agricultural production guidelines
m
Veld in KwaZulu-Natal
Co-ordinated Extension KwaZulu-Natal Veld 8.1 1999
FACTORS AFFECTING ANIMAL PERFORMANCE
D M Gammon
Agric Foods (Pvt) Ltd, P.O. Box 559 Bulawayo, Zimbabwe
Good Performance Norms
The Task of Grazing
Factors Affecting Performance
Management for High Performance
INTRODUCTION
Good performance of grazing animals is a pre-requisite for maximum profits and economic production. This involves good mass gains by animals on veld, which are reflected in high mass to age ratios, good animal condition, and high conception rates.
In virtually any veld type that is in good condition, a mass gain of approximately 1 kg/day is possible in growing cattle in early summer (figures which are quoted in excess of this are usually a result of increased gut fill). As the season advances the rate of gain decreases due to the decline in nutritive value of the veld, compounded by reduced intake by the animal as the palatability of the grass declines. This decrease in gain is rapid in sourveld, and, by winter, mass losses usually occur.
In sweetveld the decrease in gain is less rapid, and a slow gain, or approximate maintenance, may be recorded through the winter. Table 1 presents examples of good mass gains that have been recorded from growing animals at various sites in KwaZulu-Natal on well-managed veld. In each case, the animals had been wintered previously at approximately maintenance to take advantage of compensatory gains.
There is little difference in the gains of different age groups, but heifer gains are approximately 90% of those of steers. The total gain of a cow and its calf over the growing season should be at least 50% higher than that of growing animals. For example, 190 kg would be a good gain for a cow plus calf (this excludes calf mass at the start of the season) in most sourveld and mixed-veld areas.
In order to manage the grazing animal for high performance it is important to appreciate what is involved in grazing. A 450 kg cow has a potential daily intake of about 10 kg of dry matter (DM), or about 30 kg of green grass. For good economical performance it is essential that the animal's capacity for grass is met. The cutting surface of a cow's teeth, however, is less than 8 cm wide, and the amount of grass that can be taken per bite from veld in ideal grazing condition is only about 0.5 g DM. This means that to achieve an intake of 10 kg DM the animal has to take approximately 20 000 bites per day.
Table 1. Mass gains of yearling steers on various veld types in KwaZulu-Natal.
Veld type
Stocking rate (ha/AU)
Average daily gain
Total summer gain (kg)
Nov
Dec
Jan
Feb
Mar
Apr
May
Jun
Highland Sourveld (moist)
1.5-2.01
1.0
1.0
0.7
0.5
0.4
0.3
0.1
-
121 (Nov-May)
Highland Sourveld (dry)
2.2-2.52
1.0
0.7
0.7
0.6
0.5
0.2
0.0
-
112 (Nov-Apr)
Moist Tall Grassveld
2.5-3.53
1.0
1.0
0.6
0.5
0.6
0.5
0.2
-
133 (Nov-May)
Dry Tall Grassveld
3.53
0.9
0.8
0.6
0.5
0.5
0.3
0.0
-
109 (Nov-Apr)
Lowveld
5.04
1.0
1.2
1.0
1.0
0.9
0.7
0.4
0.2
194 (Nov-Jun)
1
With mineral supplement (M B Hardy, personal communication)2
With mineral supplement (Kokstad Research Station, Report N-Ko 5/2)3
With mineral supplement; urea lick from March (J R Turner, personal communication)4
No supplement (J R Turner, personal communication)
Under favourable veld conditions, cows spend approximately 8 hours grazing, and a further 8 hours ruminating, leaving 8 hours for rest. The biting rate during the period of grazing is approximately 1.4 seconds/bite. Grazing is, therefore, an enormous task, and veld management has to ensure favourable grazing conditions if high intake and good performance are to be achieved.
There are a number of factors, beyond the control of the manager, which affect the performance of grazing animals (e.g. veld types differ in potential, the time of year affects performance). Performance also varies from year to year, depending on such factors as amount and distribution of rainfall, temperatures, and the occurrence of frost. There are, however, certain factors which can be influenced by management. These are discussed below.
The effects of the height and quantity of herbage available (kg DM per ha) on animal performance are interrelated. In general, dry matter intake, and hence performance, tends to increase at a progressively decreasing rate with increasing quantity and height of herbage, and then declines again beyond a certain level. In veld of a certain density, the height of herbage, rather than the quantity, is usually the factor of immediate importance. No specific information is available on the optimum heights for veld grasses, but this may vary from about 200 mm extended leaf height in dense sourveld to over 300 mm in sparse sweetveld.Quantity and height of herbage
Quality of herbage
The quality of herbage refers to its palatability, nutrient content and digestibility. Intake of grass is controlled by the rate of digestion, and so, as digestibility decreases, intake also decreases. Quality in veld thus has a compound effect on performance. As quality declines, the digestible nutrients in a given amount of material grazed by the animal also decrease, digestion is slowed down, and thus the intake is decreased.Herbage quality is also interrelated with quantity and height of herbage. The leveling off or decrease in intake beyond a certain quantity or height of herbage is largely attributable to declining quality. Due to these effects, performance can be poor on abundant but low-quality herbage, and thus procedures which produce increased herbage yields do not necessarily produce proportional increases in animal production.
Scope for selection
Cattle and sheep, in common with other herbivores, feed selectively, although there are differences in the material selected and the degree of selection. They select certain areas in preference to others (area or site selection); they select certain species in preference to others (species selection); and they select certain plant parts, such as leaf in preference to stem, or green leaf in preference to dead leaf (plant part selection). The more palatable material of higher nutritive value is selected and this results in higher levels of intake and animal performance than would be achieved were animals not selective.The effect of palatability is such that intake has been shown to vary by more than 50% on pastures of different species. It has often been demonstrated that production declines towards the end of a period of grazing, even when there is still ample herbage of suitable height, due to reduced scope for selection. If the scope for selection is restricted and animals are forced to graze unpalatable grass, intake and performance will decrease.
MANAGEMENT FOR HIGH PERFORMANCE
Veld management influences each of the above factors, and thereby has a very marked effect on animal performance. The most important aspects of management which affect performance are discussed below.
Stocking rate affects animal performance more than any other factor, and, because of its importance, it is dealt with specifically in Production Guideline 8.2 in this series. Generally, as the stocking rate increases, individual animal gains decrease linearly. This is because increasing stocking rate results in a reduction in the quantity and height of herbage available and reduces the scope for selection. In the longer term, excessive utilization resulting from increasing stocking rate leads to reduced grass vigour, and an increase in the proportion of less-palatable and/or less-productive species. Once again, this results in reduced intake and performance.Stocking rate
The most important factor in veld management is the application of that stocking rate which results in maximum, sustained profit.
Period of stay or occupation : camp size :
herd size
Any one of these factors will affect performance if
the others are kept constant. Increasing the period for which a given herd is
kept in a camp (period of occupation or period in) will result in reduced animal
performance because the quantity and height of grass, and the scope for
selection, will be reduced. Similarly, a reduction in camp size will result in
poorer animal performance if herd size or period of occupation is not reduced,
even if the total area grazed is unchanged (i.e. in a system with more camps per
herd). Increasing herd size, with the period of occupation and camp size kept
constant, will also result in reduced animal performance, even if the number of
camps and the total area are increased to maintain the
same overall stocking rate.
Table 2. Tentative guide to maximum stocking intensities and periods of occupation (period in) for good animal performance on veld in good condition at different times in the grazing season.
|
Grazing capacity (ha/AU) |
Spring to early summer |
Remainder of season |
|||||||||||
|
Stocking intensity (AU d/ha)1 |
Camps per herd |
Stocking intensity (AU d/ha) |
Camps per herd |
||||||||||
|
3 |
4 |
5 |
6 |
8 |
3 |
4 |
5 |
6 |
8 |
||||
|
1 2 3 4 5 6 7 8 |
28 14 9 7 6 5 4 3 |
9 9 9 9 9 9 9 9 |
7 7 7 7 7 7 7 7 |
6 6 6 6 6 6 6 6 |
5 5 5 5 5 5 5 5 |
4 4 4 4 4 4 4 4 |
56 28 19 16 14 13 11 10 |
19 19 19 21 23 27 27 27 |
14 14 14 16 18 20 20 20 |
11 11 11 13 14 16 16 16 |
9 9 9 11 12 13 13 13 |
7 7 7 8 9 10 10 10 |
|
1
Animal Unit days per ha.The effects of herd size, camp size and period of occupation are interdependent, and their combined effect is best expressed in the term stocking intensity. This refers to the number of animal unit days of grazing per hectare in a camp during the period of occupation. The stocking intensity is calculated by multiplying the number of animal units (AU) in the herd by the number of days they are in the camp, and dividing by the area of the camp.Stocking intensity
For example, a herd of 100 cows (assume 1 lactating cow = 1.2 AU), and 100 calves (assume 1 calf = 0.3 AU) grazes a camp of 100 ha for 10 days.
Herd size = (100 x 1.2) + (100 x 0.3) = 150AU
Stocking intensity = (150 x 10) / 100 = 15.0AU days/ha
In general, as the stocking intensity increases, animal performance decreases. In any particular grazing situation there will be a critical stocking intensity above which animal performance will decline, and this will vary according to several factors.
- The inherent grazing capacity of the veld: the higher the grazing capacity, the higher the stocking intensity that can be tolerated.
- Veld type and condition: the higher the proportion of palatable grasses, the higher the stocking intensity can be.
- Time of year: in spring and early summer, when the quantity and height of grass may be limiting, the stocking intensity should be reduced, and as the season advances it can be increased.
Little information is available from which to draw recommendations on stocking intensities. Table 2 provides a tentative guide to maximum stocking intensities that will allow good animal performance in veld of varying grazing capacities in the earlygrazing season and for the remainder of the season.
In practice, camp sizes are fixed and the herd size is usually constant, so that the stocking intensity is controlled by the period of occupation. The periods provided in Table 2 apply only to camps of average size. For camps larger or smaller than average the appropriate period of occupation can be calculated from the required stocking intensity figure:
Days in = (stocking intensity) x (camp area) / (herd size)
or by simple proportion:
Days in = (total days to graze all camps) x (camp area) / (total area)
If the herd size is changed, the appropriate period of occupation can be calculated from the first equation above. Some camps may have a lower grazing capacity than others due to poor veld condition or a poorer veld type. In such cases, records and experience should be used as a guide to suitable periods of occupation.
Grazing cycle and period of
absence (period out)
If the interval between grazings is too long, older
material of poorer nutritive value accumulates, resulting in poor animal
performance. For this reason the grazing cycle (time taken to complete one
rotation through all the camps in the system) should not exceed approximately 40
days (sourveld) to approximately 80 days (sweetveld). Alternatively, the period
animals are out of a camp should not exceed approximately 35 days (sourveld) to
approximately 80 days (sweetveld). The grazing cycle is simply the product of
the number of camps and the period of occupation, while the period of absence is
the product of the number of unoccupied camps at any time and the period of
occupation. These factors are therefore not independent of the period of
occupation, and the adverse effects of a long period of occupation are simply
added to by the consequent long periods between grazings.
Herd size, composition and
handling
Animals generally perform best in small herds
consisting of a single age group and sex. In such groups, social dominance
effects are reduced and individuals receive a fair share of supplements, which
also can be supplied according to the requirements of a particular category of
animal. The handling time for various operations is reduced with small groups so
that interference with normal grazing routines is minimised. Usually a
compromise has to be reached between the number of groups that may be desirable
for animal management and performance, and the number of groups desirable for
good veld management with the number of camps available. The maximum herd size
that is desirable varies according to the efficiency of handling facilities and
of handling, and the uniformity of the animals. Ideally, groups should not
exceed approximately 150 breeding cows, or 300 head of young stock.
Mixing different animal species (e.g. cattle, sheep, goats, various game species) may result in improved performance of individual species and increased total production. The optimum ratios of different species varies in different veld types (refer also to Production Guideline 8.3 in this series).
Supplementary feeding and
compensatory growth
In sour and mixed veld, animal performance is limited
by deficiencies of protein, and/or energy, and/or minerals such as phosphorus,
depending on the time of year and the level of performance required.
Supplementation with these nutrients may therefore have a marked effect on
performance (refer to Production Guideline 9.6 in this series).
The summer performance of grazing animals is also affected by their level of performance during the previous winter. Due to the phenomenon of compensatory growth, animals on a relatively low plane of nutrition during winter will gain more in the following summer than animals wintered on a higher plane of nutrition. High levels of winter feeding may therefore often be uneconomical.
LITERATURE CONSULTED
ALLDEN, W.G. & WHITTAKER, I.A.M. 1970. The determinants of herbage intake by grazing sheep : The interrelationship of factors influencing herbage intake and availability. Australian Journal of Agricultural Research 21 : 755 - 766.
DENNY, R.P. & BARNES, D.L. 1977. Trials of multi-paddock grazing systems on veld. 3. A comparison of six grazing procedures at two stocking rates. Rhodesian Journal of Agricultural Research 15 : 11 - 23.
HODGSON, J. 1982. Influence of sward characteristics on diet selection and herbage intake by the grazing animal. In: Hacker, J.B. (ed.). Nutritional limits to animal production from pastures. Farnham Royal, U.K. : C.A.B.
STOBBS, T.H. 1973. The effect of plant structure on the intake of tropical pastures. Australian Journal of Agricultural Research 24 : 809 - 819.