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Performance of First-Calf Dairy Heifers under a Limited-Season Early-Freshening Management System1
Performance of First-Calf Dairy Heifers Under a LimitedSeason Early-Freshening Management System ~ C. J. WILCOX Department of Dairy Science University of Florida Institute of Food and Agricultural Sciences, Gainesville Abstract
was 25.S months (8); average age of 2:t,803 U.S. animals summarized in 1961 by Salisbury and VanDemark (6) was 27.92 months. To have an average age at first freshening of near 24 months, heifers obviously must be bred for the first time at Jess than 15 months. Amir et al. (1) suggested that the earliest possible insemination of a heifer was at about five months of ag'e, when the calf was only about one-third of its eventual adult size. One of their Israeli-Friesian heifers freshened at 13.5 months. Nigh-level feeding accelerated onset of sexual maturity, and uterine and udder development; it had no adverse effects on secretive tissue of the udder. The objectives of the present investigation were to determine productive and reproductive performance of heifers bred to freshen only during six months of the year~ and, during the corre.~ponding breeding season, bred at the tirst heat after reaching' 13 months of age, regardless uf body weight or condition.
Productive and reproductive performances of 371 dairy heifers of five breeds were evaluated. All females were served at first beat after attaining 13 months of age, but only if such service would result in due dates during mid-July to mid-January. Average first service age was 455 days; average age at freshening was 781 days. Significant positive relationships between age and weight at freshening, milk yield, fat yield, gestation length, and birth weight of calf were detected and were consistent with previous research. A slight positive relationship existed between age of freshening and days open during the first lactation. Although tIolsteins had a consistently higher frequency of calving problems, it was not possible to detect differences in frequency due to age at parturition. Overall frequencies were: retained plaeenta, 2.4~ ; uterine prolapse, 1.1% ; dystoeia, 4.9c} : metritis, 10.5%; dead calves, 10.2%; and nne or more problems, 21.6%. Dairymen should expect no increase in problems at freshening if animals are managed according to standard recommendations and are bred at 13 months of age.
Experimental Procedure
A nmnber of advantages exist in having dairy heifers freshen at younger ages than commonly practiced (~1, 2, 4, 5, 7). Perhaps of primary importance is having the heifer freshen at the desired time of year. I n many parts of the United States~ for example, high milk prices and high lactation yields favor a fall freshening" pattern. Offspring' of fail-freshening dams would themselves freshen in winter or spring, however, if first bred at 18 months of age~ as is sometimes recommended. With the smaller dairy breeds, whose recommended first service age has been 15 months, many freshen at 27 months or older because of delayed conception. Average age at first freshening of 933 animals in a large Piorida herd Received for publication October 30. 1967. ' Florida Agricultural Experiment Stations •Iournttl Series, no. 27T6. 591
So~rc'e of d~,ta. During 1959-65, all heifers of the Dail\y Research Unit of the Florida Agricultural Experiment Station were assigned to the project. All live dairy breeds were repre.~ented, though only a few were Ayrshires and Brown Swiss. Productive attd reproductive peri'ormanee at parturit.ion and first laetatim~ of 371 heifers was available for analysis. Records on an additional Holstein with twins were exeiaded. Body weights were estimated by taping at the first test period of the lactation. Milk was weighed twice daily i milk fat tests were conducted once monthly. 3.[~m, gement o/" heifers. Routine management from birth to freshening has been described by Wing (9). Many animals, however, were assigned at birth to projects concerning nutrition, growth and development of calves, etc., and were handled according to various experimental programs. During 1959-65, these were terminated at between 21 and 90 days of age. A small number of heifers have been used as yearlings for grazing and digestion trials. As far as could be determined, the research to which these animals were assigned had no detectable effect upon their condition during
592
WmC0X considered abortions study.
TABLE 1. Freshening pattern of first-calf heifers. Breed Age fresh Ayr- Brown Guern- FIol(months) shire Swiss sey stein 5 5 4 6 20
17 27 6 13 63
excluded f r o m
the
Results and Discussion
Freshening pattern of the 371 heifers is shown in Table 1. Mean age at first service was 455 days. Over 37% freshened at 23 months or less. According to traditional recommendations of 27 months or more for Holsteins and Brown Swiss, and 24 months or more for other breeds, 64% were underage. Over-all productive and reproductive performance is shown in Table 2. Mean age at freshening for all animals was 25.6 months; mean number of days f r o m first service to successful service was 47. Both values were inflated by the practice of not breeding the heifers during the off-season. The small differences among breeds in age at freshening shown in the table could not validly be considered as true breed differences, since the nmnth of birth of the animals depended considerably on management practices of the older animals in the herd. Many of these animals (second-calf heifers and older) were assigned to research projects of various nature, resulting in differing freshening patterns among breeds. Breed differences are well known for several of the traits listed; in these cases specific breed comparisons were not attempted. Analysis of days open, adjusted by covariance for age at freshening on a within-season basis, showed significant (P < 0.05) breed differences. Over-all average for all breeds was 140 days, Of the 371 heifers, 73% remained in the herd to start a second lactation. Chi-square analysis did not show differences among breeds to be significant,
Jersey
(nO.)
~23 6 24-26 8 27-29 1 ~30 5 Total 20
and
41 41 7 8 97
66 55 19 31 171
the latter stages of gestation or at parturition. The over-all feeding p r o g r a m p r i o r to freshening was calculated to result in maxinml or nearmaximal growth without excessive fatness. Subjective appraisal of the animals at p a r t u r i t i o n suggested that this was accomplished. Breeding. The desired six-month freshening season for heifers was m i d - J u l y to m i d - J a n u a r y of each year. H e i f e r s were not bred to freshen out of season. F o r the first year, heifers were not bred until reaching 14 months. T h e r e a f t e r during the breeding season, roughly October 1 to March 31, all heifers were bred at first heat, regardless of body weight or condition upon reaching 13 months. In general, animals which did not conceive to ten services were considered nonbreeders. Those not conceiving during the breeding season, but with less than ten services, were held over to the following season. P r e g n a n c y checks were made 40-60 days postservice, with competent veterinary assistance available at all times. A placenta was considered retained if not expelled 24 hours postpartum. Stillbirths and calves unable to survive 24 hours were p u t into a single class, dead calves. Gestations of less than 240 days were
TABLE 2. Performance of first-calf heifers. Breed Trait Number Age fresh (months) Body weight (kg) Milk yield (kg) F a t yield (kg) Gestation length (da~*s) Calf birth weight (kg) Days open" Second lactation (%) Calving problems (no.) Retained placenta Uterine prolapse Dystocia Metritis Dead calf One or more b
Ayrshire 20 26.9 464 3,333 142 276.5 29.2 184 65 3 0
Brown Swiss
Guernsey
ttolstein
Jersey
20 27.3 542 4,155 167 285.4 35.6 187 85
63 25.6 433 3,355 171 283.8 31.0 126 75
97 24.6 534 5,278 193 276.5 35.7 146 76
171 25.7 355 3,039 156 278.7 22.0 132 71
1 0
1
3
1
0
4
0
8
9
2 1 3
7 6 12
22 14 36
7 17 26
0 1 0 3
4
Days open during first lactation. b One or more of the five calving problems listed. J . DAIRY SCIENCE ~7OL. 51, NO. 4
HEIFER
MANAGEMENT
Of m a j o r i n t e r e s t was the effect of age of f r e s h e n i n g u p o n the f r e q u e n c y of calving p r o b lems. There was no evidence suggesting the presence of breed-age h e t e r o g e n e i t y in frequency of occurrence a n d breeds were, therefore, ignored in testing the frequencies of the different ages. M o n t h s of age were g r o u p e d into t h r e e categories: 1) a11~---23 months, 2) 24 to 26 m o n t h s inclusive, a n d 3) ~ 2 7 m o n t h s ; G r o u p (3) resulted f r o m the c o m b i n a t i o n of the older two g r o u p s in T a b l e i. F r e q u e n c i e s of dystocia, metritis, dead calves, a n d one or more p r o b l e m s were subjeeted to Chi-square analysis. I n no ease were there significant differences in frequencies a m o n g the age groups. Age a t first calving thus h a d no deteetable effect u p o n the incidence of p r o b l e m s at p a r t u r i tion. Likewise, no effect of age u p o n the fraction r e m a i n i n g f o r a second lactation could be detected. One or more calving p r o b l e m s occurred at $0 p a r t u r i t i o n s . B r e e d differences were significant ( P < 0.01), due p r i m a r i l y to the high frequency ( 3 7 % ) f o r Holsteins. R e t a i n e d placentas did not a p p e a r to be a p r o b l e m ; B r o w n et aI. (3) have shown t h a t n o r m a l subsequent
593
AND P E R F O R M A N C E
r e p r o d u c t i v e p e r f o r m a n c e can be expected f r o m these animals, i f t r e a t e d p r o p e r l y . The f o u r cases of u t e r i n e p r o l a p s e in H o l s t e i n s occ u r r e d in individuals 22, 22, 23, a n d 25 m o n t h s of age at f r e s h e n i n g . I n each ease the calf was b o r n d e a d ; in two eases the d a m was lost also. B r e e d frequencies of dystocia, metritis, a n d dead calves were c o m p a r e d f o r Guernseys, Holsteins, a n d Jerseys. F o r metritis, frequencies differed ( P < 0.01), due p r i m a r i l y to h i g h rates f o r Holsteins. T h o u g h b r e e d differences were n o t significant f o r dystoeia a n d dead calves, Holsteins were h i g h e r t h a n expected f o r these t r a i t s also. Chi-square tests f o r the effect of sex on the frequencies of all conditions except u t e r i n e p r o l a p s e were made, a g a i n i g n o r i n g breeds. Of the f o u r u t e r i n e p r o l a p s e eases, three calves were male a n d one female. W i t h every- p r o b lem, the f r e q u e n c y was g r e a t e r following male 1)irths, though significantly to only f o r met r i t i s ( P < 0.05) a n d one or more p r o b l e m s ( P < 0.01). P r e s m n a b l y , size of calf r a t h e r t h a n sex p e r se was the m a j o r cause. R e l a t i o n s h i p s between age at f r e s h e n i n g a n d six o t h e r variables are shown in Table 3. E r r o r
TABLE 3. Linear relationships between age at freshening and productive and reproductive traits. Trait Body weight (kg)
Milk yield (kg)
F a t y i e ] d (kg)
Gestatlonlength (days)
Calf birth weight (kg)
Days open ~
d.f.
Error variance"
Ayrshire Brown Swiss Guernsey Holstein Jersey Ayrshire Brown Swiss Guernsey Holstein Jersey Ayrshire Brown Swiss Guernsey Holstein Jersey
10 11 53 86 156 10 11 53 86 156 ]0 11 53 86 156
2,633 2,288 2,589 2,885 1,590 723,261 2,046,131 327,993 1,152,342 294,433 1,784 5,186 568 1,413 846
,1.4.63± 3.45 ,1.5.56--+3.00 ,1.3.01-+ 1.69 +8.15-+ °~ .°0 ~ ,1.6.44-+ 0.92 97 ___57 118 ± 9 0 27 -+19 69 -+42 37 _+11 +3.6 ± 2.8 --0.1 ± 4.5 .1.3.4 -+ 1.4 +2.9 -+ 1.5 +1.6 ± 0.6
+0.39 .1.0.49 .1.0.24 -t-0.28 ~ +0.49 ~ ,1.0.47 .1.0.37 4-0.34 ~ .1.0.18 -/-0.25 ~ +0.38 --0.00 ,+0.50 ~ +0.21 ~ +0,20 ~
Ayrshire Brown Swiss Guernsey Holstein Jersey Ayrshire Brown Swiss Guernsey Holstein Jersey Breeds pooled
11 11 53 86 161 11 11 53 86 161 327
17 48 30 23 34 12 17 12 22 10 6,503
-t-0.15± .27 ,1.0.72-+ .43 +0.18-+ .18 .1.0.43-+ .18 .1.0.35-+ .12 +0.51-+ .23 +0.29-+ .26 ,1.0.25-+ .12 .1.0.38± .18 ,1.0.11-+ .07 ,1.2.32--+1.73
+0.17 ,1.0.45 .1.0.14 -{-0.25~ -}-0.22 ~ +0.55 ~ +0.33 -}-0.29 ~ -}-0.22 ~ +0.13 .1.0.10 °
Breed
CorreRegression
b
]ation
* P < P <
0.05. 0,01, :Represents mean square for within-season deviations from regression. b Change in trait for ea(,h month increase in age ( + standard error). " P ~ 0.05. J. DAIRY
SCIEXCE ~roL.
51, NO.
4
594
WILCOX
variances represent the within-season deviations from regression of each of the traits upon age in months. They contain an aggregate of genetic and environmental factors known to be real but not included in the mathematical model (e.g., sex effects on birth weights and gestation lengths). Though based on limited numbers, the high variability in milk and fat yields of Brown Swiss heifers seems to be consistent with comments of numerous Brown Swiss breeders. Changes in body weight with age seemed considerably lower than most reports in the literature, ranging from 3.01 kg per month for Guernseys to 8.15 kg for Holsteins. The large increase in milk yield for Brown Swiss without an accompanying increase in fat yield seemed somewhat incongruous; examination of the 20 production records showed a marked decrease in fat percentage among the older heifers, presumably due to chance. Within the limits of the standard errors of the regression coefficients, the changes in milk and fat yields are entirely consistent with USDA age adjustment factors, as would be expected. Likewise, changes in gestation length and birth weights are in general agreement with the literature. Whether the increase in days open, 2.32 days per month, has practical significance is not clear. I t is certainly indicated, however, that over-all, postpartum reproductive performance was not hampered by early freshening. The individual breed regressions were not different, hence they were pooled. The within year-season regression for Holsteins, the breed experiencing the greatest frequency of problems, was --1.91 days, however. Conclusions A limited freshening season of six months is compatible with early freshening of dairy heifers, even when rigidly enforced. Considerable reduction in average age of freshening can be accomplished by breeding at 13 months of age. Slight but significant loss in body weight, milk yield, and fat yields occurred, along with shorter gestations and lighter calves. I t was not pos-
J . DAIRY SCIENCE VOL. 51, NO. 4
sible to detect differences in the frequencies of calving problems, due to age at freshening. The proportion of heifers remaining for a second lactation was likewise unaffected. Days open, a measure of postpartmn reproductive health, was actually slightly greater in older animals. Dairymen should consider the possibilities of an early service-early freshening program, at least to breeding of heifers at 13 months and older during the breeding season. Acknowledgments Technical assistance of F. C. Neal, J. P. Boggs, H. L. Somers, and D. K. Preston is appreciated. References (1) Amir, S., J. Kali, R. Voleani, and M. Perlman. 1967. Early breeding of dairy heifers. J. Brit. Soe. Anita. Prod., 2:268. (2) Anonymous. 1966. (With L. H. Sehultz and J. W. Hibbs) What about early breeding of heifers? Itoard's Dairyman, 111(10): 642. May 25. (3) Brown, N. DeD., Jr., K. O. Pfau, 1%. E. Matber, and J. W. Bartlett. 1959. Effects of various postpartum treatments upon the reproductive efficiency of dairy cows. J. Dairy Sci., 42: 1338. (4) Gardner, P,. W., and L. V. Gnrcia. 1966. Accelerated growth and early breeding studies with Holstein heifers. J. Dairy Sci., 49: 720. (5) Hibbs, J. W., and H. R. Conrad. 1966. Breeding heifers early. Sunbelt Dairyman, 4(5) : 14. May. (6) Salisbury, G. W., and N. L. Valfl:)emark. 1961. Physiology of reproduction and artificial insemination of cattle. W. It. Freeman & Co., San Francisco, California. (7) Wickersham, E. W., and L. H. Schultz. 1963. Influence of age at first breeding on growth, reproduction, and production of well-fed Holstein heifers. J. Dairy Sci., 46: 544. (8) Wilcox, C. J., J. A. Curl, J. Roman, A. H. Spurlock, and R. B. Becker. 1966. Life span and livability of crossbred dairy cattle. J. Dairy Sei., 49: 991. (9) Wing, J. M. 1960. Raising dairy herd replacements. Florida Agr. Exp. Sta., Circ. S-118.
was 25.S months (8); average age of 2:t,803 U.S. animals summarized in 1961 by Salisbury and VanDemark (6) was 27.92 months. To have an average age at first freshening of near 24 months, heifers obviously must be bred for the first time at Jess than 15 months. Amir et al. (1) suggested that the earliest possible insemination of a heifer was at about five months of ag'e, when the calf was only about one-third of its eventual adult size. One of their Israeli-Friesian heifers freshened at 13.5 months. Nigh-level feeding accelerated onset of sexual maturity, and uterine and udder development; it had no adverse effects on secretive tissue of the udder. The objectives of the present investigation were to determine productive and reproductive performance of heifers bred to freshen only during six months of the year~ and, during the corre.~ponding breeding season, bred at the tirst heat after reaching' 13 months of age, regardless uf body weight or condition.
Productive and reproductive performances of 371 dairy heifers of five breeds were evaluated. All females were served at first beat after attaining 13 months of age, but only if such service would result in due dates during mid-July to mid-January. Average first service age was 455 days; average age at freshening was 781 days. Significant positive relationships between age and weight at freshening, milk yield, fat yield, gestation length, and birth weight of calf were detected and were consistent with previous research. A slight positive relationship existed between age of freshening and days open during the first lactation. Although tIolsteins had a consistently higher frequency of calving problems, it was not possible to detect differences in frequency due to age at parturition. Overall frequencies were: retained plaeenta, 2.4~ ; uterine prolapse, 1.1% ; dystoeia, 4.9c} : metritis, 10.5%; dead calves, 10.2%; and nne or more problems, 21.6%. Dairymen should expect no increase in problems at freshening if animals are managed according to standard recommendations and are bred at 13 months of age.
Experimental Procedure
A nmnber of advantages exist in having dairy heifers freshen at younger ages than commonly practiced (~1, 2, 4, 5, 7). Perhaps of primary importance is having the heifer freshen at the desired time of year. I n many parts of the United States~ for example, high milk prices and high lactation yields favor a fall freshening" pattern. Offspring' of fail-freshening dams would themselves freshen in winter or spring, however, if first bred at 18 months of age~ as is sometimes recommended. With the smaller dairy breeds, whose recommended first service age has been 15 months, many freshen at 27 months or older because of delayed conception. Average age at first freshening of 933 animals in a large Piorida herd Received for publication October 30. 1967. ' Florida Agricultural Experiment Stations •Iournttl Series, no. 27T6. 591
So~rc'e of d~,ta. During 1959-65, all heifers of the Dail\y Research Unit of the Florida Agricultural Experiment Station were assigned to the project. All live dairy breeds were repre.~ented, though only a few were Ayrshires and Brown Swiss. Productive attd reproductive peri'ormanee at parturit.ion and first laetatim~ of 371 heifers was available for analysis. Records on an additional Holstein with twins were exeiaded. Body weights were estimated by taping at the first test period of the lactation. Milk was weighed twice daily i milk fat tests were conducted once monthly. 3.[~m, gement o/" heifers. Routine management from birth to freshening has been described by Wing (9). Many animals, however, were assigned at birth to projects concerning nutrition, growth and development of calves, etc., and were handled according to various experimental programs. During 1959-65, these were terminated at between 21 and 90 days of age. A small number of heifers have been used as yearlings for grazing and digestion trials. As far as could be determined, the research to which these animals were assigned had no detectable effect upon their condition during
592
WmC0X considered abortions study.
TABLE 1. Freshening pattern of first-calf heifers. Breed Age fresh Ayr- Brown Guern- FIol(months) shire Swiss sey stein 5 5 4 6 20
17 27 6 13 63
excluded f r o m
the
Results and Discussion
Freshening pattern of the 371 heifers is shown in Table 1. Mean age at first service was 455 days. Over 37% freshened at 23 months or less. According to traditional recommendations of 27 months or more for Holsteins and Brown Swiss, and 24 months or more for other breeds, 64% were underage. Over-all productive and reproductive performance is shown in Table 2. Mean age at freshening for all animals was 25.6 months; mean number of days f r o m first service to successful service was 47. Both values were inflated by the practice of not breeding the heifers during the off-season. The small differences among breeds in age at freshening shown in the table could not validly be considered as true breed differences, since the nmnth of birth of the animals depended considerably on management practices of the older animals in the herd. Many of these animals (second-calf heifers and older) were assigned to research projects of various nature, resulting in differing freshening patterns among breeds. Breed differences are well known for several of the traits listed; in these cases specific breed comparisons were not attempted. Analysis of days open, adjusted by covariance for age at freshening on a within-season basis, showed significant (P < 0.05) breed differences. Over-all average for all breeds was 140 days, Of the 371 heifers, 73% remained in the herd to start a second lactation. Chi-square analysis did not show differences among breeds to be significant,
Jersey
(nO.)
~23 6 24-26 8 27-29 1 ~30 5 Total 20
and
41 41 7 8 97
66 55 19 31 171
the latter stages of gestation or at parturition. The over-all feeding p r o g r a m p r i o r to freshening was calculated to result in maxinml or nearmaximal growth without excessive fatness. Subjective appraisal of the animals at p a r t u r i t i o n suggested that this was accomplished. Breeding. The desired six-month freshening season for heifers was m i d - J u l y to m i d - J a n u a r y of each year. H e i f e r s were not bred to freshen out of season. F o r the first year, heifers were not bred until reaching 14 months. T h e r e a f t e r during the breeding season, roughly October 1 to March 31, all heifers were bred at first heat, regardless of body weight or condition upon reaching 13 months. In general, animals which did not conceive to ten services were considered nonbreeders. Those not conceiving during the breeding season, but with less than ten services, were held over to the following season. P r e g n a n c y checks were made 40-60 days postservice, with competent veterinary assistance available at all times. A placenta was considered retained if not expelled 24 hours postpartum. Stillbirths and calves unable to survive 24 hours were p u t into a single class, dead calves. Gestations of less than 240 days were
TABLE 2. Performance of first-calf heifers. Breed Trait Number Age fresh (months) Body weight (kg) Milk yield (kg) F a t yield (kg) Gestation length (da~*s) Calf birth weight (kg) Days open" Second lactation (%) Calving problems (no.) Retained placenta Uterine prolapse Dystocia Metritis Dead calf One or more b
Ayrshire 20 26.9 464 3,333 142 276.5 29.2 184 65 3 0
Brown Swiss
Guernsey
ttolstein
Jersey
20 27.3 542 4,155 167 285.4 35.6 187 85
63 25.6 433 3,355 171 283.8 31.0 126 75
97 24.6 534 5,278 193 276.5 35.7 146 76
171 25.7 355 3,039 156 278.7 22.0 132 71
1 0
1
3
1
0
4
0
8
9
2 1 3
7 6 12
22 14 36
7 17 26
0 1 0 3
4
Days open during first lactation. b One or more of the five calving problems listed. J . DAIRY SCIENCE ~7OL. 51, NO. 4
HEIFER
MANAGEMENT
Of m a j o r i n t e r e s t was the effect of age of f r e s h e n i n g u p o n the f r e q u e n c y of calving p r o b lems. There was no evidence suggesting the presence of breed-age h e t e r o g e n e i t y in frequency of occurrence a n d breeds were, therefore, ignored in testing the frequencies of the different ages. M o n t h s of age were g r o u p e d into t h r e e categories: 1) a11~---23 months, 2) 24 to 26 m o n t h s inclusive, a n d 3) ~ 2 7 m o n t h s ; G r o u p (3) resulted f r o m the c o m b i n a t i o n of the older two g r o u p s in T a b l e i. F r e q u e n c i e s of dystocia, metritis, dead calves, a n d one or more p r o b l e m s were subjeeted to Chi-square analysis. I n no ease were there significant differences in frequencies a m o n g the age groups. Age a t first calving thus h a d no deteetable effect u p o n the incidence of p r o b l e m s at p a r t u r i tion. Likewise, no effect of age u p o n the fraction r e m a i n i n g f o r a second lactation could be detected. One or more calving p r o b l e m s occurred at $0 p a r t u r i t i o n s . B r e e d differences were significant ( P < 0.01), due p r i m a r i l y to the high frequency ( 3 7 % ) f o r Holsteins. R e t a i n e d placentas did not a p p e a r to be a p r o b l e m ; B r o w n et aI. (3) have shown t h a t n o r m a l subsequent
593
AND P E R F O R M A N C E
r e p r o d u c t i v e p e r f o r m a n c e can be expected f r o m these animals, i f t r e a t e d p r o p e r l y . The f o u r cases of u t e r i n e p r o l a p s e in H o l s t e i n s occ u r r e d in individuals 22, 22, 23, a n d 25 m o n t h s of age at f r e s h e n i n g . I n each ease the calf was b o r n d e a d ; in two eases the d a m was lost also. B r e e d frequencies of dystocia, metritis, a n d dead calves were c o m p a r e d f o r Guernseys, Holsteins, a n d Jerseys. F o r metritis, frequencies differed ( P < 0.01), due p r i m a r i l y to h i g h rates f o r Holsteins. T h o u g h b r e e d differences were n o t significant f o r dystoeia a n d dead calves, Holsteins were h i g h e r t h a n expected f o r these t r a i t s also. Chi-square tests f o r the effect of sex on the frequencies of all conditions except u t e r i n e p r o l a p s e were made, a g a i n i g n o r i n g breeds. Of the f o u r u t e r i n e p r o l a p s e eases, three calves were male a n d one female. W i t h every- p r o b lem, the f r e q u e n c y was g r e a t e r following male 1)irths, though significantly to only f o r met r i t i s ( P < 0.05) a n d one or more p r o b l e m s ( P < 0.01). P r e s m n a b l y , size of calf r a t h e r t h a n sex p e r se was the m a j o r cause. R e l a t i o n s h i p s between age at f r e s h e n i n g a n d six o t h e r variables are shown in Table 3. E r r o r
TABLE 3. Linear relationships between age at freshening and productive and reproductive traits. Trait Body weight (kg)
Milk yield (kg)
F a t y i e ] d (kg)
Gestatlonlength (days)
Calf birth weight (kg)
Days open ~
d.f.
Error variance"
Ayrshire Brown Swiss Guernsey Holstein Jersey Ayrshire Brown Swiss Guernsey Holstein Jersey Ayrshire Brown Swiss Guernsey Holstein Jersey
10 11 53 86 156 10 11 53 86 156 ]0 11 53 86 156
2,633 2,288 2,589 2,885 1,590 723,261 2,046,131 327,993 1,152,342 294,433 1,784 5,186 568 1,413 846
,1.4.63± 3.45 ,1.5.56--+3.00 ,1.3.01-+ 1.69 +8.15-+ °~ .°0 ~ ,1.6.44-+ 0.92 97 ___57 118 ± 9 0 27 -+19 69 -+42 37 _+11 +3.6 ± 2.8 --0.1 ± 4.5 .1.3.4 -+ 1.4 +2.9 -+ 1.5 +1.6 ± 0.6
+0.39 .1.0.49 .1.0.24 -t-0.28 ~ +0.49 ~ ,1.0.47 .1.0.37 4-0.34 ~ .1.0.18 -/-0.25 ~ +0.38 --0.00 ,+0.50 ~ +0.21 ~ +0,20 ~
Ayrshire Brown Swiss Guernsey Holstein Jersey Ayrshire Brown Swiss Guernsey Holstein Jersey Breeds pooled
11 11 53 86 161 11 11 53 86 161 327
17 48 30 23 34 12 17 12 22 10 6,503
-t-0.15± .27 ,1.0.72-+ .43 +0.18-+ .18 .1.0.43-+ .18 .1.0.35-+ .12 +0.51-+ .23 +0.29-+ .26 ,1.0.25-+ .12 .1.0.38± .18 ,1.0.11-+ .07 ,1.2.32--+1.73
+0.17 ,1.0.45 .1.0.14 -{-0.25~ -}-0.22 ~ +0.55 ~ +0.33 -}-0.29 ~ -}-0.22 ~ +0.13 .1.0.10 °
Breed
CorreRegression
b
]ation
* P < P <
0.05. 0,01, :Represents mean square for within-season deviations from regression. b Change in trait for ea(,h month increase in age ( + standard error). " P ~ 0.05. J. DAIRY
SCIEXCE ~roL.
51, NO.
4
594
WILCOX
variances represent the within-season deviations from regression of each of the traits upon age in months. They contain an aggregate of genetic and environmental factors known to be real but not included in the mathematical model (e.g., sex effects on birth weights and gestation lengths). Though based on limited numbers, the high variability in milk and fat yields of Brown Swiss heifers seems to be consistent with comments of numerous Brown Swiss breeders. Changes in body weight with age seemed considerably lower than most reports in the literature, ranging from 3.01 kg per month for Guernseys to 8.15 kg for Holsteins. The large increase in milk yield for Brown Swiss without an accompanying increase in fat yield seemed somewhat incongruous; examination of the 20 production records showed a marked decrease in fat percentage among the older heifers, presumably due to chance. Within the limits of the standard errors of the regression coefficients, the changes in milk and fat yields are entirely consistent with USDA age adjustment factors, as would be expected. Likewise, changes in gestation length and birth weights are in general agreement with the literature. Whether the increase in days open, 2.32 days per month, has practical significance is not clear. I t is certainly indicated, however, that over-all, postpartum reproductive performance was not hampered by early freshening. The individual breed regressions were not different, hence they were pooled. The within year-season regression for Holsteins, the breed experiencing the greatest frequency of problems, was --1.91 days, however. Conclusions A limited freshening season of six months is compatible with early freshening of dairy heifers, even when rigidly enforced. Considerable reduction in average age of freshening can be accomplished by breeding at 13 months of age. Slight but significant loss in body weight, milk yield, and fat yields occurred, along with shorter gestations and lighter calves. I t was not pos-
J . DAIRY SCIENCE VOL. 51, NO. 4
sible to detect differences in the frequencies of calving problems, due to age at freshening. The proportion of heifers remaining for a second lactation was likewise unaffected. Days open, a measure of postpartmn reproductive health, was actually slightly greater in older animals. Dairymen should consider the possibilities of an early service-early freshening program, at least to breeding of heifers at 13 months and older during the breeding season. Acknowledgments Technical assistance of F. C. Neal, J. P. Boggs, H. L. Somers, and D. K. Preston is appreciated. References (1) Amir, S., J. Kali, R. Voleani, and M. Perlman. 1967. Early breeding of dairy heifers. J. Brit. Soe. Anita. Prod., 2:268. (2) Anonymous. 1966. (With L. H. Sehultz and J. W. Hibbs) What about early breeding of heifers? Itoard's Dairyman, 111(10): 642. May 25. (3) Brown, N. DeD., Jr., K. O. Pfau, 1%. E. Matber, and J. W. Bartlett. 1959. Effects of various postpartum treatments upon the reproductive efficiency of dairy cows. J. Dairy Sci., 42: 1338. (4) Gardner, P,. W., and L. V. Gnrcia. 1966. Accelerated growth and early breeding studies with Holstein heifers. J. Dairy Sci., 49: 720. (5) Hibbs, J. W., and H. R. Conrad. 1966. Breeding heifers early. Sunbelt Dairyman, 4(5) : 14. May. (6) Salisbury, G. W., and N. L. Valfl:)emark. 1961. Physiology of reproduction and artificial insemination of cattle. W. It. Freeman & Co., San Francisco, California. (7) Wickersham, E. W., and L. H. Schultz. 1963. Influence of age at first breeding on growth, reproduction, and production of well-fed Holstein heifers. J. Dairy Sci., 46: 544. (8) Wilcox, C. J., J. A. Curl, J. Roman, A. H. Spurlock, and R. B. Becker. 1966. Life span and livability of crossbred dairy cattle. J. Dairy Sei., 49: 991. (9) Wing, J. M. 1960. Raising dairy herd replacements. Florida Agr. Exp. Sta., Circ. S-118.