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.     

Nutritional strategies for managing the heat-stressed dairy cow

Heat stress results from the animal's inability to dissipate sufficient heat to maintain homeothermy. Environmental factors, including ambient temperature, radiant energy, relative humidity, and metabolic heat associated with maintenance and productive processes, contribute to heat stress. The focus of this article is to identify environmental and metabolic factors that contribute to excessive heat load, describe how disruption of homeothermy alters physiologic systems of the cow, and discuss nutritional modifications that help to maintain homeostasis or prevent nutrient deficiencies that result from heat stress. Changes in diet are needed during hot weather to maintain nutrient intake, increase dietary nutrient density, or to reestablish homeostasis. Formulation for adequate nutrient intake is challenging because of the competition between nutrient density and other needs for the cow, including energy density and adequate dietary fiber. Lower DMI during hot weather reduces nutrients available for absorption, and absorbed nutrients are used less efficiently. An excess of degradable dietary protein is undesirable because of energy costs to metabolize and excrete excess N as urea. Optimizing ruminally undegraded protein improves milk yield in hot climates. Mineral losses via sweating (primarily K) and changes in blood acid-base chemistry resulting from hyperventilation reduce blood bicarbonate and blood buffering capacity and increase urinary excretion of electrolytes. Theoretical heat production favors feed ingredients with a lower heat increment, such as concentrates and fats, whereas forages have a greater heat increment. Improved dietary energy density and the lower heat increment associated with the inclusion of dietary fat must be coupled with limitations to fat feeding to avoid ruminal and metabolic disorders. Numerous nutritional modifications are used for hot weather feeding; however, many need further investigation to achieve specific recommendations.     

Biochemical markers of bone turnover in the dairy cow during lactation and the dry period

We measured a bone-formation marker recognizing osteocalcin, and a bone-resorption marker recognizing C-telopeptide (CT(x)) fragments of collagen type I, in a longitudinal study. The levels of these markers in the plasma of dairy cows (n=11) were recorded over a 12 month postpartum period, including a full lactation and a dry period. The plasma concentration of CT(x) was highest in the first week after parturition. It then declined slowly over the next 33 weeks and remained low until the next parturition. Osteocalcin concentration was lowest around parturition, reached a plateau during mid-lactation, then fell again towards term. There were large variations in bone metabolism during a lactation, that were not directly related to milk production. These results may be used to facilitate appropriate adjustments to calcium and phosphorous concentrations in the diet, reflecting the specific needs of each stage of the reproductive cycle.     

热应激期日粮添加酵母铬对奶牛体温、呼吸率和血液生理生化指标的影响

选择2～4胎次干奶期的荷斯坦奶牛20头,配对分为两组,在7-9月进行63 d的饲养试验,对照组使用基础日粮,试验组在基础日粮的基础上添加酵母铬0.8 mg/kg.结果表明:在持续高温天气下奶牛处于热应激状态,日粮中添加酵母铬能使奶牛体温与呼吸率上升幅度趋小,酵母铬组奶牛的体温与呼吸率明显低于对照组,差异显著(P<0.05).酵母铬使奶牛血液甘油三酯、尿素氮和总胆固醇水平都有下降趋势.     

营养调控技术对蛋鸡热应激的研究

温度是影响蛋鸡生产性能的重要环境因素之一，如何通过营养调控技术，减轻热应激对蛋鸡的负面影响。此文从营养物质如：蛋白质、氨基酸、能量、维生素、矿物质；非营养物质：添加中草药、酸化剂等对蛋鸡热应激的营养调控技术，阐述近几年来，营养调控关键技术在蛋鸡热应激中的应用情况。     

Immunoglobulins in piglets from sows heat-stressed prepartum

Sows were subjected to moderate heat stress in a chamber (32 C) from d 100 of pregnancy until less than 8 h before delivery of first piglet, while control sows were in a thermoneutral chamber (21 C) or farrowing house (22 C). Blood serum and colostrum at parturition of heat-stressed sows and their piglets' serum at birth had elevated cortisol concentrations. Total protein, globulin and immunoglobulin G (IgG) concentrations in sow serum tended to decrease as parturition time was approached; albumin did not change. Total protein and IgG concentrations in colostrum at parturition and in milk 24 and 48 h later tended to be lower in heat-stressed sows. Concentrations of these four protein fractions (total, globulin, IgG and albumin) in piglet serum at birth did not differ among treatment groups, but soon after colostrum ingestion they increased markedly in all groups. Therefore, in all groups total protein remained constant while globulin and IgG decreased. Globulin concentration on d 1 was lowest in piglets from heat-stressed sows, but its rate of decrease after d 1 was not affected by sow treatment. Immunoglobulin G concentration was 11 mg/ml lower, but its rate of decrease through postnatal d 20 was slower in piglets from heat-stressed sows than in those from control sows; a 10-mg/ml difference in IgG concentration on postnatal d 1 has been associated with increased preweaning mortality in piglets. Higher cortisol concentration in serum and lower IgG in colostrum of sows under heat stress was associated in their piglets with higher serum cortisol at birth and lower serum IgG for the first 20 d postnatum.     

The impact of Zearalenone on heat-stressed skeletal muscle in pigs

Heat stress (HS) and Zearalenone (ZEN) exposure affect growth, production efficiency, and animal welfare; and, under extreme situations, both can be lethal. Given that both HS and ZEN independently cause oxidative stress, we hypothesized that simultaneous exposure to HS and ZEN would cause greater oxidative stress in porcine skeletal muscle than either condition, alone. To address this hypothesis, crossbred, prepubertal gilts were treated with either vehicle control (cookie dough) or ZEN (40 μg/kg) and exposed to either thermoneutral (TN; 21.0 °C) or 12-h diurnal HS conditions (night: 32.2 °C; day: 35.0 °C) for 7 d. Pigs were euthanized immediately following the environmental challenge and the glycolytic (STW) and oxidative (STR) portions of the semitendinosus muscle were collected for analysis. In STR, malondialdehyde (MDA) concentration, a marker of oxidative stress, tended to increase following ZEN exposure (P = 0.08). HS increased CAT (P = 0.019) and SOD1 (P = 0.049) protein abundance, while ZEN decreased GPX1 protein abundance (P = 0.064) and activity (P = 0.036). In STR, HS did not alter protein expression of HSP27, HSP70, or HSP90. Conversely, in STW, MDA-modified proteins remained similar between all groups. Consistent with STR, ZEN decreased GPX1 (P = 0.046) protein abundance in STW. In STW, ZEN decreased protein abundance of HSP27 (P = 0.032) and pHSP27 (P = 0.0068), while HS increased protein expression of HSP70 (P = 0.04) and HSP90 (P = 0.041). These data suggest a muscle fiber type-specific response to HS or ZEN exposure, potentially rendering STR more susceptible to HS- and/or ZEN-induced oxidative stress, however, the combination of HS and ZEN did not augment oxidative stress.     

Viability of maternally heat-stressed mouse zygotes in vivo and in vitro

Mammalian preimplantation embryos are susceptible to heat stress. This present study examined how maternal heat stress affects the development of mouse zygotes in vivo and in vitro. In Experiment 1, zygotes collected from female mice that were heat‐stressed for 12 h on day 1 of pregnancy were cultured in vitro. Maternally heat‐stressed zygotes developed normally to the two‐cell stage, but the majority of embryos failed to develop into morulae or blastocysts. In Experiment 2, pregnant mice were heat‐stressed on day 1 or from day 1 to day 3 of pregnancy. The number of living fetuses on day 14 of pregnancy was lower in heat‐stressed mice than in non‐stressed mice, but the difference was significant only in successively heat‐stressed mice. These results demonstrate that maternally heat‐stressed zygotes have reduced in vitro viability, but this phenomenon does not necessarily lead to embryo loss in the maternal environment.     

西杂牛与哈萨克牛育肥对比试验

对 14～ 17月龄 12头西杂牛一代公牛和 12头哈萨克公牛进行 12 0天的育肥 ,西杂一代公牛平均日增重 986 5g±12 0 4 5 g ,屠宰率 5 5 2 %,净肉率 44 2 %;哈萨克公牛日增重 498 2 g± 96 3 0g ,屠宰率 46 5 %,净肉率 3 6 4 %。西杂一代公牛比哈萨克公牛日增重提高 98 0 %,屠宰率和净肉率分别提高 8 7和 7 8个百分点。     

Megaesophagus in a cow

Megaesophagus developed subsequent to presumed pharyngeal trauma in a cow. Signs resolved after prolonged antibiotic treatment and supportive care.     

Hemangiosarcoma in a cow

A 4-year-old cow initially examined because of hindlimb lameness had a waxing and waning course of illness for 31 weeks. Signs included lameness, swelling of the affected limb, and intermittent fever, and anorexia. Radiography and bacterial culturing suggested osteomyelitis. Terminally, there was peracute anemia and dyspnea. The final diagnosis was hemangiosarcoma of the metatarsus, with metastasis to the lungs.     

Endocarditis in a cow

Bacterial endocarditis of the tricuspid valve was diagnosed in a cow with weight loss, reduced milk production, and intermittent fever. Clinical signs of disease included jugular and mammary vein pulses, tachycardia, large cardiac silhouette, and grade-III/V holosystolic murmur. The diagnosis was also supported by echocardiographic findings and isolation of Streptococcus viridans from blood samples. The cow was treated with penicillin, furosemide, acetylsalicylic acid, heparin, and potassium chloride and survived 14 months after the diagnosis, producing 1 live calf and 4 viable embryos. The cow's heart rate exceeded an upper normal limit of 80 beats/min during most of the initial 4 months of treatment. Additional clinical signs of disease that were observed during treatment included diarrhea, ventral edema, and coughing. General medicine and cardiology textbooks have previously minimized the potential benefits of anticoagulant use in cases of septic endocarditis. The advent of routinely performed embryo transfer procedures may make treatment of endocarditis feasible in cattle with exceptional genetic merit.     

Cortisol in pregnancy toxaemia of sheep

Of 31 pregnant ewes with clinical signs of pregnancy toxaemia, 24 had hypoglycaemia and hyperketonaemia at the time that a single blood sample was obtained. Twenty-five of these had a plasma cortisol concentration in excess of 10 ng/ml and six had a value below this. All the seven animals which did not show both hypoglycaemia and hyperketonaemia had a plasma cortisol concentration in excess of 10 ng/ml. Taking all the sheep together, 80% had a high plasma cortisol concentration. This could be the consequence of increased adrenal output or reduced excretion by the liver.     

奶牛乳房炎多联苗(B)的临床免疫试验

用奶牛乳房炎多联苗 (B)免疫家兔 ,14 d血清中金黄色葡萄球菌抗体效价可达 1∶ 8,2 8d抗体水平明显升高 ,可达 1∶ 32 ,注苗后 35 d攻毒 ,攻毒后 2 d保护率为 93.3% (14 /15 ) ,自然保护率为 2 0 % (1/5 ) ,10 d保护率为 6 6 .6 % (10 /15 ) ,自然保护率为 2 0 % (1/5 ) ;用多联苗 (B)臀部肌肉注射免疫泌乳牛 ,试验期间 4个月内 ,3ml剂量组临床型乳房炎月平均发病率为 11.0 9% ,其对照组为 2 0 .19% ,发病率降低 4 5 .2 9% ,差异极显著 (P<0 .0 1) ;5 m l剂量组月平均发病率为 13.0 1% ,其对照组为 31.36 % ,发病率降低 5 8.5 1% ,差异极显著 (P<0 .0 1) ;3ml剂量组与 5 m l剂量组之间发病率无明显差异 (P>0 .0 5 ) ;注苗后泌乳牛血清抗体水平可持续 4个月 ,且 30 d时效价水平最高。     

奶牛胚胎移植中以改良牛做受体牛的试验

为了加快良种牛扩群步伐，促进养牛业的快速发展，目前，单靠扩大牛群规模来提高肉、奶产量是不现实的，必须通过提高牛个体肉、奶单产，即提高牛群质量来加以解决。就奶牛业来讲，依靠从国外引进活畜形式改良本地奶牛品种存在着价格昂贵、运输困难、检疫繁琐等诸多问题，     

Renal efficiency underlies adaptive heterothermy of heat-stressed hypohydrated goats

Tropical Animal Health and Production - We investigated the thermotolerance of the F1 progeny (Black Bedouin × Damascus crossbreed) to summer conditions alongside that of two pure breeds. Male...