The South African dairy industry has in recent years begun to place immense pressure on milk producers to increase their solids production, specifically butterfat, writes Nelita Hildebrandt, ruminant technical manager at Meadow Feeds. She says the industry incentivises or penalises producers heavily to enforce this pressure, which can thus have a significant impact on the economics of these dairy operations.
Whether it is lucrative to aim for this while sacrificing litres produced is up for debate, as litres are probably still the more profitable return. Most farmers however are looking for ways to maintain litres while increasing butterfat production. In pasture-based systems, this remains a challenge because of a variety of factors.
Pasture-based systems
Dairy cows on pasture visit the milking parlour twice a day, during which time they receive concentrate (this is the portion that Meadow Feeds supplies). This practice is called slug-feeding and is not ideal for rumen health because of the starch and sugar levels of this concentrate.
We will discuss rumen pH, the big driver in rumen health, in more detail later.
When these cows are not in the dairy parlour, they are grazing high-quality pasture, mostly ryegrass and at times kikuyu. Ryegrass is bred for high energy and low fibre, as this maximises milk production. Too much fibre will reduce the intake capacity of these cows because of a spatial limit to the rumen.
Research has found that even high-quality pasture can have an impact on the pH of the rumen. These pastures are also high in fats, which are mostly proportioned towards unsaturated fats. In winter, pasture growth slows down and this causes a shortage of dry matter intake (DMI) which will be supplemented with maize silage. Although maize silage will add fibre to the total diet, it can also be high in starch.
The black box called rumen
The rumen of the cow is what distinguishes a ruminant from any other species. This is where the so-called “magic” happens.
It is however not the rumen itself that is the black box, but rather the microbes that inhabit this area. These organisms are an integral part of the success of a ruminant. They enable a ruminant to utilise feedstuffs that other livestock species are not able to consume at all. The rumen microbes are able to break down and derive energy from high fibrous feedstuffs.
The challenge with this, however, is the fact that the rumen micro-organisms require a very specific pH range to function optimally. This pH range is 5.8 – 6.2. When the pH falls below 5.8, the environment becomes unfavourable for the cellulolytic bacteria or fibre-digesters.
A is for acidosis
Now for the pH: the desired pH for the fibre-digesters is 5.8 – 6.2. A pH drop below 5.8 is termed sub-acute ruminal acidosis (SARA), and below 5.2 is acute ruminal acidosis. Lactate utilising organisms are also most active within the above-mentioned pH range, which will assist in maintaining pH to a specific level.
Lactate is the strongest of the volatile fatty acids (VFA’s) and has the biggest negative impact on pH.
During SARA, the population of these crucial organisms will suffer, and when the pH further drops to 5.2 and below, the health of the cow will be dramatically impacted. If not treated with urgency, the animal will die.
It is also not just the drop below a certain pH that will impact the rumen organisms, but also the amount of time spent at these suboptimal pH levels.
Concentrates that are high in starch and sugars are detrimental to ruminal pH, but the rumen is in essence designed to withstand such a challenge when it has the correct total diet. The problem with pasture-based systems comes in when the ideal conditions are not met.
B is for buffering
Buffering is when a change in pH is resisted to maintain pH within the ideal range. This fantastic ‘black box’ is able to do this on its own, provided there is enough fibre in the diet. When ruminants chew the cud, they produce sodium bicarbonate in their saliva. Sodium bicarbonate is a natural buffer, designed to counteract the pH-depressing effect during fermentation of the carbohydrates (grains or sugars) they are fed, for improved energy and hence milk production.
There are nutritional (artificial) buffers that can be added to the in-parlour concentrate, but these do not nearly have the efficacy of the natural sodium bicarb. In fact, research suggests that the natural ruminal buffers present in saliva are six times more effective in pasture-based systems. The conditions are somewhat suboptimal for this natural system to be fully functional.
The one challenge is the fact that our pastures and silages do not have nearly enough fibre to stimulate consistent cud-chewing. The other challenge is the fact that concentrate is fed twice a day, as mentioned previously. The delivery of buffers at the exact time of the concentrate feeding is difficult and being able to add buffers that will match the fermentation pattern of these concentrates are exponentially more difficult.
C is for fatty acids
To further exacerbate the issue, ryegrass pasture is very high in fats and especially poly-unsaturated fatty acids. The C is for the carbon chain that forms the backbone of the fatty acids (FA’s). These fatty acids will be saturated in the rumen through a process called biohydrogenation, to form C18:0. This fatty acid will be used as an energy source in the small intestine and form part of the fatty acids in milk in the udder.
There are two pathways to achieve this, one of which has a severe negative impact on milk fat. The biohydrogenation pathway will follow this “negative” route when the rumen pH is even just slightly depressed. As described before, this is almost impossible to avoid. The higher passage rate experienced on pasture will cause the rumen digesta to leave the rumen before the rumen bacteria has had sufficient time to hydrogenate the unsaturated FA’s.
This has the potential to add to the milk fat depression when these unsaturated fatty acids are absorbed from the small intestine. Fibre will help to counteract this phenomenon, as it will slow down the rate of passage.
In summary
Although milk fat depression is a very complicated event, there are key fundamentals that can achieve great success in countering the outcomes. Pasture-based systems represent somewhat of a perfect storm to induce milk fat depression, and it is imperative for every operation to decide whether the changes to the diet or management practices are worth the expected outcome. The economics of milk fat production vs milk production must be carefully considered.
Be sure to feed sufficient fibre to the cows. Look for ways to spread the risk of acidosis throughout the day, instead of feeding risky feeds at coinciding events twice a day. Make use of ruminal buffers or other additives (which were not discussed today) to manage pH. Make sure that the homegrown forage varieties that you’ve chosen match what you want to achieve and understand that there will be pros and cons to each of these. It is unfortunately a dynamic system, so be prepared to be flexible and roll with the proverbial punches.
- For more information on the subject or the nearest Meadow Feeds technical advisor to your area, simply click here.
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