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A Study of Multiple Births in a Holstein-Friesian Herd1
A STUDY OF M U L T I P L E B I R T H S IN A HOLSTEIN-FRIESIAN HERD 1 K. O. P F A U , J. W. BARTLETT, .~D C. E. SHUART
Department of Dairy Industry, College of Agriculture, Rutgers University, New Brunswick, New Jersey
Dairy cows are uniparous animals. Multiple births are relatively rare and occur with variable frequency. Twin births are most frequent, and triplets, quadruplets, and quintuplets are progressively rarer. Numbers of twin births reported for individual dairy breeds range from less than 0.5 per cent to 4.5 per cent (11) and for individual herds up to 8.8 per cent (9). There still are differences of opinion as to whether twin births are desirable or undesirable in dairy cattle breeding (4, 5). Hewitt (7) considers multiple births a sign of increased fecundity and fertility, whereas Williams (12) relates such births to unsound or even diseased conditions of the genital tract, in particular of the ovary. A general study of fertility in dairy cows, in which twin births were recognized as one of the factors influencing reproductive performance, led to a more detailed investigation of multiple births. The results are presented herewith. SOURCE OF DATA
The data for this study were taken from the records of the HolsteinFriesian experimental herd at the New Jersey Agricultural Experiment Station and cover a period of about 15 years. The breeding program and operations pursued in this herd are rather unique insofar as the herd is self-containing and inbreeding is practiced to a high degree. The inbreeding with rigid selection is manifested in the preservation and corn centration of the young animals' relationship to the noted sire, Ormsby Sensation 45th. In publications of Bartlett and Margolin (1) and Bartlett et al. (2, 3) detailed accounts are given of the conduct and progress of this experimental breeding project. From these reports it is evident that the artificial selection was not specifically directed_ toward" reproductive efficiency and twinning but toward such qualities as milk and butterfat production, butterfat percentage, and body conformation. RESULTS
By nature of the character investigated, the results must be so evaluated Received for publicativn November 6, 1947. 1 Paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgers University, Department of Dairy Industry, New Brunswick. 241
242
K.O.
PFAU ET AL.
that small changes in actual numbers could have notable effect upon some of the summaries and averages. General occurrence of multiple births. F r o m 1931 to 1946 there were 937 parturitions and abortions available for observation. Of these, 37 or 3.95 per cent were twin births and 2 or 0.21 per cent triplets, making a total of 39 or 4.16 per cent multiple births. I n other words, the average incidence of twin births was one in every 25.3 and triplets one in every 468.5 births, or one multiple birth in every 24.0 births. The 39 multiple births were observed in 36 cows; three cows gave birth to twins twice. Since only two sets of triplets occurred and the gestation of one set terTABLE 1 Multiple births in relation to age of dam Age by parturL lion no.
Observed parturitions
Observed multiple births (%)
(nO.)
(nO.)
1
269
2
0.74
2
199
10
5.03
3
142
6
4.23
4
100
5
5.00
5
77
6
7.79
6
51
5
9.8o
7
41
3
7.32
8
30
0
0
1
4.35 25.00
9
23
10
4
1
11
1
0
937
39
Summary
0 4.16
minated in an abortion without sex determination of the fetuses, it was considered advisable in these investigations to include the triplets along with the twin births. T w i n births in relation to age of dam. Frequency of twinning in relation to age of dam is summarized in table 1, where age is expressed in p a r t u r i t i o n numbers. The first parturition occurred at an average age of about 29.5 mo~iths, a n d the average interval between parturitions was about 14.5 months. This tabulation shows that the number of twin births has been extremely low at the first parturition. F r o m then on it increased with age at calving, first increasing a b r u p t l y at the second p a r t u r i t i o n a n d then gradually reaching a peak at the fifth, sixth, and seventh par-
I~ULTIPLE BroTHS
243
turitions. Above these ages a decrease seemed to take place, but in view of the small number of cases not too much weight should be given to this observation. Length of twin gestations. Confirming Hewitt's findings in British Friesian cows (7), twin gestations in this herd were of shorter duration than gestations of single calves. The higMy significant difference amounted to about 7 days. Between the sexually unlike twin pairs, differences also existed, as shown in table 2." The mean length of gestation of the male pairs was greater than that of the sexually-mixed pairs and considerably greater than that of the female pairs. I t appears, as in the case of single calves (10), that sex of the fetuses has an influence upon length of gestation. Sex ratio. The sex ratio of 36 twin and one triplet births was f o u n d to be 33 males to 42 females, or 44 per cent males. The theoretical ratio TABLE 2
Length of gestation of twins No. of gestations observed
L e n g t h of gestation Mean days
S t a n d a r d deviation days
Male p a i r s .............................................
6
276.33±3.97
6.87 ___ 1.98
Sexually-mixed p a i r s ..................
11
273.64~_2.74
8.23 -4- 1.75
Female pairs
................................
14
270.00___2.56
8.86 ___ 1.68
S u m m a r y ...............................................
31
272.99___1.68
9.37 ___ 1.19
of twin pairs, 1 ~(~ : 2 ~ : 1~ was met by an actual one of 9 c~(~: 13 ~ :14 ~ , or 1 . 0 0 : 1 . 4 4 : 1 . 5 6 . Although these ratios are rather unusual, their differences f r o m the theoretical are not statistically significant. Vitality of multiple cabves. The vitality of multiple calves was evaluated according to the number born dead or that died within 2 days a f t e r birth and by following up the individual life histories of female twin pairs. The mortality rate at birth for each sex is presented in table 3. I t was slightly higher for male calves than for females. The average for both was 22.67 per cent, in contrast with only 9.65 per cent for the whole herd. The history of the 14 female twin pairs revealed that 6 individuals, or 21.43 per cent, were born dead or died soon a f t e r birth; 5, or 17.86 per cent, were sold when immature, mostly for reasons of selection; 6, or 21.43 pe~r cent, freshened in the herd but showed relatively poor production and breeding records; only 3, or 10.72 per cent, remained in the herd
244
K.O.
PFAU ET AL.
f o r the length of their n a t u r a l life, averaging 8.5 years, and exhibited relatively good production and breeding records; and 8, or 28.57 per cent, still in the herd at the time of this writing were immature, r a n g i n g in age f r o m 4 to 18 months. The m o r t a l i t y rate and life history of these heifer calves strongly indicate t h a t twins have a lower vitality and poorer prospects of productive life t h a n single calves. Retained placentae and twin births. The condition of retained placentae a f t e r twin births was v e r y much a g g r a v a t e d when compared with births of single calves. Of 31 a p p a r e n t l y normal multiple parturitions, 23, or 74.19 per cent, were accompanied b y this condition. The percentage for the whole herd was 23.10. Conception rate of dams after twin births. A f t e r giving birth to twins, the d a m ' s conception rate for a succeeding p r e g n a n c y should be another TABLE 3
Mortality of multiple calves Ma l e s
Females
Total
No. of calves ...................................................
33
42
75
Dead and aborted ealves .............................
8 24.24
9
17
21.43
22.67
Per cent mortality .........................................
indication of the possible effect of twinning on f u t u r e breeding efficiency. A n analysis of the records revealed t h a t 71 services were required for 22 safe pregnancies in as m a n y cows a f t e r twin births, corresponding with a conception rate of 3.23. This conception efficiency was almost 50 per cent lower t h a n t h a t of the herd average, which amounted to 2.21. Calving interval after twin births. A f t e r the 37 twin births, a p p a r e n t l y normal pregnancies and p a r t u r i t i o n s were noted in 13 instances. The mean calving interval was 483.5 _+ 22.3 days. This interval corresponded with a breeding efficiency of 75.41 per cent, which was considerably below the herd average of 82.59 per cent. This difference alone suggests t h a t twin births cause a reduction in reproductive efficiency. Influence of twin birth upon future reproductive performance. I n the 39 cases of multiple parturitions, 15 cows, or 38.46 per cent, contini]ed to produce in a p p a r e n t l y normal fashion, except for the higher conception rate and longer calving intervals. On the average, these cows survived their twin calving age b y 2.33 parturitions. Five cows, or 12.85 per cent, became sterile; 12 cows, or 30.77 per cent, were sold for various reasons shortly a f t e r giving birth to twins; and three cows, or 7.69 per cent, died a f t e r the twin parturitions, one because of hardware, another,
~ULTIPLE BIRTHS
245
from a r u p t u r e d uterus, and the third from an unknown cause. Of the four remaining cows which have given birth to twins within the last 9 months and which are still in the herd, two already have exhibited breeding troubles. This recorded information does not warrant definite conclusions in regard to the influence of twin births on the f u t u r e reproductive performance of the cows. The five proved cases of sterility are not in excess of the expectation for the whole population. I t must be remembered that the disposals include a number of cases which must be regarded as doubtful in this respect. On the other hand, the first group, which consists of the 15 cows with an apparently normal reproductive performance after twin births, comprises the largest proportion of the grouped twin dams. Their performance at least implies that twin births do not necessarily cause breeding troubles with sterility implications or shorten the reproductive life of the cows. Breeding efficiency of twin dams. Previously it was shown clearly that twin births exert a depressive effect upon the dam's subsequent TABLE 4 Breeding e~ciency of ~win dams compared with the herd as a whole
Group
Herd as a whole Twin d a m s
No. of cases
P e r c e n t a g e of b r e e d i n g efficiency Mean
Standard deviation
Coefficient of v a r i a t i o n
Skewness of distribution
144
83.99___0.94
11.32±0.66
13.48
+0.0483
26
83.46+1.59
7.96+_1.10
9.54
- - 0.0302
breeding efficiency. That this will affect a cow's lifetime breeding efficiency in proportion to her life span is acknowledged for the following analysis. The lifetime breeding efficiency was determined for 26 twin dams, the only ones with complete records available. Their mean breeding efficiency and the standard deviation and coefficient of variation, as well as the approximate measure of skewness, were compared with the respective values of the herd as a whole. Table 4 shows that almost no difference existed in the mean breeding efficiency between these two groups. The values for the standard deviation and coefficient of variation were considerably smaller for the twin dams than for the whole herd, denoting a greater uniformity of the twin group. Moreover, the distribution of the twin group was skewed positively, that is, toward the higher values, while the distribution of the whole herd was skewed negatively. Since twinning in itself has a depressing effect
246
K.O.
PFAU
E T AL.
upon the breeding efficiency, as already established, and since the frequency distribution of the herd as a whole markedly is skewed toward the lower values, a strong a r g u m e n t is offered for a f u n d a m e n t a l l y higher breeding efficiency in f a v o r of the twinning group. Milk production of t w i n dams. A s t u d y of the relationship between twinning and milk production was another object of this investigation. F o r this purpose the records of the 26 twin dams already employed in the analysis for breeding efficiency were considered suitable f o r a comparison of the milk production between twin dams a n d the herd as a whole. The milk yield in both groups was expressed in pounds of 4 per cent f a t corrected milk (5) per d a y on a m a t u r e equivalent twice-a-day milking basis. The actual milk yield was converted to the m a t u r e equivalent by the use of conversion factors based on the production records of the h e r d itself. The daily average was calculated on the total adult days t h e individual cow stayed in the herd, starting at the age of 27 months and continuing until her last calving. TABLE 5 Milb ~roduetion of twin dams compared with the herd as a whole
Group
Milk yield in lb.
No. of cases
Mean
Twin dams ............ Herd as a whole
deviation
Coefficient of variation
Standard
Skewness of
distribution 0.7080
26
30.08___1.06
5.32-4-0.74
17.70
--
144
29.10___0.59
7.11-~-0.42
24.42
- - 0.3047
The results are presented in table 5. The constants chosen for this comparison were the same as those used for the analysis of breeding efficiency. • The mean milk yield was insignificantly in f a v o r of the twin dams (P----0.70). The s t a n d a r d deviation and the coefficient of variation of the twin dams were considerably smaller t h a n those of the herd, indicating greater u n i f o r m i t y for the first group. The frequency distributions of both groups were skewed negatively. This analysis indicated t h a t the twin dams were at least equal in milk production to the herd as a whole. S u p e r i o r i t y on this basis alone could not be demonstrated. Comparison of various characteristics of fertility in twin dams and in the whole herd. Although the results of some investigations (7) indicate that twinning in d a i r y cows is associated with high reproductive qualities, this question is f a r f r o m settled. F e w data are available for correct evaluation of fertility itself, much less in relation to twinning. Thus, although twinning m a y be an expression of female fecundity in itself, the structural f o r m of the female reproductive t r a c t seems to obstruct the expression.
MULTIPLE
247
BIRTHS
This conflict could be noted in the records, and investigational results already cited and might interfere with most comparisons. Besides breeding efficiency, the following criteria were used in the evaluation of reproductive performance: Live and dead calves born, twin births, abortions, and retained placentae. The comparison between twin dams and a representative group of cows producing only single calves is shown in table 6. From this tabulation it will be seen that with the exception of the per cent of live calves, these measures of fertility all were in favor of the cows giving birth to single calves. That the greater percentage of living calves TABLE
6
Comparison of various measures of fertility between twin dams and other herd representatives
T w i n clams T o t a l no. of cows observed ................................................... Av. coefficient of i n b r e e d i n g per cow ...........................
28
Herd representatives 142
0.09
0.09
Av. g e s t a t i o n n u m b e r observed ............................................
3.73
3.12
Av. conception r a t e ...........................................................................
2.53
2.10
% of live calves ..........................................................................
100.00
83.35
Based on t o t a l no. of p a r t u r i t i o n s :
% o f dead calves .......................................................................
17.50
7.83
% of m u l t i p l e b i r t h s .............................................................
23.33
0.0
% o f a b o r t i o n s ..............................................................................
9.17
6.57
% of r e t a i n e d p l a c e n t a e ......................................................
30.83
18.69
for the twin dams' group was due almost exclusively to the twin births was revealed simply by adding the percentages of live and dead calves in both groups and subtracting the percentage of multiple births from the twin dams' group. Should allowance be made for the lack of vitality of twin calves, this slight superiority would vanish. Another important point in this tabulation is the average observed gestation number, which is considerably higher for the twin dams. Since the gestation numbers stand in relation to the average age at calving of the cows, their averages indicate strongly that the twin dams were older than the cows"with only single calves. Two factors might have contributed to this effect. Probably the main factor was the expression of twinning relatively late in life, making the twin dams a selected group in this respect. Many of the younger cows in the second group were potential twin dams. The other factor would be that twin dams actually were longer lived.
248
K.O.
PFAU ET AL.
Twinning and inbreeding. When twinning was set in contrast with the degree of inbreeding of the cows in the herd, as illustrated in table 7, a non-uniform positive trend between these two characteristics was observed. This feature does not mean that twinning was dependently related to the degree of inbreeding as such. It indicated rather well, however, that the factors for the twinning disposition were present in some of the foundation animals. By directing the breeding operations to the inbreeding of such animals, these factors became more concentrated in some cows and expressed themselves more often than in the foundation cows. The hereditary aspect of twinning. Heredity control of multiple births in mammals has been proved amply in sheep, goats and other animals. In TABLE
7
Comparison of inbreeding w~th Swinning Group
Coefficient of i n b r e e d i n g
No. o f cows
No. of No. of parturitions! t w i n b i r t h s
% of twin births
1
I
0.00
55
116
2
1.72
2
!
0.01-0.04
92
291
10
3.44
3
t
0.05-0.09
21
67
0
0.0
4
{
0.I0-0.14
36
87
4
4.60
5
0.15-0.19
29
73
7
9.59
6
0.20-0.24
9
16
1
6.25 4.55
7 8 Total
F
0.25-0.29
i0
22
1
0.30-0.39
3
8
1
12.50
255
680
26
3.82
dairy cows this proof is attained only with difficulty, because its relatively rare appearance and its dependence upon the dam's age frequently hide the presence of this character. The small number of offspring in dairy cows and, possibly, environmental influences upon twinning contribute to the difficulties. Statistical investigation of the problem would necessitate large numbers of reliable and complete records such as tSose accumulated in herd book organizations. Unfortunately, these generally lack completeness, because only promising offspring are reported. An alternative, used in the present study, is the investigation of individuals and family groups in large herds where complete records are kept over long periods. In table 8 the occurrence of twin births by parturition numbers is summarized for the members of 21 cow families which make up over 90 per cent of the present herd. Cows of ten of these families never had any
]¢IULTIPLE BIRTHS
249
t w i n s r e c o r d e d . I n t h e r e m a i n i n g 11 f a m i l i e s t h e r a t e of t w i n p a r t u r i tions r a n g e d f r o m 2.63 to 18.18 p e r cent. I n t a m e 9 t h e t w i n p a r t u r i t i o n s of t h e d a u g h t e r s of 19 sires a r e p r e sented. These d a u g h t e r s are, f o r the m o s t p a r t , t h e same cows r e p r e s e n t e d in~ the cow f a m i l i e s l i s t e d in t a b l e 8. I n g r o u p i n g these cows a c c o r d i n g to t h e i r sires, i t was f o u n d t h a t n i n e sires d i d n o t h a v e a n y d a u g h t e r s w i t h t w i n b i r t h s . T h e r e m a i n i n g t e n sires h a d one or m o r e d a u g h t e r s w h i c h gave b i r t h to twins. O n t h e basis of all p a r t u r i t i o n s of t h e d a u g h t e r s of TABLE 8 Occurrence of twins by cow families
Cow family no.
No. of parturitions
3 15 20 37 61 64 66 68 69 75 78 80 82 91 92 93 95 96 97 100 103
20 17 18 23 66 22 48 20 21 14: 20 26 34 7 38 24 17 14 15 13 25
Total
502
No. of twin pairs
% of twin pairs
1 0 2 0 1 1 0 2 0 0 0
0.0 5.88 0.0 4.35 9.09 18.18 4.17 0.0 4.76 0.0 5.00 0.0 5.88 0.0 2.63 4.17 0.0 14.29 0.0 0.0 0.0
22
4.38
2 0 1
these i n d i v i d u a l sires, the t e n d a u g h t e r g r o u p s v a r i e d f r o m 2.27 to 14.29 p e r c e n t in t w i n b i r t h s . T h i s v a r i a t i o n in b o t h g r o u p s m i g h t be a t t r i b u t e d to t h r e e sources, n a m e l y , p u r e chance, e n v i r o n m e n t , a n d t h e g e n e t i c t w i n n i n g d i s p o s i t i o n of sires a n d dams. T h e e m e r g i n g c o m b i n a t i o n of t h e d a u g h t e r s ' g e r m p l a s m f o u n d e d u p o n t h e p h y s i c a l basis of h e r e d i t y was the d e t e r m i n i n g p r i n c i p l e of this d i s p o s i t i o n . E n v i r o n m e n t a l f a c t o r s such as f e e d i n g a n d m a n a g e m e n t p r o b a b l y were of v e r y m i n o r influence. H o r m o n a l t h e r a p y , t h o u g h of cons i d e r a b l e i m p o r t a n c e in t w i n n i n g , as s h o w n b y H a m m o n d a n d B h a t t a c h -
250
K . O . PFAU ET AL.
a r y a ( 6 ) , w a s of no consequence i n t h i s h e r d . ~V.ith t h e g e n e r a l l y low p e r c e n t a g e o f t w i n b i r t h s , t h e e x p r e s s i o n of t h e d i s p o s i t i o n w a s v e r y u n c e r t a i n a n d t h e c h a n c e f a c t o r c o u l d n o t be d i s c o u n t e d . B y m e a n s of g e n e a l o g i c a l d i a g r a m s of cow f a m i l i e s t h a t h a v e h a d a r e l a t i v e l y h i g h n u m b e r of t w i n b i r t h s i t c a n b e d e m o n s t r a t e d t h a t t h e disp o s i t i o n f o r t w i n n i n g is i n h e r i t e d . F i g u r e 1 is a g e n e a l o g i c a l d i a g r a m of cow f a m i l y 61. I t is a r r a n g e d w i t h t h e f o u n d a t i o n cow on top, h e r f e m a l e p r o g e n y f o l l o w i n g d o w n the TABLE 9 Occurrence of twins by sires' daughters
Sire no.
No. of daughters included
No. of parturitions
A B C D E F H I L N O R T U V W X D-1 F-1
6 4 13 4 19 8 3 18 6 15 27 4 32 18 7 5 6 3 3
20 10 44 10
Total
201
:No. of twin pairs
% of twin pairs
8 4
0 0 1 0 3 1 1 3 0 2 7 0 2 2 0 0 2 O O
0.0 0.0 2.27 0.0 4.84 2.44 12.50 4.41 0.0 4.88 9.09 0.0 2.50 5.71 0.0 0.0 14.29 0.0 0.0
569
24
4.22
62 4! 8 68
21 41 77 5 35 10 11 14
',
line, g e n e r a t i o n b y g e n e r a t i o n . The i n d i v i d u a l o f f s p r i n g is d e s i g n a t e d b y h e r d n u m b e r . A f t e r t h e c o w ' s n u m b e r is g i v e n in p a r e n t h e s e s t h e n u m b e r of h e r t w i n p a r t u r i t i o n s , i f a n y . F o r t h e y o u n g e r o f f s p r i n g a l i v e in the herd at this writing, the letter P for prospect was added. Animals t h a t a r e t w i n s t h e m s e l v e s a r e so d e s i g n a t e d b y n u m b e r s i n b o l d - f a c e t y p e . B e l o w t h e f e m a l e ' s i d e n t i f i c a t i o n n u m b e r is a s c r i b e d t h e s i r e ' s i d e n t i f i c a tion, g e n e r a l l y b y a l e t t e r o r l e t t e r w i t h n u m b e r . B e y o n d t h a t , s e p a r a t e d b y a dash, t h e p e r c e n t a g e of t w i n b i r t h s of t h e s i r e ' s d a u g h t e r s is g i v e n as f a r as i t is k n o w n . T h e f i g u r e i l l u s t r a t e s how t h e t r a n s m i s s i o n of t h e d i s p o s i t i o n f o r t w i n -
MULTIPLE
251
BIRTHS
ning may work out in a relatively large cow family. Foundation cow 61, herself a twin, was sired by bull C, whose daughters born in the herd showed only 2.3 per cent twinning. Cow 61 had five daughters with reproduction records. They were sired by three different bulls, making three of them full sisters by sire E, whose daughters averaged 4.8 per cent twin births. Their records and especially those of the three full sisters suggest strongly a segregation in the Mendelian ratio. Two of the three full sisters, namely nos. 67 and 294, started progeny lines of their own. Neither of these lines exhibited any twinning. The third full sister, no. 256, produced one pair of twins in her second parturition. Unfortunately, she did not leave any progeny in the herd. IIer early expression of the twinning character suggests, however, that she was highly predisposed to it. !
8!
c - a. ~ 67
I I
o.
208
256(I
)
294
330
7
~<:~1 I I [
rr
z
308 4 8 - .
'
0
~
IV
V
I
399 R-O.O
' 2 Z-4.4
415(I)
U•5o
61)8 P F" 1 - 0 . 0
0-11,1
476 " •
607 P F" 1 - 0 . 0
0-9.1
X
\
422 " •
468 - •
553 P T-2.5
WI -
425 2-4
475 -
508 T
P
666 P "
603 P X'J 4.3
5 3 0 ,P 0,0
.),o 7,, ;;,,, 7-
533 -
$74 P 0-9 . I
534 HI-
MI -
637 P NI-
~
MI -
Fro. 1. Diagram of cow family 61 showing the extent and distribution of twin births, which amount to 9.09 per cent of all observed parturitions. For explanations of the diagram see text. Daughter no. 208, which was sired by a bull designated M. B. and for which no twinning record could be established because of lack of daughters in the herd, started the longest line of progeny. Though no. 208 herself revealed no twinning disposition, her progeny visibly exhibited it to an extreme degree. E ver y one of her three daughters gave birth to one pair of twins. In turn, their progeny (generation IV) again suggest that Mendelian segregation might have been at work. The animals listed under generations V and VI are too young at present to allow any conclusion. The fifth daughter, no. 330, of foundation cow 61 was sired by bull O, which was by progeny test a highly predisposed animal. Cow 330 calved only twice in the herd and produced single bull calves. Her disposition for twinning, therefore, never will be ascertained.
252
K . O . PFAU ET AL.
A similar investigation was made on cow family 64; her genealogy is diagrammed in figure 2. F a m i l y 64 was relatively small. Over a period covering five generations, this family was just about holding its own. In respect to twinning, this family's record, amounting to 18.18 per cent, was higher than that for any other cow family observed. The distribution of twin births extended over only three generations. The foundation cow did not visibly express any twinning disposition and the descendants in the fifth generation were too young to show any. A segregation into unusually predisposed and undisposed lines was hinted in this family, a feature closely resembling that of family 61. I
64
S -
2,3~
zoz O)
J,
o
g-
~ 1 II Iv
v
2.77
4@e
362 (2)
5o2(i )
5~//P
NI-
401
370
472
M!-
6 P
MI-
FIG. 2. Diagram of cow family 64 showing the extent and distribution of twin births, which amount to 18.18 per cent of all observed parturitions. For explanations of the diagram see text.
In both families virtually the same bulls appear as sires to the progeny. Sire 0, with a high average twinning rate, is especially conspicuous as a sire of twin dams ; so also is sire I, with a relatively low average rate. Both these sires are inbred to bull C, which is also the sire of both foundation cows. ~ires E and F, both outbreds, are conspicuously present in the nonpredisposed lines. Obviously, the low frequency of twin births does not w a r r a n t definite conclusions with respect to the mode of transmission of twinning. The continued use of inbred sons and grandsons of bull C for several generations in succession and with it a concentration of certain genes of this bull suggest the possibility that he carried genes which foster twinning. In addition, it is observed that other inbred sons and grandsons of the same bllll, as sires T and R, have very low rates for twinning. It should be
I~ULTIPLE BIRTHS
253
recalled that almost half of the cow families and half of the sires never showed any tendency for twinning. All of these observations point strongly to the conclusion that twinning in dairy cows is influenced chiefly by heredity yet expresses itself differently with age. The mode of transmission could well be understood by the assumption that twinning is under the control of a small number of autosomal genes which express themselves incompletely. The transmission seems to be recessive in character, with gene interactions or modifications. DISCUSSION AND CONCLUSIONS
The observation made in this investigation that twinning is rare in the first parturition, rises to a p e a k in the fifth, sixth, and seventli parturitions, and then decreases with advancing age harmonizes closely with the general cycle of fecundity in most multiparous mammals. From this observation alone it is most probable that twinning is an expression of fecundity or the potential reproductive capacity of a dairy cow. However, if dairy cows are considered as strictly uniparous animals, and they should be so considered according to the structural development of their reproductive tract, twinning could be regarded as cases of reversion or atavism. Evidence was presented that twinning is chiefly controlled by heredity. The effect of environment seems to be of very minor importance. The mode of transmission of the twinning character in dairy cattle is obscured by its relatively rare and incomplete expression, its sex-limited and agelimited appearance, and the small number of offspring inherent in cattle. The factual manifestations of transmission in two cow families over a number of generations provided impressive indications that twinning exhibits Mendelian segregation and seems to be under the control of a small number of genes. The character of twinning should be recessive with gene interactions or modifications. By making use of these findings it is feasible that in practical breeding operations twinning in dairy cattle could be influenced considerably in either direction. The question then arises as to whether twinning is a desirable charaeter in dairy cattle. If the available data all are accepted at their face value, twinning is associated with the increased production of calves by sheer numbers; if this fact is scrutinized from the actual reproducing value of the female line, the contrary is the case. Of the theoretical twin sex-ratio, 1 o~o~ :2 o ~ :1 ~ , for all practical purposes only the female pairs are suitable for reproduction in the direct female lines., Theoretically, the number of these female twins would just be equal to the number of single females. Since twin calves have a higher mortality rate at birth and, apparently, a lower vitality throughout life than single calves, the real fact is that twinning has a harmful effect on the continuity of the female lines.
254
K . O . PFAU ET AL.
I f the face value of data favoring the association of twinning with longevity is examined closely, the degree of association diminishes considerably. Twin births occur generally late in life, increase with advancing age, and are incomplete in appearance. I f every animal in a group is expected to show this character, almost all the animals of this group have undergone an intense selection with respect to age. Therefore, almost any comparison of twinning in regard to age is of very questionable reliability. Definite disadvantages of twin births include shortened gestation periods, greater parturition difficulties with subsequent increases in retained placentae, decreased conception rate, lower breeding efficiency, and increased sterility. I n summarizing all these factors, there is no doubt that twinning definitely is an undesirable character in dairy cattle, and efforts should be made to reduce its appearance by p r o p e r breeding methods and selection. REFERENCES (1) BARTLETT,,J'. W., ANDMARGOLIN,S. A Comparison of Inbreeding and Outbreeding
Holstein-Friesian Cattle. N . J . Agr. Expt. Sta. Bull. 712. 1944. (2) BARTLETT,J. W., REECE, R. P., AND LEPARD,O. L. The Influence of Inbreeding on Birth Weight, Rate of Growth, and Type of Dairy Cattle. J. Animal Sei., 1 : 206-212. 1942. (3) BARTLETT,J. W., RLECE, R. P., AND MIXNER, J. P. Inbreeding and Outbreeding
(4)
(5) (6) (7) (8) (9) (10) (11) (12)
Holstein-Friesian Cattle in an Attempt to Establish Genetic Factors for High Milk Production and High Fat Test. N.J. Agr. Expt. Sta. Bull. 667. 1939. ESPE, D. Secretion of Milk. 2nd Ed. The Iowa State College Press, Ames~ Iowa. 1946. GAINES,W. L. The Energy Basis of Measuring Milk Yield in Dairy Cows. Ill. Agr. Expt. Sta. Bull. 453. 1928. HA~0m), J., JR., AND BHATTACHARYA,P. Control of Ovulation in the Cow. J. Agr. Sci., 34: 1-5. 1944. H•wITT, A. C.J. Twinning in Cattle. J. Dairy Research, 5: 101-107. 1937. LUSH, J. L. Animal Breeding Plans. 3rd Ed. The Iowa State College Press, Ames, Iowa. 1945. LUSH, R.H. Inheritance of Twinning. J. Heredity, 16: 273-279. 1925. Rm~, V. A. Breeding and Improvement of Farm Animals. 3rd Ed. McGrawHill Book Company, Inc., New York, N. Y. 1942. WEBF~R,W. Untersuchungen iiber die Hfiufigkeit und Erblichkeit der Disposition zu Zwilllngsgeburten beim Simmentalerrind. Arch. Julius Klaus Stiftung, 20: 307-361. 1945. WILLIAMS, W. L. Veterinary Obstetrics. 2nd Ed. Published by the Author, Ithaca, N. Y. 1931.
Department of Dairy Industry, College of Agriculture, Rutgers University, New Brunswick, New Jersey
Dairy cows are uniparous animals. Multiple births are relatively rare and occur with variable frequency. Twin births are most frequent, and triplets, quadruplets, and quintuplets are progressively rarer. Numbers of twin births reported for individual dairy breeds range from less than 0.5 per cent to 4.5 per cent (11) and for individual herds up to 8.8 per cent (9). There still are differences of opinion as to whether twin births are desirable or undesirable in dairy cattle breeding (4, 5). Hewitt (7) considers multiple births a sign of increased fecundity and fertility, whereas Williams (12) relates such births to unsound or even diseased conditions of the genital tract, in particular of the ovary. A general study of fertility in dairy cows, in which twin births were recognized as one of the factors influencing reproductive performance, led to a more detailed investigation of multiple births. The results are presented herewith. SOURCE OF DATA
The data for this study were taken from the records of the HolsteinFriesian experimental herd at the New Jersey Agricultural Experiment Station and cover a period of about 15 years. The breeding program and operations pursued in this herd are rather unique insofar as the herd is self-containing and inbreeding is practiced to a high degree. The inbreeding with rigid selection is manifested in the preservation and corn centration of the young animals' relationship to the noted sire, Ormsby Sensation 45th. In publications of Bartlett and Margolin (1) and Bartlett et al. (2, 3) detailed accounts are given of the conduct and progress of this experimental breeding project. From these reports it is evident that the artificial selection was not specifically directed_ toward" reproductive efficiency and twinning but toward such qualities as milk and butterfat production, butterfat percentage, and body conformation. RESULTS
By nature of the character investigated, the results must be so evaluated Received for publicativn November 6, 1947. 1 Paper of the Journal Series, New Jersey Agricultural Experiment Station, Rutgers University, Department of Dairy Industry, New Brunswick. 241
242
K.O.
PFAU ET AL.
that small changes in actual numbers could have notable effect upon some of the summaries and averages. General occurrence of multiple births. F r o m 1931 to 1946 there were 937 parturitions and abortions available for observation. Of these, 37 or 3.95 per cent were twin births and 2 or 0.21 per cent triplets, making a total of 39 or 4.16 per cent multiple births. I n other words, the average incidence of twin births was one in every 25.3 and triplets one in every 468.5 births, or one multiple birth in every 24.0 births. The 39 multiple births were observed in 36 cows; three cows gave birth to twins twice. Since only two sets of triplets occurred and the gestation of one set terTABLE 1 Multiple births in relation to age of dam Age by parturL lion no.
Observed parturitions
Observed multiple births (%)
(nO.)
(nO.)
1
269
2
0.74
2
199
10
5.03
3
142
6
4.23
4
100
5
5.00
5
77
6
7.79
6
51
5
9.8o
7
41
3
7.32
8
30
0
0
1
4.35 25.00
9
23
10
4
1
11
1
0
937
39
Summary
0 4.16
minated in an abortion without sex determination of the fetuses, it was considered advisable in these investigations to include the triplets along with the twin births. T w i n births in relation to age of dam. Frequency of twinning in relation to age of dam is summarized in table 1, where age is expressed in p a r t u r i t i o n numbers. The first parturition occurred at an average age of about 29.5 mo~iths, a n d the average interval between parturitions was about 14.5 months. This tabulation shows that the number of twin births has been extremely low at the first parturition. F r o m then on it increased with age at calving, first increasing a b r u p t l y at the second p a r t u r i t i o n a n d then gradually reaching a peak at the fifth, sixth, and seventh par-
I~ULTIPLE BroTHS
243
turitions. Above these ages a decrease seemed to take place, but in view of the small number of cases not too much weight should be given to this observation. Length of twin gestations. Confirming Hewitt's findings in British Friesian cows (7), twin gestations in this herd were of shorter duration than gestations of single calves. The higMy significant difference amounted to about 7 days. Between the sexually unlike twin pairs, differences also existed, as shown in table 2." The mean length of gestation of the male pairs was greater than that of the sexually-mixed pairs and considerably greater than that of the female pairs. I t appears, as in the case of single calves (10), that sex of the fetuses has an influence upon length of gestation. Sex ratio. The sex ratio of 36 twin and one triplet births was f o u n d to be 33 males to 42 females, or 44 per cent males. The theoretical ratio TABLE 2
Length of gestation of twins No. of gestations observed
L e n g t h of gestation Mean days
S t a n d a r d deviation days
Male p a i r s .............................................
6
276.33±3.97
6.87 ___ 1.98
Sexually-mixed p a i r s ..................
11
273.64~_2.74
8.23 -4- 1.75
Female pairs
................................
14
270.00___2.56
8.86 ___ 1.68
S u m m a r y ...............................................
31
272.99___1.68
9.37 ___ 1.19
of twin pairs, 1 ~(~ : 2 ~ : 1~ was met by an actual one of 9 c~(~: 13 ~ :14 ~ , or 1 . 0 0 : 1 . 4 4 : 1 . 5 6 . Although these ratios are rather unusual, their differences f r o m the theoretical are not statistically significant. Vitality of multiple cabves. The vitality of multiple calves was evaluated according to the number born dead or that died within 2 days a f t e r birth and by following up the individual life histories of female twin pairs. The mortality rate at birth for each sex is presented in table 3. I t was slightly higher for male calves than for females. The average for both was 22.67 per cent, in contrast with only 9.65 per cent for the whole herd. The history of the 14 female twin pairs revealed that 6 individuals, or 21.43 per cent, were born dead or died soon a f t e r birth; 5, or 17.86 per cent, were sold when immature, mostly for reasons of selection; 6, or 21.43 pe~r cent, freshened in the herd but showed relatively poor production and breeding records; only 3, or 10.72 per cent, remained in the herd
244
K.O.
PFAU ET AL.
f o r the length of their n a t u r a l life, averaging 8.5 years, and exhibited relatively good production and breeding records; and 8, or 28.57 per cent, still in the herd at the time of this writing were immature, r a n g i n g in age f r o m 4 to 18 months. The m o r t a l i t y rate and life history of these heifer calves strongly indicate t h a t twins have a lower vitality and poorer prospects of productive life t h a n single calves. Retained placentae and twin births. The condition of retained placentae a f t e r twin births was v e r y much a g g r a v a t e d when compared with births of single calves. Of 31 a p p a r e n t l y normal multiple parturitions, 23, or 74.19 per cent, were accompanied b y this condition. The percentage for the whole herd was 23.10. Conception rate of dams after twin births. A f t e r giving birth to twins, the d a m ' s conception rate for a succeeding p r e g n a n c y should be another TABLE 3
Mortality of multiple calves Ma l e s
Females
Total
No. of calves ...................................................
33
42
75
Dead and aborted ealves .............................
8 24.24
9
17
21.43
22.67
Per cent mortality .........................................
indication of the possible effect of twinning on f u t u r e breeding efficiency. A n analysis of the records revealed t h a t 71 services were required for 22 safe pregnancies in as m a n y cows a f t e r twin births, corresponding with a conception rate of 3.23. This conception efficiency was almost 50 per cent lower t h a n t h a t of the herd average, which amounted to 2.21. Calving interval after twin births. A f t e r the 37 twin births, a p p a r e n t l y normal pregnancies and p a r t u r i t i o n s were noted in 13 instances. The mean calving interval was 483.5 _+ 22.3 days. This interval corresponded with a breeding efficiency of 75.41 per cent, which was considerably below the herd average of 82.59 per cent. This difference alone suggests t h a t twin births cause a reduction in reproductive efficiency. Influence of twin birth upon future reproductive performance. I n the 39 cases of multiple parturitions, 15 cows, or 38.46 per cent, contini]ed to produce in a p p a r e n t l y normal fashion, except for the higher conception rate and longer calving intervals. On the average, these cows survived their twin calving age b y 2.33 parturitions. Five cows, or 12.85 per cent, became sterile; 12 cows, or 30.77 per cent, were sold for various reasons shortly a f t e r giving birth to twins; and three cows, or 7.69 per cent, died a f t e r the twin parturitions, one because of hardware, another,
~ULTIPLE BIRTHS
245
from a r u p t u r e d uterus, and the third from an unknown cause. Of the four remaining cows which have given birth to twins within the last 9 months and which are still in the herd, two already have exhibited breeding troubles. This recorded information does not warrant definite conclusions in regard to the influence of twin births on the f u t u r e reproductive performance of the cows. The five proved cases of sterility are not in excess of the expectation for the whole population. I t must be remembered that the disposals include a number of cases which must be regarded as doubtful in this respect. On the other hand, the first group, which consists of the 15 cows with an apparently normal reproductive performance after twin births, comprises the largest proportion of the grouped twin dams. Their performance at least implies that twin births do not necessarily cause breeding troubles with sterility implications or shorten the reproductive life of the cows. Breeding efficiency of twin dams. Previously it was shown clearly that twin births exert a depressive effect upon the dam's subsequent TABLE 4 Breeding e~ciency of ~win dams compared with the herd as a whole
Group
Herd as a whole Twin d a m s
No. of cases
P e r c e n t a g e of b r e e d i n g efficiency Mean
Standard deviation
Coefficient of v a r i a t i o n
Skewness of distribution
144
83.99___0.94
11.32±0.66
13.48
+0.0483
26
83.46+1.59
7.96+_1.10
9.54
- - 0.0302
breeding efficiency. That this will affect a cow's lifetime breeding efficiency in proportion to her life span is acknowledged for the following analysis. The lifetime breeding efficiency was determined for 26 twin dams, the only ones with complete records available. Their mean breeding efficiency and the standard deviation and coefficient of variation, as well as the approximate measure of skewness, were compared with the respective values of the herd as a whole. Table 4 shows that almost no difference existed in the mean breeding efficiency between these two groups. The values for the standard deviation and coefficient of variation were considerably smaller for the twin dams than for the whole herd, denoting a greater uniformity of the twin group. Moreover, the distribution of the twin group was skewed positively, that is, toward the higher values, while the distribution of the whole herd was skewed negatively. Since twinning in itself has a depressing effect
246
K.O.
PFAU
E T AL.
upon the breeding efficiency, as already established, and since the frequency distribution of the herd as a whole markedly is skewed toward the lower values, a strong a r g u m e n t is offered for a f u n d a m e n t a l l y higher breeding efficiency in f a v o r of the twinning group. Milk production of t w i n dams. A s t u d y of the relationship between twinning and milk production was another object of this investigation. F o r this purpose the records of the 26 twin dams already employed in the analysis for breeding efficiency were considered suitable f o r a comparison of the milk production between twin dams a n d the herd as a whole. The milk yield in both groups was expressed in pounds of 4 per cent f a t corrected milk (5) per d a y on a m a t u r e equivalent twice-a-day milking basis. The actual milk yield was converted to the m a t u r e equivalent by the use of conversion factors based on the production records of the h e r d itself. The daily average was calculated on the total adult days t h e individual cow stayed in the herd, starting at the age of 27 months and continuing until her last calving. TABLE 5 Milb ~roduetion of twin dams compared with the herd as a whole
Group
Milk yield in lb.
No. of cases
Mean
Twin dams ............ Herd as a whole
deviation
Coefficient of variation
Standard
Skewness of
distribution 0.7080
26
30.08___1.06
5.32-4-0.74
17.70
--
144
29.10___0.59
7.11-~-0.42
24.42
- - 0.3047
The results are presented in table 5. The constants chosen for this comparison were the same as those used for the analysis of breeding efficiency. • The mean milk yield was insignificantly in f a v o r of the twin dams (P----0.70). The s t a n d a r d deviation and the coefficient of variation of the twin dams were considerably smaller t h a n those of the herd, indicating greater u n i f o r m i t y for the first group. The frequency distributions of both groups were skewed negatively. This analysis indicated t h a t the twin dams were at least equal in milk production to the herd as a whole. S u p e r i o r i t y on this basis alone could not be demonstrated. Comparison of various characteristics of fertility in twin dams and in the whole herd. Although the results of some investigations (7) indicate that twinning in d a i r y cows is associated with high reproductive qualities, this question is f a r f r o m settled. F e w data are available for correct evaluation of fertility itself, much less in relation to twinning. Thus, although twinning m a y be an expression of female fecundity in itself, the structural f o r m of the female reproductive t r a c t seems to obstruct the expression.
MULTIPLE
247
BIRTHS
This conflict could be noted in the records, and investigational results already cited and might interfere with most comparisons. Besides breeding efficiency, the following criteria were used in the evaluation of reproductive performance: Live and dead calves born, twin births, abortions, and retained placentae. The comparison between twin dams and a representative group of cows producing only single calves is shown in table 6. From this tabulation it will be seen that with the exception of the per cent of live calves, these measures of fertility all were in favor of the cows giving birth to single calves. That the greater percentage of living calves TABLE
6
Comparison of various measures of fertility between twin dams and other herd representatives
T w i n clams T o t a l no. of cows observed ................................................... Av. coefficient of i n b r e e d i n g per cow ...........................
28
Herd representatives 142
0.09
0.09
Av. g e s t a t i o n n u m b e r observed ............................................
3.73
3.12
Av. conception r a t e ...........................................................................
2.53
2.10
% of live calves ..........................................................................
100.00
83.35
Based on t o t a l no. of p a r t u r i t i o n s :
% o f dead calves .......................................................................
17.50
7.83
% of m u l t i p l e b i r t h s .............................................................
23.33
0.0
% o f a b o r t i o n s ..............................................................................
9.17
6.57
% of r e t a i n e d p l a c e n t a e ......................................................
30.83
18.69
for the twin dams' group was due almost exclusively to the twin births was revealed simply by adding the percentages of live and dead calves in both groups and subtracting the percentage of multiple births from the twin dams' group. Should allowance be made for the lack of vitality of twin calves, this slight superiority would vanish. Another important point in this tabulation is the average observed gestation number, which is considerably higher for the twin dams. Since the gestation numbers stand in relation to the average age at calving of the cows, their averages indicate strongly that the twin dams were older than the cows"with only single calves. Two factors might have contributed to this effect. Probably the main factor was the expression of twinning relatively late in life, making the twin dams a selected group in this respect. Many of the younger cows in the second group were potential twin dams. The other factor would be that twin dams actually were longer lived.
248
K.O.
PFAU ET AL.
Twinning and inbreeding. When twinning was set in contrast with the degree of inbreeding of the cows in the herd, as illustrated in table 7, a non-uniform positive trend between these two characteristics was observed. This feature does not mean that twinning was dependently related to the degree of inbreeding as such. It indicated rather well, however, that the factors for the twinning disposition were present in some of the foundation animals. By directing the breeding operations to the inbreeding of such animals, these factors became more concentrated in some cows and expressed themselves more often than in the foundation cows. The hereditary aspect of twinning. Heredity control of multiple births in mammals has been proved amply in sheep, goats and other animals. In TABLE
7
Comparison of inbreeding w~th Swinning Group
Coefficient of i n b r e e d i n g
No. o f cows
No. of No. of parturitions! t w i n b i r t h s
% of twin births
1
I
0.00
55
116
2
1.72
2
!
0.01-0.04
92
291
10
3.44
3
t
0.05-0.09
21
67
0
0.0
4
{
0.I0-0.14
36
87
4
4.60
5
0.15-0.19
29
73
7
9.59
6
0.20-0.24
9
16
1
6.25 4.55
7 8 Total
F
0.25-0.29
i0
22
1
0.30-0.39
3
8
1
12.50
255
680
26
3.82
dairy cows this proof is attained only with difficulty, because its relatively rare appearance and its dependence upon the dam's age frequently hide the presence of this character. The small number of offspring in dairy cows and, possibly, environmental influences upon twinning contribute to the difficulties. Statistical investigation of the problem would necessitate large numbers of reliable and complete records such as tSose accumulated in herd book organizations. Unfortunately, these generally lack completeness, because only promising offspring are reported. An alternative, used in the present study, is the investigation of individuals and family groups in large herds where complete records are kept over long periods. In table 8 the occurrence of twin births by parturition numbers is summarized for the members of 21 cow families which make up over 90 per cent of the present herd. Cows of ten of these families never had any
]¢IULTIPLE BIRTHS
249
t w i n s r e c o r d e d . I n t h e r e m a i n i n g 11 f a m i l i e s t h e r a t e of t w i n p a r t u r i tions r a n g e d f r o m 2.63 to 18.18 p e r cent. I n t a m e 9 t h e t w i n p a r t u r i t i o n s of t h e d a u g h t e r s of 19 sires a r e p r e sented. These d a u g h t e r s are, f o r the m o s t p a r t , t h e same cows r e p r e s e n t e d in~ the cow f a m i l i e s l i s t e d in t a b l e 8. I n g r o u p i n g these cows a c c o r d i n g to t h e i r sires, i t was f o u n d t h a t n i n e sires d i d n o t h a v e a n y d a u g h t e r s w i t h t w i n b i r t h s . T h e r e m a i n i n g t e n sires h a d one or m o r e d a u g h t e r s w h i c h gave b i r t h to twins. O n t h e basis of all p a r t u r i t i o n s of t h e d a u g h t e r s of TABLE 8 Occurrence of twins by cow families
Cow family no.
No. of parturitions
3 15 20 37 61 64 66 68 69 75 78 80 82 91 92 93 95 96 97 100 103
20 17 18 23 66 22 48 20 21 14: 20 26 34 7 38 24 17 14 15 13 25
Total
502
No. of twin pairs
% of twin pairs
1 0 2 0 1 1 0 2 0 0 0
0.0 5.88 0.0 4.35 9.09 18.18 4.17 0.0 4.76 0.0 5.00 0.0 5.88 0.0 2.63 4.17 0.0 14.29 0.0 0.0 0.0
22
4.38
2 0 1
these i n d i v i d u a l sires, the t e n d a u g h t e r g r o u p s v a r i e d f r o m 2.27 to 14.29 p e r c e n t in t w i n b i r t h s . T h i s v a r i a t i o n in b o t h g r o u p s m i g h t be a t t r i b u t e d to t h r e e sources, n a m e l y , p u r e chance, e n v i r o n m e n t , a n d t h e g e n e t i c t w i n n i n g d i s p o s i t i o n of sires a n d dams. T h e e m e r g i n g c o m b i n a t i o n of t h e d a u g h t e r s ' g e r m p l a s m f o u n d e d u p o n t h e p h y s i c a l basis of h e r e d i t y was the d e t e r m i n i n g p r i n c i p l e of this d i s p o s i t i o n . E n v i r o n m e n t a l f a c t o r s such as f e e d i n g a n d m a n a g e m e n t p r o b a b l y were of v e r y m i n o r influence. H o r m o n a l t h e r a p y , t h o u g h of cons i d e r a b l e i m p o r t a n c e in t w i n n i n g , as s h o w n b y H a m m o n d a n d B h a t t a c h -
250
K . O . PFAU ET AL.
a r y a ( 6 ) , w a s of no consequence i n t h i s h e r d . ~V.ith t h e g e n e r a l l y low p e r c e n t a g e o f t w i n b i r t h s , t h e e x p r e s s i o n of t h e d i s p o s i t i o n w a s v e r y u n c e r t a i n a n d t h e c h a n c e f a c t o r c o u l d n o t be d i s c o u n t e d . B y m e a n s of g e n e a l o g i c a l d i a g r a m s of cow f a m i l i e s t h a t h a v e h a d a r e l a t i v e l y h i g h n u m b e r of t w i n b i r t h s i t c a n b e d e m o n s t r a t e d t h a t t h e disp o s i t i o n f o r t w i n n i n g is i n h e r i t e d . F i g u r e 1 is a g e n e a l o g i c a l d i a g r a m of cow f a m i l y 61. I t is a r r a n g e d w i t h t h e f o u n d a t i o n cow on top, h e r f e m a l e p r o g e n y f o l l o w i n g d o w n the TABLE 9 Occurrence of twins by sires' daughters
Sire no.
No. of daughters included
No. of parturitions
A B C D E F H I L N O R T U V W X D-1 F-1
6 4 13 4 19 8 3 18 6 15 27 4 32 18 7 5 6 3 3
20 10 44 10
Total
201
:No. of twin pairs
% of twin pairs
8 4
0 0 1 0 3 1 1 3 0 2 7 0 2 2 0 0 2 O O
0.0 0.0 2.27 0.0 4.84 2.44 12.50 4.41 0.0 4.88 9.09 0.0 2.50 5.71 0.0 0.0 14.29 0.0 0.0
569
24
4.22
62 4! 8 68
21 41 77 5 35 10 11 14
',
line, g e n e r a t i o n b y g e n e r a t i o n . The i n d i v i d u a l o f f s p r i n g is d e s i g n a t e d b y h e r d n u m b e r . A f t e r t h e c o w ' s n u m b e r is g i v e n in p a r e n t h e s e s t h e n u m b e r of h e r t w i n p a r t u r i t i o n s , i f a n y . F o r t h e y o u n g e r o f f s p r i n g a l i v e in the herd at this writing, the letter P for prospect was added. Animals t h a t a r e t w i n s t h e m s e l v e s a r e so d e s i g n a t e d b y n u m b e r s i n b o l d - f a c e t y p e . B e l o w t h e f e m a l e ' s i d e n t i f i c a t i o n n u m b e r is a s c r i b e d t h e s i r e ' s i d e n t i f i c a tion, g e n e r a l l y b y a l e t t e r o r l e t t e r w i t h n u m b e r . B e y o n d t h a t , s e p a r a t e d b y a dash, t h e p e r c e n t a g e of t w i n b i r t h s of t h e s i r e ' s d a u g h t e r s is g i v e n as f a r as i t is k n o w n . T h e f i g u r e i l l u s t r a t e s how t h e t r a n s m i s s i o n of t h e d i s p o s i t i o n f o r t w i n -
MULTIPLE
251
BIRTHS
ning may work out in a relatively large cow family. Foundation cow 61, herself a twin, was sired by bull C, whose daughters born in the herd showed only 2.3 per cent twinning. Cow 61 had five daughters with reproduction records. They were sired by three different bulls, making three of them full sisters by sire E, whose daughters averaged 4.8 per cent twin births. Their records and especially those of the three full sisters suggest strongly a segregation in the Mendelian ratio. Two of the three full sisters, namely nos. 67 and 294, started progeny lines of their own. Neither of these lines exhibited any twinning. The third full sister, no. 256, produced one pair of twins in her second parturition. Unfortunately, she did not leave any progeny in the herd. IIer early expression of the twinning character suggests, however, that she was highly predisposed to it. !
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Fro. 1. Diagram of cow family 61 showing the extent and distribution of twin births, which amount to 9.09 per cent of all observed parturitions. For explanations of the diagram see text. Daughter no. 208, which was sired by a bull designated M. B. and for which no twinning record could be established because of lack of daughters in the herd, started the longest line of progeny. Though no. 208 herself revealed no twinning disposition, her progeny visibly exhibited it to an extreme degree. E ver y one of her three daughters gave birth to one pair of twins. In turn, their progeny (generation IV) again suggest that Mendelian segregation might have been at work. The animals listed under generations V and VI are too young at present to allow any conclusion. The fifth daughter, no. 330, of foundation cow 61 was sired by bull O, which was by progeny test a highly predisposed animal. Cow 330 calved only twice in the herd and produced single bull calves. Her disposition for twinning, therefore, never will be ascertained.
252
K . O . PFAU ET AL.
A similar investigation was made on cow family 64; her genealogy is diagrammed in figure 2. F a m i l y 64 was relatively small. Over a period covering five generations, this family was just about holding its own. In respect to twinning, this family's record, amounting to 18.18 per cent, was higher than that for any other cow family observed. The distribution of twin births extended over only three generations. The foundation cow did not visibly express any twinning disposition and the descendants in the fifth generation were too young to show any. A segregation into unusually predisposed and undisposed lines was hinted in this family, a feature closely resembling that of family 61. I
64
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370
472
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FIG. 2. Diagram of cow family 64 showing the extent and distribution of twin births, which amount to 18.18 per cent of all observed parturitions. For explanations of the diagram see text.
In both families virtually the same bulls appear as sires to the progeny. Sire 0, with a high average twinning rate, is especially conspicuous as a sire of twin dams ; so also is sire I, with a relatively low average rate. Both these sires are inbred to bull C, which is also the sire of both foundation cows. ~ires E and F, both outbreds, are conspicuously present in the nonpredisposed lines. Obviously, the low frequency of twin births does not w a r r a n t definite conclusions with respect to the mode of transmission of twinning. The continued use of inbred sons and grandsons of bull C for several generations in succession and with it a concentration of certain genes of this bull suggest the possibility that he carried genes which foster twinning. In addition, it is observed that other inbred sons and grandsons of the same bllll, as sires T and R, have very low rates for twinning. It should be
I~ULTIPLE BIRTHS
253
recalled that almost half of the cow families and half of the sires never showed any tendency for twinning. All of these observations point strongly to the conclusion that twinning in dairy cows is influenced chiefly by heredity yet expresses itself differently with age. The mode of transmission could well be understood by the assumption that twinning is under the control of a small number of autosomal genes which express themselves incompletely. The transmission seems to be recessive in character, with gene interactions or modifications. DISCUSSION AND CONCLUSIONS
The observation made in this investigation that twinning is rare in the first parturition, rises to a p e a k in the fifth, sixth, and seventli parturitions, and then decreases with advancing age harmonizes closely with the general cycle of fecundity in most multiparous mammals. From this observation alone it is most probable that twinning is an expression of fecundity or the potential reproductive capacity of a dairy cow. However, if dairy cows are considered as strictly uniparous animals, and they should be so considered according to the structural development of their reproductive tract, twinning could be regarded as cases of reversion or atavism. Evidence was presented that twinning is chiefly controlled by heredity. The effect of environment seems to be of very minor importance. The mode of transmission of the twinning character in dairy cattle is obscured by its relatively rare and incomplete expression, its sex-limited and agelimited appearance, and the small number of offspring inherent in cattle. The factual manifestations of transmission in two cow families over a number of generations provided impressive indications that twinning exhibits Mendelian segregation and seems to be under the control of a small number of genes. The character of twinning should be recessive with gene interactions or modifications. By making use of these findings it is feasible that in practical breeding operations twinning in dairy cattle could be influenced considerably in either direction. The question then arises as to whether twinning is a desirable charaeter in dairy cattle. If the available data all are accepted at their face value, twinning is associated with the increased production of calves by sheer numbers; if this fact is scrutinized from the actual reproducing value of the female line, the contrary is the case. Of the theoretical twin sex-ratio, 1 o~o~ :2 o ~ :1 ~ , for all practical purposes only the female pairs are suitable for reproduction in the direct female lines., Theoretically, the number of these female twins would just be equal to the number of single females. Since twin calves have a higher mortality rate at birth and, apparently, a lower vitality throughout life than single calves, the real fact is that twinning has a harmful effect on the continuity of the female lines.
254
K . O . PFAU ET AL.
I f the face value of data favoring the association of twinning with longevity is examined closely, the degree of association diminishes considerably. Twin births occur generally late in life, increase with advancing age, and are incomplete in appearance. I f every animal in a group is expected to show this character, almost all the animals of this group have undergone an intense selection with respect to age. Therefore, almost any comparison of twinning in regard to age is of very questionable reliability. Definite disadvantages of twin births include shortened gestation periods, greater parturition difficulties with subsequent increases in retained placentae, decreased conception rate, lower breeding efficiency, and increased sterility. I n summarizing all these factors, there is no doubt that twinning definitely is an undesirable character in dairy cattle, and efforts should be made to reduce its appearance by p r o p e r breeding methods and selection. REFERENCES (1) BARTLETT,,J'. W., ANDMARGOLIN,S. A Comparison of Inbreeding and Outbreeding
Holstein-Friesian Cattle. N . J . Agr. Expt. Sta. Bull. 712. 1944. (2) BARTLETT,J. W., REECE, R. P., AND LEPARD,O. L. The Influence of Inbreeding on Birth Weight, Rate of Growth, and Type of Dairy Cattle. J. Animal Sei., 1 : 206-212. 1942. (3) BARTLETT,J. W., RLECE, R. P., AND MIXNER, J. P. Inbreeding and Outbreeding
(4)
(5) (6) (7) (8) (9) (10) (11) (12)
Holstein-Friesian Cattle in an Attempt to Establish Genetic Factors for High Milk Production and High Fat Test. N.J. Agr. Expt. Sta. Bull. 667. 1939. ESPE, D. Secretion of Milk. 2nd Ed. The Iowa State College Press, Ames~ Iowa. 1946. GAINES,W. L. The Energy Basis of Measuring Milk Yield in Dairy Cows. Ill. Agr. Expt. Sta. Bull. 453. 1928. HA~0m), J., JR., AND BHATTACHARYA,P. Control of Ovulation in the Cow. J. Agr. Sci., 34: 1-5. 1944. H•wITT, A. C.J. Twinning in Cattle. J. Dairy Research, 5: 101-107. 1937. LUSH, J. L. Animal Breeding Plans. 3rd Ed. The Iowa State College Press, Ames, Iowa. 1945. LUSH, R.H. Inheritance of Twinning. J. Heredity, 16: 273-279. 1925. Rm~, V. A. Breeding and Improvement of Farm Animals. 3rd Ed. McGrawHill Book Company, Inc., New York, N. Y. 1942. WEBF~R,W. Untersuchungen iiber die Hfiufigkeit und Erblichkeit der Disposition zu Zwilllngsgeburten beim Simmentalerrind. Arch. Julius Klaus Stiftung, 20: 307-361. 1945. WILLIAMS, W. L. Veterinary Obstetrics. 2nd Ed. Published by the Author, Ithaca, N. Y. 1931.