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Cows that consume needles from Pinus ponderosa (PN) abort, but little is known about variables that affect consumption or response. These experiments were conducted to test the effects of several variables on pine needle-induced abortion. Cows were placed on experiment at 250 d of pregnancy and were either given ad libitum (AL) access to PN separate from other feed sources or the PN were ground and fed (2 kgcow-l.d-l) mixed with the diet. In Exp. 1, cows were assigned to a 2 x 2 factorial experiment with adequate ( AP) vs high-protein ( HP 1 diets and no straw vs AL straw (S). All cows ate PN and aborted, and there were no effects ( P > .5) on interval to parturition (IP). Consumption of PN (kg/ d) was increased by HP (P .5). In Exp. 3, cows were assigned to five treatments to test the effects of aging needles after they were ground, feeding bentonite, and feeding a complete mineral supplement. Pine needles decreased IP (P .2) of protein level or salt-sulfur blocks. In Exp. 5, cows were assigned to five treatments to test the effects of limit feeding vs AL availability of the basal diet and basal diets of hay vs corn silage. Access to PN decreased IP only when the basal diet was hay (P c: ,011, because silage-fed cows did not eat PN. Our conclusions are that 1) feeding high levels of protein increased PN consumption but not abortion rate, 2) weathered or aged needles had activity similar to or greater than that of dried needles, 3) feeding corn silage prevented cows from eating pine needles, and 4) none of the other diet variables prevented con- sumption of PN or response to PN.

Sperm transport through and distribution within the anterior reproductive tract were evaluated at either 2 or 22 h after artificial insemination in ewe lambs at first (1E; n = 15) or third (3E; n = 14) estrus and in mature (MAT; n = 12) ewes. Each ewe was inseminated immediately upon detection of estrus with 7.5 x 10(8) progressively motile sperm placed into the external os cervix. Ewes were hysterectomized at either 2 or 22 h after insemination. Sperm were recovered from the uterus, isthmi, and ampullae by flushing with sterile .9% saline. The distribution of sperm recovered from the uterus, isthmus, and ampulla did not differ (P > .10) among 1E, 3E, and MAT ewes at either 2 or 22 h. However, there was a tendency (P = .08) for more sperm to be recovered from the anterior reproductive tract in 3E and MAT ewes than from that in 1E ewes. There was a time of hysterectomy x anatomical segment interaction (P .10). However, sperm were recovered from the oviducts in a greater (P < .05) percentage of ewes at 22 h after insemination than at 2 h.(ABSTRACT TRUNCATED AT 250 WORDS)

Ponderosa pine (Pinus ponderosa) needles were fed to pregnant beef cows. Mean gestation lengths of 250.6 days for winter pine needles (PN) and 253.2 days for summer PN were reduced (p < 0.001) compared to controls (274.8 days). The levels of nine mycotoxins in fresh Ponderosa PN from trees, old PN from the ground, dry PN from trees, and PN collected from trees cut in the winter and summer were below detectable limits. The mycotoxins evaluated included aflatoxins BI, Bz, and GI, zearalenone, zearalenol, ochratoxin, T-2 toxin, diacetoxyscirpenol (DAS), and deoxynivalenol (DON). All of the collections of PN analyzed were either known to induce or believed to induce abortion in cattle. Inadequate cleanup prevented evaluation of zearalenone and zearalenol in winter-collected PN and dry PN from trees and T-2 toxin and DAS in winter-collected PN, fresh PN collected from trees, old PN from the ground, and dry PN collected from live trees. Pine needles collected from trees cut in the summer induced early parturition in 100% of the pregnant cows fed these PN and were successfully evaluated for all nine mycotoxins; however, levels were below detectable limits. The mycotoxins evaluated in this study do not appear to be involved in PN abortion.

Pregnant cows were fed pine needles (PN, 2 kg.cow-1.d-1) mixed with the diet to determine factors that affect abortion response. In Exp. 1, treatments were used to determine the effects of experimental stress and pelleting of pine needles. Pelleting needles and experimental stress delayed abortion response (P < .01). Stress-induced delay was associated with abnormal patterns of progesterone and cortisol (P < .01). In Exp. 2A and 2B, the role of the corpus luteum (CL) in abortion response to PN consumption was investigated by regressing the CL with prostaglandin F2 alpha. Regression of the CL and PN feeding reduced interval to parturition, but the effect of PN feeding was less when the CL was regressed (PN x CL, P < .01). The progesterone increase in response to experimental stress was decreased by CL regression (P < .01). In Exp. 3, melengestrol acetate (MGA) was fed (0, 2, or 4 mg.cow-1.d-1) in addition to PN. Parturition was blocked more effectively as dose of MGA increased (P = .075), but only parturition was blocked rather than the effects of PN. In Exp. 4, CL regression was blocked by feeding ketoprofen. Ketoprofen delayed response to PN, but the effect was only temporary (P < .01). Our conclusions are that 1) experimental stress delays abortion response to PN by increased concentrations of progesterone, 2) pelleting PN decreases their abortifacient activity, and 3) abortions caused by PN can be blocked by feeding a progestin or a prostaglandin inhibitor, but these compounds do not block the primary abortifacient effects of PN.

Multiparous cows (n = 91, 1986; n = 92, 1987) were selected from 2 populations to obtain cattle with high and low milk production. After March-April calving, high and low producing cows grazed either native range (treatment 1) or seeded range (treatment 2) until weaning in September. Seeded range included paddocks of crested wheatgrass (Agropyron desertorum, Fisch. ex [Link]Schult), contour furrowed native range interseeded with "Ladak" alfalfa (Medicago Sativa L.), and Russian wildrye grass Psathrostachys juncea[Fisch.]Nevski.). In treatment 2, crested wheatgrass was grazed mid-April to 17 June, followed by contour furrowed rangeland 18 June to 5 August, and ended with Russian wildrye 6 August to weaning (mid-September). Data were analyzed as a split plot with treatment and year in the main plot and cow type in the subplot. Number of cows exhibiting estrus before the beginning of the breeding season and fall pregnancy rate were not influenced (P > 0.05) by range treatment. Twelve-hour milk production during May, June, August, and September ranged from 11.3 to 6.8 kg and 7.6 to 3.9 kg for high and low producing cows, respectively. Cows with high milk production lost body condition during and after the breeding season, whereas cows with low milk production maintained body condition during the same period. Live weight gain of calves was greater (P 0.05) by range treatment. We concluded that native and seeded ranges were of similar nutritive value for cows with high and low milk production and that cows with high milk production may have greater nutrient requirements during late summer-early fall than what was provided by native or seeded ranges. Protein may be the primary limiting nutrient in forages during the late summer for lactating cows grazing Northern Great Plains range.

Two trials were conducted to study the effect of zeranol implants on growth and sexual development of bull calves. Trial 1 compared the effects of implanting with 72 mg of zeranol at 48 d of age (branding), at 215 d of age, or at both times with nonimplanted control bulls. Implanting at branding resulted in decreased scrotal circumference, testicle weight and proportion of bulls that could produce an ejaculate at 14 mo of age (P less than .01). Implanting at 215 d of age had no effect on any of these traits. Growth rate was not increased by implanting at either time but was decreased (P less than .02) in animals implanted at both times when compared with control bulls. In trial 2, both bulls and steers were implanted with zeranol and compared with nonimplanted control bulls and steers. Thirty-six-milligram implants were given at 21, 103, 260 and 343 d of age. Scrotal circumference, testicle weight and serum testosterone concentrations decreased (P less than .01) and the occurrence of penis abnormalities increased (P less than .01) in implanted bulls compared with control bulls. By the time of slaughter, however, testosterone concentrations were equal in control and implanted bulls; and the difference in scrotal circumference was diminishing. This is interpreted as evidence that as the bulls get older, they can overcome the effect of the implants. Carcass weights were heavier in implanted steers than in control steers but were lighter in implanted bulls than in control bulls (P less than .02). Carcasses of implanted bulls had higher quality scores and more marbling than control bulls, but carcasses of implanted steers had lower quality scores and less marbling than control steers (both interactions, P less than .01). Implanting bulls with zeranol at an early age resulted in restricted sexual development but not in total sterility. Repeated zeranol implants throughout the growing and finishing phase enhanced carcass quality in bulls slaughtered at 14 to 16 mo of age.

Age and weight at puberty in beef heifers were hypothesized to be jointly dependent random variables with the joint distribution conditional upon values of exogenous variables such as breed, date of birth and postweaning rate of gain. A statistical model was specified that tested the joint dependency hypothesis and measured the impact of variation in the explanatory variables on puberty. Model parameters were estimated by two-stage least-squares procedures from data on 556 beef heifers: 190 raised at the Northern Agricultural Research Center (NARC), Havre, Montana and 366 raised at the Livestock and Range Research Station (LARRS), Miles City, Montana. Results did not support the hypothesis that age and weight at puberty were jointly dependent; weight at puberty did depend upon age at puberty, but age at puberty did not depend upon weight at puberty when postweaning level of nutrition was known. Thus, the appropriate probability distribution was a conditional univariate probability distribution on age. Results were consistent with past research in that breed and breed-cross differences existed, and heifers heavier at weaning and fed higher levels of postweaning nutrition reached puberty at an earlier age and heavier weight.