As a vital link from one lactation to the next and preparation for calving, the dry period must be managed positively to ensure cows start their new lactation in the best possible nutritional status.  Dry cow feeding can have a direct influence on subsequent lactation performance including metabolic disorders such as displaced abomasums, milk fever and retained placenta.  Feeding at this time can be divided into three sections: dry, transition and fresh.  Mineral nutrition is considered separately.

Dry Period Length

Establishing optimum lengths for the dry period depends on lactation number; however, a full 56 day dry period is advisable to give sufficient time for damaged udder tissue to be repaired.  Assessments of farm data reveal that dry periods of less than 30 days or longer than 70 days are costly in terms of lifetime yield.

Optimum Dry Period Lengths

Lactation number	To maximize next lactation yield
1	40 – 45 days
2	40 – 45 days
3 or more	55 – 65 days

Fat cows

More than slight under-feeding of dry cows will lead to excessive fat mobilisation, but since this will primarily involve internal reserves it can go unnoticed unless cows are routinely assessed for condition.

Routine condition scoring is also important to avoid persistent over-feeding which raises insulin levels to enable excess energy to be stored as fat.  This causes cows to become increasingly less responsive to insulin which can lead to reduced energy intake and increasing weight loss in early lactation.

There is increasing evidence that cows on high concentrate diets may benefit from being in BCS 2.5 at calving rather than the traditional score of 3.0 on lower concentrate systems.

Changes in body condition should take place in late lactation rather than in the dry period as it is more efficient to change condition in late lactation rather than in the dry period.

Feeding in the dry period

In the first part of the dry period (all but the last 2-3 weeks) the dry cows can be fed on cheap feeds such as grass and straw.  Straw is useful at this time as it helps to keep the rumen enlarges, which may help avoid displaced abomasums in the following lactation.

Care must be taken that cows don’t get fat at this time.  In grazing situations, this can mean stocking cows at 8 to 12 cows/hectare.

A dietary protein content of 13-14% (130 – 140 g/kg) in the dry matter will usually be adequate for dry cows at any stage of the dry period.  However, diets with less than 12% protein can reduce colostrum quality, feed intake and early lactation milk yields.

Trials in the 1990s suggested supplementing dry cows with sources of Digestible Undegraded Protein (DUP) could improve milk yields and proteins in the subsequent lactation.

A low calcium (high magnesium) supplement should be fed, incorporating a high DUP feed.

It is also important to avoid feeding mouldy forages which can cause abortion.

Feeding in the transition period

Although forages alone can meet dry cow energy requirements, stock fed all-forage diets have very low levels of starch-digesting bacteria in their rumens which can limit their initial capacity to utilise concentrates in early lactation.  To ensure cows can make the best possible use of their early lactation rations – and so minimise early lactation energy deficits – some concentrate feeding in the later stages of the dry period is always advisable to condition rumen microbial populations.

Fourteen to 10 days before calving, the cows should be put on a diet similar to that for the medium yielding cows in the milking herd.  This will help prepare the rumen papillae and microbes for the subsequent lactation.  A low calcium (high magnesium) pre-calving nut, incorporating a high DUP supplement, such as protected soyabean meal should be fed.

As cows approach calving intakes fall and 10 kg/day will be all they can eat.  Crude protein levels should be below 16% to minimize the risk of downer cows.

A diet based solely on grass silage would have too high a crude protein content, so a mixture of grass and maize silages can lower the protein level.

The fresh calver

Nutritional management of the cow at this time should be active.  Do not leave fresh calvers to settle down, the milking cow diet should be fed as soon as possible at this time.

Ideally, the fresh calver should be fed the medium yielders ration (20 litres milk/day) for 10-14 days.  The ration differs only slightly from that offered pre-calving and so the rumen is already prepared for this diet.

Minerals

Incorrect mineral balances in the dry period can cause difficult calvings (as a result of poor muscle tone); retained cleansings (due to poor uterine contractions); milk fever (which can lead to reduced feed intake and displaced abomasums).  In copper deficient areas, it may also be necessary to supplement for copper during the dry period. It is important to avoid feeding late-season grass from areas where soil potash is likely to be high as this can increase the risk of milk fever; as can high clover silage.

Calcium, phosphorus, magnesium, potassium and sodium are primarily related to calcium supply which is critical in view of the sudden, dramatic increase in requirements at calving and the potential onset of milk fever.  The most important need is to prime the metabolism to cope with the three to fourfold increase in daily calcium requirements at calving.  While body reserves of calcium (in bone) are high, the diet can significantly influence the speed and extent to which these can be mobilised.

Three techniques can be used in the dry period to improve calcium mobilisation:

Feeding a low calcium diet pre-calving – to improve the efficiency with which dietary calcium is absorbed and stimulate increased mobilisation from bone.

Feeding extra Vitamin D very close to calving – to increase short-term bone mobilisation and gut absorption.  While Vitamin D injections 24 hours prior to calving can give the necessary boost to calcium supply, it can be difficult to accurately assess when some cows will calve.  This is important because the same injections given 3-4 days prior to calving can actually increase the risk of milk fever.

Full DCAB is a more sophisticated and costly option, involving similar feed selection and the use of a commercial mineral supplement containing a balance of anionic salts and additional calcium.  This works well under careful management but the high calcium input can make the milk fever risk worse if the supplement is not fed accurately every day.

Selenium and vitamin E are important in promoting a healthy immune system at a time when the cow is vulnerable to disease.  Although it has been associated with retained cleansings, selenium deficiency is now uncommon where high levels have been fed for the past 15-20 years as selenium is recycled via dung.  Traditionally, selenium problems have been linked to high levels of straw or root feeding, but in modern systems high inclusions of forage maize may be more significant.  Dietary selenium levels of between 0.2 to 0.3 mg/kg DM are considered adequate in dry cow rations.  Where high oil diets are fed, vitamin E supplementation may be needed. To maintain the most active cell defences and give a good transfer of vitamin E to colostrum, dietary levels of 800-1000 iu/day are suggested on silage-based diets, with less than half these levels required on fresh grass.

Iodine is also important in dry cows for its role in the hormone, thyroxine which controls metabolic rate and is involved in the immune system and brain function.

Iodine deficiency increases calf mortality and retained cleansings but is only really significant in well-defined local problem areas. Dry cow intakes of 0.5 to 2.0 mg iodine/kg DM will safeguard against deficiency – the higher levels being advisable where high levels of kale, forage rape or rapeseed meal are fed.