Effects of concurrent lactation and postpartum mating on reproductive performance in mice selected for large litter size

Reproductive and maternal performance of a line of mice selected for large first parity litter size (L+) and a control line (K) were compared under two mating systems: (1) postpartum mating (PP), in which females undergo concurrent gestation and lactation, and (2) postweaning mating (PW), in which females wean their litter before being remated. Females were evaluated in their first two parities. Litters in each line were standardized at birth to 4, 8, 12 or 16 pups in parity 1, and to 10 pups in parity 2. Concurrent gestation had no adverse effect on postnatal maternal performance in parity 1 of either line. In parity 2, both L+ and K declined in reproductive and postnatal maternal performance in PP compared with PW. The pattern of delayed implantation as number of pups nursed increased was similar in both lines under the PP regimen. Several interactions indicated that reproductive performance of L+ was more adversely affected than in K under postpartum mating. Pup mortality was greater in L+ than K under PP but not under PW. In the PP regimen, L+ dams nursing 12 and 16 pups had a lower mating success rate and dams nursing 16 pups had a smaller litter size and higher pup mortality than did K dams. Thus, when L+ dams nurse their natural litter, frequently exceeding 16 pups, their reproductive advantage over K dams observed in PW would be eliminated in PP. If the differences in the first two litters reflect subsequent parities, lifetime reproductive performance in the PP environment would be reduced in the high fecundity line. High fecundity appears to depend upon the environment of selection.     

Ovulation rate and embryo survival during gestation and the effects of ovariectomy on maternal nurturing ability

Correlated responses to selection for increased litter size were studied in mice. The selected line (L+) was compared with an unselected control line (K') in two experiments. The first experiment provided a profile of correlated changes in female reproductive traits at d 0, 6, 14 and 18 of gestation. Experiment two examined the effects of ovariectomy on d 18 of gestation, sham surgery and no surgery on litter size and maternal performance. Females of the L+ line had increased (P less than .001) body weight, ovulation rate and uterine length at d 0 of gestation compared with K' females, but uterine weight and ovarian weight did not differ. Positive correlated responses (P less than .001) in uterine weight and length at d 6 and 14 of gestation were associated with a larger number of viable fetuses. Space per fetus was reduced (P less than .001) in the uterus of L+ females, but a lower fetal mortality was still maintained in L+ throughout gestation. Prenatal survival was about 10% higher (P less than .06) in L+, the major difference (P less than .01) occurring before implantation. A second experiment was conducted to determine the effect of ovariectomy on d 18 on litter size and maternal performance. In experiment two, no significant line X treatment interactions were found for maternal performance, indicating that both lines responded similarly to ovariectomy. Line L+ showed a positive correlated response in maternal performance. Ovariectomized females had a reduced (P less than .05) number born alive compared with sham-operated females, but the nonsurgically treated females were intermediate.(ABSTRACT TRUNCATED AT 250 WORDS)     

Production characters of primiparous females of a five-breed diallel

Data included pubertal, reproductive and lactation records of primiparous females produced in a diallel of Angus, Brahman, Hereford, Holstein and Jersey. Brahman heifers were oldest, tallest and heaviest at puberty, while Jersey heifers were youngest, shortest and lightest. Crossbred heifers were 22 d younger (P less than .01) at puberty than straightbred heifers; no significant differences were detected between the two groups for weight or height at puberty. Dairy heifers (Holstein and Jersey) required fewer services (P less than .05) to conception than beef heifers. The difference between straightbred and crossbred heifers for number of services to conception was small and nonsignificant. Rank of straightbreds for age at conception was similar to their rank for age at puberty except that Holstein required 1.2 fewer services and were younger at conception than Jersey. Crossbreds were 41 d younger (P less than .05) at conception than straightbreds. Brahman had the longest gestation length and were oldest at first calving; Jersey had the shortest gestation length and Holstein were youngest at first calving. Straightbred heifers gestated 1.3 d longer and were 45 d older (P less than .05) at first calving than crossbred heifers. Dairy females had greater peak and total milk yield than beef females (P less than .01). Overall straightbred and crossbred means for peak milk yield and total milk yield did not differ significantly.     

Effects of ovulation rate and fetal number on fertility in twin-producing cattle

Effects of ovulation rate and of fetal number and distribution within the uterus on pregnancy rate and fetal survival were evaluated in nulliparous (n = 1,331) and parous (n = 3,517) cattle selected for twinning. Cattle were divided into a spring (70 d) and fall (60 d) breeding season and bred by a combination of AI and natural service. Ovulation rate, pregnancy status, and fetal number and distribution were determined by transrectal, real-time ultrasonography of the uterus and both ovaries at the end of the breeding season. Pregnancy was reconfirmed by rectal palpation at 75 to 135 d of gestation. For heifers and cows combined, ovulation rate increased (P < 0.01) from 1.46 +/- 0.4 in 1994 to 1.89 +/- 0.4 in 2004; number of calves per parturition increased (P < 0.01) from 1.34 +/- 0.3 to 1.56 +/- 0.3, respectively, which included an increase in triplet and quadruplet ovulations and triplet births. Bilateral twin ovulations yielded proportionately more (P < 0.01) twin births than unilateral twin ovulations. Ovulation rate was greater (P < 0.01) in the fall than spring breeding season. Pregnancy rate at ultrasound diagnosis did not differ among females with 1, 2, or 3 ovulations (89.1 +/- 0.7, 91.2 +/- 0.7, or 91.5 +/- 2.8%, respectively), but rates at calving decreased (P < 0.01) with increasing ovulation rate (85.1 +/- 0.6, 82.7 +/- 0.6, or 64.2 +/- 2.7%, respectively). Pregnancy rate was less (P < 0.01) after twin or triplet births than single births. For dams birthing twins or triplets, pregnancy rate was less in the fall vs. spring, but rates were similar between seasons for dams with a single birth (type of birth x season, P < 0.05). Cows 60 d, regardless of type of birth. Maintenance of pregnancy to term differed (P < 0.01) among females diagnosed with 1, 2, or 3 fetuses (95.7 +/- 0.6, 87.8 +/- 0.8, and 54.9 +/- 2.3%, respectively). The reduced survival of twin and triplet fetuses in heifers had occurred (P < 0.01) by d 75 to 135 of gestation, and fetal losses were greater (P < 0.01) for unilateral than bilateral twins or triplets, whereas loss of twin or triplet fetuses in cows occurred later in gestation, and losses were not affected by uterine location. Thus, increased calf production from selecting for increased ovulation rate in beef cattle is tempered by increased fetal mortality, partially associated with the crowding of 2 or 3 fetuses within 1 uterine horn, especially in heifers.     

Seasonal incidence of estrus and interestrous interval for bitches of seven breeds

For 7 breeds of bitches (Toy Poodle, Cocker Spaniel, Basset Hound, Boston Terrier, German Shepherd Dog, Pekingese, and Beagle), estrous activity occurred in all seasons. Differences in seasonal incidence of estrus were not statistically significant when compared within the total group or within and between breeds. The German Shepherd Dog breed had the shortest interestrous interval (149 +/- 28.5 days), which was significantly different from that of the other breeds. Means interestrous interval in parous Beagle bitches was not significantly different from that in nonparous Beagle bitches. In Beagle bitches, the mean interval between fertile estrous periods was not significantly different from the mean interval between nonfertile estrous periods.     

Observations on the patterns of embryonic mortality over the laying season of pheasants.

1. Embryonic mortality of domestic pheasant (Phasianus colchinus) eggs was recorded for a 10-week laying season for two groups of laying hens maintained under mating ratios of 8:1 and 12:1 (females:males). 2. Mating ratio had no significant effect on embryonic mortality between 1 and 4 or 5 and 20 d but values for these categories doubled as the laying season progressed, both rising to 8% to 9% of fertile eggs. 3. Higher embryonic mortality was observed between 21 and 25 d for the eggs from the 8:1 mating ratio (14.5% of fertile eggs compared with 12.1%) but this was unaffected by week of setting. 4. Reasons for these patterns of embryonic mortality were not clear and further research is needed to determine the factors affecting embryonic mortality in pheasants.     

Der Einfluß der in vitro Spermaaufbewahrung auf die Befruchtung und den Fruchttod beim Kaninchen

Contents: From 7 White Vienna male rabbits semen was collected and stored for 0, 2, 4, 6 and 8 days. One-hundred-forty White Vienna does were inseminated with semen stored at 5° C to test the effects on fertilization rate, embryonic mortality and conception rate. Seven does were removed from the experiment at 48 hr. (embryo stage), 6 days (blastocyst stage), 16 days (fetal stage), and the remaining 7 does were allowed to complete the gestation. This was complete for each semen storage time. Results:

• 1 Conception rate: The embryo stage had 100 percent conception using semen stored for 0 to 6 days. Eight days in storage showed a lower conception rate. The late developmental stages had a lower conception rate resulting from increased embryonic mortality.
• 2 Fertilizability Semen stored for 4 days or longer had a significantly (P < 0,05) reduced ability to fertilize the ova.
• 3 Prenatal mortality, The prenatal mortality was ?55, ?41, ?27, +6, ?18 percent for sperm storage times of 0, 2, 4, 6 and 8 days resp. The mortality up to implantation (6 th day) decreased until to the 4 th day and increased thereafter. The post-implantation mortality increased on the 2nd day of storage and decreased afterwards, with the lowest percentage after 6 days of in vitro storage of sperm at 5° C. The total wastage (fertilization losses and prenatal mortality) was ?58, ?51, ?66, ?54, ?94 percent for 0, 2, 4, 6 and 8 days of sperm storage resp.

     

Simulium jenningsi Malloch (Diptera: Simuliidae): a vector of Onchocerca lienalis Stiles (Nematoda: Filarioidea) in New York

Biting flies were collected from the umbilical areas of Onchocerca lienalis-infected cattle in New York (state) from June through September of 1980. Of the 766 flies collected, 705 were Simulium jenningsi. Microfilariae were detected in the midguts of 37 (50%) of 73 females dissected immediately after the flies had fed. The mean number of larvae per positive fly (fly with microfilariae) was 15.2. Third-stage larvae were recovered from 25 (21.9%) of 114 S jenningsi dissected 8 to 13 days after they had fed on the infected cattle; the mean number of 3rd-stage larvae per positive fly was 3.5. Dissections of flies performed on days 1 through 7 after feeding yielded various numbers of 1st and 2nd-stage larvae from the thoracic muscles. Ovarian dissections performed on 304 S jenningsi attacking cattle indicated an overall parous rate of 58%. Naturally occurring infections with filarial larvae indistinguishable from O lienalis were found in 7.3% of the parous females. Three of these flies, or 1.7% of the parous collection, harbored 3rd-stage larvae. The onset of naturally occurring filarial infections in the population of S jenningsi coincided with a peak in the parous rate in late June. Thereafter, filarial infections were generally detected when the parous rate was above 50%.     

An association between encephalomyocarditis virus infection and reproductive failure in pigs

An outbreak of reproductive failure, characterised by mummified foetuses and stillbirths, was investigated in an intensive piggery. Six foetuses that died towards the end of gestation had multifocal myocardial necrosis and encephalomyocarditis virus was recovered from 4 of these foetuses but not from 6 mummified foetuses. There was also a significant increase in failure of conception or early embryonic deaths in sows mated at the same time as sows which produced affected litters.     

Newly emerged nulliparous Culicoides imicola Kieffer (Diptera: Ceratopogonidae) with pigmented abdomen

The method of segregating nulliparous and parous females of Culicoides spp. based on the presence of burgundy-red pigment inside the abdominal wall of parous Culicoides midges, is used worldwide. Out of 320 females of Culicoides imicola trapped by emergence traps, set over an artificial breeding site for 10 and 24 days, 73 (22.8%) showed a red-pigmentation despite the fact that they were nulliparous. This finding indicated that 23% of the “parous” females that are examined for the presence of arboviruses and other pathogens or for age-grading purposes, are actually old nulliparous females, which had no chance of acquiring pathogens. This bias in parous rate distorts upward the calculation of vectorial capacity.     

The effect of divergent selection for uterine capacity on prenatal survival in rabbits: maternal and embryonic genetic effects

The aim of this work was to determine whether prenatal survival depends on the genotype of the mother or of the embryo and to identify the critical periods for prenatal mortality in two lines of rabbits divergently selected by high (H) and low (L) uterine capacity. Does from H (n = 124) and L (n = 115) lines were slaughtered at 72 h of gestation. Embryos recovered at 72 h of gestation were transferred to the oviducts of recipient does from the H (n = 23) and L (n = 19) lines. Each recipient does received eight embryos from the H line into one oviduct and eight embryos from the L line into the other. Recipient does were slaughtered on d 28 of gestation. No differences were found between lines in the embryo recovery either in ovulation rate (OR) or in fertilization rate of ova recovered. Recovery rate was higher for the H line (0.80 vs. 0.72, P < 0.01). The number of embryos recovered, fitting ovulation rate as a covariate, was also higher for the H line (9.74 vs. 8.78, P < 0.05). The H line showed a more advanced embryonic stage of development, having a higher percentage of blastocysts (PB) and a lower percentage of compact morulae (PCM) (38% vs. 20%, P < 0.001 for PB, and 51% vs. 64%, P < 0.01 for PCM). The percentage of early morulae was low and similar in both lines. Neither donor nor recipient lines affected embryonic survival from 72 h to 7 d of gestation. Fetal survival was affected by the recipient line (P < 0.05). An interaction between donor and recipient was found. Embryos from the H donor line had a better fetal survival rate than embryos from the L donor line (P < 0.05) in H recipient females. Within L recipient females, embryos from H and L donor lines showed similar fetal survival. Fetal survival was divided into early (from d 7 to 17 of gestation) and late (from d 17 to 28 of gestation). The high recipient line showed a higher early fetal survival than the L recipient line (P < 0.05). The same effect was observed for late fetal survival, but the difference between H and L recipient lines was lower (P < 0.10). Thus, fetal survival depends mainly on the maternal genotype, and the embryo genotype only affects fetal survival when embryo transfer is performed to a favorable maternal environment. Selection for uterine capacity in rabbits leads to modification of early embryonic survival and of early and late fetal survival, but differences are higher for early than for late fetal survival.     

基于LCMS技术对牦牛围产后期的血清动态代谢组学分析

旨在应用代谢组学的方法，阐明经产母牦牛围产后期动态代谢情况，探究营养代谢影响生殖激素的机制。本研究随机选取年龄（（7.13±0.78）岁）、体况（2.69±0.35）和胎次（（1.75±0.43）胎）相近的经产母牦牛8头作为试验动物，自分娩日开始每隔7 d收集血清至产后第28天，共5个时间点。应用液相质谱联用技术对5个时间点的血清样本进行检测，并通过生物信息学分析筛选关键代谢物，构建经产母牦牛围产后期动态代谢网络机制。试验在正、负离子模式下分别获得2 841和1 326种代谢物定性分析的结果，通过计算各时间点代谢物表达量的差异倍数、VIP值及每两个时间点T-test检验的P值，共筛选出117种差异代谢物。根据生物信息学分析，分别获得与繁殖性能、脂类代谢和氨基酸代谢相关的3种、7种和8种关键代谢物。基于关键代谢物构建动态代谢网络机制发现，糖代谢在围产后期的起始阶段作用效率较低，末期升高，脂类和氨基酸代谢在起始阶段作用效率较高，末期降低，推测经产母牦牛在产后发生能量负平衡。生殖激素的合成和分泌作用效率在围产后期一直维持较低水平。根据对经产母牦牛动态代谢谱的检测和网络机制的构建发现，经产母牦牛产后发生了能量负平衡，由于过度脂肪动员导致雌激素的合成和分泌受阻，这可能是导致经产母牦牛产后生殖机能不能及时恢复的主要原因，但具体机制还需要进一步验证。     

Duration of lactation,endocrine and metabolic state,and fertility of primiparous sows

The objectives of this study were to determine factors affecting the reproductive performance of primiparous sows early weaned (EW; n = 35) at d 14 or conventionally weaned (CW; n = 35) at d 24 of lactation. Sow BW and backfat were recorded at farrowing, weekly until weaning, and at standing heat. Feed intake was controlled throughout lactation to standardize nutritional effects on subsequent reproductive performance. Litter size was standardized across treatments within 48 h after farrowing, and litter weight was recorded until weaning. In subsets of sows, blood samples were collected from 10 h before to 10 h after weaning, and then every 6 h until ovulation. Sows were heat checked twice daily and bred at 24-h intervals during standing heat using pooled semen. Ultrasonography every 6 h determined time of ovulation. Sows were either slaughtered within 24 h after ovulation to assess ovulation rate, fertilization rate, and embryonic development in vitro, or at d 28 of gestation to determine ovulation rate and embryonic survival. Compared with CW sows, EW sows had more backfat at weaning (15.9 +/- 0.5 vs. 14.7 +/- 0.5 mm; P < 0.001). Also, CW sows tended to lose more BW and to have lower IGF-I concentrations, indicating poorer body condition. Duration of lactation did not affect ovulation rate (EW = 17.6 +/- 0.7; CW = 18.7 +/- 0.6), fertilization rate (EW = 96.0 +/- 2.2; CW = 88.2 +/- 4.7%), or embryo survival to d 28 (EW = 62.5 +/- 4.5; CW = 63.1 +/- 5.0%). There was a marginal effect of duration of lactation on weaning-to-estrus interval (EW = 120 +/- 3; CW = 112 +/- 3 h; P < 0.06) and duration of estrus (EW = 52.4 +/- 2.3; CW = 46.3 +/- 2.2 h; P < 0.08). Overall, embryonic survival, not ovulation rate, seems to be the limiting factor for potential litter size in the second parity. Although fertility in both EW and CW sows studied was compromised, endocrine and metabolic data indicate that the mechanisms affecting reproductive performance may differ between the two weaning systems. The LH, FSH, and estradiol data from the EW sows are characteristic of animals with limited follicular development and incomplete recovery of the hypothalamic-pituitary-ovarian axis; consequently, the integrity of the uterine environment may be adversely affected and limit embryonic survival. In CW sows, variability in metabolic state seemed to be the key factor limiting the fertility, again adversely affecting embryonic survival.     

Fetal development in cattle with multiple ovulations.

Treatment of lactating and nonlactating parous cows (n = 379) with 12 mg of FSH-P to evaluate development of multiple bovine fetuses resulted in ovulation rates ranging from 1 to 27 corpora lutea (CL). Fertilization rate (i.e., ova fertilized at 6 to 8 d postmating, 80.0%) was not affected by ovulation rate. The percentage of fetuses developing normally at 51 to 53 d postmating decreased (P less than .01) as ovulation rate increased; 1 CL, 100.0%; 2 CL, 100.0%; 3 CL, 66.7%; 4 CL, 45.8%; 5 CL, 33.3%; 6 to 10 CL, 13.6%; and greater than 10 CL, 8.9%. Of the 86 cows permitted to calve, 47 produced singles, 22 twins, 9 triplets, 7 quadruplets, and 1 quintuplets. Calf birth weight and gestational length decreased (P less than .01) as the number of calves born increased from one to two to three. Smaller decreases (P less than .05) in birth weight occurred among triplets, quadruplets, and quintuplets, whereas gestational length did not differ (P greater than .1) among these groups. Systemic progesterone concentrations in the dam were proportional (P less than .01) to the number of fetuses in utero between d 126 and 266 for dams gestating one, two, or three or more fetuses; estrone sulfate was lower (P less than .01) in dams with one than in those with two or more fetuses. Placental weight (i.e., cotyledons plus intercotyledonary membranes) per fetus at 52 +/- 1 d of gestation and at term decreased as the number of fetuses increased. The chorioallantoic membranes were often fused among multiple fetuses and contained either all viable or all dead fetuses, but not both, within the same anastomosed placental unit. These results suggest that ovulation rate is the first limiting factor to increasing cow productivity for beef cattle because some bovine females had the capacity to gestate up to three fetuses per uterine horn, or a total of five fetuses, above which pregnancy was terminated.     

Steroid hormone secretion during the ovulatory cycle and pregnancy in farmed Alaskan reindeer

Seasonal endocrine changes in 5 non-bred and 10 pregnant Alaskan reindeer have been documented. Blood samples were collected from early September until early May, spanning the breeding season, gestation, or the anovulatory period. Plasma was analyzed by RIA for progesterone (P4), estradiol-17beta, estrone, and estrone sulfate. Elevated P4 in 80% of the reindeer at the onset of the study indicated that ovarian activity had been initiated. The median date for the onset of the first recorded full-length ovulatory cycle was September 23. In nonbred reindeer, the mean ovulatory cycle length from September to May was 24 +/- 1 d (range 18 to 29 d). Nonbred females continued to cycle throughout the winter, displaying 6 to 8 ovulatory cycles after the beginning of blood sampling. Cycle length (mean 22 to 24 d) did not vary between individuals (P = 0.170) or over the course of the winter (P = 0.244). In early April, ovulatory cycles ceased with normal demise of the corpus luteum in 2 females, whereas the remaining 3 females formed apparently persistent corpora lutea. Natural service breeding occurred between September 10 and October 2, and P4 profiles indicated that all breeding females conceived to the first mating. Concentrations of P4 rose steadily after conception and remained elevated throughout gestation, with mean concentrations not varying significantly (P = 0.104) from 4 to 28 wk of gestation. Estrogens all followed patterns similar to each other, remaining at baseline concentrations until approximately 24 wk of gestation and rising coincidently as P4 declined just before parturition. There was a continual overlap throughout the winter in peak P4 concentrations observed in cycling and pregnant reindeer. Calving occurred between April 8 and May 2, resulting in a mean gestation length of 211 +/- 2.2 d (range 198 to 221 d). Information from this study can be used by Alaskan reindeer producers to improve management and profitability of reindeer production.     

Y are you not pregnant: identification of Y chromosome segments in female cattle with decreased reproductive efficiency

Reproductive efficiency is of economic importance in commercial beef cattle production, since failure to achieve pregnancy reduces the number of calves marketed. Identification of genetic markers with predictive merit for reproductive success would facilitate early selection of females and avoid inefficiencies associated with sub-fertile cows. To identify regions of the genome harboring variation affecting reproductive success, we applied a genome-wide association approach based on the >700,000 SNP marker assay. To include the largest number of individuals possible under the available budget, cows from several populations were assigned to extremes for reproductive efficiency, and DNA was pooled within population and phenotype before genotyping. Surprisingly, pools prepared from DNA of low reproductive cattle returned fluorescence intensity data intermediate between fertile females and males for SNP mapped to the Y chromosome (i.e., male sex chromosome). The presence of Y-associated material in low reproductive heifers or cows was confirmed by Y-directed PCR, which revealed that 21 to 29% of females in the low reproductive category were positive by a Y chromosome PCR test normally used to sex embryos. The presence of the Y chromosome anomaly was further confirmed with application of additional Y-specific PCR amplicons, indicating the likelihood of the presence of some portion of male sex chromosome in female cattle in various beef cattle herds across the U.S. Discovery of this Y anomaly in low reproductive females may make an important contribution to management of reproductive failures in beef cattle operations.     

Effects of pregnancy and lactation on the body composition of first-litter female swine

A total of 64 gilts initially weighing 120 kg were used to evaluate body composition occurring during pregnancy and lactation. All animals were fed a 14% protein corn-soybean meal diet. Eight gilts were slaughtered each at breeding, 57 and 105 d postcoitum and at 5 and 25 d postpartum, with a corresponding number of nongravid females killed at similar periods except at 5 d postpartum. Chemical composition of the empty body (ingesta-free) and maternal body (empty body minus reproductive products) was determined. Gravid gilts were heavier with larger quantities of water, protein and fat than nongravid gilts by the termination of pregnancy, but these differences were attributable to the products of conception. After the reproductive tissue components were subtracted, no indication of pregnancy anabolism was evident. Hydration in gravid swine was evident at 105 d postcoitum but was attributed to the higher water contribution from conceptus products, not maternal tissue. Maternal body fat appeared to fluctuate during gestation and lactation, whereas body protein and ash content were less affected. Both the empty body and maternal body contained approximately 83.5% protein and 16.5% ash when expressed on a fat-free dry basis, suggesting that compositional changes during reproduction largely reflect water and fat content changes in the dam's body. Carcass measurements generally reflected body compositional data.     

Factors contributing to early embryonic mortality in gilts bred at first estrus

Gilts bred at first (n = 18) and third (n = 18) estrus were assigned in replicates of equal numbers to be slaughtered on d 3, 15 and 30 post-mating to assess fertilization rate, embryonic losses and serum concentrations of estrogen (estradiol-17 beta + estrone) and progesterone. Mean number of ovulations was lower among gilts bred at first vs third estrus (12.2 vs 14.5; P less than .05), with no difference in fertilization rate (100 vs 98%). Embryonic survival was lower (P less than .05) among gilts bred at first vs third estrus on d 15 (78.1 vs 95.4%) and 30 (66.7 vs 89.4%) of gestation. Serum estrogen (pg/ml) and progesterone (ng/ml) levels, although lower in gilts bred at first vs third estrus, were not significantly different at the three stages of gestation studied. The ratio of progesterone to estrogen in gilts bred at first estrus was higher than in those bred at third estrus on d 15 (439 +/- 71 vs 210 +/- 17) and 30 (597 +/- 106 vs 179 +/- 50), but was lower on d 3 (187 +/- 37 vs 444 +/- 123; stage of gestation X estrous period interaction, P less than .05). These data suggest that changes in the ratio of systemic levels of estrogen and progesterone may be related to early embryonic mortality in gilts bred at pubertal estrus.     

Teat stimulation-induced release of prolactin and basal concentrations of prolactin and growth hormone in pregnant dairy and beef heifers

The physiological bases for differences in milk production between breeds of cattle selected for beef or milk production are largely unknown. This study was conducted to determine concentrations of prolactin (PRL) and growth hormone (GH) in serum before and after teat stimulation in primiparous Hereford and Holstein heifers. Blood was collected from 6 beef and 9 dairy heifers at 115, 175, 230 and 250 d of gestation. Sampling times were -15, -10, -5, 0, 2, 4, 6, 8, 10, 12, 15, 20, 25 and 30 min relative to test stimulation. Mean areas under PRL response curves for beef and dairy heifers at 115, 175, 230 and 250 d of gestation were 427, 447, 556, 273 and 243, 189, 167, 343 ng/ml/30 min, respectively. Calculations of area (but not basal levels) excluded instances when no PRL response to test stimulation was obtained (22%). Neither stage of gestation nor breed affected PRL response. Basal PRL did not differ between breeds and was 1.8, 2.6, 2.4 and 9.2 ng/ml at 115, 175, 230 and 250 d of gestation. GH did not differ between breeds and was 6.6, 6.2, 5.5 and 7.4 ng/ml at 115, 175, 230 and 250 d. No difference between breeds was apparent with regard to PRL or GH secretion during first gestation.     

Culling and mortality in breeding rabbits

In this study, we determined culling and mortality in adult breeding rabbits on 130 commercial farms in Spain during 2000-2005. The median size of the farms was 595 does (minimum to maximum: 131-5500 does). The median culling age per doe was 14.9 months old and 6 kindlings. The median monthly removal risk (MMR) in does was 9.3%, with 3.4% dead and 5.7% culled (including euthanized does). The MMR was negatively correlated with the degree of intensification of the reproductive rhythm (r=-0.37), age at first mating (r=-0.31) and kindling interval (r=-0.36). The MMR in males was 5.8% (1.2% dead and 4.2% culled or euthanized). Our estimation of the causes of culling does was based on a population of 82,352 does, 50,834 of which were culled or euthanized. The highest causes, calculated using the median of the monthly cumulative incidence (MCI), were 1.3% low productivity (0.9% infertility and 0.4% other causes), 0.5% mastitis, 0.5% poor body condition and 0.3% sore hocks. The causes of culling males were estimated based a population of 6514 males, 5313 of which were culled. The highest causes were 2.0% MCI low productivity (0.9% infertility and 0.5% no libido); 0.3% abscesses, 0.3% sore hocks and 0.2% poor body condition. The mortality and culling risks after first kindling were 8.7% and 7%, respectively. The highest risks of mortality and culling in does occurred during the first three kindlings, but remained stable thereafter. The gestation stage affected mortality; the risk of mortality per day increased as pregnancy progressed. There was a bimodal distribution with a peak of dead females between days 10 and 15 of gestation (0.1-0.2% mortality risk per day (MD)) and another larger peak between days 25 and 33 (0.3% MD). In 1046 on-farm necropsies performed on females we found alterations of the respiratory and digestive tracts compatible with being causes of death in 29.4% and 27%, respectively.