Sweeter grass does not lead to more milk
Contrary to general expectations, the characteristics of different varietiesof perennial ryegrass such as sugar content do not influence the food intakeof grazing dairy cows. Moreover cell wall degradability characteristicswere not different among perennial ryegrass varieties. Research carriedout by Hassan Z. H. Taweel at Wageningen University shows that an increaseddry matter intake can be achieved by gaining more insight into the regulatorymechanisms behind the maximum use of rumen capacity.
Taweel will be defending his doctoral thesis Perennial Ryegrass for DairyCows: Grazing Behaviour, Intake, Rumen Function and Performance at WageningenUniversity on September 14th.
In highly productive grazing dairy stock, dry matter intake (and consequentlyprotein and energy intake) is a limiting factor in milk production. Toaugment milk production, grazing dairy cattle are therefore generally givensupplements of feed concentrates and energy-rich corn silage.
In his study, Taweel examined eating motivation as well as the capacityand speed of digestion in the rumen of dairy cattle. The first hypothesiswas that eating motivation is strongly related to taste, and that tastinessis primarily determined by sugar, i.e., water-soluble carbohydrates (WSC)content. The second hypothesis was that plants with more easily digestiblecell walls pass through the rumen faster, and the expectation was thatthis increased the processing capacity and hence grass intake.
Taweel carried out an experiment in which cows were given cut grass inthe shed for two years, and were then allowed to graze in various pasturesfor two years. At the same time, they were given unlimited quantities ofa single variety of perennial ryegrass for periods of two weeks. The varietieswere 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 differentgrass strains were observed. The experiment concluded that WSC levels wereirrelevant to the voluntary feed intake of the animals, and that relativedifferences in degradability of cell walls were very small and offeredfew perspectives to improve intake. Varieties with a high sugar contentdid result in reduced ammonia content in the rumen and lower urea levelsin milk, which is interesting for N-surplus reduction issues in dairy farms.Recent research at Wageningen University (in partnership with NIZO foodresearch) also showed that cows that are put to pasture and eat fresh grassproduce milk with a healthier composition of fatty acids than cows thatare fed on silage.
Follow-up research by Taweel into grazing periods and rumen capacity alsoyielded groundbreaking results. Grazing cows feed during three importantperiods in a day – early in the morning, around midday and at sunset – duringeach 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 consideredone of the factors that end a grazing period. He found that the rumen wasentirely full only at midnight. This implied that, at other moments duringthe 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 capacitycould result in higher intake and therefore absorption of energy from freshgrass, and, hence, in increased milk production.
NOTE FOR THE EDITOR
This research has been co-financed by Senter (an agency of the Dutch Ministryof Economic Affairs) and carried out in partnership with Barenbrug HollandBV and Wageningen University (Plant and Animal Sciences).
Hassan Z. H. Taweel will defend his thesis Perennial Ryegrass forDairy Cows: Grazing Behaviour, Intake, Rumen Function and Performance on 14 September2004 at 16.00 in the assembly hall of Wageningen University at GeneraalFoulkesweg 1a in Wageningen.
For more information, contact:
Wageningen University
Edwin Luijks, tel: +31 (0)317 483915, e-mail: edwin.luijks@wur.nl
Questions concerning content:
tutor Seerp Tamminga, e-mail: seerp.tamminga@wur.nl
co-tutor Anjo Elgersma,e-mail: anjo.elgersma@wur.nl
or Jan Dijkstra, e-mail: jan.dijkstra@wur.nl