The Research Column

Discipline: cheese; Key words: pasture, total mixed ration, Cheddar cheese, fatty acid.

Discipline: dairy & health; Key words: cardiovascular disease, consumer acceptance, dairy product, monounsaturated fatty acid, saturated fatty acid. 

Discipline: dairy &health; Key words: oestrogens, dairy products, endometrial cancer, nutrients, meta-analysis. 

Consumers complain about spoilage due to bacterial growth and spoilage also contributes to dairy product waste, which in a developing country we cannot really afford. We probably do not have figures in South Africa, but milk spoilage in the US amounts to $6.4 billion per year. Microbial spoilage is of particular concern and can be caused by either psychrotolerant spore formers, which likely originate from raw milk, or by post-pasteurization contamination (PPC).

In the studies, primary research papers were found through targeted Web of Science searches, the reference lists of recent reviews for each topic, and the reference lists of papers identified from these sources. Studies were included if they were published in English, the full text was accessible, and they compared treatments with and without contact between dairy cows and calves for a specified period. The resulting manuscripts underwent a 4-step appraisal process, and further manuscripts were sourced from reference lists.

Infectious diseases, such as metritis and mastitis, have  serious economic consequences due to the use of antibiotic treatment, the withdrawal period thereafter, delayed onset of cyclicity after calving, extended intervals between calving, and poor fertility . Most high-yielding dairy cows struggling with such diseases also have metabolic disorders, and some results have shown a connection between immunological defense and metabolic regulatory mechanisms.

Choline is a known essential nutrient as it is required for synthesis of essential membrane phospholipids, acts as a precursor for synthesis of acetylcholine, and in particular, has a role in lipid intermediary metabolism. Improving choline status pre-calving has the potential to reduce the risk of fatty liver and improve health and lactation.

As carbon dioxide, methane is a potent greenhouse gas (GHG), but when it comes to ruminant livestock and climate change there are many other characteristics which need to be considered. The important ones are: (1) it stays in the atmosphere only for about 12 years versus 1000+ years for carbon dioxide; (2) it is derived from atmospheric carbon such as carbon dioxide; (3) it is part of the biogenic (photosynthetic) cycle, and (4) it eventually returns to the atmosphere as carbon dioxide, which means it is recycled carbon.

Numerous studies have shown the negative effects of heat stress during the dry period on dairy cow performance during the subsequent lactation. Exposure of cows to heat stress during the dry period is associated with compromised mammary cell formation and decreases in milk yield in the subsequent lactation. Moreover, a greater incidence of postpartum disorders and lower reproductive performance are associated with exposure of cows to heat stress during the dry period. Dry period heat stress also decreases dry matter intake and body weight, gestation length, and calf weight.

Heat stress has been estimated to cost the dairy industry in the United States more than $900 million annually due to production losses. The main contributors to heat stress are temperature, humidity, and the temperature-humidity index (THI). A THI of 68 to 72 has been reported to induce heat stress in cows and decrease milk production. Prior research has been conducted on heat abatement measures in free stall barns with sprinklers, evaporative cooling, and fan design.