CARE AND FEEDING OF THE DRY AND POST-PARTURIENT COW
P G Stewart
Cedara Agricultural Development Institute
The dry period is the time from the end of lactation until the cow calves again. Usually 56 days (8 weeks), the dry period is necessary to allow the cow time to replenish body reserves, especially minerals which are depleted during lactation, and to allow the udder tissue to involute, and be renewed before the next lactation.
THE IMPORTANCE OF THE DRY PERIOD
THE REASONS FOR THE DRY PERIOD
Involution of the udder
The principal reason for the dry period is to allow the secretory tissue of the udder to involute. During this period, the secretory cells actually break down and are resorbed, and a new set of secretory cells is formed. This cell renewal process takes approximately six weeks and, if a cow is allowed no dry period at all, will result in a loss of milk of at least 30% in the subsequent lactation.
During the last eight weeks before calving the foetus gains almost 60% of its birth weight, an overall rate of gain for the cow of about 0,75 kg/day. At the very least, the cow must be fed for foetal growth. Mineral nutrition, including the trace elements, especially iodine in the KwaZulu-Natal midlands, must not be neglected.
Replenishment of body reserves
If a cow is thin at drying-off, some replenishment of body reserves can be achieved but a gain of more than about 20 to 25 kg is not desirable. If an attempt is made to feed for more than half a condition score, in addition to feeding for foetal growth, there will be a marked increase in dystocia and metabolic problems at calving. Feed conversion is also significantly less efficient when a cow is dry. The conversion of feed energy into body reserves is about 62% efficient in the lactating cow and only 48% in the dry cow. It is simply good economics to feed for condition before drying off.
Mineral reserves are an entirely different matter to energy reserves. The high-producing cow will have severely depleted her body reserves of minerals, especially calcium and phosphorus, during her lactation. These reserves can only be completely replenished when the cow is dry. Adequate mineral nutrition during the dry period is very important. See section on "Metabolic Problems" in this leaflet for further discussion of this topic.
THE LENGTH OF THE DRY PERIOD
Many studies have shown that dry periods of less than 45 days will markedly reduce the milk yields in the subsequent lactation, primarily because of the time needed for involution and regeneration of secretory cells. There is no advantage in dry periods of more than 60 days. Long dry periods such as may occur after an abortion, are distinctly disadvantageous, since cows can easily become too fat, leading to metabolic problems and to disappointing milk yields after calving. The exact date of calving is never known, and these cows will often calve a week or more before the estimated date.
Given these facts it is wise to aim for a dry period of eight weeks (56 days). Do not make a practice of drying off for two calendar months before the due date; this merely wastes milk from four or more days, milk which could otherwise have been sold.
MANAGEMENT AT DRYING OFF
WHEN TO DRY OFF
Dry off either when the cow is within 56 days of recalving or when the cow's milk yield drops to a level sufficiently low be cost effective (uneconomic), or too much trouble, to warrant continued milking. Uneconomic milk production, usually considered to be about 5 l per day, should be a rare event. This level may vary seasonally depending on the need to build quotas and the cost of feeding. On well-managed farms nearly all cows will be dried off eight weeks before calving. The actual dry-off date can be calculated as 224 days from the last service date, or simply read off Table 1 of KwaZulu-Natal Dairy Leaflet 4.1. Do not rely on a cow calendar because the magnets can easily be accidentally misplaced; rather mark the dry-off date clearly in the milk recording book once the cow has been confirmed in calf, or use a computer-produced action list as a guide.
HOW TO DRY OFF THE COW
The first step is to cut out all concentrates, and even keep the cow on poor roughage, for three or four days before and after the dry-off date. Cows do not like to be separated from their herd mates and such separations, combined with the low plane of nutrition, will assist rapid cessation of milk secretion. Cows, however, should not be separated if there is any chance that they will damage themselves in attempting to break through fences to rejoin the herd. Having made them as "unhappy" as possible, most cows can then be dried off simply by ceasing to milk them.
However, cows are increasingly being dried off at yields over 20 kg per day. Under these circumstances, undesirable swelling of the udder can occur. Excessive udder enlargement can lead to udder damage. When enlargement occurs, the cow can be left unmilked for two or at most three milkings, then milked out for the last time. Cessation of milking for two milkings will cause an immediate suppression of milk secretion through damage to the secretory cells, and the single milking out will help relieve pressure in the udder and reduce the chances of udder injury.
In consultation with the local veterinarian, a decision will have been made on dry cow therapy. In general, a recognized "dry cow treatment" appropriate for the most prevalent mastitis organisms should be used immediately after the last milking. Disinfect the ends of the teats well, insert the dry cow remedy into each quarter and then teat dip. Keep the cow on a low plane of nutrition for another three or four days. By now a week will have passed since drying off, and for the remainder of the dry period the cow should be fed to meet her nutritional requirements only.
MASTITIS AND DRYING OFF
Cows exhibiting clinical signs of mastitis should not be dried off until the mastitis is clear. Any cow with a history of mastitis during her lactation should definitely have dry cow treatment. All recently dried off cows must be very closely inspected for at least the first week after drying off and the cause of any excessive swelling or redness ascertained and, if necessary, treated. Maintain strict hygiene when handling the teats of any cows, but especially dry cows and pregnant heifers.
MANAGEMENT DURING THE DRY PERIOD
NUTRITION OF THE DRY COW
Once the cow is dry, usually from about a week after the dry-off date, she must be fed correctly for the growth of the foetus and the replenishment of her body reserves. Many dairy textbooks also recommend that the cow be given a chance to adapt to the nutrition she will be getting after calving. A common recommendation is to feed the same dairy meal that the lactating cows receive, for a week or two before calving. This practice is probably overrated, except where there is a very marked difference between the diets of the lactating and dry cows. It can also increase the incidence of parturient paresis (see section on "Milk fever" in this leaflet). If roughages are good (ME greater than 9,6 MJ/kg) and similar to those which the cows in milk are eating (the same silage, hay and/or pasture), then the microbial population will adapt rapidly enough to the concentrates in the first week or so of lactation. See section on "Management at calving" in this leaflet for important considerations on feeding in the days immediately before and after calving.
Actual amounts and kinds of supplements that need to be fed will depend on the roughages and on the condition of the individual cows. The amounts required are detailed in KwaZulu-Natal Dairy Leaflets 5.3 and 5.4. Dry cows should not normally be fed more concentrates than about 0,5% of their body weight per day. If calculations show that a great deal more is needed then, either the cows were far too thin at drying off, or the roughage quality is hopelessly inadequate. Most dry cows will need nothing but mineral supplementation if roughage quality is good (ME greater than 9,6 MJ/kg) and they have been dried off at target condition. As a general rule dry cows should not be fed diets which are high in calcium or phosphorus. Therefore, no legumes, especially not lucerne hay, should be fed. Well-fertilized temperate pastures sometimes contain more minerals than required by the dry cow. Tropical pastures (e.g. Kikuyu, Coast cross 11), are unlikely to be a problem and can even be advantageous. Mineral nutrition, as indicated in section "The reasons for the dry period" must not be neglected, but excess calcium contributes to milk fever.
NUTRITION AT CALVING
If the dry cows are on dry feeds and their dung is firm, then a slightly laxative ration should be fed in the few days prior to calving. Feeding about two kilograms of wheaten bran, in lieu of concentrates, will usually loosen up the faeces and facilitate calving.
The cows' appetite is depressed at calving and on no account should the cow be fed a high level of concentrates, because acidosis, laminitis and oedematous udders are all aggravated by excess concentrates at calving. A practical strategy is simply to increase concentrates, at the rate of a kilogram a day, from the day of calving until the desired maximum rate has been reached. This strategy also gives the rumen's microbial population time to adjust to the change in diet. If a high level of minerals was fed in the few days immediately before and after calving, this should be reduced to normal levels after the first 2 to 3 days.
MANAGEMENT AT CALVING
As discussed in KwaZulu-Natal Dairy Leaflet 1.5, parturition is the time in the animal's life when she is most sensitive to environmental stimuli. It is, therefore, very important that the cow has good experiences at calving. Ideally the cow should calve down in a clean pasture or maternity stall, with a minimum of other animals to disturb her. In particular, there should be no cows in milk which may try to steal the calf, or horses and dogs which may interfere with the calving. The calf must get colostrum, by stomach tube if necessary, within a few hours of birth. The calf should be removed from its mother within the first 24 hours. This is far less traumatic for both cow and calf than allowing them to form a firm bond over several days. The only advantage of leaving a calf with its mother is that suckling promotes the production of the hormone oxytocin. This hormone causes contractions of the uterus and assists to expel the afterbirth.
Heifers need especially careful handling at parturition and should have been thoroughly accustomed to the milking parlour in the weeks before calving. If possible, bring the first calver's calf with her into the parlour for the first couple of milkings. This will significantly relax the mother and make training her to the milking machine a good deal easier. The better the "vibes" at calving, the better the milk production for her whole lactation. Do read the relevent sections in KwaZulu-Natal Dairy Leaflet 1.5.
The most common mistake at calving is to assist too soon. There is no substitute for experience, but the study of a good veterinary textbook will help. If it is necessary to assist at the birth (in the case of Holstein-Frieslands this could be at more than 10% of calvings) do not chase the mother around. When you have ascertained that she needs help, say after being in labour for three hours and beginning to look tired, bring the cow very quietly into a hospital pen where she can be easily restrained with a head clamp at a manger. Tame cows (they should all be tame!) can often be handled in the field. This is less stressful than bringing them in. Wash your hands thoroughly with an antiseptic soap and identify the problem. If presentation is normal, i.e. either both front feet and the head engaged in the birth canal, or both hind feet are engaged (breech presentation), attach calving chains or ropes and pull in a downward direction (towards the hocks) as the mother pushes. Be patient; if, after half an hour, two strong men have failed to pull the calf gently out into the world then seek professional help. NEVER apply more force than can be exerted by two men pulling together. If the presentation is abnormal (e.g. two front feet and no head, or one front leg left behind) and a few minutes of strenuous shoving and heaving cannot rectify the position, then get professional help.
An assisted birth is often followed by a retained afterbirth, which is one that does not come away naturally within 24 hours. Never attempt to remove an afterbirth by pulling. To prevent anyone else on the farm being tempted to do so, it is good practice to cut off any afterbirth which may be hanging from the vulva, leaving no more than 100 to 150mm, too short for anyone to get a grip on. Consult your veterinarian on the best procedure to adopt and follow his advice. The metritis (dirty cow) problems that follow assisted births and retained afterbirths significantly delay reconception. Every effort should be made to maintain scrupulous hygiene and not simply to rely on antibiotics to clear up the problems introduced by carelessness at an assisted birth. Problems identified early mean more live calves and fewer cows suffering from obturator paralysis.
A Caesarian section does not necessarily result in a severely diminished lactation, provided the farmer does not wait until the cow is completely exhausted, or a dead and decaying foetus has to be removed piecemeal from the uterus, before calling the veterinarian.
Many cows will be unsteady on their feet for a day or two after calving owing to pressure on the obturator nerve during calving. Some will even be unable or unwilling to stand up. If there is any likelihood of the cow slipping and falling, or worse, slipping and doing the splits, then either provide a separate safe area where the cow can be milked (for example a stall where a bucket milking machine can be used) or put loose horse hobbles on the back legs for a few days. If the hobbles are far enough apart, the cow will be able to walk normally, but, in the event of a foot slipping from under her, she will be prevented from spread-eagling herself and doing possibly irreparable damage to hips and ligaments.
Cows which are unable or unwilling to stand can be assisted in a variety of ways with hoists and inflatable bags. Prognosis must always be guarded, but if nursing is good, and the cow is assisted to change position frequently and kept well fed and milked, in most cases she will eventually stand up. Do try and keep her in a place where she has company because cows find loneliness very stressful. The author and his wife once nursed a cow for more than three weeks before she stood up on her own. Admittedly she gave a poor first lactation, but went on for another five calvings without difficulty and was an above-average producer in these later lactations.
Figure 1. Calcium requirements of a high-yielding cow
Milk fever, more correctly termed parturient hypocalcemia or parturient paresis, can be a very costly problem. It is by far the most common metabolic disorder experienced in early lactation in South Africa, especially in Jersey herds. It usually occurs within the first day or two after calving and is characterized by a progressive paralysis culminating, if not treated, in shock and finally death through bloating and cardiac arrest. During the dry period the cow's calcium requirement is very low relative to her immediate post-calving requirement, as illustrated in Figure 1.
The data shown assume a high-yielding 600 kg cow but will be similar for any size of cow. The level of calcium in the plasma or extra-cellular fluid (ECF) is controlled by a homeostatic mechanism which effectively prevents excess calcium from being absorbed by the gut. Conversely, when calcium is deficient, calcium is mobilized from the skeleton and absorption from the gut is stimulated. Milk fever occurs when the response to the sudden demands of lactation is too slow. The mechanisms involved are diagrammatically represented by Figure 2.
Figure 2. Homeostatic control mechanisms for calcium (After Holmes and Wilson, 1984)
The diagram is relatively simple and leaves out the involvement of sunlight and the liver in the production of `Active' vitamin D. The complexity of the system, and the need for an immediate response at parturition, leaves non-physiologists such as the writer amazed that so few cows go down with milk fever.
Milk fever is more common in older cows than in first-calvers since older cows are less able to mobilize calcium from the skeleton. Milk fever is treated by the intravenous injection of 6 to 12 g calcium, usually as 100 to 200 g calcium borogluconate in a 25% solution (i.e. 400 to 800 ml solution). Nothing is apparently more miraculous than the effect of a bottle of this solution into an otherwise "dead" cow. As a preventive measure, subcutaneous injections can be administered at calving, to cows with a previous history of milk fever and to prevent relapses after the first intravenous injection.
In Jersey herds that are prone to milk fever, dry cows should be fed a calcium deficient diet for at least two of the three weeks immediately prior to calving in order to stimulate bone calcium mobilization and intestinal absorption. The intake of calcium and phosphorus should be increased by 50 g/day for each element, beginning 2 to 3 days before calving. For example, a typical mineral supplement for dairy cows might contain 17% Ca and 13% P. Feed this at the rate of 300 g/cow/day. Add molasses meal if not palatable enough. The crucial aim of this programme is to stimulate the production of parathyroid hormone (PTH), without which the extra minerals at calving will not help. This all requires extra management but will result in a marked reduction in the incidence of milk fever. To sum up:
Do not overfeed calcium and phosphorus in the dry period by feeding lucerne and the same meal as fed to the cows in milk.
Do feed a low-calcium ration for three weeks of the dry period.
Do start feeding a mineral supplement high in calcium and phosphorus for 2 to 3 days before and after calving.
Ketosis is characterised by lethargy, dullness and lack of appetite. The cow will smell of acetone due to a breakdown in the mechanisms controlling fat metabolism. It is best avoided by not allowing cows to get too fat prior to calving. Severely ketotic cows usually have livers so infiltrated by fat that the best place for them is the abattoir, because they are likely to be infertile as well as poor producers.
Hypomagnesaemic tetany ("grass staggers") is not as common in South Africa as it is in many other dairy countries. It is caused by an acute magnesium deficiency. Unlike milk fever, the onset of the condition can be sudden and fatal. It is not necessarily associated with calving and can occur at any time in the lactation. Magnesium levels in the plasma are not controlled by a sophisticated homeostatic mechanism as is the case with calcium and the cow must get enough magnesium in her diet. Webster (1987) hypothesizes that the lack of a homeostatic mechanism has come about because the ancestors of the domestic cow evolved under conditions of adequate magnesium in the herbage. Certainly, the problem is almost unique to well-fertilized, cultivated pastures. Where grass staggers is likely to occur it is best prevented by adding sufficient magnesium to the concentrates and by adding magnesium to the drinking water. Magnesium bullets can be dosed to heifers and other animals not receiving concentrates.
Work at Cedara showed that sub-clinical magnesium deficiencies, possibly induced by high potassium levels in the herbage, do depress fertility and can be prevented by the addition of magnesium compounds to the diet. This topic is covered in detail in KwaZulu-Natal Dairy Leaflet 5.3, dealing with mineral nutrition.
Acidosis, often associated with laminitis, occurs when cows are fed too little good roughage in proportion to their concentrates. The pH (acidity) of the rumen drops, and in extreme cases rumen atony can occur. At best there will only be a marked drop in butterfat. Laminitis is an excruciatingly painful inflammation of the sensitive lamina of the hooves and can follow acidosis. Acidosis/laminitis is best prevented:
through the feeding of roughages with sufficient long fibre
by restricting the proportion of starchy, rapidly fermentable constituents in the concentrates (wheat and barley are examples)
by the use of buffers such as sodium bicarbonate (NaHCO3). To be effective, the cows must get 100 to 200 g NaHCO3 per cow per day.
Displaced abomasum and other abomasal problems usually occur when the abomasum becomes overloaded with unfermented carbohydrates (especially starches). These continue to ferment in the abomasum producing gas and volatile fatty acids and the abomasum distends, becomes atonic (lacking muscle tone) and ceases to expel its contents. The sudden increase in space within the abdominal cavity following the expulsion of a calf combined with a distended and atonic abomasum can result in the condition known as "displaced abomasum", the abomasum becoming trapped under the rumen. This condition requires veterinary intervention and is recognized by lack of appetite, sharp drop in milk yield and acute ketosis. It is avoided by proper feeding in the weeks before and after calving.
The dry period is necessary to allow the cow time to replenish body reserves (especially minerals) depleted during lactation and to allow the udder tissue time to involute, and to be renewed before the next lactation. A dry period of less than 45 days will have a markedly deleterious effect on the subsequent lactation. The heavily pregnant heifer and the dry cow must be fed for her particular requirements. In particular, she should not allowed to get too fat (CS > 3 to 3,5) nor be over-fed minerals, especially calcium. Quiet, gentle, patient handling in the days immediately before and after calving is essential for good milk let-down. Concentrates must not be over-fed if metabolic problems are to be avoided. No more than 0,5% of live-mass should be fed per day during the dry period. This level should be built up slowly in the week to ten days following calving. Acidosis, laminitis, displaced abomasum, ketosis and even milk fever can all be avoided through correct nutrition and management.
HOLMES, C.W. & WILSON, G.F.,1984. Milk production from pasture. Wellington: Butterworths.
WEBSTER, J., 1987. Understanding the dairy cow. Oxford: BSP Professional Books.