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In the next two decades, the world population will increase significantly; the majority in the developing countries located in the tropics of Africa, Asia, Latin America, and the Caribbean. To feed such a population, it is necessary to increase the availability of food, particularly high-value animal protein foods produced locally, namely meat and dairy products. Dairy production in tropical regions has a lot of growth potential, but also poses a series of problems, particularly as dairy production systems were developed in temperate countries and in most cases are difficult to implement in the tropics. Drawbacks include hot weather and heat stress, the lack of availability of adequate feeds, poor infrastructure, and cold chain and the competition with cheap imports from temperate countries. This position paper reviews the major drawbacks in dairy production for the five major dairy species: cattle, water buffalo, sheep, goat, and camel, as well as the future trends in research and development. It also concerns the major trends in reproduction and production systems and health issues as well as environmental concerns, particularly those related to greenhouse gas emissions. Tropical Animal Health and Production now launches a topical collection on Tropical Dairy Science. We aim to publish interesting and significant papers in tropical dairy science. On behalf of the editorial board of the Tropical Animal Health and Production, we would like to invite all authors working in this field to submit their works on this topic to this topical collection in our journal.

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This study aimed to evaluate the effect of dietary chromium (Cr) supplementation on the apparent metabolism of some trace elements in camel calves reared under hot summer conditions. The study was conducted on a total of 15 male camel calves (5–6 months old) reared under hot summer conditions for 12 weeks. The animals were housed individually under shelter and divided into three dietary treatment groups (diets supplemented with 0.0, 0.5, or 1.0 mg Cr/kg DM), five animals each. At the end of the study, a metabolic trial was conducted on all camels for the evaluation of trace elements metabolism. Cr excretion, absorption, and retention showed an increasing trend with the increasing level of dietary Cr supplementation. Dietary Cr supplementation at 0.5 mg Cr/kg DM to camel calves resulted in a significant (P < 0.05) increase in Cu and an increasing trend in Zn and Mn excretion via urine and feces. However, Fe retention increased significantly (P < 0.05) in camel calves fed on diet supplemented with Cr. Dietary Cr supplementation to camel calves resulted in an increasing trend of plasma Cr concentration, while plasma concentration of Cu and Zn tended to decrease and without any effect on plasma Fe concentration. The results of the present study suggests that care should be taken for the negative interaction of Cr with the utilization of other trace elements, in cases where Cr is supplemented to the diet as a feed additive to promote growth and immunity under hot climatic conditions.  相似文献   
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Twelve 9-mo-old Merino wethers (30.4 ± 3.2 kg of BW) were used in a crossover study to investigate the heat tolerance of Australian Merino sheep by testing their physiological responses to repeated heat loads that occurred during summer months. Wethers were randomly divided into 2 groups of 6 wethers each, housed individually in an environmental chamber, and subjected to 2 d of thermoneutral conditions (TNC) followed by either 7 d of TNC (maximum temperature of 24°C, minimum temperature of 16°C) or 7 d of hot conditions (maximum temperature of 38°C, minimum temperature of 28°C), and then 2 d of TNC. These treatments were applied in 2 replicates, with each replicate in a separate environmental chamber. Rectal temperature (RT) and respiration rate were measured daily at 0600, 0800, 1000, 1200, 1400, 1600, and 1800 h. Feed and water intakes were measured daily, and wethers were weighed on d 1 and 11. Blood samples were collected from each whether on d 2 and 6, and serum was assayed for concentrations of creatine, glucose, total protein, cholesterol, NEFA, calcium, sodium, and potassium. Exposure to a high ambient temperature resulted in an 0.8°C increase in RT (P < 0.001), an increase in respiration rate (P < 0.001) by 66 breaths/min, and a 2.7 L/d increase in water intake (P < 0.0001). Feed intake decreased by 22% (P < 0.0001), BW decreased by 5.2% (P < 0.03), and creatine concentration was reduced (P < 0.05). No differences (P > 0.05) between treatments were observed for any of the remaining serum variables. These results indicate that Australian Merino sheep were able to maintain RT within the normal range during exposure to a prolonged increase in heat and that they recovered quickly from the negative effect of heat stress within 2 d of conditions returning to TNC. It would appear that they have a high heat tolerance, and further studies are needed to examine the effects of a greater heat load to determine the temperature-humidity index thresholds for Australian Merino sheep.  相似文献   
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The aim of the study was to determine the effects of various doses of injected Se on the physiological responses of sheep to heat load. Fifteen 9-mo-old Australian Merino wethers (mean BW = 27.2 ± 2.1 kg) were randomly assigned to 1 of 3 treatments: 0 (control), 0.5, and 5 mg of Se, which was administered as a subcutaneous sodium selenate injection (5 mg/mL Se) on d 1, 8, and 15 of exposure to heat stress. The animals were housed individually in an environmental chamber and exposed to high temperature from 0700 to 1800 h (maximum = 38°C; minimum = 24°C) and to thermoneutral temperature from 1800 to 0700 h (maximum = 24°C; minimum = 20°C) for 21 d. Rectal temperature (RT) and respiration rate (RR) were measured daily at 0800, 1200, and 1600 h. Feed intake was measured daily, and sheep were weighed on d 1, 8, 15, and 21. Blood samples were collected on d 1 and 21. The 5 mg Se treatment decreased RT by 0.3°C (P = 0.02) and BW loss by 4.5% (P < 0.05) and increased eosinophil count (P < 0.05). There were no differences (P > 0.05) between treatments in RR and DMI, serum concentrations of glucose, total protein, cholesterol, and NEFA or in blood hematology variabl6es. The findings of this study have important implications for the sheep industry. Further studies are warranted to elucidate the dynamics of Se on productivity and health during hot conditions.  相似文献   
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