@article{cox_britt_armstrong_alhusen_1983, title={EFFECT OF FEEDING FAT AND ALTERING WEANING SCHEDULE ON REBREEDING IN PRIMIPAROUS SOWS}, volume={56}, ISSN={["0021-8812"]}, DOI={10.2527/jas1983.56121x}, abstractNote={Primiparous sows that farrowed on a commercial farm during late summer in 1980 (n = 65) or late winter in 1981 (n = 62) and lactated 3 to 4 wk were used. Sows were assigned in a factorial experiment to one of two lactation diets (control or 10% fat-supplemented) and one of three periods (0, 2 or 5 d) of early weaning of the heaviest one-half of the litter. Days from weaning to estrus averaged 16.7 +/- 1.5 and 8.7 +/- 1.6 in summer and winter, respectively, and the season X diet interaction was significant for days from weaning to estrus and percentage of sows that exhibited estrus after weaning. In summer, supplementing diets with fat reduced the weaning-to-estrus interval from 20.9 +/- 2.1 to 12.6 +/- 2.1 d and increased percentage of sows in estrus by 10 d postweaning from 34 to 59. In winter, days from weaning to estrus tended to be greater and percentage of sows in estrus by 10 d postweaning tended to be less in sows fed fat-supplemented diets (10.3 +/- 2.5, 74%) than in sows fed control diets (7.1 +/- 2.9, 82%). Over both seasons, weaning one-half the litter 2 d early (2-d group) increased the percentage of sows in estrus by 10 d after weaning (77%) compared with 5-d (58%) or 0-d (51%) groups. Total litter weight at weaning was not affected by season, diet or days with one-half litter. However, piglets of lightest weight remaining on sows two or five extra days gained .09 +/- .03 kg/d more than lightest weight pigs in control (0-d) litters over the same interval. Early weaning of heaviest pigs may improve reproductive performance of primiparous sows in summer and winter, while supplementing lactation diets with fat may improve performance in summer, when weaning-to-estrus interval is longer than in winter.}, number={1}, journal={JOURNAL OF ANIMAL SCIENCE}, author={COX, NM and BRITT, JH and ARMSTRONG, WD and ALHUSEN, HD}, year={1983}, pages={21–29} }
 @article{cox_esbenshade_britt_1983, title={TREATMENT OF LONG-TERM ANESTROUS SOWS WITH ESTRADIOL BENZOATE AND GNRH - RESPONSE OF SERUM LH AND OCCURRENCE OF ESTRUS}, volume={20}, ISSN={["0093-691X"]}, DOI={10.1016/0093-691X(83)90072-9}, abstractNote={Seventeen primiparous sows, anestrous for 41 ± 4 days after weaning, received i.m. injections of 500 μg estradiol benzoate (EB) or corn oil. At 48 hr after treatment, LH averaged 12.1 ± 2.6 ng/ml in EB-treated sows and 0.7 ± 0.1 ng/ml in corn oil-treated sows. At 55 hr after EB or corn oil, each sow was given 50 μg gonadotropin releasing hormone (GnRH). Average LH 1 hr after GnRH was 5.7 ± 1.1 and 5.1 ± 0.9 ng/ml in EB- and corn oil-treated sows, respectively. All EB-treated sows exhibited estrus 2.3 ± 0.2 days after treatment and were mated. None of the corn oil-treated sows exhibited estrus and all were slaughtered two weeks after treatment. Examination of reproductive tracts revealed that the ovaries of corn oil-treated sows were small and did not contain corpora lutea. In mated sows, progesterone concentrations in blood two weeks after mating indicated luteal function in eight of the nine animals. Positive pregnancy diagnoses were made in all eight animals; however, only three sows farrowed, with litter sizes of four, five and seven, respectively. Results of the present experiment indicate that the hypothalamus and anterior pituitary of long-term anestrous sows are capable of responding to endocrine stimuli (i.e. estradiol and GnRH). Moreover, estradiol induced estrus and ovulation, but subsequent farrowing rate was only 33 percent and size of litters was small.}, number={5}, journal={THERIOGENOLOGY}, author={COX, NM and ESBENSHADE, KL and BRITT, JH}, year={1983}, pages={499–507} }
 @article{cox_britt_1982, title={EFFECT OF ESTRADIOL ON HYPOTHALAMIC GNRH AND PITUITARY AND SERUM LH AND FSH IN OVARIECTOMIZED PIGS}, volume={55}, ISSN={["0021-8812"]}, DOI={10.2527/jas1982.554901x}, abstractNote={: Two experiments were conducted to measure pituitary gonadotropins, hypothalamic-gonadotropin releasing hormone (GnRH) and pituitary response to GnRH during periods when serum luteinizing hormone (LH) was suppressed by estradiol-17 beta (e2) in ovariectomized pigs. In the first experiment, 10 ovariectomized gilts were assigned to two groups of five each according to time of slaughter (24 or 36 h after injection). Within each group, gilts were given corn oil (n = 2) or 400 micrograms E2 (n = 3). Neither serum nor anterior pituitary (AP) concentrations of follicle-stimulating hormone (FSH) were affected by E2. Serum LH was suppressed from 12 to 26 h after E2. Concentrations of LH in AP were unchanged at 24 h, but increased at 36 h after E2 injection. Concentrations of GnRH in medial basal hypothalamus (MBH), stalk-median eminence (SME) and hypophyseal portal area (HPA) were lower at 24 h after E2 than in oil-treated gilts. At 36 h after E2, suppressive effects of E2 on LH in serum had subsided and concentrations of LH in AP and GnRH in MBH and SME were greater than in oil-treated controls. The observation that E2 suppressed LH in serum without a detectable suppression of LH in AP led to the hypothesis that E2 had caused the suppression of serum LH by suppression of GnRH release. In a second experiment, 12 ovariectomized gilts were assigned to receive corn oil (n = 4), 400 micrograms E2 (n = 4) or 400 micrograms E2 plus GnRH (1.5 micrograms/h; n = 4). Patterns of LH in sera of E2-treated animals were similar to those in the first experiment, with serum LH in E2-treated gilts suppressed from 4 to 32 h after treatment. However, in gilts receiving GnRH in addition to E2, serum LH concentrations during 20 to 32 h after treatment were intermediate between gilts receiving E2 alone and controls. Thus the pituitary of the pig is capable of responding to GnRH when LH is normally suppressed by E2. These experiments provide two lines of evidence that suppression of serum LH by E2 is due at least in part to suppression of GnRH. These experiments also establish the hypothalamus as a site for negative feedback of E2 in the female pig.}, number={4}, journal={JOURNAL OF ANIMAL SCIENCE}, author={COX, NM and BRITT, JH}, year={1982}, pages={901–908} }
 @article{cox_1982, title={Hormonal determinants of estrus during and after lactation in the postpartum sow}, volume={43}, number={3}, journal={Dissertation Abstracts International. B, Sciences and Engineering}, author={Cox, N. M.}, year={1982} }
 @article{cox_britt_1982, title={PULSATILE ADMINISTRATION OF GONADOTROPIN-RELEASING HORMONE TO LACTATING SOWS - ENDOCRINE CHANGES ASSOCIATED WITH INDUCTION OF FERTILE ESTRUS}, volume={27}, ISSN={["0006-3363"]}, DOI={10.1095/biolreprod27.5.1126}, abstractNote={Two experiments were conducted to determine whether pulsatile administration of gonadotropin releasing hormone (GnRH) would induce estrus and ovulation in lactating, anestrous sows. In each experiment, six lactating sows received GnRH, i.v. (2.5 micrograms every 2 h, Exp. 1; 1.5 micrograms every h, Exp. 2) until 24 h after estrus or 7 days, whichever came first. In Experiment 1, three of six GnRH-treated lactating sows exhibited estrus 4.0 +/- 0.0 days after GnRH treatment began. All three GnRH-treated sows conceived at the estrus induced during lactation. Patterns of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in serum around estrus were similar between GnRH-treated sows that exhibited estrus during lactation and weaned control sows. However, in GnRH-treated sows that did not show estrus, a preovulatory-like surge in FSH, but not in LH, occurred on Day 4 of GnRH treatment. Prolactin concentrations in serum dropped from 25.6 +/- 2.4 ng/ml during lactation to less than 6 ng/ml within 12 h after weaning (Exp. 1). In Experiment 2, all six GnRH-treated sows exhibited estrus 3.8 +/- 0.3 days after initiation of GnRH treatment, and five sows conceived. Patterns of LH and FSH during lactation were similar between GnRH-treated and lactating control sows during the first 3 days of GnRH treatment. During 3 days before estrus, LH concentrations were lower (P less than 0.05) and FSH concentrations tended to be higher (P less than 0.20) in lactating GnRH-treated sows than in control sows whose litters had been weaned. Concentrations of estradiol in GnRH-treated sows were greater than those in controls during lactation but were similar in both groups on the day of estrus. In both experiments, concentrations of progesterone were greater in GnRH-treated than in control sows prior to and during estrus. We conclude that, despite some differences in hormone secretion between GnRH-treated lactating sows and sows with litters weaned, pulsatile administration of GnRH caused requisite endocrine changes for fertile estrus during lactation.}, number={5}, journal={BIOLOGY OF REPRODUCTION}, author={COX, NM and BRITT, JH}, year={1982}, pages={1126–1137} }
 @article{cox_britt_1982, title={RELATIONSHIPS BETWEEN ENDOGENOUS GONADOTROPIN-RELEASING HORMONE, GONADOTROPINS, AND FOLLICULAR DEVELOPMENT AFTER WEANING IN SOWS}, volume={27}, ISSN={["0006-3363"]}, DOI={10.1095/biolreprod27.1.70}, abstractNote={Two experiments were conducted to examine relationshipsbetween endogenous gonadotropinreleasing hormone (GnRH), concentrations of gonadotropins in the anterior pituitary and blood and ovarian follicular development in weaned sows. In the first experiment, 48 sows were slaughtered during 0 to 5 days after weaning. Because effects of breed, parity, farm and season of slaughter were confounded with day after weaning, data were analyzed solely on the basis of follicular development. Sows were divided into 4 groups based on the size and number of the largest ovarian follicles. Group 1 consisted of 11 sows with largest follicles 14) follicles 5 to 10mm in diameter. Group 4 coniisted of sows (n=12) with follicles>10 mm in diameter. Data from 3 sows that had ovulated were omitted from the analyses.Sows in Groups 1,2, 3 and 4 were killed atm average of 0.7 ± 0.4, 2.5 * 0.2,4.7 ± 0.1 and 4.8 ± 0.2 days after weaning, respectively. Concentrations of GnRH in medial basal hypothalamus (MBH), stalk median eminence (SME) and hypophyseal portal area (HPA) were greater in sows with greater follicular development (Groups 3 and 4). Concentrations of luteinizing hormone (LH) in anterior pituitary (AP) and serum were also greater in Groups 3 and 4. Concentrations of follicle-stimulating hormone (FSH) in AP and serum were not significantly different among groups. In the second experiment, 27 second parity Duroc sows were slaughtered 0, 60 or 96 h after weaning (9 sows per group). Concentrations of both LH and FSH in serum samples obtained at 6-h intervals from weaning to slaughter increased after weaning, and by 96 h levels of LH indicated a preovulatory surge was beginning. Follicular diameter increased with time after weaning, with increases in number of follicles >5 mm in diameter, and decreases in number of follicles <5 mm in diameter. Concentrations of LH, but not FSH, in AP were greater at both 60 and 96 h than at 0 h after weaning (P<0.01). Concentrations of GnRH in MBH and SME were greater at 60 and 96 h than at 0 h (P<0.05). The concentration of GnRH in HPA was increased only at 96 h after weaning. In both experiments, concentration of GnRH increased after weaning, concurrently with postweaning increases in serum FSH, serum and pituitary LH and follicular development. Thus we propose that initiation of estrus and ovulation after weaning may be associated with changes in production of GnRH.}, number={1}, journal={BIOLOGY OF REPRODUCTION}, author={COX, NM and BRITT, JH}, year={1982}, pages={70–78} }