Use of Silvafeed® ByPro in Grazing Systems for Dairy Cows

In dairy farming, especially with high-producing grass-fed cows, the optimisation of rumen fermentation parameters poses an important challenge. In this context, obtaining an adequate dietary energy: protein ratio is a key nutritional goal, not only for the level of performance but also for the fertility of dairy cows. When referring to the relationship between energy and proteins, it is important to consider also the composition of dietary proteins, namely, how much of these proteins are degradable in the rumen.

In the case of cows fed with an excess of degradable proteins (e.g. grazing on alfalfa just after regrowth), rumen bacteria are not able to make use of all the available nitrogen for the synthesis of bacterial proteins. Therefore, excess ammonia is absorbed through the ruminal wall and is converted to urea in the liver as a detoxifying process, which consumes two moles of Adenosine Triphosphate (ATP) for each mole of urea produced. The urea passes to the bloodstream and is recycled or excreted in the urine and milk. Hence, the level of urea in milk is a key indicator to determine the amount circulating in the blood that is responsible for the animal energy loss.

Another aspect to take into consideration is the relationship between an excess of rumen degradable proteins and a reduction of cow fertility. Several explanatory mechanisms have been proposed in many publications, one of which stating that high levels of blood urea depress progesterone secretion and, therefore, impact negatively embryo nidation. This is reflected by a higher repetition of oestrus cycles and thus longer lasting birth intervals.

In a nutshell, the supply of an excessive amount of degradable proteins in the rumen threatens optimal production due primarily to a lower energy efficiency and a decrease in fertility.

In such situations, the addition of Silvafeed® ByPro, a blend of plant extracts rich in bioactive substances, to the diet of high-producing grazing cows allows to improve the animal response against the above mentioned issues.

In fact, Silvafeed® ByProdecreases the urease activity in ruminal liquor, reducing ammonia concentration and therefore the amount of urea in the liver,saving metabolism energy. At the same time, Silvafeed® ByPro favours a reduction in the ruminal degradability of dietary proteins.

A five-week trial was carried out in a dairy farm in the Province of Santa Fe (Argentina) to assess the effect of Silvafeed® ByPro on milk urea level of cows grazing tender alfalfa sprouts at the beginning of spring.

Sixty high-producing multiparous cows in the same lactation period were used for this trial.

In the first week, the cows had no access to alfalfa pasture and were not yet supplemented with Silvafeed® ByPro.

During weeks two to four, the cows grazed the same plot of alfalfa, four hours a day. At milking time, cows were divided in different groups receiving two dietary treatments, either a standard commercial pelletized feed with Silvafeed® ByPro or without it (control).

In week five, the cows continued grazing but the supplementation with Silvafeed® ByPro was stopped.

Individual samples of milk were taken on a daily basis (afternoon milking) to assess the urea content in milk (Figure 1).

Figure 1: Milk urea amount throughout the five-week trial

As the cows entered the pasture of tender alfalfa in the second week, the amount of urea in milk increased abruptly. However, this was much less pronounced for cows treated with Silvafeed® ByPro. This situation was maintained during the following three weeks of supplementation with Silvafeed® ByPro. During week five, the average values of the two groups tended to equalise again, as the supplementation with ByPro was removed.

In conclusion, the addition of Silvafeed® ByPro is an efficient solution to prevent urea levels from rising too much in the blood and milk of dairy cows grazing pastures containing high amounts of rumen degradable protein. This could have a beneficial impact on many aspects such as cow fertility, energy usage and milk productivity.