HEAL ▶▶▶TH


A closer look at bovine coronavirus in calves


B


ovine coronavirus (BCoV) is a major viral pathogen associated with respiratory tract disorders and en- teric disease problems in the neonatal calf. The virus is shed both through respiratory and enteric secre- tions in high amounts (1 billion virus particles per ml) for up to 14 days. Consequently, BCoV infection is transmitted by fecal- respiratory route from the mother to the offspring or between calves.


Why calves? Calves are born with an underdeveloped immune system. Key parts of a calf’s immune system are present, but at much low- er levels than an adult cow. This means the newborn calf’s im- mune system is slower to respond to pathogens (dis- ease-causing bacteria, viruses, or microorganisms) and when it does, the response is weak. The immune system is not very effective until the calf is two to four weeks of age, and devel- opment continues until the calf reaches breeding age. This leaves the calf vulnerable to disease for a significant period of time at a crucial point in its development.


Predisposing factors of infection The incidence of BCoV varies between 15% and 70% in natu- rally occurring outbreaks worldwide. The following are the key factors determining the magnitude of infection:


Bovine coronavirus (BCoV) infection in calves causes major economic losses to the dairy (and beef) industry worldwide. We dig deep into what the respiratory signs of the infection are, treatment, and control measures.


Parity: The first-lactation heifers produce lower yields of co- lostrum and lower immunoglobulin (Ig) concentration in co- lostrum than cows in their second or subsequent lactation (Table 1). Therefore, calves born to these heifers are more susceptible to BCoV infection.


Cold stress: Cold stress has negative effects on the absorptive function by the intestine, and hence on the concentration of all classes of colostrum Ig in the serum of the hypothermic calves.


Husbandry systems: Under intensive management systems adopted in dairy farms, there is a close interaction between calves since these animals are reared and fed milk replacers lacking antibodies, in stark contrast with beef cattle farms, where herds are reared under extensive management sys- tems and calves are fed directly from the dams’ milk until they reached 6 months of age.


BCoV is associat- ed with respira- tory tract disor- ders and enteric disease prob- lems in the neonatal calf.


▶DAIRY GLOBAL | Volume 7, No. 2, 2020 21


PHOTO: HENK RISWICK


Page 1  |  Page 2  |  Page 3  |  Page 4  |  Page 5  |  Page 6  |  Page 7  |  Page 8  |  Page 9  |  Page 10  |  Page 11  |  Page 12  |  Page 13  |  Page 14  |  Page 15  |  Page 16  |  Page 17  |  Page 18  |  Page 19  |  Page 20  |  Page 21  |  Page 22  |  Page 23  |  Page 24  |  Page 25  |  Page 26  |  Page 27  |  Page 28