The effect of the F gene on male reproductive traits in Booroola × South Australian Merino rams

The effect of the Booroola (Bo) F gene on the reproductive development of Bo × South Australian Merino ($\text{1}\text{2}\text{Bo}$) rams was examined. Half Bo rams were offspring of FF (homozygous carrier), F+ (heterozygous carrier) or ++ (homozygous non-carrier) Bo sires, so that the expected frequency of $\text{1}\text{2}\text{Bo}$ rams carrying the gene should be approximately 1.0, 0.5 or 0.0, respectively. The genotype of each Bo sire was defined on the basis of the proportion of daughters with ? 3 ovulations. The reproductive development of the $\text{1}\text{2}\text{Bo}$ rams corresponding with each sire genotype was studied between 5 and 15 months of age. Traits recorded were: live weight, testicular volume, preputial adhesion score, semen volume, semen density, proportion of rams with ejaculates containing spermatozoa, proportion of rams that mounted and proportion of rams that served oestrous ewes. There were no significant differences among sire genotypes in the traits studied, except for preputial adhesion score (FF < F+ = ++, P < 0.05) and proportion of rams that mounted (FF = F+ < ++, P < 0.05) at 5 months of age. The relevance of these differences is not known but could result from sampling problems. It is concluded that (1) the F gene had no discernible role in male reproductive development between 5 and 15 months of age and (2) the traits examined did not allow a distinction between carrier and non-carrier rams of the F gene.     

Ovulation rate in ewes after single oral glucogenic dosage during a ram-induced follicular phase

A 2-factor factorial array with three replicates (N = 280) was used to simultaneously assess the effects on ovulation rate of two alternative doses of medroxy-progesterone acetate (MPA) (10 or 60 mg), applied during a 6-day priming period, and the effect of a single dosage of a glucogenic formulation, administered immediately before ram exposure to groups of adult seasonally anovular Corriedale ewes. The glucogenic formulation contained 1,2,3-propanetriol (glycerol; 70% $\text{v}\text{v}$), 1,2-propanediol (propylene glycol; 20% $\text{v}\text{v}$) and distilled water (10% $\text{v}\text{v}$). At sponge withdrawal, a single oral dose of 100 ml of this formulation or the same volume of distilled water was administered to treated and control groups, respectively, and ewes were immediately exposed to rams and hormonally-induced oestrous ewes. Data from an ancillary experiment (n = 10) showed significantly (P < 0.005) above normal plasma glucose levels in treated animals at 3 and 6 h after dosage. A significant interaction (P = 0.0006) between MPA priming doses and glucogenic supplementation was detected. Supplemented ewes, among those exposed to the lower dose of MPA, exhibited a higher (P = 0.0098) mean ovulation rate (1.56 ± 0.076) than ewes that did not receive glucogenic treatment (1.31 ± 0.060). In contrast, ovulation rate was significantly decreased (P = 0.021) from 1.30 ± 0.058 to 1.13 ± 0.042 after glucogenic treatment in ewes that were primed with sponges containing 60 mg of MPA. Ewes exposed to 60 mg of MPA were marked by the rams at a significantly later (P < 0.00001) mean time (54.8 ± 1.44 h) than ewes receiving 10 mg sponges (43.6 ± 1.08 h). These results reveal the potential for modifying ovulation rate through short-term glucogenic manipulations, at least during the compressed follicular phase typical of ram-induced ovulations.     

Altered motility of myometrium from estrous ewes after the regulation of estrus with progestagen or prostaglandin

The $\text{in}$$\text{vitro}$ motility of strips of myometrium was studied in estrous ewes after administration of melengestrol acetate (MGA), medroxyprogesterone acetate (MAP) or prostaglandin F_2α (PG) to regulate estrus. Ewes were killed during estrus, 2 to 4 days after the end of progestagen or PG treatment. The contractions of strips of myometrium were recorded by kymograph and compared to contractions of control ewes.Muscle relaxation was indicated by an interval of tracing that was nearly horizontal and close to the baseline. A major contraction was indicated by a sharp upward movement of the tracing pen and an interval of tracing above the baseline.Treating ewes with MAP by intravaginal sponge lengthened contraction time. Feeding MGA or MAP tended to shorten relaxation time, and injecting PG tended to both lengthen contraction time and shorten relaxation time. As a result of these effects, the proportion of time that myometrium spent in contraction averaged 74% for 42 ewes treated with progestagen or prostaglandin and 56% for 24 control ewes. These results indicate that treatments that inhibit sperm transport when used to regulate estrus also affect the nature of myometrial contractions $\text{in}$$\text{vitro}$.     

Induced breeding in anestrous milking ewes of dairy breeds: Comparison of norgestomet,medroxyprogesterone and fluorogestone in two regimes of PMSG

The present investigation compares the suitability of norgestomet versus medroxyprogesterone and fluorogestone in inducing breeding in anestrous lactating ewes. Six hundred lactating ewes of two local dairy breeds were randomly divided into three equal groups during the spring. Ewes in group I were treated with 60 mg of medroxyprogesterone and in group II with 40 mg of fluorogestone using impregnated polyurethane vaginal sponges for 14 days. Ewes in group III were treated with 1.3 mg of norgestomet in impregnated mini-implants, placed subcutaneously in dorsal pinnae of the ear. The day the sponges and implants were removed, the ewes in each group were randomly allocated in two subgroups, a and b, and received 500 I.U. and 1,000 I.U. of PMSG, respectively. Vasectomized rams were used for estrus detection and fertile rams for hand mating. The percentage of estrus exhibition and subsequent mating was similar among groups (98 and 84%, subgroups Ia and Ib $\text{vs}$ 100 and 100%, subgroups IIa and IIb $\text{vs}$ 100 and 96%, subgroups IIIa and IIIb). The meantime of estrus exhibition ranged between 40.1h ± 6.2h to 42.3h ± 4.1h in IIIa and IIIb, 46.4h ± 6.1h to 49.2h ± 3.9h in Ia and Ib, and 48.3h ± 6.1h to 50h ± 4.6h in IIa and IIb, respectively. The lambing percentage ranged between 59 to 49% in IIIa and IIIb, 62 to 39% in Ia and Ib, and 71 to 28% in IIa and IIb, respectively. The percentage of subsequent estrus returns was ranged between 39 to 50% in IIIa and IIIb, 38 to 59% in Ia and Ib, and 26 to 70% in IIa and IIb, respectively. The lambing percentage of the returns ranged in the same level (86 to 100% in group I $\text{vs}$ 92 to 96% in group II $\text{vs}$ 91 to 90% in group III, respectively) as well as the prolificacy (178 to 209 in group I $\text{vs}$ 187 to 176 in group II $\text{vs}$ 200 to 188 in group III, respectively). It was concluded that induction of breeding in anestrous lactating ewes of dairy breeds, using implants containing only 1.3 mg norgestomet, might be a useful tool to improve efficiency of sheep production.     

Nasal vasoconstrictor activity of a novel PGE2 analog

A novel PGE₂ analog (CL 116,069) was shown to be effective in dogs as a nasal decongestant. Threshold doses were approximately 0.1 μg/kg with intravenous administration and between 0.08 and 4 μg with topical administration. CL 116,069 was compared to 17-phenyl-trinor PGE₂ (CL 116,147), a compound recently studied in humans, and xylometazoline, a well-known nasal decongestant. When given i.v., efficacious doses of xylometazoline tended to raise blood pressure and be shorter acting than the PGs, which did not affect blood pressure. When given topically, all three were long-acting. CL 116,069 usually had the lowest threshold and CL 116,147 usually induced the smallest response. All three agents were more effective than PGE₁ or PGE₂. A 30-day (b.i.d., topical) toxicity test with CL 116,069 produced no inflammation or nasal pathology and no loss in tissue sensitivity. $\text{In}$$\text{vitro}$ examination of xylometazoline and CL 116,069 for vascoconstrictor activity on dog isolated mucosa revealed a response profile similar to that observed with these agents $\text{in}$$\text{vivo}$; i.e., the magnitude of response was comparable for both agents but the t $\text{1}\text{2}$ was only 74 minutes for xylometazoline and greater that 6.5 hours for CL 116,069. The data suggest that CL 116,069 may provide a therapeutic alternative in which constriction of the nasal blood vessels need not be associated with a generalized vasoconstrictor liability.     

Use of gonadotropin releasing hormone to improve reproductive responses of ewes introduced to rams during seasonal anestrus

Three experiments were conducted on anestrous ewes of Suffolk, Dorset, and Katahdin breeding to examine the potential value of GnRH to improve ovulation and pregnancy in response to introduction of rams. In Experiment 1, treatment with GnRH 2 d after treatment with progesterone (P₄; 25 mg i.m.) at introduction of rams was compared to treatment with P₄ alone at the time of introduction of rams. Treatment with GnRH did not increase percentages of ewes with a corpus luteum (CL) 14 d after introduction of rams, pregnant 32 d after treatment with PGF₂α 14 d after introduction of rams, or percent of treated ewes lambing to all services. In Experiment 2, treatments with GnRH on day 2, 7, or both after introduction of rams were compared. Treatments did not differ in mean estrous response, percentages of ewes with a detectable CL or number of CL present on day 11, or mean pregnancy and lambing rates. Therefore, neither one nor two injections of GnRH at these times appeared to be effective to induce anestrous ewes to breed. In Experiment 3, treatments compared included GnRH 4 d before introduction of rams, GnRH 4 d before and 1 d after introduction of rams, ram introduction alone, and treatment with P₄ (25 mg i.m.) at the time of introduction of rams. Percentages of ewes with concentrations of P₄ greater than 1 ng/mL (indicating formation of CL had occurred) 7 d after ram introduction tended to be greater (P < 0.07) in ewes treated with GnRH or P₄ than in control ewes treated with ram introduction alone. However, there was no difference in P₄ concentrations between groups by day 11 or 12 after introduction of rams. Estrous response rates and percentages of ewes pregnant 95 d after PGF₂α was administered (on day 12 after introduction of rams) tended to be greater (P = 0.08 and 0.06, respectively) in ewes treated with GnRH or P₄ than in ewes exposed to rams only. There was no difference in response variables between ewes treated with GnRH 4 d before introduction of rams and ewes treated with GnRH 4 d before and 1 d after introduction of rams. In conclusion, treatment with GnRH 4 d before ram introduction showed promise as an alternative to treatment with P₄ to improve the ovulatory response and reproductive performance of ewes introduced to rams during seasonal anestrus.     

Early identification of non-pregnant and pregnant ewes in the field using circulating progesterone concentration

A method for early indentification of non-pregnant and pregnant ewes is described. It is applicable to field research situations where mating data for individual ewes cannot be collected and requires three plasma progesterone measurements from each ewe over a 12-days period.Ewes were diagnosed non-pregnant according to whether their lowest progesterone concentration (p) was below or above a “discriminatory value”. This value was chosen after examining the overall frequency distribution of values of log₁₀p.In experiment 1, $\text{25}\text{27}$ non-pregnant ewes and $\text{64}\text{65}$ pregnant ewes (20 to 31 days post-mating) were diagnosed correctly (96.7% accuracy). In experiment 2, $\text{40}\text{41}$ non-pregnant ews and $\text{45}\text{48}$ pregnant ewes (21 to 34 days post-mating) were diagnosed correctly (95.5% accuracy).     

Induction of fertile oestrus in seasonally anoestrous ewes with low doses of Gn-RH

Oestrus, conception and lambing performance were assessed in progesterone-primed seasonally anoestrous ewes induced to ovulate with gonadotrophin-releasing hormone (Gn-RH), which was administered intravenously for 48 h as either injections of 250 ng at 2-h intervals (n = 15) or as a continuous infusion at the rate of 125 ng/h (n = 12) or 250 ng/h (n = 12).In $\text{14}\text{15}$ of the ewes injected with Gn-RH, a preovulatory LH peak was recorded at a mean time interval of 33.9 ± 1.8 h after the start of treatment. All ewes displayed oestrus and all ovulated, with a mean ovulation rate of 1.67 ± 0.13. Eleven ewes were diagnosed as pregnant and subsequently lambed. Following infusion of Gn-RH, preovulatory LH peaks were recorded in $\text{21}\text{24}$ ewes at a mean time of 36.1 ± 2.9 h (125 ng/h) and 34.7 ± 2.0 h (250 ng/h). All but two of the ewes displayed oestrus and $\text{23}\text{24}$ ovulated. The group mean ovulation rates of 1.27 ± 0.14 (125 ng/h) and 1.75 ± 0.22 (250 ng/h) were not significantly different. Eleven of the 22 ewes mated were diagnosed as pregnant and produced live lambs.These results suggest that fertility of Gn-RH-induced ovulations in seasonally anoestrous ewes is comparable to that apparent in ewes ovulating spontaneously during the breeding season.     

The effect of microsomal enzyme inducing drugs on reproductive function in the ewe.

A number of drugs cause marked increases in the steroid hydroxylase activity of hepatic microsomes. Beginning 2 days after estrus, 117 mature ewes were each given 14 injections over a 27-day period of phenobarbital sodium, diphenylhydantoin, chlorcyclizine HCl or phenylbutazone. Blood samples for luteinizing hormone (LH) and progesterone determination by radioimmunoassay (RIA) were taken on day 10 of the first estrous cycle (day 18 if no heat was observed) and on days 5 and 10 of the second cycle. On day 10 of the second cycle, the ewes were given an intravenous injection of 1 ml of 6% solution of pentobarbitol sodium anesthetic per 4.5 kg body weight, and the length of anesthetic sleep time was measured. The ewes were then killed and corpora lutea and liver were weighed.In 33 ewes treated with either phenobarbitol sodium or phenylbutazone, sleep time was shortened (18 min $\text{vs}$ 29 min in untreated controls, P<.01), indicating that enzyme induction had occurred. For 41 ewes treated with either chlorcyclizine HCl or diphenylhydantoin, sleep time was lengthened to 93 min (P<.01 $\text{vs}$ controls), indicating impaired liver function. Electron micrographs of liver cells verified that enzyme induction or hepatic degeneration had occurred.     

Influence of the blood concentration of prolactin on the length of the sensitive period for establishing maternal behavior in sheep at parturition

The fading of postpartum maternal interest for the neonate (sensitive period) in ewes separated from their young at lambing is delayed when parturition is induced with 20 mg of estradiol benzoate (EB). An experiment was carried out to investigate the role of prolactin in this phenomenon. The sensitive period was studied in three groups of parturient ewes. In all groups lambs were removed at birth and reintroduced to their mothers 24 hr later. Maternal acceptance was tested at this time. In group 1 (dexamethasone D), ewes were induced to lamb with dexamethasone (15 mg im). In group 2 (EB), ewes were treated with 20 mg of estradiol benzoate (im). In group 3 (EB + CB 154) ewes received 20 mg of EB as in group 2 and 1 mg of CB 154 (sc) every 12 hr to prevent the enhanced secretion of prolactin which normally occurs after EB injection. The concentration of prolactin was highest in group 2 (EB), lowest in group 3 (EB + CB), and intermediate in group 1 (D) (p ? 0.001 between groups). By contrast, the proportion of ewes showing maternal behavior was similar in groups 2 and 3 ($\text{15}\text{23}$ and $\text{17}\text{22}$), both of which differed from group 1 ($\text{3}\text{22}\text{; p ? 0.005}$). It is concluded that the lengthening of the sensitive period for establishing maternal behavior in sheep following EB induced parturition is not related with high levels of prolactin in the peripheral circulation.     

Estimates of early embryonic loss in ewes mated to rams selected for high and low prolificacy

Two closed lines of sheep selected for high and low prolificacy were established in 1969. Rams within each line were selected on the basis of their dams' lambing records. Foundation ewes were assigned at random to selected rams, and no ewe selection was practiced until replacement yearlings were selected for mating. Selection of the rams used to mate the foundation ewes resulted in more lambs born per 100 ewes exposed to the ram (P<.10) and more lambs born per 100 ewes lambing from the high line rams (P<.05).Seven rams from each line were then used to estimate fertilization rate and embryonic survival rate when mated to an unrelated group of ewes. There was no difference in ovulation rate or fertilization rate of ewes mated to low and high line rams. Percent eggs recovered per CL was 80 and 92 (P<.01) for low and high line rams, respectively. At 35 days 82 and 86% of the ewes were pregnant, and 84 and 93% of the CL were represented by embryos in the pregnant ewes mated to low and high lines, respectively. Estimated embryonic survival rates were 81 and 89% in ewes mated to low and high line rams, respectively.     

Escherichiacoli endotoxin absorption from the ewe's uterus and peritoneal cavity

An experiment was conducted to assess the effects of estrogen or parturition on absorption of endotoxin from the ovine uterus. Twelve cycling ewes were assigned to one of four treatment groups (three ewes/group): Group I, no estrogen (NE) + intrauterine infusion of sterile saline (IUS); Group II, NE + intrauterine infusion of 100 mg endotoxin - Lipopolysaccharide W./$\text{E.}$$\text{coli}$ 0127:B8, Difco Laboratories, Detroit, MI (IUE); Group III, 3 days pretreatment with estradiol-17β (50 μg/da, E) + IUS; and Group IV, E + IUE. In addition, the uteri of three early postpartum ewes were infused with 100 mg endotoxin (Group V). Rectal temperatures (RT) and jugular blood samples were obtained at ?40, ?20, 0 (infusion), 20, 40, 60, 80, 100, 120, 180, and 240 minutes. The blood samples were analyzed for total white blood cell counts (WBC) and Limulus Amebocyte Lysate Assays (LAL). There were no alterations in RT, WBC, or LAL observed in Groups I–V. These results indicated that neither prior treatment with estradiol in cycling ewes nor parturition affected absorption of $\text{E.}$$\text{coli}$ endotoxin from the ovine uterus.A second study was conducted to characterize the changes in RT, WBC, and LAL during endotoxemia in cycling ewes. Three ewes received intraperitoneal infusions of 100 mg endotoxin and three ewes received intraperitoneal infusions of sterile saline. Evidence that endotoxin was absorbed from the peritoneal cavity was a decrease (P<0.10) in WBC and positive LAL in endotoxin-infused ewes. WBC and LAL did not change in saline-infused ewes. No changes in RT were observed in either group.     

A comparison of the periparturient rise in fecal egg counts of exotic and domestic ewes

Ewes of three exotic breeds (Florida Native, Barbados Blackbelly and St. Croix) showed no periparturient rise in fecal egg counts (PPR) when housed from late fall through lambing and weaning. Domestic breed ewes (Rambouillet and Finn-Dorset × Rambouillet) showed a pronounced PPR 6–7 weeks post-lambing while St. Croix × domestic ewes showed an intermediate PPR under similar conditions. There was no PPR in non-lambing ewes.In a second experiment, breed differences in the PPR were not as pronounced when ewes were allowed to graze a contaminated pasture after lambing. Florida Native, St. Croix and $\text{3}\text{4}$ St. Croix × $\text{1}\text{4}$ domestic showed lower PPRs than the remaining breeds (Barbados Blackbelly, F₁ hybrids of exotic and domestic breeds and domestic ewes), but the magnitude of the PPR was generally small in all breeds. No relationship was observed between hemoglobin genotype and PPR in either experiment.It was concluded that a low or absent PPR is an important manifestation of breed resistance in exotic ewes and that this may be useful as a marker for breeding parasite-resistant sheep.     

Effects of phyto-estrogenic alfalfa consumption on plasma LH levels in cycling ewes

Plasma luteinizing hormone (LH) concentrations were determined in five Dorset ewes fed orchard grass hay (Dactylus glomerata) and five ewes fed alfalfa (Medicago sativa). Total phyto-estrogen content ($\text{X}\text{±}\text{SEM}$ genistein equivalents) of the orchard grass hay and alfalfa was 16.9 ± 2.9 and 118 ± 12.3 ppm respectively. LH was determined at regular intervals during the estrous cycles synchronized with progesterone impregnated pessaries and characterized by marker ram and vaginal cytology.Peak LH levels in control ewes (40.1 ± 5.5 ng/ml) were lower (P<0.05) than in ewes fed phyto-estrogenic alfalfa (66.0 ± 16.8 ng/ml). Results also indicate that the LH peak may occur later (P<0.05) in the estrus period of ewes fed phyto-estrogenic alfalfa (15.4 ±4.5 h). These experiments may suggest that peak LH concentrations are elevated and delayed further into the estrus period in ewes fed phyto-estrogenic alfalfa.     

A new method for thawing frozen ram semen

The purpose of this work was to facilitate the on-farm use of frozen semen by initially thawing the straws in laboratory treated sperm (TS) rather than on-farm control sperm (CS), as is usually done. After thawing, TS was diluted, centrifuged, and extended in skim milk for storage at +15° C until utilized 3 to 6 hours later. $\text{In}$$\text{vitro}$: immediately after preparation and addition of skim milk for TS and thawing for CS, the percentage of stained cells and abnormal cells was higher (P < 0.01) in TS than in CS. In contrast, following a 3 hour incubation, TS and CS had the same proportion of motile cells. $\text{In}$$\text{vivo}$: fertility and prolificacy of FGA + PMSG-treated ewes were slightly higher following AI (1 AI/female) with TS than with CS: 52.4% $\text{vs}$ 44.2% and 155.0% $\text{vs}$ 148.0%, respectively. Fertility was also higher (P < 0.01) with fresh semen than with TS, but the difference was only 9.2 points (70.3% $\text{vs}$ 61.1% for the respective 798 and 242 ewes inseminated once). Prolificacy rates were similar (164.3% $\text{vs}$ 167.6%).     

In vitro synthesis of progesterone and prostaglandin F by luteal tissue and prostaglandin F by endometrial tissue from the pig

The relationship between progesterone (P₄) synthesis $\text{in vitro}$ by luteal tissue and prostaglandin F (PGF) synthesis $\text{in vitro}$ by endometrium and luteal tissue from two stages of the cycle, Days 7 to 8 and 15 to 16, was determined. Luteal and endometrial tissues were collected from pigs in three experimental groups at two stages of the cycle: (A) 6 pigs on Days 7 to 8 with spontaneous, 5 to 6 day old corpora lutea (CL); (B) 5 pigs on Days 15 to 16 with spontaneous, 13 to 14 day old CL; and (C) 6 pigs on Days 15 to 16 with spontaneous, 13 to 14 day old CL and 5 to 6 day old CL induced by pregnant mares serum gonadotropin (PMSG) and human chorionic gonadotropin (HCG) injections. Pigs with spontaneous, 13 to 14 day old CL of the cycle and PMSG-HCG induced accessory, 5 to 6 day old CL were used so that P₄ and PGF synthesis in tissue from old and new CL could be compared in the same pig on Day 15 to 16 of the cycle. Tissues (100 mg minces) were incubated in 5 ml of Krebs Ringer solution in an atmosphere of 95% 0₂:5% CO₂ for 2 hours at 0° C, 37° C, or 37° C with 1.3 x 10^?4M indomethacin (IND). An aliquot of the incubation medium and an aliquot of the supernatant after homogenization of the tissue in the remaining medium of each flask was quantified for P₄ and PGF by radioimmunoassay. P₄ and PGF release into the medium and total accumulation of P₄ and PGF in the flasks indicated that $\text{de novo}$ synthesis had occured at 37° C. Compared to tissue from 13 to 14 day old CL, tissue from 5 to 6 day old CL synthesized more P₄ per flask (53.9 $\text{vs}$ 25.0 ng/mg tissue, P<.001) and released more P₄ into the medium (20.8 $\text{vs}$ 8.8 ng/mg, P<.001). P₄ synthesis by luteal tissue from 5 to 6 day old and 13 to 14 day old CL from pigs in group C was similar to P₄ synthesis by luteal tissue from pigs in group A and group B, respectively. Luteul PGF synthesis was not affected significantly by either the age of the CL or by PMSG-HCG treatment. For endometrial samples, the synthesis of PGF was not significantly different among pigs in groups A, B and C. If uterine PGF is involved in luteal regression in the pig, the sensitivity of the CL to PGF may be more important than an increase in PGF secretion during the late luteal phase of the estrous cycle.     

Induction of parturition in ewes with a single injection of oestradiol benzoate

A single $\text{im}$ injection of 20 mg of oestradiol benzoate administered to ewes at 142 – 148 days of gestation resulted in parturition in 65% and 84% of ewes within 48 and 96 hr respectively. The remaining 16% of treated ewes suffered a higher incidence of dystocia and lamb survival was poorer than in untreated ewes or the treated ewes which lambed within 96 hr of treatment.     

Resistance of nonlambing exotic and domestic ewes to naturally acquired gastrointestinal nematodes

No breed differences in Haemonchus contortus burdens were found when nonlacfating exotic (St. Croix and Barbados Blackbelly), domestic (Finn-Dorset × Rambouillet) and $\text{1}\text{2}\text{exotic}\text{-}\text{1}\text{2}$ domestic ewes grazed fall pasture, but all ewes had significantly (p < 0.05) lower worm burdens at necropsy than tracer lambs grazing the same pasture. Florida Native ewes grazing the same pasture showed significantly (p < 0.05) less packed cell volume (PCV) decrease and significantly (p < 0.05) lower fecal egg counts than the other ewe breeds but were not available for necropsy. Tracer lambs had a significantly (p < 0.05) greater PCV decrease and significantly (p < 0.05) higher fecal egg counts than ewes.The results of this study suggest that breed differences in the periparturient rise in fecal egg counts of exotic and domestic ewes observed in an earlier study may have been caused by breed differences in the periparturient relaxation of immunity rather than breed differences in the ability to acquire immunity to worms.     

Enhancement of aryl hydrocarbon hydroxylase activity in cultured rodent cells by X-irradiation.

X-irradiation (500 rads) was found to enhance the aryl hydrocarbon hydroxylase (AHH) activity of three cell lines. Radiation followed by induction with benz (a) anthracene (5–15 μg/ml) produced a synergistic effect on AHH. These effects were highly significant and were observed most dramatically with a hamster tumor cell line, A(T_l)Cl-3,a nd to a lesser extent in secondary hamsters embryo cells and mouse $\text{C}\text{3}\text{H}\text{/10}\text{T}\text{1}\text{2}$ CL8 cells.