From a nutritional point of view, the lactation cycle is divided into 3 periods:
1 Dry period
2 Early lactation
3 Mid- and late lactation.
With a calving interval of about one year, the first 3 months after calving the cow is not pregnant and has a “peak” production. Then, after 90 days, she should be pregnant and continue milk production till month 10 after calving, leaving a dry period of two months before the next calving. In high yielding cows, the calving interval and therefore the lactation period, may be somewhat longer, due to a negative energy balance in the first stage of lactation.
Feeding of A Dry and Pregnant Cow
Because a cow is without milk production during the dry period, feeding is sometimes neglected. Nevertheless it is of enormous importance that the animal is in a good condition (not too fat!) at the time of calving as to obtain maximum production level during the early stage of lactation. One should aim for a maximal condition score of 3-3½ (see appendix 5).
It is recommended to restrict feeding (withhold concentrates) one day prior to the date of drying-off, as this will reduce milk production and decreases the risk of mastitis.
The dry period should be used to allow an animal to recover from the previous lactation (if necessary) and to form sufficient body reserves for the next one. Level of nutrition during the pre-calving period depends on following 3 factors:
1-Overall nutrition level related to production during lactation
2-The length of the dry period
3-Demands of the cow in calf and just before calving
Overall Nutrition Level Related to Production During Lactation
At the moment of calving the condition of the cow should be good. A pregnant cow in poor condition at the end of the lactation needs more food during the dry period than a cow already in a good condition. High yielding cows can be expected to repeat that performance during the next lactation, provided they are given the opportunity to replenish their body reserves before calving.
First calving heifers should attain the growth rates as indicated in paragraph 6.3.2, to allow for growth and pregnancy. The recommended growth rate during the last two months of pregnancy is given as 1,000 gram/day. First cows calving should reach a good condition at calving (score 3-3½), which may influence the feeding management of heifers.
The Length of the Dry Period
It is generally recommended to have a dry period of two months for animals still producing substantial quantities of milk at the scheduled date of drying-off, but also for animals with lower productions and/or longer calving intervals. A long dry period appears, for biological reasons, to have a negative residual (carry-over) effect into the next lactation. Cows with a long dry period most likely lack so-called “dairy merit”, or milk production potential and tend to become too fat. One should very carefully watch the condition and feeding may have to be restricted and exercise provided to facilitate calving.
Demands of the Cow in Calf and Just Before Calving
During the last two months of pregnancy the uterus and the calf develop rapidly (the total gain is 40-50 kg in this period). Feed requirements depend on the condition of the animal.
The requirements for pregnancy itself are: as for production of 2 – 5 kg milk
8th month (1st dry month): 9th month (2nd dry month): as for production of 5 – 10 kg milk
Live weight-gain during late pregnancy should be about 500 gram/day or about 300 gram/day for animals in good condition. Recommended feeding levels for pregnancy are given in paragraph 6.3.2.1. Usually no extra pregnancy allowances are recommended during the first 7 months of pregnancy.
The present tendency is to bring animals in good condition during the late stage of lactation, as apparently the development of body reserves during lactation is much more efficient than during the dry period. The old approach of “steaming up”, giving extra concentrates during the last 3-5 weeks before calving, is now considered to have negative effects by having animals too fat at time of calving. Bringing the cow in a too fat condition before calving is costly and has many negative effects on health and production capacity of the cow.
A (too) fat condition at calving time should be avoided, as this may have the following consequences:
1—Difficult birth
2– Lower feed intakes
– Large scale mobilization of body fat reserves: “Fat Cow Syndrome”
-Acetonaemia or “Liver ketosis”
-Acidosis, and as a consequence laminitis
3. Diseases like retained placenta and metritis
4. Oedematic conditions
5. Milk fever
Difficult birth
Fat-deposits in the birth-path increase the possibility of difficulties at birth and possibly weak calves.
Lower feed intakes
A fat cow eats less and thus reduces her energy intake during early lactation. This may lead to:
– Large scale mobilization of body fat reserves to compensate for the lack of available energy. As the liver may not be able to cope with large amounts of fats, liver-cells will be damaged or killed. Others will lose their functional capacity as they fill up with fat. This malfunction of the liver is known as “Fat Cow Syndrome” or “Fat Liver Syndrome” and may cause a cow to be depressed, with reduced appetite and possibly death.
– A disease associated with the “Fat Liver Syndrome” is acetonaemia or “Liver ketosis”. The mobilization of fats due to shortage of energy results in production of ketones, which in large quantities are poisonous. A cow with ketosis in early lactation will become dull and lethargic, loses appetite, refuses concentrates and possibly roughage which aggravates the condition of ketosis since it was caused by lack of energy. Many mild cases of ketosis may go unnoticed. They are self-limiting as milk production may decrease to a level at which the energy balance is more or less restored. Some cases may become chronic. Ketosis seldom kills a cow, but it ruins productivity for the rest of the lactation (low peak yield and low lactation yield).
– Acidosis, and as a consequence laminitis, are also associated with mobilization of large amount of body fat reserves caused by low intake of energy by a (too) fat cow. Breakdown of body fats may lower the rumen pH as result of increased production of propionic acid from the fats.
Retained placenta and metritis
Diseases like retained placenta and metritis are associated with problems related to difficult births and lower feed intakes, leading to a lower fertility status.
Oedematic conditions
Overfeeding may cause oedematic conditions during the last stage of pregnancy. It possible cause for a more pendulous udder, as the suspension ligaments may become weakened due to the heavy udder.
Milk fever
Milk fever is another serious disease which may be associated with a too fat body condition at calving (although not necessarily). Concentrate supplements in late pregnancy may have a severe negative effect on the mineral resorption, particularly Calcium (Ca), from the gastro- intestinal tract. The daily requirement of Ca varies according production level. Ca require- ments are higher during lactation as the cow excretes Ca in the milk. During the dry period, the daily need for Ca is much smaller. This has two major effects in the cow:
——the resorption of Ca from the intestines slows down to a very low
level
—the resorbed Ca, not required for maintenance and fetal growth, is being deposited in the skeleton as reserves.
The skeleton plays an important role in the metabolism of some minerals, particularly Ca. During peak demands (high milk production), the skeleton releases minerals into the circulation and in time of abundant supply it can store the excess. Supplements of (extra) concentrates, containing “natural” and supplemented minerals, strengthens the process of further reduction in resorption and more deposits in the skeleton. At calving, a cow suddenly meets a very high demand for Ca, as large amounts are being secreted into the colostrum. This causes a sudden drastic lowering of Ca-levels in the blood, resulting in the acute occur- rence of milk fever (hypocalcaemia) and its complications.
The low level of Ca in the blood triggers off various processes in the body, of which the most important are:
—-Rapid increase of resorption capacity of Ca from the intestines
—-Reversal of the process of depositing Ca, to again the release of Ca from the skeleton into the bloodstream
However, it takes some time before these processes are adjusted again to the situation of milk production and consequently the high(er) needs for Ca. It is therefore advised, to reduce or withhold Ca during the last 7-10 days of the dry period as to force the animal at this stage already to reverse the process of deposit of Ca into the skeleton to releasing the Ca from the skeleton in the blood and to increase the resorption capacity of Ca from the intestines. The supplementation of Ca to be resumed again on the day of calving to increase the Ca in the blood-levels during the early lactation and thus reduce the chance of milk fever. Milk fever is usually also associated with retained placenta and a reduced fertility status.
Conclusion
Overfeeding during the last month of pregnancy is costly in terms of money, potential production performance, health and fertility during the early lactation and subsequently affects the total lactation performance. It is wiser to save on concentrates during the dry period, preventing an animal from becoming too fat and spend extra money on concentrates during the period of early lactation as to “guide” the cow to a high peak yield (and thus a high lactation yield).
Underfeeding during the dry period (condition score below 3) will result in a low yield during the next lactation. This can not be corrected any more during the lactation period. Requirements for peak milk yield are already in excess due to intake capacity. Underfeeding or unbalanced feeding can also disrupt the breeding cycle (lowered fertility status during early lactation) and influence the health of an animal, both directly and indirectly, by reducing its resistance against infections and stress.
A lower peak yield will result in a lower lactation yield, as will be discussed later in this chapter. The aim is to reach a body condition score of 3-3½ at calving for maximum health, production and fertility status.