Heterosis and the Genetic effects of Crossbred

Parents on Long-term Performance of the

Reproductive Traits per Feed Intake in

Two Strains of Mice

Masahiro SATOH*,Yutaka MIZUMA and Toshihiro YAMAGISHI

Faculty of Agriculture,Tohoku University,Sendai-shi 980*National Institute of Animal Industry

Tukuba Norindanchi,Ibaraki-ken305

(Received October 23,1986)

Abstract Two strains of mice(ICR,ddY)were used to evaluate their long-

term reproduction.Each female(the pure strain and reciprocal F1)was pair-mated at day 49 with a male from the pure strain and R,and each pair was

maintained for 150 days after mating.When dams pmduced their litters,litter

size was reduced to eight.The young were weaned at 17 days of age.Levels of

matemal heterosis were 16.2 and 16.1%(P<0.05),for the total weight of the

young born alive and the weight of the young raised to weaning over 150 days,respectively.ddY was superior to ICR in the average direct genetic efrect on the

total weight of the young born aliveve(P<0.05).But there was no direct genetic

effect on the tota humber of young born,the total number of young born alive

and the total number of young alive atweaning.In long-term production per

feed intake(10009),the total number of young born al ive was significantlyinfiuenced by both the average diect genetic efrect(P<0.01)and the average

matenal genetic efrect(P<0.05).Maternal heterosis was 8.4%(P<.10)for the

weight of the young raised to weaning per feed intake.Butdirectheterosis was

not significant for any traits per feed intake.These results showed that cross

dams improve not only intotal long-term production but also inproductivity perfeed intake.

JPN.J.Zootech.Sci.,58(5):421-428,1987

Key words:maternal heterosis,reproduction,feed intake,long-term performance,

mice

Few studies on life timeproduction genetlcs inpurebred livestock have been

conducted(Gill and ALLAIRE,1) and MOQUE and HODGES 2)in dairy cattle,BAKER et al.3)

insheep)because they require much time and money.In their studies on mice,TOMITAet al.4)

,WALLINGA and BAKKER,5) and SCHULER and BUNGER 6)reported on long-term

reproduction,but their studies only compared lines,different mating systems and

different mating ages.Though studies of hybrid vigor in lifetime performance on

livestock are rare,ROoBBERTS 7),NAGAI et al. 8,9),and NAGAI and YoKoYAMA 10)reported

on lifetime production in many strains of mice and their F1.and F2.However,these

studies do not consider feed intake inconnection with long-termperformance.The

objective of this study is to examine heterosis and the genetic efrects of long-term

performance,also via feed intake.

Jpn.J.Zootech.Sci.,58(5)421-428 421 1987

SATOH,MIZUMA and YAMAGISHI

Materials and Methods

Two strains of mice(ICR,ddY),which have large littler size,and their reciprocal

F1 crosses were used in this experiment.Each strain and cross were pair-mated at 49

days of age by the mating design shown in Table 1,and maintained in the same cage

continuously for 150 days after mating.Females that did not produce a litter for 90

days after the previous parturition or first mating were discarded.When females

produced their litters,litter size was reduced to eight(4 males and 4 females)whenever

possible.Litters of less than eight mice were not augmented.The young were weaned

at 17 days of age.Throughout this experiment,a commercial pellet feed and tap

water were supplied.Temperature and humidity in the mouse room were 21•}1•Žand

40•}5%,respectively.The light regime was 12 hours of artificial illumination

followed by 12 hours of darkness.The following traits were recorded for each pair:

total number of young born alive and dead,total body weight(number of young alive

in a litter)at birth,total number of and total body weight of young alive at day 17,

and feed intake per pair.

If each trait was influenced by additive and maternal components,and heterosis

effects with respect to strain origin of allelic pairs11),a simple linear model via multiple

regression analysis may be written as below.

Y=ƒÊ+GI•EX1+GM•EX2+GM'•EX3+HI•EX4+HM•EX5+RI•EX6+e

where Y is the measurement for the mating pair,where u is the least-squares mean,

and the superscripts I,M and M' signify individual,maternal and grandmaternal

components,respectively;X1,X2 and X3 are measures of strain composition recorded

as a proportion of ICR(ICR=1,ddY=-1,reciprocalF1=0,etc.),for offspring,dam

and grand dam respectively,while X4 and X5 are corresponding measurements of strain

heterozygosis setting values for the F1 crosses at 1,backcrosses and F2 at 0.5,and pure

strains at zero.X6 is the setting value for the F2 crosses at 1,backcrosses at O.5,F1

crosses and pure strains at zero.The coefficients GI,GM,GM',HI,HM and RI are the

regressions of Y on the respective Xi variables.GI,GM and GM' are the average strain

differences for progeny,maternal and grandmaternal effects,respectively.The terms

HI and HM are estimated heterosis levels in F1 crosses for offspring and maternal

effects,and RI is the estimated recombination loss.e is a random error with zero

mean and variance,ƒÐe2.The equations were solved simultaneously to obtain estimates

for GI,GM,GM',H',HM and RI.Heterosis level was calculated by dividing the

Table 1.Mating structure

422

Heterosis in Long-term Performance of Mice

estimated value by u.

Results

The changes over parities on the number of young born alive and the litter weight

of young born alive are shown in Figure 1 and on litter weight of young at weaning

is presented in Figure 2,respectively.In all traits,F1 cross progeny tended to excel

over those of the pure strains and the performance of F1 cross dams tended to excel

over those of the pure strain dames.

The results of the analysis of variance,the least-squares means and the standard

errors of total production at birth are presented in Table 2 and Table 3,respectively.

The number of parturitions and total weight of young born alive during the 150 day

period were significantly(P<0.05)influenced by both the average direct genetic effect

and maternal heterosis.And in the average maternal genetic effect,the number of

parturitions tended to be significant(P<0.10).ddY was superior to ICR in the

average direct genetic effect and ICR was superior to ddY in the average maternal

genetic effect on these traits(Table 3).It was observed that hybrid vigor levels in

maternal heterosis(P<0.05)on the number of parturition and total weight of young

born alive during 150 days were 11.7 and 16.2%,respectively.

The results of the analysis of variance,and the least-squares means and standard

errors of total production at weaning are presented in Table 4 and Table 5,respectively.

Observed hybrid vigor levels in maternal heterosis(P<0.05)on the total weight of

Fig.1.The changes over parities on the number of young born alive and litter weight of

young born alive.

423

SATOH,MIZUMA and YAMAGISHI

Fig.2.The changes over parities on the litter weight of young at weaning.

Table2.Mean squares of total production at birth

Table3.Least-squares means and standard errors of total production at birth

(LS mean•}S.E.)

424

Heterosis in Long-term Performance of Mice

Table4.Mean squares of total production at weaning

Table5.Least-squares means and standard errors of total production at weaning

Table6.Mean squares of total production per feed intake(1,000g)

and total gain of young were 16.1 and 16.8%,respectively.But all effects,except for

maternal heterosis,were insignificant.

The results of the analysis of variance,and the least-squarses means and standard

errors of productive traits per feed intake(1000g)are presented in Table 6 and Table

7,respectively.The total number of young born alive per feed intake was influenced

by the average direct genetic effect(P<0.01)and the average maternal genetic effect

425

SATOH,MIZUMA and YAMAGISHI

Table 7.Least- squares means and standard errors of total production per feedintake(1,000 g)

(P<0.01).ddY was superior to ICR in the average direct genetic effect and ICR was

superior to ddY in the average maternal genetic effect on that trait.Also,the

total litter weight of young born alive per feed intake tended to be similar to the

above.The average grandmaternal genetic effect was significant (P<0.05) on the

number of young and litter weight at weaning per feed intake,and ICR was superior to

ddY in that effect.Maternal heterosis tended to be significant (P<0.10) on total

litter weight at weaning per feed intake,and the hybrid vigor level in crosses was 8.4

%.This level was about half compared to that of the total litter weight,not

considerning feed intake.But there was no direct heterosis effect on any traits.

Discussion

Crossbred dams tended to excel over pure strain dams.Moreover,crossbred

progenies tended to excel over pure strain progenies for reproductive traits in each

parity.These results are caused by individual heterosis on each trait.There is no

report on the above about long-term production in animals.But hybrid dams are

generally used for better livestock performance,because of improved reproduction.In

the present study,it was obvious that progeny genotype(dominance effect of progeny)

and dam genotype(dominance effect of dam) influenced reproductive traits vis-a-vis

the number of young born alive,etc..These results suggest that itis better to use

crossbreds for lone-term animal nroductinn_

Hybrid vigor levels in maternal heterosis which were obvious via the number of

parturitions,total number of young born,and total number and total weight of young

which lived for 150 days,were 11.7,10.5,10.4 and 16.2%,respectively.And ,maternal heterosis levels were 11.5,16.1 and 16.3%,on total number,total weight

and total gain of young raised to weaning,respectively.Hence maternal heterosis

effects on the total number of young and alive young were influenced by the number of

parturitions over 150 days,and maternal heterosis effects on the total number of

young raised to weaning indicates that crossbred dams were superiorto pure strain

dams for nursing ability.Still more,high hybrid vigor levels in maternal heterosis

426

Heterosis in Long-term Performance of Mice

for each weight were about 16%.These took into account that the body weight of

progeny was heavier,since crossbred dams have high uterine environment and lactation

ability in addition to a maternal heterosis level of 11% on the total number of young

born alive.NAGAI et al.8)reported that crossbreds showed higher performance than

those of pure strains in total 20-day litter weight(10%)and total number of young

raised(7%)over 200 days per dam on average,respectively.The results of the present

study were similar to their results.

In the present study,feed intake per pair was measured,which became a new index

of productivity for long-term reproduction.Hybrid vigor levels in maternal heterosis

on the number of and weight of young born alive,and number of and weight of young

at weaning per feed intake were 4.8,6.0,4.2 and 8.4%,respectively.When considered

in terms of feed intake,hybrid vigor levels in maternal heterosis were reduced to about

half,but these levels were still positive.Hence it was shown that the use of crossbred

dams improve not only long-term reproduction but productivity per feed intake.And

differences in some traits between the two strains were obvious from the results that

were on the average direct,the average maternal and the average grandmaternal

genetic effect.

Acknowledgements

The helpful comments and suggestions of Dr.J.NAGAI(Animal Research Centre.

Agriculture Canada)and Dr.T.KAYABA(Faculty of Agriculture,Yamagata Univer-

sity)are gratefully acknowledged.

References

1) GILL, G. S. and F. R. ALLAIRE, J. Dairy Sci., 59 1319-1324. 1976.2) MOQUE,M.and J. HODGES ,J. Dairy Sci., 63 1900-1910. 1980.3) BAKER, R. L., T. A. STEIN, A. W. VABENO ,A. BEKKEN and T. GJEDREM,Acta. Agric.

Scan., 28 203-217. 1978.4) TOMITA, S., T. HAYATO , T. SAWADA and J. HAYAKAWA ,Exp. Anim., 27 399-404. 1978.5) WALLINGA, J. H.and H. B. BAKKER ,J. Anim. Sci., 46: 1563-1571. 1978.6) SCHULER, L. and L. BONGER ,Arch. Tierzucht, 25 275-281. 1982.7) ROBERTS,R. C.,Heredity, 16 369-381. 1961.8) NAGAI, J., D. L. HARRIS and A. J. MCALLISTER, Theor. Appl. Genet., 58 59-69. 1980.9) NAGAI, J., A. J. MCALLISTER and A.YOKOYAMA, 2 nd World Conger. Genet. Appl.

Livestock Prod., 8 33-38.1982.10) NAGAI ,J. and A. YOKOYAMA, 2 nd World Congr. Genet. Appl. Livestock Prod., 8 39-

43.1982.11) DICKERSON ,G. E., Anim. Breed. Abst., 37 191-202. 1969.

427

SATOH,MIZUMA and YAMAGISHI

2系 統 のマ ウスにおける飼料摂取量 当た りの長期連産能力

の雑種 強勢 な らび に遺伝 的効 果について

佐藤正寛*・水間 豊 ・山岸敏宏

東北大学農学部,仙 台市980*農林水産省畜産試験場 ,茨 城県筑波農林研究団地305

2系 統 のマ ウ スICR,ddYを 用 いて,雄 親,雌 親が

純 系お よび正逆F1と なるよ うな144ペ アの組合わせ交

配を行ない,交 配 後150日 間連続妊娠 させ,長 期連産能

力における統 計遺伝学的分析 を行 なった.交 配後150日

間 の繁 殖成 績 で は,総 産子体重(16.2%),離 乳時総体

重(16.1%)で 母性 ヘテ ロシス効 果が認め られた(い ず

れ もP<0.05).ま た,総 産子体重で平均直接遺伝 効果

に 有 意 差 が み られ(P<0.05),ddYの 産 子 の能力が

ICRの それ を上回 って いた.し か し,総 産子数,離 乳

時総生存数ではいずれの遺伝効果 も認め られなか った.

交配後150日 間の飼料摂取量1kg当 た りの繁殖成績 で

は,生 時 生存数で平均直接遺伝効果(P<0.01)お よび

平 均母 性遺伝効果(P<0.05)に,産 子体重で平均直接

遺 伝効 果(P<0.05)に それぞれ有 意差が認め られた.

また,離 乳 時体 重で母性 ヘテ ロシス効果(8.4%)が 有

意 な傾 向 にあ った(P<0.10).し か し,直 接 ヘテロシ

ス効果 にはいずれの形質 に も有意差 はみ られなか った.

以上の ことか ら雑種 の雌親 は長期連産 能力 に加え,飼

料摂取量当 りの繁 殖能力 において もす ぐれていることが

明 らか とな った.日 畜会報,58(5):421-428,1987

日畜 会 報,58(5):421-428 428 1987