Milk fever in dairy cows: A review of pathophysiology and control principles

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Abstract

The periparturient or transition period of 4 weeks before and 4 weeks after calving is characterised by a greatly increased risk of disease. Hypocalcaemia around calving is a risk factor for many of these diseases and is an indirect risk factor for increased culling. The incidence of clinical hypocalcaemia (milk fever) in the field generally ranges from 0–10%, but may exceed 25% of cows calving. In research trials conducted on milk fever the incidence has approached 80% of cows calving.

Homeostasis of calcium (Ca) is regulated by calcitonin, parathyroid hormone and 1,25(OH)2 vitamin D3. Age increases the risk of milk fever by approximately 9% per lactation. Control of milk fever has revolved around stimulation of homeostatic mechanisms through feeding a pre-calving diet low in Ca. More recently, the role of the dietary cation anion difference (DCAD) in the prevention of Ca disorders has been examined, both by field research and meta-analysis. The most appropriate form of the DCAD equation has been contentious, but recent meta-analyses have shown that the equation (Na+ + K+)  (Cl + S2−) is most effective for predicting milk fever risk. Decreased risk of milk fever is linear with DCAD, whereas the effect of DCAD on urinary pH is curvilinear. A pivotal role of providing dietary magnesium (Mg) before calving has been confirmed by meta-analysis, and a quadratic effect of Ca on milk fever risk was found with a peak occurring with dietary levels of 1.1–1.3% of dry matter.

Risks of milk fever increase with increased dietary phosphorus (P) fed pre-calving and with increasing days of exposure to a pre-calving diet. Meta-analysis has revealed that the important roles of dietary Ca, Mg and P, as well as the duration of exposure to the pre-calving diet in milk fever control strategies are independent of DCAD. Studies on the effect of exposure to well designed pre-calving diets have shown that substantial improvements in production, reproduction and animal health can be made but further examination of the influence of the period of exposure to different diets is warranted.

Introduction

The periparturient or transition period of 4 weeks before and 4 weeks after calving is characterised by greatly increased risk of disease (Shank et al., 1981, Curtis et al., 1985, Stevenson and Lean, 1998). The period is dominated by a series of adaptations to the demands of lactation, a process described as homeorhetic (Bauman and Currie, 1980). Homeorhetic processes are the long term physiological adaptations to changes in state, such as from non-lactating to lactating or non-ruminant to ruminant, and involve an orchestrated series of changes in metabolism that allow an animal to adapt to the challenges of the altered state. The problems that result from disordered homeorhetic change reflect disorders in homeostasis and include hypocalcaemia, the downer cow syndrome, hypomagnesaemia, ketosis, udder oedema, abomasal displacement, metritis and poor fertility.

These conditions are often inter-related (Curtis et al., 1983, Curtis et al., 1985, Curtis and Lean, 1998) and this, combined with the dramatic changes in endocrine function and metabolism associated with calving and the initiation of lactation, makes transition an inherently difficult period to study. Notwithstanding these challenges, the potential to increase subsequent production, improve health and improve reproduction has made nutritional manipulation of the periparturient cow a focus for research.

It can be broadly stated that the transition cow should be adapted to provide minimal risk of metabolic disorders of macro-mineral metabolism including absolute or conditioned calcium (Ca), magnesium (Mg) or phosphorus (P) deficiencies, or excesses of sodium (Na) and potassium (K); disorders of lipid metabolism arising from inadequate energy intake in the dry period and early lactation; disrupted rumen function associated with dietary change and impaired immune response.

The aims of this paper are to review some of the changes that occur around calving related to hypocalcaemia and to examine the potential to modify the risk of disease, reproductive failure and milk production through better nutritional management.

Section snippets

Incidence and background

While the focus on nutritional management of hypocalcaemia is appropriate, not all of the risks for periparturient hypocalcaemia results from ration formulation. Recumbency is often caused by hypocalcaemia, but other significant causes include hypomagnesaemia, musculo-skeletal injury predisposed by calving and hypocalcaemia, ketosis associated with twinning, hypophosphataemia and a number of less frequent problems such as peracute mastitis and other infections. Dystocia is a major cause of

The pathophysiology of hypocalcaemia

Changes in Ca metabolism induced by lactation are more significant than parturition per se to the pathogenesis of parturient paresis, as the loss of blood Ca to milk may exceed 50 g per day. Before calving, the approximate daily requirement for Ca is only 30 g, comprising 15 g in faecal and urinary loss and 15 g to fetal growth. This demand for Ca may only be satisfied by increasing absorption from the rumen or intestines, and increasing mobilisation from tissue, especially bone reserves of Ca, as

Milk fever prevention: Dietary Ca, Mg and P

One of the areas of continuing contention is the role of pre-calving dietary Ca intake as a risk factor for milk fever. Beede et al. (1992) stated that high Ca intake pre-calving is not the primary cause of subclinical hypocalcaemia and milk fever. However, it is important to note that the improved understanding of the role of the monovalent cations in hypocalcaemia does not refute the research on Ca and vitamin D metabolism over the previous 40 years (Ramberg et al., 1996).

Early studies (Boda

Milk fever prevention: Dietary cation anion difference (DCAD)

Early studies by Norwegian workers found that diets high in Na and K and low in chlorine (Cl) and sulfur (S) tended to increase the incidence of milk fever, while those high in Cl and S and low in Na and K or containing added anionic salts (AS), decreased the occurrence of milk fever (Ender et al., 1962, Dishington, 1975, Dishington and Bjornstad, 1982). Block (1984) found a significant increase in the incidence of milk fever for cattle fed on diets that differed only in their quantities of Cl,

Integrating milk fever prevention: A meta-analysis

Meta-analysis is a systematic and rigorous method of pooling data from previous studies and re-analysing them. It is a particularly powerful tool for examining rare events such as disease studies conducted in relatively small populations, such as is evident in the milk fever data. Two significant meta-analyses of milk fever risk were conducted by Oetzel, 1991, Enevoldsen, 1993 who both used fixed effects models for predicting outcomes, although it is now widely accepted that these models are

Effects of exposure to pre-calving diet: Production, reproduction and health

Grummer (1995) stated that: “If transition feeding is important, then perturbations in nutrition during this period should affect lactation, health and reproductive performance.” While physiological research on the impact of manipulating various fractions of the pre-calving diet is substantial, studies on the effects of integrating dietary strategies and providing an ‘optimal’ pre-calving diet are rare. A prospective cohort study was used to examine the effect of increasing days of exposure to

Conclusions

While further studies are required on a number of aspects of milk fever, particularly in relation to the length of exposure to diets and Ca concentrations, many tools are now present to control the risk of milk fever. The exposure studies conducted by DeGaris et al., 2004a, DeGaris et al., 2004b, DeGaris et al., 2004c suggest that positive dietary changes in the pre-calving diet will result in substantial production, reproduction and health benefits.

Conflict of interest statement

The two authors of the paper entitled Milk fever in dairy cows: A review of pathophysiology and control principles are Peter Degaris and Ian Lean. Peter Degaris advises on feeds that control milk fever risk and sells products to treat and prevent milk fever. Ian Lean has conducted research and consulted to companies producing products to control milk fever; he is involved with importation to Australia and sale of products that control milk fever risk.

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