Studies in pasture utilization by the grazing animal

It is shown that information was required on the factors affecting the daily herbage intake of grazing cattle, and methods of estimating herbage intake under grazing conditions are reviewed. A new method which was devised is described by which the herbage dry matter intakes of individual cows in small plots were to be determined from the difference between the yields of herbage before and after grazing periods of 24- hours duration. The yields were to be estimated from herbage samples clipped by hand to ground level. The aim of this method was (a) to eliminate bias, (b) to allow the determination of the errors of the estimates by analysis of variance and (c) to achieve precision by replication of both cows and days. Five grazing experiments are described in which this method was used to estimate the herbage intake of Ayrshire cattle of various body weights and milk yields when grazing swards of various qualities and yields per acre. In the last of these the effects of supplementary feed on herbage intake and milk production are also reported. A sixth experiment is described in which herbage of a similar quality to that provided in the grazing experiments was cut and fed fresh or dried to housed cattle in order to compare their rate of intake with that estimated at pasture. Finally some data on the effects of excrements on pasture utilization are given and an estimate is made of their probable effects at various intensities of stocking. The results are discussed with reference to the results reported by other workers, and it is concluded that the method of intake estimation used here gives a higher degree of precision than most other methods and is relatively free from bias. The present experiments are cori5)ared and it is shown that although the daily dry matter intake of the cattle was in general related to their body weight, there were differences in intake iDetween individual cows which were related to their stage of lactation and milk yield. Their herbage intake increased with increasing yields of herbage per acre but decreased with a heavier rate of stocking per acre. Supplementary feed gave only slight increases in milk yield and depressed the intake of herbage in poor grazing conditions. The dry matter content of the herbage was found to have no influence on the amounts of herbage consumed, but the cows varied their water consumption from day to day so as to maintain an almost constant ratio between dry matter and total water consumption. It is concluded that the effect of herbage yields and of stocking intensity on intake and the low general level of dry matter intake which was found relative to accepted feeding standards may be ascribed to the effects of the grazing system on the quality of herbage consumed. The need is suggested for studies on the optimal stage of growth of pasture herbage required to gain maximal outputs of animal produce per acre