The Research Column

Globally, unhealthy diets have been recognised as a major cause of death and cardiovascular disease (CVD). Limitations to these reports include recommendations based on associations of individual foods, or nutrients or dietary patterns with CVD, and from studies conducted mostly in North America, Europe and East Asia, and otherwise numerous short-term randomized intervention trials of physiologic risk factors or clinical trials of dietary patterns on clinical outcomes.

In pasture systems, milk production is aimed to be maximised from grazed pasture with merely minimum supplementation to meet dairy cow requirements when necessary. The economic impacts of increased pasture production and utilization on farm profitability is well known, but the influence of maximising utilisation in different circumstances is not always known, one being soil type.

It is accepted that the best economic results, informed by the yearly peak milk, is a one-year calving interval (CI), which includes a 10-month lactation and a two-month dry period. However, as a consequence of this cycle, cows experience several transitions during the year, including drying-off, calving and the start of the next lactation. During these transitions, large changes in both physiology and management are associated with an increased risk of diseases and disorders, such as clinical mastitis, milk fever and ketosis.

The transition period in dairy cows imposes metabolic challenges that often reduce milk production and reproductive efficiencies. Energy, nutrients and oxidative balances are often compromised during this period, resulting in impaired immunity, increased susceptibility to disease, thereby further compromising nutrient intake and partition. Health problems and extensive mobilization of body reserves after calving have enduring effects on reproductive performance.

It has been known for more than 50 years that rumen bacteria can convert NPN sources into bacterial protein which can then be utilised by the ruminant. The advantage of the conversion is that NPN sources are cheaper than true protein supplements. There are however two issues which should be considered: (1) urea as the major NPN sources may be toxic at high levels, and (2) it has been shown that at high milk yields, microbial protein is limiting in certain amino acids, which then have to be supplemented by protein sources with rumen-bypass characteristics.

According to the literature, mild lameness in dairy herds may exceed 20% and severe cases could be 5 to 10%. This not only reflects negative on the economy of the enterprise, but also on animal welfare because of the pain the animal has to endure, and also due to implications to feeding, lying and locomotion. Therefore, methods to reduce lameness are required to reduce prevalence in the herd. To that effect, it has been shown that free-choice access to pasture may benefit lame cows by providing a softer and more comfortable lying and standing surface.

Increasing starch in dairy diets are beneficial to milk yield and efficiency of production, but the practice has limitations due to lactate accumulation in the rumen and inflammation-based negativity to immune function. Although the effects can be minimized by forage and TMR particle size, decreased sorting behaviour, increased passage rate, and manipulating starch fermentability as affected by grain processing, these practices have limitations.

Facial eczema, also referred to as pithomycotoxicosis in some countries, and now referred to in South Africa as sporidesmin induced liver disease (SILD), is a photosensitization of ruminants grazing pasture, particularly perennial ryegrass in South Africa. Facial eczema is a poor description as the photosensitization affects the skin also, in fact mostly, in cows over the back and backsides; therefore the change in terminology.

Provision and utilisation of vitamin D pre-calving have substantial implications during the transition and early lactation periods. The negative effects of hypocalcaemia with immune function, risk of disease, lactation performance and reproduction have been well-documented. As vitamin D is a key contributor to calcium (Ca), attempts have been made to prevent hypocalcaemia by supplementing vitamin D, since the amount and source of vitamin D can influence Ca balance during the transition phase.

Six treatments were compared, with two grazing intensities and three ways of supplementation, investigated at both grazing intensities. The two grazing intensities were severe and light grazing: (1) herbage allowance of 15 (severe) or 30 (light) kg DM per cow per day at 3 cm above ground level or, (2) post-grazing sward height, depending on the supplementation strategy.