Characteristics of lambs fed concentrates or grazed on ryegrass to traditional or heavy slaughter weights. II. Wholesale cuts and tissue accretion.

Targhee x Hampshire lambs (average BW 24 +/- 1 kg) were used to determine the effect of finishing on concentrate or by grazing ryegrass forage on slaughter weights of 52 kg (N) or 77 kg (H) on tissue accretion and lamb wholesale cutout. When fed to similar slaughter weights, the wholesale cuts of concentrate-fed lambs were heavier (P < 0.05) than the same cuts from forage-fed lambs; however, when expressed as a percentage of side weight, carcasses of forage-fed lambs had a higher (P < 0.001) percentage of leg than concentrate-fed lambs. Increasing slaughter weight from 52 to 77 kg resulted in a 1-kg increase in loin weight for lambs finished on concentrate and a 0.60-kg increase for lambs finished on forage (diet x slaughter weight, P < 0.03); however, the increased loin weight for lambs finished on concentrate was due largely to increased fat deposition. For lambs slaughtered at 77 kg, those finished on forage had more lean mass in the leg, loin, rack, and shoulder than those finished on concentrate, but lean mass in these cuts did not differ between diets for lambs slaughtered at 52 kg (diet x slaughter weight, P < 0.01). At the normal slaughter weight (52 kg), concentrate-fed lambs had 50% more dissectible fat than forage-fed lambs, whereas at the heavy slaughter weight, a 79% greater amount of dissectible fat was observed for concentrate- vs. forage-fed lambs (diet x slaughter weight, P < 0.001). Lean and fat accretion rates were higher (P < 0.001) for concentrate-fed lambs than for forage-fed lambs. The lean-to-fat ratio of forage-fed lambs was higher (P < 0.001) than that of concentrate-fed lambs; however, forage finishing decreased accretion rates of all tissues compared with concentrate feeding, and these differences between forage and concentrate feeding were magnified at heavier slaughter weights.

Comparison of characteristics of lambs fed concentrate or grazed on ryegrass to traditional or heavy slaughter weights. I. Production, carcass, and organoleptic characteristics.

The objectives of this study were to determine the effects of finishing lambs on concentrate (C) or by grazing ryegrass forage (F) to slaughter end weights of 52 (N) or 77 kg (H) on carcass characteristics and organoleptic properties. This experiment included 64 Targhee x Hampshire lambs (average BW = 24 +/- 1 kg) in a 2 x 2 x 2 factorial arrangement of treatments to compare wethers vs. ewes, C vs. F, and N vs. H slaughter weights. No interactions (P > 0.10) were observed between gender and other main effects. Hot carcass weight and dressing percent were greater (P < 0.001) for C- than for F-fed lambs. Backfat thickness also was greater (P < 0.001) for lambs fed C than for those fed F. Moreover, USDA lean quality score and USDA yield grades were higher (P < 0.001) for C- than for F-fed lambs, as well as for lambs slaughtered at H vs. N market weights. There was a higher (P < 0.005) incidence of off odors and off flavors in cooked muscle from F- vs. C-fed lambs, and also from H vs. N slaughter-weight lambs. The heavy C-fed lambs had juicier (P < 0.001) meat than other treatment combinations. Cooked meat from C-fed lambs received higher (P < 0.001) overall acceptability scores. Concentrate-finished lambs produced fatter carcasses and more palatable meat than forage-finished lambs; however, forage finishing allowed for slaughter at heavier weights without excessive fat deposition.

Tissue fatty acid profiles can be used to quantify endogenous rumenic acid synthesis in lambs.

Proportions of vaccenic (trans-11 18:1) and rumenic (cis-9, trans-11 18:2) acids in mesenteric adipose, subcutaneous adipose, and longissimus muscle tissue lipids from lambs fed varying proportions of forages and concentrates were used to develop a mathematical model to predict exogenous and endogenous contributions to rumenic acid (RA) in the several tissues. From the model, we were able to estimate the proportion of absorbed RA, the proportion of vaccenic acid (VA) desaturated, the original proportion of VA in the tissue (before desaturation), and finally the proportion of RA synthesized endogenously. Estimates of endogenous RA were in the range of published data estimated by independent procedures. An independent data set of VA and RA in milk fat was used to challenge the model. Predictions were concordant with observations, although estimates of endogenous RA synthesis were lower than previous reports. Changing the amount of exogenous RA through manipulation of the diet influenced desaturation of VA inversely, so that endogenous RA synthesis was decreased when exogenous supply was increased (r = -0.80). The model should be challenged with data from human and nonruminant, as well as ruminant studies.

Length of docked tail and the incidence of rectal prolapse in lambs.

A multistate cooperative study was conducted to study the current issue of tail length in docked lambs and its relationship to incidence of rectal prolapse. A total of 1,227 lambs at six locations were randomly allocated to two or three tail dock treatments: 1) short--tail was removed as close to the body as possible, 2) medium--tail was removed at a location midway between the attachment of the tail to the body and the attachment of the caudal folds to the tail, and 3) long--tail was removed at the attachment of the caudal folds to the tail. Short-docked lambs had a greater (P < 0.05) incidence of rectal prolapse (7.8%) than lambs with a medium (4.0%) or a long (1.8%) dock. Female lambs had a higher (P < 0.05) incidence of rectal prolapse than male lambs. At two stations, lambs were finished either in a feedlot on a high-concentrate diet or on pasture with no grain supplementation. At one station, with a very low incidence of rectal prolapse, there was no difference in incidence between lambs finished in the feedlot or on pasture; however, at the station with a relatively high incidence of rectal prolapse, lambs in the feedlot had a higher (P < 0.05) incidence than lambs on pasture. The half-sib estimate of heritability for the incidence of rectal prolapse was low (0.14). The results of this study strongly implicate short dock length as a cause of rectal prolapse in lambs finished on high-concentrate diets. Furthermore, the results of this study and the only other study known conducted on this issue strongly suggest that docking lambs at the site of the attachment of the caudal folds to the tail will result in a negligible incidence of rectal prolapse.

Alpha-tocopherol concentrations and case life of lamb muscle as influenced by concentrate or pasture finishing.

Two experiments were conducted to evaluate alpha-tocopherol accumulation in muscle of lambs finished on pasture or concentrates. The objective for Exp. 1 was to compare accumulation of alpha-tocopherol in the longissimus muscle of pasture-fed lambs to that of lambs fed three concentrations (15, 150, and 300 IU/kg of DM) of supplemental vitamin E (all rac alpha-tocopheryl acetate) in all-concentrate diets. The objective in Exp. 2 was to investigate the effect of duration of supplemental vitamin E feeding on alpha-tocopherol content and color change during display case storage of lamb muscle. Treatments evaluated in Exp. 2 were: 15 IU of supplemental vitamin E/kg DM fed to finish; 15 IU/kg followed by 300 IU/kg of DM during the last 21 d; and 15 IU/kg DM until 7 d prior to finish, then 300 IU/kg DM. In Exp. 1, alpha-tocopherol concentration of rotational grazed alfalfa and perennial ryegrass averaged 137 and 169 mg/kg of DM. Vitamin E treatments for lambs fed concentrate diets did not affect ADG (P > 0.15), but ADG was greater (P < 0.01) for concentrate-fed lambs than for grazing lambs. For the concentrate-fed lambs, alpha-tocopherol in longissimus muscle increased quadratically (P < 0.05) as dietary concentrations of vitamin E increased. Predicted maximum alpha-tocopherol concentration in muscle occurred at about 400 IU/kg of diet DM. Longissimus muscle from lambs grazing alfalfa or ryegrass had similar (P > 0.50) alpha-tocopherol concentrations, and those concentrations were similar to values obtained when the concentrate diet supplemented with 150 IU of vitamin E/kg was fed. In Exp. 2, no differences (P > 0.10) in ADG were observed. Concentrations of longissimus alpha-tocopherol were highest when 300 IU supplemental vitamin E was fed for 21 d prior to slaughter. During a 6-d display period, semimembranosus steaks from lambs fed 300 IU of supplemental vitamin E/kg for either 7 or 21 d had higher a* and b* color readings than steaks from lambs fed 15 IU/kg of supplemental vitamin E. Increased consumption of vitamin E either via pasture or supplementation results in higher alpha-tocopherol concentrations in meat.

Body weight and tissue gain in lambs fed an all-concentrate diet and implanted with trenbolone acetate or grazed on alfalfa.

Targhee x Hampshire lambs (average BW 23 +/- 1 kg) were used in two experiments to determine the effects of finishing on concentrate with an anabolic implant or forage grazing after concentrate feeding on growth, organ and viscera weights, and carcass tissue accretion. In Exp. 1 and 2 lambs were penned by sex and assigned for slaughter at initial (23 kg), intermediate (37 kg), or end BW (ewes, 47.7; wethers 50.4 kg). From 23 to 37 kg BW, lambs were fed all-concentrate diets in drylot (DL) or grazed on alfalfa (ALF). Experiment 1 was a 2 x 2 factorial with 28 lambs; factors were wether vs ewe lambs and unimplanted vs DL implanted with trenbolone acetate-estradiol benzoate. There were no differences in organ and viscera weights due to implant status. However, ADG (P < .03) and lean gain (P < .02) were greater for implanted than for unimplanted wethers (507 vs 357 g and 1,314 vs 656 g, respectively). Ewes did not respond to the implant. Fat accretion was not affected by implantation. Experiment 2 was a 2 x 3 factorial with 42 lambs; factors were wether vs ewe lambs and drylot during growing and finishing phases (DL-DL) vs drylot during growing and alfalfa grazing during finishing (DL-ALF) vs alfalfa grazing during growing and finishing phases (ALF-ALF). In Exp. 2, ADG of DL-DL lambs was greater (P < .01) than ADG of DL-ALF or ALF-ALF lambs. Lambs on ALF-ALF had smaller (P < .05) livers and rumen/reticulum weights but heavier (P < .04) kidney, omasum, small and large intestine, and cecum weights than those on DL. In Exp. 2, DL-ALF and ALF-ALF lambs had overall hindsaddle lean gain equal to those on DL-DL with less mesenteric fat and 100 g less separable fat. Finishing lambs on alfalfa reduced fat accretion without decreasing lean accretion, whereas trenbolone acetate implants for lambs fed concentrate increased BW gain and lean accretion without affecting fat accretion.

Energy source and ionophore supplementation effects on lamb growth, carcass characteristics, visceral organ mass, diet digestibility, and nitrogen metabolism.

In Exp. 1, 72 Targhee lambs (initial BW 22.1+/-.3 kg) were used to determine the effects of energy source (alfalfa pasture vs limit-fed, all-concentrate) and ionophore addition on performance, visceral organ mass, and carcass characteristics. There were no differences (P > . 10) in ADG or gain/ feed due to ionophore supplementation. Lambs that grazed alfalfa had greater (P < .05) liver, omasum, abomasum, small intestine, cecum, and large intestine weights than did lambs fed the concentrate diet. Lambs fed the concentrate diet had greater (P < .01) hot carcass weights, larger (P < .01) loin eye areas, and greater (P < .001) dressing percentages than lambs that grazed alfalfa. In Exp. 2, lambs offered the concentrate diet had greater (P < .001) DM and OM digestibilities than lambs offered alfalfa (89.5 and 91.1 vs 72.4 and 74.2%, respectively). Apparent and true N digestibilities were greater (P < .001) for the concentrate diet than for alfalfa (90.9 and 101.7 vs 77.7 and 91.9%, respectively). Likewise, grams of N retained per day were twice as great (P < .001) with the concentrate diet than with alfalfa (14.9 vs 6.0 g/ d). The greater visceral organ mass and resulting increases in energy and protein requirements in lambs that grazed alfalfa were probably responsible for the lesser hot carcass weight and dressing percentage compared with lambs fed 100% concentrate.

Effects of dietary energy intake and protein concentration on performance and visceral organ mass in lambs.

Eighty-eight early-weaned Hampshire x Targhee crossbred lambs (initial BW 23 +/- 3.9 kg) were used in a 2 x 2 factorial design experiment to determine the effects of DM and CP intake on lamb performance and weight and accretion rates of visceral organs during two periods of growth, divided at 36 kg live weight. There were 10 lambs per replicate and two replicate pens per treatment. Dry matter intake was 100 or 85% of ad libitum, and protein intake was 100 (normal) or 125% (high) of the calculated NRC (1985) requirement. Over both periods, lambs allowed ad libitum access to feed had greater (P < .05) ADG, rumen/reticulum, large intestine, and liver weights and faster accretion rates than lambs fed at 85% of ad libitum; however, there were no differences (P = .87) in feed efficiency. For the total trial, lambs fed high protein had greater (P < .01) DMI, ADG, liver and kidney weight and accretion rates, and increased (P < .01) feed efficiency during period 1 compared with lambs fed normal protein concentrations. Diets containing high concentrations of dietary protein resulted in greater DMI and ADG throughout the feeding period compared with diets formulated at NRC (1985) recommended concentrations, indicating that NRC (1985) protein recommendations may limit lamb performance. Restricted feeding resulted in reduced visceral organ mass compared with offering feed for ad libitum consumption. Restricted feeding increased efficiency of feed utilization for gain, in part, through reductions in visceral organ mass.

Effects of feeding a high-grain diet at a restricted intake on lactation performance and rebreeding of ewes.

Fifty-six mature Polypay ewes were used in two experiments to examine the effects of feeding a high-grain diet at a restricted intake on milk production and composition, lamb performance and out-of-season breeding. Ewes were fed either a high-grain diet (85% concentrate and 15% forage) or a high-forage diet. The high-forage diets were 68% forage and 32% concentrate in Experiment 1 and 80% forage and 20% concentrate in Experiment 2. Forage forage and 20% concentrate in Experiment 2. Forage source was orchardgrass hay (Experiment 1) or alfalfa cubes (Experiment 2). Feed intake of the high-grain diet was restricted by 20% (compared with ewes fed high forage) so that intake of energy was similar for both dietary groups. Daily milk production was 19% higher (P < .05) in Exp. 1 and 8% higher (P < .10) in Exp. 2 for ewes fed high grain than for those fed high forage (2.71 vs 2.28 kg/d and 3.18 vs 2.95 kg/d in Exp. 1 and 2, respectively). Milk protein percentage and daily amount of milk protein were higher (P < .05) and the percentage of milk fat was lower (P < .03) for ewes fed the high-grain diet than for those fed the high-forage diet. Diet did not affect milk fat production (grams/day) or lamb growth rate. In both experiments blood insulin concentration was higher for ewes fed the high-grain diet than for those fed the high-forage diet; however, no improvements in reproductive performance were observed. Limit feeding high-grain diets is an effective alternative to forage for lactating ewes.

Effects of limit feeding a high-grain diet on puberty and reproductive performance of ewes.

In Exp. 1, 39 ewe lambs (initial BW 29 +/- .1 kg) were used in a 2 x 2 factorial arrangement with two breeds (Polypay and Targhee) and two diets (high-forage and high-grain) to examine the effects of restricting intake of a high-grain diet on onset of puberty and lamb performance. The experimental diets were fed from 13 to 40 wk of age. The high-forage diet was composed of 80% alfalfa cubes and 20% supplement. The high-grain diet was 90% concentrate and 10% alfalfa cubes. Feed intake of the diets was controlled so that lambs fed the high-grain diet had the same growth rate as those fed the high-forage diet. Plasma insulin concentration was higher (P < .001) for lambs fed the high-grain diet than for those fed the high-forage diet. However, no diet effect on age at puberty was observed. In Exp. 2, 88 mature Targhee ewes were used to determine the effects of limiting intake of a high-grain diet on pregnancy and number of lambs born per ewe. Intake of the high-grain diet was restricted to achieve similar ME intake between diets. There were no diet effects on number of lambs born per ewe or subsequent lamb performance. Ewes fed the high-forage diet had a lower (P < .001) weight gain than those fed the high-grain diet. It was concluded that restricting intake of high-grain diets is an effective alternative to feeding high-forage diets for meeting the nutrient requirements of ewe lambs and gestating ewes; however, no improvements on reproductive performance were observed.

Growth and tissue accretion of lambs fed concentrate in drylot, grazed on alfalfa or ryegrass at weaning, or after backgrounding on ryegrass.

Weaned Targhee x Hampshire lambs (average BW 27.6 kg) were used to determine the effects of concentrate feeding, forage grazing, or finishing on concentrate after grazing upon growth and carcass tissue accretion. Lambs were assigned randomly and balanced by weight and sex to five replicated treatments (12 lambs/treatment): all-concentrate in drylot (DL); rotational grazing alfalfa (ALF); rotational grazing ryegrass (RG); RG for 62 d, then DL (RGDL); RG for 62 d, then ALF (RGALF). Lambs were slaughtered when fat thickness over the ribeye was estimated at 3.8 to 5.6 mm. Lamb growth and carcass measurements included ADG, accretion of bone, lean, and fat in the carcass, and final BW. Lambs on DL had the highest (P = .001) ADG, whereas lambs on RG treatments tended to have the lowest ADG and heaviest final BW. Compared with DL lambs, ALF lambs had lower (P < .05) ADG but comparable final BW. Lambs that grazed RG had more (P = .001) carcass lean weight than lambs fed in DL, but carcass lean weight of lambs grazed on ALF did not differ (P > .05) from that of lambs on the DL or RG treatment. Carcass fat was less (P = .001) for ALF lambs than for the DL, RGDL, or RGALF treatment group. Daily accretion of bone, lean, and fat was highest (P = .001) for DL. Daily accretion of lean and fat for the RG group was less (P = .001) than for the ALF group but did not differ (P > .05) from that of RGALF lambs. Lean:fat ratio in weight gain for DL lambs was less (P < .01) than ratios for the ALF and RG groups, which were similar to those for RGDL and RGALF lambs. When slaughtered at the same level of fat over the ribeye, DL-fed lambs had higher ADG and fewer days on test than grazed lambs. However, lambs finished or backgrounded on forage had high lean:fat tissue gain and a higher percentage of lean in their carcasses than DL-fed lambs.

Effects of restricted feeding on growth performance and carcass composition of lambs.

Fifty-eight crossbred lambs (26 kg BW) with moderate growth potential were used in a completely randomized design experiment to determine the effects of restricted feeding of all-concentrate diets on performance and carcass composition. Feeding levels studied were 100, 85, and 70% of ad libitum intake. Diets that were restricted-fed were formulated to have increased nutrient concentrations to provide equal daily intakes of protein, vitamins, and minerals among DM intake levels. Lambs were fed to a final weight that would yield carcasses of equal weight (24 kg). Average daily gain was reduced linearly (P < .02) and days on feed were increased linearly (P < .02) because of restricted feeding. Feed efficiency, however, was not affected by intake level. The quantity of separable lean tissue within carcass sides was increased (P < .05) with restricted feeding. Total separable fat within the side was reduced (P < .05) in an amount equal to the increase in lean tissue accretion. Chemical analysis of the carcass side showed a decrease (P < .05) in fat percentage and a corresponding increase (P < .05) in water percentage because of restricted feeding. Daily accretion rates of lean and bone tissue were not affected by restricted feeding; however, fat accretion was decreased linearly with decreasing feeding levels. Separable lean tissue within the primal cuts was generally increased with decreasing intakes, which led to a corresponding decrease in separable fat. Restricted feeding strategies can lead to the production of leaner carcasses. Reductions in fat content occur in the subcutaneous, seam, and mesenteric depot sites, but intramuscular fat content of consumable product also is reduced.

Effects of grain or pasture finishing systems on carcass composition and tissue accretion rates of lambs.

The effects of finishing system on growth performance and carcass composition were determined in an experiment using 40 crossbred, early-weaned lambs (28 kg BW). Finishing systems were 1) grazed alfalfa, 2) 100% concentrate diet fed in drylot, and 3) grazed ryegrass for 42 d followed by a 100% concentrate diet fed in drylot. All lambs were fed to similar final weights (48 kg). Average daily gain was greater for lambs placed directly in the feedlot than for lambs on the other two finishing protocols. The quantity of separable lean tissue and bone were not affected by finishing system. However, quantity of total fat and each of the three major fat depot sites (subcutaneous, seam, and mesenteric) were reduced (P < .05) in alfalfa-finished lambs compared with fat in lambs fed concentrate at some time during finishing. Daily accretion rates of lean and fat tissue were greater (P < .05) for lambs placed directly in drylot than for lambs that consumed forage at some time. In addition, daily fat accretion rates were greater in lambs placed directly in drylot than in lambs that initially grazed ryegrass. Composition of individual primal cuts revealed reductions (P < .05) in total separable fat with alfalfa finishing compared with the other two systems. However, chemical composition of the lean tissue within the primal cuts was not affected by finishing system, with the exception of the loin and breast. Finishing systems based on grazed forage can lead to the production of leaner carcasses, but major differences in the composition of consumable product were not observed.

Performance and carcass characteristics of weaned lambs either grazed on orchardgrass, ryegrass, or alfalfa or fed all-concentrate diets in drylot.

Four-paddock rotational grazing of orchardgrass, ryegrass, or alfalfa was compared to an all-concentrate diet fed in drylot using 202 weaned lambs. Comparisons of animal performance ended in each of the 3 yr (1983, 1984, 1985) for all animals when drylot lambs reached a subjective body condition score of 12 (range 1 to 15) and estimated fat depth over the rib was 5.5 to 7.0 mm. A total of 84 representative lambs were slaughtered over the 3 yr for carcass evaluation. Mature put-and-take ewes were used to maintain forages in the vegetative stage. Average daily gain and total gain of lambs were in the order of drylot > alfalfa > grasses; performance of lambs grazing alfalfa approached performance of those fed the drylot diet. Better performance (P < .01) of lambs grazing alfalfa than of those grazing grasses is atributed to more CP (P < .01) and less NDF, ADF, and hemicellulose (P < .01) in alfalfa. Lambs grazed on grasses had smaller carcasses with less muscle, fat, and bone (P < .01) than either of the other two treatments. Although carcasses of lambs grazed on alfalfa were lighter, they had the same muscle mass as concentrate-fed lambs, indicated by leg conformation, longissimus muscle area, and by physically separated absolute muscle weight. However, these carcasses contained less fat (P < .01) and had more desirable yield grades (P < .01) than the carcasses of concentrate-fed lambs.

Periparturient rise in the excretion of Giardia sp. cysts and Cryptosporidium parvum oocysts as a source of infection for lambs.

The possibility of a periparturient rise (PPR) in the excretion of Cryptosporidium parvum oocysts and Giardia duodenalis-type cysts and its implications in the epidemiology of these 2 pathogens were investigated. Fecal samples were taken from 32 lambing ewes every 2 wk from 4 wk before lambing until 8 wk after the start of lambing. Samples from both ewes and lambs were examined with a quantitative immunofluorescence assay. Excretion of Giardia sp. cysts by ewes increased at 2 wk prepartum, peaked at zero and 4 wk postpartum, and returned to low levels at 6 and 8 wk postpartum. Some ewes also excreted C. parvum oocysts at the start of lambing. Excretion rates and intensities of Giardia sp. cysts by lambs were high, whereas those of C. parvum oocyst excretion were light. The PPR in excretion of Giardia sp. cysts by ewes was considered to be the major source of giardiasis for lambs. Excretion of C. parvum oocysts by ewes at parturition also played a role in initiating cryptosporidiosis in lambs.

Effects of administration of human chorionic gonadotropin or progesterone before maternal recognition of pregnancy on blastocyst development and pregnancy in sheep.

A series of four experiments with 258 ewes was conducted to determine whether blastocyst size could be altered before normal luteolysis and, if so, how this affected fertility. In Exp. 1 and 2, nonmated and mated ewes, respectively, were treated with hCG (100 IU), progesterone (12 mg), or vehicle on d 11.5 (d 0 = onset of estrus). In Exp. 3 and 4, field trials were conducted to compare the effects of either hCG or progesterone treatment on d 11.5 on subsequent pregnancy rates. In Exp. 1, hCG transiently increased (P < .01) concentrations of progesterone and estradiol in plasma, whereas progesterone treatment increased only plasma progesterone. Neither hCG nor progesterone affected the duration of the estrous cycle. In Exp. 2, d-13 blastocysts were longer (3.5 +/- 1.6 vs .8 +/- .5 cm; Mean +/- SE; P < .05), and concentrations of protein and interferon tau (IFN tau) in uterine flushings were greater (10.7 vs 1.2 micrograms; P < .05) in hCG than in vehicle-treated ewes. Progesterone treatment did not affect blastocyst development. In Exp. 3, pregnancy rates tended to be greater (P < .10) in ewes given hCG than in those given vehicle (44/47; 94% vs 40/48; 83%); however, administration of progesterone in Exp. 4 had no effect on pregnancy rates (P < .14; 41/45; 91% vs 37/46; 80%; control ewes). These results indicate that treatment with hCG on d 11.5 stimulated uterine secretions and conceptus growth sufficiently to influence pregnancy rates.

Luteal function and blastocyst development in ewes following treatment with PGF(2)alpha and GnRH.

Luteal function and blastocyst development were compared in ewes treated with GnRH (100 mug) on Day 1 (Day 0 = day of estrus) or in ewes previously induced into estrus with PGF(2)alpha. In Experiment 1, the duration of estrous cycles of ewes previously treated with PGF(2)alpha were longer (P<0.06) than those that received PGF(2)alpha plus GnRH, GnRH alone, or remained untreated (control) ewes. Progesterone concentrations were lower (P<0.07) on Day 1 and higher (P<0.01) on Days 16 and 17 of the estrous cycles following PGF(2)alpha treatment relative to those of the natural (control) cycles. In Experiment 2, blastocysts of ewes treated with PGF(2)alpha were less developed (P<0.06) by Day 13 of pregnancy than those of the control ewes. The GnRH treatment did not influence any of these characteristics. Treatment with PGF(2)alpha delayed luteal formation during the subsequent estrous cycle, increased the duration of the estrous cycle and slowed the rate of blastocyst development relative to GnRH-treated and untreated ewes.

Influence of the embryo on intrauterine migration in sheep.

Mechanisms of intrauterine migration were examined in 55 ewes. In the first experiment, corpora lutea were removed from unilaterally ovariectomized ewes on d 4 (d 0 = estrus) and pregnancy was maintained by giving exogenous progesterone. In Exp. 2, the reproductive tract was altered surgically such that embryos initially entered the uterine horn contralateral to the site of ovulation. In Exp. 3, ewes received beads of silastic polydimethylsiloxane that released either cholesterol or estradiol-17 beta in an attempt to mimic embryonic synthesis of estradiol. In the fourth experiment, unilaterally ovariectomized ewes were superovulated and spacing of embryos within the uterus was then examined. In all experiments, ewes were slaughtered on d 15 and recovery of embryos or beads from each uterine horn indicated that migration had occurred. All ewes in Exp. 1 and 2 that had two conceptuses experienced embryonic migration. Beads impregnated with estradiol migrated farther (P less than .01) than cholesterol-containing beads (27.6 +/- 4.3 vs 12.5 +/- 1.6 cm, respectively). In Exp. 4, only one conceptus had migrated into the contralateral horn in all ewes. These results demonstrated that 1) embryonic migration was not affected by local vs systemic exposure to progesterone, 2) embryos migrated into the unoccupied horn, regardless of the initial horn of entry, 3) estradiol may stimulate embryonic migration, and 4) conceptuses were not equally distributed between horns.

Relationship between variation in conceptus development and differences in estrous cycle duration in ewes.

The objective of this study was to examine conceptus development on Day 13 in ewes with estrous cycles of different durations. Ewes (n = 80) were screened according to the length of their estrous cycles. Subsequently, ewes that had either SHORT or LONG cycles were utilized (15.9 +/- 0.1 or 18.6 +/- 0.4 days; mean +/- SEM, p less than 0.01; 10 ewes per group). Jugular blood samples were collected twice daily from Days 0-6 after mating and then once a day until slaughter on Day 13. Concentrations of progesterone in plasma and amounts of ovine trophoblast protein-1 (oTP-1), protein, and prostaglandins (PG) E2 and F2 alpha (PGF2 alpha) in uterine flushings were determined. Concentrations of progesterone were greater (Day by treatment interaction, p less than 0.01) on Days 2-4 for ewes in the SHORT group. On Day 5 and thereafter, progesterone concentrations were not different between groups. More (p less than 0.05) oTP-1 and protein (8.1 +/- 1.3 micrograms and 1.8 +/- 0.3 micrograms versus 2.4 +/- 1.3 micrograms and 0.8 +/- 0.3 mg) were recovered from uterine flushings from ewes in the SHORT versus LONG groups, respectively. The ratio of PGE2:PGF2 alpha was higher (p less than 0.06) in flushings from ewes in the SHORT versus LONG group (1.4 +/- 0.2 versus 0.9 +/- 0.2, respectively). Conceptuses were classified by stage of morphological development. Conceptus development was accelerated (p less than 0.01) in ewes of the SHORT group, as shown by filamentous conceptuses recovered from 78% versus 0% of SHORT versus LONG ewes, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of intramuscular administration of recombinant bovine interferon-alpha I1 during the period of maternal recognition of pregnancy.

One hundred ewes were utilized to determine the effects of interferon supplementation on the number of ewes pregnant and embryonic survival. Ewes were checked twice daily (0700 and 1600) for estrus using fertile rams. On d 12 through 16, ewes received twice-daily i.m. injections of either recombinant bovine interferon alpha I1 (2 mg IFN) or vehicle. Ewes remained penned with rams and were observed for subsequent estrous activity for at least 35 d after mating. To determine the number of fetuses and corpora lutea, all ewes were subjected to one surgery during mid-pregnancy (d 45 to 80). More (P less than .05) ewes were pregnant after treatment with IFN vs vehicle (45 of 49, 92% vs 37 of 49, 76%, respectively). The interestrous interval for ewes that were treated with IFN and did not conceive was longer (P less than .05) than for ewes given vehicle (26 +/- 1 vs 17 +/- 2 d, respectively). Embryonic survival (98.2 vs 87.9%; P less than .05), calculated as the number of fetuses present at the time of laparotomy and expressed as a percentage of the ovulation rate, and percentage of ewes with 100% fetal survival (96 vs 76%; P less than .05) were greater after treatment with IFN. It was concluded that supplementation of IFN increased both the number of ewes pregnant and embryonic survival.