Congruence between selection on breeding values and farmers' selection criteria in sheep breeding under conventional nucleus breeding schemes

Designing breeding schemes suitable for smallholder livestock production systems in developing regions has hitherto been a challenge. The suggested schemes either do not address farmers' breeding goals (centralized station-based nucleus schemes) or yield slow genetic progress (village-based schemes). A new breeding scheme that integrates the merits of previously suggested schemes has been designed for Menz sheep improvement in Ethiopia. It involves selection based on breeding values in nucleus flocks to produce elite rams, a one-time only provision of improved rams to villagers and a follow-up village-based selection to sustain genetic progress in village flocks. Here, we assessed whether conventional selection of breeding rams based on breeding values for production traits, which is the practice in station-based nucleus flocks, meets farmers' breeding objectives. We also elicited determinants of farmers' ram choice. Low but significant correlations were found between rankings of rams based on farmers' selection criteria, estimated breeding values (EBV) and body weight (BW). Appearance traits (such as color and horn) and meat production traits (BW and linear size traits) significantly determined farmers' breeding ram choice. The results imply that conventional selection criteria based solely on EBV for production traits do not address farmers' trait preferences fully, but only partially. Thus, a two-stage selection procedure involving selection on breeding values in nucleus centers followed by farmers' selection among top- ranking candidate rams is recommended. This approach accommodates farmers' preferences and speeds up genetic progress in village-based selection. The Menz sheep scheme could be applied elsewhere with similar situations to transform conventional station-based nucleus breeding activities into participatory breeding programs.     

A note on the effect of vasectomised rams and short-term exposures to entire rams prior to the breeding period on the reproductive performance of ewe lambs

The aim of this study was to determine the effects of either a 17-day exposure to vasectomised rams or a short-term exposure to entire rams on ewe lamb reproductive performance. Seven hundred and twenty-one Romney ewe lambs, 7–9 months of age, were randomly assigned to one of four treatment groups. Treatments included exposure to vasectomised rams for 17 days prior to breeding, exposure to entire rams for 4 or 2 days prior to breeding or not being exposed to either vasectomised or entire rams. Unteased ewe lambs and those exposed to entire rams for either 2 and 4 days were less (P < 0.05) likely to be mated in the first 17 days of breeding only and pregnant in the first 17 days of breeding compared to ewe lambs exposed to vasectomised rams for a full 17 days pre-breeding. Ewe lambs exposed to entire rams for 2 days were more (P < 0.05) likely to be mated in the first 8 days of breeding, mated in the first 17 days of breeding only and pregnant in the first 17 days of breeding compared to unteased ewe lambs. Therefore, a short-term exposure to entire rams can be used to induce breeding activity in ewe lambs, although it is not as effective as a full 17-day exposure to vasectomised rams.     

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.     

The relationship of libido and serving capacity test scores in rams on conception rates and lambing percentage in the ewe

A procedure for assessing sexual activity (libido) and serving capacity (number of ejaculations) in individual rams is described. Libido and serving capacity was measured by this procedure in 10 Lincoln, 10 Suffolk, 2 Columbia, and 2 Polypay rams prior to the breeding season. Semen was evaluated, and the scrotal circumference measured. The rams were single-sire mated to 10-12 whiteface, crossbred ewes during a 35-day breeding season (September 26 - October 29). First-service conception rates, total conception rate, lambing percentage per ewe lambing, and lambing percentage per ewe exposed were calculated for each ram. The mean libido score for the 24 rams was 8.95 and the mean serving capacity score was 3.16. The 24 rams were classified as low serving capacity (<2 ejaculation), medium serving capacity (2-3 ejaculations), or high serving capacity (>3 ejaculations). There were no significant differences in either conception rate or lambing percentages between the 3 groups of rams. The first-service conception rate, total conception rate, lambing percentage per ewe lambing, and lambing percentage per ewe exposed were 74.8, 93.8, 148.6, and 139.4 percent, respectively, for the 24 rams. Libido and serving capacity tests in the rams, as used in this experiment, prior to the breeding season, were not successful in predicting fertility or prolificacy in ewes.     

A note on ram preference by oestrous ewes: Influence of rams’ age and sexual performance

Ewes in oestrus, besides being receptive to rams, develop an active search for them. We performed two experiments to determine if oestrous ewes prefer: (1) high or low sexual-performance rams, and (2) 2-year-old or aged (>8-years-old) rams. In the first experiment, the preference of ewes for rams with high or low sexual performances was compared in 16 tests. In the second experiment, 17 tests were performed comparing ewes’ preference for aged rams (>8-years-old) or young rams (2-years-old). In each test, two rams were tied at equal distances from the point of entrance of the ewe, with a maximum mobility for each ram of 2 m. The first approach to a ram, the quantity of approaches toward each ram (less than one body length), and the total time that the ewe remained near each ram were registered during 5 min. Oestrous ewes did not display any preference according to sexual performance of rams, but spent significantly more time (P = 0.02), and did it in more tests (P = 0.025), with young than with aged rams. Ewes also tended to approach first (P = 0.07), and more times in more tests (P = 0.06), to young than to aged rams. We conclude that ram's sexual performance seems not to influence oestrous ewes preference, and that ewes’ prefer young (2-years-old) rather than aged rams (>8-years-old).     

The influence of breeding intensity on above- and below-average sexual performance rams in single- and multiple-sire breeding environments

Two studies were conducted to evaluate the relationship between serving capacity scores and breeding performance of rams. The first study was conducted to determine whether rams with above or below mean serving capacity scores could perform equally in greater and lesser breeding intensity, single-sire mating schemes. The second study was conducted to determine whether rams with above and below mean serving capacity scores could perform equally well when only one or two ewes were in estrus daily in a multiple-sire breeding scheme (two rams/pen). Rams (n=68) were ranked according to average number of ejaculations recorded in serving capacity tests. Sixteen rams with the greatest scores (above-average) and 16 rams with least scores (below-average) were identified for breeding. Half of above-average and half of below-average rams were used in the two studies. For study 1, each ram was individually introduced to 23 estrus-synchronized ewes for 9 d to simulate high breeding intensity. Rams were given a 5-d rest before they were individually introduced to 23-24 naturally cyclic ewes for 17 d (low breeding intensity). For study 2, 16 rams were paired across ram types, and each pair competed for 20 ewes for 18 d (8 pens). For study 1, ewe fertility (ewes lambing/ewes present at lambing) and number of lambs born were greater (P<0.001) for above-average (0.67+/-0.03 and 27.6+/-1.2, respectively) than for below-average rams (0.39+/-0.07 and 15.3+/-2.7) with greater breeding intensity. Ewe fertility and lambs born did not differ for above-average (0.91+/-0.03 and 37.8+/-1.9, respectively) and below-average rams (0.86+/-0.03 and 39.0+/-1.9) with less breeding intensity. For study 2, number of ewes lambing (99+/-8.0 compared with 72+/-13.6; P=0.12) and number of lambs sired (149+/-18.5 compared with 101+/-22.8; P=0.14) did not differ between above- and below-average rams, respectively, in direct competition. Sexual classifications based on serving capacity tests are related to breeding performance of rams in certain breeding environments. When breeding intensity is greater, above-average rams impregnate more ewes and sire more lambs than below-average rams. When only a small number of ewes are in estrus daily, below-average rams for serving capacity scores perform as well as above-average rams in multiple-sire and single-sire breeding environments. We suggest that above-average rams should be used to reduce number of rams required when breeding intensity is greater.     

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%.     

Direct responses in males and correlated responses for reproduction in females to selection for testicular size adjusted for body weight in young male lambs

Selection based upon testicular diameter adjusted for body weight at 6, 10 and 14 weeks of age was used to produce two lines of sheep, with either high or low testicular size. Ten generations of selection were carried out and the estimate of the realized heritability of the selection criterion was 0.53 +/- 0.01. There were significant positive correlated responses to selection for testicular diameter at 6, 10 and 14 weeks of age, but the correlated responses in body weight at these ages were negative. In mature females, there were significant negative correlated responses to selection in premating body weight in the 1st, 2nd and 3rd breeding season and in the day of the first oestrus in the 2nd breeding season. Litter size per ewe mated had a small positive correlated response to selection in the second breeding season. This latter response appeared to be due to a positive correlated response in fertility, ewes from the High-line having a significantly higher probability of conceiving to a single mating than those from the Low-line. There was no significant correlated response in ovulation rate or litter size per ewe lambing and the genetic correlation between these traits and the selection criterion is likely to be close to zero. This may be due to the adjustment for body weight used, but it is possible that, in any event, body weight in young rams may be a better predictor of female ovulation rate than testicular diameter. These results do not rule out the possibility that testicular size in rams older than those selected would provide a good predictor of genetic merit for female ovulation rate.     

Fertility in the ewe following cervical insemination with fresh or frozen-thawed semen at a natural or synchronised oestrus

Artificial insemination (AI) in sheep is currently limited by the poor fertility obtained following non-surgical intracervical insemination of frozen-thawed semen. An exception to this general finding is the non-return rate of around 58% reported for large scale on-farm AI in Norway. The objective of the present study was to determine if similar results could be obtained under Irish conditions. Comparisons were made between semen collected, and frozen, from rams in Norway (NOR) and Ireland (IRL). The effects of synchronisation and inseminator were also examined. Parous ewes (n=297) of various breed types were inseminated to a natural (N) or synchronised (S) oestrus with either fresh (from Irish rams) or frozen-thawed (IRL and NOR) semen. Ewes were randomly assigned, within breed, to the following treatment groups: (i) Fresh-N: n=28, (ii) Fresh-S: n=30, (iii) IRL-N: n=62, (iv) IRL-S: n=50, (v) NOR-N: n=68, (vi) NOR-S: n=59. Within each group, ewes were inseminated by an experienced Norwegian or by an Irish inseminator. Pregnancy rate did not differ significantly between ewes inseminated to a natural or synchronised oestrus nor between Norwegian and Irish frozen semen. The proportion of ewes pregnant after insemination with fresh semen was 0.82 and 0.70 (treatments i and ii) compared with 0.40, 0.52, 0.34 and 0.37 (treatments (iii)-(vi)) for frozen semen (P<0.001). Corresponding litter sizes (+/-S.E.), adjusted for ovulation rate, were 2.9+/-0.22, 3.3+/-0.23, 2.2+/-0.21, 1.7+/-0.21, 2.2+/-0.21 and 2.1+/-0.21 (fresh versus frozen; P<0.001). There was an interaction between semen type (fresh or frozen) and oestrus type (N or S) for litter size due to an increased adverse effect of frozen semen on litter size in synchronised ewes (P<0.05). Pregnancy rate was significantly influenced by breed of ewe (P<0.01) and inseminator (P<0.05). These results suggest that ewe breed may be a critical determinant of the potential for the exploitation of cervical insemination of frozen-thawed semen in sheep breeding programmes.     

Comparison of oestrous synchronization regimens for lactating dairy cows.

The objective of this experiment was to evaluate various programmes for synchronization of oestrus. The focus of the study was to evaluate rates of detection of oestrus, synchrony of oestrus, pregnancy rate, and effect of ovarian status at initiation of the programmes on rates of detection of oestrus and pregnancy rate. Spring-calving, lactating dairy cows (n = 2009) were allocated at random to one of six treatments: (1) A (n = 335), progestogen (controlled intravaginal drug release; CIDR) inserted per vaginum 10 d before breeding season for 8 d, 10 microg of buserelin at CIDR insertion, PGF2alpha treatment on the day prior to CIDR removal, and AI of cows detected in oestrus within 6 d after CIDR withdrawal; (2) B (n = 330), as in A, plus 1 mg of oestradiol benzoate i.m. 10 h post CIDR withdrawal; (3) C (n = 347), as in A, except buserelin was replaced by 10 mg of oestradiol benzoate; (4) D (n = 335), as in A, plus PGF2alpha and oestradiol benzoate at CIDR insertion; (5) E (n = 332), CIDR containing a 10 mg oestradiol benzoate capsule inserted per vaginum for 12 d; or (6) F (n = 330), as in E, plus PGF2alpha on the day prior to CIDR withdrawal. The oestrous detection rate (number of cows detected in oestrus within 6 days of CIDR withdrawal as a proportion of the number of cows submitted for synchronization of oestrus) and oestrous synchrony (oestrous detection rate within 2 d of CIDR withdrawal), respectively, were greater (P<0.05) following B (95.7% of 330, 98.7% of 316) compared with any of the other programmes for synchronization of oestrus (A: 87.5 of 335, 79.4% of 293; C: 86.7% of 347, 80.0% of 301; D: 90.1% of 335, 89.8% of 302; E: 74.4% of 332, 70.4% of 247; F: 76.4% of 330, 78.5% of 252). The oestrous detection rate was reduced (P<0.05) among cows in metoestrus administered E (64.0% of 50) relative to similar cows administered F (82.8% of 64). Pregnancy rate was greater (P<0.05) following B (57.9% of 330) than A (48.9% of 335, P = 0.06), C (43.2% of 347), E (40.0% of 332), and F (35.1% of 330) but not D (59.3% of 302), when based on those cows presented for oestrous synchronization programmes. In conclusion, 1 mg of oestradiol benzoate administered 10 h post CIDR withdrawal (B) resulted in the best overall oestrous detection, oestrous synchrony, and pregnancy rates, which would be beneficial to a fixed-time AI program.     

Effect of oestrus synchronization methods on oestrus behaviour, timing of ovulation and pregnancy rate during the breeding and low breeding seasons in Nili-Ravi buffaloes

The objective of this study was to determine the effect of oestrous synchronization methods on oestrous behaviour, timing of ovulation and pregnancy rate during the breeding and low breeding seasons in Nili-Ravi buffaloes. In Experiment 1, oestrous behaviour and timing of ovulation were determined from (n=34) oestruses. The mean (+/- S.E.M.) time of ovulation after the onset of standing oestrus was greater (P<0.05) in PGF(2alpha)-induced luteolysis (30.6+/-1.5h) compared to Ovsynch buffaloes (15.0+/-0.8h). In Experiment 2, pregnancy rates were compared between two methods of synchronization (detected oestrus and Ovsynch protocol) during the breeding and low breeding seasons. Pregnancy rates of buffaloes bred at detected oestrus (62.5%) or by the Ovsynch protocol (36.3%) during the breeding season did not differ significantly (P>0.05) from those which were inseminated during the low breeding season (55.5%) and (30.4%), respectively. This study demonstrates clearly that (1) timing of ovulation in Nili-Ravi buffalo is about 30h after the onset of standing oestrus and (2) buffaloes can be successfully synchronized with optimum fertility using either PGF(2alpha) alone (detected oestrus) or using (Ovsynch protocol) during low breeding season, to calve during the period when milk availability is short.     

Oestrous cycle dynamics in peri-pubertal and mature Javanese thin-tail sheep

Duration of oestrus, time of ovulation and hormone profiles for progesterone and LH in prepubertal, pubertal and mature Javanese thin-tail sheep were studied at synchronized oestrus following progestagen-PMSG treatment and at the first natural oestrus after synchronization.The ewe lambs responded to progestagen-PMSG treatment by showing earlier onset of oestrus and an earlier and higher peak of LH concentration than mature ewes. For pre-pubertal, pubertal and mature ewes the mean LH peaks were 49.9, 43.9 and 37.9 ng/ml (P>0.05) at mean intervals of 7.5, 8.4 and 16.5 h (P < 0.05), respectively, after onset of oestrus. Duration of oestrus was 41.2 h in pubertal lambs and averaged 37.5 h in the other two groups (P>0.05). Except in one mature ewe, ovulation occurred between 24 and 36 h after onset of oestrus and the majority ovulated at around the end of oestrus. The corpora lutea developed normally, as indicated by plasma-progesterone changes. The patterns of plasma-progesterone changes were similar in all three groups, though the concentrations were lower in the ewe lambs.At the first natural oestrus after synchronization, mature ewes showed longer (P>0.05) oestrus (31.5 vs. 24.3 h), longer time interval from onset of oestrus to the LH peak (16.0 vs. 12.0 h) and from the LH peak to ovulation (21.0 vs. 19.6 h) than peri-pubertal lambs. Six of eight pre-pubertal lambs did not ovulate at their first natural oestrus, resulting in a conception rate of 11% for that group, while in pubertal lambs and mature ewes conception rates were 70% and 100%, respectively.     

Correlation of flehmen by male sheep with female behaviour and oestrus

Flehmen by rams occurred after the ram sniffed urine voided by the female but each flehmen was very variable in both duration (range 1–34s) and intensity. The duration of each flehmen was not affected by the stage of the oestrous cycle of the female. Flehmen to urine occurred least often in the presence of the oestrous ewe due to the low occurrence of marking behaviour by the female at this time. Flehmen also occurred after the ram investigated the vulva of the ewe but such flehmens were always short (range 1–8 s). Again the duration of each flehmen was not greatly influenced by the reproductive state of the female. Flehmen following investigation of the vulva occurred most frequently on the day before oestrus. These observations support the hypothesis that flehmen by the ram is an olfactory mechanism for confirming the reproductive state of the ewe. The pheromone detected by flehmen appears to be produced in the vagina and carried in the urine.     

Effect of ram exposure at the end of progestagen treatment on estrus synchronisation and fertility during the breeding season in ewes

Two experiments were conducted to examine the effects of ram exposure during the breeding season, in combination with progestagen treatment on estrus synchronization, fertility the LH surge and ovulation in ewes. Experiment 1 was subdivided into experiments 1a and 1b. In all experiments cross-bred ewes were treated with an intravaginal sponge for 12-14 days and three days before sponge withdrawal ewes were divided into control (no further treatment; n=191, 103 and 50 for experiments 1a, 1b and 2, respectively) or ram exposed (three mature rams per 50 ewes were introduced; +Ram; n=187, 99 and 49 for experiments 1a, 1b and 2, respectively). At sponge withdrawal ewes in Experiments 1a and 2 received 500 IU eCG and rams were removed from all the +Ram groups. In Experiments 1a and 1b, raddled, entire rams were introduced to ewes 48 h after sponge withdrawal. The timing of mating was recorded and ewes were maintained until lambing. In Experiment 2, estrus behavior was determined every 4 h and the time of the LH surge and ovulation were determined from a subset of 10 ewes per group. In Experiment 1a, less +Ram ewes were bred by 48 h after ram introduction (control 98% versus +Ram 89%, P<0.001) and in Experiments 1a and 1b 14% fewer (P<0.05) of the ewes bred in the first 3 h after ram introduction lambed to that service. In Experiment 1a, ram exposed ewes had a lower litter size than control ewes (1.93+/-0.06 versus 1.70+/-0.06 lambs per ewe; P<0.05). In Experiment 2, rams advanced (P<0.05) estrus, the LH surge and ovulation by 2-6 h compared with control ewes. We speculate that exposure of ewes to rams increased LH secretion and that this in turn increased follicle development and the production of oestradiol that led to a more rapid onset of estrus, the LH surge and ovulation compared to control ewes. Unexpectedly, ewes that were bred had lower fertility in the +Ram groups than control groups.     

Artificial insemination of ewes with frozen-thawed semen at a synchronized oestrus. 1. Effect of time of onset of oestrus, ovulation and insemination on fertility

In three experiments, the onset of oestrus, time of ovulation and lambing after intrauterine insemination with frozen-thawed semen were examined following synchronisation of oestrus using intravaginal progestagen-impregnated sponges (inserted for 12 days) and an injection of PMSG at sponge removal.

The number (and percentage) of ewes detected in oestrus 12, 24, 36, 48, 60 and 72 h after sponge removal was 1 (0.3), 2 (0.6), 17 (5.2), 120 (36.7), 65 (20.0) and 10 (3.1) respectively. One hundred and twelve ewes (34.3%) remained unmarked. Egg fertilisation rates were not different between ewes irrespective of time of onset of oestrus or whether or not ewes were marked.

The median time of ovulation with respect to sponge removal (with 95% fiducial limits) for ewes joined with vasectomised rams (10:1) at spronge removal (teased ewes) was 55.8 h (54.61–57.09) and for unteased ewes 59.7 h (58.27–61.12).

In the third experiment, a total of 394 ewes were inseminated by laparoscopy with frozen-thawed semen. The percentage of ewes lambing and lambs born per ewe inseminated, and number of lambs born per ewe lambing for inseminations 48, 60, 72 and 78 h after sponge removal were 45.9, 57.7 and 1.25; 55.1, 72.0 and 1.31; 57.4, 80.9 and 1.41; and 39.3, 60.7 and 1.54, and for 59 control ewes receiving fresh semen by cervical insemination 47.5, 69.5 and 1.46 respectively. The lambing data after insemination with frozen semen was not different to that of the controls. The percentage of ewes lambing and lambs born per ewe inseminated increased with time of insemination at 48, 60 and 72 h (linear, P < 0.01) but was lower for inseminations at 78 h after sponge removal. Number of lambs born per ewe lambing increased with time of insemination after sponge removal (linear, P < 0.05).     

The effect of hCG treatment on Day 12 post-mating on ovarian function and reproductive performance of ewes and ewe lambs

The objectives of this study were to determine the effect of a single intramuscular injection of 200 IU hCG (Chorulon) on Day 12 post-mating on ovarian function and subsequent lambing performance in ewes and ewe lambs bred at synchronised oestrus during the breeding season and on the lambing performance of ewes induced to breed during late anoestrus. All animals were mated to rams at synchronised oestrus and on Day 12 post-mating given normal saline or 200 IU hCG.In Experiment 1, laparoscopic results showed that hCG treatment induced accessory corpora lutea in ewes (control = 0/7; hCG = 5/7) but not in ewe lambs (control = 0/7; hCG = 0/7).In Experiment 2, hCG treatment did not improve the lambing rate (control = 50; hCG = 57) or the litter size (control = 1.80; hCG = 1.96) in ewes (control = 100; hCG = 91). However, hCG treatment significantly (P > 0.05) improved the lambing rate (control = 29; hCG = 58; P < 0.05) in ewes conceiving at the first oestrus after treatment. hCG treatment (control = 42; hCG = 42) also failed to improve the lambing rate in ewe lambs (control = 48; hCG = 41).In Experiment 3, hCG treatment had no significant (P > 0.05) effect on the lambing rate (control = 72; hCG = 62) or the litter size (control = 1.59; hCG = 1.58) in ewes (control = 111; hCG = 115) induced to breed during anoestrus or on ewes returning to oestrus and conceiving after treatment (lambing rate: control = 86; hCG = 72; litter size: control = 1.44; hCG = 1.35). In conclusion, the data obtained in this study suggest that during the breeding season hCG may, by stimulating ovarian function, improve embryo survival in ewes conceiving at the first post-treatment oestrus. This effect, however was not observed in ewe lambs.     

Serum follicle stimulating hormone, luteinizing hormone, and testosterone in sexually stimulated intact and unilaterally castrated rams

Ten two-year-old intact (IN) and unilaterally castrated (UC) Targhee rams were exposed to an estrogenized ewe each week from June to October. Each week the rams were subjectively evaluated for libido (10 for high interest and 1 for no interest). Semen was collected from all cooperating rams and evaluated for volume, concentration, and motility. Every 2 wk, blood samples were obtained at -30 and 0 min before and 30 and 60 min after ewe access. Serum was harvested; follicle stimulating hormone (FSH), luteinizing hormone (LH), and testosterone concentrations were quantified by radioimmunoassay (RIA). Week 5 of ewe access was assigned as Week 1. Libido scores rose from a low on Week 1, with eight rams ejaculating, to a high on Week 12, with all rams ejaculating (Week 1, 5.0 +/- 1.0; Week 12, 10.0 +/- 0.0). The product of testis length and width was significantly greater in UC compared with IN rams (88.4 +/- 1.4 versus 73.2 +/- 1.0 cm(2), respectively). Serum FSH concentrations (ng/ml) were greater (P < 0.05) in UC than IN rams and dropped over the experimental period. Serum LH concentrations (ng/ml) were significantly greater in UC compared with IN rams. This difference was more pronounced in Weeks 1 and 3 compared with Weeks 11 and 13. Serum testosterone concentrations (ng/ml) were similar in UC and IN rams throughout the experiment. In conclusion, serum testosterone was not altered in UC rams; however, serum FSH and LH concentrations were increased in UC rams. Unilateral castration did not enhance the normal changes in semen quantity and quality in the rams from July to October.     

The ovariectomized ewe: its contribution to controlled breeding

The ovariectomized ewe has been used to establish principles and procedures which have proved invaluable in controlled breeding in entire animals. Bioassays in the ovariectomized ewe, the end-point of oestrous behaviour, have been used to identify potent and rapidly metabolized progestagens which were subsequently used to control the time of oestrus and ovulation in cyclic ewes effectively, and to induce oestrus and ovulation in anoestrous ewes. Steroid hormone treatment of the ovariectomized ewe has been used to study relationships between the ovary and the pituitary-hypothalamic axis, to examine transport of embryos within the female tract and to establish the steroid hormone requirements of early pregnancy.     

Use of field data in pig genomic selection schemes: a simulation study

The aim of this study was to test how genetic gain for a trait not measured on the nucleus animals could be obtained within a genomic selection pig breeding scheme. Stochastic simulation of a pig breeding program including a breeding nucleus, a multiplier to produce and disseminate semen and a production tier where phenotypes were recorded was performed to test (1) the effect of obtaining phenotypic records from offspring of nucleus animals, (2) the effect of genotyping production animals with records for the purpose of including them in a genomic selection reference population or (3) to combine the two approaches. None of the tested strategies affected genetic gain if the trait under investigation had a low economic value of only 10% of the total breeding goal. When the relative economic weight was increased to 30%, a combination of the methods was most effective. Obtaining records from offspring of already genotyped nucleus animals had more impact on genetic gain than to genotype more distant relatives with phenotypes to update the reference population. When records cannot be obtained from offspring of nucleus animals, genotyping of production animals could be considered for traits with high economic importance.     

Ewe lambs with higher breeding values for growth achieve higher reproductive performance when mated at age 8 months

We studied the relationships among growth, body composition and reproductive performance in ewe lambs with known phenotypic values for depth of eye muscle (EMD) and fat (FAT) and Australian Sheep Breeding Values for post-weaning live weight (PWT) and depth of eye muscle (PEMD) and fat (PFAT). To detect estrus, vasectomized rams were placed with 190 Merino ewe lambs when on average they were 157 days old. The vasectomized rams were replaced with entire rams when the ewe lambs were, on average, 226 days old. Lambs were weighed every week and blood was sampled on four occasions for assay of ghrelin, leptin and ß-hydroxybutyrate. Almost 90% of the lambs attained puberty during the experiment, at an average live weight of 41.4 kg and average age of 197 days. Ewe lambs with higher values for EMD (P < 0.001), FAT (P < 0.01), PWT (P < 0.001), PEMD (P < 0.05) and PFAT (P < 0.05) were more likely to achieve puberty by 251 days of age. Thirty-six percent of the lambs conceived and, at the estimated date of conception, the average live weight was 46.9 ± 0.6 kg and average age was 273 days. Fertility, fecundity and reproductive rate were positively related to PWT (P < 0.05) and thus live weight at the start of mating (P < 0.001). Reproductive performance was not correlated with blood concentrations of ghrelin, leptin or ß-hydroxybutyrate. Many ewe lambs attained puberty, as detected by vasectomized rams, but then failed to become pregnant after mating with entire rams. Nevertheless, we can conclude that in ewe lambs mated at 8 months of age, higher breeding values for growth, muscle and fat are positively correlated with reproductive performance, although the effects of breeding values and responses to live weight are highly variable.