The Research Column

The onset of lactation markedly increases nutrient requirements of dairy cows. The concomitant reduction in feed intake around calving predisposes transition cows to a negative nutrient balance. High-yielding dairy cows may mobilize as much as 1 kg of tissue protein per day from skeletal muscle during the first 7 to 10 days of lactation to meet their amino acid requirements. Additionally, protein mobilization starts before parturition, likely to meet amino acid requirements for growth of the foetus, uterus, and udder tissue.

Compared with Holstein milk, some conventional milk replacer (MR) formulations provide high amounts of lactose, low concentrations of fat, and comparable crude protein levels. Consequently, MR provides a lower dietary energy density than whole milk. Fat inclusion in MR compositions should raise the energy content, but the literature shows both positive and negative results.

The nitrogen (N) use efficiency (conversion of feed N into milk N) of dairy cattle is poor, typically ranging from 25 to 35%. The unused feed N is excreted about equally via the faeces and urine, although the proportion depends on the crude protein (CP) level and the ratio of rumen degradable protein (RDP) to rumen undegradable protein (RUP) in the diet. The excreted N is lost at each stage of manure management (e.g., during collection, storage, and after land application) in several forms: ammonia (NH3), nitrous oxide (N2O) and nitrate.

Up to 90% of administrated antibiotics are eliminated from the animal body through the faeces or urine, implying that manure generated from animal production represents a major route of antibiotic transfer to the environment. The presence of antibiotics, even at very low concentrations, can contribute to emergence of antibiotic resistance genes (ARG) and selection of antibiotic resistant bacteria.

In a report by Dr Indur Goklany who was a founding member of the International Panel on Climate Change (IPCC), the effects we currently experienced and other evidence which are considered as evidence of climate change, the author challenged the interpretations. The reference to the paper is: I.M. Goklany, 2021. Impacts of Climate Change: Perception and reality. Report 46, The Global Warming Policy Foundation. The question is what should we make of this.

The foods we eat may have a direct impact on our cognitive acuity in our later years. This is the key finding of an Iowa State University research study by Dr B.S. Klinedinst and colleagues, published in the November 2020 issue of the Journal of Alzheimer's Disease, with reference: doi.org/10.3233/JAD201058. The title of the paper is: Genetic factors of Alzheimer’s Disease modulate how diet is associated with long term cognitive trajectories: A UK Biobank Study.

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.

In the ultra-high temperature (UHT) process, milk is subjected to high temperatures, above 135 oC for a few seconds, resulting in a product with a shelf-life of several months when stored at ambient temperature. However, chemical and physical changes in the milk can lead to off-flavours, browning, fat separation, sediment formation or gelation during  storage. Important associated factors are processing parameters, storage conditions (time and temperature) and type of packaging.

branched-chain volatile fatty acids, valerate. 

Time of dry-off, calving and the start of a new lactation are critical transition events for a dairy cow. Large changes in both physiology and management increase the risk for disease and culling. The cow faces these transition events every year, as a one-year calving interval is usually aimed for. A one-year calving interval is usually associated with a good average 305-day yield and better economic results compared with longer calving intervals.