness or the coat type that could intervene in the thermoregulation capacity of the newborn. Implementing tools to analyze species-specific characteristics that help prevent a critical decline in temperature is deemed a fundamental strategy for avoiding the adverse effects of a compromised thermoregulatory function. Although thermography is a non-invasive method to assess superficial temperature in several non-human animal species, in newborn ruminants there is limited information about its application, making it necessary to discuss the usefulness of this tool. This review aims to analyze the effects of hypothermia in newborn ruminants, their thermoregulation mechanisms that compensate for this condition, and the application of infrared thermography (IRT) to identify cases with hypothermia.

A review of factors affecting the welfare of dairy calves in pasture-based production systems

Current research on factors affecting the welfare of dairy calves is predominantly based on indoor, year-round calving systems. Calf rearing in these systems differs from that in more seasonal, pasture-based dairy production, meaning that risks to the welfare of dairy calves may not always be comparable between the two systems. The aim of this review was to consolidate the scientific literature relating to calf welfare in pasture-based dairy systems from birth until weaning, allowing for (1) the identification of current and emerging risks to calf welfare and (2) the formation of recommendations to mitigate these risks. Many of the risks to calf welfare discussed in this review are not exclusive to pasture-based dairies. This includes a global trend for increasing perinatal mortalities, a significant number of calves failing to achieve effective passive transfer of immunity, the low uptake of best practice pain relief when calves are disbudded, and the feeding of restricted milk volumes. In addition to these persisting welfare risks, two factors discussed in this review pose an immediate threat to the social license of dairy farming; the separation of cow and calf soon after birth and the management of surplus calves (i.e. calves not needed by the dairy industry). Several recommendations are made to improve the uptake of best-practice calf rearing and progress the development of alternative pasture-based rearing systems that accommodate changing community expectations. These include communication strategies that strengthen farmer beliefs regarding the welfare and productivity benefits achieved by best practice calf rearing and challenge beliefs regarding the associated costs. Farmers should also be encouraged to benchmark their rearing practices through improved record keeping of key rearing inputs and outcomes. Biological research is needed to advise the development of new calf rearing recommendations and the evolution of existing recommendations. Research priorities identified by this review include the effects of dystocia on the neonate and strategies to mitigate these effects, relationships between features of pen design and calf health and welfare, feasibility of dam rearing in large pasture-based dairy systems, and strategies that increase the value of the surplus calf.

Thermoregulatory Responses and Performance of Dairy Calves Fed Different Amounts of Colostrum

Simple Summary

Colostrum is an important source of antibodies, nutrients, and energy for thermogenesis by the newborn calf. However, the amount of colostrum required for thermoregulatory responses and improved performance is not well established. This study evaluated newborn thermoregulatory responses during a cold challenge (10 °C) at 24 h of life and performance in the preweaning period for calves fed different volumes of colostrum. Newborn calves fed higher volumes of colostrum exhibited increased thermoregulatory responses, improved growth performance, and immunity.

Abstract

This study investigates the newborn thermoregulatory responses to cold and the performance of calves fed different colostrum volumes. Thirty newborn Holstein calves were blocked by birth body weight (BW; 39.4 ± 6.5 kg) and fed different high-quality colostrum volumes: 10%, 15%, or 20% of BW, which was split and fed at 2 and 8 h after birth. At 24 h of life, calves were placed in a chamber at 10 °C for 150 min. Skin and rectal temperature (RT), heart and respiratory rate, and shivering were measured every 15 min. Blood samples were taken every 30 min. After the cold challenge, calves were housed in ambient temperature (26.8 ± 5.9 °C), with free access to water and concentrate and received 6 L/d of milk replacer. Feed intake, fecal score, and RT were recorded daily, until 56 d of age. Blood samples, BW, and body measures were taken weekly. During the cold challenge, prescapular temperature and total serum protein were greater for calves fed 15% or 20%. Leukocytes increased preweaning, presenting higher values for calves fed 20%. Even though there was a benefit for the calf submitted to cold stress on the first day of life, feeding higher volumes of colostrum resulted in no differences in performance during the preweaning phase. Nevertheless, calves fed a higher volume of colostrum (20% BW) presented increased immune responses during the preweaning phase.