Responses of bovine lymphocytes to heat shock as modified by breed and antioxidant status

Differences in body temperature, cell viability, and HSP-70 concentrations between Pelibuey and Suffolk sheep under heat stress

Pelibuey and Suffolk sheep were compared as to their capacity to regulate body temperature under environmental hyperthermia by measuring their differences in cellular response to heat stress (HS). In a first experiment, seven Pelibuey and seven Suffolk ewes were kept in a climatic chamber for 6 h daily during 10 days (temperatures within the 18 to 39.5 °C range). As chamber temperature rose, sheep rectal temperature increased in both groups, but to a lesser extent in Pelibuey (0.3 °C) than in Suffolk sheep (0.7 °C) (P < 0.05). In a second experiment, cellular viability was assessed using cultured blood mononuclear cells from 15 Pelibuey and 15 Suffolk sheep. They were incubated at 37 °C for 24 h (control) or 43 °C for 6 h followed by 18 h at 37 °C (HS). In a third experiment, another blood mononuclear cells culture from eight Pelibuey and eight Suffolk sheep was kept at 37 °C for 15 h; these were subsequently cultured for 6 h at 37 °C (controls) or 43 °C (HS). Next, HSP-70 concentration was determined. HS reduced the percentage of viable cells to a greater extent in Suffolk [37 °C (73.7 %) vs. 43 °C (61.9 %); P < 0.05] than in Pelibuey sheep [37 °C (74.9 %) vs. 43 °C (66.7 %); P > 0.05]. HS significantly increased HSP-70 average concentrations for both breeds at 43 °C. A significant effect was observed for the breed by temperature interaction (P < 0.05) caused by a greater difference between Pelibuey and Suffolk at 43 °C (2.85 vs. 0.53 ng/mL, respectively; P < 0.05) than at 37 °C (0.05 vs. 0.03 ng/mL, respectively; P > 0.05). In conclusion, Pelibuey sheep show more effective body temperature regulation under conditions of environmental hyperthermia. Also, cell viability after HS was higher in Pelibuey than in Suffolk, an effect that could be mediated by an HSP-70-related mechanism.

How selection for reproduction or foundation for longevity could have affected blood lymphocyte populations of rabbit does under conventional and heat stress conditions

The present work characterises how selection for reproduction (by comparing two generations - 16th and 36th - of the V line selected for litter size at weaning) or foundation for reproductive longevity (the LP line) can affect the blood lymphocytes populations of reproductive rabbit does under normal [conventional housing, average daily minimum and maximum temperatures of 14°C and 20°C, respectively] and heat stress conditions [climatic chamber, 25°C and 36°C] from the first to the second parturition. Housing under heat stress conditions significantly reduced the B lymphocytes counts in female rabbits (-34 × 10(6)/L; P<0.05). The highest lymphocytes population value in blood (total, T CD5(+), CD4(+) and CD8(+)) was noted at the first parturition, while the B lymphocytes count was significantly lower at the second parturition (-61 × 10(6)/L; P<0.05). Selection for litter size at weaning (V females) reduced the average counts of total and B lymphocytes in blood (-502 and -60 × 10(6)/L, respectively; P<0.01), mainly because these populations in V36 females continuously lowered from the first to the second parturition under normal housing conditions. Thus, more selected females (V36) at the second parturition showed significantly lower counts in blood for total, T CD5(+) and CD25(+) lymphocytes (-1303, -446 and -33 × 10(6)/L, respectively; P<0.05). The main differences in blood counts between V36 and V16 females disappeared when housed under heat stress conditions, except for T CD5(+) and CD25(+), which significantly increased (T CD5(+): +428 × 10(6)/L; CD25(+): +41 × 10(6)/L; P<0.01) in the V16 vs. V36 females on day 10 post-partum. Under normal conditions, no differences between LP and V36 females were found for most lymphocyte populations; only higher counts were noted in CD25(+) (+20 × 10(6)/L; P<0.05) for LP females. However, the lymphocytes counts [especially total (+1327 × 10(6)/L; P<0.01) and T CD5(+) (+376 × 10(6)/L; P<0.10)] of LP females increased under heat vs. normal conditions when lymphocytes populations presented the lowest values (second parturition), while V36 females' counts remained invariable. Positive correlations were found between feed intake (r=+0.51; P<0.001) and females' perirenal fat thickness (r=+0.40; P<0.001) with B lymphocytes counts in the blood of primiparous rabbit females in the week 2 of lactation. These results indicate that selection for litter size at weaning might diminish their immune system's response and adaptation capacity, while the foundation for reproductive longevity criteria leads to more robust rabbit females as they present greater modulation under heat stress conditions when the immune system is affected.

Characterization and comparison of the leukocyte transcriptomes of three cattle breeds

In this study, mRNA-Seq was used to characterize and compare the leukocyte transcriptomes from two taurine breeds (Holstein and Jersey), and one indicine breed (Cholistani). At the genomic level, we identified breed-specific base changes in protein coding regions. Among 7,793,425 coding bases, only 165 differed between Holstein and Jersey, and 3,383 (0.04%) differed between Holstein and Cholistani, 817 (25%) of which resulted in amino acid changes in 627 genes. At the transcriptional level, we assembled transcripts and estimated their abundances including those from more than 3,000 unannotated intergeneic regions. Differential gene expression analysis showed a high similarity between Holstein and Jersey, and a much greater difference between the taurine breeds and the indicine breed. We identified gene ontology pathways that were systematically altered, including the electron transport chain and immune response pathways that may contribute to different levels of heat tolerance and disease resistance in taurine and indicine breeds. At the post-transcriptional level, sequencing mRNA allowed us to identify a number of genes undergoing differential alternative splicing among different breeds. This study provided a high-resolution survey of the variation between bovine transcriptomes at different levels and may provide important biological insights into the phenotypic differentiation among cattle breeds.

Taguchi approach for anti-heat stress prescription compatibility in mice spleen lymphocytes in vitro

Heat stress (HS) may induce immunosuppression as well as inhibit the proliferation of lymphocytes. This study evaluated the effects on immune function of our prescription on splenic lymphocytes under HS as well as its compatibility. The effects of four herbal extracts from Agastache rugosa, Atractylodes lancea, Cortex Phellodendri, and Gypsum Fibrosum on heat treated splenic lymphocytes were investigated and the compatibility of the prescription was also explored by using the Taguchi method. This study revealed changes in proliferation by traditional Chinese medicines of splenic lymphocytes after HS. Proliferation in the HS group was significantly lower than the control group. Under HS, the effects of higher concentrations of Agastache rugosa (100 and 200 μg/mL), Atractylodes lancea (100 and 200 μg/mL), Cortex Phellodendri (50 and 100 μg/mL) and Gypsum Fibrosum (100 and 200 μg/mL) caused a significant increase on ConA/LPS-induced proliferation of lymphocytes than lower concentrations. We, therefore, conclude that the prescription of traditional Chinese medicines may recover splenic lymphocytes from the immunosuppression induced by HS. The Taguchi design, which allows rapid and high efficiency for the selection of the best conditions for our prescription on HS-treated splenic lymphocytes, demonstrated that Agastache rugosa (200 μg/mL), Atractylodes lancea (200 μg/mL), Cortex Phellodendri (100 μg/mL) and Gypsum Fibrosum (100 μg/mL) were the optimal conditions for the prescription. The validation experiment confirmed that our composition in optimum extraction conditions enhanced effects on ConA or LPS-stimulated lymphocytes under HS. The results showed that the Taguchi optimization approach is a suitable method for optimization of the composition of prescription.

In Vitro Immune Competence of Buffaloes (Bubalus bubalis) of Different Production Potential: Effect of Heat Stress and Cortisol

Twelve healthy lactating Murrah buffaloes of similar parity (3rd) between 90 and 120 days of lactation, selected from the herd of National Dairy Research Institute (Karnal, India) and maintained at managemental practices as followed at the Institute they were included in this experiment. The animals were divided into two groups based on their production level in previous lactation. The average milk production level of group 1 and II was 9.3 and 6 lit/day, respectively. Blood was collected from these buffaloes on three occasions 10 days apart. The lymphocytes were separated and cultured in RPMI 1640 medium with PHA-P for 24 h at 37°C in a humidified CO(2) incubator (95% air and 5%  CO(2)). The lymphocyte responsiveness was also evaluated in response to the in vivo heat stress and in vitro cortisol. Mitogen-induced stimulation index was not affected by production level (P < .01). Stimulation index was significantly reduced (P < .01) in both the groups when cortisol was added at 2.0 ng level in the culture. However, in heat-stressed buffaloes stimulation index did not vary despite increasing levels of cortisol, thus indicating that lymphocyte may become cortisol resistant during periods of acute heat stress. The results showed that lymphocyte proliferation response can be effectively used to study buffalo cell-mediated immunity in vitro.

Effect of heat challenge on peripheral blood mononuclear cell viability: comparison of a tropical and temperate pig breed

We evaluated the effect of heat challenge on cell viability, concanavalin A-induced proliferation and heat shock protein (HSPs) mRNA expression in peripheral mononuclear blood cells (PBMC) isolated from Creole (CR) and Large White (LW) pigs. The PBMCs were cultured for 9 h at 37 °C before being subjected to heat challenge: (1) at 42 °C or 45 °C for 2, 4, 6 and 9 h to monitor cell viability;(2) at 45 °C for 2 and 9 h followed by stimulation for 24 h at 37 °C with concanavalin A to evaluate mitogen-induced proliferation; and (3) at 45 °C for 3, 6 and 9 h to measure induction of HSP70.2 and HSP90 mRNA. Cell viability was affected by breed and temperature (P < 0.01), and the viability decrease caused by heat challenge was greater for LW than CR pigs. For mitogen-stimulated PBMCs, incubation at 45 °C reduced lymphoblastogenesis equally in both breeds (P < 0.01). Although heat challenge for 3 and 6 h at 45°C induced expression of HSP70.2 and HSP90 mRNA, no breed difference was observed. In conclusion, differences in heat resistance between these two breeds at the whole organism level are reflected at the cellular level. Neither HSP70.2 nor HSP90 mRNA expression levels explain this effect.

Heat stress abatement during the dry period influences prolactin signaling in lymphocytes

Heat stress perturbs prolactin (PRL) release and affects dairy cow lactational performance and immune cell function. We hypothesized that greater PRL concentration in plasma of heat-stressed cows relative to cooled cows would decrease expression of prolactin receptor (PRL-R) mRNA and increase mRNA expression of suppressors of cytokine signaling (SOCS) in lymphocytes, altering their cytokine production. To test this hypothesis, multiparous Holstein cows were dried off 46 d before their expected calving date and assigned randomly to heat stress (HT; n=9) or cooling (CL; n=7) during the entire dry period. A second study was conducted the following year with an additional 21 cows (12 HT; 9 CL). Lymphocytes were isolated from cows at -46, -20, +2, and +20 d relative to expected calving date and mRNA expression of PRL-R, SOCS-1, SOCS-2, SOCS-3, cytokine-inducible SH2-containing protein (CIS), and heat shock protein 70 KDa A5 (HSPA5), and housekeeping genes hydroxymethylbilane synthase (HMBS), ATP synthase, H+ transporting mitochondrial F1 complex, beta subunit (ATP5B), and ribosomal protein S9 (RPS9) was analyzed by quantitative real-time reverse transcriptase polymerase chain reaction (RT-PCR). Cows exposed to HT had greater PRL concentration in plasma compared with CL cows. Measurement of lymphocyte proliferation indicated that lymphocytes of CL cows proliferated more than those from HT cows and exressed more PRL-R mRNA and less SOCS-1 and SOCS-3 mRNA relative to HT cows. Further, lymphocytes from CL cows produced more tumor necrosis factor-alpha (TNF-alpha) than those from HT cows. These results suggest that changes in PRL-signaling pathway genes during heat stress are associated with differential cytokine secretion by lymphocytes and may regulate lymphocyte proliferation in dairy cows.

Heat stress elicits different responses in peripheral blood mononuclear cells from Brown Swiss and Holstein cows

This study was undertaken to assess whether peripheral blood mononuclear cells (PBMC) isolated from Brown Swiss (Br) and Holstein (Ho) cows and stimulated with concanavalin A differ in response to chronic exposure to incubation temperatures simulating conditions of hyperthermia. Five multiparous Br and 5 Ho cows were utilized as blood donors. Peripheral blood mononuclear cells were subjected for 65 h to each of 5 treatments (T). Cells were exposed to 39 degrees C continuously (T39) and three 13-h cycles at 40 (T40), 41 (T41), 42 (T42) or 43 degrees C (T43), respectively, which were interspersed with two 13-h cycles at 39 degrees C. Treatment T39 was adopted to mimic normothermia; T40, T41, T42, and T43 mimicked conditions of more severe hyperthermia alternating with normothermia. Measures evaluated at the end of the incubation period were proliferative response (DNA synthesis), intracellular reactive oxygen species (ROS) concentrations, and mRNA abundance of the 72-kDa heat-shock protein (Hsp72). In Br cows, DNA synthesis began to decline when PBMC were repeatedly exposed to 41 degrees C (-22%), whereas DNA synthesis in cells isolated from Ho cows did not begin to decline until 42 degrees C (-40%). Furthermore, under T41 and T42, DNA synthesis from Br cows was lower than in Ho(-24 and -54%, respectively). In both breeds, increased incubation temperatures caused a reduction of intracellular ROS (from -39.6 and -69.7%). Increase in incubation temperatures enhanced Hsp72 mRNA levels only in PBMC isolated from Br cows. The Hsp72 mRNA in Br cows increased significantly under T41 and T43 compared with T39. In both breeds, DNA synthesis was positively and negatively correlated with intracellular ROS and Hsp72 mRNA abundance, respectively (r = 0.85 and r = -0.70, respectively). Results indicated that PBMC from Br cows are less tolerant to chronic heat exposure than those from Ho cows, and that the lower tolerance is associated with higher expression of Hsp72, suggesting that the same level of hyperthermia may be associated with a differential decline of immune function in the 2 breeds.

Development of a method of measuring cellular stress in cattle and sheep

In the current studies, flow cytometric methods were used to demonstrate that heat shock protein (hsp) 70 is constitutively expressed in ovine and bovine leukocytes but that the level of expression varies considerably between different leukocyte types and between species. We also show that expression of hsp70 is upregulated in response to an in vitro heat shock treatment. The optimal temperature for heat shock of leukocytes from sheep and cattle is 43.5 degrees C. In sheep and cattle, the relative susceptibility of leukocyte type to upregulation of hsp70 expression, as assayed as percent positive cells, by in vitro heat shock was cell type specific. Best results were obtained from fresh samples; after storage at room temperature for 24h upregulation was highly variable between animals and less than in fresh samples. These studies demonstrate that evaluation of leukocyte hsp70 expression by flow cytometry is a robust, reproducible method for use in the evaluation of cellular stress responses in cattle and sheep. The application of the methods described may be a valuable tool in assessing in vivo stress responses in livestock species.

To be or not to be—Determinants of embryonic survival following heat shock

Elevated temperature can reduce developmental competence of the preimplantation embryo. Whether an embryo survives elevated temperature depends on its genotype, stage of development, exposure to regulatory molecules and redox status. Following fertilization, the embryo is very sensitive to heat shock. By Days 4-5 after insemination, however, the embryo has acquired increased resistance to elevated temperature. One system that may potentiate embryonic survival at later stages of embryonic development is the apoptosis response-inhibition of apoptosis responses at Day 4 exacerbated effects of heat shock on development. Embryo responses to heat shock at Days 4-5 also depend upon genotype because Bos indicus embryos are more resistant than embryos from non-adapted B. taurus. Some experiments (although not all) indicate that survival following heat shock can be increased by reducing oxygen tension, suggesting involvement of reactive oxygen species or hypoxia-induced factors. Embryonic responses to heat shock are also affected by regulatory molecules that act to modify cellular physiology and improve cell survival. The best characterized of these is insulin-like growth factor-1 (IGF-1). Actions of IGF-1 to allow development following heat shock are independent of its anti-apoptotic actions because inhibition of the phosphatidylinositol-3 kinase pathway through which IGF-1 blocks apoptosis does not prevent thermoprotective effects of IGF-1 on development. Identification of specific determinants of embryonic survival creates the opportunity for new strategies to improve pregnancy rates in animals exposed to heat stress. Many environmental perturbations activate similar cellular responses. Therefore, molecular and cellular systems that improve embryonic survival to heat shock may confer protection from other embryotoxic conditions.

Lymphocyte functions in dairy cows in hot environment

This study was carried out to ascertain the effects of intense high environmental temperatures (HET) on lymphocyte functions in periparturient dairy cows. The study was undertaken from the beginning of March through the end of July 2003 in a commercial dairy unit located approximately 40 km north of Rome. Thirty-four Holstein cows were utilised in the study. Twenty-two of these cows gave birth in spring (SP cows), from 28 March to 30 April. The remaining 12 cows gave birth in summer (SU cows), between 15 June and 2 July. The two groups of cows were balanced for parity and were fed the same rations. Blood samples were taken 4, 3, 2 and 1 week before calving, and 1, 2 and 4 weeks after calving, in order to evaluate peripheral blood mononuclear cell (PBMC) function in vitro, and to determine plasma cortisol concentrations. After isolation, the PBMC were stimulated with mitogens and their response in terms of DNA synthesis and IgM secretion was measured. During spring, either the day (9-20 h) or the night (21-8 h) temperature humidity index (THI) was below the upper critical THI (72) established for dairy cows. During summer, the mean daily THI values were 79.5+/-2.9 during the day and 70.1+/-4.7 during the night. Furthermore, during summer, three heat waves (a period of at least 3 consecutive days during which there were less than 10 recovery hours) occurred. Recovery hours were intended hours with a THI below 72. The first heat wave lasted 5 days, the second 6 days, and the third 15 days. Compared to the SP cows, over the entire periparturient period the extent of DNA synthesis and IgM secretion levels were lower (P ranging from <0.01 to 0.0001) and higher (P<0.01) respectively, in the SU cows. Before calving, the SU cows also presented higher (P<0.01) concentrations of plasma cortisol compared to the SP cows. This study indicates that the effects of HET on the immune response depend on the specific immune function under consideration, and that neuroendocrinal changes due to HET may play a role in the perturbation of immune functions.

Physiological and cellular adaptations of zebu cattle to thermal stress

During their separate evolution from Bos taurus, zebu cattle (Bos indicus) have acquired genes that confer thermotolerance at the physiological and cellular levels. Cattle from zebu breeds are better able to regulate body temperature in response to heat stress than are cattle from a variety of B. taurus breeds of European origin. Moreover, exposure to elevated temperature has less deleterious effects on cells from zebu cattle than on cells from European breeds. Superior ability for regulation of body temperature during heat stress is the result of lower metabolic rates as well as increased capacity for heat loss. As compared to European breeds, tissue resistance to heat flow from the body core to the skin is lower for zebu cattle while sweat glands are larger. Properties of the hair coat in zebu cattle enhance conductive and convective heat loss and reduce absorption of solar radiation. At the cellular level, genetic adaptations to resist deleterious effects of elevated temperature result in preimplantation embryos from zebu being less likely to be inhibited in development by elevated temperature than are embryos from European breeds. The zebu genotype has been utilized in crossbreeding systems to develop cattle for beef and dairy production systems in hot climates but success has been limited by other unfavorable genetic characteristics of these cattle. An alternative scheme is to incorporate specific thermotolerance genes from zebu cattle into European breeds while avoiding undesirable genes. Once specific genes responsible for thermotolerance in zebu have been identified or mapped, breeding strategies such as marker-assisted selection and transgenics can be applied to further the exploitation of the zebu genotype for cattle production systems.

Differences in heat tolerance between preimplantation embryos from Brahman, Romosinuano, and Angus breeds

Exposure to 41 degrees C reduces development of embryos of heat-sensitive breeds (Holstein and Angus) more than for embryos of the heat-tolerant Brahman breed. Here it was tested whether embryonic resistance to heat shock occurs for a thermotolerant breed of different genetic origin than the Brahman. In particular, the thermal sensitivity of in vitro produced embryos of the Romosinuano, a Bos taurus, Criollo-derived breed, was compared to that for in vitro produced Brahman and Angus embryos. At d 4 after insemination, embryos > or = 8 cells were randomly assigned to control (38.5 degrees C) or heat shock (41 degrees C for 6 h) treatments. Heat shock reduced the proportion of embryos that developed to the blastocyst stage on d 8 after insemination. At 38.5 degrees C, there were no significant differences in development between breeds. Among embryos exposed to 41 degrees C, however, development was lower for Angus embryos than for Brahman and Romosinuano embryos. Furthermore, an Angus vs. (Brahman + Romosinuano) x temperature interaction occurred because heat shock reduced development more in Angus (30.3 +/- 4.6% at 38.5 degrees C vs. 4.9 +/- 4.6% at 41 degrees C) than in Brahman (25.1 +/- 4.6% vs. 13.6 +/- 4.6%) and Romosinuano (28.3 +/- 4.1% vs. 17.5 +/- 4.1%). Results demonstrate that embryos from Brahman and Romosinuano breeds are more resistant to elevated temperature than embryos from Angus. Thus, the process of adaptation of Brahman and Romosinuano breeds to hot environments resulted in both cases in selection of genes controlling thermotolerance at the cellular level.

Differences between Brahman and Holstein cows in response to estrus synchronization, superovulation and resistance of embryos to heat shock

Embryos from Bos indicus are more resistant to elevated culture temperature (i.e. heat shock) than embryos from some Bos taurus breeds. The present experiment was designed to determine if Brahman embryos have greater resistance to heat shock than Holstein embryos at a stage in development before the embryonic genome was fully activated. A second objective was to test breed effects on estrus synchronization and superovulation responses. A total of 29 Brahman and 24 Holstein cows were subjected to estrus synchronization using gonadotropin releasing hormone (GnRH) and prostaglandin F2alpha (PGF2alpha) superovulation. Embryos were collected at 48 h and day 5 after insemination. There was a tendency for a lower proportion of Brahmans to be detected in standing estrus than Holsteins. There were no differences between breeds in the proportion of cows detected in estrus using both tailpaint and standing estrus as criteria or in interval from PGF2alpha to estrus. The degree of synchrony in estrus was greater for Brahmans. Superovulation response was generally similar between breeds. At 48 h after insemination, there was a tendency for a greater proportion of Brahman oocytes to have undergone cleavage. Uncleaved oocytes were cultured for an additional 24 h-at this time, cleavage rate was similar between breeds. When embryos reached the 2-4-cell stage, they were heat-shocked for 4.5 h at 41 degrees C. This heat shock reduced the proportion of embryos that developed to the blastocyst stage but there was no breedxtreatment interaction. At day 5 after insemination, the number of embryos recovered was too low to allow comparison of breed effects. In conclusion, genetic effects on cellular thermotolerance that make Brahman embryos more resistant to heat shock are not expressed at the 2-4-cell stage. There were few differences between Brahman and Holstein in response to estrus synchronization and superovulation. The fact that cleavage tended to occur earlier in Brahman than Holstein embryos suggests breed differences in timing of ovulation, fertilization or events leading to cleavage.

Inheritance of resistance of bovine preimplantation embryos to heat shock: relative importance of the maternal versus paternal contribution

Brahman preimplantation embryos are less affected by exposure to heat shock than Holstein embryos. Two experiments were conducted to test whether the ability of Brahman embryos to resist the deleterious effects of heat shock was a result of the genetic and cellular contributions from the oocyte, spermatozoa, or a combination of both. In the first experiment, Brahman and Holstein oocytes were collected from slaughterhouse ovaries and fertilized with spermatozoa from an Angus bull. A different bull was used for each replicate to eliminate bull effects. On day 4 after fertilization, embryos >or= 9 cells were collected and randomly assigned to control (38.5 degrees C) or heat shock (41 degrees C for 6 hr) treatments. The proportion of embryos developing to the blastocyst (BL) and advanced blastocyst (ABL; expanded and hatched) stages was recorded on day 8. Heat shock reduced the number of embryos produced from Holstein oocytes that developed to BL (P < 0.001, 55.6 +/- 4.2% vs. 29.8 +/- 4.2%) and ABL (P < 0.01, 37.7 +/- 3.6% vs. 12.2 +/- 3.6%) on day 8 as compared to controls. In contrast, heat shock did not reduce development of embryos produced from Brahman oocytes (BL = 42.1 +/- 4.8% vs. 55.6 +/- 4.8% for 38.5 and 41 degrees C, respectively; ABL = 17.6 +/- 4.2% vs. 32.4 +/- 4.2%). In the second experiment, oocytes from Holstein cows were fertilized with semen from bulls of either Brahman or Angus breeds. Heat shock of embryos >or= 9 cells reduced development to BL (P < 0.002) and ABL (P < 0.005) for embryos sired by both Brahman (BL = 54.3 +/- 7.7% vs. 23.4 +/- 7.7%; ABL = 43. +/- 7.4% vs. 7.9 +/- 7.4%, for 38.5 and 41 degrees C, respectively) and Angus bulls (BL = 57.9 +/- 7.7% vs. 31.0 +/- 7.7%; ABL = 33.6 +/- 7.4% vs. 18.4 +/- 7.4%, for 38.5 and 41 degrees C, respectively). There were no breed x temperature interactions. Results suggest that the oocyte plays a more significant role in the resistance of Brahman embryos to the deleterious effects of heat shock than the spermatozoa.

Adverse impact of heat stress on embryo production: causes and strategies for mitigation

The production of embryos by superovulation is often reduced in periods of heat stress. The associated reduction in the number of transferable embryos is due to reduced superovulatory response, lower fertilization rate, and reduced embryo quality. There are also reports that success of in vitro fertilization procedures is reduced during warm periods of the year. Heat stress can compromise the reproductive events required for embryo production by decreasing expression of estrus behavior, altering follicular development, compromising oocyte competence, and inhibiting embryonic development. While preventing effects of heat stress can be difficult, several strategies exist to improve embryo production during heat stress. Among these strategies are changing animal housing to reduce the magnitude of heat stress, utilization of cows with increased resistance to heat stress (i.e., cows with lower milk yield or from thermally-adapted breeds), and manipulation of physiological and cellular function to overcome deleterious consequences of heat stress. Effects of heat stress on estrus behavior can be mitigated by use of estrus detection aids or utilization of ovulation synchronization treatments to allow timed embryo transfer. There is some evidence that embryonic survival can be improved by antioxidant administration and that pharmacological treatments can be developed that reduce the degree of hyperthermia experienced by cows exposed to heat stress.

Short communication: lack of breed differences in responses of bovine spermatozoa to heat shock

An experiment was conducted to test whether the magnitude of effects of heat shock on spermatozoal function were less for thermotolerant breeds (Brahman and other breeds with Brahman influence) than for breeds that evolved in northern Europe (Angus and Holstein). Frozen spermatozoa were thawed, purified by Percoll gradient centrifugation and incubated at 38.5, 41, or 42 degrees C for 4 h. Sperm motility was then analyzed with a Hamilton Thorn Motility Analyzer. Heat shock reduced the percentage of sperm that were motile, mean track speed, and mean path velocity. There were no significant breed x temperature interactions for these traits. The mean frequency of tail beat tended to be reduced by heat shock in bulls of Brahman-influenced breeds and, to a lesser extent, in Brahman bulls, but it was not affected by heat shock in Angus or Holstein bulls. For no traits were there significant temperature x bull within breed interactions. Overall, results indicate that 1) heat shock reduces motility of bovine spermatozoa and 2) genetic effects are unlikely to be an important determinant of the function of ejaculated sperm following heat shock.

Enhancement of mitogen-induced lymphocyte proliferation in sheep

Conditions were established to optimize the lymphocyte proliferation test in sheep, a species where proliferation under standard conditions is lower than for other species. Optimum proliferation of phytohemagglutinin-stimulated lymphocytes was achieved in TCM-199 supplemented with 5% (v/v) horse serum, 0.2 mM sodium pyruvate and 5 x 10(-5) M beta-mercaptoethanol. Proliferative responses in this medium were 2.5-fold higher or more than when using a standard medium (RPMI-1640 + 10% heat-inactivated fetal bovine serum). Lymphocytes cultured in medium containing horse serum also responded to concanavalin A as well as or better than lymphocytes cultured in medium with bovine serum. For both PHA and Con A, optimal incorporation of radioactivity was achieved when cells were pulsed with [3H-methyl]-thymidine 72 h after addition of mitogen. The medium based on TCM-199 + horse serum could support interleukin-2-induced proliferation. Furthermore, known inhibitors of lymphocyte proliferation in sheep were effective in inhibiting lymphocytes cultured in this medium.