Contrary to general expectations, the characteristics of different varieties of perennial ryegrass such as sugar content do not influence the food intake of grazing dairy cows. Moreover cell wall degradability characteristics were not different among perennial ryegrass varieties. Research carried out by Hassan Z. H. Taweel at Wageningen University shows that an increased dry matter intake can be achieved by gaining more insight into the regulatory mechanisms behind the maximum use of rumen capacity. Taweel will be defending his doctoral thesis Perennial Ryegrass for Dairy Cows: Grazing Behaviour, Intake, Rumen Function and Performance at Wageningen University on September 14th.

In highly productive grazing dairy stock, dry matter intake (and consequently protein and energy intake) is a limiting factor in milk production. To augment milk production, grazing dairy cattle are therefore generally given supplements of feed concentrates and energy-rich corn silage.

In his study, Taweel examined eating motivation as well as the capacity and speed of digestion in the rumen of dairy cattle. The first hypothesis was that eating motivation is strongly related to taste, and that tastiness is primarily determined by sugar, i.e., water-soluble carbohydrates (WSC) content. The second hypothesis was that plants with more easily digestible cell walls pass through the rumen faster, and the expectation was that this increased the processing capacity and hence grass intake.

Taweel carried out an experiment in which cows were given cut grass in the shed for two years, and were then allowed to graze in various pastures for two years. At the same time, they were given unlimited quantities of a single variety of perennial ryegrass for periods of two weeks. The varieties were all commercially available and selected for their varying WSC content. The research looked also at the different rates of cell wall degradability.

No significant variations in grass intake or milk yield due to different grass strains were observed. The experiment concluded that WSC levels were irrelevant to the voluntary feed intake of the animals, and that relative differences in degradability of cell walls were very small and offered few perspectives to improve intake. Varieties with a high sugar content did result in reduced ammonia content in the rumen and lower urea levels in milk, which is interesting for N-surplus reduction issues in dairy farms. Recent research at Wageningen University (in partnership with NIZO food research) also showed that cows that are put to pasture and eat fresh grass produce milk with a healthier composition of fatty acids than cows that are fed on silage.

Follow-up research by Taweel into grazing periods and rumen capacity also yielded groundbreaking results. Grazing cows feed during three important periods in a day - early in the morning, around midday and at sunset - during each of which they continuously graze for more than an hour. Interestingly, however, the evening grazing went on for a much longer time than the others. This led Taweel to study the filling up of the rumen, which is considered one of the factors that end a grazing period. He found that the rumen was entirely full only at midnight. This implied that, at other moments during the day, cows stopped grazing long before reaching maximum rumen capacity.

Further research will be necessary to find out the reason for this behaviour. Meanwhile, it is clear that causing cows to use their full stomach capacity could result in higher intake and therefore absorption of energy from fresh grass, and, hence, in increased milk production.


This research has been co-financed by Senter (an agency of the Dutch Ministry of Economic Affairs) and carried out in partnership with Barenbrug Holland BV and Wageningen University (Plant and Animal Sciences).

Hassan Z. H. Taweel will defend his thesis "Perennial Ryegrass for Dairy Cows: Grazing Behaviour, Intake, Rumen Function and Performance" on 14 September 2004 at 16.00 in the assembly hall of Wageningen University at Generaal Foulkesweg 1a in Wageningen.

The Plant Sciences Group of Wageningen UR is a collaboration between:
* Wageningen University, Plant Sciences
* Plant Research International
* Applied Plant Research (PPO)