Factors Affecting Ketosis on a Large Southern Ontario Dairy Farm

Melissa L. Davies

Ontario Veterinary College, University of Guelph, Ontario

Tavistock Veterinarians, Tavistock, Ontario

Abstract

Subclinical ketosis is an important metabolic disease in transition dairy cows, which can lead to a decrease in milk production and increased incidence of diseases such as retained placenta, metritis, fatty liver and mastitis. Heat stress and feeding of a ration that contains butyric acid are two factors that could result in an increase in herd prevalence of subclinical and clinical ketosis. This study on a dairy herd in Southern Ontario examined the correlation of elevated ambient temperature, feeding silage containing high levels of butyric acid on the herd prevalence of ketosis. In this herd the increased baseline prevalence of ketosis in fresh cows, along with the variability of herd prevalence between tests was attributed to elevated ambient temperatures and feeding of silage containing high levels of butyric acid.

Introduction

Subclinical ketosis (SCK) has been defined as a condition marked by increased levels of circulating ketone bodies without the presence of clinical signs of ketosis (1). SCK causes economic losses in dairy herds directly by decreasing milk production and indirectly by increasing the risk for displaced abomasum and other periparturient diseases. Not only can SCK be a result of numerous disease processes that drive down feed intakes but it can also initiate further intake suppression, potentially resulting in other disease events such as displaced abomasum, fatty liver, endometritis, mastitis, retain placenta, or infertility. The first few weeks of lactation are associated with a negative energy balance and low dry matter intake (DMI), with a peak intake at eight to ten weeks post-calving. The resulting low serum concentrations of glucose and insulin can lead to the mobilization of body fat stores for use as energy causing a release of non-esterified fatty acids (NEFAs) into the blood stream, which in turn increases serum β-hydroxybutyrate (BHBA) (2).

The fresh cows included in this study calved between July 8th and August 30th, 2010 on a 150 cow, well- managed Holstein dairy herd in Southern Ontario. The cows are milked in a double 12 parallel parlour and housed in a 4 row free-stall mattress barn. Herd production in June, 2010 was 36Kg 3.5% BF and 3.1% protein with a pregnancy rate of 21%. Dry cows are housed in the free-stall barn and then moved to the close-up straw pack 3 weeks prior to expected calving. Immediately after calving, the dams are moved to the fresh pen, where they remain for a minimum of fourteen days, until moving to the free stall barn with the milking herd. The fresh pen is a straw bedding pack with self-locking headgates and a slatted floor along the feed bunk. The fresh cows were fed a haylage, corn silage, straw, protein supplement and mineral ration and the dry cows were fed straw, corn silage, protein, and mineral ration. Any animal that required treatment for ketosis after fourteen days fresh remained in the fresh pen until deemed “healthy” upon which they were moved to the free stall barn.

The cows, one to fourteen days fresh, were tested bi-weekly for fourteen days (minimum 4 tests/cow) for ketosis using a milk Keto-Test strip (Elanco Animal Health, Greenfield, IN) in addition to a basic physical exam including rectal temperature. For each cow, fresh milk was placed directly onto the pad of the Keto-Test strip, excess milk was shaken off and the strip was read after sixty seconds. A result of 100 µmol/L of BHBA was diagnosed as subclinical ketosis and the cow was treated by drenching with 300mL of glycol or Ketamalt (Bimeda®-MTC Animal Health Inc. Cambridge, Ontario)). A result of 200 µmol/L of BHBA or greater was treated with intravenous dextrose and Vitamaster (Vétoquinol Canada Inc. Lavaltrie, QC) along with pumping of water mixed with a fresh cow energy blend, and Ketamalt.

Results

Prevalence of Ketosis

This study was completed at this particular farm due to the high incidence of ketosis and the decrease of milk production from thirty six to thirty two kilograms. The prevalence of ketosis in the fresh cows was determined for each test dateand was examined over the period of two months: July and August. The Elanco Animal Health data sheet offers tools for investigation and implementation of action to reduce ketosis. One suggestion is that a herd ketosis prevalence of 20% should be the goal of most dairy farms (3). They have also set criteria that,if met, reveal the suspicion of a possible ketosis issue in the herd which may warrant further examination(Elanco Animal Health). One of Elanco Animal Health’s criteria for investigation of ketosis is the discovery of a herd prevalence that was three standard deviations above the 20% prevalence goal on one test date. This herd met the criteria withthree peaks greater than three standard deviations (Fig 1). This indicatedthat there was a ketosis issue in the fresh cows. These peaks occurred on July 19th(71%), July 28th(78%),and August 5th (88%), and were preceded by multiple days with maximum ambient temperatures above 26°C (Environment Canada; Appendix I).

Another interpretation guideline set by Elanco Animal Health states that an investigation is required if eight consecutive herd test results were above the 20% prevalence mark. On this dairy farm, all of the test dates resulted in a herd prevalence of 30% or higher (Fig 1) (Elanco Animal Health).

Figure 1: Herd prevalence of ketosis over fifteen test dates. The target herd prevalence of 20% has been starred and is marked as zero standard deviation (SD; red numbers). A standard deviation of three has also been marked. A vertical black line between test numbers 7 and 8 separates the tests completed in July and August, respectively.

Laboratory Data

Feed samples were collected in response to a decrease in butter fat, DMI and milk production. The samples were submitted to for laboratory analysis; which revealed a butyric acid level of 5.7% x 4.5kg DM. This feed had been fed to the fresh cows from July 1st to the beginning of September.

To examine if the elevated herd prevalence of ketosis was due to a close up dry cow issue, blood samples were drawn from all the cows in that pen on one test date. The blood was submitted to the laboratory to evaluate the NEFA level and all cows were within normal limits.

Disease Incidence

During the two month period in the fresh cow group there were two deaths; one from rupture of pelvic ligaments that was euthanized and one death from unknown causes. A necropsy was carried out on the cow that died from an unknown diagnosis; however, the decomposition was too severe to interpret the findings. There was a slightly increased incidence of metritis in the fresh cows; especially the cows that were positive on the Keto-Test strip.

Discussion

Silage containing Butyric Acid

Clostridial fermentation of silage can lead to the production of butyric acid and protein degradation products causing the feed to have a unique odor which is easy to detect. Published papers describing the feeding of silage containing butyric acid indicate that daily levels of over 50-100g/head/day can cause ketosis and levels over 200g/head/day may lead to severe ketosis (5,6,7,8). About 750g of butyrate is produced by the ruminal bacteria each day, and is used as metabolic energy for the muscles of the rumen; however, any excess butyrate is converted to serum BHBA, a volatile fatty acid, which increases the risk of developing ketosis (9). Silage containing butyric acid must not be fed in significant quantities to lactating animals, especially those cows in early lactation and close to calving. Instead, the producer can either: divert, dilute, or destroy the contaminated silage. Silage with low levels of butyric acid can be used to feed replacement heifers, late lactation cows, or far-off dry cows, but levels need to be monitored as it could impair DMI in these groups. Any feed containing over 2% butyric acid on a dry matter basis should be destroyed (9).

The level of butyric acid in the silage in this study equates to 250g/head/day, which is above the level suggested for causing severe ketosis. The reason the silage on this farm underwent abnormal fermentation that created butyric acid was that the first cut haylage was harvested and ensiled at 27% dry matter, which is extremely wet. This level of butyric acid can account for the herd prevalence of ketosis being greater than the goal of 20% in eight consecutive tests. It cannot, however, be the sole reason for the ketosis issue on this farm due to the presence of the dramatic peaks and troughs seen on the graph of herd prevalence (Fig 1). If this silage was the only contributing factor to the prevalence of ketosis in the fresh cows, the recorded herd prevalence should not vary so dramatically over such a short time period. In August the prevalence of ketosis in the herd slowly decreased which is in part because as the silage was fed from the bunker the level of butyric acid decreased. Also since the NEFA results from the dry cows were within normal limits it was ruled out that the elevated herd ketosis prevalence was a dry cow issue as well as the fact that the dry cows were not fed the haylage containing the butyric acid.

Heat Stress

Heat stress is a major factor that can negatively affect milk production in dairy cows, especially high-producing animals in early lactation. Roenfeldt (10) stated that the thermoneutral zone (TNZ) occurs when ambient temperatures are between 5°C and 25°C. When the environmental temperature is above this level the cow enters a state of heat stress due to the fact that she is not able to adequately decrease her temperature via thermoregulatory mechanisms. The shift in the dairy industry to higher producing cattle has potentially indirectly contributed to the sensitivity of cows to thermal stresses. As milk production increases, the cow must consume more nutrients, resulting in an increase in metabolic heat production. This, in turn, makes her more susceptible to heat stress at a lower ambient temperature (11). A cow responds to heat stress using numerous mechanisms, such as, increasing her respiratory rate and rectal temperature, panting, drooling, sweating, reducing her milk production, and decreasing DMI (11). Heat stress can be reduced by installing methods to cool the cows more effectively such as, sprinklers at the feed bunks and in the parlor, appropriately placed fans, open curtains, avoidance of over-crowding pens, etc.

The ambient temperature in Southern Ontario during the months of July and August 2010 reached record highs; therefore, heat stress was a significant concern among Ontario dairy producers throughout those months. As ambient temperature changes daily it potentially is the cause of the large peaks seen on the prevalence graph (Fig 1). The peaks correlate to multiple days of 26°C or greater temperatures causing a decrease in DMI and an increase in ketosis (Environment Canada).

The summative effects of heat stress and the feeding of silage containing butyric acid created an underlying ketosis concern on this particular dairy farm. However, during the period of high ketosis prevalence it was through consistent monitoring of the fresh cows with the KetoTest strips and treatment of positive cows, the incidence of disease as a result of severe clinical ketosis was averted in most cases. Monitoring of fresh cows for ketosis is a valuable tool and allows for treatment of subclinical cows in the hopes of improving their milk production before a dramatic decreases occurs and to avoid other medical conditions and associated treatments.

Acknowledgments

The author would like to thank the producer who allowed the study to be conducted on-farm and the bovine veterinarians at Tavistock Veterinarians especially Dr. Wayne Shewfelt for his guidance, support, and advice. Thank you.

References

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Appendix I

(Environment Canada)