Identify Opportunities for Better Heifer Health

By: Jason Lombard, DVM, MS, Natalie Urie, MPH, DVM, Chelsey Shivley, DVM, PhD, DACAW, USDA:APHIS:VS:Center for Epidemiology and Animal Health

Contributors to these reports also include: C. A. Kopral, A. E. Adams, T. J. Earleywine, J. D. Olson, F. B. Garry, D. M. Haines, R. Sargent, M. Santin, C. Stenkamp-Strahm, R. J. Magnuson, L. M. Linke, S. Magzamen, and C. S. McConnel.

Raising heifer calves costs producers approximately $5.50 per calf per day, but that generally does not exceed the expense of purchasing a springing heifer. Therefore, ensuring that preweaned heifer calves are managed properly to produce healthy dairy cows is extremely important to the industry.

In January 2014, the USDA’s National Animal Health Monitoring System (NAHMS) launched its sixth national dairy study. As with all NAHMS national studies, objectives for the Dairy 2014 study were identified through focus groups and a needs assessment survey completed by various stakeholders in the U.S. dairy industry.

The study encompassed a broad range of dairy practices for managing cows, heifers and calves, and generated a series of summary reports, available online at the NAHMS website:

https://www.aphis.usda.gov/aphis/ourfocus/animalhealth/monitoring-and-surveillance/nahms

In addition, researchers from USDA and Colorado State University drew upon data from the Dairy 2014 study to generate six research reports specifically on preweaned heifer management in the United States. The six reports were published in the Journal of Dairy Science in 2018. This article summarizes key points from the first three of those reports, and summaries of the final three reports will follow in part two of this series.

Descriptive characteristics of preweaned heifer raising practices

In this report, we describe preweaned dairy heifer calf management practices used to analyze factors associated with colostrum quality and passive transfer, Cryptosporidium and Giardia, morbidity and mortality, and average daily gain.

The study included 104 dairy operations in 13 states that participated in the NAHMS Dairy 2014 calf component study. This 18-mo longitudinal study focused on dairy heifer calves from birth to weaning, and data were collected on 2,545 heifer calves. The research team generated data regarding colostrum feeding, preweaning housing, milk feeding and consumption, growth, morbidity and mortality, and weaning practices.

Key findings include:

• Most calves enrolled (89.4%) were Holsteins.
• Over half the calves enrolled in the study (63.2%) received the majority of their colostrum via bottle, though twenty-two percent of calves from 51% of operations received colostrum via suckling from their dams.
• For all calves, the mean time to the first colostrum feeding was 2.8 hours after birth.
• The average amount of colostrum at the first feeding was 2.9 liters, with 4.5 liters provided in the first 24 hours.
• The mean serum immunoglobulin G (IgG) of all calves was 21.7 grams per liter (g/L); however, 76.0% of operations had at least one calf with failure of passive transfer of immunity with a serum IgG below 10 g/L.
• The majority of calves in the study (86.6%) were housed individually, while 20.2% of operations housed some calves in groups, representing 13.4% of all calves.
• Approximately one-half of the calves in the study (52.3%) were dehorned or disbudded during the preweaning period, and only 27.8% of those calves received analgesics or anesthetics during the dehorning or disbudding procedure.
• Producers fed whole or waste milk to 40.1% of calves, and milk replacer to 34.8% of calves, with 25.1% of calves receiving a combination of milk and milk replacer.
• Calves, on average, were fed 2.6 liters per feeding and fed 2.6 times per day, resulting in a total of 5.6 liters of liquid diet fed per day.
• On average, the average daily gain for calves enrolled in the study was 0.7 kilograms per day.
• Based on fecal samples, 94.2% of operations had at least one calf positive for Cryptosporidium while 99% had at least one positive for Giardia, and 84.6% of operations had calves that tested positive for both Cryptosporidium and Giardia.
• Over one-third of calves (38.1%) had at least one morbidity event during the preweaning period, and the mortality rate was 5%.
• The mean age at weaning was 65.7 days.

This study, along with the overall Dairy 2014 Study, show areas that have improved within the dairy industry, such as decreased mortality and decreased failure of passive transfer. Additionally, this study describes areas where producers can continue to advance heifer calf management and welfare, such as enhanced feeding programs to increase ADG, detection of clinical disease signs, and weaning programs to efficiently and effectively wean calves. As stated earlier, rearing heifer calves is an expensive endeavor. Therefore, research to maximize the efficiency of raising replacement heifers and minimize losses due to morbidity and mortality is extremely important.

Factors associated with colostrum quality and passive transfer status of dairy heifer calves

Passive transfer of immunity via colostrum is essential for the short- and long-term health of dairy calves. Researchers have understood the importance of colostrum for prevention of disease in neonatal ruminants for over 100 years, yet 19.2% of calves in the United States still had failure of passive transfer (FPT) in 2007, with a serum IgG below 10 g/L. Consumption and absorption of maternal Immunoglobulins via colostrum are critical for reducing disease and mortality in calves in the first weeks of life, because calves are essentially agammaglobulinemic at birth.

The primary components of colostrum that contribute to passive immunity are immunoglobulins, which include IgG, IgA, and IgM. IgG comprises about 85% of the immunoglobulin in colostrum. Relative to IgG content, high-quality colostrum is defined as having an IgG concentration greater than 50 g/L. In addition to water, colostrum contains important components, such as protein, vitamins, minerals, and fat, which provides neonatal calves essential nutrients. Factors previously determined to be associated with colostrum quality included parity, breed and season of calving.

The objective of this study was to evaluate factors associated with colostrum quality and passive transfer status of U.S. heifer calves. This study included 104 operations in 13 states that participated in the calf component of the NAHMS Dairy 2014 study. This 18-mo longitudinal study included 1,972 Holstein heifer calves from birth to weaning.

The research team used multivariable mixed linear regression models to determine which factors were associated with colostrum IgG and serum IgG concentrations. Key findings include:

• The mean colostrum IgG concentration was 74.4 g/L with 77.4% of colostrum samples having IgG concentrations greater than 50 g/L. The final model for colostrum IgG included colostrum source and a categorized temperature-humidity index value (cTHI) for the month before calving.
• Mean colostrum IgG concentrations were highest for dams in third and higher lactations (84.7 g/L) and lowest for commercial colostrum replacers (40.3 g/L).
• Colostrum IgG concentrations were highest for cTHI greater than or equal to 70 (72.6 g/L) and lowest for cTHI less than 40 (64.2 g/L).
• The mean serum IgG concentration was 21.6 g/L, with 73.3% of calves having serum IgG concentrations greater than 15 g/L.
• The final model for serum IgG concentration included region, heat treatment of colostrum, colostrum source, timing to first feeding, volume of colostrum fed in the first 24 hours, age of the calf at blood sampling, and colostrum IgG concentration.
• Mean serum IgG concentrations were highest for calves that received colostrum from first-lactation dams (25.7 g/L) and lowest for calves fed commercial colostrum replacer (16.6 g/L).
• Serum IgG concentrations were higher for calves fed heat-treated colostrum (24.4 g/L) than for calves fed untreated colostrum (20.5 g/L).
• Serum IgG concentration was positively associated with the volume of colostrum fed in the first 24 hours and colostrum IgG concentration, and negatively associated with the number of hours from birth to colostrum feeding and age, in days, at blood collection.

Colostrum quality is generally defined by IgG concentration, with concentrations of IgG greater than 50 g/L indicating excellent quality colostrum. Results from this study showed that overall colostrum quality available to heifer calves on U.S. dairy farms was excellent. The mean concentration of 74.4 g/L of IgG was significantly higher than the goal of 50 g/L and similar to the mean of 68.8 g/L previously reported.

Additionally, more than three-fourths of colostrum samples tested (77.4%) were above the target IgG concentration of 50 g/L. This shows significant improvement in colostrum quality since 1992, when 93.3% of samples on a Florida dairy had colostrum IgG concentrations below 50 g/L. However, 22.6% of colostrum samples in the current study had IgG less than 50 g/L and 13.2% had concentrations below 40 g/L. Considering the ease and availability of on-farm assessment tools for colostrum quality, including colostrometer and Brix refractometers, producers can test and avoid feeding poor-quality colostrum.

Based on research results, veterinarians should encourage dairy producers to measure the quality of colostrum before administering it to calves and to measure serum IgG or a proxy such as serum total protein or Brix to evaluate passive immunity and colostrum management programs.

Factors associated with Cryptosporidium and Giardia in preweaned dairy heifer calves

Cryptosporidium parvum and Giardia duodenalis are intestinal protozoa that are commonly found in calves and have the potential to cause diarrhea. Cryptosporidium causes diarrhea via destruction of the small intestinal epithelium. Epithelial destruction results in villus atrophy, crypt hyperplasia, and cell death, which lead to impaired nutrient digestion and transport. Cryptosporidium in endemic herds has morbidity rates that may reach 100%; however, mortality is infrequently observed.

Giardia causes diarrhea via diffuse shortening of the brush border microvilli and decreased activity of the small intestinal brush border enzymes, specifically lipase. The microvillus shortening leads to a decrease in absorptive capacity of the small intestine. The combined effects of decreased resorption and brush border enzyme deficiencies results in malabsorptive diarrhea and decreased weight gain.

The objective of this study was to evaluate management practices and environmental factors associated with cryptosporidiosis and giardiasis in preweaned heifer calves on U.S. dairy operations.

For this 18-month study, researchers collected fecal samples from 2,249 calves: 839 calves in the West region (CA, CO, and WA) and 1,410 calves in the East region (IA, MI, MN, MO, NY, OH, PA, VT, VA, and WI). A single fecal sample per calf was collected from three to 66 days of age, with a mean of 22 days.

The team used backward elimination logistic model selection after univariate screening to determine which management practices and environmental factors significantly affected the presence of Cryptosporidium or Giardia. The final Cryptosporidium model included herd size, days of age at fecal collection, and average temperature-humidity index for the month of fecal collection (fTHI).

The final Giardia model included herd size, days of age at fecal collection, average fTHI, failure of passive transfer status, and average daily gain (kg/d) during the preweaning period.

Key findings include:

• Overall, Cryptosporidium and Giardia were detected in 43.1 and 30.5% of fecal samples, respectively.
• Cryptosporidium was found on a higher percentage of large operations (500 or more cows) than small operations (30 to 99 cows).
• Younger calves were more likely to have a fecal sample positive for Cryptosporidium than samples from older calves.
• Fecal samples from calves during the warmer parts of the year (fTHI greater than 70) were more likely to be positive for Cryptosporidium than samples collected in colder months (fTHI less than 20).
• Giardia was isolated more frequently from calves on small operations than on large operations
• Older calves were more likely to have a fecal sample positive for Giardia than younger calves.
• Giardia was more frequently isolated in warmer months.
• Samples from calves with failure of passive transfer were more likely to have Giardia than calves with adequate passive transfer (greater than 10 g/L IgG).
• Average daily gain during the preweaning period was lower in calves from which Giardia was isolated.

Currently, there are no licensed drugs in the United States available to treat Cryptosporidium or Giardia in ruminants. Supportive therapy, including fluids and electrolytes, is recommended for calves with

Cryptosporidium- or Giardia-induced diarrhea. Additionally, because infection of both protozoans occurs via the fecal-oral route, directly via the ingestion of feces or indirectly via ingestion of contaminated food or water, good husbandry, including the removal of feces from calf environments, will help minimize re-infection and transmission of Cryptosporidium and Giardia.

Infections with Cryptosporidium and Giardia are of public health concern because some of their species and assemblages are zoonotic.

Our results show that various factors play a role in the prevalence of Cryptosporidium and Giardia in preweaned dairy heifer calves. The Cryptosporidium prevalence of 43.1% and the Giardia prevalence of 30.5% were similar to those of previously reported studies, illustrating the persistence of these pathogens in the dairy industry. Ensuring adequate passive transfer will decrease the likelihood of protozoal infection. Additionally, decreasing the likelihood of protozoal infection may result in calves with a higher ADG throughout the preweaning period.

The next article in this series will summarize three more reports on management issues affecting preweaned dairy heifers:

• Factors associated with the presence of Escherichia coli O157 in preweaned dairy heifers
• Factors associated with morbidity and mortality in preweaned dairy heifer calves
• Factors associated with average daily gain in preweaned dairy heifer calves