Metabolic adaptations to heat stress in growing cattle

To differentiate between the effects of heat stress (HS) and decreased dry matter intake (DMI) on physiological and metabolic variables in growing beef cattle, we conducted an experiment in which a thermoneutral (TN) control group (n = 6) was pair fed (PF) to match nutrient intake with heat-stressed Holstein bull calves (n = 6). Bulls (4 to 5 mo old, 135 kg body weight [BW]) housed in climate-controlled chambers were subjected to 2 experimental periods (P): (1) TN (18 °C to 20 °C) and ad libitum intake for 9 d, and (2) HS (cyclical daily temperatures ranging from 29.4 °C to 40.0 °C) and ad libitum intake or PF (in TN conditions) for 9 d. During each period, blood was collected daily and all calves were subjected to an intravenous insulin tolerance test (ITT) on day 7 and a glucose tolerance test (GTT) on day 8. Heat stress reduced (12%) DMI and by design, PF calves had similar nutrient intake reductions. During P1, BW gain was similar between environments and averaged 1.25 kg/d, and both HS and PF reduced (P < 0.01) average daily gain (-0.09 kg/d) during P2. Compared to PF, HS decreased (P < 0.05) basal circulating glucose concentrations (7%) and tended (P < 0.07) to increase (30%) plasma insulin concentrations, but neither HS nor PF altered plasma nonesterified fatty acid concentrations. Although there were no treatment differences in P2, both HS and PF increased (P < 0.05) plasma urea nitrogen concentrations (75%) compared with P1. In contrast to P1, both HS and PF had increased (16%) glucose disposal, but compared with PF, HS calves had a greater (67%; P < 0.05) insulin response to the GTT. Neither period nor environment acutely affected insulin action, but during P2, calves in both environments tended (P = 0.11) to have a blunted overall glucose response to the ITT. Independent of reduced nutrient intake, HS alters post-absorptive carbohydrate (basal and stimulated) metabolism, characterized primarily by increased basal insulin concentrations and insulin response to a GTT. However, HS-induced reduction in feed intake appears to fully explain decreased average daily gain in Holstein bull calves.     

热应激对奶牛血液中内毒素含量和抗氧化指标的影响

选用16头健康的中国荷斯坦奶牛,随机分为两个处理（夏季组和冬季组）,每个处理8个重复,每个重复1头牛。当夏季组奶牛牛舍温湿度指数（THI）〉72的时间连续达到15d,冬季组牛舍THI〈72的时间连续达到15d时,颈静脉采血15mL制备血清,检测血清中内毒素、超氧化物歧化酶（SOD）、谷胱甘肽过氧化物酶（GSH-Px）的活性,以及丙二醛（MDA）的含量。结果表明：夏季热应激可导致奶牛血清内毒素、MDA含量极显著升高,SOD和GSH-Px活性极显著和显著（P〈0.05）下降。     

热应激对奶牛机体的影响及防控措施

随着全球气候变暖,以及奶牛产奶性能的提高,热应激成了影响我国奶牛生产的一大难题,尤其在南方高温高湿的夏季,奶牛极易发生热应激。本文就热应激对奶牛产奶量、乳品质和繁殖性能的影响等方面进行了综述,并提出了一些预防奶牛热应激的措施,以期指导生产实践,提高奶牛养殖的经济效益。     

Sustained heat stress elevated corneal and body surface temperatures and altered circulating leukocytes and metabolic indicators in wether lambs supplemented with ractopamine or zilpaterol

Understanding how β adrenergic agonists influence the physiology of heat stress could lead to mitigation options. We sought to investigate body surface temperatures in feedlot wethers supplemented with ractopamine or zilpaterol and exposed to heat stress for 18 d. Corneal and skin temperatures were assessed via infrared thermography at 1- and 2-m distances. Rectal temperatures and circulating leukocytes, metabolites, and electrolytes were also measured. Heat stress increased (P < 0.05) rectal temperatures in unsupplemented and zilpaterol-supplemented lambs but not in ractopamine-supplemented lambs. Heat stress also increased (P < 0.05) surface temperatures of the cornea, nose, ear, and back, regardless of supplement. Observations were comparable between thermography performed at 1 and 2 m, and higher emissivity settings generally produced less variation. Heat stress tended to increase (P = 0.08) blood monocytes in unsupplemented but not ractopamine- or zilpaterol-supplemented lambs. Granulocytes were increased (P < 0.05) by heat stress in ractopamine-supplemented lambs but decreased (P < 0.05) in zilpaterol-supplemented lambs. Blood glucose, triglycerides, and cholesterol did not differ among groups, and blood lactate was reduced (P < 0.05) by heat stress in zilpaterol-supplemented lambs only. Blood Na⁺ was reduced (P < 0.05) and Ca²⁺ increased (P < 0.05) by heat stress, regardless of supplement. These findings indicate that β1- and β2-adrenergic agonists differentially relieve some but not all heat stress-induced changes in stress indicators. Moreover, corneal and skin surface temperatures measured by infrared thermography reasonably identified body temperature changes at a distance of 2 m.     

Zinc alleviates the heat stress of primary cultured hepatocytes of broiler embryos via enhancing the antioxidant ability and attenuating the heat shock responses

Zinc (Zn) has been shown to attenuate the adverse effects of heat stress on broilers, but the mechanisms involving this process remain unclear. We aimed to investigate possible protective mechanisms of Zn on primary cultured hepatocytes of broiler embryos subjected to heat stress. Three experiments were conducted. In Exp. 1, hepatocytes were treated with 0, 50, 100, 200, or 400 μmol/L added Zn as inorganic Zn sulfate (iZn) for 12, 24 or 48 h. In Exp. 2, cells were exposed to 40 °C (a normal temperature [NT]) and 44 °C (a high temperature [HT]) for 1, 2, 4, 6, or 8 h. In Exp. 3, cells were preincubated with 0 or 50 μmol/L Zn as iZn or organic Zn lysine chelate (oZn) for 8 h under NT, and then incubated with the same Zn treatments under NT or HT for 4 or 6 h. The biomarkers of antioxidative status and heat stress in cells were measured. The results in Exp. 1 indicated that 50 μmol/L Zn and 12 h incubation were the optimal conditions for increasing antioxidant ability of hepatocytes. In Exp. 2, the 4 or 6 h incubation under HT was effective in inducing heat shock responses of hepatocytes. In Exp. 3, HT elevated (P < 0.01) malondialdehyde content and expressions of heat shock protein 70 (HSP70) mRNA and protein, as well as HSP90 mRNA. However, Zn supplementation increased (P < 0.05) copper zinc superoxide dismutase (CuZnSOD) activity and metallothionein mRNA expression, and effectively decreased (P < 0.05) the expressions of HSP70 mRNA and protein, as well as HSP90 mRNA. Furthermore, oZn was more effective (P < 0.05) than iZn in enhancing CuZnSOD activity of hepatocytes under HT. It was concluded that Zn (especially oZn) could alleviate heat stress of broiler hepatocytes via enhancing their antioxidant ability and attenuating heat shock responses.     

水分逆境对发草脯氨酸及其代谢途径的影响

本研究以发草为研究对象,通过盆栽模拟水分胁迫,研究干旱、水涝胁迫下发草地上部分及根系中脯氨酸(Pro)积累状况及其代谢途径中底物、中间产物和关键酶的变化.结果显示:1)干旱胁迫和水涝胁迫均使发草Pro含量显著升高(P<0.05),相同的水分处理下发草地上部分及根系中Pro含量相差不大.2)干旱胁迫和水涝胁迫下,发草地上...     

Cooling and feeding strategies to reduce heat load of grain-fed beef cattle in intensive housing

Six Murray Grey × Hereford yearling steers were used to determine the effect of two cooling treatments (ENV) (day cooled (0600–1400) or night cooled (1400–2200), and two dietary treatments (DIET) – control (CON) no added fat or added fat (FAT) – on rectal temperature, respiration rate and dry matter intake (DMI). Cattle were exposed to 2 d of thermoneutral conditions followed by four hot days in a controlled climate facility. This was replicated 6 times. Steers were given a 10 d rest in outside pens between each replication. Sprinklers (2.84 L min^− 1; 5 min on, 20 min off) and fans (continuous; 2 m s^− 1) were used when ambient temperature (T_A) ≥ 28 °C. Rectal temperature (5 min intervals) and respiration rate (hourly) were measured for 12 × 24 h periods on hot days (2 per replication). Individual DMI over two time periods (PER) (period 1; 0600–1500, and period 2; 1500–0600) and daily metabolisable energy (ME) intakes were also recorded. Steers fed FAT had greater (P < 0.05) DMI then the CON steers during day cooling. However, there were no DIET or PER differences for DMI during night cooling. DMI of FAT and CON fed steers during night cooling was similar to the DMI of the FAT fed steers during day cooling. Overall DMI was greater during night cooling (DMI from both diets pooled). There were PER differences for DMI, with more (P < 0.05) feed consumed during period 2 irrespective of ENV or DIET. ME intake was 22.9% greater (P < 0.05) for the FAT fed steers during day cooling then for the CON fed steers. There were no DIET effects on ME intake during night cooling. DIET had no effect (P > 0.05) on respiration rate however differences were seen for rectal temperature. Mean rectal temperature for the FAT steers was lower (P < 0.05) than the mean of the CON steers, however there were no within ENV differences. Day cooled cattle had a higher (P < 0.05) respiration rates (71.8 breaths/min; bpm) than the night cooled steers (65.3 bpm). There were no differences for rectal temperature. However, day cooled steers had lower (P < 0.05) rectal temperature and respiration rate than the night cooled steers during the day — which corresponded with the day cooling period. Night cooling appears to be beneficial in lowering mean rectal temperature and respiration rate, and in maintaining DMI. There is no suggestion that feeding fat will replace the need for supplementary measures to alleviate heat exposure of confined cattle. However feeding fat may be worthwhile in maintenance DMI when combined with strategies involving day cooling.     

Alterations of endotoxin distribution across different biofluids and relevant inflammatory responses by supplementing L-theanine in dairy cows during heat stress

The present trial was performed to reveal the regulatory effects of L-theanine on the levels of lipopolysaccharide (LPS) endotoxin within different biofluids, as well as relevant inflammatory responses of dairy cattle under heat stress conditions. Thirty lactating Chinese Holstein dairy cattle (189 ± 47 d in milk, and 2 ± 1 parities) were allocated in a completely randomized design to each of 3 dietary treatments: the control (CON, 0 g/d per cow L-theanine), the low L-theanine dosage treatment (LL, 16 g/d per cow L-theanine), and the high L-theanine dosage treatment (HL, 32 g/d per cow L-theanine). This trial consisted of 38 d (7 d for adaption and 31 d for data and sample collection), and sample collection for rumen liquid, blood plasma or serum, and milk were conducted on the d 27 and 38, respectively. Dairy cattle were constantly exposed to environmental heat stress during this experiment according to the recorded temperature-humidity index (THI). In the LL treatment, LPS concentration in rumen liquid was higher (P < 0.05), whilst LPS densities in plasma and milk were lower (P < 0.05) than those of the CON. Supplementing L-theanine at 2 dosages both significantly lowered (P < 0.05) the level of interleukin (IL)-1β in the serum. Results of the present study suggested that L-theanine could be a promising additive in reducing the detrimental effects of heat stress on dairy cows, and L-theanine supplementation at 16 g/d per cow is preferred because it reduced the LPS translocation into the peripheral blood and LPS accumulation in the milk, as well as mitigated LPS-induced inflammatory reactions in dairy cows during heat stress. Further studies are necessitated to investigate the underlying mechanisms of L-theanine in LPS alteration and inflammation alleviation.     

减缓肉牛热应激最新研究进展

为了减少肉牛热应激对肉牛生产性能、生理生化指标、抗氧化能力、妊娠牛激素及免疫功能等方面产生的影响,笔者检索了国内外相关文献,从品种、中草药方剂和饲料添加剂、环境控制三方面归纳在肉牛抗应激能力的最新研究进展,为肉牛健康高效养殖提供参考。     

浅谈热应激对奶牛的影响及调控措施

在炎热的夏季,热应激会导致奶牛生理机能发生紊乱,采食量下降,生产性能降低,甚至导致奶牛发病,严重者造成死亡。预防夏季奶牛热应激的发生,为奶牛创造适宜的、良好的饲养环境,可使奶牛安全、顺利地度过炎热的夏季,防止热应激造成不必要的损失。笔者等从奶牛热应激发生的原因与生理机制入手,综合论述热应激对奶牛的危害和预防热应激的调控措施。     

Dietary nano chromium picolinate can ameliorate some of the impacts of heat stress in cross-bred sheep

Two studies were conducted to evaluate the effect of nano chromium picolinate (nCrPic) during heat stress (HS) in sheep. In the initial study, 36 Merino × Poll cross-bred sheep were individually penned and allocated to 3 dietary treatments (0, 400 and 800 μg/kg nCrPic) for 8 wk. Body composition was determined at the beginning and end of the experiment using dual energy X-ray absorptiometry. The sheep remained in their dietary groups but were then placed in metabolic cages and randomly allocated within the dietary group to differing ambient temperature regimes, i.e., thermo-neutral (TN) (n = 18) and HS (n = 18), for 3 wk. Dietary nCrPic had no effect on growth performance and body composition during the initial study conducted under TN conditions. Heat stress decreased average daily feed intake (ADFI) (P = 0.002) whereas sheep under HS had reduced average daily gain (ADG) and indeed lost weight (P < 0.001). Dietary nCrPic increased both ADFI (P = 0.041) and ADG (P = 0.049) under both TH and HS conditions such that the performance of sheep receiving supplemental nCrPic and exposed to HS was similar to that of control sheep maintained under TN conditions. Heat stress increased rectal temperature (P < 0.001) and respiration rate (P < 0.001), particularly during the hottest parts of the day as indicated by interactions (P < 0.001) between time of day and thermal treatment. Rectal temperature was lower in sheep fed nCrPic (P = 0.050), particularly under peak HS conditions during the afternoon as indicated by the interactions between dietary nCrPic and time of day (P < 0.001) and dietary nCrPic, thermal treatment and time of day (P = 0.010). Similarly, respiration rate was lower in sheep fed nCrPic under peak HS conditions during the afternoon as indicated by the interactions between dietary nCrPic and thermal treatment (P < 0.001) and dietary nCrPic and time of day (P = 0.030). In conclusion, dietary nCrPic can partially ameliorate the negative effects of HS as indicated by the maintenance of ADFI and decreased physiological responses, such as elevations in rectal temperature and respiration rate.     

Perspectives on improvement of reproduction in cattle during heat stress in a future Japan

Heat stress (HS) causes hyperthermia, and at its most severe form, can lead to death. More commonly, HS reduces feed intake, milk yield, growth rate and reproductive function in many mammals and birds, including the important cattle breeds in Japan. Rectal temperatures greater than 39.0°C and respiration rates greater than 60/min indicate cows are undergoing HS sufficient to affect milk yield and fertility. HS compromises oocyte quality and embryonic development, reduces expression of estrus and changes secretion of several reproductive hormones. One of the most effective ways to reduce the magnitude of HS is embryo transfer, which bypasses the inhibitory effects of HS on the oocyte and early embryo. It may also be possible to select for genetic resistance to HS. Cooling can also improve reproductive performance in cows and heifers, and probably, the most effective cooling systems currently in use are those that couple evaporative cooling with tunnel ventilation or cross ventilation. Its effect on improving reproductive performance in Japan remains to be evaluated.     

Effect of daidzein on production performance and serum antioxidative function in late lactation cows under heat stress

Forty Chinese Holstein cows were randomly divided into 4 groups according to birth, milk yield, and close lactation. The cows in 4 groups were fed with basic diet, basic diet plus 200, 300, 400 mg/day daidzein, respectively; and the experimental period was 60 days. The milk yield in all cows was monitored everyday and the quality of milk was examined regularly. Blood was collected on days 0, 10, 30, 60 of experiment to isolate serum, and the activities of superoxide dismutase (SOD), glutathione peroxidase (GSH-Px) and catalase (CAT), malondialdehyde (MDA) content, and total antioxidant capacity (TAC) in the serum were measured. Results showed that the milk yield and the percentage of milk fat were significantly higher after feeding daidzein (P<0.01), and the percentage of milk protein was significantly elevated on day 60 in three daidzein groups (P<0.05 or P<0.01), especially in 400 mg/day daidzein group (P<0.01). Compared with the control group (basic diet), the TAC and activities of SOD, GSH-Px and CAT were markedly elevated in three daidzein groups (P<0.05 or P<0.01), while the MDA content was significantly reduced in three daidzein groups (P<0.05 or P<0.01). All data suggest that daidzein has positive effects on increasing the production performance and antioxidative activity in late lactation cows, and enhancing the body adaptability and resistance to heat stress.     

Effects of heat stress on the endometrial epidermal growth factor profile and fertility in dairy cows

The endometrial epidermal growth factor (EGF) profile is an indicator of uterine function and fertility in cattle. The present study aimed to investigate the effects of heat stress on the endometrial EGF profile and fertility in lactating Holstein cows. The endometrial EGF profiles of 365 cows in the Hokkaido and Kyushu regions were examined between June and September (heat stress period, n = 211) and between October and January (control period, n = 154). EGF profiles were investigated using uterine endometrial tissues obtained by biopsy 3 days after estrus (Day 3). The proportion of cows with an altered EGF profile was higher between June and September than between October and January (41.2 vs. 16.2%, P < 0.05). The effects of rectal temperature on Days 0 and 3 on the endometrial EGF profile were also assessed in cows (n = 79) between June and September in the Kyushu region. A single embryo was transferred to cow on Day 7 to evaluate fertility (n = 67). Regardless of the rectal temperature on Day 3, the proportion of cows with an altered EGF profile was higher (64.1 vs. 30.0%, P < 0.05) and the pregnancy rate after embryo transfer (ET) was lower (26.7 vs. 51.4%, P < 0.05) in cows with a rectal temperature ≥ 39.5°C on Day 0 than in cows with a rectal temperature < 39.5°C on Day 0. The present results indicate that alterations in the endometrial EGF profile induced by an elevated body temperature on Day 0 contributed to reductions in fertility in lactating dairy cows during the heat stress period.     

Ultrasonographic findings of the corpus luteum and the gravid uterus during heat stress in dairy cattle

The objectives of this study were to assess alterations in, echogenic appearance, size and blood flow in the corpus luteum, the placentomes and the blood flow in umbilical and uterine arteries that heat stress can cause in cooled pregnant dairy cows. Pregnant cows were allocated in two groups and the gravid uteri, along with the ipsilateral corpora lutea were examined during the winter (group W, n = 9) or the summer (group S, n = 10). The grey-scale ultrasound and colour flow imaging of the corpus luteum and placentome were performed. In addition, the umbilical and uterine artery diameters and haemodynamic parameters in the vessels were calculated. At the time of ultrasonographic examination, cortisol concentrations were higher, and progesterone levels tended to be lower in group S compared to group W. The grey-scale ultrasound evaluation of corpora lutea and placentomes was lower in group S compared to group W. The diameter of umbilical artery and the blood volume in the vessel were less in group S than in group W. We infer that heat stress affects foetal blood supply and possibly the structure of placentomes and corpora lutea, but it differently affects the blood flow characteristics in the umbilical and uterine arteries.     

Heat-tolerant versus heat-sensitive Bos taurus cattle: influence of air temperature and breed on the metabolic response to a provocative immune challenge

The response of the immune and stress systems have been assessed in response to a lipopolysaccharide (LPS) challenge, yet the role of metabolism in mediating energy requirements during the acute phase response has not been sufficiently studied. This study tested heat-tolerant (Romosinuano [RO]) and heat-sensitive (Angus [ANG]) Bos taurus breeds at different ambient temperatures (T_a) to determine differential metabolic responses to LPS challenge. Twenty-one heifers (ANG: n = 11, 306 ± 26 kg BW; RO: n = 10, 313 ± 32 kg BW) were housed in stanchions in 4 temperature-controlled chambers. Initially, T_a in all 4 chambers was cycling at thermoneutrality (TN; 18.5°C–23.5°C) for a 1-wk adjustment period, followed by an increase in 2 chambers to cycling heat stress (HS; 24°C–38°C) for 2 wk. Five ANG and 5 RO heifers were housed at TN, whereas 6 ANG and 5 RO heifers were housed at HS. On day 19, heifers were fitted with jugular catheters. On day 20, heifers were challenged with LPS (0.5 μg/kg BW; 0 h), and blood samples were collected from −2 to 8 h and at 24 h relative to LPS challenge. Serum was analyzed for glucose, insulin, and NEFA concentrations. In addition, feed intake was measured 3 d before and on the day of the challenge. Feed intake decreased over time (P < 0.001) and was decreased in heifers housed at HS compared with heifers housed at TN (P = 0.013). Glucose concentrations before LPS challenge were greater in RO (P = 0.01) than in ANG heifers and greater in TN-housed heifers (P = 0.02) than in HS heifers. Glucose after LPS challenge initially increased before decreasing below baseline concentrations (P < 0.01) in all heifers. In addition, there was a breed by T_a interaction (P < 0.004), such that HS decreased glucose concentrations in ANG heifers compared with ANG heifers housed at TN (P < 0.001), whereas HS did not affect glucose concentrations after LPS challenge in RO heifers (P = 0.941). Nonesterified fatty acid concentrations before LPS challenge were not affected by breed (P = 0.37) or T_a (P = 0.60). Although NEFA concentration after LPS challenge was unaffected by T_a (P = 0.78), there tended to be a breed by T_a interaction (P = 0.07) such that, when housed at HS, RO heifers had greater serum NEFA concentrations after LPS challenge than ANG heifers (P = 0.009). Insulin concentration before LPS challenge was greater in RO heifers than in ANG heifers (P < 0.01). Insulin after LPS challenge increased (P < 0.01), with RO heifers producing a greater insulin response than ANG heifers (P < 0.01). These data suggest that HS decreases the metabolic response of heat-sensitive ANG heifers in response to LPS challenge, thus providing physiological evidence that may explain differences observed in the acute phase response between heat-sensitive ANG and heat-tolerant RO cattle breeds.     

Effect of cooling Holstein cows during the dry period on postpartum performance under heat stress conditions

Two experiments were completed to determine whether cooling Holstein cows during their 60-day prepartum period improved their immediate physiological status as well as subsequent postpartum performance. In Experiment 1, 38 cows were divided into two pens that were not cooled, or where the cows were moved twice daily to be cooled by soaking until their body was completely wet. Prepartum respiration rate (RR) and rectal temperatures (RT) did not differ between groups, indicating that the cooling system was largely ineffective, which was consistent with differences that only numerically favored the treated group in postpartum productive (milk production, milk fat content and related response variables), and reproductive (services per conception and days open) performance. In Experiment 2, 52 Holstein cows were used over 3 years (n = 24 in year one; n = 12 in year two; n = 16 in year three) and cows were housed in pens either not cooled or cooled with water spray and fans. Cooled cows had lower RR and RT prepartum at 14:00 and 18:00 h vs. non-cooled cows, indicating that the cooling system was effective, and this was consistent with improved productive (milk production, milk fat content and related response variables), and reproductive (services per conception and days open) performance postpartum. In addition, there was a trend (P = 0.10) to higher birth weights of calves from cooled mothers (which was consistent with a numeric difference in Experiment 1). Use of effective cooling systems under hot and dry conditions during the dry period can improve postpartum productive and reproductive performance of Holstein cows.     

Effects of chronic heat stress on the reproductive capacity of male Rex rabbits

The effects of chronic heat stress on the reproductive system of rabbits have not been thoroughly examined. Therefore, we investigated the effects of heat stress on the reproductive performance of male Rex rabbits and documented the recovery process after stress withdrawal. Thirty age-matched, male Rex rabbits were placed into artificial climate chambers and randomly divided into three groups: control, heat stress, and recovery. Our results indicate that both libido of rabbit and sperm density were decreased significantly during the 9 weeks exposure to heat stress. Semen volume was mildly affected. Histomorphological and TUNEL assay results showed that chronic heat treatment adversely affected microscopic structure of the testes, and elevated the apoptosis of germ cells in the seminiferous tubules distinctly. However, these adverse effects induced by heat were transient as all measured parameters returned to control levels following the recovery period.