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Effects of Mild Inbreeding on Productive and Reproductive Performance of Guernsey Cattle1, 2
Effects of Mild Inbreeding on Productive and Reproductive Performance of Guernsey Cattle z,2 S. A. H E R M A S , C. W. Y O U N G ? and J. W. RUST 4 Department of Animal Science University of Minnesota St. Paul 55108 ABSTRACT
estimates were not significantly different from zero. Except for the study by Hillers and Freeman (5), no other recent studies have been with Guernseys. The purpose of this investigation was to study the effects of low coefficients of inbreeding on productive and reproductive performance in Guernsey dairy cattle.
Production and reproduction records that spanned a 24-yr period were used to study the effects of low coefficients of inbreeding in two experiment station Guernsey herds. Inbreeding ranged from 0 to 25.3% and averaged 4.1%. Milk and fat yields were all first lactations standardized to a mature equivalent, twice daily milking, and 305 d. Intrasire regressions of production traits on percent inbreeding were - 2 3 . 8 kg of milk, - 1 . 2 5 kg of fat, and .002% for fat percentage. Estimates of the effect of inbreeding on reproductive traits had large standard errors but suggested that inbreeding depressed reproductive performance. Age at first calving decreased 3.7 d per 1% increase in inbreeding.
MATERIALS AND METHODS
INTRODUCTION
Effects of inbreeding on productive traits of dairy cattle have been investigated thoroughly (1, 4, 5, 7, 9, 10, 11). Young et al. (13) summarized inbreeding investigations in the north central United States and reported average reductions per 1% increase in inbreeding of 22.7 kg of milk and .68 kg of fat. Inbreeding also affected fertility in dairy cattle by delaying estrus and increasing services per conception. Hodges et al. (6) found that each additional 1% inbreeding reduced 305-d milk yield by 22.85 kg and fat yield by .53 kg and increased calving interval by 2 d. Fat yield and calving interval
Received September 11, 1986. Accepted December 1, 1986. 1Scientific Journal Series Paper Number 15,073, Minnesota Agricultural Experiment Station. 2Contribution from Regional Research Project NC-2. 3 Reprint requests. 4 North Central Experiment Station, Grand Rapids, MN 55744. 1987 J Dairy Sci 70:712--715
712
Data were records of production and reproduction from two Guernsey herds for the period from 1958 to 1981. The two herds were initially located at the North Central Experiment Station, Grand Rapids, and the Northeast Experiment Station, Duluth. The latter herd was moved to the Rosemount Experiment Station, Rosemount in late 1966. Prior to 1961, both herds had been part of a line development project. In 1961, both herds were divided into two breeding groups. One breeding group was continued in the linebreeding program, while the other breeding group was bred thereafter to Guernsey artificial insemination (AI) sires with highest estimated transmitting abilities for milk yield. Nearly all members of the latter group had inbreeding coefficients of zero, and the entire group was excluded from this study. Linebreeding has been described by Lush (8) and here involved continuous use of descendants of Flying Horse Masters Monarch 327238 and Cesor Pontiff's Anchor 281510, the sire and maternal grandsire of Langmeadow Minnie 1104226. In 1957, Langmeadow Minnie produced 663 kg of milk fat in 365 d, which at that time was a world record for all breeds. Complete pedigrees for all linebred females were traced to 1937, because the bulls to which linebreeding was directed were born after that date. Inbreeding coefficients, calculated by the method of Wright (12), ranged from 0 to 25.3% and averaged 4.1%. Only first lactation production records were used to avoid effects of cow selection. Re-
PRODUCTION TECHNICAL NOTE productive records were for heifers and first parity cows. Numbers of records were 335 for heifer reproduction, 246 for first parity reproduction, and 238 for first lactation production. Thirty sires were represented for heifer reproduction, and 27 were represented for first lactation production and reproduction. Milk and fat yields were standardized to a mature equivalent (ME) twice daily milking and 305-d lactation. Reproductive traits studied were days open, service period, days in milk at first breeding, number of services, conception rate, and age at first calving. Only service period, number of services, and conception rate were available for heifers. Service period was defined as days from first service to final service or to disposal if pregnancy did not occur. Conception rate was defined as the ratio of successful services to total services. Descriptions of other traits indicate their definitions. Age at first calving was measured in months. In order to include all possible variation in reproductive traits, this study included records for all cows and heifers bred regardless of whether or not conception occurred. Where conception did not occur, days open and service periods terminated at date of disposal. Regressions were calculated within herd and within sire. Most sires were used for relatively short periods, usually less than 2 yr, so time periods were not considered. Dam's record was ignored, as regressions obtained with and without holding dam's record constant have been similar (13). Estimates were calculated as pooled intrasire regressions weighted by number of daughters per sire. RESULTS A N D DISCUSSION
Regressions of first lactation production on percent inbreeding are in Table 1. The intrasire
713
regressions of milk yield and fat yield on percent inbreeding were - 2 3 . 8 -+ 19.3 kg and - 1 . 2 -+ .8 kg, respectively. Percentage of milk fat increased by .002% for each 1% increase in the coefficient of inbreeding. The estimate for milk yield agrees well with that of Thomson and Freeman (10), who studied Holstein first lactations, and is generally comparable to estimates reported by others (5, 6, 11) using average records. Our estimate for fat production is comparable to some (2, 4, 11) and larger than other estimates (1, 3, 10). All those reports were based on first lactation records. The small positive estimate for fat percentage suggests no change or a very small increase in fat percentage due to inbreeding. This agrees well with many other estimates (13). Results for fat test may be due to the lower milk production resulting from inbreeding and to the negative relation between milk yield and fat test. Also, fat test is controlled to a greater degree by additive genetic differences than are yields, and environmental factors, which affect milk and fat production adversely, tend to raise fat percentage. Generally, all estimates for production traits, even though standard errors were large, were similar to estimates in the literature. Estimates for the effects of inbreeding on first parity and heifer reproduction are in Tables 2 and 3. Regression coefficients for these traits had large standard errors so little can be inferred from them. However, the sign and the trend of these estimates is in agreement with the concept that inbreeding has detrimental effects on reproductive performance. Estimates for first lactations were that a 1% increase in inbreeding coefficient increased number of services by .17, reduced conception rate by 3.3%, increased both days in milk at
TABLE 1. Regressions of first lactation production in Guernseys on percent inbreeding.
Trait
Observations
.X
Regression on % inbreeding
SE
ME2 Milk, kg ME Fat, kg Fat, %
238 238 238
5082 253.2 5.02
-23.8 -1.2 .002
19.3 .8 .009
Regression coefficients are in same units as means. a ME = Mature equivalent. Journal of Dairy Science Vol. 70, No. 3, 1987
714
HERMAS ET AL.
TABLE 2. Regressions of first lactation reproduction in Guernseys on percent inbreeding.
Trait
Observations
Number of services Conception rate, % Service period, d Days in milk at first breeding, d Days open, d Age at first calving, d
246 246 246 246 246 246
X 2.19 57.2 37.7 82.6 129.3 785.0
Regression on l % inbreeding
SE
.17 -3.3 1.4 1.9
.19 4.5 4.5 1.6
2.3 -3.7
7.1 7.5
Regression coefficients are in same units as means.
TABLE 3. Regressions of heifer reproductive performance in Guernseys on percent inbreeding.
Trait
Observations
X
Number of services Conception rate, % Service period, d
335 335 335
2.04 68.0 39.8
Regression on t % inbreeding .19 -4.8 3.6
SE .12 3.5 4.8
t Regression coefficients are in same units as means.
first b r e e d i n g a n d d a y s o p e n b y a b o u t 2 d, a n d increased service p e r i o d b y a b o u t 1 d. E s t i m a t e s for heifers were larger t h a n t h o s e for c o w s in first l a c t a t i o n . The e s t i m a t e f o r d a y s o p e n is similar to an e s t i m a t e o f a 2-d increase in calving interval f o u n d b y H o d g e s et al. (6). E s t i m a t e s were in t h e same d i r e c t i o n b u t larger t h a n ones obt a i n e d b y B o n c z e k and Y o u n g (2) f r o m t w o l i n e b r e d H o l s t e i n p o p u l a t i o n s . T h e age at first calving e s t i m a t e suggests a r e d u c t i o n in age at first calving as i n b r e e d i n g increases. This is c o n t r a r y t o results r e p o r t e d b y o t h e r s . CONCLUSI ON
Results o f this s t u d y are in general agreem e n t with results o f o t h e r s and suggest t h a t i n b r e e d i n g is d e t r i m e n t a l t o p r o d u c t i v e a n d r e p r o d u c t i v e p e r f o r m a n c e in dairy cattle. Results also suggest t h a t i n b r e e d i n g has similar e f f e c t s o n p r o d u c t i o n and r e p r o d u c t i o n in G u e r n s e y s a n d Holsteins. REFERENCES
1 Allaire, F. R., and C. R. Henderson. 1965. InJournal of Dairy Science Vol. 70, No. 3, 1987
breeding within an artificially bred dairy cattle population. J. Dairy Sci. 48:1366. 2 Bonczek, R. R., and C. W. Young. 1980. Comparison of production and reproduction traits of two inbred lines of Holstein cattle with attention to the effect of inbreeding. J. Dairy Sci. 63 (Suppl. 1):106. (Abstr.) 3 Brum, E. W., T. M. Ludwick, D. O. Richardson, E. R. Rader, C. W. Hines, A. K. Fowler, and D. Plowman. 1963. Some effects of low levels of inbreeding on production in Holstein cattle. J. Dairy Sci. 46:619. (Abstr.) 4 Gaalaas, R. F., W. R. Harvey, and R- D. Plowman. 1962. Effect of inbreeding on production in different lactations. J. Dairy Sci. 45:671. (Abstr.) 5 Hillers, J., and A. E. Freeman. 1964. Effects of inbreeding and selection in a closed Guernsey herd. J. Dairy Sci. 47:894. 6 Hodges, J., L. Tannen, B. J. McGillivray, P. G. Hiley, and S. Ellis. 1979. Inbreeding levels and their effect on milk, fat and calving interval in Holstein-Friesian cows. Can. J. Anim. Sci. 59:153. 7 Laben, R. C., P. T. Cupps, S. W. Mead, and W. M. Regan. 1955. Some effects of inbreeding and evidence of heterosis through outcrossing in a Holstein-Friesian herd. J. Dairy Sci. 38:525. 8 Lush, J. L. 1945. Animal breeding plans. 3rd ed. Iowa State Univ. Press, Ames. 9 Nelson, R. H., and J. L. Lush. 1950. The effects of mild inbreeding on a herd of Holstein-Friesian
PRODUCTION TECHNICAL NOTE cattle. J. Dairy Sci. 33:186. 10 Thomson, G. M., and A. E. Freeman. 1967. Effects of inbreeding and selection in a closed HolsteinFriesian herd. J. Dairy Sci. 50:1824. 11 Von Krosigk, C. M., and J. L. Lush. 1958. Effect of inbreeding on production in Holsteins. J. Dairy Sci. 41:105.
715
12 Wright, S. 1922. Coefficients of inbreeding and relationship. Am. Nat. 56: 330. 13 Young, C. W., W. J. Tyler, A. E. Freeman, H. H. Voelker, L. D. McGilliard, and T. M. Ludwick. 1969. Inbreeding investigations with dairy cattle in the North Central region of the United States. North Central Reg. Res. Publ.
Journal of Dairy Science Vol. 70, No. 3, 1987
estimates were not significantly different from zero. Except for the study by Hillers and Freeman (5), no other recent studies have been with Guernseys. The purpose of this investigation was to study the effects of low coefficients of inbreeding on productive and reproductive performance in Guernsey dairy cattle.
Production and reproduction records that spanned a 24-yr period were used to study the effects of low coefficients of inbreeding in two experiment station Guernsey herds. Inbreeding ranged from 0 to 25.3% and averaged 4.1%. Milk and fat yields were all first lactations standardized to a mature equivalent, twice daily milking, and 305 d. Intrasire regressions of production traits on percent inbreeding were - 2 3 . 8 kg of milk, - 1 . 2 5 kg of fat, and .002% for fat percentage. Estimates of the effect of inbreeding on reproductive traits had large standard errors but suggested that inbreeding depressed reproductive performance. Age at first calving decreased 3.7 d per 1% increase in inbreeding.
MATERIALS AND METHODS
INTRODUCTION
Effects of inbreeding on productive traits of dairy cattle have been investigated thoroughly (1, 4, 5, 7, 9, 10, 11). Young et al. (13) summarized inbreeding investigations in the north central United States and reported average reductions per 1% increase in inbreeding of 22.7 kg of milk and .68 kg of fat. Inbreeding also affected fertility in dairy cattle by delaying estrus and increasing services per conception. Hodges et al. (6) found that each additional 1% inbreeding reduced 305-d milk yield by 22.85 kg and fat yield by .53 kg and increased calving interval by 2 d. Fat yield and calving interval
Received September 11, 1986. Accepted December 1, 1986. 1Scientific Journal Series Paper Number 15,073, Minnesota Agricultural Experiment Station. 2Contribution from Regional Research Project NC-2. 3 Reprint requests. 4 North Central Experiment Station, Grand Rapids, MN 55744. 1987 J Dairy Sci 70:712--715
712
Data were records of production and reproduction from two Guernsey herds for the period from 1958 to 1981. The two herds were initially located at the North Central Experiment Station, Grand Rapids, and the Northeast Experiment Station, Duluth. The latter herd was moved to the Rosemount Experiment Station, Rosemount in late 1966. Prior to 1961, both herds had been part of a line development project. In 1961, both herds were divided into two breeding groups. One breeding group was continued in the linebreeding program, while the other breeding group was bred thereafter to Guernsey artificial insemination (AI) sires with highest estimated transmitting abilities for milk yield. Nearly all members of the latter group had inbreeding coefficients of zero, and the entire group was excluded from this study. Linebreeding has been described by Lush (8) and here involved continuous use of descendants of Flying Horse Masters Monarch 327238 and Cesor Pontiff's Anchor 281510, the sire and maternal grandsire of Langmeadow Minnie 1104226. In 1957, Langmeadow Minnie produced 663 kg of milk fat in 365 d, which at that time was a world record for all breeds. Complete pedigrees for all linebred females were traced to 1937, because the bulls to which linebreeding was directed were born after that date. Inbreeding coefficients, calculated by the method of Wright (12), ranged from 0 to 25.3% and averaged 4.1%. Only first lactation production records were used to avoid effects of cow selection. Re-
PRODUCTION TECHNICAL NOTE productive records were for heifers and first parity cows. Numbers of records were 335 for heifer reproduction, 246 for first parity reproduction, and 238 for first lactation production. Thirty sires were represented for heifer reproduction, and 27 were represented for first lactation production and reproduction. Milk and fat yields were standardized to a mature equivalent (ME) twice daily milking and 305-d lactation. Reproductive traits studied were days open, service period, days in milk at first breeding, number of services, conception rate, and age at first calving. Only service period, number of services, and conception rate were available for heifers. Service period was defined as days from first service to final service or to disposal if pregnancy did not occur. Conception rate was defined as the ratio of successful services to total services. Descriptions of other traits indicate their definitions. Age at first calving was measured in months. In order to include all possible variation in reproductive traits, this study included records for all cows and heifers bred regardless of whether or not conception occurred. Where conception did not occur, days open and service periods terminated at date of disposal. Regressions were calculated within herd and within sire. Most sires were used for relatively short periods, usually less than 2 yr, so time periods were not considered. Dam's record was ignored, as regressions obtained with and without holding dam's record constant have been similar (13). Estimates were calculated as pooled intrasire regressions weighted by number of daughters per sire. RESULTS A N D DISCUSSION
Regressions of first lactation production on percent inbreeding are in Table 1. The intrasire
713
regressions of milk yield and fat yield on percent inbreeding were - 2 3 . 8 -+ 19.3 kg and - 1 . 2 -+ .8 kg, respectively. Percentage of milk fat increased by .002% for each 1% increase in the coefficient of inbreeding. The estimate for milk yield agrees well with that of Thomson and Freeman (10), who studied Holstein first lactations, and is generally comparable to estimates reported by others (5, 6, 11) using average records. Our estimate for fat production is comparable to some (2, 4, 11) and larger than other estimates (1, 3, 10). All those reports were based on first lactation records. The small positive estimate for fat percentage suggests no change or a very small increase in fat percentage due to inbreeding. This agrees well with many other estimates (13). Results for fat test may be due to the lower milk production resulting from inbreeding and to the negative relation between milk yield and fat test. Also, fat test is controlled to a greater degree by additive genetic differences than are yields, and environmental factors, which affect milk and fat production adversely, tend to raise fat percentage. Generally, all estimates for production traits, even though standard errors were large, were similar to estimates in the literature. Estimates for the effects of inbreeding on first parity and heifer reproduction are in Tables 2 and 3. Regression coefficients for these traits had large standard errors so little can be inferred from them. However, the sign and the trend of these estimates is in agreement with the concept that inbreeding has detrimental effects on reproductive performance. Estimates for first lactations were that a 1% increase in inbreeding coefficient increased number of services by .17, reduced conception rate by 3.3%, increased both days in milk at
TABLE 1. Regressions of first lactation production in Guernseys on percent inbreeding.
Trait
Observations
.X
Regression on % inbreeding
SE
ME2 Milk, kg ME Fat, kg Fat, %
238 238 238
5082 253.2 5.02
-23.8 -1.2 .002
19.3 .8 .009
Regression coefficients are in same units as means. a ME = Mature equivalent. Journal of Dairy Science Vol. 70, No. 3, 1987
714
HERMAS ET AL.
TABLE 2. Regressions of first lactation reproduction in Guernseys on percent inbreeding.
Trait
Observations
Number of services Conception rate, % Service period, d Days in milk at first breeding, d Days open, d Age at first calving, d
246 246 246 246 246 246
X 2.19 57.2 37.7 82.6 129.3 785.0
Regression on l % inbreeding
SE
.17 -3.3 1.4 1.9
.19 4.5 4.5 1.6
2.3 -3.7
7.1 7.5
Regression coefficients are in same units as means.
TABLE 3. Regressions of heifer reproductive performance in Guernseys on percent inbreeding.
Trait
Observations
X
Number of services Conception rate, % Service period, d
335 335 335
2.04 68.0 39.8
Regression on t % inbreeding .19 -4.8 3.6
SE .12 3.5 4.8
t Regression coefficients are in same units as means.
first b r e e d i n g a n d d a y s o p e n b y a b o u t 2 d, a n d increased service p e r i o d b y a b o u t 1 d. E s t i m a t e s for heifers were larger t h a n t h o s e for c o w s in first l a c t a t i o n . The e s t i m a t e f o r d a y s o p e n is similar to an e s t i m a t e o f a 2-d increase in calving interval f o u n d b y H o d g e s et al. (6). E s t i m a t e s were in t h e same d i r e c t i o n b u t larger t h a n ones obt a i n e d b y B o n c z e k and Y o u n g (2) f r o m t w o l i n e b r e d H o l s t e i n p o p u l a t i o n s . T h e age at first calving e s t i m a t e suggests a r e d u c t i o n in age at first calving as i n b r e e d i n g increases. This is c o n t r a r y t o results r e p o r t e d b y o t h e r s . CONCLUSI ON
Results o f this s t u d y are in general agreem e n t with results o f o t h e r s and suggest t h a t i n b r e e d i n g is d e t r i m e n t a l t o p r o d u c t i v e a n d r e p r o d u c t i v e p e r f o r m a n c e in dairy cattle. Results also suggest t h a t i n b r e e d i n g has similar e f f e c t s o n p r o d u c t i o n and r e p r o d u c t i o n in G u e r n s e y s a n d Holsteins. REFERENCES
1 Allaire, F. R., and C. R. Henderson. 1965. InJournal of Dairy Science Vol. 70, No. 3, 1987
breeding within an artificially bred dairy cattle population. J. Dairy Sci. 48:1366. 2 Bonczek, R. R., and C. W. Young. 1980. Comparison of production and reproduction traits of two inbred lines of Holstein cattle with attention to the effect of inbreeding. J. Dairy Sci. 63 (Suppl. 1):106. (Abstr.) 3 Brum, E. W., T. M. Ludwick, D. O. Richardson, E. R. Rader, C. W. Hines, A. K. Fowler, and D. Plowman. 1963. Some effects of low levels of inbreeding on production in Holstein cattle. J. Dairy Sci. 46:619. (Abstr.) 4 Gaalaas, R. F., W. R. Harvey, and R- D. Plowman. 1962. Effect of inbreeding on production in different lactations. J. Dairy Sci. 45:671. (Abstr.) 5 Hillers, J., and A. E. Freeman. 1964. Effects of inbreeding and selection in a closed Guernsey herd. J. Dairy Sci. 47:894. 6 Hodges, J., L. Tannen, B. J. McGillivray, P. G. Hiley, and S. Ellis. 1979. Inbreeding levels and their effect on milk, fat and calving interval in Holstein-Friesian cows. Can. J. Anim. Sci. 59:153. 7 Laben, R. C., P. T. Cupps, S. W. Mead, and W. M. Regan. 1955. Some effects of inbreeding and evidence of heterosis through outcrossing in a Holstein-Friesian herd. J. Dairy Sci. 38:525. 8 Lush, J. L. 1945. Animal breeding plans. 3rd ed. Iowa State Univ. Press, Ames. 9 Nelson, R. H., and J. L. Lush. 1950. The effects of mild inbreeding on a herd of Holstein-Friesian
PRODUCTION TECHNICAL NOTE cattle. J. Dairy Sci. 33:186. 10 Thomson, G. M., and A. E. Freeman. 1967. Effects of inbreeding and selection in a closed HolsteinFriesian herd. J. Dairy Sci. 50:1824. 11 Von Krosigk, C. M., and J. L. Lush. 1958. Effect of inbreeding on production in Holsteins. J. Dairy Sci. 41:105.
715
12 Wright, S. 1922. Coefficients of inbreeding and relationship. Am. Nat. 56: 330. 13 Young, C. W., W. J. Tyler, A. E. Freeman, H. H. Voelker, L. D. McGilliard, and T. M. Ludwick. 1969. Inbreeding investigations with dairy cattle in the North Central region of the United States. North Central Reg. Res. Publ.
Journal of Dairy Science Vol. 70, No. 3, 1987