BREEDING AND GENETICS

Transcription

1 Swine Production Handbook Section 9: Breeding and Genetics Page 99 BREEDING AND GENETICS 1. Traditional Common Breeds in the U.S. INTRODUCTION A. Berkshire Originated in Berkshire, South Central England. 1) Introduced into the U.S. in ) Black color with six white points (feet, nose and tail), and has erect ears & short nose. 3) Work well in the enclosed facility, and are noted for their siring ability. B Chester White Originated in Chester County in Penn ) Foundation stocks are various white breeds from England (Yorkshire, Lincolnshire, Cheshire & Bedfordshire). 2) White color with medium sized droopy ears. 3) Prolific, milking well, and excellent dams. C. Duroc Originated from old Duroc of New York and Jersey Red of New Jersey during ) Red color & the shade varies from golden to very dark, and has droopy ears. 2) Noted for their meaty carcasses, fast growth and good feed efficiency. D. Hampshire Originated from old English breeds. 1) Foundation stocks introduced into the US around 1800, and then moved to Kentucky in ) Black color with a white belt that entirely encircles the body and strikes both front legs, and has erect ears. 3) Popular for their lean, meaty carcasses. E. American Landrace Originated from Danish Landrace imported in 1934 & 1938, and Norwegian Landrace imported in ) White color with large floppy ears and long body. 2) Noted for their mothering ability. F. Poland China The oldest breed originated in the U.S. (southwestern Ohio). 1) Exact origin is uncertain, but Berkshire & Irish Grazier are credited with making the greatest contribution. 2) Black color with white markings confined mainly to the face, legs and tail, and has medium sized droopy ears.

2 Swine Production Handbook Section 9: Breeding and Genetics Page 100 G. Spotted Originated from Poland China and a pair of Gloucester Old Spots imported in ) Spotted black and white & must have at least 20% of either color to qualify! 2) Has heavy, drooping ears. 3) Known for producing pigs with a high growth rate. H. American Yorkshire Originated from Large White imported from England ( ). 1) White color with erect ears. 2) Prolific, heavy milkers, and excellent dams. 2. General Use of Various Breeds A. Five dark breeds, Berkshire, Duroc, Hampshire, Poland China and Spotted, are used for their siring ability & the durability & leanness/meatiness. B. Three white breeds, Chester White, Landrace and Yorkshire, are used for their reproductive traits & mothering ability. 3. Chinese Pigs A. In China, there are over 100 different breeds and varieties, and. 40% of them are economically important! B. The reason for interest is the large average litter size in certain breeds e.g., See a picture of Fengjing sow with 31 piglets (McLaren, NC103 Project). C. Characteristics: 1) Reach sexual maturity at 90 days of age, and produce up to 1617 live pigs/litter. (1618 functional teats!) 2) No difference in ovulation rate, ˆ somehow manage to achieve a higher rate of embryonic survival! 2) Very hardy, longlived, docile, and adapted to production systems where forages are fed routinely. 3) Disadvantages? Slow growth rate, poor feed efficiency, and obesity. D. Chinese crosses? 1) Effects on performance? See examples! 2) The bottom line? a) To improve the reproductive performance, may have to use ½ Chinese sows! b) ½ & ¼ Chinese pigs are similar in weight gain & efficiency, but low in carcass quality! Chinese crosses & reproductive performance: Item 1/2 a 1/4 b Contr. a )))))))))))))))))))))))))))) Total born Born alive No. weaned Weaned/sow/yr )))))))))))))))))))))))))))) a Rothschild, 1986 (NHF); b McLaren (NC103). Pig performance: (McLaren: NC103) Item 1/2 1/4 Contr. ))))))))))))))))))))))))))))) Weight gain, g/d Feed to gain Dressing percent Carcass lean, % )))))))))))))))))))))))))))))

3 Swine Production Handbook Section 9: Breeding and Genetics Page Inheritance REVIEW OF SOME TERMS A. In breeding swine, dealing with extremely complicated phenomena because: 1) Many traits of interest, such as litter size, backfat & feed efficiency, are affected by many genes, and perhaps controlled by hundreds of pairs of genes? 2) A constantly changing environment affects the expression of those genes. B. Thus, to be successful in the selection program, have to apply known genetic principles, and also have to provide the environment that will allow pigs to express their genetic potential. 2. Heritability A. Heritability refers to the percentage of variation in the trait due to genetic effects, in which values can be estimated in many different ways, thus should not be regarded as mathematically exact! B. Heritability estimates of some economically important traits See a box. 1) Most litter traits are low in heritability, thus less responsive to selection pressure... but, still very important! 2) Production and carcass traits are high in heritability, thus can make a rapid progress. Heritability (PIH106) Trait Heritability, % )))))))))))))))))))))))) Survival to weaning 0 No. farrowed 10 No. weaned 10 Birth wt 20 Weaning wt 20 Feed efficiency 25 Growth rate 30 Age at puberty 35 Backfat 40 )))))))))))))))))))))))) 3. Selection Differential A. The difference between averages of the selected group & entire group, and can expect a greater differential with a larger group size. B. More traits in selection criteria, the lower the selection differential for each trait! 4. Inbreeding & Linebreeding A. Inbreeding refers to the mating of animals that are more closely related than the average of the breed or line of origin Useful in concentrating favorable genes for the overall improvement. B. Linebreeding is less intensive form of inbreeding, e.g., mating of halfbrothers and halfsisters. C. Both can be useful in forming a new breed or line, but 8 in inbreeding can lead to 9 reproductive and growth performance, ˆ not recommended for the commercial herd! 5. Outcrossing A. An opposite of inbreeding, i.e., mating of unrelated animals of the same breed. B. The most common breeding system of purebred producers, and can be used to correct problems with inbreeding.

4 Swine Production Handbook Section 9: Breeding and Genetics Page Crossbreeding A. Mating animals of different breeds. B. Used by the commercial producer to obtain hybrid vigor or heterosis & combine desirable traits of various breeds! 7. Heterosis A. Advantages in the performance of crossbred pigs over the avg. of parent breeds. B. Average percent heterosis See a box. B There is an inverse relationship between heritability and heterosis, i.e., traits with low heritability (reproduction) are high in heterosis & traits with high heritability (carcass) are low in heterosis! Heterosis: (PIH106) st cross Mult. cross Trait using purebred & using Xbred & )))))))))))))))))))))))))))))))))) No. born alive Litter size (21 d) d litter wt d litter wt/& exposed Day to 220 lb Feed to gain Backfat Loin muscle )))))))))))))))))))))))))))))))))) C. To improve the overall performance: 1) Maximize heterosis by crossbreeding to improve reproductive performance, and 2) Selection or new stocks to improve production & carcass traits! 8. EBV and PPD or EPD A. EBV (Estimated Breeding Value) The genetic value of individual as a parent is unknown, but can be estimated from the performance information: EBV = Heritability x (Individual Group average) B. PPD or EPD (Predicted or Expected Progeny Deviation) Performance of individual s offspring over the progeny of average boars: PPD = 1/2 of the Estimated Breeding Value. C e.g., Backfat (BF) Assuming heritability for BF = 0.40, individual BF = 0.66 in, and ; group average BF = 0.73 in: 1. Introduction EBV = 0.40 ( ) = in. PPD = x 0.5 = in. SELECTION A. Emphasis must be placed on characteristics that will improve the herd performance and profits, and important traits include: 1) Sow productivity Litter size, mothering ability, and lactation rate. 2) Production Growth rate, and feed efficiency. 3) Carcass Backfat, loin muscle area, and percent muscle or lean.

5 Swine Production Handbook Section 9: Breeding and Genetics Page 103 B. The objective is to assemble many desirable genes! C. Problems? Those genes may or may not be compatible, e.g., selection for 9 backfat may also 9 weight gain! D. To avoid possible problems, the use of selection indexes might be beneficial! 2. Selection Indexes A. Considerations: 1) Economical importance of traits may differ from a herd to herd because of differences in production costs & performance level. 2) Variability of each trait! Difference(s) must exist to make any improvement, and some traits are more variable than others! 3) Degree of genetic influence for each trait (i.e., heritability). 4) Relationships among the traits! May be sacrificing other traits by placing too much emphasis on one aspect! L Need to consider each of these factors in developing the index, i.e., appropriate weighting of each trait! B. Examples of Indexes: 1) Central testing program Can be used to evaluate animals from several sources under uniform conditions. (Krider et al., 1982) a) Pens with only one animal: I = (G G avg ) 65(F F avg ) 60(B B avg ) b) Pens with > one animal: I = (G G avg ) 75(F F avg ) 70(B B avg ) c) Measure only gain and backfat: I = (G G avg ) 105(B B avg ) G = average daily gain; F = feed to gain; B = backfat adjusted to 230 lb;? avg = test group average for G, F and B. 2) Onfarm testing Can be used to evaluate performance of individuals, and use these records for genetic improvement within the herd. (Krider et al., 1982) a) Sow productivity index: I = (L L avg ) 1.0 (W W avg ) b) General index: I = (L L avg ).4(W W avg ) 1.6(D D avg ) 65(B B avg ) c) Maternal index: I = (L L avg ).5(W W avg ) 1.5(D D avg ) 45(B B avg ) d) Paternal index: I = (L L avg ).3(W W avg ) 1.8(D D avg ) 80(B B avg ) L = number born alive; W = adjusted 21day litter weight; D = adjusted day to 230 lb; B = adjusted backfat at 230 lb;? avg = test group average for L, W, D and B. 3. General Guidelines for Selection A. Replacement boars Should be selected from the top 50%! 1) Important traits? See the results of a survey (Thulin & Schwab, 1989). 2) From litters of 10 or more pigs farrowed & 8 or more pigs weaned. 3) Have 12 or more fully developed, well placed teats.

6 Swine Production Handbook Section 9: Breeding and Genetics Page 104 4) Physical attributes Medium to large bone structures, wide stance both front and rear legs, free in movement, good cushion to both front and rear feet & equal sized toes. 5) ADG of 2 lb or better (60230 lb) with feed efficiency of 2.75 (60230 lb), and weigh 230 lb at 155 days of age. 6) Backfat is 1 in or less (adjusted to 230 lb), and loin muscle area of 5.6 sq. in or more. 7) Normal penis, testicle and possibly semen. C. Replacement gilts Pay special attention to the litter size, underline and dam's productivity! 1) Important traits for selecting gilts? See the results of one survey (Thulin and Schwab, 1989). 2) From litters of 8 (probably too low!) or more pigs farrowed. 3) From sows having: a) no problems at farrowing, b) largest No. of live, uniformsized pigs at farrowing, c) highest weaning percentage of live pigs born, d) heaviest weaning weight, e) less skeletal problems during farrowing and nursing, and f) desirable temperament & disposition. 4) Have 12 or more evenlyspaced, functional teats (at least 6 per side). 5) From the sow line showing good longevity. 4. Use of General Selection Index Example Important traits in selecting replacement boars (Thulin and Schwab, 1989) Index # ranking of most Measure Rank rank a important ))))))))))))))))))))))))))))))))))))))) Paternal sires: Average daily gain Feed efficiency Dam's litter size Backfat Loin muscle area Estimated breeding value Sow's productivity index Maternal sires: Dam's litter size Average daily gain Feed efficiency Sow's productivity index Estimated breeding value Backfat Loin muscle area ))))))))))))))))))))))))))))))))))))))) a An index of 100 would result if all respondents ranked that item most important. Important traits in selecting replacement gilts (Thulin and Schwab, 1989) Index # ranking of most Measure Rank rank a important ))))))))))))))))))))))))))))))))))))))) Dam's litter size Average daily gain Sow s productivity index Feed efficiency Estimated breeding value Backfat Loin muscle area ))))))))))))))))))))))))))))))))))))))) a An index of 100 would result if all respondents ranked that item most important. A. Data See a box. B. Make adjustments: 1) Adjustment for W (litter wt at 21 days): Adjustment factors: Age b Age b Age b )))))))))))))))))))))))))))))))))))))) )))))))))))))))))))))))))))))))))))))) [Adjusted wt = actual litter wt (lb) x b] a) For the age when weighed Use a coefficient from the table (the weight taken at 22 days, ˆ 0.97). Example: Individual: Sow L (number born alive) 10 Dam Sow No. pigs nursed 9 Litter weight, lb 100 Age (weighed), day 22 Actual weight, lb 210 Actual BF, in 1.3 Actual age, day 180 Averages for the test group: L avg 7.5 W avg 95.0 D avg 185 ))))))))))))))))))))))) 0.97 X (100) = 97 lb

7 Swine Production Handbook Section 9: Breeding and Genetics Page 105 b) For the number nursed: (Dam = sow, ˆ 10 lb) = 107 lb Add 9 or 10 lb to the adjudted wt for gilts (or primiparous sows) or sows, respectively, for each pig under litter size 10 after standardization. If the number of pigs after standardization is more than 10, then do not adjust! 2) Adjustment for D (days to 230 lb): B Formula = Act. age (230 Act. wt) x (Act. age 38/Act. wt), thus 180 ( )(180 38/210) = d 3) Adjustment for B (backfat at 230 lb): B Formula = Act. BF (230 Act. wt) X (Act. BF/Act. wt 25), thus 1.3 ( )(1.3/210 25) = 1.44 in. C. Calculate index: I = (L L avg ).4(W W avg ) 1.6(D D avg ) 65(B B avg ) I = (10 7.5).4(107 95) 1.6( ) 65( ) I = Heterosis CROSSBREEDING SYSTEMS A. Crossbreeding systems & maximum heterosis (%): (PIH106) System Offspring Maternal )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) F 1 (A x B) Backcross (A x AB) breed rotation breed rotation breed rotation Terminal with F 1 sows Rotaterminal with 2breed rotation Rotaterminal with 3breed rotation )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) B. To maximize individual heterosis, should use sows and boars of different breeds, and to maximize maternal heterosis, should use crossbred females. 2. Terminal System A. Used for both individual and maternal heterosis, and three or fourbreed terminal is the most commonly used system See an example of the threebreed terminal in a box. B. Very simple & market pigs have 100% heterosis. C. Can purchase or produce own F 1 gilts: 1) Purchasing gilts? a) Face a risk of introducing

8 Swine Production Handbook Section 9: Breeding and Genetics Page 106 disease(s), b) may be difficult to find quality gilts, and c) may have to pay a premium for gilts ($100 to $150/head over market price?). 2) Producing own gilts? a) Have to maintain purebred sows/gilts (15 to 20% of sow herd), and b) have to have at least one more breed of boars. 3. Rotational Systems A. Maximum heterosis over a long term: Twobreed, 67%; Threebreed, 86%; Fourbreed, 93%,..., etc. B. Can produce replacement females, ˆ 9 a chance of disease introduction, and also can 9 costs of replacement &. C. Proper matings are essential to maintain expected levels of heterosis, i.e., mate each sow to the least related breed of boar. A color coded eartagging system may be very useful for this purpose! 4. Rotaterminal System A. Simply a combination: 1) Use a rotational system (1520% of herd) to produce gilts Usually use white breeds. 2) Use lean, fast growing boars to produce market pigs. B. Taking advantages of the two systems: 1) Excellent system for producers who want to raise own replacement females. 2) At the same time, market hogs will have 100% heterosis. C. Drawbacks: 1) Maximum heterosis for sow productivity is not achieved, e.g., 67% for the twobreed system & 86% for the threebreed system. 2) Requires a higher degree of management. (The twobreed system is easier to manage, but has low maternal heterosis!) 5. Breeding Systems Used in the U.S.? (The results of a survey!) Systems used (Thulin and Schwab, 1989) Type Percent )))))))))))))))))))))))))))))))) Terminal cross with F1 sows breed rotational cross breed rotational cross breed rotational cross 10.5 Rotaterminal (2breed rotation for &) 5.3 Rotaterminal (3breed rotation for &) 5.8 )))))))))))))))))))))))))))))))) Systems used & size of operation a (%; Thulin and Schwab, 1989) Pigs/year TCF1 2BRR 3BRR 4BRR RT2B RT3B ))))))))))))))))))))))))))))))))))))))))))))))))))))))) < ,0002,999 3,0004, ,0009,999 > 9, ))))))))))))))))))))))))))))))))))))))))))))))))))))))) a TCF1 = terminal cross; 2BRR = 2breed rotational; 3BRR = 3breed rotational; 4BRR = 4breed rotational; RT2B = rotaterminal with 2breed rotation; RT3B = rotaterminal with 3breed rotation; # resp. = No. of responses.

9 Swine Production Handbook Section 9: Breeding and Genetics Page Based on the Computer Program EVALUATING CROSSBREEDING SYSTEMS L See Ahlschwede & Johnson (1988) for details! (H = Hampshire; D = Duroc; Y = Yorkshire; L = Landrace; CW = Chester White) Offspr. Pigs Concep. Days Back Feed: Net per % of heter. mkt./ rate to fat gain litter % & matings (%) litter (%) mkt. (in) (GF) ($) )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) Purebred matings: H H D D Y Y L L CW CW Purebred Avg [1] Three breed rotation: H YxD,H D HxY,D Y DxH,Y Weighted Avg [2] Three breed terminal: Y Y D Y H DxY Weighted Avg [3] Four breed terminal: Y Y L Y HxD LxY Weighted Avg [4] Four breed terminal YxD,L sow: L L D L Y DxL H YxD,L Weighted Avg [5] Rotaterminal with two breed sow: Y LxY,L HxD YxL,Y L YxL,Y HxD LxY,L Weighted Avg [6] Rotaterminal with three breed sow: Y CW,L,Y HxD Y,CW,L L Y,CW,L HxD L,CW,Y CW L,CW,Y HxD CW,L,Y Weighted Avg [7] Twoway rotation with four breeds: HxL DY,HL DxY HL,DY Weighted Avg [8] Threeway rotation with four breeds: HxL Y,D,HL D HL,Y,D Y D,HL,Y Weighted Avg ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))

10 Swine Production Handbook Section 9: Breeding and Genetics Page Effects of Changing Market Prices & Cost of Replacement Gilts [Kuhlers et al., NHF 35(9):18] A. Comparison of threebreed (Yorkshire, Duroc & Landrace) terminal & rotational systems: Item Rotational Terminal ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) Sow performance: Conception, % Litter size: Birth days Market Litter wt, lb: Birth days Pig performance: Birth wt, lb d wt, lb Days to 220 lb Ultrasound BF, in Feed:gain ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) B. Net returns to land, labor & management for a 120sow operation: L Assumptions: Corn = $2.75/bu & SBM = 275/ton, anual sow replacement rate = 40%, and market pigs at 220 lb Price of market pigs ))))))))))))))))))))))))))) System Gilts, $ $35 $45 $55 ))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) Rotational Prod. costs $3,177 $39,125 $81,428 Terminal Mkt 50 $8,290 $38,767 $85,833 Mkt 100 $11,526 $35,540 $82,606 Mkt 150 $14,753 $32,314 $79,380 )))))))))))))))))))))))))))))))))))))))))))))))))))))))))))))) CHOOSING A CROSSBREEDING SYSTEM? 1. Heterosis Try to take advantages of heterosis. 2.. Breed Strengths & Weaknesses Should consider & take advantage of breed strengths & try to minimize breed weaknesses. See a summary of traditional common breeds in the U.S. by Ahlschwede & Johnson (1988). 3. Practicality & Management Skills Should be practical and fit the management capability of the producer! Strengths/weaknesses (Ahlschwede & Johnson, 1988) Concep. Pigs 21day Age at Back Breed rate raised weight 220 lb fat ))))))))))))))))))))))))))))))))))))) Berkshire Chester W. A Duroc Hampshire A A A A Landrace Poland A A Spotted Yorkshire ))))))))))))))))))))))))))))))))))))) a A = average of breeds; = superior vs average; = substantially better than average; = inferior vs average; = substantially inferior vs average. 4. Availability of Replacement Consider the availability of the quality stocks & economical feasibility of using those stocks!

11 Swine Production Handbook Section 9: Breeding and Genetics Page 109 BREEDING FOR LEAN 1. Lean Pigs & Pale, Soft & Exudative (PSE) Pork A. Classification of pork: See a figure [1992. NHF 37(9):32] B. Porcine stress syndrome (PSS) & PSE: 1) > 50 yr ago, swine breeders began their quest for producing lean pigs, which led the discovery of undesirable mutant gene that can cause the PSS. a) PSS gene can be found in most every farm! b) Homozygous show outward signs of stress, whereas heterozygous are not stressprone. 2) PSS gene: a) Can cause neuromuscular disease that produces rigid muscles & fever 6 poor performance & sudden death. b) Triggered by stress associated with travel, restraint, fighting, mating, exercise, and hot, humid weather. c) Can contribute to PSE pork Most pigs with PSS produce PSE pork, but not all PSE pork comes from PSS pigs. 2. Selection/Breeding for Lean Pigs A. Continue to select for lean pigs despite its drawbacks associated with the PSS/PSE. B. An additional problem? Possible reproductive inefficiency, for instance! C. With the new DNA test (uses blood samples), may be possible to prevent/reduce incidence of the PSS! L The halothane test (previously the 1 test) detects only homozygous PSS animals!