Thermoregulatory response to outdoor heat stress of hair sheep females at different physiological state.

Forty Dorper × Pelibuey sheep females were used to evaluate the effects of physiological state on physiological variables and serum concentrations of metabolites, thyroid hormones, and electrolytes under outdoor heat stress conditions. Females were selected as follows (n = 10 per group): weaning ewe lambs (WEL; 3 months old), replacement nulliparous ewes (RNE; 8 months old), non-pregnant and non-lactating multiparous ewes (NME; 3-4 years old) and lactating multiparous ewes (LME; 3-4 years old). While physiological variables were measured both morning and afternoon, blood samples were collected before feeding in the morning to determine all blood components. Three contrasts were constructed: (1) WEL vs. older ewes, (2) RNE vs. multiparous ewes, and (3) NME vs. LME. Compared with older ewes, WEL had higher (P < 0.01) rectal temperature (RT) and hair coat temperatures through the day, and also higher (P < 0.01) respiratory rate (RR) only in the afternoon. Serum levels of glucose and cholesterol were lower (P ≤ 0.02) in WEL than in older ewes. Nulliparous ewes compared with multiparous had always similar RT but higher (P ≤ 0.05) hair coat temperatures in most of the body regions by the morning and higher (P < 0.01) RR, without difference for hair coat temperatures in the afternoon. Only serum glucose (P = 0.07) and urea nitrogen (P < 0.01) levels were affected by parturition number, being lower in multiparous ewes. Regarding the effect of lactation, while RR was unaffected, afternoon RT and hair coat temperatures in most of the body regions through the day were higher (P ≤ 0.03) in lactating ewes. In addition, LME had lower (P < 0.01) serum levels of glucose, cholesterol, and urea nitrogen, but higher (P = 0.02) triiodothyronine levels than NME. In conclusion, ewe lambs and lactating ewes were less tolerant to heat stress, while nulliparous and multiparous ewes showed similar thermoregulatory ability.

Effects of dietary ferulic acid on reproductive function and metabolism of pre-pubertal hairbreed ewes during the anestrous season.

This study aimed to evaluate the effects of dietary supplementation of ferulic acid (FA) on reproductive tract weight (RTW), ovarian activity and serum concentrations of some metabolites and thyroid hormones of pre-pubertal hairbreed ewe lambs during the natural anestrous season. Twenty Dorper x Pelibuey crossbred ewe lambs (initial body weight = 28.5 ±â€¯0.5 kg and age = 5.0 mo) were fed a basal diet and assigned to two treatments (n = 10) under randomized complete block design: FA supplementation to dosages of 0 (control) or 300 mg of FA/d animal-1. Females were treated with FA during 34 d and then slaughtered to evaluate RTW and ovary. Blood samples were collected at days 1 and 34 to determine serum concentrations of metabolites (i.e. glucose, cholesterol, triglycerides, urea and total protein) and thyroid hormones. Final weight, dry matter intake, and serum concentrations of metabolites (except glucose) and thyroid hormones were unaltered by FA. Compared to control, FA-fed ewe lambs had lower (P = 0.05) serum glucose level but higher (P ≤ 0.05) RTW, ovarian mass, number of larger follicles and corpus luteum (CL). While percentage of ewe lambs with small follicles and number of small follicles per female did not vary, percentage of ewe lambs with large follicles and CL increased (P = 0.02) with FA. In conclusion, FA supplementation improves the reproductive tract development and ovarian activity of pre-pubertal hairbreed ewe lambs during the natural anestrous season. An improvement in functionality of the glucose-insulin system could be related with this benefic effect of FA.

Impacto del estrés oxidativo sobre las lesiones cutáneas causadas por radiaciones ionizantes / Impact of the oxidative stress on cutaneous lesions caused by ionizing radiations

Los efectos inducidos por exposición de manera accidental o terapéutica a dosis de radiaciones ionizantes inducen varios eventos celulares que afectan el proceso de cicatrización de la piel, y tiene gran impacto en la prognosis y supervivencia de individuos afectados. La información existente sobre los efectos nocivos por altas exposiciones a radiaciones proviene a partir de los accidentes ocurridos por las bombas atómicas en Hiroshima y Nagasaki produciendo problemas de salud por leucemias y linfomas en los sobrevivientes. El síndrome de radiación aguda (SRA) generalmente inicia durante las dos horas inmediatas posteriores a la exposición, y la severidad de las lesiones depende de la dosis y del tiempo de exposición. El desarrollo de las lesiones por el daño como efectos tardíos a exposiciones por radiaciones es más complejo y determina no únicamente el daño al parénquima celular sino también se presentan daños en el tejido vascular y en otros tejidos de soporte. Al menos parcialmente estos eventos se presentan a consecuencia del estrés oxidativo generado por el excesivo incremento de especies reactivas del oxígeno (EROs). Se han estado estudiando componentes comerciales como blancos potenciales para la prevención de los daños causados por radiaciones en piel que tienen una amplia actividad contra múltiples citocinas involucradas en los procesos de la lesión cutánea y por otro lado se están estudiando fármacos que reaccionan con los radicales libres o indirectamente inhiben la expresión de las enzimas que generan la producción de EROs o bien aumentan la expresión de enzimas antioxidantes intracelulares

Effect of the administration program of 2 ß-adrenergic agonists on growth performance and carcass and meat characteristics of feedlot ram lambs.

The aim of the study was to determine the effects of 3 feeding dose programs of the ß-adrenergic agonists (ß-AA) ractopamine hydrochloride (RH) or zilpaterol hydrochloride (ZH) for the final 30 d before slaughter on growth performance and carcass and meat characteristics of feedlot ram lambs. Eighty-four Dorper × Katahdin ram lambs (30.0 ± 1.6 kg) were blocked by BW and randomly assigned to pens (4 lambs per pen and 3 pens per treatment). Pens within a block were assigned randomly to 1 of 7 dietary treatments: 1) control (CTL) = diet without ß-AA; 2) RH constant (RHC) = 20.0 mg/kg of RH, d 1 to 30; 3) RH increasing (RHI) = 10.0 mg/kg, d 1 to 10; 20.0 mg/kg, d 11 to 20; and 30.0 mg/kg, d 21 to 30; 4) RH decreasing (RHD) = 30.0 mg/kg, d 1 to 10; 20.0 mg/kg, d 11 to 20; and 10.0 mg/kg, d 21 to 30; 5) ZH constant (ZHC) = 6.0 mg/kg of ZH, d 1 to 30; 6) ZH increasing (ZHI) = 3.0 mg/kg, d 1 to 10; 6.0 mg/kg, d 11 to 20; and 9.0 mg/kg d 21 to 30; and 7) ZH decreasing (ZHD) = 9.0 mg/kg, d 1 to 10; 6.0 mg/kg, d 11 to 20; and 3.0 mg/kg, d 21 to 30. Overall, ß-AA supplementation reduced DMI (P < 0.001) compared with CTL lambs, but lambs fed RHI and ZHI programs had greater (P < 0.05) total BW gain, ADG, and G:F. Carcass weight was improved (P < 0.05) by RHI and ZHI programs, but dressing percentage was enhanced (P < 0.05) by only ZHC or ZHI treatments. Fat thickness and yield grade were reduced (P < 0.05) by ZH or RH regardless of feeding program. Most LM characteristics (pH, moisture loss, and chemical composition) were not different among treatments (P > 0.05), with the exception of fat content that was reduced (P < 0.001) in lambs fed ß-AA, and diameter of muscle fibers that was increased (P < 0.05) by ZHI treatment. Constant and increasing doses of ZH reduced (P < 0.05) the a* value of LM and semitendinosus muscles, with no effects on L* or b* values. The mass of liver was reduced (P < 0.05) in ZHI-treated lambs compared with CTL lambs, and plasma urea concentration was reduced (P < 0.05) by RH or ZH administration regardless of feeding program, although there were no other differences in organ mass weight (P ≥ 0.35) or blood metabolites (P ≥ 0.16). Increasing doses of RH or ZH augmented the growth performance response without negative effects on organ mass weight or blood metabolites. Although a ZHI program improved carcass characteristics, the increased LM fiber diameter of lambs fed ZHI program could be unfavorable because of the potential negative effect on tenderness.

Effects of gossypol from cottonseed meal and dietary vitamin E on the reproductive characteristics of superovulated beef heifers.

Superovulated Hereford-Angus crossbred heifers (average 397 kg BW) were used to test the effect of feeding cottonseed meal (gossypol) and vitamin E on embryo quality and ovarian characteristics. Twenty-four heifers were assigned randomly to four treatments with six heifers per treatment. Treatments were the following dietary supplements: 1) SBM (soybean meal + 30 IU vitamin E/kg of diet DM); 2) SBM+E (soybean meal + 4,000 IU vitamin E x animal(-1) x d(-1)); 3) CSM (cottonseed meal + 30 IU vitamin E/kg of diet DM); and 4) CSM+E (cottonseed meal + 4,000 IU vitamin E x animal(-1) x d(-1)). Supplements based on cottonseed meal provided 43.5 g of total gossypol/d (37% negative isomer (-) and 63% positive isomer (+)). Blood samples were collected at the start of the experiment and every 3 wk thereafter up to 12 wk. Plasma a-tocopherol (alpha-T) concentration was affected by treatments (P < 0.05). Heifers supplemented with cottonseed meal had greater (P < 0.05) alpha-T concentration in plasma than heifers supplemented with soybean meal at each concentration of vitamin E. Supplementation at 4,000 IU vitamin E x animal(-1) d(-1) increased (P < 0.05) the concentration of a-T in plasma. Weight gain, hemoglobin and hematocrit were not affected by treatment. Erythrocyte osmotic fragility (EOF) increased (P < 0.05) in cottonseed meal-fed animals; however, EOF was lowered (P < 0.05) with vitamin E supplementation. Heifers fed CSM and CSM+E supplements had greater (P < 0.01) concentrations of (-)-, (+)-, and total-gossypol in plasma, corpora lutea (CL), liver, and endometrium than heifers fed SBM and SBM+E supplements. Tissue alpha-T concentration increased with increased dietary supplemental vitamin E, particularly in great amounts in the CL. Because there was no adverse effect of gossypol on superovulation response or embryo development despite concentrations of gossypol in endometrium that are toxic to embryos, it is likely that systems exist in the reproductive tract to limit gossypol toxicity.

Strategies for managing reproduction in the heat-stressed dairy cow.

Establishment and maintenance of pregnancy is difficult in lactating dairy cows exposed to heat stress because of reductions in estrous detection rate and the proportion of inseminated cows that maintain pregnancy. The most common approach to ameliorate heat stress in developed countries has been to alter the cow's environment through provision of shade, fans, sprinklers, and so on. Nonetheless, seasonal variation in reproductive function persists. Increased understanding of bovine reproductive function and its alteration by heat stress has led to additional strategies for reducing deleterious consequences of heat stress on reproduction. These include hormonally induced timed artificial insemination, which can reduce losses in reproductive efficiency caused by poor detection of estrus, and embryo transfer, which can increase pregnancy rate by allowing embryos to bypass the period when they are most sensitive to elevated temperature (i.e., in the first 1 to 2 d after breeding). Other efforts are directed toward developing methods to protect the embryo from harmful actions of elevated temperature. Approaches being studied include manipulation of embryonic synthesis of heat shock proteins and use of antioxidants to reduce free radical damage associated with heat stress. It may also be possible to reduce the magnitude of hyperthermia caused by heat stress. This might be possible physiologically, for example by feeding of agents that affect thermoregulatory systems, or genetically by selecting for specific traits conferring thermal resistance. Finally, the development of bovine somatotropin as a lactational promotant means that it may be possible to extend lactations beyond 305 d and voluntarily discontinue inseminations during periods of heat stress.

Response of preimplantation murine embryos to heat shock as modified by developmental stage and glutathione status.

Objectives were to characterize developmental changes in response to heat shock in the preimplantation mouse embryo and to evaluate whether ability to synthesize glutathione is important for thermal resistance in mouse embryos. Heat shock (41 degrees C for 1 or 2 h) was most effective at disrupting development to the blastocyst stage when applied to embryos at the 2-cell stage that were delayed in development. Effects of heat shock on ability of embryos to undergo hatching were similar for 2-cell, 4-cell, and morula stage embryos. The phenomenon of induced thermotolerance, for which exposure to a mild heat shock increases resistance to a more severe heat shock, depended upon stage of development and whether embryos developed in vitro or in vivo. In particular, induced thermotolerance was observed for morulae derived from development in vivo but not for 2-cell embryos or morulae that developed in culture. Administration of buthionine sulfoximine to inhibit glutathione synthesis did not increase thermal sensitivity of 2-cell embryos or morulae but did reduce subsequent development of 2-cell embryos at both 37 degrees and 41 degrees C. In summary, changes in the ability of 2-cell through morula stages to continue to develop following a single heat shock were generally minimal. However, 2-cell embryos delayed in development had reduced thermal resistance, and therefore, maternal heat stress may be more likely to cause mortality of embryos that are already compromised in development. There were also developmental changes in the capacity of embryos to undergo induced thermotolerance. Glutathione synthesis was important for development of embryos but inhibition of glutathione synthesis did not make embryos more susceptible to heat shock.

Effects of timed insemination and supplemental beta-carotene on reproduction and milk yield of dairy cows under heat stress.

In three experiments, we tested the efficacy of timed artificial insemination (AI) and beta-carotene supplementation for improvement of reproduction and milk yield. Experiments 1 and 2 were conducted during hot months, and Experiment 3 was conducted during cooler months. Cows were fed rations supplemented with beta-carotene at 0 or 400 mg/d per cow for > or = 15 d before the first AI. Cows were inseminated at each observed estrus after 70 d (Experiment 1) or at 50 d postpartum (Experiments 2 and 3) or were included in a timed AI program [d 0 (i.e., approximately 40 or 60 d postpartum), 8 micrograms of GnRH agonist; d 7, 25 mg of PGF2 alpha; d 9, 8 micrograms of GnRH agonist; d 10, AI] for first breeding. Pregnancy rate at first AI was similar among groups, but the percentage of cows that were pregnant by 90 d postpartum was greater for cows in the timed AI group in Experiments 1 (16.6% vs. 9.8%) and 2 (34.3% vs. 14.3%) but not in Experiment 3 (24.1% vs. 28.7%). Overall, beta-carotene had no effect on reproductive function. For cows fed supplemental beta-carotene for > or = 90 d, however, pregnancy rate at 120 d postpartum was increased in Experiment 1 (35.4% vs. 21.1%). In all experiments, beta-carotene increased cumulative milk yield on the last test day by 6 to 11%. In conclusion, timed AI can improve pregnancy rates during periods of heat stress. Supplemental beta-carotene may increase pregnancy rates for cows in the summer and can increase milk yield.

Effect of injection of beta-carotene or vitamin E and selenium on fertility of lactating dairy cows.

Experiments tested whether supplemental antioxidants improved fertility. To test effects of beta-carotene, cows in a hot environment were injected with prostaglandin F2 alpha (PGF2 alpha) and were given 3 injections, i.m., of 800 mg beta-carotene or saline at Days -6 and -3 before the anticipated date of insemination and at insemination (n = 37-41 inseminated cows/group). There was no effect of beta-carotene on the proportion of cows detected in estrus following PGF2 alpha, timing of estrus after PGF2 alpha injection or pregnancy rate in inseminated cows. In a second trial, cows in a temperate climate received intramuscular injections of vitamin E (500 mg) and selenium (50 mg) at 30 d post partum (n = 97) or were untreated controls (n = 89). Treatment did not affect interval from calving to first insemination or the proportion of cows pregnant at first service, but it increased the pregnancy rate at second service (69.8 vs 52.1%; P = 0.07) and reduced services per conception (1.7 vs 2.0; P < 0.05) and interval from calving to conception (84.6 vs 98.1; P < 0.05). Thus, injection of vitamin E and selenium increased fertility in cattle that did not become pregnant at first service.

Evidence that glutathione is involved in thermotolerance of preimplantation murine embryos.

Experiments were conducted to determine whether or not glutathione (GSH) is involved in thermotolerance responses of murine morulae. In the first experiment, morulae were exposed to either homeothermic temperature (37 degrees C), mild heat shock (40 degrees C for 1 h), severe heat shock (43 degrees C for 2 h), or a mild heat shock followed by severe heat shock (to induce thermotolerance). Exposure to mild heat shock did not affect viability and development, but severe heat shock reduced viability (i.e., live/dead staining) and the proportion of morulae that developed to blastocysts. This effect of 43 degrees C was reduced if embryos were first exposed to a mild heat shock of 40 degrees C. In the presence of DL-buthionine-[S,R]-sulfoximine (BSO), an inhibitor of GSH synthesis, the ability of 40 degrees C to confer thermotolerance was reduced. BSO decreased embryonic GSH content but did not decrease overall protein synthesis. In another experiment, administration of S-adenosyl-L-methionine, an inducer of GSH synthesis, decreased the deleterious effects of heat shock of 43 degrees C for 2 h on viability and percentage of embryos that became blastocysts. Addition of 5 microM GSH or GSH ester reduced the effect of 42 degrees C for 2 h on viability but not on continued development. The results suggest a role for GSH-dependent mechanisms in the processes by which murine embryos limit deleterious effects of heat shock.

Developmental changes in sensitivity of bovine embryos to heat shock and use of antioxidants as thermoprotectants.

Experiments were conducted with in vitro-produced bovine embryos to determine whether 1) increased culture temperatures (i.e., heat shock) adversely affected embryonic development, 2) embryos become more resistant to heat shock as they advance in development, and 3) selective antioxidant molecules alleviate heat shock effects on embryonic development. Development of 2-cell embryos to > or = 16-cell stage on d 5 after in vitro fertilization was not affected by a heat shock of 40 degrees C for 3 h, but 41 or 42 degrees C for 3 h decreased (P = .004) development. In a separate experiment, development of 2-cell embryos was decreased (P = .01) by exposure to 41 degrees C for 3 h but not for 1 h. In contrast, development of morulae to blastocysts was not affected by heat shock of 41 degrees C for 1 or 3 h. Medium supplementation with 50 nM glutathione or 50 mM taurine before heat shock did not reduce the effects of heat shock (41 degrees C for 3 h) on 2-cell embryos. Likewise, addition of glutathione ester, a more membrane-permeable analog of glutathione, did not protect 2-cell embryos from heat shock. In conclusion, early bovine embryos are susceptible to disruption in development caused by heat shock. As embryos progress in development, they acquire resistance to heat shock. Glutathione, taurine, and glutathione ester were not effective in alleviating the effects of heat shock on development of 2-cell embryos. Consequently, molecules have yet to be identified that can protect early-stage bovine embryos from the adverse effects of heat shock.

Effectiveness of short-term cooling and vitamin E for alleviation of infertility induced by heat stress in dairy cows.

Four experiments were performed to determine whether cooling cows during final maturation of oocytes and early embryonic development or injection of vitamin E at AI prevented adverse effects of heat stress on pregnancy rates in lactating Holstein dairy cows. In Experiment 1, cows were placed in a cooling facility containing sprinklers and forced ventilation or received shade only from 2 to 3 d before until 5 to 6 d after breeding. Although cooling had no effect on detection of estrus, pregnancy rates were increased slightly for cooled cows (8 of 50 cows; 16.0%) compared with those for cows exposed to shade only (2 of 32 cows; 6.2%). In Experiments 2 through 4, cows were administered 3000 IU of vitamin E or placebo i.m. at AI during two consecutive summers and one winter in Florida. Administration of vitamin E had no consistent beneficial effect on pregnancy rates during summer or winter. Short-term cooling improved pregnancy rates slightly in heat-stressed cows, but administration of vitamin E had no beneficial effects on pregnancy rates during heat stress. Further improvements in cooling schemes during early pregnancy and delineation of antioxidant effects are necessary before such systems become practical for improvement of fertility in heat-stressed dairy cows.

Effect of prepartum injection of vitamin E and selenium on postpartum reproductive function of dairy cattle.

A total of 198 cows were randomly assigned to treatment with a single intramuscular injection of 10 ml of a preparation containing vitamin E and selenium or placebo 3 wk before expected parturition. Incidence of retained fetal membranes was 3.0% for the treated group and 10.1% for the control group (P=0.06). Administration of MU-SE also increased the percentage of cows pregnant to the first service (41.2 vs 25.3%; P=0.02), reduced the number of services per conception (2.3 vs 2.8; P=0.03), and reduced the interval from calving to conception (121 vs 141 days; P=0.06). The effect of MU-SE on fertility was apparent in cows with and without retained fetal membranes. There was no effect of MU-SE on the interval from calving to the first estrus. In conclusion, prepartum supplementation with vitamin E and selenium can decrease the incidence of retained fetal membranes, increase pregnancy rates and, thereby, reduce the interval from calving to conception in lactating dairy cows.