
%0 Journal Article
%A Wales, W. J. 
%A Doyle, P. T. 
%A Dellow, D. W. 
%T Dry matter intake and nutrient selection by lactating cows grazing irrigated pastures at different pasture allowances in summer and autumn
%J Australian Journal of Experimental Agriculture
%D 1998/09/18
%V 38
%N 5
%P 451-460
%K 
%R https://doi.org/10.1071/EA98043
%U https://www.publish.csiro.au/paper/EA98043 
%X Summary. Three experiments investigating the effects of herbage allowance on the consumption of nutrients by lactating cows were conducted on irrigated perennial pastures in northern Victoria during summer and autumn. Experiment 1 was conducted in mid lactation (autumn&#8211;early winter) with perennial ryegrass &#91;54% of dry matter (DM)&#93;&#8211;white clover (22% of DM) pasture offered at allowances of 15, 20, 30 and 40 kg DM/cow.day. Herbage intake increased (P&#60;0.001) from 8.0 to 14.6 kg DM/cow.day as allowance increased and this was associated with a decrease (P&#60;0.001) in utilisation from 54 to 37%. The cows consistently selected a diet 11% higher in in vitro dry matter digestibility than that in the pasture on offer, but selection for crude protein increased (P&#60;0.001) from 21 to 41% above that in herbage on offer as herbage allowance increased. Neutral detergent fibre content of the diet selected was lower (P&#60;0.001) than that in herbage on offer. Along with these changes, milk production increased (P&#60;0.001) from 9.0 to 15.5 kg/day as herbage allowance increased at a marginal response of 0.99 kg milk/kg extra DM consumed. Experiments 2 and 3 were conducted in mid lactation (summer) on pasture containing 28% paspalum, 26% weeds, 17% perennial ryegrass or 36% paspalum, 19% weeds and 24% ryegrass respectively. Pasture allowances were between 20 and 70 kg DM/cow.day. Herbage intake increased (P&#60;0.001) from about 8 to 17 kg DM/cow.day as allowance increased in both experiments and was accompanied by a decrease (P&#60;0.001) in utilisation from about 40 to less than 25%. In experiment 2, the cows consistently selected a diet with a similar in vitro dry matter digestibility to that of the herbage pregrazing, regardless of allowance, but selection for crude protein increased (P&#60;0.05) from 25 to 45% above that in herbage on offer, as allowance increased. In experiment 3, the diet selected was 13% greater (P&#60;0.001) in in vitro dry matter digestibility and 42% greater (P&#60;0.001) in crude protein than the herbage on offer. Neutral detergent fibre content of the diet selected was lower (P&#60;0.001) than that in herbage on offer in experiment 3, while the difference was small in experiment 2. Along with these changes, milk production increased (P&#60;0.001) (in experiment 2, 12.3&#8211;15.0 kg/cow.day; experiment 3, 10.0&#8211;15.8 kg/cow.day) as herbage allowance increased, but the marginal responses were lower (0.28 kg milk/kg extra DM consumed in experiment 2, 0.64 kg milk/kg extra DM consumed in experiment 3) than observed in experiment 1 reflecting the differences in pasture quality. 
