Theme 09: Forage Quality
Description
This experiment is one of a series designed to investigate the efficiency of nitrogen (N) use in Holstein-Friesian dairy cows grazing perennial ryegrass (Lolium perenne) which has been bred to express high water soluble carbohydrate (WSC) concentrations. Animals grazed either a High Sugar (HS) grass or a Control (C) variety chosen on the basis of heading date compatibility. Dry matter (DM) intakes were estimated using herbage mass. Milk yields, milk constituent concentrations and plasma concentrations of b-hydroxybutyrate, glucose, total protein, albumin and urea were also measured. Forage DM intakes were similar for the two grasses. However, because of differences in the nitrogen content of the varieties (128 vs 176 g crude protein (CP) kg-1 DM; s.e.d. 10.5; P < 0.01) the animals consuming the C diet received ca. 35% more dietary N. Despite this, milk yields and outputs of milk fat, lactose and total protein were similar between treatments. These data indicate that the partition of dietary N for milk protein biosynthesis was much higher (P < 0.01) in animals consuming the HS grass, which is reflected by the lower plasma urea concentrations in these animals. It is proposed that by providing grass varieties with a better match of readily available energy and protein, significant improvements in N use efficiency can be achieved.
Included in
Efficiency of Nitrogen Use in Dairy Cows Grazing Ryegrass with Different Water Soluble Carbohydrate Concentrations
This experiment is one of a series designed to investigate the efficiency of nitrogen (N) use in Holstein-Friesian dairy cows grazing perennial ryegrass (Lolium perenne) which has been bred to express high water soluble carbohydrate (WSC) concentrations. Animals grazed either a High Sugar (HS) grass or a Control (C) variety chosen on the basis of heading date compatibility. Dry matter (DM) intakes were estimated using herbage mass. Milk yields, milk constituent concentrations and plasma concentrations of b-hydroxybutyrate, glucose, total protein, albumin and urea were also measured. Forage DM intakes were similar for the two grasses. However, because of differences in the nitrogen content of the varieties (128 vs 176 g crude protein (CP) kg-1 DM; s.e.d. 10.5; P < 0.01) the animals consuming the C diet received ca. 35% more dietary N. Despite this, milk yields and outputs of milk fat, lactose and total protein were similar between treatments. These data indicate that the partition of dietary N for milk protein biosynthesis was much higher (P < 0.01) in animals consuming the HS grass, which is reflected by the lower plasma urea concentrations in these animals. It is proposed that by providing grass varieties with a better match of readily available energy and protein, significant improvements in N use efficiency can be achieved.
