Effects of sire genotype on lamb performance at weaning in extensive sheep systems

A low finishing weight and poor carcass characteristics are major causes of lower incomes in extensive sheep flocks; however, the use of terminal sire crossbreeding would improve lamb performance and carcass traits under these conditions. The aim of this study was to evaluate sire breed effects on the performance of lambs born to Corriedale ewes in extensive sheep systems in Western Patagonia. A total of 10 Corriedale, 10 Dorset, nine Suffolk and seven Texel sires, 16 of which were under a genetic recorded scheme and 20 selected from flocks not participating in genetic improvement programmes, were used across six commercial farms for 2 successive years. Data were collected from 685 lambs of the four resulting genotypes. Overall, Corriedale lambs were 0.47 kg lighter at birth than crossbred lambs (P<0.001). Suffolk and Texel sired lambs required more assistance (P<0.01) at birth than Corriedale or Dorset sired lambs, with Suffolk sired lambs requiring the most assistance (8%). Ewes sired with Suffolk rams had larger (P<0.05) litters than ewes sired with Texel or Corriedale rams. Lamb live weight gain from birth to weaning was higher (P<0.001) in crossbred lambs compared with Corriedale lambs, therefore, crossbred lambs averaged 2.9 kg heavier BW (P<0.001) than Corriedale lambs. A significant sire breed x sire source interaction was detected for lamb live weight gain (P<0.05) and lamb live weight at weaning (P<0.01), showing that the heaviest lambs were from recorded sires, except for Suffolk crossbred lambs. Mortality rate to weaning was increased (P<0.05) in Suffolk cross lambs (31%), with Corriedale lambs showing the lowest (17%) mortality. Terminal sire breeds increased (P<0.001) cold carcass weight, with 13.8, 16.0, 15.2 and 14.9 kg for the Corriedale, Dorset, Suffolk and Texel sired lambs, respectively. Carcass length, kidney knob and channel fat, fat grade, grade rule and fat depth measurements were not affected by sire breed (P>0.05). Carcass conformation was higher in Texel sired lambs compared with Corriedale lambs (P<0.05), with Dorset and Suffolk sired lambs being intermediate. Crossbred lambs showed a greater (P<0.001) eye muscle than Corriedale. Commercial cuts were affected by sire breed, as a result of the Corriedale lambs being smaller and having lighter carcass than crossbred lambs. Significant improvement in lamb weights at weaning and carcass traits could be expected when using a terminal sire on Corriedale ewes in Western Patagonia. However, no advantages were detected with the use of recorded sires under these production systems.     

Transferrin types and reproduction in sheep

Transferrin types were determined for flocks of Finnish Landrace, Clun Forest, Soay and Merino sheep and gene frequencies were calculated. Analysis of ratios of transferrin types in segregating matings of Finnish Landrace and Clun Forest revealed a significant excess of heterozygotes in matings of heterozygous rams with heterozygous and with homozygous ewes. In Finnish Landrace, matings of sheep homozygous for Tf ^c to those heterozygous for Tf ^C gave a significant excess of homozygous male lambs and heterozygous female lambs. Finnish Landrace ewes of transferrin type BD had smaller litters than ewes of other types.     

Causes of lamb mortality in two highly prolific Booroola crossbred flocks and a Romney flock

The causes of lamb mortality in two highly prolific flocks (mean litter size 1.83–2.45) and a flock of medium prolificacy (litter size 1.4) were determined by autopsy. Causes of death were categorised into six major groups (prenatal, dystocia, prolonged birth, starvation, starvation/CNS, others) and the effects of year, ewe age, and litter size on the distribution of mortality between these groups were examined. Year and litter size effects were large, with ewe age effects relatively small.Dystocia was the dominant cause of death for single lambs (2.5–15.9% of lambs born) while for large litters “prenatal” and “prolonged birth” categories were of increasing importance with increased litter size (6.9–26.1% of lambs born). “Starvation” contributed a smaller proportion of deaths than previously reported for less prolific flocks.     

Familiarity breeds progeny: sociality increases reproductive success in adult male ring-tailed coatis (Nasua nasua)

The ring-tailed coati (Nasua nasua) is the only coati species in which social groups contain an adult male year round, although most males live solitarily. We compared reproductive success of group living and solitary adult male coatis to determine the degree to which sociality affects reproductive success. Coati mating is highly seasonal and groups of female coatis come into oestrus during the same 1-2 week period. During the mating season, solitary adult males followed groups and fought with the group living male. This aggression was presumably to gain access to receptive females. We expected that high reproductive synchrony would make it difficult or impossible for the one group living male to monopolize and defend the group of oestrous females. However, we found that group living males sired between 67-91% of the offspring in their groups. This reproductive monopolization is much higher than other species of mammals with comparably short mating seasons. Clearly, living in a group greatly enhanced a male's reproductive success. At the same time, at least 50% of coati litters contained offspring sired by extra-group males (usually only one offspring per litter); thus, resident males could not prevent extra-group matings. The resident male's reproductive advantage may reflect female preference for a resident male strong enough to fend off competing males.     

Who's your daddy? Paternity testing reveals promiscuity and multiple paternity in the carnivorous marsupial Dasyurus maculatus (Marsupialia: Dasyuridae)

Female promiscuity is common among mammals but its advantages, particularly for marsupials, remain unclear. Using microsatellite DNA from pouch young of known mothers, we identified the most likely fathers of 25 wild spotted-tailed quolls ( Dasyurus maculatus ) from six litters. We aimed to determine whether young within the same litter had different fathers, and whether breeding success of males was associated with large body mass (consistent with inter-male competition) or scrotal width (consistent with sperm competition). We also explored the possible influence of promiscuity on relatedness within litters. Finally, we used data on paternity and relatedness to make inferences regarding movement and dispersal.
Four litters were sired by more than one male, and three males sired offspring in more than one litter. Known fathers had higher body mass, but not scrotal width, than males of unknown paternity status, suggesting that males may compete for access to females. Sires were less related to dams than expected by chance, and litters with multiple paternity had lower relatedness than litters sired by a single male.  © 2009 The Linnean Society of London, Biological Journal of the Linnean Society , 2009, 96 , 1–7.     

Age-dependent sexual selection in bighorn rams.

Although mating systems and sexual selection have been intensively studied in ungulate model systems, very few studies have combined genetic paternity analysis with individual phenotypic data over several breeding seasons. We used microsatellite paternity analysis to determine the parentage of 83 bighorn sheep (Ovis canadensis) born between 1995 and 2000 at Ram Mountain, Alberta, Canada. We could assign the paternity of 64 lambs at a high level of statistical confidence (95%). Within each season, the most successful ram sired an average of 35.5% of the lambs with assigned paternity, and a single ram sired 26.1% of all lambs over the six mating seasons. Although a few large-horned, mature (age 8+ years) rams had very high reproductive success, younger rams sired ca. 50% of the lambs. Mixed-effects models indicated that mating success increases as a nonlinear function of age, with horn length increasingly positive in correlation with mating success in older rams. These results indicate that young or small rams possibly achieve mating success through alternative mating tactics that are less dependent on body and weapon size, such as coursing and blocking. Sexual selection is therefore likely to have age-dependent effects on traits such as agility, body and horn size.     

Heritability of ram mating success in multi-sire breeding situations

Multi-sire mating of a mob of ewes is commonly used in commercial sheep production systems. However, ram mating success (defined as the number of lambs sired by an individual) can vary between rams in the mating group. If this trait was repeatable and heritable, selection of rams capable of siring larger numbers of lambs could reduce the number of rams required for mating and ultimately lead to increased genetic gain. However, genetic correlations with other productive traits, such as growth and female fertility, could influence the potential for ram mating success to be used as a selection trait. In order to investigate this trait, parentage records (including accuracy of sire assignment) from 15 commercial ram breeding flocks of various breeds were utilised to examine the repeatability and heritability of ram mating success in multi-sire mating groups. In addition, genetic and phenotypic correlations with growth and female fertility traits were estimated using ASReml. The final model used for the ram mating success traits included age of the ram and mating group as fixed effects. Older rams (3+years old) had 15% to 20% greater mating success than younger rams (1 or 2 years of age). Increasing the stringency of the criteria for inclusion of both an individual lamb, based on accuracy of sire assignment, or a whole mating group, based on how many lambs had an assigned sire, increased repeatability and heritability estimates of the ram mating success traits examined. With the most stringent criteria employed, where assignment of sire accuracy was >0.95 and the total number of lambs in the progeny group that failed to have a sire assigned was<0.05, repeatability and heritability for log_e(number of lambs) was 0.40±0.09 and 0.26±0.12, respectively. For proportion of lambs sired, repeatability and heritability were both 0.30±0.09. The two ram mating traits (log_e(nlamb) and proportion) were highly correlated, both phenotypically and genetically (0.88±0.01 and 0.94±0.06, respectively). Both phenotypic and genetic correlations between ram mating success and growth and other female fertility traits were low and non-significant. In conclusion, there is scope to select rams capable of producing high numbers of progeny and thus increase selection pressure on rams to increase genetic gain.     

Genetic polyandry and sexual conflict in the sandbar shark, Carcharhinus plumbeus, in the western North Atlantic and Gulf of Mexico

To investigate patterns of polyandry in the sandbar shark (Carcharhinus plumbeus), 20 pregnant females were sampled from the western North Atlantic and Gulf of Mexico. Five species-specific microsatellite markers were used to genotype each shark and its litter. Of 20 litters, 17 (85%) were shown to have multiple sires. In multiply sired litters, the estimated minimum number of sires ranged from two to five with an average of 2.3 males per litter. Regression analysis did not demonstrate a significant relationship between female reproductive success and female body size or sire number and female body size. There was a high incidence of reproductive skew noted in litters, and two groups of males with significantly different mean reproductive success were observed. Analyses using Bateman's principles suggest that there is less direct benefit for females that acquire multiple mates than for males who bias paternity within litters. In light of past morphological and behavioural studies, these data suggest that patterns of polyandry in elasmobranchs may be determined by coercive mating, and that breeding behaviour has likely evolved in the context of sexual conflict.     

Bio-economic modelling of sheep meat production systems with varying flock litter size using field data

Sheep meat producers derive the majority of income from sales of weaned lambs, determined by flock conception rates, litter size, and lamb survival. Field data from commercial flocks can inform sensitivity analyses of the effect of litter size on flock productivity, feed demand, and gross margin. This study adapted an established bio-economic model of a flock of breeding ewes informed by statistical relationships (from linear models) between flock litter size (lambs born per ewe lambing) and production factors (such as flock barren rate, litter birth type and lamb birth weight) identified using 156 145 animal records from the Irish national sheep breeding database. Sensitivity analyses were undertaken to investigate the effects of flock litter size on flock production, feed demand, and gross margin. Results showed that as flock litter size increased, the proportion of lambs born as multiples increased, with 14 % of lambs born as singles when flock litter size was 2.2 lambs born per ewe lambing. Flock gross margin increased from €2 205 to €7 730 as litter size increased from 1.0 to 2.0 lambs born per ewe lambing. As litter size increased from 1.0 to 2.2 lambs born per ewe lambing, flock gross margin increased linearly by, on average, €52 per 0.01 increase in litter size. At a litter size of > 2.2 lambs born per ewe lambing, flock gross margin increased on average €12 per 0.01 increase in litter size. At a litter size of 2.2 lambs born per ewe lambing, flock efficiency (at 65.0 kg of lamb weaned per ewe presented for breeding), weaning rate (at 1.5 lambs weaned per ewe presented for breeding; not including excess lambs from large litters sold within a week after birth and thus not weaned on-farm), and gross margin (at €8 500) began to plateau. The results indicate lower marginal returns in gross margin at very high flock litter size, due to the lower value of additional lambs born as triplets and quadruplets compared with single- and twin-born lambs. However, the diminishing economic returns occurred at higher flock litter size than are currently biologically achieved in most flocks. Quantification from this analysis demonstrates how the value of increasing the number of lambs born changes at very high flock litter size, which can inform the priorities and performance benchmarking for international sheep meat production industries.     

Artificial selection of rams for sexual performance and its effect on the sexual behavior and fecundity of male and female progeny

The objective of this study was to determine the effect of a single generation of artificial selection for sexual performance in rams on the sexual behavior and fecundity of their male and female progeny. Ninety-two ram lambs born to sires selected for either high or low sexual performance were evaluated for their sexual behaviors at approximately 8 months of age when individually exposed to four estrous ewes for 30min in four weekly serving capacity tests. Number of mounts and successful matings (ejaculations) were recorded. Fourteen of the 17 high-performing ram lambs identified were sired by high-performing sires, whereas 22 of 37 low-performing ram lambs were sired by low-performing sires (P<0.01). Sons of high-performing sires exhibited more ejaculations (P<0.04) and more mounts without ejaculation (P<0.02) than sons of low-performing sires. The two groups of ram lambs did not differ in mating efficiency (ratio of ejaculations to total mounts). Daughters of high-performing rams (N=79) exhibited their first behavioral estrus approximately 8 days earlier than daughters (N=61) of low-performing sires (P<0.005). Ovulation rates for the two groups of ewe lambs did not differ (P=0.55). It was concluded that there was sufficient genetic variation in the population of sheep studied to obtain a significant response to selection for ram sexual performance in both male and female offspring in a single generation.     

Ovarian follicles of new-born Merino lambs from genetic lines which differ in fecundity

Ovaries were obtained from 78 new-born lambs (12 singletons, 25 twins, 28 triplets, 10 quadruplets and 3 quintuplets) from flocks selected for (T902, T903 and Booroola) or against (O) multiple births. Sections of the ovaries were examined with a projection microscope and the numbers of all types of follicles were estimated. There were no differences between genetic lines in the number of primordial follicles, after adjustment for litter size and sire; however, there were significantly more of these follicles in single-born lambs than in lambs born in litters of two or more within genetic lines. The number of vesicular follicles was lower in Booroola than in O lambs.     

Hierarchical polygyny in multiparous lesser flat-headed bats

How males gain access to mates and the potential for female choice will determine whether polygyny can operate at several levels, from within litters and groups to the wider population. Female lesser flat-headed bats (Tylonycteris pachypus) form maternity groups in bamboo stems. Unusually for bats, they are multiparous, providing the opportunity to test whether multi-level polygyny differs among males depending on whether they roost with females, with males or are solitary. We genotyped 662 individuals from 54 internodes and analysed parentage of 165 litters. Our results revealed 170 sets of paternal twins/triplets, of which 96 were full-sibs and 74 were half-sibs. We found that males captured roosting with females typically sired more offspring overall than did other males and also showed a greater tendency to monopolize paternity within both litters and roosting groups. In comparison, males that sired fewer full-sibs were assigned more maternal half-sibs. These latter individuals, which included solitary males and those from all-male groups, might gain copulations either via roaming with furtive mating or during visits by females. Indeed, female lesser flat-headed bats store sperm, so could benefit from multiple mating to reduce genetic incompatibilities. At the same time, however, we found no evidence of outbreeding. Finally, relatedness and mtDNA analyses revealed that polygyny also operated within matrilineal kin, suggesting a system that might promote social cohesiveness. Future studies of individual movements will help to determine the extent to which mixed paternities in litters, matrilines and groups are driven by male or female behaviour.     

Screening for polymorphism at the prion protein (PrP) locus (PRNP) in Awassi and Assaf populations in Israel, the Palestinian Authority and Jordan

Screening for polymorphism at the prion protein (PrP) locus (PRNP) was carried out in 33 flocks of Local Awassi (LA) sheep in Israel, the Palestinian Authority (PA) and Jordan. In addition, PRNP genotyping was carried out in two flocks of Improved Awassi (IA) in Israel and the PA and in 11 flocks of Assaf sheep in Israel. Most of the rams present in the flocks at the time of the survey 328, 44 and 298 rams from the LA, IA and Assaf breeds, respectively, were genotyped. The ARQ allele was found to be predominant in all three breeds with average frequencies of 0.74, 0.78 and 0.86 for the LA, IA and Assaf breeds, respectively. Frequencies of the desirable ARR allele in these breeds were 0.10, 0.05 and 0.06, respectively. ARH, AHQ and ARK alleles were identified at low/absent frequencies. Only one Assaf ewe carried the undesirable V allele at codon 136. A few scrapie outbreaks have been documented in the past in the region. To increase ARR allele frequencies in the Awassi and Assaf populations, distribution of homozygous ARR/ARR rams is recommended.     

Efficiency of selection for body weight in a cooperative village breeding program of Menz sheep under smallholder farming system

We evaluated the efficiency of selection for body weight in a cooperative village breeding program for Menz sheep of Ethiopia under smallholder farming system. The design of the program involved organizing villagers in a cooperative breeding group to implement selective breeding of their sheep. The program was jump-started through a one-time provision of elite rams from a central nucleus flock, but subsequent replacement rams were selected from within the village flocks. We also evaluated body weight trends in a village where cooperative breeding was not implemented and individual farmers managed their flocks under traditional breeding practices. Under traditional breeding practices, genetic progress over 8 years either stagnated or declined in all the weights recorded. In the cooperative villages, selection differentials of 2.44 and 2.45 kg were achieved in 2010 and 2011 selection seasons, respectively. Birth weight, 3-month weight and 6-month weight increased, respectively, by 0.49, 2.29 and 2.46 kg in the third-generation lambs over the base generation. Improved rams supplied from the central nucleus flock gave an initial genetic lift of 14.4% in the 6-month weight. This was higher than the gain achieved from selection in the village flocks, which was 5.2%. Our results showed that village-based genetic improvement in body weights under smallholder conditions could be feasible if appropriate designs are adopted and that commencing with elite central nucleus rams help jump-start village-based programs.     

Modelling sub-binomial variation in the frequency of sex combinations in litters of pigs

In some samples of pig litters, the number of males per litter exhibits significant sub-binomial dispersion: there are fewer unisexual and more "sex-balanced" litters than expected under a binomial model. It is argued here that the explanation is that the sex of zygotes may be subject to hormonal control with the consequence that, within a litter, the zygotes do not all have the same probability of being male. This variation in probability is approximated by a quadratic function of the time during oestrus that a zygote is formed so as to parallel the variation in maternal hormone levels. Other explanations are examined briefly, but each seems to have serious weaknesses.     

Relatedness Does not Affect Competitive Behavior of Rival Males or Offspring Growth in Multiply Sired Litters of Bank Voles (Myodes glareolus)

Kin selection operates through the fitness of an organism's relatives. In the polyandry context, kin selection may be observable on the one hand in competition between rival males and, on the other hand, in competition between litter mates. Sperm competition theory predicts that males should invest less into mating when competing for fertilizations against a close relative as compared to an unrelated male. We tested this hypothesis with bank voles (Myodes glareolus) by mating each focal male to two females: one of which had previously mated with a full sibling of the focal male and the other one with a male unrelated to the focal male. However, we found no effect of rival male relatedness on mating behavior or proportion of offspring sired by the 2nd male to mate. Possibly, the probability of successive mating of related males with the same female is too low in natural bank vole populations for selection to have fine‐tuned mating behavior in relation to rival male relatedness. Further, polyandry often results in litters sired by multiple males. Litter mates of such litters have a reduced relatedness and are thus expected to be less cooperative during gestation and lactation, which may impair growth. Following double matings with either two full‐sibling males or two unrelated males, we compared offspring growth at birth and during lactation. Against our prediction, there was no difference in growth between litters sired either by two full‐sibling males or by two unrelated males. Either the conflict was not severe enough to be visible with our sample size (N = 16) or it may have been resolved by maternal control of offspring provisioning.     

Multiple paternity in free-living root voles (Microtus oeconomus)

We used 10 microsatellite loci to determine the mating system and male reproductive success in a natural population of the root vole (Microtus oeconomus). By genotyping 21 females and their 111 offspring (5.28 ± 0.27 S.E. pups per female), we found evidence for multiple paternity in 38% of the litters sired by two or three males. Paternity was not significantly skewed away from the null expectation of equal proportions of offspring sired in any of the multiple-sired litters, and the most successful male fathered between 40% and 60% of the pups in a litter. The results indicate that promiscuity is a common mode of reproduction, consistent with the previous classification of the mating system based on the spatial structure of the root vole population.     

A genetic assessment of polyandry and breeding-site fidelity in lemon sharks

We here employ 11 microsatellite markers and recently developed litter reconstruction methods to infer mating system parameters (i.e. polyandry and breeding-site fidelity) at a lemon shark nursery site in Marquesas Key, Florida. Four hundred and eight juvenile or subadult sharks were genotyped over eight complete breeding seasons. Using this information, we were able to infer family structure, as well as fully or partially reconstruct genotypes of 46 mothers and 163 fathers. Multiple litter reconstruction methods were used, and novel simulations helped define apparent bias and precision of at least some mating system parameters. For Marquesas Key, we find that adult female lemon sharks display high levels of polyandry (81% of all litters sampled) and stronger fidelity to the nursery site than do males. Indeed, few male sharks sired offspring from more than one litter during the course of the study. These findings were quite similar to previous results from another lemon shark nursery site (Bimini, Bahamas), suggesting conserved mating system parameters despite significant variation in early life-history traits (i.e. body size and growth) among sites. The finding of at least some site fidelity in females also supports the need for careful conservation of each nursery.     

The effect of scrotal circumference, sperm motility and morphology in the ram on conception rates and lambing percentage in the ewe

Ten Suffolk and ten Lincoln yearling rams were examined for breeding soundness. Semen was evaluated, and the scrotal circumference measured. They were single-sire mated to ten to twelve, whiteface ewe lambs during a 45-day breeding season (October 15 - December 1). First-service conception rates, total conception rate, lambing percentage and lambing percentage per ewe exposed were calculated for each ram and breed. The mean scrotal circumference was 36.5 cm (range 31 - 41.5 cm). The breeding data was then compared for eleven rams with a scrotal circumference of less than 36.5 cm and nine rams greater than 36.5 cm. No direct relationship was demonstrated between scrotal circumference, sperm motility or morphology with fertility in the rams used in this experiment. However, there was a tendency for rams with a high first-service conception rate to have sired more lambs per ewe exposed. The mean first-service conception rate was 63.2% (range 44.4 - 80.0%). When rams with greater than 63.2% first-service conception rate were compared to those with less than 63.2%. the lambs born per ewe exposed were 1.04 and .89, respectively, a significant difference (P<.05). There were no significant differences (P<.05) in performance between the two groups when rams with a scrotal circumference less than 36.5 cm and greater than 36.5 cm were compared, nor were there any differences between scrotal circumference, sperm motility, and morphology when rams with total conception rates greater than 80% were compared to those with conception rates less than 80%.