BREED STRUCTURE AND GENETIC HISTORY OF HAMPSHIRE SHEEP

Transcription

1 BREED STRUCTURE AND GENETIC HISTORY OF HAMPSHIRE SHEEP Robert C. Carter* THE systems of breeding used in 1925, 1935, 1945 and 1955, was drawn the development of pedigreed from the American Hampshire Flock breeds of livestock are of considerable theoretical and practical interest extended beyond the sire and dam of Book. Random two-line pedigrees were to geneticists and breeders. Of special each animal in the sample to the imported foundation animal. Only one an- interest are the degree of departure from random mating and the development cestor per generation beyond the sire of family structure within the breeds. and dam was recorded, the choice of The publication in 1922 of Wright's 8 the male or female ancestor in any generation being random. It was not pos- method of computing inbreeding and relationship coefficients from irregular sible to extend these pedigrees beyond pedigrees made possible accurate and the ancestor imported into the United systematic evaluation of pedigrees of individuals and small groups. The further ual registration was practiced in Eng- States because flock rather than individ- development of pedigree sampling methods land. by Wright and McPhee 9 made prac- The resulting pedigree information tical the pedigree analysis of entire was transferred to punched cards. The breeds. These sampling methods were percentages of inbreeding and inter se used by McPhee and Wright 4 in a study relationships were calculated for each of the Shorthorn breed in sample by methods outlined by Brandt A number of breeds of several species and McCrabb 1. Important ancestors of of livestock were analyzed by these the breed were identified by counting methods in the 1930's. Most of these the number of times they appeared in have been reviewed by Willham 7 and by the sample pedigrees. Their relative importance was determined by calculation Carter 2. Only one such breed study in the United States has been published of their direct, collateral and total relationship to the breed at each of the four since 1940, that of Sprague et al. 5, who extended Stonaker's 6 earlier analysis of periods studied. the Aberdeen Angus breed from 1940 to The present report is an extension of the author's earlier study of the Hampshire breed of sheep 2. In the earlier work random samples of pedigrees of lambs born in 1925 and 1935 were Results and Discussion Inbreeding and inter se relationship Inbreeding and inter se relationship are shown for each of the four samples in Table I. The values for 1925 and 1935 are from the earlier study. The studied. This has been extended two base dates are the average birth dates more decades in the present study with samples of lambs recorded in 1945 and The results of the earlier work are repeated below for completeness and convenience. Procedure A random sample of 400 lambs, 200 of each sex, born in each of the years of the imported foundation animals in the particular sample. Inbreeding increased rather steadily from 1.4 percent in 1925 to 4.3 percent in This indicates that 1.4 percent of the heterozygosity present in the breed in 1911 had been lost by Similarly, by 1955 the breed had lost 4.3 percent of the heterozygosity present in There *Department of Animal Husbandry, Virginia Polytechnic Institute, Blacksburg, Virginia. The author is indebted to Messrs. Edwin B. Wilson and Dietmar K. Flock, former graduate research assistants, who assembled most of the pedigree information from the Flock Books. 209

2 ARISTOCRATIC HAMPSHIRES Figure 4 Two prominent sires of the breed are Mt. Haggin C-1659 and Whitestone 86806, shown in the photographs above.

3 Carter: Genetic History of Hampshire Sheep 211 is no way of estimating how heterozygous the imported foundation stock was, due to the inability to trace individual pedigrees in the English Flock Books. The rate of loss of heterozygosity ranged from.4 percent to.5 percent per generation. This rate of decline is similar to that found for other breeds of livestock studied. In the Rambouillet, the only other breed of sheep studied 3, the total amount of inbreeding was higher, but the base dates were earlier (largely because Rambouillet importation practically ceased in 1906) and the rate per generation was a little lower than was found here. The inter se relationship coefficient is an estimate of the average relationship between pairs of animals chosen at random from the breed. The estimated relationship increased from zero in the 1925 sample to 1.7 percent in It decreased to 1.4 percent in This is not significantly different from 1.7 TABLE I. Inbreeding and inter se relationship in Hampshire sheep Estimate Inbreeding, total* Inbreeding per generation Inter se relationship** Base date of sample Generation interval, years ±.4% 0.4% percent but suggests that the average relationship was not increasing during the decade. This may be partially explained by the considerable expansion in numbers in the breed during this period. Even if mating were truly at random, a certain amount of inbreeding would be expected simply because the breed is a closed population. The inbreeding (F) expected is approximately one-half the average inter se relationship (R) or, more precisely, F = R/2-R. The inbreeding expected because of the average relationship (Table I) is very much less than that actually found in each of the four samples, indicating that some separation into families has taken place. Interval between generations The interval between generations is the average age of the parents when the offspring is born. The generation interval ranged from 3.5 to 3.8 years, averaging 3.6. The longest interval, 3.8 Year of sample ±.6% 0.5% ±.6% 0.4% 1.7 ± ±.7% 0.5% 1.4 ± ^Estimated increase in inbreeding, relative to the base date. Increase in homozygosity since foundation animals imported. **Average relationship between random pairs of animals within the breed. TABLE II. Prominent animals (two percent or more relationship* to breed) Bullet Keystone Valor Mr. Mitchell C-1659 (Mt. Haggin) Keystone Sensation Blendworth Herriad (Buck and Doe) A-2267 (Bonny Leas 290) Whitestone (Robert Blastock) (J. C. Penny) (Anoka Farms) Foxhill 45 (L-253) Relationship includes direct relationship through animals' offspring, plus collateral relationship through relatives

4 212 The Journal of Heredity Prominent animals of the breed The relationship of an animal to the breed as a whole provides a measure of the relative importance of various ancestors. Direct relationship is estimated by dividing the number of lines in which an ancestor actually appeared in a particular sample by the maximum number (800 in each sample) in which it could have appeared. Collateral relationship measures the additional relationship of an animal through its collateral relatives, i.e., brothers, cousins, etc. The total relationship of an animal to the breed is the sum of the direct plus the collateral. Table II lists the ancestors having two percent or more total relationship to the breed in any of the four samples. In 1925 no animal was related to the breed by as much as two percent. Two ancestors achieved prominence by 1935, Blendworth Herriad, 45215, and his son C Blendworth Herriad, bred by Mrs. Beatrice Jervoise, was imported and used extensively as a stud ram by the Mt. Haggin Land and Livestock Company, Anaconda, Montana. C-1659 was champion ram at the 1926 International Livestock Exposition at Chicago and sired many outstanding show and breeding animals in the Mt. Haggin flock. The influence of these two rams remained important in 1945 and The number of ancestors with two percent or more relationship to the breed increased considerably in The outstanding rams were Bullet, , and his two sons Keystone Valor, , and Mr. Mitchell, Bullet was bred in England by H. A. Benyon and imported by John Goater, manager of the Buck and Doe Run Valley Farms, AN OUTSTANDING RAM Figure 5 Bullet, was bred in England, later imported to this country and had a six percent relationship to the breed in Coatesville, Pennsylvania. Used extensively in the Buck and Doe flock and later in the Vandiver flock in Missouri, Bullet had six percent relationship (all direct) to the breed in Another outstanding ram family in the 1955 sample, commonly known as the Whitestone family, are the descendants of the English ram Blendworth Basildon, K-527. Ram 61839, imported by J. C. Penny, was bred by James Goldsmith and was a son of Blendworth Basildon. Whitestone, 86806, a son of 61839, was used in the Buck and Doe flock and sired ram , who had a 4.2 percent relationship to the breed in Keystone Sensation, , the fifth-place ram in 1955 with a relationship of 4.6 percent, was a son of Family formation There was little evidence of family formation in the 1925 sample. The average inter se relationship was estimated at zero, and no individual animal had a relationship to the breed of as much as two percent; however, the estimated inbreeding of 1.4 percent indicated that some departure from random mating had occurred. The lack of family structure reflected perhaps the relatively re- years for the 1935 sample, occurred when there was little expansion in breed numbers. A shorter generation interval is expected during a time of expanding numbers rather than when a breed is in numerical equilibrium or declining in numbers. A somewhat longer generation interval, 4.2 years, was found in the Rambouillet breed by Dickson and Lush3.

5 Carter: Genetic History of Hampshire Sheep 213 cent introduction of the mass of the breed to the United States. Several small importations had occurred before 1890, and the American Hampshire Sheep Association was organized in 1889, with publication of the first volume of the flock book in Numbers remained small, however, until the period 1906 to 1912 when many Hampshires were imported. The peak of importation was reached in 1909 when one firm brought in over 1,000 head. The beginning of family formation in the 1930's was marked by the prominence of the Mt. Haggin rams Blendworth Herriad and C This family continued to be important in the 1945 and 1955 samples. In the 1940 and 1950 decades the Bullet and Whitestone (or Blendworth Basildon) families became increasingly prominent and remain so to the present. Whether these three families achieved their prominence through promotion and show-yard winnings or because of true genetic merit is an interesting speculation. Probably it was a combination of the two. At any rate, they do represent a definite trend toward increased family formation in the breed. It is interesting to note the proportion of the random lines tracing to various flocks in the 1945 and 1955 samples (Table III). Fifty-seven percent of the lines in 1945 and 65 percent in 1955 traced to 10 flocks. The predominant influence of some of these flocks is due largely to the fact that they were large importers in the period 1900 to Others achieved prominence as breeders or owners of the sires having a high TABLE III. Percentage of random lines tracing to 10 top flocks Robert Blastock 14.2 Buck and Doe Run Valley Farms 2.5 Dr. H. C. Gardiner 8.4 Wm. Cooper and Nephews 8.5 Anoka Farms 6.0 L. V. Harkness 5.7 J. C. Penny 3.7 Mrs. Minnie Miller 2.8 St. Armour Company 2.0 Mrs. A. R. Hamilton 3.1 Total 57.0 relationship to the breed. Summary Inbreeding in Hampshire sheep in the United States since the importation of the foundation stock increased to 1.4 percent in 1925, 2.9 percent in 1935, 3.0 percent in 1945 and 4.3 percent in Average rate of increase was from 0.4 percent to 0.5 percent per generation. The average inter se relationship in the breed was estimated at zero in 1925, 0.5 percent in 1935, 1.7 percent in 1945 and 1.4 percent in The inbreeding actually found is higher than would be expected from this relationship if random mating had been practiced, indicating a tendency toward family formation. No ancestor had as much as two percent relationship to the breed in 1925, and there were only two in By 1945 there were five rams with two percent or more relationship to the breed, and by 1955, 11, indicating an increase in family differentiation. The most prominent ancestors in 1955 were the ram Bullet and two of his sons, Keystone Valor and Mr. Mitchell, with relationships to the breed of 6, 5.4, and percent, respectively. The average interval between generations was 3.6 years. Fifty-seven percent of the random lines in 1945 and 65 percent of those in 1955 traced to foundation animals in 10 flocks. Literature Cited 1. BRANDT, A. E. and MARJORIE MCCRABB. Animal and plant breeding. In Practical Application of the Punched Card Method in Colleges and Universities (Chapter I, Part VIII). Columbia University Press. New York CARTER, ROBERT C. A genetic history of Hampshire sheep. Jour. Hered. 31: DICKSON, W. F. and J. L. LUSH. Inbreeding and the genetic history of the Rambouillet breed of sheep. Jour. Hered. 24: MCPHEE, H. C. and S. WRIGHT. Mendelian analysis of the pure breeds of livestock. III. The Shorthorns. Jour. Hered. 16: SPRAGUE, J. I., JR., W. T. MACEE and R. H. NELSON. A pedigree analysis of Aberdeen

6 214 The Journal of Heredity Angus cattle. Jour. Hered. 52: STONAKER, H. H. The breeding structure of the Aberdeen-Angus breed. Jour. Hered. 34: WILLHAM, O. S. A genetic history of the Hereford cattle in the United States. Jour. Hered. 28: WRIGHT, SEWALL. Coefficients of inbreeding and relationship. Amer. Nat. 56: and H. C. MCPHEE. An approximate method of calculating coefficients of inbreeding, etc. Jour. Agr. Res. 31: WINTERING OF PLANTS HIS book* is "the first of what is planned safe at that time in discussing the origination Tas a series of translations of recent contributions to Plant Science published in the Rus- valuable part because it is colored by the Ly- of winter-resistant varieties. It is the least sian language." It was selected by a committee of the Botanical Society of America that However, it is useful as a picture of the thinksenko thinking, and it is the shortest part. surveyed Russian publications (in fields in ing of Russian breeders and should be helpful which Russian progress has been most active) to research workers and advanced students for those books which would be especially useful to English-speaking readers. The com- Plants under cultivation "due to more abun- who have a background in modern genetics. mittee chose well. dant food" or to a changed environment, and The book, of 246 pages plus 53 pages of hybrids are said to have a "loosened heredity." bibliography, is an unusually well-digested review of plant wintering as related to practical seedlings are said to occur so that by selection As a result, mutants and greater variations in problems in growing. Much non-russian literature is included, although it is less thorly. Also, changing a plant just once in a given desirable new varieties are obtained most freeoughly covered. The subject matter of the direction, e.g., winter hardiness, makes it more book is nearly as applicable to winter conditions in America as in Russia. Part I reviews quired hardiness due to shattered heredity is likely to change in that direction. Newly ac- the concepts of winter killing from early times not stable at first and must be fixed through to the present; Part II, the physiology of several generations by duplicating the conditions responsible for the change. It was, how- winter resistance in plants; and Part III, the breeding of winter-resistant varieties. The ever, possible for Vasil'yev to say, "This led book is organized as a college text and reference work and is made very readable by many hardy varieties by grafting from mature plants Michurin to abandon this approach [obtaining examples from the extensive research and experience of the author in different parts of ties] and concentrate on hybridization." It is of southern varieties onto hardier winter varie- Russia. Parts I and II will be the most useful stated that apples have been originated that to Americans for gaining a better understanding of the many types of cold injury and what northern Urals and tomatoes that endure 3 withstand temperatures of 50 C. in the to do about them. Even in those aspects of or 4 C. Chapter 5 of Part III on polyploids presents a considerable discussion of winter injury and cold resistance most familiar to Americans the historical development of Gerasimov's work ( ) on obtaining ideas in Russia and the studies on winter injury are very stimulating. GEORGE M. DARROW polyploids of Spirogyra by chilling. Part III of the book (first published in Horticultural Field Russian in 1956) seems to go as far as it was Beltsville, Maryland *Wintering oj Plants. I. M. Vasil'yev. Translated from the Russian by Royer and Roger. American Institute of Biological Sciences. Washington, D. C. 246 pages $9.00.