Does β-hydroxybutyrate concentration influence conception date in young postpartum range beef cows?

Cows in negative energy balance after calving often have reduced reproductive performance, which is mediated by metabolic signals. The objective of these studies was to determine the association of serum metabolites, days to first postpartum ovulation, milk production, cow BW change, BCS, and calf performance with conception date in spring-calving 2- and 3-yr-old beef cows grazing native range. In Exp. 1, cows were classified by conception date in a 60-d breeding season as early (EARLY; conceived in first 15 d of breeding) or late conception (LATE; conceived during the last 45 d of breeding). Beginning on d 35 postpartum, blood samples were collected twice per week for serum metabolite analysis and progesterone analysis to estimate days to resumption of estrous cycles. As a chute-side measure of nutrient status and glucose sufficiency, whole-blood β-hydroxybutyrate (BHB) concentrations were measured 14 ± 2 d before breeding. In Exp. 2, cows were classified by subsequent calving date resulting from a 55 ± 2 d breeding season as conceiving either early (EARLY; conceived in first 15 d of breeding) or late (LATE; conceived during the remaining breeding season). Blood samples were collected in 2 periods, 30 ± 4 d before calving and 14 ± 3 d before the initiation of breeding, to determine circulating concentrations of IGF-I and BHB. In Exp. 1, BHB and serum glucose concentrations were less (P ≤ 0.04) in EARLY cows than LATE cows. Serum insulin concentrations were greater (P = 0.03) in EARLY cows relative to LATE cows. Milk production and composition did not differ (P ≥ 0.24) by conception date groups. In Exp. 2, cow age × sample period × conception date interaction (P < 0.01) occurred for serum BHB concentrations. Serum BHB concentrations were similar (P > 0.10) for 2-yr-old cows (in greater nutritional plane compared with Exp. 1) regardless of their conception date classification and sampling period. However, precalving serum BHB concentrations were greater (P < 0.01) for LATE than EARLY in 3-yr-old cows with no difference (P = 0.86) at prebreeding. Serum IGF-1 concentrations were greater (P < 0.01) for EARLY cows relative to LATE cows at precalving and prebreeding. This study indicates that blood BHB concentrations during times of metabolic dysfunctions may provide a more sensitive indicator of energy status than body condition, predicting rebreeding competence in young beef cows as measured by interval from calving to conception.

Joint Alpharma-Beef Species Symposium: implications of beef heifer development systems and lifetime productivity

Research emphasis has been placed on heifer development strategies in recent years, comparing traditional, more intensive systems to more extensive systems using less feed and relying on compensatory gain to reach a target BW. Recent research has indicated that developing heifers to a lighter target BW at breeding (i.e., 50 to 57% of mature BW compared with 60 to 65% BW) reduced development costs and did not impair reproductive performance. Research published through the late 1980s demonstrated greater negative effects of limited postweaning growth on age at puberty and pregnancy rates whereas more recent studies demonstrate less of a negative impact of delayed puberty on pregnancy rate. A limitation of most research concerning influences of nutrition on heifer development and cow reproductive performance is little or limited consideration of long-term implications. Longevity has relatively low heritability; therefore, heifer development and other management strategies have a greater potential to impact cow retention. Establishing the impact of heifer development protocols on longevity is complex, requiring consideration of nutritional factors after the start of breeding and through subsequent calvings. Lower-input heifer development, where all heifers are managed together after the postweaning period, did not impair rebreeding, but continued subsequent restriction in the form of marginal winter supplementation resulted in decreased retention in the breeding herd. Therefore, the compensatory BW gain period for restricted-growth heifers may be important to longevity and lifetime productivity. Adequate growth and development to ensure minimal calving difficulty can be of critical importance for longevity; however, providing additional supplemental feed during postweaning development to accomplish this may be less efficient than later in development. Restricting gain during postweaning development by limiting DMI or developing heifers on dormant winter forage resulted in increased economic advantages compared with developing heifers at greater rates of ADG to achieve a greater target BW. Implications of heifer development system on cow longevity must be considered when evaluating economics of a heifer enterprise; however, studies evaluating the effects of heifer development systems on cow longevity are extremely limited.

Physiology and Endocrinology Symposium: Nutritional aspects of developing replacement heifers

Studies in numerous species provide evidence that diet during development can mediate physiological changes necessary for puberty. In cattle, several studies have reported inverse correlations between postweaning growth rate and age at puberty and heifer pregnancy rates. Thus, postweaning growth rate was determined to be an important factor affecting age of puberty, which in turn influences pregnancy rates. This and other research conducted during the late 1960s through the early 1980s indicated puberty occurs at a genetically predetermined size, and only when heifers reach their target BW can increased pregnancy rates be obtained. Guidelines were established indicating replacement heifers should achieve 60 to 65% of their expected mature BW by breeding. Traditional approaches for postweaning development of replacement heifers used during the last several decades have primarily focused on feeding heifers to achieve or exceed an appropriate target BW and thereby maximize heifer pregnancy rates. Intensive heifer development systems may maximize pregnancy rates, but not necessarily optimize profit or sustainability. Since inception of target BW guidelines, subsequent research demonstrated that the growth pattern heifers experience before achieving a critical target BW could be varied. Altering rate and timing of BW gain can result in compensatory growth periods, providing an opportunity to decrease feed costs. Recent research has demonstrated that feeding replacement heifers to traditional target BW increased development costs without improving reproduction or subsequent calf production relative to development systems in which heifers were developed to lighter target BW ranging from 50 to 57% of mature BW.

Differential gene expression in anterior pituitary glands from anestrous and cycling postpartum beef cows

Oligonucleotide microarrays (GeneChip Bovine Genome Arrays, Affymetrix Inc., Santa Clara, CA) were used to evaluate gene expression profiles in anterior pituitary glands collected from 4 anestrous and 4 cycling postpartum primiparous beef cows to provide insight into genes associated with transition from an anestrous to a cycling status. Tissues were collected 40 to 61 d after calving from anestrous cows and from cyclic cows between d 7 and 13 of the estrous cycle (luteal phase) from d 54 to 77 after calving. Hybridization signals were normalized across arrays, and genes with mean differences in expression that were at least 1.5-fold apart and with a minimum difference in mean signal intensity of 10 were compared. Based on these criteria, 47 transcripts were increased (P < 0.025) and 31 transcripts were decreased (P < 0.025) in pituitary gland tissue from cycling compared with anestrous cows. Few transcripts identified in this analysis were associated previously with reproductive function. To provide greater detail on the influence that stage of the estrous cycle (i.e., collection during the luteal phase) might have on the differences detected in gene expression, quantitative real-time PCR was used to compare gene expression in anterior pituitaries of anestrous cows with an additional independent set of anterior pituitary glands collected at 4 different stages of the estrous cycle: 0.5 to 2 d (n = 9), 5 to 6.5 d (n = 5), 11.4 to 13.7 d (n = 5), and 17.9 to 19 d (n = 6) after the onset of estrus. Gastrin-releasing peptide, the gene that exhibited the largest fold increase in expression in the microarray experiment, and IGFBP3 mRNA were expressed at greater (P < 0.004) amounts in samples from the different stages of the estrous cycle than in samples from anestrous cows. In addition, expression of IGFBP3 mRNA was proportional to serum progesterone concentrations throughout the estrous cycle (P < 0.05). Expression of versican mRNA was decreased (P = 0.03) in samples from the different stages of the estrous cycle compared with anestrous cow samples. Results identified numerous genes that may be involved in the transition from anestrous to cycling status, providing novel insight into mechanisms regulating reproductive function.

Reproductive performance of heifers offered ad libitum or restricted access to feed for a one hundred forty-day period after weaning

Reproductive performance was evaluated in composite heifers born over a 3-yr period that were randomly assigned to control (fed to appetite; n = 205) or restricted (fed at 80% of that consumed by controls adjusted to a common BW basis; n = 192) feeding for a 140-d period, beginning about 2 mo after weaning at 6 mo of age and ending at about 12.5 mo of age. Heifers were fed a diet of 67% corn silage, 18% alfalfa, and 9% of a protein-mineral supplement (DM basis). Restricted heifers consumed 27% less feed over the 140 d and had less ADG (0.53 +/- 0.01 vs. 0.65 +/- 0.01 kg/d; P < 0.001) than control heifers. After 140 d, all heifers were placed in common pens and subjected to an estrous synchronization protocol to facilitate AI at about 14 mo of age. Heifers were then exposed to bulls for the remainder of a 51-d breeding season. Average BW of heifers diverged within 28-d after initiation of feed restriction, and differences (P < 0.001) persisted through the prebreeding period (309 +/- 1 vs. 326 +/- 1 kg at approximately 13.5 mo of age) and subsequent grazing season (410 +/- 2 vs. 418 +/- 2 kg at about 19.5 mo of age). From the end of the 140-d restriction at about 12.5 to 19.5 mo of age, ADG was greater (P < 0.001) in restricted heifers than control heifers (0.51 +/- 0.01 vs. 0.47 +/- 0.01 kg/d). Proportion of heifers attaining puberty by 14 mo of age tended to be less (P = 0.1) in restricted (60 +/- 3%) than control-fed heifers (68 +/- 3%). Mean BW at puberty was less (P < 0.01) in restricted (309 kg) than control (327 kg) heifers. Pregnancy rate from AI tended to be less (P = 0.08) in restricted (48 +/- 4%) than control heifers (57 +/- 3%). Proportion of animals that were pubertal at breeding and pregnant from AI were positively associated (P < 0.1) with heifer age and ADG from birth to beginning of study. Final pregnancy rates were 87 and 91% for restricted and control heifers, respectively (P = 0.27). Day of breeding season that conception occurred was negatively associated with ADG from birth to weaning (P = 0.005), but was not associated with ADG within treatment (P = 0.60). Economic analysis revealed a $33 reduction in cost to produce a pregnant heifer under the restricted protocol when accounting for pregnancy rates and differences in BW and market prices between selection at weaning and marketing as open heifers at l.5 yr of age. A potential economic advantage exists for rearing replacement heifers on a restricted level of feeding during the postweaning period.

Physiological and functional impact of an unsupervised but supported exercise programme for claudicants

OBJECTIVES

To evaluate an unsupervised home-based exercise programme for physiological, functional, and quality of life impact in patients with symptomatic peripheral arterial disease.

DESIGN

Prospective cohort with exercise intervention.

MATERIALS

Human performance laboratory with non-invasive haemodynamic assessment facilities.

METHODS

Forty-seven patients with symptomatic peripheral arterial disease (mean age 67.6+/-7 years, 33 males) participated in an unsupervised home-based exercise programme. Heart rate (HR), ankle brachial blood pressure index (ABPI), leg blood flow (BF), and blood lactate were measured before and after a graded treadmill walk at baseline and after the 12-week exercise programme. Maximum walking distance (MWD) during the treadmill walk was measured at baseline and 12 weeks. Exercise compliance, functional parameters, and quality of life (VascuQoL) were assessed by questionnaire.

RESULTS

MWD, leg BF, and VascuQoL scores increased significantly, while resting HR, exercise HR, and end of walk rate-pressure-product (RPP) decreased significantly after 12 weeks. Exercise compliance was significantly correlated with increase in MWD (r=0.89, p<0.001) and QOL score improvement (r=0.61, p<0.001).

CONCLUSIONS

This supported but unsupervised exercise programme generated improvements in walking distance and leg blood flow without detectable increases in cardiorespiratory work. Exercise compliance is related to MWD and VascuQoL score in a dose-response manner.

Large variation in steroid concentrations and insulin-like growth factor binding proteins exists among individual small antral follicles collected from within cows at random stages of the estrous cycle

Variation in the biochemical status of individual small (< or = 5 mm diameter) antral follicles within the ovaries of a cow at any given time likely influences the capacity for undergoing recruitment, selection, and establishing dominance. The objectives of this study were to provide insight into the magnitude of variation in follicular fluid concentrations of steroids and activities of IGFBP that exists among individual small antral follicles within and between cows, and to determine the relationships between follicular fluid IGFBP and steroid concentrations in these follicles. A total of 108 small antral follicles were collected from 6 cows at random stages of the estrous cycle, with 10 to 26 follicles/cow. Concentrations of steroids (ng/mL of follicular fluid) in the overall population of follicles ranged from 0.1 (lowest detectable limit) to 51 for estradiol (E2), 4 to 1,149 for progesterone (P4), and 5 to 504 for androstenedione (A4). Concentrations of E2 and A4 were associated positively (r = 0.2; P < 0.02), but E2 (r = -0.4) and A4 (r = -0.4) were associated negatively, with P4. The proportion of variation in steroid concentrations accounted for by differences among animals (P < 0.05) was small for E2 (12%), moderate for P4 (43%), and greatest for A4 (74%). Least differences between minimum and maximum concentrations of steroids observed in follicles from within a cow were 21-, 5.5-, and 3.5-fold for E2, P4, and A4, respectively, whereas the greatest differences between minimum and maximum concentrations were 505-, 108-, and 26-fold for E2, P4, and A4, respectively. Ranges of IGFBP concentrations (arbitrary densitometer units) detected in fluid from a sub-sample of 43 follicles were 1.18 to 4.50 for IGFBP-3, 0.54 to 4.68 for IGFBP-2, 0.07 to 2.56 for IGFBP-4, and 0.01 to 6.71 for IGFBP-5. Concentrations of E2 were correlated negatively with each IGFBP (r = -0.4 to -0.8; P < 0.05) except IGFBP-3. In contrast, concentrations of A4 were correlated positively with IGFBP-3 (r = 0.4; P < 0.05) but were not correlated with other IGFBP. Concentrations of P4 were correlated positively (r > 0.4; P < 0.05) with IGFBP-4 and -5. The results indicate that steroid concentrations and IGFBP activities vary substantially among small antral follicles collected from within and among individual animals and that increasing production of E2, the hallmark of a developing follicle, was associated with reduced activity of all IGFBP except IGFBP-3, thereby implicating these IGFBP in the regulation of follicular recruitment.

Utilization of soybeans or corn milling by-products in beef heifer development diets

Whole raw soybeans (SB), wet corn gluten feed (WCGF), and corn dried distillers grains (DDG) are sources of protein in heifer development rations. The objectives of this study were to compare puberty status before synchronization of estrus, response to synchronization, and AI and final pregnancy rates in heifers developed on diets containing SB, WCGF, or DDG that were formulated to be similar in energy and CP. These ingredients vary substantially in fat content, which may affect reproductive performance. Rate of gain during the feeding period and post-AI performance were also compared. In a preliminary experiment, 104 crossbred heifers were fed diets containing either 1.25 kg of SB/d or 2.0 kg of WCGF/d for 110 d (DM basis), beginning at 10 mo of age. In Exp. 1, 100 crossbred heifers received either 1.25 kg of SB/d or 2.5 kg of WCGF/d from approximately 7 to 10 mo of age (91 d; 4 pens/diet), and then were fed 1.25 kg of SB/d for an additional 114 d (4 pens/diet). In Exp. 2, 1.25 kg of SB/d or 1.25 kg of DDG/d was fed to 100 crossbred heifers for 226 d, beginning at 6 mo of age (4 pens/diet). At approximately 13 mo of age, heifers were fed melengestrol acetate (0.5 mg/d) for 14 d, followed by an i.m. injection of PGF(2 alpha) (25 mg) 19 d later to synchronize estrus. Heifers (14 mo of age) received AI for 5 d after PGF(2 alpha), at which time the dietary treatments were ended. Heifers were commingled while grazing on native pasture and were exposed to bulls for approximately 60 d beginning 10 d after the last day of AI. Pregnancy to AI was determined by ultrasound 45 d after the last day of AI. Heifers fed SB in the preliminary experiment had a lower (P < 0.05) synchronization rate (81 vs. 96%) and longer interval (P = 0.05) from PGF(2 alpha) to estrus (76.6 vs. 69.2 h) compared with heifers fed WCGF. In Exp. 1, the age at which the heifers were begun on SB diets did not alter (P > 0.10) the synchronization rate (79%) or timing of estrus after PGF(2 alpha) (77.8 h). In Exp. 2, the synchronization rate (86%) and timing of estrus after PGF(2 alpha) (69.3 h) did not differ (P > 0.10) because of diet. No differences (P > 0.10) were due to diet for AI conception rates (overall mean for each experiment: 76.5, 60, and 68.5%), percentage of all heifers becoming pregnant to AI (67, 46, and 59%), or final pregnancy rates (92, 90, and 90%) in the preliminary experiment, Exp. 1, or Exp. 2, respectively. In summary, SB, DDG, and WCGF can be used as sources of protein in heifer development diets at the inclusion rates used in these studies.

Milk yield of primiparous beef cows from three calving systems and varied weaning ages

Primiparous beef cows produced in 3 calving systems were used in a 2-yr study with a completely random design to measure milk yield throughout a 190-d lactation (2002, n = 20; 2003, n = 24 per calving system). Calving occurred in late winter (average calving date = February 4 +/- 2 d), early spring (average calving date = March 30 +/- 2 d), and late spring (average calving date = May 26 +/- 1 d). Additionally, cows used in this study had been weaned at varied ages as calves, creating 6 dam treatments. Dam age at weaning was 140 (late spring), 190 (late winter, early spring, late spring), or 240 (late winter, early spring) d of age. Milk production was measured by using the weigh-suckle-weigh technique at an average of 20, 38, 55, 88, 125, 163, and 190 d in milk. Milk yield for the 190-d lactation period was calculated as area under the curve by trapezoidal summation. Data were analyzed with a model containing treatment, year, and their interaction. Orthogonal contrasts were used to separate effects when treatment was significant (P < 0.10). Total milk yield did not differ (P = 0.42) between cows in the late winter and early spring systems, but cows in the late spring system tended to differ (P = 0.09) from the average of the other 2 systems. Cows in the late spring calving system had increased milk yield in 2002 and lesser milk yield in 2003 compared with the other calving systems (treatment x year interaction, P < 0.001). Cows born in late spring that had been weaned at 140 d of age produced more (P = 0.05) total milk than those weaned at 190 d of age. Peak milk yield was affected (P < 0.001) by treatment and showed a treatment x year interaction (P = 0.006). Day of peak lactation differed among treatments (P = 0.002), with cows in the late winter system peaking later (P = 0.007) than early spring cows, and late spring cows peaking earlier (P = 0.004) than the average of late winter and early spring cows. The average date of peak lactation was May 4 for the late winter system, May 31 for the early spring system, and July 19 for the late spring system. Calf ADG differed (P < 0.001) for the late spring system compared with the average of the late winter and early spring systems, but the relationship interacted with year (P < 0.001). Cow BW and BW change differed among treatments (P < 0.004), with much of the difference associated with the amount of milk produced or the timing of peak lactation. Season of calving affects milk yield of primiparous cows grazing Northern Great Plains rangelands and ADG of their calves.

Effects of restricted feeding of beef heifers during the postweaning period on growth, efficiency, and ultrasound carcass characteristics1

Traits used for identification of replacement beef heifers and feeding levels provided during postweaning development may have major financial implications due to effects on maintenance requirements and level of lifetime production. The current study evaluated the effects of 2 levels of feeding during the postweaning period on growth, G:F, and ultrasound carcass measurements of heifers, and the associations among these traits. Heifers (1/2 Red Angus, 1/4 Charolais, and 1/4 Tarentaise) born in 3 yr were randomly assigned to a control (fed to appetite; n = 205) or restricted (fed at 80% of that consumed by controls adjusted to a common BW basis; n = 192) feeding during a 140-d postweaning period. Heifers were individually fed a diet of 68% corn silage, 18% alfalfa, and protein-mineral supplement (DM basis) in pens equipped with Calan gates. Ultrasound measurements of LM area, intramuscular fat, and subcutaneous fat thickness over the LM were made on d 140 (382 +/- 0.8 d of age). Average daily DMI was 4.1 and 5.6 kg/d for restricted and control heifers, respectively (P < 0.001). Feed restriction decreased (P < 0.001) BW (292 vs. 314 kg), ADG (0.52 vs. 0.65 kg/d), LM area (55 vs. 59 cm2), intramuscular fat (3.2 vs. 3.5%), and subcutaneous fat thickness over the LM (3.2 vs. 3.9 mm), but increased G:F (0.12 vs. 0.11) when compared with control at the end of the 140-d study. The magnitude of the associations of DMI with ADG (r = 0.32 vs. 0.21), 140-d BW (r = 0.78 vs. 0.36), hip height (r = 0.57 vs. 0.17), LMA (r = 0.30 vs. 0.18), and BCS (r = 0.17 vs. 0.11) was greater in restricted- than control-fed heifers. Variance of residual feed intake, calculated within each treatment, was greater (P < 0.01) in control (0.088) than restricted (0.004) heifers, and magnitude of association between residual feed intake and average DMI was greater in control (r = 0.88) than restricted (r = 0.41) heifers. Pregnancy rate tended (P = 0.11) to be reduced in heifers that had been developed on restricted feeding (86.3 +/- 2.3 vs. 91.5 +/- 2.3%). However, ADG was greater (P < 0.001) in restricted than control heifers (0.51 vs. 0.46 kg/d) while grazing native range in the 7 mo after restriction. In summary, restricted heifers consumed 22% less feed on a per-pregnant-heifer basis during the development period and had a greater magnitude of association between DMI and several growth-related traits at the end of the 140-d postweaning feeding period, which is indicative of improved efficiency.

Influence of seasonal forage quality on glucose kinetics of young beef cows1

Extensive range livestock production systems in the western United States rely heavily on rangeland forages to meet the nutritional needs of grazing livestock throughout the year. Interannual variation in the quantity and quality of rangeland forage in the Northern Great Plains, as well as throughout much of the western United States, may play a pivotal role in how well grazing ruminants sequester nutrients in their tissues. This variation in forage quality may influence the ability of a beef cow to utilize dietary nutrients via changes in tissue responsiveness to insulin. Identifying specific periods and production states in which this phenomenon is manifested will provide insight into the development and implementation of strategic and targeted supplementation practices that improve nutrient utilization during times of nutritional imbalance and may improve the lifetime productivity of grazing range beef cows. A 2-yr study was conducted to monitor serum metabolites, glucose kinetics during glucose tolerance tests, and forage chemical composition every 90 d in young cows (2 to 4 yr of age; n = 28). In yr 1 and 2, cows were managed on 4 pastures varying in size from 36 to 76 ha in yr 1 and 49 to 78 ha in yr 2. Regardless of year, cow age, or cow physiological status, the main factor influencing glucose half-life was season of the year (P = 0.02). Effects of season on glucose half-life closely followed assessments describing forage quality, with glucose half-lives of 46, 39, 43, and 51 +/- 3.9 min for May, August, December, and March, respectively. Elevated glucose half-life during seasons in which forage quality is of lower nutritive value indicated that tissue responsiveness to the actions of insulin followed seasonal changes in forage quality. Glucose half-life tended (P = 0.09) to decrease between May and August, increased (P = 0.04) between December and March, and showed a tendency (P = 0.10) to decrease in seasons of greater nutrient density (May and August) compared with seasons of lower nutrient density (December and March). Seasonal changes in serum metabolites were also observed and corresponded with changes in forage quality. The results support our hypothesis that as the season progresses and forage quality declines, maternal tissues become less responsive to insulin, indicating that targeted supplementation with glucogenic precursors during these seasons of nutritional stress may improve cow performance.

Caries Prevalence Four Years after the End of a Randomised Controlled Trial

This study measured dental caries in children after cessation of a 30-month randomised clinical trial in which the intervention group received supervised toothbrushing once a day at school with 1,000 ppm fluoride toothpaste and a home support package encouraging twice-daily toothbrushing. The non-intervention group did not brush at school or receive the home support package. Children were aged 5 years at baseline and were examined every 6 months during the trial, then at 6, 18, 30 and 54 months after the end of the trial. Significantly less caries developed in first permanent molars of intervention children at the end of the trial. Of the 428 children who were examined at the end of the trial 329 (77%) were examined 54 months later when the children were aged 12 years on average. The intervention group still had less caries (D3FS caries increment 1.62) than the non-intervention children (D3FS caries increment 2.65, p < 0.05). Prolonged benefits have been found for intervention children principally in less caries in first permanent molars. Further follow-up at an age when the second molars and premolars have all erupted will help determine whether this benefit is due to a long-term behavioural change or a prolonged biological effect.

Increased response to morphine in mice lacking protein kinase C epsilon

The protein kinase C (PKC) family of serine-threonine kinases has been implicated in behavioral responses to opiates, but little is known about the individual PKC isozymes involved. Here, we show that mice lacking PKCepsilon have increased sensitivity to the rewarding effects of morphine, revealed as the expression of place preference and intravenous self-administration at very low doses of morphine that do not evoke place preference or self-administration in wild-type mice. The PKCepsilon null mice also show prolonged maintenance of morphine place preference in response to repeated testing when compared with wild-type mice. The supraspinal analgesic effects of morphine are enhanced in PKCepsilon null mice, and the development of tolerance to the spinal analgesic effects of morphine is delayed. The density of mu-opioid receptors and their coupling to G-proteins are normal. These studies identify PKCepsilon as a key regulator of opiate sensitivity in mice.

Relationship between size of the ovulatory follicle and pregnancy success in beef heifers1

Previous research indicated that the size of the ovulatory follicle at the time of insemination significantly influenced pregnancy rates and embryonic/fetal mortality after fixed-timed AI in postpartum cows, but no effect on pregnancy rates was detected when cows ovulated spontaneously. Our objective was to evaluate relationships of fertility and embryonic/fetal mortality with preovulatory follicle size and circulating concentrations of estradiol after induced or spontaneous ovulation in beef heifers. Heifers were inseminated in 1 of 2 breeding groups: (1) timed insemination after an estrous synchronization and induced ovulation protocol (TAI n = 98); or (2) AI approximately 12 h after detection in standing estrus by electronic mount detectors during a 23-d breeding season (spontaneous ovulation; n = 110). Ovulatory follicle size at time of AI and pregnancy status 27, 41, 55, and 68 d after timed AI (d 0) were determined by transrectal ultrasonography. Only 6 heifers experienced late embryonic or early fetal mortality. Interactions between breeding groups and follicle size did not affect pregnancy rate (P = 0.13). Pooled across breeding groups, logistic regression of pregnancy rate on follicle size was curvilinear (P < 0.01) and indicated a predicted maximum pregnancy rate of 68.0 +/- 4.9% at a follicle size of 12.8 mm. Ovulation of follicles < 10.7 mm or > 15.7 mm was less likely (P < 0.05) to support pregnancy than follicles that were 12.8 mm. Ovulatory follicles < 10.7 mm were more prevalent (28% of heifers) than ovulatory follicles > 15.7 mm (4%). Heifers exhibiting standing estrus within 24 h of timed AI had greater (P < 0.01) follicle diameter (12.2 +/- 0.2 mm vs. 11.1 +/- 0.3 mm) and concentrations of estradiol (9.9 +/- 0.6 vs. 6.6 +/- 0.7) and pregnancy rates (63% vs. 20%) than contemporaries that did not exhibit behavioral estrus. However, when differences in ovulatory follicle size were accounted for, pregnancy rates were independent of expression of behavioral estrus or circulating concentration of estradiol. Therefore, the effects of serum concentrations of estradiol and behavioral estrus on pregnancy rate appear to be mediated through ovulatory follicle size, and management practices that optimize ovulatory follicle size may improve fertility.

Aged APP23 mice show a delay in switching to the use of a strategy in the Barnes maze

Spatial learning and memory deficits in the APP23 transgenic mice have mainly been studied using the Morris water maze (MWM). However learning in the MWM relies on swimming abilities and may be confounded by the stressful nature of this test. We have therefore assessed spatial learning and memory in 12-month-old APP23 using a dry-land maze test developed by Barnes. Mice were given daily learning trials for a total of 41 successive days. After a 12-day interval the mice were re-tested for 4 additional days in order to examine the spatial memory retention. Immediately following this phase, reversal learning was examined for 13 additional days by moving the escape tunnel to the opposite position. During the initial learning phase, APP23 mice showed a significantly longer latency to find the escape tunnel as well as an increased number of errors compared to non-transgenic littermates. These deficits appeared to be due to a delay in switching from a "no strategy" to a spatial strategy. Indeed, this same delay in the use of spatial strategy was observed in the reversal phase of the study. Our results suggest that impairments in APP23 mice in learning and memory maze tests may be due to a specific deficit in the use of spatial strategy.

Genetic partitioning of variation in ovulatory follicle size and probability of pregnancy in beef cattle1

The objectives of this research were to partition variation in ovulatory follicle size into genetic and nongenetic components and to assess the utility of ovulatory follicle size as an indicator trait associated with reproductive success in beef cattle. Data were collected during the years 2002 to 2005 from 780 beef females that ranged in age from 1 to 12 yr (mean of 2.4 observations per female). Data were analyzed with a multiple trait Gibbs sampler for animal models to make Bayesian inferences from flat priors. A chain of 500,000 Gibbs samples was thinned to every 200th sample to produce a posterior distribution composed of 2,500 samples. Heritability estimates (posterior mean +/- SD) were 0.16 +/- 0.03 for follicle size and 0.07 +/- 0.02 and 0.02 +/- 0.01 for pregnancy rate as a trait of the female and service sire, respectively. Posterior means of genetic correlations were all <0.10, with 0.00 contained within the respective 90% probability density posterior intervals. Results indicate that whereas follicle size is of greater heritability than pregnancy rate, its usefulness to improve reproductive rate is greatest as an ancillary phenotype in multiple trait selection.

Effects of varying energy intake and sire breed on duration of postpartum anestrus, insulin like growth factor-1, and growth hormone in mature crossbred cows1

Objectives of this study were to evaluate effects of seven sire breed groups and three levels of daily ME intake (DMEI = 132 or 189 kcal ME/kg BW(0.75) or ad libitum), beginning 5 mo prepartum, on BCS, length of postpartum anestrus, and circulating concentrations of IGF-1 and GH in F1 cows (six to eight cows per sire breed in each DMEI group) out of Angus or Hereford dams. At the initiation of the study, BW were 522, 530, 548, 572, 575, 577, and 595 kg for cows sired by Longhorn, Galloway, 1960s Hereford or Angus, 1980s Hereford or Angus, or Nellore, Salers, and Shorthorn bulls, respectively (SE = 13; P < 0.001 for sire breed). After 4 mo on DMEI treatment during the pre-partum period, cows fed 132 kcal of ME/kg BW(0.75)gained little to no BW; cows fed 189 kcal ME/kg BW(0.75) gained 50 kg; and cows fed ad libitum gained 70 kg (all groups differ P < 0.05). Concentrations of progesterone in weekly blood samples collected 2 to 14 wk after calving were used to establish when normal luteal function resumed to predict length of postpartum anestrus. Length of anestrus was affected by level of DMEI in cows sired by Galloway, Longhorn, and Nellore bulls, but not other breeds (P < 0.02 for interaction of sire breed and DMEI). Level of DMEI, but not sire breed, affected (P < 0.01) BCS at wk 2 postpartum. Concentrations of IGF-1 at wk 2 postpartum differed (P < 0.001) due to sire breed, and changes in concentrations of IGF-1 from wk 2 to 14 were influenced (P < 0.03) by the interaction of sire breed and level of DMEI; which was primarily the result of differences in rate of decrease over time among different sire breed x level of DMEI groupings. Concentrations of GH did not differ due to sire breed but varied (P < 0.001) due to the interaction of DMEI and week postpartum, for which concentrations of GH did not differ at wk 2 but increased over time at rates that were inversely proportional to level of DMEI. Length of anestrus was negatively associated (P < 0.05) with day of calving, BCS, and BW. When effects of sire breed and level of DMEI were accounted for (residual correlation), length of anestrus was inversely associated (P < 0.01) with IGF-1 concentrations. Breed of sire influenced length of postpartum anestrus and energy balance, as predicted by IGF-1, in crossbred cows fed varying levels of DMEI.

Effect of administration of human chorionic gonadotropin after artificial insemination on concentrations of progesterone and conception rates in beef heifers1,2

The objective of this study was to determine whether administration of hCG approximately 5 d after AI would increase plasma progesterone concentrations and conception rates in beef heifers. Heifers from two locations (Location 1: n = 347, BW = 367 +/- 1.72 kg; Location 2: n = 246, BW = 408 +/- 2.35 kg) received melengestrol acetate (0.5 mg.heifer(-1).d(-1)) for 14 d and an injection of PGF2alpha (25 mg i.m.) 19 d later. Heifers were observed for estrus continuously during daylight from d 0 to 4.5 after PGF2alpha and artificially inseminated approximately 12 h after the onset of estrus. Half of the heifers inseminated at Location 1 were assigned randomly to receive an injection of hCG (3,333 IU i.m.) 8 d after PGF2alpha, and a blood sample was collected from all heifers 14 d after PGF2alpha for progesterone analysis. Half of the heifers inseminated at Location 2 were administered hCG on d 9 after PGF2alpha, and a blood sample was collected from all heifers 17 d after PGF2alpha. Heifers at Location 1 had a 94% synchronization rate, exhibited estrus 2.45 +/- 0.03 d after PGF2alpha, and received hCG 5.55 +/- 0.03 d after AI. Heifers at Location 2 had an 85% synchronization rate, exhibited estrus 2.69 +/- 0.03 d after PGF2alpha, and received hCG 6.31 +/- 0.03 d after AI. Progesterone concentrations were greater (P < 0.01) for hCG-treated heifers than for controls at both locations (8.6 vs. 4.6 ng/mL for treatment vs. control at Location 1, and 11.2 vs. 5.6 ng/mL for treatment vs. control at Location 2). Pregnancy status was determined by ultrasound approximately 50 d after AI. Conception rates (65 vs. 70% for treatment vs. control, respectively) did not differ at Location 1. Conception rates tended (P = 0.10) to be increased with hCG treatment at Location 2 (61 vs. 50% for treatment vs. control, respectively). A second experiment was conducted with 180 heifers at a third location to determine the effects of hCG administration 6 d after timed insemination at approximately 60 h after PGF2alpha in heifers synchronized as in Exp. 1. Pregnancy rate to timed AI did not differ between hCG-treated (62%) and control heifers (59%). Final pregnancy rate after timed AI and bull exposure (92%) was not affected by treatment. In summary, administration of hCG 5 to 6 d after AI did not improve conception or pregnancy rates at two out of three locations evaluated, suggesting insufficient progesterone is not a major factor contributing to early pregnancy failure in beef heifers.

Ovarian follicular development in cattle selected for twin ovulations and births12

Comparisons of numbers of antral ovarian follicles and corpora lutea (CL), of blood hormone concentrations, and of follicular fluid steroid concentrations and IGFBP activity were conducted between cows selected (twinner) and unselected (control) for twin births to elucidate genetic differences in the regulation of ovarian follicular development. Ovarian follicular development was synchronized among cows by a single i.m. injection of PGF2alpha on d 18 of the estrous cycle; six cows per population were slaughtered at 0, 24, 48, and 72 h after PGF2alpha. Jugular vein blood was collected from each animal at PGF2alpha injection and at 24-h intervals until slaughter. Ovaries of twinner cows contained more small (< or = 5 mm in diameter, P < 0.05), medium (5.1 to 9.9 mm, P < 0.05), and large (> or = 10.0 mm, P < 0.01) follicles and more (P < 0.01) CL than ovaries of controls. Follicular fluid concentrations of estradiol, androstenedione, testosterone, and progesterone reflected the stage of follicular development and were similar for twinner and control follicles at the same stage. Earlier initiation of follicular development and/or selection of twin-dominant follicles in some twinner cows resulted in greater concentrations of estradiol in plasma at 0, 24, and 48 h and of estradiol, androstenedione, and testosterone in follicular fluid of large follicles at 0 h after PGF2alpha for twinner vs. control cows (follicular status x time x population, P < 0.01). Binding activities of IGFBP-5 and -4 were absent or reduced (P < 0.01) in follicular fluid of developing medium and large estro-gen-active (estradiol:progesterone ratio > 1) follicles but increased with atresia. Only preovulatory Graafian follicles lacked IGFBP-2 binding, suggesting a possible role for IGFBP-2 in selection of the dominant follicle. Concentrations of IGF-I were twofold greater (P < 0.01), but GH (P = 0.10) and cholesterol (P < 0.05) were less in blood of twinners. Three generations of selection of cattle for twin ovulations and births enhanced ovarian follicular development as manifested by increased numbers of follicles within a follicular wave and subsequent selection of twin dominant follicles. Because gonadotropin secretion and ovarian steroidogenesis were similar for control and twinner cattle, enhanced follicular development in twinners may result from decreased inhibition by the dominant follicle(s), increased ovarian sensitivity to gonadotropins, and/or increased intragonadal stimulation, possibly by increased IGF-I.

Effect of increasing levels of undegradable intake protein on metabolic and endocrine factors in estrous cycling beef heifers1,2

To determine the influence of three levels of undegradable intake protein (UIP) supplementation on metabolic and endocrine factors that influence reproduction, 23 yearling crossbred heifers (body condition score = 4.5 +/- 0.5; initial BW = 362 +/- 12 kg) were stratified by BW and assigned randomly to one of three supplements: 1) low UIP (1,135 g x heifer(-1) x d(-1); 30% CP, 115 g UIP, n = 7); 2) mid UIP (1,135 g x heifer(-1) x d(-1); 38% CP, 216 g UIP, n = 8); or 3) high UIP (1,135 g x heifer(-1) x d(-1); 46% CP, 321 g UIP, n = 8). Heifers were estrually synchronized before initiation of supplementation. Supplement was individually fed daily for 30 to 32 d, at which time heifers were slaughtered (d 12 to 14 of the estrous cycle) and tissues collected. Heifers were fed a basal diet of sudan grass hay (6.0% CP) ad libitum. On d 28 of supplementation (d 10 of the estrous cycle), no differences were observed (P > 0.10) in serum insulin or IGF-I among treatments. At slaughter (d 10 to 12 of the estrous cycle), treatments did not influence corpus luteum weight, cerebral spinal fluid leptin, or IGFBP; serum estradiol-17beta, progesterone, leptin, IGF-I, and IGFBP; or anterior pituitary content of IGFBP (P > 0.10). Follicular fluid IGFBP-2 and IGFBP-4 were greater in high-UIP heifers than low- or mid-UIP heifers on d 12 to 14 of the estrous cycle (P < 0.05). Basal serum LH concentrations and LH area under the curve (every 15 min for 240 min) did not differ (P > 0.10) following 28 d of supplementation (d 10 of the estrous cycle); however, basal serum FSH concentrations were greater (P = 0.06) in low- and mid- vs. high-UIP heifers (5.2 and 5.2 vs. 4.6 ng/mL, respectively), and FSH area under the curve was greater (P = 0.03) in low- vs. high-UIP heifers. At slaughter (d 12 to 14 of the estrous cycle), anterior pituitary LH and FSH content and steady-state mRNA encoding alpha, LHbeta, and GnRH receptor did not differ (P > 0.10) among treatments. However, FSHbeta mRNA was increased approximately twofold (P = 0.03) in mid vs. low UIP. In summary, low and mid levels of UIP supplements fed to estrous cycling beef heifers seemed to enhance pituitary expression and/or secretion of FSH relative to high levels of UIP. Moreover, high-UIP supplementation was associated with increased low-molecular-weight IGFBP compared with supplementation of low and mid levels of UIP. These data suggest that differing levels of UIP supplementation may alter pituitary and ovarian function, thereby influencing reproductive performance in beef heifers.