Correlated response in reproduction, growth and composition to selection in gilts for extremes in age at puberty and backfat

Livestock Production Science, 24 (1990) 237-247 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

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Correlated Response in Reproduction, G r o w t h and Composition to Selection in Gilts for E x t r e m e s in Age at P u b e r t y and B a c k f a t 1 A.H. NELSON, J.W. MABRY, L.L. BENYSHEK and M.A. MARKS

Animal and Dairy Science Department, The University of Georgia, Athens, GA 30602 (U.S.A.) (Accepted for publication 8 August 1989)

ABSTRACT Nelson, A.H., Mabry, J.W., Benyshek, L.L. and Marks, M.A., 1990. Correlated response in reproduction, growth and composition to selection in gilts for extremes in age at puberty and backfat. Livest. Prod. Sci., 24: 237-247. Females ( n = 5 0 ) were selected for extremes in early vs. late sexual maturity (12 EP, 13 LP) based on age at first detectable estrus; or, high vs. low backfat (13 HF, 12 LF) based on backfat at the tenth rib adjusted to 105 kg basis. These selected females were then heat checked daily, bred during scheduled breeding periods and allowed to farrow. Reproductive performance was then monitored. More EP than LP females demonstrated a normal cycling pattern. Also, more HF than LF females had normal cycling patterns. Early puberty (EP) female farrowed more litters per sow ( P < 0.05 ) and more pigs per litter ( P < 0.10 ) than LP. Low -fat females farrowed fewer pigs alive (P<0.10) than HF. Early puberty (EP) and HF females had the highest Sow Productivity Indexes (SPI), while LP females were intermediate. Low-fat females had the lowest SPI ( P < 0.05 ). These results indicate that single-trait selection for extreme leanness or late puberty could be detrimental to reproductive performance. Progeny (371 gilts and 173 barrows) from these litters were then performance tested. The correlated responses in the offspring to selection for extremes for puberty in the dams indicates that selection for early puberty in the females will result in faster gaining offspring with an increased amount of backfat. The correlated responses in offspring of the backfat lines indicates that selection for low backfat thickness in cycling females will decrease fat and increase the amount of lean deposited by her offspring. Also, LF offspring reached puberty and market weight at an earlier age.

INTRODUCTION

Two important traits in swine are sexual maturity (measured as age at first detectable estrus) and compositional maturity (measured as backfat at a constant weight). Early onset of estrus may increase genetic progress through a shorter generation interval and reduce the time and expense of feeding the 1This research was supported by State and Hatch funds allocated to the Georgia Agricultural Experimental Station.

0301-6226/90/$03.50

© 1990 Elsevier Science Publishers B.V.

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animal prior to production of a saleable product. Fat is an unacceptable consumer product that requires more energy to deposit than lean. Furthermore, with the use of value-based marketing systems, fat hogs are penalized by the packer. Therefore, selection for early sexual maturity and a later compositional maturity is indicated. The usefulness of a selection scheme depends not only upon the direct response itself, but also upon the associated changes in other economically or biologically important traits caused by correlated responses to selection (Quijandria et al., 1983). This study examined the reproductive performance of females selected for extremes in age at puberty or fat thickness, and the direct and correlated responses in their offspring. MATERIALSAND METHODS Seventy-one Yorkshire-based U.S. commercial crossbred females were mated to Landrace or Duroc sires in six bimonthly breeding seasons at the University of Georgia Swine Center. In their progeny, estrus detection was initiated when gilts reached a weight of 70 kg using once-daily heat checking with a boar. This continued until 75% of the gilts (a previously determined percentage, Rampacek et al., 1981 ) in each farrowing group exhibited heat. In the first phase of the project, 210 gilts were produced over the six breeding seasons. From the gilts produced in each of these six farrowing groups, eight gilts were selected. The earliest cycling and latest cycling Duroc and Landrace sired gilts were selected (early or late puberty, EP or LP). The fattest and leanest Duroc and Landrace sired gilts, based on backfat measured ultrasonically at the tenth rib, 5 cm offthe midline and adjusted to a 105 kg basis, were also selected (high or low fat, HF or LF). Differences in the selected females are given in Table 1. These selected gilts were heat checked daily after selection and bred (backcross mated) to Duroc or Landrace sires if they cycled during a breeding season. The estrus number at which the selected gilts were mated varied, but all were greater than one because each gilt had to show estrus to be selected. Both EP and LP females were mated to the same boars, as were HF and LF females. Any differences in the offspring then would be due to differences transmitted from their respective mothers. Cycling patterns, conception rates, number of pigs born alive (NBA), number weaned (NW), 21-day litter weight, and Sow Productivity Indexes (SPI) (National Swine Improvement Federation, 1981) were recorded. The normal cycling pattern was defined as a female cycling every 18-24 days and returning to estrus 3-10 days after weaning. Litters were farrowed in bimonthly farrowing groups from march 1983 to May 1985. These litters were farrowed in elevated crates and the reproductive performance of the sow was monitored. Normal management procedures included equalization

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TABLE la Means for age at puberty, growth rate and backfat of the selected females Selection group

Number selected Age at puberty (range) (days) Average daily gain (kg) Backfat at 105 kg (range) (ram)

Early puberty ~

Late puberty ~

High

Low

fat 2

fat 2

12 185(148-205) 0.84 17.3(14-22)

13 239(210-254) 0.75 15.7(13-22)

13 207(184-235) 0.80 19.3(16-24)

12 220(179-248) 0.77 13.5(11-16)

~Selectionbased on age at puberty. 2Selection based on backfat at 105 kg.

TABLE l b Performance of sows that were selectedfor early vs. latepuberty or high vs. low backfat Selection group

Early puberty 1 Number selected Number (%) with normal cycling pattern 34 Number litters per sow 3 Number born alive7"8 21-daylitterweight34 (kg) Sow productivity index3 ADG (kg) Loindepth 4 (ram) Days to 105 kg

12 10(83) 5 2.2 ___0.3e 9.32 _+0.35 46.4 _+_1.1 127 _+20 0.84-+0.19 42.9 _+0.41 182 -+4.5

Late puberty 1 13 7(54) 1.4 _+0.2 8.34 _+0.61 39.2 _+2.3 81 _+31 0.75-+0.24 43.1 +0.49 195 -+ 12.0

High fat ~ 13 10(77) 2.0 _+0.3 10.54 _+0.56 40.7 _+0.9 118 ± 21 0.80-+0.15 45.2 ±0.33 187 ±4.0

Low fat 2 12 5(42) 2.2_+0.3 8.69 _+0.99 37.4 _+1.8 99 -+30 0.77_+0.21 41.2 _+0.34 186 _+5.1

ISelection based on age at puberty 2Selection based on backfat at 105 kg.

3puberty groups differ (P<0.05). 4Fat groups differ (P<0.05). SPercentage of those selected which showed normal cycling pattern. eStandard error. 7puberty groups differ (P<0.10). SFat groups differ ( P < 0.10 ).

of littersby transfer of average size males within 36 h after farrowing and access to creep feed at 14 days of age. From these litters,371 giltswere performance tested (Table 2). At approximately 25 kg, four giltssimilar in size were randomly placed in 2.5 X 5 m pens with solidconcrete floorsand side walls. W h e n the pen of giltsaveraged 30 kg

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TABLE 2 Correlated Responses (means +-SE) in daughters of dams selected for early vs. late pubertyI or high vs. low backfat2 Selection group

Age at first estrus2 (days) Percent cycling Backfat at shoulder (ram) Backfatattenthrib4'S (mm) Backfat at last lumbar vertebras's (mm) Loindepth5 (mm) Average daily gain4.e (kg)

Early puberty (n=l14)

Late puberty (n=55)

High fat (n=105)

Low fat (n=97)

198 +_3.1 76 32.9 _+0.5 20.2 +_0.3

204.5 +_3.7 75 30.2 +-0.8 18.3 +_0.4

217.6 +_3.3 77 33.6 +_0.5 21.5 +_0.4

208.4 +_2.9 79 30.7 +_0.4 18.2 _+0.3

27.4 +-0.4 44.2 +_0.4 0.93 +_0.03

24.5 +-0.6 44.9 +_0.5 0.83 +_0.04

25.4 +-0.4 48.1 +_0.3 0.73 +_0.02

24.1 +-0.4 45.1+_0.3 0.83 +_0.03

1Based on age first detectable estrus. 2Based on backfat at 105 kg. SFat groups differ (P < 0.05). 4puberty groups differ (P<0.05). 5Fat groups differ (P<0.01) ePuberty groups differ (P < 0.01 ).

TABLE

3

Correlated responses in sons of d a m s selected for early vs. late puberty I or high vs. low backfat 2

Selection group

Average backfat4 (ram) Backfat at tenth rib5 (ram) Loin muscle area4 (cm2) Loin depth 4 (ram) Percent muscles Days to 105 kg~'e

Early puberty (n=39)

Late puberty (n=27)

SE 3

High fat (n=61)

Low fat (n=46)

SE

34.3 30.0 30.5 45.7 51.5 175

33.5 30.5 30.3 46.4 51.3 183

0.68 0.86 0.67 1.27 0.45 2.8

35.8 31.8 27.9 42.9 50.3 185

34.0 27.4 30.2 45.5 52.3 175

0.70 0.90 0.91 1.31 0.50 2.9

~Based on age at first detectable estrus. 2Based on backfat at 105 kg. 3pooled standard error. 4Puberty groups differ ( P < 0.05). SFat groups differ (P < 0.05). SFat groups differ (P<0.01).

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body weight, testing began and continued until an average pen weight of 105 kg body weight was reached. Gilts were then moved to pasture lotswhere they were mixed with other giltsfrom their farrowing group. The biweekly measurements taken prior to movement consisted of weight (WT), fat depth 5cm offthe midline at the shoulder,tenth rib and stifle(BFA, BFB, BFC) and loin depth (LD). An Ithaca Scanoprobe (model 371A) and a Renco Leanmeter were used to measure loin depth and backfat, respectively.Estrus detection began when the females reached 70 kg and continued until 75% of the gilts (a previously determined percentage, Rampacek et al.,1981 ) in a test group had cycled. Barrows (n= 173) produced by selected females in three of the farrowing groups were tested also (Table 3). At approximately 30 kg, males were placed in confinement pens (partiallyslatted,modified open fronts) in groups of 1015. W h e n pigs reached approximately 105 kg, they were slaughtered in weekly groups. Carcass measurements were obtained on 173 barrows. Carcass traits were measured after24 h chilling.Three midline fat measurements were taken (at the firstand lastrib thoracic vertebra and the lastlumber vertebra) on the halved carcass. Tenth rib fat and longissimus muscle area (LMA) were measured between the tenth and eleventh ribs.The loin muscle was traced on acetate paper and the area determined with a planimeter. Carcass traitswere evaluated using the guidelines and procedures outlined by the American Meat Science Association (1967) and the National Pork Producers Council (1983). The number of female and male offspringtested per selectionline is shown in Tables 2 and 3. The low number of offspring representing the late puberty line reflectsthe poor reproductive performance of those selectedfemales. The puberty lines and fat lines were analyzed separately. The statistical model used in the analysis of the reproductive traitsof the dams (number of littersproduced per sow, number born aliveand number weaned, 21-day litter weight and average SPI) was:

Yijkt = ll + Ti + Bj + ( TB ) ij + Rk + eijkt

(1)

where:/z = overall mean; T/= fixed effect of selection line (early puberty, late puberty; or, high fat, low fat); Bj=fixed effect of breed composition; (TB) ij= interaction of selection line with breed composition; Rh = fixed effect of replicate; eoht= random residual effect. Line differences in percentage with normal cycling pattern were analyzed using X2 (Snedecor and Cochran, 1980). The model used for analyses of composition and growth traits in the gilts was: Yijkl=lz+Ti+Fj+Bk+(TF)ij+(TB)ik+(FB)jk+bl(X--.~)+eijht

(2)

where:/t= overall mean; Ti= fixed effect of selection line (early puberty, late puberty; or, high fat, low fat); Fj= fixed effect of farrowing seasoni Bh=fixed effect of breed composition; (TF)ij = interaction of selection line with farrow-

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ing season; (TB)ih=interaction of selection line with breed composition; bt ( X - . ~ ) = linear effect of off-test weight; eijht = random residual effect. The model for analysis of ADG did not include the covariate for off-test weight. Sire effects and dam effects nested within line were examined in each of these models for analysis and were not significant sources of variations and thus were not included. The model used for statistical analysis of composition and growth traits in the barrow was: Yijklm =/~'b T i + D ( T) ij -b Kk "}"Sl "b eijklm

(3)

where:/z = overall mean; Ti = fixed effect of selection line (early puberty, late puberty; or, high fat, low fat); D ( T ) i j = r a n d o m effect of dam within selection line; Kk=fixed effect of slaughter group; St=random effect of sire; e~jk~m= random residual effect. The analysis of all carcass traits also included a covariate for carcass weight. Traits were analyzed by the General Linear Models procedure of the Statistical Analysis System (SAS Institute, Inc., 1982) using the statistical models previously described. RESULTS AND DISCUSSION

From the 210 gilts tested in the first generation 12 gilts were selected for the early puberty (EP) line and 13 gilts were selected for the late puberty (LP) line based on age at first estrus. Also, 13 gilts were selected for the high fat (HF) line and 12 gilts were selected for the low fat line (LF) based on tenth rib backfat adjusted to a 105 kg basis. Results on the additional selected female in the LP and HF lines was due to duplicate records of performance. Mean performance of the selected dams for each of the four selection lines are shown in Table 1. The difference in age at puberty between the early puberty and late puberty dams was 54 days. Early puberty females grew faster and had more backfat than late puberty females. The difference between the high-fat and low-fat females for adjusted tenth rib backfat was 5.8 ram. High-fat selected females grew faster and cycled at a younger age than the low-fat females. Only gilts that cycled were considered for selection. After selection the Generation 1 females were placed in the breeding herd and were monitored daily for estrus and were bred to farrow in bimonthly farrowing groups. Females remained in the breeding herd until the end of the project unless they died. Table 2 shows the reproductive performance of these selected females. A significantly greater percentage of early puberty dams exhibited a normal cycling pattern when compared with late puberty dams. Those females selected for early puberty farrowed significantly more litters per sow than the late puberty dams, and had a greater number of pigs born alive per litter farrowed. The early puberty females also produced significantly higher

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21-day litter weights when compared with litter by the late puberty females. Late puberty females had a significantly lower SPI when compared with early puberty females. Selection for early puberty appears to improve reproductive performance as shown in normal cycling ability. Selection for late puberty appears to result in reduced reproductive performance. A greater percentage of high-fat dams displayed normal cycling patterns than low-fat dams. This suggests that selection for extremely lean gilts could create a problem in the breeding herd with irregular cycling. However, when low-fat females were successfully settled they farrowed a similar number of litter per sow as high-fat females. This supports findings reported by Legault (1971) who found litter performance to be independent or very slightly correlated to production traits. However, females selected for low fat farrowed significantly fewer pigs alive than high fat females. This suggests that selection for extreme leanness could reduce fertility as measured by the number of pigs born alive. This finding is in agreement with results reported by Berruecos et al. (1970) who found a significant decline in litter size when selecting for low backfat thickness. This does not agree with work done by Gueblez and Gestin (1985), who saw the first and second litters of leanest sows at 100 kg to be 0.30.5 piglets larger than those of the fattest sows at the same weight. These sows were as lean as the ones used in this experiment. Legault and Gruand (1981) found a very low correlation between the number of live embryos and backfat, indicating no relationship between decreased backfat and fertility. Also, in disagreement are findings by Gray et al. (1965) and Hetzer and Miller (1970) that no significant changes in litter sizes occurred when selecting for low backfat. However, their lean lines were not as extreme as those used in this experiment. High fat dams also had significantly heavier 21-day litter weights and a slightly higher SPI than LF dams. This suggests that selection for extreme leanness could also result in a reduced milking ability of the sow, which agrees with DeNise et al. (1983) who reported that litter traits from birth to weaning were detrimentally affected by selection for leanness. This difference could be caused by lack of energy stores in the low-fat females. Gueblez and Gestin (1985) also reported that sows selected for low backfat at 100 kg had a lower herd longevity than sows selected for high backfat at 100 kg. These results indicate that selection for extreme leanness alone in cycling females could have detrimental effects on reproductive performance as evidenced by more irregular cycling, fewer pigs born alive and reduced milking ability. This supports Lerner's (1954) theory that natural selection favors phenotypic intermediates and that artificial selection for extremes lowers reproductive fitness. In all selection lines, breed was nonsignificant for all reproductive traits. In the puberty lines, all three fixed effects (selection type, breed and farrowing season) and their interactions were significant sources of variation for ADG of gilts. In the composition lines, all fixed main effects were also significant. However, no interactions approached significance. In both the fat and puberty

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lines only farrowing season was significant for age at first estrus. Only slaughter group was significant for days to 105 kg in barrows. Responses in offspring to selection of dams for extremes in sexual maturity or fatness are given in Tables 2 and 3. Estimates of genetic parameters from this data can be found in Hixon et al. (1987). The gilts produced by the dams selected for early puberty had significantly higher average daily gains than females produced by the dams selected for late puberty. Early puberty gilts also tended to cycle at an earlier age than late puberty gilts. The absence of significance for this direct response is not unexpected owing to the mating of both early and late puberty dams to the same sires to produce the offspring. The barrows produced by the early puberty dams reached 105 kg significantly earlier than barrows produced by late puberty females. These results suggest that the offspring of dams selected for early puberty will be faster growing, cycle earlier and reach market weight at an earlier age than those offspring produced by late puberty dams. This is in agreement with Mabry et al. (1985) who reported that faster growing females from the first generation cycled earlier and reached market weight sooner than the slower growing ones. Gilts produced by the low-fat line had significantly higher average daily gains than gilts produced by the high-fat lines and cycled at a significantly earlier age. This agrees with results reported by DeNise et al. (1983) that selection for leanness may in fact enhance the ability of a gilt to express estrus and supports work done by LeGault (1971) where the correlation between reproduction and carcass characteristics was 0.028. Also, barrows produced by the low-fat line took significantly less time to reach 105 kg than barrows produced by the high-fat dams. Thus, offspring from dams selected for low fat grew faster, reached market weight and puberty earlier than offspring from dams selected for high fat. This disagrees with the phenotypic description of the parents of these offspring, where there was no difference in growth between the high and low-fat dams, and the high-fat dams cycled significantly earlier than the lowfat dams. Correlated responses in composition of gilts produced by the selected dams are shown in Table 2. The analysis of variance results were used to obtain leastsquare means by line for the composition traits. Gilts produced from early puberty dams had significantly more backfat at the tenth rib and last lumbar vertebra than gilts produced by late puberty dams. There were no significant differences between offspring from the two puberty lines for shoulder backfat and loin depth, although early puberty offspring had a trend towards more shoulder fat. Gilts produced by high-fat dams had significantly more tenth rib backfat, backfat at the last lumbar vertebra, and deeper loin depth than gilts produced by low-fat females. Again, there was no difference in backfat at the shoulder between offspring of the two lines. These results indicate that gilts produced by early puberty dams grow faster, and deposit more fat than gilts produced by late puberty dams. Also, gilts produced by the low-fat lines are

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both gaining more per day and depositing less fat than gilts produced by the high-fat females. Carcass trait response of barrows to selection in the dams is shown in Table 3. There were no significant differences in fat deposition or muscling between barrows produced by the dams selected for early puberty or for late puberty. However, there were significant differences between offspring from the two divergent backfat lines. Barrows produced from the high-fat dams had more average backfat and backfat at the tenth rib than low-fat barrows; however, low-fat barrows had a greater loin eye area, more loin depth and higher percent muscle t h a n barrows from the high-fat dams. This agrees with work done by Hetzer and Miller (1973) that depth of carcass backfat, dressing percentage, percentage fat cuts and fat in ham were positively correlated with backfat genetically; and, percent lean cuts, loin eye area ham weight and percent lean meat were negatively correlated genetically with backfat thickness. Also, DeNise et al. (1983) reported strong evidence that selection for decreased backfat will increase lean. The response of the offspring to selection for extremes in age at puberty in the d~ms indicates that selection for early puberty in the female will result in enhanced reproductive ability in the dam and her offspring will be faster gaining with an increased amount of backfat. The correlated responses in offspring of the backfat lines indicates that selection for low backfat thickness in cycling females will decrease fat and increase the amount of lean deposited by her offspring. It also suggests that her offspring will reach puberty and market weight at an earlier age with the puberty response due perhaps to this faster growth rate. When selecting for leanness and only considering gilts that had cycled within the earliest 75%, some indirect emphasis on growth rate could have been exerted. This could enhance the growth rate and age at cycling in the offspring of low-fat dams. However, the reproductive performance of these selected lean females could be a detrimental factor (perhaps because of insufficient fat reserves ). If there were some way to manipulate these extremely lean females environmentally to cycle at regular intervals and then provide t h e m with an adequate nutritional regime so they can reproduce normally, then selection for decreased backfat can be incorporated in selection of replacement females and the detrimental effects on reproduction could be minimized.

REFERENCES American Meat ScienceAssociation, 1967. Proposed procedurefor carcass evaluationcontests. AmericanMeat ScienceAssociation,Chicago,IL. Berruecos, J.M., Dillard, E.V. and Robison, O.W., 1970. Selectionfor low backfat thickness in swine. J. Anim. Sci. 30:844 DeNise, R.S., Irvin, K.M., Swiger,L.A.and Plimpton,D.F., 1983.Selectionfor increasedleanness

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of Yorkshire swine. IV. Indirect responses of the carcass,breeding efficiencyand preweaning littertraits.J. Anita. Sci.,56: 551. Gray, R.G., Tribble, L.F., Day, B.N. and Lasley, J.F.,1965. Five generations of selectionfor thinner backfat. J. Anita. Sci.,24:848 (Abstract). Gueblez, R. and Gestin, J.M., 1985. Effect of age and backfat thickness on reproductive performance of 100 kg Large White sows. Journ. Rech. Porcine France, 17: 113-120. Hetzer, H.O. and Miller,R.H., 1970. Influence of selectionfor high and low fatnesson reproductive performance of swine. J. Anita. Sci.,30: 481. Hetzer, H.O. and Miller, R.H., 1973. Selection for high and low fatness in swine: correlated response of various carcass traits.J. Anita. Sci.,37: 1289. Hixon, A.L., Mabry, J.W., Benyshek, L.L. and Weaver, W.M., 1987. Estimates of genetic parameters for sexual and compositional maturity in gilts.J. Anita. Sci.,64: 977. Legault, C., 1971. Relationship between fattening and carcass performances and litterperformance in pigs.Ann. Genet. Set. Anirn., 3: 153-160. Legault, C. and Gruand, J., 1981. Additive and non-additive effectof genes on age and weight at puberty, ovulation rate and embryonic mortality in gilts.Journ. Rech. Porcine France, 247254. Lerner, I.M., 1954. Genetic Homeostasis. Oliver and Boyd, Edinburgh. Mabry, J.W., Weaver, W.M., Benyshek, L.L. and Marks, M.A., 1985. Phenotypic and genetic parameters for growth, puberty and compositional traitsin gilts.Growth 49" 282. National Pork Producers Council, 1983. Procedure to evaluate market hog performance. National Pork Producers Council, Des Moines, IA. National Swine Improvement Federation, 1981. Guidelines for uniform swine improvement programs. Program Aid 1157, USDA. Quijandria, B., Muscari, J. and Robison, O.W., 1983. Selection in guinea pigs: III. Correlated responses to selectionfor littersize and body weight. J. Anita. Sci.,56: 829. Rampacek, G.B. and Kraeling R.R. and Kiser, T.E., 1981. Delayed puberty in giltsin total confinement. Tberiogenology, 15: 491. SAS Institute,Inc.,1982. SAS User's Guide. Cary, NC. Snedecor, G.W. and Cochran, W.G., 1980. StatisticalMethods. The Iowa State University Press. Ames, IA.

RESUME Nelson, A.H., Mabry, J.W., Benyshek, L.L. et Marks, M.A., 1990. R~ponzes correlatives de la reproduction, de la croissance et de la composition tissulaire ~ la s~lection de jeunes truies pour des ages ~ la pubert~ et des dpaisseurs de lard extremes. Livest. Prod. Sci., 24:237-247 (en anglais). Des femelles ( n = 5 0 ) ont ~t~ s~lectionn~es pour des maturit~s sexuelles extremes, pr~coce (12 EP) ou tardive (13 LP), bas~es sur l'~ge au premier oestrus d~tectable, ou des ~paisseurs de lard extremes, ~lev~e (13 HF) ou faible (12 LF), ~ partir de l'~paisseur de lard ~ la 10brae cSte ajust~e au poids vif de 105 kg. Les chaleurs de ces femelles ~taient ensuite d~tect~es quotidiennement. Elles dtaientsaillies~ des l~riodes programmdes et gard~es jusqu'~ la mise bas. Les performances de reproduction dtaient ensuite enregistr~es.Davantage de truies E P avaient des cycles sexuels norrnaux clueles LP. IIen allaitde m ~ m e pour les H F par rapport aux LF. Les femelles ~ pubert~ pr~coce (EP) mettaient bas davantage de portL~/truie (P <0,05 ) et de procelets/port~e (P <0,10) que les LP. Les truies ~ faible ~paisseur de lard mettaient bas moins de procelets n~s vivants (P < 0,10) que les LF. Les truies~ pubert~ pr~coce (EP) et ~ forte~paisseur de lard (HF) avaient

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l'index de productivit~ (SPI) le plus ~levd, tandis que celles h pubert~ tardive (LP) dtaient intermSdiaires. Les femelles h faible Spaisseur de lard (LF) avaient le SPI le plus bas (P<0,05). Ces rdsultats indiquent qu'une s~lection basde sur un seul caract~re, adiposit~ faible ou puberte tardive, peut ~tre ddfovorable pour les performances de reproduction. La descendance de ces potties (371 femelles et 173 m~les castr~s) a ensuite ~t~ test~e sur ses performances de production. Leurs r6ponses corrdlatives h une selection en faveur d~ges h la pubert~ extremes des m~res montrent qu'une pubert~ pr~coce de ces derni~res conduit h une croissance plus rapide et une adiposit~ plus forte de leur descendance. Les r$ponses correlatives dans les ligndes sdlectionn$es sur l'dpaisseur de lard indiquent que la sdlection pour une faible dpaisseur de lard des femelles cycliques diminue la quantit~ de graisses et accrolt la quantit~ de tissu maigre ddpos~es chez leur descendance. De plus, les porcs issus de la lignde LF atteignent plus rapidement la pubert~ et le poids commercial d'abattage. KURZFASSUNG Nelson, A.H., Mabry, J.W., Benyshek, L.L. und Marks, M.A., 1990. Korrelierter Selectionserfolg in Fortpflanzungs- und Wachtumsleistung sowie in der KSrperzusammensetzung bei der Selektion von Jungsauen auf Extreme in Geschlechtsreife und Riickenspeckdicke Livest. Prod. Sci., 24:237-247 (auf englisch). Flinfzing Jungsauen wurden aufgrund der ersten erkennbaren Brunst einerseits auf extrem friihe bzw. extrem spiite Geschlechtsreife (12 FG, 13 SG) selektiert oder anderseits auf hohe bzw. geringe Riickenspeckdicke (13 HD, 12 GD), gemessen an der 10. Rippe und korigiert auf 105 kg KSrpergewicht. Diese so selektierten Jungsauen wurden sodann ~glich auf Brunstanzeichen gepriift, in bestimmten Zuchtperioden belegt und zum Abferkeln gebracht. Die Fortpflanzungsleistung wirde ermittelt. Mehr FG- als SG-Sauen hatten einen normalen Brunstzyklus, ebenso mehr HD- als GD-Sauen. Die FG-Sauen lieferten mehr Wfirfe/Sau (P < 0.05) und mehr Ferkel/Wurf (P < 0.10) als die SGSauen. Die GD-Sauen brachten weniger lebendgeborene Ferkel zur Welt ( P < 0.10) als die HDSauen. Die FG- und HD-Sauen hatten den hSchsten Sauenleistungsindex (SLI), w~thrend die SG-Sauen sich in diesem Merkrnal intermedi~ verhielten. Die GD-Sauen hatten den niedrigsten SLI (P < 0.05). Die Ergebnissen lassen erkennen, daf~ Selektion auf Einzelmerkmale, wie extrem geringe Rtickenspeckdicke oder spiite Geschlechtsreife, sich auf die Fortpflanzungsleistung nachteilig auswirken kann. Die Nachkommen (371 Jungsauen, 173 kastrierte Jungeber) aus den Wiirfen der 50 selectierten Sauen wurden sodann leistungsgepriift. Die korrelierten Selektionserfolge bei den Nachkommen der auf extrem friihe oder extrem spiite Geschlechtsreife selektierten MUtter weisen darauf hin, daf~ eine Selection yon Sauen auf friihe Geschlechtsreife bei ihren Nachkommen zu beschleunigeter Gewichtszunahme und vermehrter Rtickenspeckdicke Rihrt. Die korrelierten Selektionserfolge bei den Nachkommen der auf hohe oder geringe Riickenspeckdicke selektierten Sauen lassen erkennen, dal~ eine Selektion geschlecthreifer Sauen auf geringe Riickenspeckdicke die Rfickenspeckdicke bei ihren Nachkommen vermindert und den Fleischanteil bei diesen erhSht. Auch erreichten diese Nachkommen die Geschlechtsreife und das Vermarktungsgewicht in jiingerem Alter.