Very few studies have recorded grass intake during the early spring (March/April) period. Intake will be generally lower during this period for three main reasons.

Firstly, the DM content of grass can significantly effect herbage intake at pasture (Forbes, 1995; McGilloway and Mayne, 1996). The grass nutrient content will be markedly diluted by the presence of water, which is predominantly intra-cellular in nature and thus makes a large contribution to the bulk of the diet (McGilloway and Mayne, 1996). The water content of fresh herbage includes both the internal and surface water. Verite and Journet (1970) feeding the same grass, fresh or dried, reported that the water content limits voluntary intake of dairy cows below a DM concentration of 18%, with a decrease of 0.34kg DM for each percentage drop in DM. In an experiment with zero-grazed dairy cows they found that herbage intake decreased by 0.21kg DM for each percentage drop in DM below 15%. Average dry matter content of pasture can vary from 15% in spring to 25% in mid-summer (McGilloway and Mayne, 1996) but can fall to, as low as 10-12% during wet weather. Reasons suggested for the decrease in intake at low dry matters include, physical limitations from excess water in the rumen or from water content entrapped in the cell structure, behavioural limitations related to rate of intake or simply reduced palatability from herbage surface water (Demment et al., 1995).

Secondly, this decrease in DM intake is compounded by the interaction of "adverse grazing conditions" during wet weather. These include, poaching effects, grass soiling etc and occur frequently during the early spring and especially during "late springs". These latter effects increase in importance, the further north and west you go in Ireland. Dillon et al. (1997) attributed the low daily grass intakes to poor grazing conditions and inclement weather in the early part (May) of their study.

Thirdly, the fact that cow voluntary intake is minimal at calving and then increases slowly (a lag relative to milk yield) until it peaks during the third month of lactation (Coulon et al., 1989) or between 10-16 weeks after calving (Murphy and Fitzgerald, 1998) means that grass intake capacity of spring-calving cows is relatively lower during this period, all else being equal.

It can be suggested that grass intake in the early part of the year is the most important factor in terms of energy balance and reproductive performance of the spring-calving dairy cow, especially with high genetic merit animals.