Opportunities for genetic evaluation of reproductive performance in accelerated lambing systems

Vanimisetti, Hima Bindu; Notter, D. R.

doi:10.1016/j.livsci.2012.05.022

Cited by 9 publications

(3 citation statements)

References 33 publications

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“…These values compared favorably to published results for Finnsheep crossbred ewes joined in the spring [24,25]. However, spring fertility of 8-month-old ewe lambs in line S averaged only 0.12 in Phases 1 and 2, but increased to 0.28 in Phase 3, which emphasizes the challenges involved in selecting replacement ewe lambs in production systems that involve autumn lambing [26]. Autumn-born lambs were anticipated to be genetically superior but were phenotypically unlikely to lamb at 1 year of age.…”

Section: Discussionsupporting

confidence: 73%

“…However, when lactating S ewes were joined with rams at an average of 40 d postpartum in May, 53% of the ewes mated within 39 d of joining but only 21% of the ewes produced viable offspring, which suggest problems with maintenance of pregnancy and placental insufficiency. Selection to improve reproductive performance in accelerated lambing is challenging [26]. Our results suggest that genetic improvement of reproduction in accelerated and other multi-season lambing systems could be achieved as a correlated response to selection for fertility in May and June in nucleus flocks used to produce commercial replacement ewes.…”

Section: Discussionmentioning

confidence: 89%

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Direct and correlated responses to selection for autumn lambing in sheep

2020

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Background Seasonal reproduction limits productivity, flexibility, and profitability in commercial sheep production. Hormonal and (or) photoperiodic manipulation can be used to control estrous cycles in sheep and reduce limitations that are imposed by the seasonal anestrous but are often impractical or incompatible with the extensive management systems preferred for ruminant livestock. Thus, the current study investigated the use of selection to improve realized fertility (i.e., the proportion of ewes that lambed) following an out-of-season spring joining period (May and June) in a crossbred sheep population. Results Over 17 years, estimated breeding values (EBV) for fertility in selected (S) ewes increased by 0.175 (0.01 per year). The mean EBV for fertility of S ewes was greater than that of control ewes by year 10 (P = 0.02), and the fertility of adult (≥ 3 years old) ewes reached 0.88 ± 0.05 by year 17. Lambing began approximately 140 days after the introduction of rams, and 64% of the S ewes that lambed did so in the first 17 days of the potential lambing season, which indicated that most of the S ewes were cycling at the time of ram introduction and were not induced to cycle by the introduction of breeding males (i.e., the so-called “ram effect”). Animals in the S line had modest increases in body weight and scrotal circumference. A modest negative trend in the additive maternal effect on birth weight was observed but was reversed by additional selection on EBV for maternal birth weight. The heritability of litter size in autumn lambing was low (0.04) and could potentially limit the response to selection for this trait. Conclusions Selection improved realized ewe fertility in out-of-season mating, with absolute increases of approximately 1% per year in the percentage of joined ewes that lambed in the autumn. Genetic antagonisms with other performance traits were generally small. A modest antagonism with maternal breeding values for birth weight was observed but it could be accommodated by selection on EBV for maternal birth weight. Our results support results of previous studies that indicate that these selected ewes had one of the shortest seasonal anestrous periods reported for temperate sheep breeds and that spring-lambing lactating ewes from the selection line were capable of relatively rapid rebreeding in the spring.

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Section: Discussionsupporting

confidence: 73%

Section: Discussionmentioning

confidence: 89%

Direct and correlated responses to selection for autumn lambing in sheep

2020

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“…Significant (P<0.05) differences in LI regarding litter type were recorded in Romanov (María and Ascaso, 1999), Djallonke, (Gbangboche et al, 2006), Jezersko-Solčava (Komprej et al, 2011) and Pelibuey (Tec Canché et al, 2015) breeds. Vanimisetti and Notter (2012) reported non-significant (P>0.05) differences in the first and second lambing intervals of Polypay ewes with different litter types. María and Ascaso (1999) discussed that one of the possible reasons for the longer LI in ewes with larger litters might be higher milk production in multiparous ewes.…”

Section: Resultsmentioning

confidence: 85%

Non-genetic factors affecting litter size, age at first lambing and lambing interval of Romanov sheep in Croatia

Vlahek

Kabalin²,

Faraguna

et al. 2022

Vet. stn. (Online)

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Reproductive traits are of paramountimportance in an efficient lamb production system. In Croatia, values of reproductive traits of Romanov sheep are below the average expected for this breed, indicating the need for improvement of these traits to exploit the breed’s full reproductive potential. This study was conducted on 260 Romanov ewes located at a commercial Romanov sheep farm in Croatia. All ewes were kept under similar conditions, and reproductive management was based on accelerated lambing with continuous mating. Linear models with fixed effects were used to estimate the influence of year of birth/lambing, season of birth/lambing, ram, parity and litter type on litter size (LS), age at first lambing (AFL) and lambing interval (LI). Average LS was 2.11 ± 0.71, while the year of lambing and parity were the most important factors affecting this trait. The smallest litters were recorded after 1st parity (1.77 ± 0.06), and the largest after 5th parity (2.21 ± 0.08). AFL averaged 388.5 ± 72.4 days. All investigated non-genetic factors had a significant (P<0.05) influence on AFL, with year of birth as most important. The average LI was 241.2 ± 70.8 days. A significant (P<0.05) influence of all factors on LI was observed. Ewes lambing in spring (200.2 ± 7.9 days) or summer (190.5 ±6.6 days) had a significantly (P<0.05) shorter LI than ewes lambing in autumn (227.7 ± 8.3 days) or winter (237.2 ± 6.7 days). The longest LI was observed after the first parity (284.0 ±5.5 days). Average values for reproductive traits in the examined population of Romanov sheep were higher than those reported in the official Croatian database for breeding sheep. Non-genetic factors have a significant influence on the variation of reproductive traits of Romanov sheep, and therefore should be considered when assessing ewes’ reproductive performance.

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Phenotypic and genetic parameter estimates for reproductive traits in Zandi sheep

Mohammadi

Nassiri

Rahmatnejad

et al. 2012

Trop Anim Health Prod

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This study reports on the phenotypic and genetic (co)variance components for reproductive traits in Zandi sheep, using between 1,859 and 2,588 records obtained from 577 ewes. The data were collected from the Khojir Breeding Station of Zandi sheep in Tehran, Iran from 1994 to 2008. The basic traits were litter size at birth (LSB), litter size at weaning (LSW), litter mean weight per lamb born (LMWLB), and litter mean weight per lamb weaned (LMWLW), and the composite traits were total litter weight at birth (TLWB) and total litter weight at weaning (TLWW). Genetic analyses were carried out using the restricted maximum likelihood method that was explored by fitting the additive direct genetic effects and permanent environmental effects of the ewes as random effects and the ewe age at lambing and lambing year as fixed effects for all of the investigated traits. Akaike's information criterion was used to choose the most appropriate model. LSB, LSW, LMWLB, LMWLW, TLWB, and TLWW direct heritability estimates were 0.07, 0.05, 0.12, 0.10, 0.08, and 0.14, respectively. The estimated fractions of variance due to the permanent environmental effects of the ewe ranged from 0.03 for LMWLB to 0.08 for LMWLW and TLWW. Corresponding repeatability estimates ranged from 0.10 for LSW to 0.22 for TLWW. Direct genetic correlations varied from -0.61 for LSB-LMWLB to 0.88 for LSB-LSW and LSB-TLWB. Results indicate that genetic change depends not only on the heritability of traits, but also on the observed phenotypic variation; therefore, improvement of non-genetic factors should be included in the breeding programs.

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Opportunities for genetic evaluation of reproductive performance in accelerated lambing systems

Cited by 9 publications

References 33 publications

Direct and correlated responses to selection for autumn lambing in sheep

Direct and correlated responses to selection for autumn lambing in sheep

Non-genetic factors affecting litter size, age at first lambing and lambing interval of Romanov sheep in Croatia

Phenotypic and genetic parameter estimates for reproductive traits in Zandi sheep

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