The veld, the trees and the grass, is intimately bound up with the animals which graze upon it. The well-being of the vegetation as it exists is dependent upon the grazing animal. The well-being of the grazing animal is dependent on the vigour of the veld. Neither is more or less important than the other. The point must be made here that it is interdependence rather than a dependence by one member upon the other.
In this lecture, we shall consider the various aspects of animal behavior in relation to grazing management. Let us first talk about feed intake. Basically, the reason that animals are kept on grazing is to get them to take in as much nourishment as possible. Generally, the higher the nutrient intake, the higher the production, or the higher the production, the greater the efficiency per unit of intake. Let us look at this in a little more detail. If you have a veld which is of poor nutritional value, then, irrespective of the intake, there is going to be little marked production by the livestock. On the other hand, if you consider a high level of nutrition within the veld, then obviously there is going to be a high level of performance by those animals grazing under those conditions.
Sheep and cattle are primarily converters of pasture and of veld, and this is a very inefficient process, both in intake and conversion. What we ought to do now is to look at the factors influencing the intake, then we shall take a look at the animal factors and at the nature of the feed factors, and finally we shall look at the water distribution and the grazing factors.
2. FACTORS INFLUENCING FOOD INTAKE
Animal Factors: Amongst individuals there is a big variation, depending on body size andindividuality, in the ratio of intake, rumination and digestion. For example, young animals tend to eat 10% to 15% more per kg of body mass. Older animals tend to eat less and also if you compare the difference in intake between a large animal of one species, for example, a cow, and a small animal of another species for example, a sheep, then you can quite easily see that there is variation in the intake.
Lactation: Here we differentiate between the lactation. Lactating cows do not eat the same amountof dry matter throughout the lactation. They start off by eating approximately 70% of the daily re-quirements and this increases up to about 100% after day 20 of the lactation and then it decreases slowly as the calf increases in size prior to the onset of the next lactation.
Pregnancy: Intake does -vary with the stage of the pregnancy. At the beginning of the pregnancy,the intake is normal, but towards the end of pregnancy, when the fetus is fairly large, the intake will be reduced.
Degree of fatness: It has been shown that the very fat animals tend to eat less than the very thinanimals, so this is a factor which should also be considered.
Herd Influence: This covers stocking pressure, herd size, class of animal and species of stock. Thereis very definitely what we refer to as a ‘butting order’. Now this is a factor where the older animals tend to bully the younger animals, and even within, the same group and age there is very definitely a ‘butting order’.
Ruminants on forage differ from men, fowls and pigs, all of which tend to eat a constant energy intake. In ruminants, this depends to a large extent on the quality and type of feed. Let us look at these factors:
Digestibility: The amount of fiber affects the rate of digestion, hence the rate of passage and so therate of intake of fresh food. If a food is high in fiber, then it is low in digestibility.
Chemical Composition: At the same level of digestibility, different forages may be eaten in differentamounts. For example, there might be pH differences. This results in higher or lower rates of digestion. Also the nitrogen status of the feed will affect intake. Nitrogen, as used here, is in the form of protein.
Moisture Content: Forages with a higher proportion of moisture, contents reach the digested stagemore rapidly, and are therefore eaten in greater amounts; for example, silage, or young green grass, as compared to dry grass.
Palatability: As this obviously affects intake, it is an integral part of feeding value of a forage. If aparticular forage is unpalatable then the animals will be inclined to reduce their intake of that particular forage.
- GRAZING FACTORS INFLUENCING FOOD INTAKE BY THE ANIMAL
Here we have to look at a few other factors which affect the intake.
Herbage Availability: The height of the grass, the distance to water, the shape of he paddock andstocking pressure all affect the rate of intake of feed in one way or another. Let us say, for example, that within a paddock water is not readily available. This factor alone could restrict the harvesting of forage to a short distance around the water point. In this case, if the paddock is correctly stocked, there might be a reduction in the amount of forage immediately available, and animals will reduce their intake. Let us consider the height of the grass. If the grass is extremely high, for example, Hyparrhenia rufa, which grows up to about 2 or 3 meters, then again you can assume that intake is going to be affected adversely. If the grass is extremely short, i.e. about 6 or 8 cm, then again the intake is going to be affected adversely. If it is a mixed sward, of average height, then the intake will be high.
Sward Type and Structure: Bunch or runner grasses, dense or sparse, dormant or growing, speciescomposition and opportunities for selection are all factors which can affect intake. Let us look at these one by one.
Tufts or Runner Grasses: runner grasses tend to grow low to the ground and if the fertility is right,these can grow a little higher, in which case the intake could be high,
With tufts (or bunch grasses), when the tufts are young, intake is high. With many grass species, tufts become less palatable as they mature, so intake will be lower. If there is a lot of dead grass mixed in with new growth in tufts (i.e. top hamper) intake will be reduced because the animal is trying to avoid the dead grass while it is grazing. This does not happen with runner grasses.
Dense or Sparse: obviously if the grass is dense or if the population of the grass is dense, then theintake will be high per unit area. If it is sparse, then it will be low for the same unit area.
Dormant or Growing Grasses: we know that dormant grasses tend to be unpalatable and thereforethe intake is low. On the other hand, growing grass, which is lush, does tend to be more palatable. In this case, the intake would be high.
Species composition: some species are palatable; others are unpalatable. Where this occurs then the animals will be inclined, to select the palatable type species. Animals are selective grazers and this means that they tend, under natural conditions, to select the grasses which are more palatable.
Fouling: Generally speaking, this factor is observed only on pastures where the area is small, and thestocking pressure is high. Fouling does affect the intake and this is not normally associated with veld grazing situations. Fouling, of course, is the deposited residue by the animals on the grass.
Weather Conditions: Here we refer specifically to temperature, wind and rain. We will not go intothese factors in any great detail. However, when considering the data, one should at all times ask the following questions: How many of these factors are significant under our situation? Do any of them cancel others out? How much does the overall benefit of any grazing system make up for its deficiencies? One can spend a lot of time talking about these factors, but one can say that high temperature affects grazing adversely. Wind could affect it either way, and rain could affect it equally. But again, one should be aware of the effects being cancelled out by other factors. We must now look at the animal factors in a little more detail, that is, the mechanics of grazing.
4. ANIMAL BEHAVIOUR FACTORS
The Mechanics of Grazing: Research has shown that, from jaw structure and lip thickness, theclosest a bovine can graze to the ground is about 1.25 cm. With sheep and goats the lips are parted and this enables the incisor teeth to nip off the grasses right at ground level. Grazing action varies with grass length. Where the grass is greater than 20 cm the bovine crops the grass, where the grass is less than 20 cm, the tongue action becomes prevalent where the animal is actually pulling and biting at the same time. What do we mean when we talk about biting time? Feed intake is affected by 1) the number of bites per minute and 2) the duration of continuous biting time. On a perfect short sward, 30 to 90 bites per minute have been recorded and up to 30 minutes continuous duration on a perfect sward. On succulent feed, animals eat a great amount at a faster rate. Low fiber feeds are the more palatable.
Grazing Time: There appear to be upper limits of how much of a 24 hour day a cow will spendgrazing. Johnston Wallace (1944) at Cornell University, observed that, in one day, the time spent by a dairy cow in her harvesting (that is the grazing of grass and walking) never exceeded 8 hours even when grazing went off. Bonsma and La Rue at Mara Research Station (1940) also observed a grazing time of 8 to 9 hours. Subsequent work in various -other countries indicate that cattle will graze for even longer periods when the amount of available forage declines below 750kg per hectare. Normally, at least 60% of the grazing time occurs during day-time.
Rumination Time: Generally, this is similar to grazing time, but is proportionately longer on poorerquality forage.
Routine: The natural undisturbed routine of cattle is grazing, then idling, then ruminating. There arehereditary differences in grazing time;
- between individuals and;
- between breeds.
Sound selection policies based on performance will take these differences into account, thus ensuring that you have a herd which is going to derive maximum benefit from whatever forage is available.
Grazing Periods: Usually there are two main meals per day, after sunrise and before sunset and for a while afterwards. Minor snacks are taken at midmorning, in the early afternoon and perhaps a bit at night.
Herd Group Behaviour: In general, a herd functions as a unit, that is, all individuals seem to carry outthe same activity at the same time. There appears to be a kind of majority decision as to when to start each phase of grazing, idling and ruminating.
Non-Homogeneous Groups: Different classes and species of animals have different grazing needs.
- Weaners, milking cows and oxen all have different feed requirements.
- When there is a goat in a sheep flock, the sheep will usually follow him although his grazing habits are not the same as theirs would be if they were on their own.
Owing to the differences in grazing methods and tastes, two different species will ensure greater utilization of available forage to their mutual benefit. An experiment was carried out in Wales, where Herefords and Friesland Herefords of about 250kg and Welsh ewes and lambs were grazed alone and together on highly fertilized pastures at two different stocking rates. There was an improved performance in the combination of cattle with sheep. It is important; however, to note that this stocking rate should not exceed the carrying capacity of that particular veld type. Where sheep and cattle are to be grazed in a complementary situation, advice should be sought before embarking on this programme, as a certain amount of damage can be affected if the grazing is not controlled.
Rank Order of Dominance: This is an important aspect of animal behaviour. With animals which know each other, there is peace, leading to better productivity. If strange animals are mixed, absence of order leads to fighting and stress, resulting in reduced productivity. Factors affecting dominance are the animals’ age, weight, height, aggressiveness and agility. Dominance is less marked amongst the younger groups. Therefore it is essential to separate different age groups of animals for effective utilization of the grazing.
The following list can be drawn up.
THE EFFECTS OF SOCIAL DOMINANCE ON BEEF SUPPLEMENTATION
|Live-mass gain or loss||in kg|
|2-year-old Heifers with older cows||Loss of||– 12 kg|
|2-year-old Heifers alone||Gain of||+ 23 kg|
|2-year-old Heifers with 3-year old Heifers||Gain of||+21 kg|
|3-year-old Heifers with older cows including calving cows||Loss of||– 108 kg|
|3-year-old Heifers with 2-year Heifers||Loss of||– 23 kg|
|3-year-old Heifers in a mixed herd including 2-year-olds||Loss of||– 75 kg|
|Mature cows loss including calving||Loss of||– 58 kg|
Under ideal conditions, maximum intake is achieved from 12 cm long mature pastures. The animal bites off and swallows the top half of the grass. But on thinner, less mature pasture, for example, 20 cm long is ideal the animal uses its tongue and teeth, tears off a mouthful, and chews for 30 seconds before swallowing. This procedure is probably equivalent to that which occurs on the veld.
This is an important aspect of livestock behaviour and cannot be ignored. For example, the cafeteria experiment which was carried out in West Virginia:
- Cows were grazed on a selection of different swards, and the preference order noted.
- Cows were then put on pasture consisting entirely of the favourite sward. Several weeks later they were returned to the ‘cafeteria’ or preference. The previous favourite sward went to the bottom of the list. Favourite species vary in palatability, and vary in feeding value at different stages of their growth cycle. Fistula experiments show that the protein content of feed in the fistula samples is consistently higher than the average for the area of sward graze, i.e. the animals selected out the better parts.
This effect has also been shown in experiments done in France with dairy cows. Because of selective grazing by the animals, and the progressive loss of leaf by the grasses, as time goes on, the grazing animals eat less and less of poorer quality grass, and their production falls.
|Grazing Time||Production of Milk as a Percentage of Day 1|
|Day 1||100 %|
|Day 2||102 %|
|Day 3||98 %|
|Day 4||95 %|
|Day 5||90 %|
|Day 6||89 %|
|Day 7||86 %|
This shows that animals select the leafiest part of the plant to eat first, and only the best areas of the pastures or paddock are grazed. As the grass matures, selection by the animals becomes even more stringent.
Animals that are grazing freely on good veld will walk 4 to 5 kilometres a day, and they will have to walk further than this if the grazing is poor. The main purpose of walking is to look for the best grasses and to look for calves. The breed of the animals and the topography of the ground also affect the distances walked. If animals are kraaled at night and have to walk long distances to reach their grazing each day, this will reduce their grazing time and will increase their maintenance requirements. They will use up energy by walking a long distance, and this energy will have to be replaced from their food intake. Their energy requirement will be increased by 1,4% per 100 kg of body mass for every kilometer walked.
Water points should always be provided in grazing areas, and they should be sited so that animals have easy access to the water without having to walk too far. Animals will graze only at a certain distance away from water, and areas of veld that are beyond that distance will not be grazed.
As the temperature increases, so does the intake of water as shown by the following table:-
| Maximum Daily |
|Liters of Water Drunk Per Day|
Experiments have shown that, when animals are restricted and allowed to drink water only every other day, their daily water consumption was about 70% of the normal intake, that is the amount they would drink with free access to water. However, this appeared to have no effect on their growth rate. This applies to growing animals, but any restriction of water for dairy cattle will have a very marked affect on their milk yields.
In managing the veld, the farmer must try to balance the productivity of his animals with the productivity of his veld, so that the best results are obtained. A knowledge of how animals behave when grazing the veld is useful in order to obtain this maximum productivity. Overgrazing by overstocking the veld leads to poor veld growth. This results in a larger number of poor animals, instead of the smaller number of good animals which are produced when the veld is correctly stocked.