Ewe productivity of Booroola Merino–Rambouillet crossbred sheep during early stages of the introgression of the FecB allele into a Rambouillet population

Assessing the performance of Moghani crossbred lambs derived from different mating systems with Texel and Booroola sheep

In our ongoing project, which focuses on the introgression of Booroola/FecB gene and the myostatin (MSTN) gene into purebred Moghani sheep, we assessed the performance of second-generation Moghani crossbreds such as second crossbreds (F2) and initial backcross generation (BC1). These crossbreds were generated through different mating systems, including in-breeding, outcrossing, first paternal backcrossing (PBC1), and first maternal backcrossing (MBC1). Notably, F2 strains exhibited lean tail, woolly fleece and a higher percentage of white coat color compared to BC1. The impact of mating systems and birth types on pre-weaning survival rates was found to be statistically significant (P < 0.0001), with singleton offspring resulting from paternal backcross showing a particularly substantial effect. The F2 crossbred lambs carrying the Booroola gene did not show a statistically significant difference in survivability compared to those carrying the MSTN gene, implying the Booroola prolificacy gene had no significant impact on survival outcomes. However, the occurrence of multiple births had a significant negative impact on lamb survival (P < 0.0001). The PBC1 sheep strains, specifically Texel Tamlet ram strains carrying the MSTN mutation, exhibited superior growth rates compared to others (P < 0.05). Interestingly, the MSTN mutation in the homozygous variant genotype significantly impacts growth rate before weaning compared to other genotypes and pure Moghani sheep (P < 0.05). In conclusion, this study objectively underscores the pivotal role of genetic factors, specifically through strategic mating systems like paternal backcrossing, in enhancing desired traits and growth rates in Moghani sheep, thereby contributing valuable insights to the field of sheep breeding programs.

Comparison of the growth performance between pure Moghani sheep and crosses with Texel or Booroola sheep carrying major genes contributing to muscularity and prolificacy

This study aimed to compare growth performance between Moghani sheep and crossbred lambs resulting from crossbreeding between Moghani pure breed ewes and the lines of rams e.g., Texel Tamlet, Texel Dalzell, Booroola Merino, and Booroola Romney. The first visible phenotypic characteristic was the presence of lean tail in all F1 crossbred lambs, whereas Moghani pure sheep is a well-known large fat-tailed breed. Moreover, the first generation of backcross (BC1) lambs from mating four types of F1 crossbred rams with Moghani pure ewes revealed lean-tailed to short fat-tailed. Comparative results showed that the F1 crossbred lambs had significantly (p < 0.0001) greater birth weight (BW) than the Moghani pure breed lambs. Despite no significant differences observed between Moghani pure breed sheep and its F1 crossbred lambs for body weight at pre-weaning, but F1 crossbred lambs achieved significantly (p < 0.0001) greater body weight after weaning compared to Moghani sheep. The growth performance of BC1 lambs was outperformed than F1 crossbred and Moghani sheep. These results encourage the continuation of the Moghani sheep crossbreeding programs to improve overall lamb growth, particularly post-weaning and to benefit from a better reproductive efficiency by elimination or reduction of the fat tail.

Impact of Booroola fecundity gene introgression on sheep production: Indian perspective

Surge of demand for meat from diverse sources in a time of decling land and other natural resources shifted the trend of producing more sheep per sheep. Prolificacy aspect in sheep can be used as an important arsenal to fulfil this objective. FecB gene mutation perhaps spread from Garole microsheep of India, has been widely used for introduction of prolificacy in monotocus sheep worldwide. The ovulation rate and litter size are two most important reproductive parameters influenced by FecB gene besides small influences on other sheep production parameters. While implementing the FecB introgression programmes precaution needs to be observed to avoid lamb mortality. The results of the experiments conducted worldwide on FecB introgression programmes suggest that high prolificacy is economically beneficial under intensive and semi-intensive management system of sheep rearing. There were variable effects of FecB genotype documented from different parts of the world. With goal oriented research efforts, the prolificacy in FecB carrier Avishaan sheep, a triple breed cross developed from Garole, Malpura and Patanwadi at ICAR-CSWRI are showing promising sheep for future. There are several challenges for using FecB gene in the future using assisted reproductive and genome editing technology. The effect of FecB gene on different sheep production parameters as reported in the literature are summarized in present work.

Effect of the Booroola fecundity (FecB) gene on the reproductive performance of ewes under assisted reproduction

Reproductive traits are important factors in sheep production. The Booroola fecundity (FecB) gene-the first major gene for prolificacy identified in sheep-has a positive effect on ovulation rates and litter size under natural reproductive conditions. However, the effect of the FecB gene on reproductive performance under assisted reproduction, which uses many artificial hormones, remains unclear. In the present study, we evaluated the effect of FecB (BMPR-1B mutation) on reproductive performance under assisted reproduction, and examined offspring body weight at birth and weaning and survival rate at weaning. There were no differences among three genotype groups (homozygous carrier, BB; heterozygous carrier, B+; non-carrier, ++) in terms of estrus detection rate, time to estrus onset, or estrus duration following estrus synchronization (P > 0.05). The pregnancy rates at 60 d were similar among three genotype groups after artificial insemination (P > 0.05). However, the B allele had an additive effect on litter size (one copy resulted in an increase of 0.88 lambs and two copies produced an additional 0.41 lambs; P < 0.01), and increased lambing and fecundity rates (P < 0.01). After multiple ovulation, the average numbers of recovered embryos per ewe were 9.16 ± 0.79, 8.20 ± 0.77, and 8.44 ± 0.61 in the BB, B+, and ++ ewes, respectively (P > 0.05). There were no differences in the fertilization rate or numbers of grade 1-2 embryos among different groups (P > 0.05). The birth and weaning weights of lambs from BB and B+ ewes were lower than those of lambs born from ++ ewes (P < 0.01) owing to the high fecundity. The survival rate of lambs at weaning did not differ among groups (P > 0.05). Our results indicated that the presence of the B allele had an additive effect on litter size after artificial insemination, but it did not influence the parameters of estrus synchronization and multiple ovulation. Furthermore, the higher prolificacy in ewes carrying the B allele was associated with a reduction in offspring body weight at birth and weaning.

Prolificacy and lamb survival at birth in Awassi and Assaf sheep carrying the FecB (Booroola) mutation

Prolificacy up to the fifth parity and lamb survival at birth were investigated in >or=31/32 Awassi and >or=31/32 Assaf sheep belonging to the ++, B+ and BB genotypes at the FecB locus. In the Awassi, prolificacy of ++, B+ and BB ewes was 1.28, 1.90 and 1.92 lambs born/lambing (LB/L), respectively. In the Assaf, prolificacy of ++, B+ and BB ewes was 1.68, 2.40 and 2.55LB/L, respectively. Lamb survival at birth in the ++ Awassi and the ++ Assaf averaged 0.98 and 0.94, respectively. It declined to 0.93 and 0.86, and 0.85 and 0.78 in the B+ and BB Awassi and B+ and BB Assaf, respectively. For singles, twins, triplets, quadruplets and quintuplets, lamb survival rate at birth was 0.98, 0.92, 0.86, 0.78 and 0.65, respectively. FecB genotype-litter size interactions were not significant (P<0.05). A compilation of study results in which prolificacy of the ++ and B+ genotypes at the FecB locus were investigated in a range of breed-environment combinations revealed that the B allele has a multiplicative effect on prolificacy as B+ prolificacy was significantly (P<0.05) linearly associated with ++ prolificacy.

Carrying the FecB (Booroola) mutation is associated with lower birth weight and slower post-weaning growth rate for lambs, as well as a lighter mature bodyweight for ewes

The present study was conducted in an Assaf flock in which the FecB (Booroola) mutation was segregated to determine whether the FecB mutation affects birthweight and the pre- and post-weaning growth rate of ewe lambs, as well as the mature bodyweight of ewes. Significant differences (P = 0.01) in birthweight (mean ± s.e.m.) were found between BB ewe lambs (4.03 ± 0.08 kg) and B+ and ++ ewe lambs (4.16 ± 0.04 and 4.32 ± 0.07 kg, respectively), which themselves did not differ significantly (P > 0.05). An FecB-associated maternal effect on the birthweight of ewe lambs was also detected, with the birthweight of lambs born to BB mothers (3.93 ± 0.08 kg) being significantly (P < 0.0001) different from the birthweight of lambs born to B+ and ++ mothers (4.26 ± 0.04 and 4.33 ± 0.07 kg, respectively), which did not differ significantly. The genotypes of the lambs did not affect their preweaning growth rate. However, the post-weaning growth rate of ewe BB lambs (274 ± 5 g day−1) was significantly (P = 0.05) different from the similar (P > 0.05) post-weaning growth rates of B+ and ++ lambs (284 ± 3 and 290 ± 4 g day−1, respectively). The genotype at the FecB locus also affected the mature bodyweight of ewes, with that of BB ewes (67.3 ± 1.4 kg) being significantly (P < 0.001) different from the similar mature bodyweight of B+ and ++ ewes (70.8 ± 1.1 and 70.1 ± 1.7 kg, respectively).