Phenotypic Response and Time Trends to Date of Birth Selection in Southdown Sheep

Thrift, F. A.; Dutt, Ravi; Woolfolk, P. G.

doi:10.2527/jas1971.3361216x

Cited by 15 publications

(8 citation statements)

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“…The reasons for this are not known. Year effects of similar magnitude with differences up to 31 d between years in lambing dates were reported for Southdown sheep by Thrift et al (1971).…”

Section: Lambing Performancesupporting

confidence: 69%

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Lambing Date and Lamb Production of Spring-Mated Rambouillet, Dorset and Finnsheep Ewes and Their F1 Crosses1

Iñíguez

Bradford

Mwai

1986

Journal of Animal Science

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The reproductive performance of 255 Rambouillet (R), Dorset (D), Finnsheep (F) and F1 ewes born in 1978-1979 (group I) and 1979-1980 (group II) and managed in a semiconfinement fall/winter lambing system was evaluated through 4 yr of age of all ewes and through 5 yr for a portion of group I ewes. Ewes were with rams from approximately May 1 to late September each year, with a 2-wk break late in July/early August. Traits considered were fertility (ewes lambed/ewes exposed), lambing date, litter size, lamb survivial and 70-d lamb weights. Breeds and crossbred groups differed significantly in lambing date, with DR crossbred ewes earliest and F ewes latest. Repeatabilities for groups I and II were .31 and .22, .24 and .24 and .11 and .07 for lambing date, fertility and litter size, respectively. There was no significant heterosis in lambing date, although DR ewes in both groups I and II were superior to (D + R)/2, by about 1 wk on average. There was significant positive heterosis for fertility and traits of which fertility is a component in FR ewes in group I, but none in group II. The FD ewes showed negative heterosis for litter size, -.23 (P less than .05) for group I and -.09 for group II. The results indicate: F and FD ewes are not well adapted to the Mediterranean climate where this experiment was conducted; there is little, if any, useful heterosis in crosses among these three breeds for lambing date or other reproduction traits and RD and R ewes are most suitable of the groups tested, while late onset of the breeding season limits the usefulness of even 50% Finnsheep ewes for an autumn lambing system in this environment.

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“…The reasons for this are not known. Year effects of similar magnitude with differences up to 31 d between years in lambing dates were reported for Southdown sheep by Thrift et al (1971).…”

Section: Lambing Performancesupporting

confidence: 69%

“…In contrast, estimates of residual variance were fairly consistent (Ve = 686 vs Ve = 680). Thrift et al, (1971), estimated the heritability of lambing dates in Southdown ewes under a spring lambing program to be .21. It seems possible that much of the present repeatability estimate is due to the genetic component.…”

Section: Lambing Performancementioning

confidence: 99%

Lambing Date and Lamb Production of Spring-Mated Rambouillet, Dorset and Finnsheep Ewes and Their F1 Crosses1

Iñíguez

Bradford

Mwai

1986

Journal of Animal Science

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“…Seasonality of breeding is a major impediment to improvement of reproductive efficiency in sheep. Results of previous attempts to develop sheep populations with an extended breeding season have been equivocal because of inadequate control populations and(or) failure of apparent accumulated genetic superiority to be expressed in other environments (Thrift et al, 1971;Lindahl and Terrill, 1975;Jenkins and Ford, 1982). Documentation of realized selection response is also often complicated by the low heritabilities of fertility traits (Fogarty, 1995) and by the large population sizes that are therefore required.…”

Section: Introductionmentioning

confidence: 99%

Response to selection for fertility in a fall-lambing sheep flock.

Al-Shorepy

Notter

1997

Journal of Animal Science

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Selection for fertility in a fall lambing system was applied for 5 yr (1.45 generations) in a crossbred sheep population. Three flocks were involved: a fall-lambing selected (S) flock of 125 ewes and 10 rams, a fall-lambing environmental control (EC) flock of 55 ewes and five rams, and a spring-lambing genetic control flock of 45 ewes and five rams used to produce replacements for EC. Estimated breeding values for fertility (ewes lambing per ewe exposed) were calculated for animals mated in each year of the study using a single-trait animal model and increased more rapidly in S (.0138/yr) than in EC (.0067/yr). After accounting for genetic drift, EBV of ewes mated in S in the final year of the study averaged .070 +/- .032 (P = .08). A correlated response of .0087 lambs/yr was observed in S for fall litter size Genetic trends in all body weights were positive in EC, likely because of supplemental selection on body size in ram lambs used in EC. Ninety-day weight, maternal effects on weaning weight, and 90-d scrotal circumference increased in S, but direct effects on birth and weaning weights declined. In order to focus on realized selection response in fertility, EBV for fertility of 330 replacement ewe lambs from S and EC were calculated using only data collected after their birth. These realized EBV were then regressed on pedigree EBV calculated at the time the ewe lambs were born. The regression was significant when all relationships were used to calculate both EBV (.20 +/- .08) but only approached significance (.13 +/- .07) when only records of the ewe lambs themselves, their descendants, and their paternal half-sibs were used to calculate realized EBV. Also, EBV for all ewes were calculated at the start of each breeding season and were higher (P < .01) for ewes that subsequently lambed than for open ewes. These results suggest that selection can be used to improve fertility in fall-lambing sheep flocks.

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“…Dans un projet, qui a dur6 18 mois, on a utilis6 29 brebis DLS (l/2 Dorset,1i4 Leicester, l/4 Suffolk) pour 6tudier la caract6ristique de la longueur (Thrift et al 1971;Fahmy 1976;Fahmy et al 1980) and increasing the length of the breeding season (Dufour 1914 (Fahmy 1976 …”

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Ovarian and Estrous Activity Throughout the Year in Pregnant and Nonpregnant Ewes Selected for Extended Breeding Season

Dufour¹,

Fahmy²,

Adelakoun³

et al. 1982

Can. J. Anim. Sci.

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Twenty-nine DLS (l/2 Dorset, 1/4 Leicester, 1/4 Suffolk) ewes selected for extended breeding season, were involved in this study which lasted for 18 mo. According to their lambing date relative to January first, 15 ewes had a high lambing index whereas the others had a low index, the difference being 33 days (P<0.01). Half the ewes were assigned at random to remain nonpregnant throughout the study, whereas the other half was mated in July and August. From I May to 15 July, 20 ewes (69%') were cycling of which 817o were from the high and 54Vo from the low index group (0.05>P<0.10). Two ewes (7Va)

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Phenotypic Response and Time Trends to Date of Birth Selection in Southdown Sheep

Cited by 15 publications

References 0 publications

Lambing Date and Lamb Production of Spring-Mated Rambouillet, Dorset and Finnsheep Ewes and Their F1 Crosses1

Lambing Date and Lamb Production of Spring-Mated Rambouillet, Dorset and Finnsheep Ewes and Their F1 Crosses1

Response to selection for fertility in a fall-lambing sheep flock.

Ovarian and Estrous Activity Throughout the Year in Pregnant and Nonpregnant Ewes Selected for Extended Breeding Season

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