The utilization of irrigated pastures by dairy cows II. The effect of stocking rate

Abstract

In an earlier experiment (Freer, 1959) it was found that the efficiency of year-round pasture utilization by dairy cows on irrigated pasture was no greater with a strip-grazing system (twice daily shifts) than with a rotational grazing technique (5-to 7-day shifts). The results of that experiment, in which both treatments were maintained at the same overall stocking rate, were discussed in relation to experiments of other workers in which differential stocking rates had been used. It became apparent during the experiment at Werribee (and has been suggested by McMeekan & Hancock (1954) and McMeekan (1956) who obtained similar results from experiments in New Zealand) that the increased production per acre from strip grazing, that has been reported by others, was probably due to the effect on grazing efficiency of stocking rate per se rather than of the grazing management technique. In the earlier paper of this series the necessity for considering the effects of these two factors separately was stressed.In view of this, an experiment was designed to compare the efficiency of pasture utilization at two rates of stocking by milking cows on irrigated pasture, using the same grazing technique at both stocking rates. As there can be little question of the fact that animal production per acre will increase with stocking rate up to the point where the production of the individual animal is depressed through depression of nutrient intake, two stocking rates were chosen for this experiment which were at levels estimated to be at or about this point and above it.The experiment ran for two complete grazing seasons-1955-56 and 1956-7-and during these periods the treatments were compared on the basis of the animal production obtained from pasture. At the beginning of the second season the stocking rates on both areas were raised, to extend the range of the information obtained during the first season. Supplementary information was obtained on the effect of these treatments on the pastures, on the herbage intake of the cows, and on their grazing behaviour. EXPERIMENTALThe general features of the design of the experiment were as follows.(1) The two groups of cows were of equal size and grazed on unequal areas of pasture. During the first season the two stocking rates were 1-0 and 1-7 cows/acre, and during the second season 1-2 and 2-0 cows/acre (on irrigated dairy farms in Victoria a stocking rate of over 1-0 milking cows per acre is considered high). The two groups (known as the L and H groups, respectively) remained on their respective areas throughout the experiment.(2) The same grazing technique, rotational grazing, was used on both areas and the management was identical in all respects other than stocking rate.(3) The herbage that was surplus to immediate grazing requirements was conserved as hay (from the same proportion of both grazing areas) and fed back to the appropriate cows in the autumn so that the pasture utilized in each treatment could be assessed solely in terms of animal production. Cows usedAt the start of the f...

The effect of daily herbage allowance and sward characteristics upon the ingestive behaviour and herbage intake of calves under strip‐grazing management

“…Continuously-stocked sheep increase grazing time to compensate for low rates of intake (Allden, 1962;Arnold, 1964). The grazing time of rotationally grazed cattle also tends to increase on short swards (Hancock, 1954;Freer, 1960), though Chacon and Stobbs (1976) found that the grazing time of their cows first increased, and then declined as Setaria swards were grazed down progressively over 10-14 d. The reduction in grazing time at low allowance in both experiments (Table 6) was therefore unexpected, though it is substantiated by recent evidence for strip-grazed dairy cows (Combellas and Hodgson, 1979;Le Du et al, 1979).…”

Grazing Management for Beef Production*

“…The main factor which can infiuence production per acre is stocking rate, but to achieve maximum production per acre, liveweight gain per animal is reduced. This has been demonstrated by many workers for both dairy and meat-producing animals (2,20,26,28,30,31,32,38,39). With dairy cattle, where the final product is milk, the intensity of stocking should be taken to the level where maximum production per acre is achieved, provided such treatment does not impair subsequent lactations, calf birth-weight and performance.…”

Strip Grazing Versus Paddock Grazing Under Tropical Conditions

“…In one of the earlier trials Holmes et al (1) found a 20-40% increase in production per acre from strip grazing in relation to paddock rotational grazing, when a 30% higher stocking rate was used in the former treatment. On the other hand McMeekan (9) and Freer (2) were unable to repeat this difference consistently when common treat-ment stocking rates were used. Lucas and McMeekan (8) and Line (7) have recently reported on experiments designed to diiferentiate between the contributions of stocking rate and grazing management to the differences obtainable from these two management systems.…”