Antibodies to Bovine Leukemia Virus in a Leukosis Dairy Herd and Suggestions for Control of the Infection G. A. A. Ferdinand, A. Langston, R. Ruppanner, S. Drlica, G. H. Theilen and D. E. Behymer* ABSTRACT A closed herd of 765 Holstein-Friesian dairy cattle with a history of multiple cases of leukosis was tested for antibodies to bovine leukemia virus by the bovine leukemiaglycoprotein immunodiffusion test. A total of 355 animals (46.4%) were antibody positive. Prevalence was 60% in the 373 milking cows and 100% in the breeding bulls. Antibodies were present in 59% of newborn calves. Prevalence of antibodies was higher in older animals and cows in second lactation had a higher prevalence than cows in first lactation (72% vs 43%). Proposed control measures in this herd aim at preventing infection of calves, heifers and lactating cows by: 1) separating them into groups negative and positive for bovine leukemia virus antibodies, 2) not allowing calves to receive colostrum or milk from infected cows and 3) by using seronegative bulls for natural breeding tested at three month intervals. Calves should be tested after six months of age. Before this time calves of positive mothers should be treated as being positive.
de 765 sujets Holstein-Friesian au sein duquel on avait deja diagnostique plusieurs cas de cette maladie. Les resultats de l'epreuve spavererent positifs chez 355 sujets, i.e. 46.4% du troupeau; 60% des 373 vaches en lactation et 100% des taureaux reproducteurs donnerent des resultats positifs; 59% des veaux nouveau-nes recelaient aussi des anticorps. Le taux d'anticorps s'avera plus 0leve chez les sujets plus ages, e.g. 72% des vaches qui en etaient 'a leur deuxieme lactation et, 43% de celles qui en etaient a leur premiere eurent des anticorps. Afin de prevenir l'infection des veaux, des taures et des vaches en lactation de ce troupeau, les auteurs proposerent les mesures sanitaires suivantes: 1 - La separation des sujets seronegatifs d'avec les seropositifs; 2 Le retrait du colostrum et du lait des vaches seropositives, de l'alimentation des veaux; 3 - L'utilisation exclusive de taureaux reagissant de faqon negative 'a des dpreuves serologiques trimestrielles, pour les saillies naturelies. II faudrait aussi soumettre "a l'epreuve serologique les veaux ages de six mois et considerer comme positifs les plus jeunes, issus de vaches seropositives.
RASUMA
INTRODUCTION
Les auteurs ont utilise l'epreuve de l'immunodiffusion sur gelose pour proceder 'a la recherche d'anticorps a l'endroit du virus de la leucemie bovine, dans un troupeau ferme *Department of Epidemiology and Preventive Medicine (Ferdinand, Langston, Ruppanner and Behymer), Department of Veterinary Surgery (Theilen), School of Veterinary Medicine, University of California, Davis, California 95616 and the USDA, Veterinary Services (Drlica), Sacramento, California 95825. Supported in part by NIH, USPHS and Trinidad Tobago Government, PAHO/WHO. Submitted February 7, 1978.
Volume 43 - April, 1979
Bovine leukosis, a disease of low incidence, produces economic loss in the forms of decreased milk production, decreased reproductive efficiency, weight losses, deaths and condemnations at slaughter (13,19). There is evidence that bovine leukemia virus (BLV) can be transmitted horizontally from cow to cow (8,17,19,21), vertically from infected cows to 14% of their fetuses in utero (10) and experimentally via milk (3,19). The disease has been shown to be more prevalent in certain cow families (1,
173
6,7), suggesting possible genetic or epi- Friesian dairy cattle varying from day old genetic transmission and heritable sus- calves to 12 year old cows. The herd had ceptibility factors. Antibodies to BLV have multiple cases of leukosis over the past 16 been reported in 2 to 16% of cattle in years. Four breeding bulls are routinely certain leukosis-free herds and in 24 to used for natural service and artificial in42% of cattle in herds with histories of semination is used for difficult breeders. clinical leukosis (9) as well as in 80 to Newborn calves are removed from their 100% of clinically normal cattle with per- dams during the first day of life at the sistent lymphocytosis in multiple-case convenience of the caretaker. All calves are herds (8). Persistent lymphocytosis, one given 2 L of refrigerated colostrum from way in which certain cattle respond to in- any available cow via esophageal tube. fection with BLV, has been used as an Colostrum from first calf heifers is not indicator of infection in the Danish pro- used for this purpose (Fig. 1). Animals were bled from a jugular or gram for control of bovine leukosis (5). No antibodies to BLV are found in coccygeal vein via 18-gauge needles into animals with juvenile, thymic and skin evacuated blood-collection vials without forms of leukosis (16). No studies have anticoagulant. Serum was separated by demonstrated that infection with BLV in centrifugation after overnight storage at dairy cows has public health significance. 4°C. Serum samples were tested by the The virus in milk is inactivated by pas- bovine leukemia glycoprotein immunodifteurization (3). Studies in Iowa, Wisconsin fusion (BL-GID) test.' Immunodiffusion and Sweden found no antibodies to BLV plates were read at 24 and 48 hours and in such high risk groups as veterinarians, the results recorded as either negative or laboratory workers and farm families who positive. The Chi-square statistic (17,18) drink unpasteurized milk, nor have such was used to investigate whether BLV antiantibodies been found in humans suffering body status was associated with: 1) age from leukemia or other forms of cancer (3, and lactation number 2) pregnancy and 3) 12,14). A concurrent study has shown that calving. Statistical analyses were carried clinically normal cows serologically positive out at the 95% confidence level. for BLV antibodies did not have lower milk production nor lower reproductive efficiency than antibody-negative cows RESULTS
(15).
These findings, together with the demonstrated lack of public health significance of BLV, the low incidence of clinical disease (19,24) and the incomplete success of control programs based on slaughter of animals with "high" lymphocyte counts (11), suggest recourse to a type of program based on prevention of infection by the virus. This study examines: 1) the prevalence of BLV infection in different age groups of cattle, 2) the effect of sexual maturity, pregnancy and calving on the prevalence of infection and 3) the individual and combined effects of age and number of lactations on antibody status in one dairy herd. A relatively inexpensive, practicable program for the control of infection with BLV in this herd is suggested.
MATERIALS AND METHODS The herd consisted of 765 Holstein-
174
The prevalence of BLV antibodies was 46.4 % in the herd and 60 % in the 373 milking cows. In age groups with ten or more animals prevalence was lowest (7%) among five month old calves and highest (72%) among 23 month old heifers. It was 18% among the 22 steers and 100% among the five bulls (Table I). Prevalence was 29 % among the 174 heifers of this dairy herd (Table I). It was 25% for 85 heifers which had no contact with bulls and 37% for the 89 heifers that did. On this dairy farm most heifers are exposed to the bulls at the age of 18 months and remain in contact with the bulls for varying periods of time. Since age and duration of contact with bulls increase simultaneously the effects of these two variables on prevalence may be confounded (Table II). Prevalence was 35 % among 37 nonLeukassay-B, Pitman-Moore, Inc., Washington Crossing, N.J. 08560.
Can. J. comp. Med.
Birth of a calf 1
Calf may nurse its dam
Removed from dam on the first day of life Given refrigerated colostrum from any one dam
1
Bull-calves are sold before 2 wks old
Housed individually until 7 weeks old Fed milk, water and vitamins Free choice of grain after 1 week old Housed in groups of 3 to 10 until 3½ months old Hay is added to ration Groups of about 60 calves in drylot until 8 months old (without bull)
Groups of about 100 heifers in drylot until 15 months old (without bull)
Heifers are moved to drylot with bull when about 15 to 20 months old Heifer's and bull's identification and date are recorded Average time spent with bull (until pregnant) = 2 to 3 months Heifers remain with bull until 7 to 8 months pregnant Pregnant heifers now moved to dry-cow drylot
de 765 sujets Holstein-Friesian au sein duquel on avait deja diagnostique plusieurs cas de cette maladie. Les resultats de l'epreuve spavererent positifs chez 355 sujets, i.e. 46.4% du troupeau; 60% des 373 vaches en lactation et 100% des taureaux reproducteurs donnerent des resultats positifs; 59% des veaux nouveau-nes recelaient aussi des anticorps. Le taux d'anticorps s'avera plus 0leve chez les sujets plus ages, e.g. 72% des vaches qui en etaient 'a leur deuxieme lactation et, 43% de celles qui en etaient a leur premiere eurent des anticorps. Afin de prevenir l'infection des veaux, des taures et des vaches en lactation de ce troupeau, les auteurs proposerent les mesures sanitaires suivantes: 1 - La separation des sujets seronegatifs d'avec les seropositifs; 2 Le retrait du colostrum et du lait des vaches seropositives, de l'alimentation des veaux; 3 - L'utilisation exclusive de taureaux reagissant de faqon negative 'a des dpreuves serologiques trimestrielles, pour les saillies naturelies. II faudrait aussi soumettre "a l'epreuve serologique les veaux ages de six mois et considerer comme positifs les plus jeunes, issus de vaches seropositives.
RASUMA
INTRODUCTION
Les auteurs ont utilise l'epreuve de l'immunodiffusion sur gelose pour proceder 'a la recherche d'anticorps a l'endroit du virus de la leucemie bovine, dans un troupeau ferme *Department of Epidemiology and Preventive Medicine (Ferdinand, Langston, Ruppanner and Behymer), Department of Veterinary Surgery (Theilen), School of Veterinary Medicine, University of California, Davis, California 95616 and the USDA, Veterinary Services (Drlica), Sacramento, California 95825. Supported in part by NIH, USPHS and Trinidad Tobago Government, PAHO/WHO. Submitted February 7, 1978.
Volume 43 - April, 1979
Bovine leukosis, a disease of low incidence, produces economic loss in the forms of decreased milk production, decreased reproductive efficiency, weight losses, deaths and condemnations at slaughter (13,19). There is evidence that bovine leukemia virus (BLV) can be transmitted horizontally from cow to cow (8,17,19,21), vertically from infected cows to 14% of their fetuses in utero (10) and experimentally via milk (3,19). The disease has been shown to be more prevalent in certain cow families (1,
173
6,7), suggesting possible genetic or epi- Friesian dairy cattle varying from day old genetic transmission and heritable sus- calves to 12 year old cows. The herd had ceptibility factors. Antibodies to BLV have multiple cases of leukosis over the past 16 been reported in 2 to 16% of cattle in years. Four breeding bulls are routinely certain leukosis-free herds and in 24 to used for natural service and artificial in42% of cattle in herds with histories of semination is used for difficult breeders. clinical leukosis (9) as well as in 80 to Newborn calves are removed from their 100% of clinically normal cattle with per- dams during the first day of life at the sistent lymphocytosis in multiple-case convenience of the caretaker. All calves are herds (8). Persistent lymphocytosis, one given 2 L of refrigerated colostrum from way in which certain cattle respond to in- any available cow via esophageal tube. fection with BLV, has been used as an Colostrum from first calf heifers is not indicator of infection in the Danish pro- used for this purpose (Fig. 1). Animals were bled from a jugular or gram for control of bovine leukosis (5). No antibodies to BLV are found in coccygeal vein via 18-gauge needles into animals with juvenile, thymic and skin evacuated blood-collection vials without forms of leukosis (16). No studies have anticoagulant. Serum was separated by demonstrated that infection with BLV in centrifugation after overnight storage at dairy cows has public health significance. 4°C. Serum samples were tested by the The virus in milk is inactivated by pas- bovine leukemia glycoprotein immunodifteurization (3). Studies in Iowa, Wisconsin fusion (BL-GID) test.' Immunodiffusion and Sweden found no antibodies to BLV plates were read at 24 and 48 hours and in such high risk groups as veterinarians, the results recorded as either negative or laboratory workers and farm families who positive. The Chi-square statistic (17,18) drink unpasteurized milk, nor have such was used to investigate whether BLV antiantibodies been found in humans suffering body status was associated with: 1) age from leukemia or other forms of cancer (3, and lactation number 2) pregnancy and 3) 12,14). A concurrent study has shown that calving. Statistical analyses were carried clinically normal cows serologically positive out at the 95% confidence level. for BLV antibodies did not have lower milk production nor lower reproductive efficiency than antibody-negative cows RESULTS
(15).
These findings, together with the demonstrated lack of public health significance of BLV, the low incidence of clinical disease (19,24) and the incomplete success of control programs based on slaughter of animals with "high" lymphocyte counts (11), suggest recourse to a type of program based on prevention of infection by the virus. This study examines: 1) the prevalence of BLV infection in different age groups of cattle, 2) the effect of sexual maturity, pregnancy and calving on the prevalence of infection and 3) the individual and combined effects of age and number of lactations on antibody status in one dairy herd. A relatively inexpensive, practicable program for the control of infection with BLV in this herd is suggested.
MATERIALS AND METHODS The herd consisted of 765 Holstein-
174
The prevalence of BLV antibodies was 46.4 % in the herd and 60 % in the 373 milking cows. In age groups with ten or more animals prevalence was lowest (7%) among five month old calves and highest (72%) among 23 month old heifers. It was 18% among the 22 steers and 100% among the five bulls (Table I). Prevalence was 29 % among the 174 heifers of this dairy herd (Table I). It was 25% for 85 heifers which had no contact with bulls and 37% for the 89 heifers that did. On this dairy farm most heifers are exposed to the bulls at the age of 18 months and remain in contact with the bulls for varying periods of time. Since age and duration of contact with bulls increase simultaneously the effects of these two variables on prevalence may be confounded (Table II). Prevalence was 35 % among 37 nonLeukassay-B, Pitman-Moore, Inc., Washington Crossing, N.J. 08560.
Can. J. comp. Med.
Birth of a calf 1
Calf may nurse its dam
Removed from dam on the first day of life Given refrigerated colostrum from any one dam
1
Bull-calves are sold before 2 wks old
Housed individually until 7 weeks old Fed milk, water and vitamins Free choice of grain after 1 week old Housed in groups of 3 to 10 until 3½ months old Hay is added to ration Groups of about 60 calves in drylot until 8 months old (without bull)
Groups of about 100 heifers in drylot until 15 months old (without bull)
Heifers are moved to drylot with bull when about 15 to 20 months old Heifer's and bull's identification and date are recorded Average time spent with bull (until pregnant) = 2 to 3 months Heifers remain with bull until 7 to 8 months pregnant Pregnant heifers now moved to dry-cow drylot
