The influence of embryos on growth of the uterus was determined by comparing uterine length, weight and diameter between gravid and nongravid horns within unilaterally pregnant gilts. Eighty-two prepubertal gilts were ovariectomized unilaterally at 5 mo of age, and the ipsilateral uterine horn was ligated near the junction of the uterine horns. Gilts were mated and were assigned randomly for examination on either d 9, 12, 15, 18, 21, 24 or 27 of gestation. Absolute differences and ratios in length, weight and diameter between gravid and nongravid horns of unilaterally pregnant gilts were analyzed. The gravid horn was 40% longer than the nongravid horn from d 18 to 27. Uterine horns with embryos increased linearly in weight and diameter (P < .01) between d 15 and 27. Embryos, or the signals that they might give, apparently caused increases in length, weight and diameter of the uterine horn by d 18, but not before. (

Estrogen, progesterone or testosterone were administered orally to ovariectomized gilts fitted with indwelling catheters. Blood samples were taken from the jugular and hepatic portal veins at intervals varying from a few minutes to daily over periods that varied from 1 d to several months. Concentrations of free steroids rose dramatically in the hepatic portal vein within a few min of feeding steroids and remained high for 3–8 hr before declining to base levels. Concentrations in the jugular vein sometimes rose very slightly for the same period. At 48 hr after administration the concentrations remained at baseline in the hepatic portal vein, but rose several-fold in the jugular and remained elevated for several days. Autotransplantation of the ovaries to the intestine resulted in very large ovaries consisting of many large, heavily luteinized cystic follicles. Concentrations of progesterone and estrogen in the hepatic portal vein were very high, but were low in the jugular vein. The gut wall allows for passage of some orally administered free steroids to the liver via the hepatic portal vein. The free steroids are essentially metabolized before they reach the jugular vein, but can be recirculated via the enterohepatic route.

Journal Article Comment on the need for thoroughness in literature searches Get access P. J. Dziuk P. J. Dziuk Search for other works by this author on: Oxford Academic PubMed Google Scholar Journal of Animal Science, Volume 75, Issue 12, December 1997, Page 3369, https://doi.org/10.2527/1997.75123369x Published: 01 December 1997

Relationships of the length of the uterus at one reproductive stage to the length at other stages and the effect on potential litter size were determined. In Experiment 1, the length of the uterus was measured in situ at 20, 60, or 100 days of age at laparotomy with 20 gilts in each of the three age groups. Forty days after the initial measurement, the uterus was again measured in situ, gilts were ovariectomized and hysterectomized, and associations among uterine measurements at the two different stages were determined. Correlations between uterine length in situ and between uterine length and weight 40 days later were all greater than 0.75 (P < 0.001). The length of one uterine horn increased from 13.9 cm at 20 days of age to 36.7 cm at 140 days of age (P < 0.01). In Experiment 2, 66 gilts were unilaterally hysterectomized and ovariectomized (UHOX) at 150 days of age and the ovary was weighed. Length of the one horn was measured in 36 gilts. At 10 days after first estrus, the length of the remaining uterine horn was measured at laparotomy and corpora lutea were counted in 53 gilts. In 15 of the 53 gilts the remaining uterine horn was removed to obtain uterine weights. At the second or third estrus, 38 gilts were mated and at Day 30 of gestation, 31 gilts were pregnant. The gilts were killed, and the length of the uterus measured and corpora lutea (CL) and fetuses were counted. The length of one uterine horn at 150 days of age was 70 cm with a range of 47–110 cm. At 10 days after first estrus, length had increased to a mean of 141 cm with a range of 86–194 cm and at 30 days of gestation the mean was 244 cm with a range of 186–311 cm. There were 12.2 CL at first estrus, which was not different from 12.4 CL at the second or third estrus. The mean number of fetuses in one horn at 30 days of gestation was 9.5 with 77% prenatal survival. Length of uterine horn at 150 days of age was correlated with uterine horn length (r = 0.56, P < 0.001) at 10 days after first estrus and number of live fetuses (r=0.39, P<0.05) at 30 days of gestation. At Day 10 after first estrus, uterine length was not correlated with the number of CL, whereas at Day 30 of gestation, the number of CL and uterine length were correlated with the number of live fetuses in those gilts with below the mean number of live fetuses, but not in those gilts with above the mean of live fetuses. The number of live fetuses (r=0.66, P < 0.001) and fetal survival (r=0.63; P < 0.001) were correlated with uterine horn length in pregnant UHOX gilts. Length of the prepubertal uterus gives an indication of postpubertal length and the potential litter size in pigs.

The objective of this research was to determine the effect of administration of porcine relaxin to gilts during early gestation, or during the follicular phase of the estrous cycle immediately preceding mating, on the length of the uterus and consequently the number of surviving fetuses. Experiment 1 determined the individual and combined effects of 10 days of administration of relaxin (0.5 mg, 4 times daily), estradiol benzoate (1 mg, 2 times daily), and progesterone (50 mg, 2 times daily) on uterine wet weight and length in 58 ovariectomized 8-mo-old pubertal gilts. Relaxin alone had no effect on either uterine length or wet weight. Estrogen increased uterine wet weight, and this effect was augmented by relaxin. Progesterone increased uterine length, and this effect was augmented by estrogen. Combined treatment with progesterone, estrogen, and relaxin increased both uterine length and wet weight maximally. Experiment 2 determined the effects of relaxin administration in early gestation or prior to mating on uterine length and fetal survival in 75 unilaterally ovariectomized-hysterectomized gilts. Relaxin (0.5 mg, 4 times daily) was administered during three treatment periods, and uteri were collected on Day 40 of gestation. In this study, relaxin administration from Days 11 to 20 of gestation reduced the number of live fetuses (p = 0.01) and percentage survival (p = 0.01) and resulted in shorter uterine length (p = 0.01) and lower uterine wet weight (p = 0.03) than in controls, but did not affect length of uterus or uterine dry weight. Relaxin administration from Days 22 to 31 of gestation did not influence fetal survival, uterine length, uterine length per fetus, uterine wet weight, or uterine dry weight.(ABSTRACT TRUNCATED AT 250 WORDS)

The purposes of this project were: 1) to introduce the FecB gene to the Awassi and Assaf breeds in Israel and the Rambouillet breed in the U.S.A. aiming in the long run to establish Awassi, Assaf and Rambouillet nucclei breeding flocks homozygous for the F gene in which the contribution of the Booroola Merino genetic background will be less than 10%; (In the U.S., Booroola crosses with Suffolk and Targhee were also studied. 2) to evaluate the effect of the FecB gene and different proportions of Booroola Merino genetic background on lamb survival, growth, milk production and wool production in Booroola crosses with the native breeds; 3) to reveal the specific effect of the FecB gene on ovarian development, follicle stimulating hormone (FSH) and inhibin secretion in prepubertal ewe lambs and in adult ewes in order to define physiological criteria for distinguishing carriers of the FecB allele from non-carriers and 4) to identify genetic markers linked to the FecB gene to assist in selection of genotypes within the Booroola crosses. Introgression of the Booroola gene reached the stage of the third backcross in the Awassi, Assaf and the Rambouillet crosses. In all cases the Booroola crosses were superior in prolificacy. However, they were inferior in comparison to the local breeds in production due to Booroola Merino genes other than the FecB. It is expected that the beneficial economic contribution of the Booroola gene will increase along with the upgrading to the local breeds. FSH plasma levels and induced ovulation rate of 5 month old FecB carriers among the crossbreeds. The OarAE101 marker can assist in detecting FecB carriers among Booroola-Awassi crosses. However, this marker is informative only in some of the families.

Three experiments were conducted to determine the concentration of estradiol glucuronide (E2G), and estrone glucuronide (E1G) in the blood of gilts after mating (Day 0). Blood samples were taken from 20 mated gilts at weekly intervals from Day 14 to Day 34 and analyzed by radioimmunoassay (RIA) for concentration of E2G and E1G. The concentrations of both hormones rose from about Day 19 to a peak at Day 26 and then declined. The concentration of E2G rose to 1700 pg ml−1 and E1G rose to 8000 pg ml−1 at Day 26. Eleven mated gilts in a second study were bled on Days 20, 22, and 24 and plasma analyzed for E2G and E1G. At slaughter on Days 29–35, gilts with more than 100 pg ml−1 of E2G or more than 1000 pg ml−1 of E1G on Day 20 or later were pregnant. In a third study, 31 gilts were bled at 48 h intervals from Day 20 to 28 and plasma was analyzed for concentration of E2G and E1G. All gilts with over 100 pg ml−1 of E2G and 30 of 31 with over 1000 pg ml−1 of E1G were pregnant when killed at Days 30–35. When gilts were classified according to the concentration of E2G at Day 20, 86% of gilts with over 200 pg ml−1 had eight fetuses or more and at Day 24, 77% of gilts with over 1100 pg ml−1 had eight or more fetuses. When gilts were sorted on the basis of over 1500 pg ml−1 on Day 20 and on Day 22 for over 3400 pg ml−1 of E1G, the percentages of correct classification for eight or more fetuses were 87% and 81% respectively. Concentration of E2G or E1G from Day 20 to 28 after mating can be used to detect pregnancy and estimate litter size at the time of analysis.

To determine the absorption and metabolism of 17 beta-estradiol (E2) by the rectum of the pig, 10 mg of crystalline E2 was placed in the rectum of prepubertal gilts in Experiment 1. Blood samples were subsequently obtained from hepatic portal and jugular veins and plasma was assayed for E2, estrone (E1), 17 beta-estradiol-glucuronide (E2G), estrone-glucuronide (E1G) and estrone-sulfate (E1S). Concentrations of E2, E1, E2G, E1G, and E1S rose in the hepatic portal vein within 30 min and remained elevated for several hr. Concentrations of E2 in the hepatic portal vein represented 3% of the total estrogen detected in the hepatic portal vein during the 5 hr sampling period, indicating that most of the E2 was metabolized prior to entering the hepatic portal vein after absorption by the rectal mucosa. Concentrations of E2, E1, E2G, E1G, and E1S rose in the jugular vein and remained elevated for several hr. The rise in E2 and E1 in the jugular vein may have come from E2 and E1 in venous circulation from the rectum that entered the inferior vena cava bypassing the hepatic portal vein and liver. The net result of absorption of E2 from the rectum of gilts was a large rise in unconjugated and conjugated E2 and E1 in the peripheral circulation. In Experiment 2 prepubertal gilts fitted with jugular, hepatic portal, duodenal, and gall bladder catheters were infused into the duodenum with bile from pregnant gilts. Concentrations of E2, E1, E2G, and E1G were determined in gallbladder bile of gilts before infusion and at 470 min.(ABSTRACT TRUNCATED AT 250 WORDS)

To determine the absorption and metabolism of 17 beta-estradiol (E(2)) by the stomach and liver of the pig, crystalline E(2) was placed in the stomach of prepubertal gilts. Blood samples were subsequently obtained from the hepatic portal and jugular veins and plasma was assayed for E(2), estrone (E(1)), 17 beta-estradiol-glucuronide (E(2)G), estrone-glucuronide (E(1)G) and estrone-sulfate (E(1)S). Concentrations of E(2), E(1), E(2)G and E(1)S rose in the hepatic portal vein within five min and remained elevated for several hr. Concentration of E(2) represented only 6% of the total estrogen detected in the hepatic portal vein during the sampling period, indicating that most of the E(2) was converted or conjugated prior to entering the hepatic portal vein. The metabolism of E(2) presumably occurred in the stomach mucosa because food had been withheld for 26 hr before infusion of E(2). Concentrations of E(2)G, E(1)G and E(1)S, but not E(2) and E(1), rose in the jugular vein and remained elevated for several hr. The lack of a rise in E(2) and E(1) in the jugular vein indicates that the E(2) and E(1) from the hepatic portal vein were completely converted and/or removed by the liver. Most of E(2) was converted to E(1) and then to E(1)G. The infusion of bile containing normal estrogens from pregnant gilts into the duodenum of prepubertal gilts resulted in a peak of E(1)G and E(2)G in the hepatic portal and jugular veins within a few minutes. This was followed in about 180 min by a second sustained rise. The first peak was essentially abolished by extracting E(1) and E(2) from the bile before infusion. The second peak failed to occur in gilts given antibiotics orally to reduce gut bacteria before infusion of bile.

The objective of this study was to investigate the effect of induction or depression of mixed-function oxidases (MFO) by xenobiotics on the peripheral concentration of estrogens, plasma Ca, rate of egg lay, and eggshell thickness in laying hens. In Exp. 1, 100 mg of phenobarbital (PB) administered orally each day for 3 or 7 d reduced concentrations of estrone and estradiol (E2) in serum. In Exp. 2, 25, 50, or 100 mg of PB was administered orally to laying hens for 3 or 7 d. Treatment with 100 mg of PB for 3 d or with 25, 50, or 100 mg for 7 d significantly increased liver:body weight ratios. Microsomal protein increased after 7 d of 50 or 100 mg of PB administration. Feeding PB decreased concentration of E2 and total plasma Ca in a dose- and period-dependent manner. Concentration of E2 was reduced to 10% of control, whereas hepatic cytochrome P-450 increased significantly with dose. The correlation between concentration of E2 and P-450 was negative and significant. Total Ca in the plasma was highly, positively correlated with concentration of E2. Eggshells were thinner from hens treated with 100 mg of PB for both 3 or 7 d than those from control hens. Rate of egg lay was reduced by 100 mg of PB for 7 d. In Exp. 3, .5 mL of CCl4 given orally for 1 d decreased P-450 and increased E2.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of uterine length per embryo and stage of gestation on prenatal survival, development, and sex ratio were determined by systematically restricting embryos to 5, 10, 15, 20, 25, 30, 35, 40, 45, or > 50 cm of initial uterine length per potential embryo and examining the reproductive tracts at d 17, 23, 29, 35, or 41 of gestation. At d 3 the mean length of a uterine horn was 169 +/- 35 cm, with a range of 80 to 255 cm. The mean total number of corpora lutea (CL) was 12.4 +/- 2.34. Ovulation rate tended to be correlated with the length of uterine horns (r = .38; P > .1). Prenatal survival was highly correlated with initial assigned uterine space from 5 to 25 cm/CL (r = .95; P < .05). Prenatal survival was not affected by space (r = .53; P < .1) when space was > 25 cm/CL. In all groups, regardless of space available, some prenatal loss occurred before d 17. In sections with < 25 cm/CL, a second loss took place between d 29 and 35. Before d 35, there was no significant effect of restriction on either fetal length or weight, but after d 35, fetuses from sections with > 25 cm/CL were longer and heavier than those from sections with less space (P < .05). Greater uterine space was occupied by larger fetuses (P < .05). Male fetuses occupied more uterine space than female fetuses did in both crowded and roomy sections (P < .05).(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the ovulation rate, prenatal survival and litter size of Chinese Meishan pigs have given widely divergent results depending on the extent of inbreeding of the animals, their original genetic diversity, the age and parity, and the conditions of management. To obtain meaningful results, it is necessary to characterize the population under study. The following report characterizes populations of Meishan and Yorkshire of a widely diverse background. First farrowing data were collected on 21 Meishan and 20 Yorkshire gilts. Meishan gilts had 12.4 fully formed piglets and Yorkshire gilts had 7.4 fully formed piglets (P < 0.01). Meishan gilts averaged 1.86 mummified fetuses per litter vs 0.05 per Yorkshire litter (P < 0.01). Yorkshire piglets averaged 1.3 kg body weight at birth vs 0.9 kg for Meishan piglets (P < 0.01). At 47 days of second gestation, 19 Meishan and 12 Yorkshire sows averaged 22.7 and 16.3 corpora lutea (CL), respectively (P < 0.01). Uterine length and number of fetuses were not different (P > 0.40) in the two breeds. Daily estrous detection of 50 Meishan and 34 Yorkshire gilts began at 60 and 120 days of age, respectively. Meishan gilts reached sexual maturity at 95 days of age, which was 105 days earlier than Yorkshire gilts (P < 0.01). Meishan gilts were in estrus nearly 1 day longer than Yorkshire gilts at first, second and third estrus (P < 0.05). No differences in cycle length between breeds were detected for the first or second estrous cycle (P > 0.60). Nineteen Meishan gilts were slaughtered at 51 days of gestation and their reproductive tracts were recovered. The mean number of dissected CL (17.0), number of fetuses (13.1), total uterine length (396 cm), spacing per fetus (29.9 cm), allantoic (124.9 ml) and amniotic (32.2 ml) volumes, crown-rump length (82.8 mm), weight (35.4 g), sex, and direction of each fetus were determined. Chinese Meishan gilts reached puberty much earlier and were in estrus longer than Yorkshire gilts and Meishan sows had more CL than Yorkshire sows.

Embryos and fetuses of domestic animals grow and develop at a very orderly rats. At the beginning cell numbers increase followed by differentiation and finally development of organs and systems. Although the rate of development and growth are orderly, they can be influenced by a number of factors. Genetic potential of both parents, plane of nutrition of the mother, environmental temperature, size of the mother, toxicants, number of litter-mates, and uterine space are among the many factors that can have an affect on the fetus. Because the prenatal period constitutes a significant portion of the total post-conception life of many domestic animals and because of the profound effect that prenatal conditions can have on postnatal life it is very important to consider all the possible implications of management decisions that affect prenatal growth and development.

Reciprocal cross differences have been reported for growth rate and carcass traits in F1 pigs with the Duroc (D) as a parent breed. Such differences are synonymous with maternal effects if effects of sex linkage and genomic imprinting are negligible. In the present study, transfer of embryos (ET) to paternal breed recipients partitioned effects occurring at or before fertilization from postfertilization effects for growth and carcass traits in F1 D-Landrace (L) pigs. Fifteen boars sired 115 F1 litters, 49 produced by ET. Growth rate of 349 barrows and 361 gilts and carcass measurements on 256 barrows and 159 gilts were analyzed assuming mixed linear models with animal and litter as random effects. Contrasts among genotype (D x L, L x D)- treatment (ET, non-ET) means were tested. Reciprocal cross differences were not detected for growth rate or for carcass weight, length, average backfat thickness, estimated carcass lean, or lean per day of age. Reciprocal cross differences for 10th rib backfat thickness (BF) and longissimus muscle area (LMA) were detected only in barrows. The sexual dichotomy for reciprocal cross differences followed expectations for a Y-linked gene(s), consistent with the fact that reciprocal D-L crossbred barrows exhibited a paternal effect, with responses more like the sire breed than the dam breed. Barrows that were non-ET from D sires and L dams had 3.9 cm2 larger LMA and 5.8 mm less BF than barrows from L sires and D dams (P less than .001). Barrows from ET sired by D boars had 3.8 cm2 larger LMA than did barrows from ET sired by L boars (P less than .001), although no difference was detected for BF. Barrows sired by D boars reared in a D postfertilization environment (ET) had 6.2 cm2 greater LMA and 4.1 mm less BF (P less than .05) than barrows sired by L boars gestated and reared by D dams (non-ET). Barrows sired by D boars reared by L dams (non-ET) had 1.5 cm2 greater LMA and 2.3 mm less BF (P greater than .10) than barrows sired by L boars reared by L dams (ET). In conclusion, reciprocal cross differences detected for BF and LMA in barrows were established before or at fertilization and seemed to be Y-linked.

The effects of relaxin on the biochemical properties of both the uterine and vaginal portions of the cervix were examined between days 80-110 of pregnancy in ovariectomized gilts given progesterone to maintain pregnancy. In the cervix of control gilts and those ovariectomized and given progesterone plus relaxin, wet and dry weights, water content, and the glycosaminoglycan/collagen ratio increased between days 80-110 of gestation. Collagen concentrations based on wet or dry weight and glycosaminoglycan concentrations based on wet weight decreased during this period. After ovariectomy, there were no changes in these cervical connective tissue components when relaxin was not given. The glycosaminoglycans hyaluronic acid, heparan sulfate, and dermatan sulfate were found in the cervices of all treatment groups, with dermatan sulfate predominating. The ratio of the individual glycosaminoglycans did not change during pregnancy or with treatment. The major dermatan sulfate proteoglycan from the pig cervix was isolated and found to be similar in size, immunoreactivity, amino acid composition, and amino acid sequence to the major dermatan sulfate proteoglycans isolated from the cervices of other mammals. It is concluded that the relaxin-induced changes in the connective tissue composition of the cervix may contribute at least in part to increased extensibility and growth of the cervix during the last third of gestation in pigs.

Behavioral and endocrine changes in the sow following injection with prostaglandin F2 alpha (PGF2 alpha) or its analogue, cloprostenol (CLO), were monitored to identify endocrine correlates of prepartum activity (nest-building). On Day 112 postcoitum, within 15 min after injection with 10 mg PGF2 alpha, sows offered straw in pens engaged in intense prepartum activity, but few behavioral changes occurred during the first 2 h following administration of 175 micrograms CLO. The temporal pattern of prepartum activity, however, was affected by both prostaglandins. In control sows, most prepartum activity came during Hours 16-0 before delivery of first piglet (delivery). After CLO, sows engaged in nest-building more during Hours 32-17 and less during Hours 16-0. In another experiment, sows in farrowing crates were injected with saline, 175 micrograms CLO, or 10 mg PGF2 alpha on Day 112 and blood was collected 0, 15, 30, 60, and 90 min later. Another sample was collected when spontaneous prepartum activity was first observed. For approximately 90 min after PGF2 alpha treatment, sows rooted, pawed, and bit and rubbed faces on crate bars; after saline and CLO, this behavior was rarely observed. After prostaglandin treatment, plasma progesterone tended to decline, a 10-fold rise in relaxin came within 15 min, but estrone did not change. Plasma prolactin rose 10-fold within 30 min after PGF2 alpha treatment, and rose more gradually after CLO treatment. When sows exhibited spontaneous prepartum activity (approximately 7 h before delivery), endocrine status was characterized by low progesterone, high estrone:progesterone ratio, and high prolactin.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of relaxin on the physical properties of both the uterine and vaginal portions of the cervix were studied between days 80 and 110 of pregnancy in ovariectomized gilts given progesterone to maintain pregnancy. In controls gilts the extensibility, lumen diameter, and wet weight of the uterine portion of the cervix were less than those of the vaginal portion of the cervix on day 80, but increased thereafter, and by day 110 did not differ (extensibility and wet weight) or approached (lumen diameter) those values of the vaginal portion of the cervix. When gilts were ovariectomized on either days 80 or 100 and given progesterone only (groups OP-100 and OP-110) extensibility, lumen diameter, and wet weight failed to increase in both the uterine and vaginal portions of the cervix. After replacement therapy with progesterone plus relaxin (groups OPR-100 and OPR-110), extensibility, lumen diameter, and wet weight increased to values as least as large as those in control groups in both portions of the cervix. In all groups the uterine portion of the cervix changed more dramatically than the vaginal portion. After hormone replacement therapy, blood levels of relaxin were moderately higher, and blood levels of progesterone were somewhat lower than those in control gilts. There was little or no difference in estrogen levels between ovariectomized and control gilts. We conclude that relaxin plays an important role in promoting increased growth and extensibility in both the uterine and vaginal portions of the cervix after day 80 of gestation in the gilt.

Influence of initial length of uterus available to each embryo on its subsequent survival and development was determined by systematic restriction of the length available to each potential embryo. Fifty-seven pregnant crossbred gilts were laparotomized at d 3 of gestation, length of uterine horns was measured in situ and corpora lutea (CL) were counted. In Exp. 1, uterine space available to each potential embryo was restricted by ligating one uterine horn 5 cm from the tip per CL. Uteri were examined at d 20, 25 or 50. In Exp. 2, one uterine horn was ligated on d 3 at 10, 20 or 30 cm from the tip per CL and uteri were examined at d 50. Embryos in the restricted section (RS) had a specific mean uterine length available to each potential embryo of 5, 10, 20 or 30 cm. Embryos in the nonrestricted section (NRS) had a variable mean uterine length available to each potential embryo of 44 +/- 4 cm. When embryos were restricted to 5 cm, the proportion of surviving fetuses at d 20, 25 and 50 was 61, 12 and 8%, respectively, whereas in combined NRS it was 82%. When the uterus was examined at d 50 after restricting embryos to 10, 20 or 30 cm/CL, 25, 33 and 52% of fetuses survived; in combined NRS survival was 71%. Each fetus surviving to d 50 in RS was associated with 36 cm of initial uterine length but fetal survival was not associated with number of CL. In RS, 59% were female fetuses and in NRS 50% were females.(ABSTRACT TRUNCATED AT 250 WORDS)

This study attempted to determine a basis for the previously observed greater sensitivity of heterospermic tests when compared to homospermic tests for detecting differences in fertility between males. In theory, the results of heterospermic tests are an indication of the proportion of eggs fertilized per unit time whereas results of homospermic inseminations measure only the cumulative or final proportion of eggs fertilized. The fertilizing ability of sperm from males of CF1 and C57BL/6N strains of mice was compared homospermically using both relatively high and low concentrations of sperm and by measuring the proportion of eggs penetrated per unit of time. The fertilizing ability of sperm from these strains was also compared using heterospermic inseminations. When females were inseminated with a high concentration of sperm, males of both strains fertilized a high and indistinguishable percentage of eggs when examined after 30 hr. When females were inseminated with either a low concentration of sperm or when the proportion of eggs penetrated was measured at 5 hr, differences between strains of mice were distinguishable. Heterospermic insemination further magnified the observed difference between strains. The results of this study confirm that measuring the percentage of eggs fertilized per unit of time can enhance the magnitude of differences between males in fertility as compared to measuring only the final percentage of eggs fertilized. Measuring the percentage of eggs fertilized per unit of time does not, however, entirely account for the large differences observed between fertility of males when they are compared using heterospermic inseminations.

Hepatic monoxygenases metabolize steroids that in turn influence reproduction. Experiments were conducted to establish the effect of dose of phenobarbital and level of dietary protein on hepatic monoxygenase. In Exp. 1, ewes were given either 0, .5, 1, 2 or 3 g phenobarbital (PB) daily for 4 to 8 d. After 48 h after last dose of PB, cytochrome P-450 was higher (P less than .01) in all ewes given PB than in controls and was higher (P less than .01) in ewes given PB for 8 d than in ewes treated for 4 d. In Exp. 2, either 0 or 1 g of PB was given orally for 8 d. Liver samples were collected 1, 4, 7 or 10 d after last treatment. Both cytochrome P-450 (P less than .01) and nicotinamide adenine dinucleotide phosphate (NADPH) cytochrome c reductase (P less than .06) were higher in ewes receiving PB than in controls. Cytochrome P-450 was twice as high in treated ewes as in control ewes on the 8th d of treatment, but concentrations returned to control levels 10 d after last treatment. Microsomal protein and cytochrome b5 were not affected by PB (P greater than .10). Ewes in Exp. 3 receiving a diet containing 14.8% crude protein for 10 d had higher levels of cytochrome P-450 (P less than .01) than ewes fed 4.7% crude protein. Protein did not affect microsomal protein or NADPH cytochrome c reductase. These data suggest that a relationship among PB, dietary protein and monoxygenases exists and provide information that will lead to a better understanding of the relationship between diet and reproduction.