Basics of veld management: A practical guide for cattle farmers
By Dr D.M. “Mick” Gammon
The cattle farmer has been blessed with the most wonderful crop: grass. It requires no cultivation, no planting, no fertilisation, and no weeding or disease control. It is reaped by unpaid harvesters that process it into a high-quality product and in their spare time they see to fertilisation and soil conditioning. However, grass tends to be taken for granted, with insufficient done to improve or maintain it, or to make the job of the harvesters easier and more efficient. If we take from the veld with insufficient inputs into it, there are costs in the form of depressed animal performance, increased supplementary feed costs and veld deterioration.
- Grass growth and defoliation effects
To manage grass effectively it is important to understand the basics of grass growth and how it reacts to defoliation, which is the removal of leaf. The rate of growth of grasses typically follows a sigmoid, or S-shaped curve, with variation caused mainly by rainfall. At the start of the growing season, grass grows relatively slowly, the growth being produced from food reserves stored in the roots and crowns of the plant during the previous season. As the leaf area increases, the amount of food manufactured in the leaves increases and the rate of growth becomes more rapid. Finally, towards the end of the season, the rate of growth slows down as the food produced is directed towards flowering, seed production and the restoration of reserves in the roots.
During the early period of growth at the expense of root reserves the level of these reserves falls and root development is interrupted. This continues until there is sufficient leaf area to produce a surplus of food over and above requirements of growth. This surplus is translocated to the roots and crowns to restore the level of reserves.
Defoliation of grass at any time during the growing season results in a reduction in nutrient reserves in the roots and crown of the plant, interruption of root development and a loss of vigour. Consider the growth of grass cut four times during the season at monthly intervals. Each time the grass is cut it has to regrow at the expense of root reserves. As each successive cut occurs before the grass can restore reserves, each successive regrowth takes place on a lower level of reserves. In this scenario the total yield from the four cuts is approximately half that from a single cut at the end of the season. The result of this repeated clipping is that the yield in the current year is reduced and, with depleted reserves, the yield in the following year will be reduced. Of course, the quality of the yield from uninterrupted growth will be poorer than that from repeated cuts, so there is always a compromise between yield and quality.
In clipping trials, Barnes found that with two, four, and six cuts per season, the yields were, respectively, 90%, 73% and 51% of that from uninterrupted growth. The degree of the effects of defoliation depends on the frequency of defoliation and severity, which is the height of defoliation. These two factors are inter-dependant in their effects and their combined effect is referred to as the intensity of defoliation. Prolonged intense defoliation results in the death of plants, initially the most palatable plants, and progressive veld degradation, including soil erosion.
As a general guide, management should aim to limit the number of defoliations during the growing season to approximately three to four, or less, and the severity of defoliation to not less than 5 cm for medium height grasses and to 10 cm for tall grasses during the growing season.
Frequency and severity of defoliation are affected by stocking rate, grazing cycle, grazing period, and stocking intensity. Whatever the system of management, the heavier the stocking rate, the greater will be the intensity of defoliation. The longer the grazing period in a paddock, the more likely it is that plants will be re-grazed within the period. With a moderate stocking density and six paddocks in the system, research found that little re-grazing occurred within 7 to 14 days. A grazing trial comparing various combinations found that the yield from 10 days grazing period and 60 days rest treatment, which required 7 paddocks, was 94% of the highest yield achieved with 2 days grazing and 60 days rest requiring 31 paddocks.
- Rest
After defoliation, rest during the growing season results in slow regrowth initially, followed by rapid growth, then slow growth again as the grass approaches maturity, along with flowering and seed production. During this time there is resumption of root growth and restoration of depleted root reserves. However, there is also progressive decrease in nutritive value and palatability as the grass grows, particularly in sourveld.
A short period of rest, such as less than one month, will only allow the period of slow growth to occur and will result in depressed grass production. A satisfactory compromise between yield and quality can be achieved with rests ranging from approximately 40 days in sourveld to approximately 60 days in sweetveld.
To permit restoration of depleted nutrient reserves and encourage root development, occasional rest of 3 to 4 months, or even the entire growing season, may be desirable for most tufted grass species. The need for and frequency of these physiological recovery rests will depend on the veld type, the veld condition and the intensity of defoliation that has occurred. Generous rest can compensate for intense defoliation, but only to a certain extent.
- Stocking rate
Stocking rate needs special attention as it has a greater effect than any other factor of management on defoliation and ultimately veld stability and on animal production and profitability.
Whatever the system of veld management, an excessive stocking rate will result in increased intensity of defoliation and ultimately veld deterioration, and in poor animal performance. Generally, as stocking rate increases gain per individual animal decreases. Initially, as stocking rate increases, gain per hectare increases because the increased number of animals more than compensates for decreased gain per head. However, beyond a certain point increased numbers no longer compensate for the decreasing gain per head, and gain per ha decreases with increasing stocking rate.
It is commonly believed that the optimum stocking rate at which to aim is that at which gain per ha is maximised. This is seldom the case. In sensitive veld types this point is often at a stocking rate at which the veld will deteriorate and so production will not be sustained. Further, maximum profit per ha seldom coincides with maximum gain per ha.
Assuming maximum profit is the object in animal production, then the optimum stocking rate is that at which profit per ha is maximised, provided this is consistent with veld stability. In normal market situations this occurs between the stocking rates for maximum gain per head and maximum gain per ha, and it is usually closer to the former. Economic analyses of stocking rate trials suggests that the economic optimum stocking rate is at a point at which gain per head is more than 90% of the maximum. In practice, a good and conservative approximation can be achieved by adjusting the stocking rate to produce animal performance close to the maximum per head.
An example from Matopos Research Station illustrates these principles. Two breeding herds were run at heavy and conservative stocking rates for four years. The conservative herd was stocked at one animal unit per 7.2 hectares, while the heavy herd was stocked at one unit per 3.5 hectares. The conservative herd achieved a 74% calving percentage compared to 57% for the heavy herd, weaning weights of 189 kg versus 159 kg, and lower mortality rates. While production per hectare was higher at the heavy stocking rate at 26 kg compared to 17 kg, the gross margin told a very different story: $126,089 for the conservative stocking versus only $12,669 for the heavy stocking. At the heavy stocking rate, production was very susceptible to fluctuations in rainfall, whereas at the light stocking rate there was little difference in production between years. By the fourth year at the heavy stocking rate, weaning weight was considerably lower than in year one, indicating veld deterioration.
- Selective grazing
All animals feed selectively to meet their nutritional requirements. Grazers select certain areas, certain species and leafy material of varying heights. This benefits the animal by ensuring maximum nutrient intake and hence performance, but it can have detrimental effects on the grass sward with over or under utilisation. Selective grazing cannot be prevented and efforts to force non-selective grazing result in depressed animal performance and increased pressure on the preferred palatable species. Management should aim to control the intensity of defoliation of the palatable species.
- Soil and moisture conservation
Soil protection is necessary to reduce rain drop action, run off, erosion and desiccation. This protection is provided by ensuring maximum grass cover and a litter cover on the soil surface. The first requirement to achieve this is a vigorous grass sward, provided by application of all the principles of management that will ensure sufficient surplus of grass to become litter. Over-grazing and fire reduce the supply of potential litter.
- Fire effects
Fire will always occur in veld through natural causes, accident or design and it can have beneficial or harmful effects, depending on its timing and management after the fire. Fire can be a good servant but a bad master. This makes it imperative to have adequate fire guards and fire-fighting equipment.
The most important effects of fire include the destruction of potential forage, which can be a problem early in the dry season. However, the removal of old material prevents grasses from becoming moribund, reduces palatability differences in the sward and facilitates grazing of high-quality grass, resulting in improved animal performance. Fire prevents or retards the establishment of bush and tree seedlings and kills a percentage of woody plants. Fire does some damage to grass and yields are depressed, the effects being greatest in early winter burning and burning after grass has begun to shoot. Grazing too soon after a fire can do more damage than the fire itself, except in some sour veld types. Generally, fire should be applied only to vigorous veld and the burnt area should be rested until at least 20 cm of new growth has been produced. The removal of grass cover and litter exposes the soil to rain drop action and results in increased runoff and erosion.
- Bush encroachment
In many veld types the succession tends towards encroachment or thickening of the stand of woody species, particularly under conditions of over-grazing, exclusion of fire and reduction in browsers. Bush encroachment is accompanied by reduction in grass cover and grass production. Reclamation of densely encroached veld may be economically unfeasible. The first approach should be to prevent encroachment in veld that is still in good condition. This can be done by applying grazing management which will ensure maximum grass vigour, by applying occasional hot fires at the end of the dry season when woody plants are beginning to shoot and the grass is still dormant. Inclusion of browsers can help.
- Animal performance
In most situations in Zimbabwe, for beef production to be profitable, the veld must provide the bulk of the nutritional requirements of the breeding herd and growing animals. Good animal performance on the veld is essential for profitable production.
Production levels achieved on veld vary greatly between different agro-ecological regions and between farms within the same region. Research station records at Grasslands, Henderson, Matopos and Tuli provide figures which can be used as guidelines to performance achievable in seasons of average rainfall. In sweetveld it is possible for a 200 kg weaner to reach a marketable weight for slaughter of 460 kg at about 2½ years off the veld alone. In sour and mixed veld this could be achieved with appropriate phosphorus and protein supplementation. Female weaners weighing approximately 200 kg could reach recommended minimum mating weight by just over 2 years. Calving percentages of 80% or higher can be achieved on sweetveld alone, and in sour and mixed veld areas with appropriate supplements.
Intake: The first fundamental requirement for good performance on the veld is that the animals' capacity must be filled with grass. A 450 kg cow grazing dense veld that is 30 cm high can achieve a dry matter intake of 10.3 kg per day with 20,640 bites over 8 hours. In sparse veld only 5 cm high, even with 25,800 bites over 10 hours, the cow achieves only 5.2 kg dry matter intake per day. This illustrates how veld condition dramatically affects both intake and energy expenditure.
Intake by the grazing animal is determined by the quantity and height of the herbage, the quality of the herbage and the scope for selection. Cattle select the more palatable material of higher nutrient value which results in increased intake and higher performance. If the scope for selection is restricted, intake and performance will decrease.
Stocking rate and animal performance: Stocking rate affects the quantity, height, and quality of herbage and hence intake and performance. In the long term, excessively high stocking rate results in loss of grass vigour, decreased grass production and a decrease in palatable species.
There has always been a tendency to stock more heavily in the belief that this will increase profits. This belief is negated by numerous experimental results which demonstrate that profitability can be improved by conservative stocking, as illustrated by the Matopos example discussed earlier.
Stocking intensity: Grazing period, paddock size and herd size affect animal performance interdependently. The combined effects are expressed in the term ‘Stocking Intensity,’ which is the number of animal unit days of grazing per ha in a paddock during the grazing period. In general, as stocking intensity increases, animal performance decreases. In any particular grazing situation, there will be a critical stocking intensity above which animal performance will decline.
Research has provided tentative guides to maximum intensities that will allow good animal performance. For sourveld with a grazing capacity of 3-4 hectares per animal unit, maximum stocking intensities are 10-12 animal unit days per hectare in early growing season, 20-24 in mid-season, and 30-36 in late season. For sweetveld at 8-10 hectares per animal unit, they are 3-5, 7-11, and 10-16 respectively. In practice, paddock size and herd size are usually fixed and the stocking intensity is controlled by the length of the grazing period.
Rest period: If the interval between grazings is too short, the grass may be too short for maximum intake. Research indicates high intake on grass with an extended leaf height of 30 cm. If the interval between grazings is too long, older material of poorer nutrient value is produced, on which intake and animal performance will be reduced. A compromise rest period in the interests of both the grass and the grazing animal could be approximately 35 days for sour veld to approximately 60 days for sweet veld.
Supplementary feeding: During the growing season phosphorus supplementation of breeding stock has been shown to increase calving percentage by 5 percentage points, weaning weight by 10% and steer summer gains by 18 to 45kg, depending on the veld type.
Finishing off veld: Acceptably finished slaughter stock can be produced off sweet veld at 2½ to 3½ years of age with no supplements, and off sourveld at 3½ years with dry season protein and summer phosphorous supplements only. However, if the age of marketing is to be reduced, or if better finish and higher slaughter weights are required, it becomes necessary to provide a summer finishing supplement during the last three to four months on grass.
For optimum nutritional efficiency and cost effectiveness it is important to restrict the veld finishing supplement to a small quantity of highly concentrated feed. As a general guide, the concentrate level should not exceed approximately 0.75% of the animal's weight for early summer finishing, increasing to approximately 1% of body weight for late summer finishing. Gains can be expected to be increased by approximately 0.3 kg per day in the early summer to 0.35 kg per day in the late summer.
Usually, feeding a concentrate on the veld is profitable if it results in a substantially higher priced slaughter grade but not if it results in only a heavier carcass.
Practical considerations for finishing: Select only animals with adequate starting weight to achieve target slaughter weight. Sort into uniform groups, avoiding herds larger than about 100 head. Select paddocks with abundant good quality grass and apply a conservative stocking rate. If finishing in early summer, start with the supplement at least a week before the green flush. Feed at the same time every day with sufficient trough space. Move the feeding site before the area becomes over-grazed, and weigh a marked sample of about 30 animals fortnightly to monitor progress.
- Grazing behaviour
For farmers who herd and night kraal their cattle, some knowledge of the behaviour of unrestricted cattle could be useful in planning to minimise disturbance and improve performance.
Research at Matopos Research Station found that in December grazing started up to 30 minutes before sunrise, progressively starting closer to sunrise through the season, and from mid-June to late October within 10 minutes of sunrise. Cessation of day grazing occurred 10 to 55 minutes after sunset depending on the season.
Usually there were three to four grazing spells during the day, with average lengths of 117 minutes. The time of day when grazing occurred most consistently was between 16:00 and 18:00. The average distance walked per day was 3,726 metres, 83% of which occurred while grazing.
From mid-March to mid-May animals drank once a day and outside this period, twice a day, usually between 11:00 and 12:45. Supplements were usually taken during the same period.
The information in this article is based on extensive research conducted at Matopos Research Station and other research facilities in Zimbabwe, providing practical guidance for cattle farmers on sustainable veld management practices that maximise both animal performance and long-term veld productivity.
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