K. DiGiacomo

Amelioration of thermal stress impacts in dairy cows

Heat stress negatively impacts on a variety of animal production parameters. Advances in management strategies have alleviated some of the negative impacts of thermal stress on farm animals, but production continues to markedly decrease during heat events in summer, particularly in dairy cattle. In this paper we introduce a Dairy Risk Assessment Program (DRAP). The DRAP is a user-friendly software package designed to assist users in predicting heat loads in dairy cow herds. DRAP was developed over three Australian summers using climatic data (temperature, humidity, solar radiation and wind speed), cow production data (milk yield and milk quality), and physiological data (respiration rate and body temperature). The data were used to develop mathematical algorithms which can predict animal response to climatic variables. This software package is designed to be used by the dairy industry to better manage cows during times of elevated environmental temperatures by equipping producers, managers, and dairy industry personnel with Dairy Heat Load Index (DHLI) values which were calculated based upon site information, stock characteristics, management practices, and mitigation variables specific to their dairy production unit. When a heat event is imminent producers can then introduce management strategies such as providing shade or additional water troughs or implementation of nutritional strategies. Some of these nutritional strategies include dietary chromium picolinate, betaine and antioxidant supplementation or altering the rate of starch fermentation. These nutritional strategies are discussed at some length in this paper.

Thermoregulatory differences in lactating dairy cattle classed as efficient or inefficient based on residual feed intake

It is suggested that one-third of the inter-animal differences in efficiency is explained by differences in digestion, heat production, body composition and activity; while the remaining variation is the result of energy expenditure due to biological processes such as ion pumps and mitochondrial function. Inefficient animals may be wasting energy on inefficient processes resulting in increased heat production that may be reflected by differences in skin and core temperature. While the association between heat production and residual feed intake (RFI) has been touched on, it is yet to be fully elucidated. It is hypothesised that more efficient animals will expend less energy as heat, which will be reflected by differences in core and skin temperature measures. Fifty-four primiparous, Holstein-Friesian cows previously assessed for RFI (26 inefficient/high RFI, 28 efficient/low RFI) were selected and drafted into outdoor holding yards for measurements on two occasions (once during lactation and once during the non-lactating ‘dry’ period). Measures of body temperature were obtained using an infrared (IR) camera to obtain skin (surface) temperatures at multiple locations [muzzle, eye, jaw, ear, leg (front and back), rump, shoulder, teat, udder, side and tail] and rectal temperatures were measured using a digital thermometer. Respiration rates (RR) were obtained by counting the number of flank movements in 1 min. A subset of 16 cows (8 efficient and 8 inefficient) were utilised for further IR imagery in an undercover environment (to eliminate the influences of external environments). Skin temperature measurement obtained using an IR camera during the outdoor period demonstrated that inefficient cows had higher (0.65°C) teat temperatures (P = 0.05). Rectal temperature and RR were not influenced by efficiency group. When IR images were obtained undercover inefficient cows tended to have higher shoulder (0.85°C) and neck (0.98°C) temperatures than efficient cows (P < 0.087); while udder temperature was significantly greater (1.61°C) for inefficient than efficient cows (P = 0.018). These data indicate that some of the differences in efficiency may be attributed to differences in thermoregulation, as reflected by differences in skin (but not core) temperature and that IR imagery is a suitable method for determining these differences in a non-invasive manner. Further research is required to further establish these relationships, and the measurement of skin temperatures should be undertaken indoors to eliminate external environmental influences.

Potential nutritional strategies for the amelioration or prevention of high rigor temperature in cattle – a review

Environmental conditions influence animal production from an animal performance perspective and at the carcass level post-slaughter. High rigor temperature occurs when the animal is hyperthermic pre-slaughter, and this leads to tougher meat. Hyperthermia can result from increased environmental temperature, exercise, stress or a combination of these factors. Consumer satisfaction with beef meat is influenced by the visual and sensory traits of the product when raw and cooked, with beef consumers commonly selecting tenderness of the product as the most important quality trait. High rigor temperature leads to a reduction in carcass and eating quality. This review examines some possible metabolic causes of hyperthermia, with focus on the importance of adipose tissue metabolism and the roles of insulin and leptin. Potential strategies for the amelioration or prevention of high rigor temperature are offered, including the use of dietary supplements such as betaine and chromium, anti-diabetic agents such as thiazolidinediones, vitamin D, and magnesium (Mg) to provide stress relief.

Responses of dairy cows to short-term heat stress in controlled-climate chambers

The objective of the present research was to describe the physiological and production responses of lactating dairy cows during and after sudden exposure to temperate-climate heat-wave conditions, compared with cows in thermoneutral conditions. Twelve lactating multiparous Holstein–Friesian dairy cows were housed in controlled-climate chambers for 4 days. Six were exposed to a short-term temperature and humidity challenge (THc, diurnal temperature and humidity fluctuations inducing moderate heat stress; temperature humidity index 74–84) and six cows were exposed to thermoneutral conditions (THn, temperatur humidity index 55–61). Cows were also measured during a 7-day pre-experimental and 14-day post-experimental period. Physiological indicators of heat stress were measured, including rectal and vaginal temperature and respiration rate, which indicated that the THc in controlled-climate chambers induced moderate heat stress. The cows exposed to the 4-day THc reduced their milk yield by 53% and their dry-matter intake by 48%, compared with the cows in the THn treatment. Milk yield of THc cows returned to pre-experimental milk yield by Day 7 and dry-matter intake by Day 4 of the post-experimental period. The short-term heat challenge induced metabolic adaptations by mobilising adipose tissue, as indicated by increased non-esterified fatty acids, and amino acids from skeletal muscle, as indicated by increased urea nitrogen to compensate for reduced nutrient intake and increased energy expenditure. Endocrine responses included greater prolactin concentrations, which is associated with thermoregulation and water metabolism. The cows exposed to THc displayed production and physical responses that facilitated lower metabolic heat production and greater heat dissipation in an attempt to maintain homeostasis during the short-term heat exposure. These results indicated that the conditions imposed on the cows in the controlled-climate chambers were sufficient to induce heat-stress responses and adversely affected production in the lactating dairy cow, and the delay between the return to normal feed intake and milk yield following the heat challenge suggests a period of metabolic recovery was occurring.

Feeding slowly fermentable grains has the potential to ameliorate heat stress in grain-fed wethers

During heat stress (HS), livestock reduce metabolic heat production by lowering activity and feed intake. Because this has obvious consequences for productivity, the aim of these experiments was to investigate nutritional methods for reducing digestive metabolic heat production, thereby allowing livestock more opportunity to dissipate excess heat. In the first experiment, the fermentation rates of corn and wheat grains were compared in an in vitro gas production system containing buffered rumen fluid. This experiment showed that corn had a slower (-15%; < 0.001) rate of gas production than wheat and no differences in total amount of gas production after 24 h of incubation. In the second experiment, we hypothesized that the lower rate of fermentation of corn would reduce metabolic heat load in wethers and, in turn, improve tolerance to HS. Twenty-two Merino × Poll Dorset wethers were housed in 2 climate-controlled rooms and were fed either corn grain plus forage (CD; 39% starch) or wheat grain plus forage (WD; 37% starch) during 3 experimental periods: period 1 (P1), which consisted of 7 d of thermoneutral conditions (18 to 21°C and 40 to 50% relative humidity [RH]) and restricted feed intake (1.3 times maintenance); period 2 (P2), which consisted of 7 d of HS (28 to 38°C and 30 to 50% RH) and restricted feed intake; and period 3 (P3), which consisted of 7 d of HS as in P2 with unrestricted feed intake (1.5 times maintenance) in a randomized control experiment. Water was offered ad libitum. The level of HS was quantified by increases in rectal temperature (RT), respiration rate (RR), and left and right flank skin temperature (LFT and RFT, respectively) and blood acid-base balance. Rectal temperature, RR, LFT, and RFT were elevated ( < 0.001) during HS, especially when wethers had unrestricted feed intake (P3). Wethers fed CD had lower RR, RT, LFT, and RFT ( < 0.001) than wethers fed WD, and this benefit was greatest during HS (P2 and P3). The reduction in RR with CD resulted in less CO exhalation (greater partial pressure of CO2) and greater HCO3 ( < 0.05) than with WD, indicating reduced efforts to dissipate heat by evaporative heat loss via panting. The greatest heat from fermentation was apparent in WD wethers, which had elevated LFT compared with RFT ( < 0.001). Crucially, this large difference was not observed with the CD wethers, indicating that the slow rate of fermentation of CD was expressed as low heat released during feed fermentation in the rumen. These data demonstrated that feeding CD may be a useful management strategy to reduce the impact of high environmental heat loads in sheep.

Dietary betaine supplementation has energy-sparing effects in feedlot cattle during summer, particularly in those without access to shade

Dietary betaine supplementation improves water retention in steers and may influence lean-tissue deposition, while also acting as an osmolyte to help regulate cellular osmotic balance. This study investigated the interactions between shade and dietary betaine on carcass characteristics, tissue enzyme activity and gene expression in 48 feedlot steers during summer. Steers were randomly allocated to a 4 × 2 factorial design with the factors being dietary betaine (0, 10, 20 or 40 g) and shade (with and without shade) for 120 days. Tissue samples were obtained at slaughter and analysed for gene expression of heat shock proteins 70 and 90 (HSP70/90) and expression of heat shock factor 1 (HSF1), and enzyme activity of fatty acid synthase (FAS) and glycerol-6-phosphate dehydrogenase (G6PDH). Carcasses were evaluated for quality. Carcass weight at slaughter was not altered by shade (P = 0.18) but tended to be increased by dietary betaine (306 v. 314 kg, P = 0.09). The P8 backfat was not altered by shade (P = 0.43) or dietary betaine (P = 0.32), although there was a within dietary betaine effect whereby P8 backfat tended to be greater in steers fed 10 g compared with 40 g betaine/day (17.4 v. 14.5 mm, P = 0.06). Muscle pH at 1 h (5.97 v. 6.03, P = 0.01) and 2 h (5.73 v. 5.80, P = 0.04) post-slaughter was higher in shaded steers, and muscle pH at 1 h post-slaughter was higher in steers fed 10 or 20 g than those fed 40 g betaine/day (6.03 v. 6.03 v. 5.95, P = 0.005). Gene expression was not altered by betaine, while adipose tissues expressed more of each gene than muscle (P < 0.001). The mRNA expression of HSF1 and HSP90 was influenced by a shade × betaine interaction, although the direction of this interaction was irregular (P = 0.03 and 0.03, respectively). Adipose tissue FAS and G6PDH enzyme activity was unaffected by shade and betaine. The results of this study indicate that betaine supplementation may be a successful carcass modifier in growing feedlot steers during summer. Provision of shade during summer may reduce the rate of pH decline in the first 2 h after slaughter and reduce the risk of high rigor temperature.

Dietary Betaine Impacts the Physiological Responses to Moderate Heat Conditions in a Dose Dependent Manner in Sheep

Simple Summary Heat stress in sheep initiates physiological methods to dissipate heat that result in decreased production. This study investigated the use of a dietary supplement, the osmolyte betaine fed at two doses (2 or 4 g/day), on the physiological responses to heat in sheep. Heat exposure initiated physiological responses such as an increased rectal temperature and respiration rate as expected, while betaine supplemented at 2 g/day ameliorated these responses. Thus, dietary betaine supplementation may have beneficial effects for sheep exposed to heat. Abstract Heat exposure (HE) results in decreased production in ruminant species and betaine is proposed as a dietary mitigation method. Merino ewes (n = 36, 40 kg, n = 6 per group) were maintained at thermoneutral (TN, n = 18, 21 °C) or cyclical HE (n = 18, 18–43 °C) conditions for 21 days, and supplemented with either 0 (control), 2 or 4 g betaine/day. Sheep had ad libitum access to water and were pair fed such that intake of sheep on the TN treatment matched that of HE animals. Heart rate (HR), respiration rate (RR), rectal (TR) and skin temperatures (TS) were measured 3 times daily (0900 h, 1300 h, 1700 h). Plasma samples were obtained on 8 days for glucose and NEFA analysis. The HE treatment increased TR by 0.7 °C (40.1 vs. 39.4 °C for HE and TN respectively p < 0.001), TS by +1.8 °C (39.3 vs. 37.5 °C, p < 0.001) and RR by +46 breaths/min (133 vs. 87 breaths/min, p < 0.001) compared to TN. The 2 g betaine/day treatment decreased TR (39.8, 39.6 and 39.8 °C, p < 0.001), TS (38.7, 38.0 and 38.5 °C, p < 0.001) and RR (114, 102 and 116 breaths/min for control, 2 and 4 g betaine/day, p < 0.001) compared to control. Betaine supplementation decreased plasma NEFA concentrations by ~25 μM (80, 55 and 54 μmol/L for 0, 2 and 4 g/day respectively, p = 0.05). These data indicate that dietary betaine supplementation at 2 g betaine/day provides improvements in physiological responses typical of ewes exposed to heat stress and may be a beneficial supplement for the management of sheep during summer.

Effects of chromium supplementation on physiology, feed intake, and insulin related metabolism in growing pigs subjected to heat stress1

Abstract Improving insulin sensitivity may reduce impacts of heat stress (HS) in pigs by facilitating heat dissipation. Chromium (Cr) has been reported to improve insulin sensitivity in pigs. Therefore, the aim of this experiment was to investigate whether Cr supplementation can mitigate HS in growing pigs. Thirty-six gilts were randomly assigned to 2 diets containing 0 (control) or 400 ppb Cr. After 14 d the supplemented pigs were allocated to either 8 d thermoneutral (20°C constant; TN) or cyclic HS (35°C, 0900 h to 1700 h) conditions and continued their respective diet (n = 9 per group). Growth performance was recorded during the 14-d supplementation period. The physiological responses to HS were monitored by measuring respiration rate, rectal temperature, blood gas chemistry, and feed intake during thermal exposure. Kinetics of plasma glucose, insulin and NEFA were studied by intravenous glucose tolerance test (IVGTT) on d 8 of thermal treatment. Results showed Cr alleviated the HS-increased rectal temperature (P < 0.05) and respiration rate (P < 0.01) at 1300 h and 1600 h during thermal exposure. However, Cr did not mitigate the reduction in average daily feed intake which was reduced by 35% during HS or the HS-induced respiratory alkalosis. Chromium tended to increase average daily gain (0.86 vs. 0.95 kg, P = 0.070) during the 14-d supplementation under TN conditions before thermal exposure, which might be associated with the potential of Cr in improving overall insulin sensitivity, as evidenced by a reduced insulin resistance index calculated by Homeostatic Model Assessment (HOMA-IR; 0.65 vs. 0.51, P = 0.013) and a tendency of reduced fasting plasma insulin concentration (1.97 vs. 1.67 μU/mL, P = 0.094). Heat stress decreased the acute insulin releasing rate (P = 0.012) and consequently slowed glucose clearance rate (P = 0.035) during IVGTT. Besides, HS enlarged the values of area under the curve of NEFA during IVGTT (P < 0.01), indicating a reduced lipid mobilization. In conclusion, HS reduced insulin response to IVGTT. Chromium supplementation exhibited a potential in improving insulin sensitivity and mitigating HS symptoms in growing pigs.

Evaluation of growth hormone response to insulin-induced hypoglycaemia in dairy cattle during a 670-day lactation

Plasma growth hormone secretion in response to insulin-induced hypoglycaemia was evaluated in cows undergoing an extended lactation. Twelve multiparous Holstein-Friesian cows that calved in late winter and were managed for a 670-day lactation by delaying mating. Four experimental periods of 40 days commenced at ~73, 217, 422 and 520 (±9.1; mean ± s.d.) days in milk (DIM) during which cows were individually offered a diet of perennial ryegrass (73 and 422 DIM) or pasture hay and pasture silage (217 and 520 DIM) supplemented with either 1 kg DM grain (CONT) or 6 kg DM grain (GRAIN). Cows were fitted with jugular catheters during the final week of each experimental period. Seven blood samples over a 24-h period were collected and an insulin tolerance test was performed on each cow using a dose of 0.12 µU insulin/kg liveweight at ~100, 250, 460 and 560 DIM. This resulted in an increase in plasma growth hormone concentration occurring at 100 DIM, an intermediate and delayed response at 250 DIM, and no response at both 460 and 560 DIM. Cows in the CONT treatment had higher basal plasma growth hormone concentrations and tended to have a greater peak growth hormone response than GRAIN cows. The growth hormone response at 100 and 250 DIM is likely a homeorhetic mechanism to support milk yield during early-mid lactation. These observations are consistent with the known actions of growth hormone to promote lipid mobilisation, hepatic glucose production and an overall state of catabolism. With further research, the insulin tolerance test may be a useful tool to identify cows with greater growth hormone secretory response and increased milk production or persistency.

Responses of dairy cows with divergent residual feed intake as calves to metabolic challenges during midlactation and the nonlactating period

Residual feed intake (RFI) is defined as the difference between the actual and expected feed intake required to support animal maintenance and growth. Thus, a cow with a low RFI can obtain nutrients for maintenance and growth from a reduced amount of feed compared with a cow with a high RFI. Variation in RFI is underpinned by a combination of factors, including genetics, metabolism, thermoregulation and body composition; hypothalamic-pituitary-adrenal (HPA) axis responsiveness is also a possible contributor. Responses to 3 metabolic challenges were measured in lactating and nonlactating dairy cattle. Sixteen Holstein Friesian cows with phenotypic RFI measurements that were obtained during the growth period (188-220 d old) were grouped as either low-calfhood RFI (n = 8) or high-calfhood RFI (n = 8). An ACTH (2 µg/kg of body weight), insulin (0.12 U/kg), and epinephrine (a low dose of 0.1 µg/kg and a high dose of 1.6 µg/kg of epinephrine) challenge were each conducted during both midlactation (122 ± 23.4 d in milk) and the nonlactating period (dry period; approximately 38 d after cessation of milking). Cows were housed in metabolism stalls for the challenges and were fed a diet of alfalfa cubes ad libitum for at least 10 d before the experiment (lactating cows also were offered a total of 6 kg of dry matter/d of crushed wheat grain plus minerals fed as 3 kg of dry matter at each milking) and were fasted for 12 h before the challenges. The efficiency of conversion of feed into milk (the ratio of feed consumed to milk produced over the 7 d before the experiment) during midlactation was better (lower) in low-calfhood RFI cows, although dry matter intake did not differ between RFI groups. Low-calfhood RFI cows exhibited a lower plasma cortisol response to the ACTH challenge than high-calfhood RFI cows, particularly in midlactation (-15%). The low-calfhood RFI cows had a greater plasma insulin-like growth factor-1 response to the insulin challenge and plasma fatty acid response to epinephrine compared with the high-calfhood RFI cows. These data suggest that high-calfhood RFI cows exhibit a more responsive HPA axis. As divergence in RFI measured during growth is retained (although reduced) during lactation, it is possible that energy is used to respond to HPA axis activation at the expense of production in high-calfhood RFI dairy cattle during lactation and contributes to a decrease in overall feed use efficiency.