Jm. O'Connell et al., The effects of cow genetic merit and feeding treatment on milk production,herbage intake and grazing behaviour of dairy cows, IRISH J A F, 39(3), 2000, pp. 369-381
The objective of the present study was to investigate the effects of cow ge
netic merit and grass-based feeding treatment on milk production, herbage i
ntake and grazing behaviour of first lactation Holstein-Friesian dairy cows
. A total of 48 high genetic merit cows (HG) and 48 medium genetic merit co
ws (MG) were assigned, within merit group to three grass-based feeding trea
tments: 1) standard feeding treatment, 2) high concentrate and 3) high gras
s allowance. The HG cows had a higher milk yield (24.7 nu. 21.2 kg/day; P <
0.001), fat yield (0.87 <nu>. 0.82 kg/day; P < 0.05), protein yield (0.81
<nu>. 0.73 kg/day; P < 0.001) and lactose yield (1.14 <nu>. 1.00 kg/day; P
< 0.001) than the MG cows. The milk of the HG cows had lower fat (35.6 <nu>
. 38.7 g/kg; P < 0.01), protein (33.2 <nu>. 34.5 g/kg; P < 0.01) and lactos
e (46.4 <nu>. 47.6 g/kg; P < 0.01) concentrations. The HG cows had a higher
(P < 0.01) grass dry matter (DM) intake. Total grazing time was not affect
ed by cow genetic merit but the HG cows had more (P < 0.10) grazing bouts o
f shorter (P < 0.05) duration. The HG cows also had higher (P < 0.001) biti
ng rates and spent a greater (P < 0.01) proportion of time ruminating than
the MG cows. Offering a higher level of concentrate (Treatment 2) significa
ntly increased yield of milk (P < 0.001), fat (P < 0.05), protein (P < 0.00
1) and lactose (P < 0.001). The higher concentrate feeding treatment also r
esulted in a significantly (P < 0.001) higher lactose concentration with no
effect on fat or protein concentrations. Allocating a higher allowance of
grass (Treatment 3) had no effect on milk production except for lactose con
centration which was higher (P < 0.05). Offering a higher level of concentr
ate reduced (P < 0.001) grass DM intake. Feeding treatments 2 and 3 both re
duced (P < 0.05) the duration of grazing bouts and biting rate during the d
ay.