30 5 4 6 3 24 34 . 5 93 4 2 5 9 24 29 . 9 219 4 2 5 4 20 32 . 7 124 6 4 4 12 36 36 . 3 165 5 2 6 7 27 34 . 0 95 2 2 9 9 12 39 . 5 106 2 0 6 6 11 38 . 6 1 5 3 6 7 32 31 . 8 223 6 2 5 4 15 30 . 4 29 6 5 5 2 32 34 . 0 41 4 2 5� 5 27 40 . 8 19 5� 4 5 6 14 44 . 5 173 5 3 6 8 14 39 . 0 188 3 4 3� 6 38 34 . 0 206 3 2 4� 6 15 41 . 3 215 5 3 4 6 26 36 . 3 117 2 2 6 9 14 39 . 5 72 5 2 6 5 14 44 . 0 113 6 5t 5 2 48 31 . 3 121 8 4 5 2 36 36 . 7 115 6 3 5 2 36 33 . 6 1124 6t 4� 4� 2 24 33 . 1 26 3 1 4� 7 18 44 . 0 156 6 3 4 6 48 33 . 6 174 3 1 5 9 14 42 . 6 20 6 4� 4! 3 52 34 . 5 130 5 2i 5 9 14 36 . 3 1128 5 2 5i 8 16 34 . 5 6 4 2 7 13 12 37 . 6 207 1 .1. 2 2 6 14 34 . 0 172 5 2 8 7 15 34 . 9 78 6 4 3 12 30 40 . 8 84 8 4! 6 6 36 41 . 3
but develop peak titres after suckling as soon as 11 hours after birth ( Table 3 . 11 ) . A single feed of colostrum is all that i s necessary for the development o f the usual level of agglutinating antibody found in new-born calve s . This was shown when two litres
of colostrum, with a hardjo titre of 1 : 543, were fed to a _.calf :
resulting in the development of a titre of 1 : 384 .
The finding that 80% of new-born c alves had hardjo titres
and 24% had pomona titres of 1 : 24 or greater ( Table 3 . 1 ) probably
underestimates the true situation . A proportion of the calves
sampled, particularly from the first two c alvings , were up to 47 days old when first sampled , and may have lost low titres present at b irth . The regression lines fitted to the data for spring 197 5 , spring 1976 and autumn 1977 predi ct that 1 0n average , titres o f 2 . 5 t o 2 . 7 � : 68 - 1 : 92) at birth will be lost by about 45 days ( Figures IV , V
and VI ) . The more detailed data from the last two calvings ( Tables 3 . 8 and 3 . 9 ) shows that of 79 calves sampled within a few days of birth, 67 ( 85% ) had titres of 1 : 24 or more against
hardjo and of those born to sero-positive dams 67 of 74 ( 91% )
had such titres . This result is in close agreement with that of Cacchione et al ( 1968 ) , who observed hardjo titres in 90% of
three-day-old calves b orn to 103 sero-positive dams and is simi lar
to the report that 95% to 100% of approximately 100 calves in a
herd with endemi c hardjo and pomona infec tion had passive1y-
acquired titres ( Hanson et al , 1964 ) . Passively-acquired titres
have also been reported in 16 out of 16 calves ( 100% ) born to dams experimentally-infected with various serovars ( Fennestad and
Borg-Petersen, 1956 ) and 25 of 26 calves ( 96% ) born to dams vaccinated with a pomona bacterin ( McDonald and Rudge , 1957 ) .
A number of studies have shown that approximately 10% of new
born calves are hypogammaglobulinaemic after suckling is completed
( Klaus e t al , 1969 ; Selman e t al , 1970 ; 1971; Bailey and McLean,
1972; Mohamad, 1975 ; McGuire et al , 1976 ) . A similar result was
obtained in this study where seven calves failed to develop titres following suckling from sero-positive dams and another calf
developed only a very low titre . All these animals were hypogamma globu1inaemi c , making a total of eight out of 74 calves ( 11% )
immunoglobulin .
A number of explanations have been given by different
authors for the failure of calves to acquire colostral immuno globulins or speci fic antibody . Kruse ( 1970b ) demonstrated that a low level of immunoglobulin in colostrum was a maj or factor ,
and Cac chione et al ( 1968 ) believed that this was the reason for
10% of 103 calves failing to acquire hardjo titres from sero posi tive dams . }futching colostrum samples were taken from three
of the eight dams of hypogammaglobulinaemi c calves detected in the course of the present study ( dams 146 , 193 and 139 ) . In these three case s , colostral titres were similar to those which produced titres in many other calves ( Table 3 . 9 ) , indicating that the failure of these calves to acquire passive titres was not associated with colostral levels of antibody .
Th,e premature loss of absorptive capacity of immunoglobulins
by the c alf has also been - reported as the c ause of hypogamma
globulinaemia ( Kruse , 1970b ; Selman e t al , 1970 ) . In contrast
recent s tudies on hypogammaglobulinaemic calves in the Massey No .
1 dairy herd showed that their absorptive c apacity was normal ( Mohamad , 1975 ) . Mohamad ( 1975 ) considered that neonatal calf hypogammaglobulinaemia resulted ' from a low intake of colostrum and was caused by such factors as parent rej ection , environmental
conditions and udder conformation , and McGuire et al ( 1976 )
claimed delayed suckling, which could result from these factors ,
was the maj or cause . A calf examined in the present study was
sero-negative when removed from its dam 16 hours after birth and appeared not to have suckled . When c olostrum was taken from the dam and fed to the c alf it sero-converted . This case supports the
conclusions of Mohamad ( 1975 ) and McGuire e t al \( 1976 ) .
Geometric mean titres against l1ardjo at time of first sampling ranged from 1 : 138 - 1 : 199 for the three calvings spring 1975 , spring 1976 and autumn 1977 ( Table 3 . 2 ) with the GMT for autumn 1976 of 1 : 21 being very sub stanti ally less than observed at the other calvings . Thi s i s probably explained by the greater mean age at sampling of this group as no other factor could be found to explain this difference .
The strong positive correlation between dam titre and calf titre observed in thi s study confirms the impressions of Fennestad
and Borg-Petersen ( 1956 ) and Hanson et al ( 1964 ) that new-born
calf titres are generally equal to or greater than maternal titres . Similarly, the fact that the small negative correlation between colostral titre and calf titre is non-significant agrees with both the observation of Fennestad and Borg-Petersen ( 1956 ) that c alf ' s serum generally has a lower titre than does the corresponding
colostral whey, and the finding of McGuire et al ( 1976 ) that
colostral immunoglobulin levels were not correlated with calf serum immunoglobulin levels . Since the dam' s colostral levels of
speci fic antibody and immunoglobulin decline very rapidly after
calving (Porter , 1972 ) and since there is also considerable
variation in the amount of colostrum ingested by indivi dual calves
(Mbhamad, 1975 ) , sampling a dam ' s colostrum after a variable
suckling period, as occurred in this study (Table 3 . 11 ) is likely
to produce highly variable results and explain the non-significant correlation obtained .
Although both dam titre and calf titre are significantly correlated with dam age , the multiple regres sion analysis showed that maternal titre alone is the best predi c tor o f calf titre . This suggests that the age effect results from the fact that younger dams generally have higher titres .
Passively-acquired titres in calves decline logarithmically
from birth (Tables 3 . 3 , 3 . 4 , 3 . 5 and 3 . 6 and Figures IV, V and VI).
The length of time over which a calf remains sero-positive is positively correlated with the size of the ini ti al titre . The
fitted regression lines (Figures IV, V and VI) indicate that a calf
with a titre of 1 : 3072 will on average remain sero-positive for 125 to 135 days and that the half -li fe of a titre is 15 to 17 days . Since the sampling of calves at that age has been carried out only at approximately monthly intervals the actual day on which in dividual calves became sero-negative cannot be determined .
However , on average at least 50% of those c alves serially sampled are still sero-positive at :1;00 days of age and approximately 25.% at l�O days ; all are sero-negative by 190 days of age (Figure VII). These results agree very closely with those previously reported
for calves by Fermestad and Borg-Petersen ( 1956 ), McDonald,
.and