There are numerous reports of the beneficial effects of rotating corn (Zea mays L.) and soybean [Glycine max (L.) Merr.]. However, few studies have been specifically designed to document the important corn‐soybean rotation effect. The objective of this study was to determine the impact of various corn and soybean cropping patterns on the yield of both crops. The 9‐year field study conducted at two locations was managed for maximum production. Cropping sequences consisted of: continuous monoculture with the same cultivar; continuous monoculture with cultivars alternated; annual rotation of the two crops; and 1, 2, 3, 4, and 5 yr of monoculture following 5 yr of the other crop. Annually rotated corn yielded 10% better, and first‐year corn yielded 15% better than corn under monoculture. Annually rotated soybean yielded 8% better, and first year soybean yielded 17% better than soybean under monoculture. With monoculture of either crop, alternating two different cultivars annually resulted in the same yield as continuous cropping of just one cultivar. There were differences in the response of the two crops to increasing years of monoculture: the lowest corn yield was from second year corn; the lowest soybean yield was from extended monoculture. Total corn dry weight was affected by cropping sequence but soybean dry weight was not. Our data suggest that, from a yield standpoint, a superior cropping sequence for Minnesota would include at least three, and possibly more crops.

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A multigeneration crossbred Meishan-White composite resource population was used to identify quantitative trait loci (QTL) for age at first estrus (AP) and the components of litter size: ovulation rate (OR; number of ova released in an estrous period) and uterine capacity (UC). The population was established by reciprocally mating Meishan (ME) and White composite (WC) pigs. Resultant F1 females were mated to either ME or WC boars to produce backcross progeny (BC) of either 3/4 WC 1/4 ME or 1/4 WC 3/4 ME. To produce the next generation (F3), 3/4 WC 1/4 ME animals were mated to 1/4 WC 3/4 ME animals yielding half-blood (1/2 WC 1/2 ME) progeny. A final generation (F4) was produced by inter se mating F3 animals. Measurements for AP and OR were recorded on 101 BC, 389 F3, and 110 F4 gilts, and UC data were from 101 BC and 110 F4 first parity litters. A genomic scan was conducted with markers (n = 157) spaced approximately 20 cM apart. All parental, F1, BC, and F4 animals but only 84 F3 animals were genotyped and included in this study. The QTL analysis fitted a QTL at 1-cM intervals throughout the genome, and QTL effects were tested using approximate genome-wide significance levels. For OR, a significant (E[false positive] < .05) QTL was detected on chromosome 8, suggestive (E[false positive] < 1.0) QTL were detected on chromosomes 3 and 10, and two additional regions were detected that may possess a QTL (E[false positive] < 2.0) on chromosomes 9 and 15. Two regions possessed suggestive evidence for QTL affecting AP on chromosomes 1 and 10, and one suggestive region on chromosome 8 was identified for UC. Further analyses of other populations of swine are necessary to determine the extent of allelic variation at the identified QTL.

There has been a trend toward narrower row width and an increase in plant population for corn (Zea mays L.) production in the northern Corn Belt. The impact of corn hybrid and plant population on grain yield may be influenced by row width. This study was designed to investigate the relationships between row width, plant population, and hybrid at three Minnesota locations from 1992 through 1994. At Lamberton and Waseca, row widths were 10, 20, and 30 in.; target populations were 25 000, 30 000, 35 000, and 40 000 plants/acre; and hybrids were Ciba ‘G4372,’ DeKalb ‘DK512,’ and Pioneer Brand ‘P3563’. At Morris, the same row widths were evaluated but the target populations were 22 000, 27 000, and 32 000 plants/acre and the hybrids were Northrup King ‘N3624,’ DeKalb ‘DK421,’ and Pioneer Brand ‘P3751’. At Lamberton and Waseca, the yield advantage for both 10‐ and 20‐in. rows compared with 30‐in. rows was 7.2% when averaged over all hybrids and all plant populations, whereas at Morris the yield advantage was 8.5%. Choice of hybrid influenced grain yield, and all hybrids responded similarly to change in row width and change in plant population at the three locations. Grain yields increased at Lamberton and Waseca with higher plant populations in 1992 and 1994, but not in 1993 when yields were limited by climatic conditions. Regression analysis of yield vs. harvest plant population showed yields were highest at populations at or above 35 000 plants/acre in 1992 at Lamberton and 1994 at Waseca and Lamberton, but were unaffected by plant populations in 1992 at Waseca and in 1993 at both locations. At Morris, regression analysis of yield vs. harvest plant population in 1993 and 1994 showed yields were highest at plant populations of 32 000 plants/acre, the highest plant population studied at that location. Choice of hybrid and the growing season climatic conditions had a greater effect on grain moisture content at harvest, test weight, and ear length than row width or plant population. These data show a yield advantage for narrowing row widths from 30 to 20 or 10 in., and that in some years maximum yields were obtained at harvest plant populations substantially higher than the current Minnesota population of 26 400 plants/acre. Research Question Most corn in the northern Corn Belt is grown in 30‐in. or wider row widths at populations ranging from 24 000 to 28 000 plantdacre. The trend has been toward narrower row widths and increasing plant populations. Some Minnesota producers want to match row width of corn and soybean with that of sugarbeet, which is typically grown in 22‐in. rows. This desire, coupled with improved genetics that have resulted in better standability and greater tolerance to higher plant populations in corn, necessitates a reevaluation of the relationship between row width, plant population, and corn hybrid. The objectives of this study were to: (i) determine whether current corn hybrids respond similarly to row width, and (ii) determine whether the response is affected by plant population. Literature Sum...

Corn (Zea mays L.) and soybean [Glycine max (L.) Merr.], the backbone of Midwestern crop production, respond to rotation, but how growing conditions affect this is not well documented. Our objectives were to determine the effect of various corn and soybean cropping patterns on yields and to evaluate environmental effects on the rotation effect. The study began in 1981 at Lamberton, MN, on a Webster clay loam (fine-loamy, mixed, mesic Typic Endoaquoll), in 1982 at Waseca, MN, on a Nicollet clay loam (fine-loamy, mixed, mesic Aquic Hapludoll), and in 1983 at Arlington, WI, on a Plano silt loam (fine-silty, mixed, mesic Typic Argiudoll). Cropping sequences were (i) continuous monoculture of each crop; (it) annual rotation of the two crops; and (iii) I, 2, 3, 4, and 5 yr of each crop following 5 yr of the other crop. Results are based on II yr of data at Lamberton, 8 yr (soybean) or 9 yr (corn) at Waseca, 9 yr at Arlington. Corn rotated annually with soybean yielded 13% more, and Ist-yr corn following multiple years of soybean yielded 15 % more than continuous corn. Soybean annually rotated with corn yielded 10% more, and Ist-yr soybean following multiple years of corn yielded 18% more than continuoos soybean. The crops differed in response to increasing years of consecutive planting: 2nd-yr to 5th-yr corn yields were no different from continuous corn yields; 2nd-yr soybean yielded 8% more than continuous soybean, 3rd-yr soybean yielded 3% more, and 4th-and 5th-yr soybe.'in yielded the same as continuous soybean. Relative increase in yields of both crops in annual rotation compared with monoculture was approximately twofold greater in low-yielding than in high-yielding environments. In low-yielding environments, the yield advantage of an annual rotation of corn and soybean compared with monoculture was frequently greater than 25%. The commonly practiced annual rotation of corn and soybean maximized corn yields, but not soybean yields, relative to the other sequences studied.

It is well established that kisspeptin signaling is necessary for the onset of puberty in laboratory animals. However, the role that kisspeptin may have in regulating puberty in large domestic animals is unknown. We tested the hypothesis that either central or peripheral infusion of kisspeptin would stimulate gonadotropin and GH secretion in prepubertal gilts. In experiment 1, prepubertal gilts were fitted with i.c.v. cannula and indwelling jugular catheters. Animals were randomly assigned to receive 0, 10, or 100 mg kisspeptin in saline. In experiment 2, prepubertal gilts, fitted with indwelling jugular catheters, randomly received 0, 1, 2.5, or 5 mg kisspeptin in saline intravenously. Serial blood samples were collected every 15 min for 3 h before and 5 h after infusions, and serum concentrations of LH, FSH, and GH were determined. Mean concentrations of LH and FSH remained at basal levels for control animals but were increased (P!0.001) for animals receiving i.c.v. infusion of kisspeptin. Area under the LH and FSH curves following i.c.v. infusion of kisspeptin increased (P!0.001) in a dose-dependent manner. Concentrations of GH were unaffected by i.c.v. treatment. Peripheral administration of kisspeptin increased (P!0.05) serum concentrations of LH but not FSH or GH. Thus, kisspeptin can activate gonadotropic but not somatotropic hormone secretion in prepubertal gilts. The present data support the concept that kisspeptin plays a role in the mechanism involved in initiating puberty in swine.

The expression of four major steroidogenic enzymes in porcine theca and granulosa cell layers of preovulatory follicles was related to the levels of steroids in follicular fluid and gonadotropin concentrations in peripheral serum at slaughter. Ovaries were collected during proestrus, early estrus, and late estrus as evidenced by behavioral signs. Follicles were dissected from the ovaries, and theca, granulosa, and follicular fluids were pooled for each of 24 sows. Cytochromes P450 17 alpha-hydroxylase/17-20 lyase (P450c17), aromatase (P450arom) and side-chain cleavage (P450scc), as well as 3 beta-hydroxysteroid dehydrogenase (3 beta HSD), were subjected to Northern and Western immunoblot analyses. The concentrations of estradiol-17 beta, testosterone, androstenedione, and progesterone were determined in follicular fluid, and peripheral serum was assayed for estradiol-17 beta, LH, and FSH. Stages of preovulatory development were verified by plasma levels of LH, FSH, and estradiol-17 beta. Thecca expressed P450c17, P450arom, P450scc, and 3 beta HSD whereas granulosa expressed only P450arom and low levels of P450scc. Thecal P450c17, thecal P450arom, and granulosa P450arom expression decreased coincidentally as serum estradiol-17 beta and follicular fluid estradiol-17 beta, testosterone, and androstenedione levels declined after the presumed gonadotropin surge. Unlike P450c17 and P450arom P450scc and 3 beta HSD remained relatively constant in theca and granulosa. From these data, we suggest that the theca interna may be the primary steroidogenic compartment of the porcine follicle during its final stages of preovulatory development. Moreover, preovulatory estrogen secretion appears to be controlled by the coordinated expression of a triad of enzymes in the porcine follicle that includes theca P450c17, theca P450arom and granulosa P450arom.

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