Heat stress in lactating dairy cows: a review

Climate change and livestock: Impacts, adaptation, and mitigation

Effects of heat stress and plane of nutrition on lactating Holstein cows: I. Production, metabolism, and aspects of circulating somatotropin

It is well documented that the stress of hot environments lowers productive and reproductive efficiency, in farm animals. Likewise, research information is available to aid in the management of livestock in such adverse conditions. However, practical methods to achieve the desired levels of productive and reproductive performance are lacking. Summer forages that will support a high level of productivity in subtropic and tropic regions are needed for ruminants. More critical information is needed on the total dietary needs of all farm animals in hot environments. Dietary emphasis should be to increase intake or to alter levels of proteins, amino acids or other nutrients to improve the conversion of feed units into production units. Increasing nutrient intake to support a higher level of production will render animals more sensitive, in terms of productive efficiency, to environmental modifications that improve comfort. This should be especially pertinent in the humid Southeast and other regions where production responses to environmental modifications have been variable. There is limited information on the effect of the night cooling cycle on productive efficiency and on the effect of severe heat stress on reproductive phenomena not related to conception.

Heat stress as it affects animal production.

When sperm of the ram, bull, boar and stallion are cold-shocked by rapid cooling to near freezing point, motility and metabolic activity are irreversibly depressed and the acrosome and plasma membrane disrupted. Ram sperm become susceptible to cold shock in the proximal corpus region of the epididymis when the cytoplasmic droplet has moved backwards to the distal portion of the sperm midpiece. The membrane constituents phospholipids and cholesterol are important in cold shock which causes loss of lipid from sperm. The susceptibility of sperm to cold shock is linked with a high ratio of unsaturated:saturated fatty acids in the phospholipids and a low cholesterol content. The high unsaturated fatty acid content of sperm also makes them susceptible to damage from peroxidation which adversely affects motility, metabolism, ultrastructure and fertility. Hydroxynonenal, a product of fatty acid peroxidation, depresses the motility and oxygen uptake of ram sperm in vitro and may react with the -SH groups of the axonemal microtubules. High calcium concentrations in the external medium may decrease the motility and metabolism of sperm and 'calcium intoxication' may be a factor in cold shock. Lowering the environmental temperature increases calcium uptake by sperm and the effect is aggravated if the rate of cooling is rapid. Phospholipids, particularly those in egg yolk, protect sperm to some extent from cold shock and also prevent increased calcium flux into the sperm. Suggestions are made for increasing the life span of sperm during preservation and microencapsulation by adding agents that may stabilize membranes, counter peroxidation and decrease calcium uptake.

Lipids and calcium uptake of sperm in relation to cold shock and preservation: a review

Effect of Ad Libitum or Force-Feeding of Two Rations on Lactating Dairy Cows Subject to Temperature Stress

Effect of drinking-water temperature upon ruminant digestion, intraruminal temperature, and water consumption of nonlactating dairy cows.

Effects of Frequency of Feeding on Production Characteristics and Feed Utilization in Lactating Dairy Cows

Effects of frequency of feeding on urea utilization and growth characteristics in dairy heifers.

A carefully controlled, multistage freezing and thawing process for the preservation of animal semen, blood, and other biological materials. A variety of diluting substances can be utilized to effectively modify the cell membrane's permeability to water and to initiate and/or alter the process of crystallization to minimize undesirable physio-chemical effects. A sample of semen is diluted with a suitable cryoprotective agent to achieve a final pH of 6.0 to 6.3 at +5°C. The sample is collected at body temperature and cooled slowly to +5°C, held at this temperature for 30 minutes or longer, followed by a rapid decrease in temperature to a nominal -4°C, or a temperature slightly below the freezing point of the diluent. The sample is held at this temperature for a period of 1 to 8 minutes to allow adjustment and stabilization of the temperature induced changes in pH and associated alterations in membrane permeability and osmotic pressure. The sample is then cooled rapidly after stabilization down to a nominal -100°C at a nominal rate of 20°C/minute. The sample is then immersed into liquid nitrogen for final cooling and storage. Rapid thawing is also an essential step in the total process to enhance cell survival. Semen or other biological materials in ampules may be thawed by immersing the ampules in +45°C water for 15 to 30 seconds while semen packaged in straws will thaw within 5 to 7 seconds in +45°C water.

C.P. Merilan

Papers

Effect of Ad Libitum or Force-Feeding of Two Rations on Lactating Dairy Cows Subject to Temperature Stress

Effect of drinking-water temperature upon ruminant digestion, intraruminal temperature, and water consumption of nonlactating dairy cows.

Effects of Frequency of Feeding on Production Characteristics and Feed Utilization in Lactating Dairy Cows

Effects of frequency of feeding on urea utilization and growth characteristics in dairy heifers.

Multistage freezing system for preservation of biological materials