In-depth data analysis: the health of older cows
The average age of cows on dairy farms has increased since 2019, an important and favourable development towards sustainable dairy farming. Previous research has shown that there is a lot of spread in lifespans and that it depends on management decisions made by the farmer. An increase in average age requires good management to allow cows to stay healthy as they age. In-depth research has therefore recently been carried out comparing various animal health metrics (such as cell count, number of inseminations, calf mortality and multiple births) between cows of different ages: those younger than 3 years, cows aged 3 to 5, 6 to 8, and 8 years and older.
The study showed that the cell count increased as the age groups became older, with cows under 3 years of age having the lowest somatic cell counts (Figure 1). The cell count increased as cows aged, even allowing for traits that could also explain some of the variation (such as farm size, milk production level and region). Cows aged 6 to 8 have somatic cell counts that average 25,100 cells/ml higher than those aged 3 to 5 years. In cows aged above 8, this difference is even greater, at an average of 53,300 cells/ml higher. This elevated somatic cell count may be the result of management decisions or may have physiological or immunological reasons. There was also a difference in the mortality percentages of non-ear-tagged calves born to mothers of various ages. The likelihood of a calf dying before the moment it was ear-tagged was higher for cows younger than 3 years than for cows aged 3 to 5. Calving problems are more common in heifers than in older cows because the birthing process is taking place for the first time. The percentage of multiple births in older cows (aged >6) is significantly higher than in younger cows, e.g. averaging 4 per cent in cows aged over six, compared to an average of 2.5 per cent in younger cows. This metric is stable over time, with seasonal variation that is perhaps related to management factors such as the feed. The metrics studied show that there is a large amount of variation between the different age groups.
Animal health monitoring
Royal GD has been responsible for animal health monitoring in the Netherlands since 2002, in close collaboration with the veterinary sectors, the business community, the Ministry of Agriculture, Fisheries, Food Security and Nature, veterinarians and farmers. The information used for the surveillance programme is gathered in various ways, whereby the initiative comes in part from vets and farmers, and partly from Royal GD. This information is fully interpreted to achieve the objectives of the surveillance programme – rapid identification of health issues on the one hand and monitoring trends and developments on the other. Together, we team up for animal health, in the interests of animals, their owners and society at large.
Eye disorders pilot Trigger
In September and October, large numbers of reports about eye abnormalities in calves were received by the Veekijker over the course of just a few weeks. We would normally receive an average of two to four calls about this, but in September and October there were ten and sixteen respectively. The vets were describing calves with a blue-white haze over the eyes, in some cases combined with a tapering protrusion, distorting the eyeball. In later stages, the eyes of in some calves had ulcers (some perforated), secondary infections and deep blood vessel formation. The calves had little or no vision. The reports were about calves in the 0-14-day age category on dairy farms, as well as calves older than 14 days on veal calf farms. Eye abnormalities can be caused by Moraxella bovis (pinkeye), Mycoplasma bovis, septicaemia, congenital hypovitaminosis A, malignant catarrhal fever (MCF) and congenital bovine viral diarrhoea (BVD) infection. It was also described in calves during the bluetongue virus (BTV) serotype 8 outbreak in the Netherlands in 2007. In some affected calves, previous investigations had shown both BTV antibodies and virus. It was unclear whether the individual mothers of affected calves had also experienced bluetongue infections and/or had been vaccinated. Given the age of the youngest calves, the possibility of antibodies being transferred through the colostrum was taken into account. After discussions in the Veekijker team, it was decided to launch a pilot study to enable these signals to be interpreted better.
Follow-up
A pilot proposal was written and then reviewed by the Animal Welfare Authority, given the involvement of live animals in the clinical diagnostics being performed. The pilot study that was drawn up aimed to answer questions about the onset, clinical picture, evolution and recovery of the condition, as well as the possible association with BTV-3. A dairy farm, a youngstock rearing farm and a veal calf farm were visited. On these farms, the case histories were taken and several calves with eye abnormalities were examined clinically, including a comprehensive eye examination. Photographic and video material was collected during the examinations for later review if necessary. In addition, samples were taken from the calves and (where possible) their mothers. Blood samples from ten calves were tested for BTV (by PCR), BTV antibodies (by ELISA), BVD virus (by PCR) and BVD antibodies (by ELISA). Eye swabs from the calves were examined bacteriologically (for both aerobic and anaerobic bacteria). Blood samples from the mother animals (where available) were tested for BTV virus and BTV antibodies.
Outcome
The calves in this pilot were not born with eye defects but developed them over a period ranging from two days up to several weeks of age. Eye examinations showed that nine out of the ten calves exhibited corneal oedema, in some cases associated with ulceration of the cornea, keratoconus and varying degrees of blindness (see Figure 2). No other unusual clinical symptoms were observed. The severity of the corneal oedema varied, as did the time to recovery, with the oedema sometimes disappearing completely without permanent damage, according to the farmers concerned. Both BTV virus particles and BTV antibodies were detected in all the calves with corneal oedema. BTV virus and BTV antibodies were also detected in the mother animals that were examined. The BVD virus was additionally detected in one calf and another had antibodies to BVD as well as to BTV. Eye swabs showed no evidence of Mycoplasma bovis; Moraxella bovoculi was cultured in a single case. The findings, for which the presence of BTV virus and BTV antibodies was the only common factor, suggest an association between BTV infection and the observed ocular abnormalities (specifically corneal oedema) in the calves studied.
Trigger
At the end of the third quarter and during the fourth quarter of 2024, it was striking that several cases of polyserositis caused by Mannheimia haemolytica (Mh) were diagnosed in breeding calves on pathological examination. Polyserositis is a condition in calves aged from about three weeks to several months. It is an acute or peracute infection of the peritoneum, pleura and/or pericardium, in which calves that were in good condition are suddenly found seriously ill or dead. Over the past fifteen years, the percentage of veal calves with polyserositis caused by Mh has increased. Studies have shown that this is due to Mh serotype A2, whereas Mh serotype A1/A6 is often diagnosed in pleuropneumonia in dairy cattle. Although polyserositis is a wellknown clinical picture in veal calves, it is rarely seen in breeding calves. To gain a clearer picture of what these section findings mean, it was decided to launch a pilot study.
Follow-up
This pilot study investigated how frequently polyserositis caused by Mh has been diagnosed in breeding calves over the past 22 years, and a farm visit was also conducted. Samples were taken at the farm where one of the calves originated. These samples were examined by PCR, bacteriological tests, susceptibility testing and whole genome sequencing (WGS). The veterinary practice of the three dairy farms that the calves came from was also contacted by phone.
Outcome
Over the past two decades, small numbers of cases (0-6) of polyserositis caused by Mannheimia haemolytica have been diagnosed every year in breeding calves; there were four cases in 2024. There has therefore been no increase in the number of cases identified. In two of the three calves submitted, multiplex PCR determined that the Mh was serotype A2, as also found in polyserositis in veal calves. Further investigations revealed that the infection was contracted in group accommodation. The Mh strains detected exhibited little or no resistance to antibiotics, in contrast to the Mh serotype A2 strains usually isolated from veal calves. The farm that was visited was a regular dairy farm.
