If the nervous form develops, the cow may lick itself or inanimate objects persistently, exhibit erratic aggressive behavior, present abnormal head posture, and even suffer from blindness. The mechanism that leads to the emergence of nerve ketosis is not yet fully understood
[41][52]. Despite the lack of understanding, Foster
[42][53] suggested that of the three more likely causes for ketosis (hypoglycemia, hyperketonemia, and isopropyl alcohol), increased serum concentrations of isopropyl alcohol are associated with the appearance of nervous signals. This fact was confirmed by another study (Adler et al., 1955 cited by Foster
[42][53], p. 258), where it was demonstrated that the injection of isopropyl alcohol causes clinical signs similar to those of animals with nervous ketosis. Isopropyl alcohol can be produced in the rumen from acetoacetate (and through the rumen wall enter the bloodstream) or in the brain from BHB
[42][53]. Contrary to this, fasting cows which have even lower levels of glucose and similar levels of blood ketones to cows with ketosis, do not show the same signs of nerve ketosis, so hypoglycemia and hyperketonemia do not seem to be the most prevalent factors in triggering nervous ketosis
[42][53].
More often than not, ketotic animals are more apathetic and less active, and some may even manifest ataxia or even the inability to get up. Signs that usually result from the installed hypoglycemia
[41][52].
The fruity odor of ketone bodies in breath and/or milk, mainly caused by ketone
[40][41][10,52], is another sign which, when present, is not always easy to detect.
According to Dar et al.
[43][54], productive breakdown and selective food intake are the signs most consistently found in cattle with ketosis (
Table 1).
Table 1. Relative frequency of the different clinical signs that can be manifested by a cow with ketosis (adapted from
[43][54]).
| Clinical Sign |
|
| Number of Animals that Showed the Sign |
|
| Percentage from the Affected Animals (%) |
|
| Nervous signs |
|
| 1 |
|
| 4 |
|
| Reluctance to movement |
|
| 1 |
|
| 4 |
|
| Constipation |
|
| 4 |
|
| 14 |
|
| Acetone odor on breath or milk |
|
| 5 |
|
| 18 |
|
| Dry and fewer feces |
|
| 6 |
|
| 21 |
|
| Complete anorexia |
|
| 7 |
|
| 25 |
|
| Prostration |
|
| 10 |
|
| 36 |
|
| Selective food intake |
|
| 21 |
|
| 75 |
|
| Abrupt drop in productivity |
|
| 28 |
|
| 100 |
|
Still, all these signs are nonspecific, and some are often not very evident, and therefore, difficult to detect, thereby increasing the risk of obtaining an erroneous diagnosis and the difficulty of correctly distinguishing clinical from subclinical ketosis
[27][15].
Parameters, such as temperature, pulse, and breathing pattern, only deviate from normal if there are other concomitant nosological conditions
[41][52].
5. Laboratory Diagnosis and Methods of Monitoring Ketosis
Deviations from metabolic homeostasis are reflected in changes in body fluids, such as blood, urine, milk, and saliva
[5]. Of these, the evaluation of some serum metabolites has been a key point in diagnosing various pathologies, particularly metabolic diseases
[38][50]. Thus, the most common diagnostic method used in diagnosing ketosis has been the analysis of some of these fluids in suspect cows
[23][16].
Concentrations of ketone bodies have been used for diagnosing ketosis in dairy cows for many years
[28][21]. Due to its stability in the blood, BHB has been the ketone body most used in the laboratory diagnosis of ketosis
[35][47], which is considered the “golden standard” method.
The hypothesis of using milk to measure BHB concentration has been increasingly investigated since the analysis and recording of parameters evaluated in milk is already a routine, non-invasive procedure that facilitates monitoring at the herd level. Moreover, unlike blood samples, milk samples reflect the animal’s metabolic state for a period of time and not just at the time of harvest
[27][15]. However, the accuracy of the BHB concentration prediction equations in milk has not been sufficiently high to predict the exact BHB concentration. Even so, it has proved useful for monitoring and signaling cows with high concentrations of BHB
[44][45][55,56].
It is important to emphasize that any instrument and method intended to be used by veterinarians or producers to detect pathologies must be non-invasive, simple to use, and low cost
[46][57].
6. Control and Prevention
In addition to the methods of monitoring ketosis described in the previous point, it is important to identify some procedures and a set of modifiable and non-modifiable risk factors that have an impact on the control and prevention of ketosis.
6.1. Ruminatory Activity
Mann et al.
[47][97] clarified that, compared to those that receive diets that provide energy well above maintenance needs, cows fed in the dry period with diets with restricted/controlled energy, have a lower risk of being affected by ketosis in the postpartum period, without prejudice to milk production. These animals manifested a less deep NEB and episodes of ketosis to a lesser extent and number.
The study by Kaufman et al.
[48][98], suggested that the monitoring of ruminatory activity during the peripartum, for example, with the use of rumination collars, may contribute to the individual and timely identification of pathologies of the initial stage of lactation. In this study, they found that multiparous cows that had reduced rumination time (by about 25 ± 12.8 min/day less than healthy cows between the 2nd week before delivery and the 4th week after giving birth) in the week immediately before giving birth were more likely to be affected by ketosis. Moreover, those who manifested this reduction (approximately 44 ± 15.6 min/day less than healthy cows between the 2nd week before delivery and the 4th week after delivery) in the week immediately after delivery would be more probably affected, not only by ketosis, but also by another pathology of early lactation. In the same year, Schirmann et al.
[49][99] testified that cows with postpartum ketosis (BHB ≥ 1.2 mmol/L) spent 14% less time ruminating during precalving (considered in the study, 10 days before calving) than healthy cows.
6.2. Assessment of Body Condition and Monitoring the Thickness of the Dorsal Fat Layer
Monitoring the BCS of cows in the precalving period had proved to be a useful tool in managing the health of the herd
[50][51][100,101], because Busato et al.
[52][102] found that high scores in the assessment of BCS (>3.25) before parturition were associated with a high loss of body mass in the first postpartum weeks since these animals experienced higher rates of fat mobilization; this phenomenon has been proven by the increased concentrations of circulating NEFA and BHB. Gillund et al.
[50][100] and Roche et al.
[51][101] verified the same phenomenon. Still, Busato et al.
[52][102] found that the metabolic state is optimal in animals of BCS = 3.25 in case they do not lose much body condition in the postpartum period (ΔBCS between prepartum and eight weeks postpartum ≤0.75).
For this monitoring, producers can use the Edmonson BCS classification table (scale 1—emaciated to 5—severely over-conditioned, with increases of 0.25 point) (Edmonson et al.
[53][103]) based on which Gillund et al.
[50][100] recommended a BCS score of <3.5 at delivery to prevent massive fat mobilization. If each animal is evaluated and this evaluation recorded at least once, the producer can, from then on, regularly check changes in the BCS
[23][16].
On the other hand, the method of measuring the thickness of the subcutaneous fat layer on the back using ultrasound necessarily involves the intervention of a veterinarian, which generally makes it more laborious; however, the results obtained are more objective and precise, and therefore, its implementation is recommended to collect measurements/results comparable to those obtained by assessing body condition within the same herd
[23][16]. The method involves measuring the thickness of the subcutaneous fat layer on the back, accumulated between the skin and the deep trunk fascia, which presents itself as a white line hyperechogenic to ultrasounds, after discounting 5–6 mm for the dermis. The sacrum region is the place of choice for this measurement because it is where the largest reserve of adipose tissue on the back is gathered; for said measurement, a horizontal line should be imagined between the ischial tuberosity and the coxal tuberosity and join the fourth to the fifth caudal part of that line, vertically, to the junction of the sacrum with the first caudal vertebra. Due to the high correlation between the amount of dorsal fat and the body fat content, we can assess the body condition of each animal from the first (Staufenbiel, 1992 cited by Schröder and Staufenbiel
[54][104] (pp. 5–6);
[23][16]).
Although these two methods seem practical and simple, the tendency to increase the size of herds discourages producers from regularly monitoring these variables, given the time and workforce required
[23][16].
6.3. Risk Factors of Ketosis
To prevent the emergence of ketosis, the study of risk factors and the most appropriate nutritional management has been the subject of discussion in various parts of the globe
[55][56][19,20]. The most prevalent and consistently referred risk factors are increased parity (number of lactations), high concentrations of NEFA in the predelivery period, and elevated body condition
[5]. Vanholder et al.
[56][20] also add the birthing season, duration of the dry period, duration of the previous lactation, and liters of colostrum produced as risk factors for developing hyperketonemia.