Management of pre-calving transition cows

The first part of this article (VT46.18) discussed the management of the freshly calved dairy cow. This part aims to review some of the key management factors implicated in a successful pre-calving transition period (defined as three weeks pre-calving).

Nutritional management and metabolic health

Appropriate nutritional management to maximise metabolic health is one of the key objectives to a successful transition period. Specifically, this is concerned with the management of calcium and energy levels.

The most effective method of preventing hypocalcaemia (both subclinical and clinical) is through the induction of a metabolic acidosis^1-3. This acidosis improves the conformation of the parathyroid hormone receptor on the bone and kidneys, facilitating the mobilisation of calcium from the bone and vitamin D synthesis. It is induced through manipulation of the dietary cation anion difference (DCAD).

The following equation illustrates the most commonly used expression of the DCAD equation⁴:

DCAD = ([Na+] +
[K+]) – ([Cl-] + [S2-])

Typically, two methods of DCAD exist that can be employed: partial and full. Partial involves the restriction of potassium and sodium without the addition of any anion salts (usually through the restriction or substitution of grass silages with lower DCAD values). Evidence as to whether the use of partial DCAD is sufficient to satisfactorily control hypocalcaemia alone is equivocal^5,6.

Full DCAD involves the restriction of potassium and sodium again, but this time with the addition of anionic salts (commonly magnesium or ammonium salts) to further increase the acidosis to around 50milliequivalents/kg dry matter (DM; a urine pH of 6.2 to 6.8).

When used and monitored appropriately, the full DCAD system is extremely effective at controlling both clinical and subclinical hypocalcaemia; however, the requirement to produce a total mixed ration (TMR) mix for pre-calving transition cows makes it more suitable to larger herds. In smaller herds, or where a single group of dry cows is employed, care needs to be taken that manipulation of DCAD (whether through restriction of potassium or sodium or the addition of anionic salts) does not occur for longer than six weeks, after which buffering with the bone will occur⁷, blunting DCAD efficacy.

In a single group, rations should be formulated to provide 110 per cent to 120 per cent of energy requirements. Richards et al⁸ compared one-group strategy (controlled energy) with two-group strategy (with a high energy close-up ration; 6.74megajoules [MJ] metabolisable energy [ME]/kg DM).

Cows fed the controlled energy one-group ration (5.52MJ ME/kg DM) for the entire dry period had improved biochemical metabolic markers – beta-hydroxybutyrate (βHB) and non-esterified fatty acids (NEFAs) relative to cows fed the two-group dry cow system. This is an extreme energy density, those closer to typical (6.1MJ ME/kg DM) would be expected to demonstrate similar performance to those of a single group⁹.

These rations are fed as part of a TMR, which should last a full 24 hours – providing true ad-lib feeding. Generally, this requires the inclusion of reasonable masses of straw, which requires adequate chopping to prevent/minimise the opportunities for sorting.

For those herds splitting cows into far-off and close-up calving groups, energy requirement of close-up calving cows should be met, but not exceeded. Energy intake below requirements results in increased NEFA level, prepartum and postpartum periods^10-12, with the elevated incidences of the postpartum diseases and poor production performance described in part one.

Similarly, excessive energy during this period can result in heightened insulin resistance, resulting in poor DM intake (DMI), increased body condition score loss, increased risk of post-parturient diseases and poorer production and reproductive indices⁹.

Regardless of whether a single-group or two-group dry cow strategy is employed, access to feed should be ad-lib and with a target feed space of 1m/cow¹³. The general principles of a pre-calving transition cow ration are summarised in Table 1.

The use of controlled monensin-releasing boluses for use in the “periparturient dairy cow/heifer, which is expected to develop ketosis” was licensed for use in 2013. Monensin is a carboxylic polyether ionophore produced by a naturally occurring strain of Streptomyces cinnamonensis¹⁶ and is provided to cattle orally as a sodium salt. Ionophores interfere with ion transport across cell membranes, thereby creating energy loss in bacterial cells, resulting in bacterial death.

Monensin selectively inhibits Gram-positive bacteria rather than Gram-negative bacteria because of differences in bacterial cell wall structure.

The result of this shift in rumen bacterial populations has several impacts on ruminant metabolism, which include:

• Increased efficiency of energy metabolism.
• Improved nitrogen metabolism.
• Effects on digestion, including reductions in both bloat¹⁷ and lactic acidosis^18,19.

Monensin changes the ratio of volatile fatty acids in the rumen, increasing propionic acid production and reducing the molar percentages of butyric and acetic. Increased production of propionic acid from the rumen increases hepatic gluconeogenic flux. Consequently, monensin use in lactating dairy cattle significantly reduced the blood concentrations of βHB by 13 per cent, NEFA by 7 per cent²⁰ and, perhaps surprisingly, DMI by 0.3kg/d (a decrease of approximately 2 per cent), but increased milk yield by 0.7kg/d (an increase of approximately 2 per cent)²¹.

Therefore, the targeted use of monensin in over-conditioned cows or cows carrying twins should form part of the dry cow management programme.

Udder health

The final few weeks of the dry period represent a significant risk to udder health as the mammary gland will be beginning the process of colostrogenesis. During this process, intramammary pressure increases and the concentration of leukocytes and lactoferrin decreases²², which, combined with the disappearance of the keratin plug 7 to 10 days pre-calving²³, makes adequate environmental management essential.

Table 2 suggests stocking densities for pre-calving transition cows – should these cows be managed at pasture, targets should be 100cows/acre/d with no return within two weeks²⁴.

Figure 1 demonstrates inappropriate management of pre-calving transition cows on farm A, where pre-calving transition cows are managed at pasture all year.

Figure 2 shows the rate of clinical mastitis occurring from the dry period (defined as mastitis occurring in the first 30 days of lactation) for the same farm and clearly illustrates the excessive level of mastitis originating from the dry period, at times three times the maximum acceptable rate.

Foot health

Despite being at lower risk of digital dermatitis (DD) than lactating cows²⁶, dry animals can act as a reservoir for DD increasing the overall infection pressure within a herd. Consequently, routine footbathing of dry cows can help reduce the incidence of DD in a herd.

Routine trimming of cows pre-drying off has become commonplace in UK herds. However, its effectiveness in reducing the incidence of sole ulcers is equivocal with better results achieved with more frequent trimming²⁷ – hence why routine trims around drying off are usually combined as part of a foot health programme to include a trim in early lactation.

Immune function

A natural decline in neutrophil function exists in late gestation²⁸, which is further compounded by a state of negative energy balance²⁹ – emphasising the need for appropriate nutritional management and metabolic health discussed previously.

Earlier in 2016, a cytokine, bovine granulocyte colony stimulating factor (bG-CSF), was licensed “to reduce the risk of clinical mastitis in periparturient dairy cows and heifers during the 30 days following calving”; bG-CSF stimulates the production and activity of neutrophils.

In a non-peer reviewed field study of 2,465 cows, Imrestor resulted in a reduction of 26 per cent in mastitis between days 3 and 30 of lactation, relative to placebo.

Summary

The transition period, both pre-calving and post-calving, represents one of the most critical parts of the production cycle for the dairy cow.

However, careful management of nutrition, environment, foot health and preventive medicine programmes can combine to reduce the incidence of “gateway diseases”, and maximise cow welfare and productivity.

• Managing freshly calved dairy cows (part 1)