Metabolizable protein supply while grazing dormant winter forage during heifer development alters pregnancy and subsequent in-herd retention rate.

Two studies were conducted to evaluate the effects of postweaning management of British crossbred heifers on growth and reproduction. In Exp. 1, 239 spring-born, crossbred heifers were stratified by weaning BW (234 ± 1 kg) and allotted randomly to 1 of 2 treatments. Treatments were fed at a rate equivalent to 1.14 kg/d while grazing dormant forage (6.5% CP and 80% NDF, DM basis) and were 1) 36% CP containing 36% RUP (36RUP) or 2) 36% CP containing 50% RUP (50RUP). Supplementation was initiated in February (1995 and 1996) or November (1997 and 1998) and terminated at the onset of breeding season (mid May). Heifers were weighed monthly up to breeding and again at time of palpation. After timed AI, heifers were exposed to breeding bulls for 42 ± 8 d. In Exp. 2, 191 spring-born, crossbred heifers were stratified by weaning BW to treatments. Heifer development treatments were 1) pasture developed and fed 0.9 kg/day of a 36% CP supplement containing 36% RUP (36RUP), 2) pasture developed and fed 0.9 kg/day of a 36% CP supplement containing 50% RUP (50RUP), and 3) corn silage-based growing diet in a drylot (DRYLOT). Heifers receiving 36RUP and 50RUP treatments were developed on dormant forage. Treatments started in February and ended at the onset of a 45-d breeding season in May. Heifer BW and hip height were taken monthly from initiation of supplementation until breeding and at pregnancy diagnosis. In Exp. 1, BW was not different (P ≥ 0.27) for among treatments at all measurement times. However, 50RUP heifers had greater (P = 0.02; 80 and 67%) pregnancy rates than 36RUP heifers. In Exp. 2, DRYLOT heifers had greater (P < 0.01) BW at breeding than 36RUP or 50RUP developed heifers. However, BW at pregnancy diagnosis was not different (P = 0.24) for between treatments. Pregnancy rates tended to be greater (P = 0.10) for 50RUP heifers than 36RUP and DRYLOT. Net return per heifer was US$99.71 and $87.18 greater for 50RUP and 36RUP heifers, respectively, compared with DRYLOT heifers due to differences in pregnancy and development costs. Retention rate after breeding yr 3 and 4 was greatest (P ≤ 0.01) for 50RUP heifers. Thus, increasing the supply of MP by increasing the proportion of RUP in supplements fed to heifers on dormant forage before breeding increased pregnancy rates, cow herd retention, and net return compared with heifers fed in drylot.

Effect of gonadotropin-releasing hormone or prostaglandin F(2α)-based estrus synchronization programs for first or subsequent artificial insemination in lactating dairy cows.

The objective was to evaluate the effects of GnRH or PGF(2α)-based synchronization and resynchronization programs on fertility in lactating dairy cows. For experiment 1, cows (n=1,521) were presynchronized with 2 injections of PGF given at 36 and 50 DIM and assigned to 1 of 3 protocols: Ovsynch [OVS; n=552; GnRH injection, PGF(2α) injection 7 d later, GnRH injection 56 h later, and timed artificial insemination (TAI) 16 h later] beginning at 14 d after presynchronization (PS), GnRH-GnRH-PGF(2α)-GnRH (GGPG; n=402) treatment with a GnRH injection given 7 d after PS and OVS 7 d later, or PGF(2α)-GnRH-PGF(2α)-GnRH (P7GPG; n=567) treatment with a PGF(2α) injection given 7 d after PS and OVS beginning 7 d later. Experiment 2 cows (n=2,327) were assigned to 1 of 3 resynchronization protocols 7 d before nonpregnancy diagnosis (NPD): GGPG cows (n=458) received a GnRH injection at enrollment and OVS at NPD; P7GPG cows (n=940) received a PGF(2α) injection at NPD and OVS 7 d later; and P11GPG cows (n=929) received a PGF(2α) injection 3 d after NPD and OVS 11 d later. In both experiments, cows were artificially inseminated upon estrus detection (ED). In experiment 1, 52.3% of cows were artificially inseminated upon ED, with GGPG having reduced ED (GGPG=46.8 vs. OVS=50.7 and P7GPG=57.7%). Treatments did not affect overall pregnancy per artificial insemination (P/AI) at 36 and 66 d after AI (OVS=34.1 and 32.3, P7GPG=34.6 and 31.9, and GGPG=31.3 and 28.1%, respectively) or pregnancy loss but cows artificially inseminated upon ED had higher P/AI than cows undergoing TAI (ED cows=37.9 vs. TAI cows=28.8%). Treatment did not affect P/AI for cows artificially inseminated upon ED or TAI at 36 and 66 d after AI (OVS=34.1 and 32.3, P7GPG=34.6 and 31.9, and GGPG=31.3 and 28.1%). Median days in milk at first AI was affected by treatment (P7GPG=59 vs. OVS=68 and GGPG=68 d). In experiment 2, GGPG reduced ED (GGPG=23.3 vs. P7GPG=74.9 and P11GPG=79.6%). Treatment did not affect overall P/AI at 36 and 66 d after AI (GGPG=29.2 and 25.8, P7GPG=28.7 and 26.6, and P11GPG=31.9 and 30.2%) or pregnancy loss. Cows artificially inseminated upon ED had greater P/AI than TAI cows (ED=32.3 and TAI=25.1%). However, treatment did not affect P/AI for cows artificially inseminated upon ED at 36 and 66 d after AI (GGPG=29.6 and 27.3, P7GPG=29.4 and 28.1, and P11GPG=35.7 and 33.7%) or TAI (GGPG=29.1 and 25.3, P7GPG=25.0 and 22.1, and P11GPG=16.9 and 16.9%). Median days between NPD and AI was affected by treatment (GGPG=10 vs. P7GPG=4 and P11GPG=7 d). Prostaglandin-based programs increased ED and reduced interval to first AI and between AI. Gonadotropin-releasing hormone-based programs increased the proportion of TAI cows. Cows artificially inseminated upon ED had increased P/AI compared with TAI cows.

The effect of increasing amount of glucogenic precursors on reproductive performance in young postpartum range cows.

Supplementing CP and propionate salts (PS) may improve economic returns in young range beef cows by increasing the dietary supply of glucogenic precursors. A 3-yr study conducted at Corona Range and Livestock Research Center (Corona, NM) from February to mid-July in 2005 (n = 80), 2006 (n = 81), and 2007 (n = 80) evaluated days to first estrus, calf weaning weight, BW change, and metabolic responses in 2- and 3-yr-old postpartum cows grazing native range. Cows were individually fed one of three 36% CP supplement treatments after parturition, with increasing glucogenic potential (GP) supplied by RUP and PS. Supplements were isoenergetic and fed at a rate of 908 g/cow per day twice weekly. Supplementation was initiated 7 d after calving and continued for an average of 95 d. Supplement treatments provided 1) 328 g of CP, 110 g of RUP and 0 g of PS (PS0); 2) 328 g of CP, 157 g of RUP, and 40 g of PS (PS40); or 3) 329 g of CP, 158 g of RUP, and 80 g of PS (PS80). Ultimately, PS0, PS40, and PS80 provided 44, 93, and 124 g of GP, respectively. Body weight was recorded weekly and serum was collected twice weekly for progesterone analysis to estimate days to first estrus. Cows were exposed to bulls for 60 d or less beginning in mid-May. Days to first estrus exhibited a quadratic (P = 0.06) response to GP resulting from the fewest days to first estrus with the consumption of PS40. Pregnancy rates were 88, 96, and 94% for cows fed PS0, PS40, and PS80, respectively (P = 0.11). Total kilograms of calf weaned per cow exposed to bulls for the supplementation and following year increased quadratically (P = 0.09). However, supplement did not affect milk composition or yield (P ≥ 0.53). Serum acetate half-life decreased linearly (P = 0.08) with increasing GP in 2007. Predicted margins were the greatest (quadratic; P = 0.03) for cows fed PS40. Even though supplement costs were greater for PS40 and PS80, cows fed PS40 had increased profits ($33.47/cow) compared with cows fed PS0 and PS80. This study implies that young postpartum cows fed additional glucogenic precursors may have improved reproductive efficiency and may wean more calf weight per cow exposed to breeding.

High periconceptional protein intake modifies uterine and embryonic relationships increasing early pregnancy losses and embryo growth retardation in sheep.

The effects of supplemented protein level (PL) during the periconceptional period and their interaction with body condition were evaluated in sheep. Multiparous Rambouillet ewes (n = 12) received two PL of rumen undegradable protein (UIP) during a 30-day pre-mating and 15-day post-mating period: low [LPL, 24% crude protein (CP), 14 g UIP and 36 g/CP animal/day] and high [HPL, 44% CP, 30 g UIP and 50 g/CP animal/day]. While ovulation rate (OR) did not differ between treatments (1.6 +/- 0.5, mean +/- SEM), a lower fertility rate, a decreased embryo number and a reduced uterine pH (UpH) was observed in the HPL group (p < 0.05), irrespective of BC. Luteal tissue weight, volume and progesterone secretion did not differ among treatments. Sheep with lower UpH also had lower conceptus weight (Cwt; p < 0.05, r = 0.65) and conceptuses with lower mass tended to secrete less INF-tau and IGF-1, and the correspondent endometrial explants had a higher basal PGF(2alpha) release. Current study indicates that high protein diets during the periconceptional period in sheep modify uterine and embryonic relationships, increasing early pregnancy losses and inducing embryo growth retardation. Surviving embryos were affected by weight reductions, which could compromise later foetal growth and birth weight. Results evidence the key role of a balanced diet in reproductive success and indicate that the quality and nutrient composition of the maternal diet are essential for an adequate establishment of pregnancy, having paramount effects on the interplay of the embryo and the uterus.

Influence of short-term fasting during the luteal phase of the estrous cycle on ovarian follicular development during the ensuing proestrus of ewes.

Short-term fasting of mature ewes during diestrus results in increased serum concentrations of progesterone and a delayed pre-ovulatory surge release of LH. To determine if these changes in reproductive hormones influence subsequent follicular development, mature ewes observed in estrus were assigned randomly to control (n=10) or fasted (n=15) groups. Control ewes had ad libitum access to feed, whereas fasted ewes were not fed from day 7 through 11 of their estrous cycle. Daily blood samples were collected from control and fasted ewes throughout the fasting period. Fasting increased (P<0.001) serum concentrations of progesterone (4.4 ng/mL versus 2.7 ng/mL [+/-0.3]). On day 12, all ewes were treated with 10mg of PGF(2alpha) and fasted ewes were returned to ad libitum feed. Ovaries were collected from ewes (n=5 each group) at 0 and 72 h following PGF(2alpha) in control and 0, 72 and 96 h in fasted ewes. Ovaries were weighed and small (< or =2mm), medium (3-4mm), and large (> or =5mm) follicles were enumerated. Total numbers of follicles were less (P<0.001) in fasted than fed ewes (14.6 versus 30.2 [+/-2.2]) at 0 h, but did not differ (P=0.9) when numbers of follicles were compared at similar times before the anticipated LH surge (i.e., at 72 h versus 96 h in control and fasted ewes, respectively). Within follicular size class, numbers of small and medium follicles were decreased (P=0.04) at 0 h in fasted ewes. Numbers of large follicles did not differ (P=1.0) between groups. Although numbers of small and medium ovarian follicles in fasted ewes recovered by 96 h to values comparable to fed ewes at 72 h following PGF(2alpha), serum concentrations of estradiol 17beta (P=0.08) and FSH (P=0.06) tended to be decreased in fasted ewes before the anticipated surge release of LH. Pituitary content of LH and FSH also tended to be lower (P< or =0.09) at 96 h in fasted ewes than at 72 h in control ewes, but did not differ (P> or =0.4) at hour 0 following PGF(2alpha). Hypothalamic and stalk median eminence contents of GnRH were not influenced (P> or =0.2) by fasting at any time period. Fasting during the luteal phase perturbs gonadotropin secretion and may influence fertility by causing a delay in ovarian follicle development.

Effects of supplements that contain increasing amounts of metabolizable protein with or without Ca-propionate salt on postpartum interval and nutrient partitioning in young beef cows.

Cattle grazing winter range forages exhibit interannual variation in response to supplementation. This variation may be mediated by circulating concentrations and subsequent metabolism of glucose, which are influenced by forage quality and availability. A study conducted at the Corona Range and Livestock Research Center during 2 dry years evaluated responses of young postpartum beef cows (n = 51, initial BW = 408 +/- 3 kg, and BCS = 5.1 +/- 0.04 in year 1; n = 36, initial BW = 393 +/- 4 kg, and BCS = 4.5 +/- 0.05 in year 2) to supplements that met or exceeded metabolizable protein (MP) requirements. Supplements were fed at 908 g/d per cow and provided 327 g of CP, 118 g of ruminally undegradable protein (RUP), and 261 g of MP from RUP (RMP), calculated to meet the MP requirement; 327 g of CP, 175 g of RUP, and 292 g of MP from RUP (RMP+), which supplied 31 g of excess MP; or 327 g of CP, 180 g of RUP, 297 g of MP from RUP, and 100 g of propionate salt (NutroCal, Kemin Industries, Inc., Des Moines, IA; (RMP+)P), which supplied 36 g of excess MP. Body weights were recorded once every 2 wk, and blood samples were collected 1x/wk in year 1 and 2x/wk in year 2 for 100 d postpartum. Postpartum anestrous was evaluated by progesterone from weekly blood samples, and pregnancy was confirmed by rectal palpation at weaning. As MP from RUP with or without propionate increased, a decrease (P = 0.03) was observed in postpartum interval; however, differences in pregnancy percentage (P = 0.54) were not influenced by treatments. We hypothesized that additional AA from RUP along with propionate would increase supply of glucogenic precursors and, therefore, glucogenic potential of the diet. Therefore, a postpartum glucose tolerance test was conducted near the nadir of cow BW to evaluate the rate of glucose clearance. Glucose tolerance tests showed that (RMP+)- or (RMP+)P-supplemented cows had greater (P = 0.03) rates of glucose clearance, which might have influenced the observed abbreviation of the postpartum interval. A glucose tolerance test conducted at the end of supplemental treatments revealed no differences in glucose clearance (P = 0.47) among previously supplemented cows. These data suggest that not only vegetative quality, duration of lactation, and season of grazing, but also type of supplementation may play a pivotal role in the young postpartum beef cow's ability to respond and incorporate nutrients into insulin-sensitive tissues.

Effect of increasing levels of undegradable intake protein on metabolic and endocrine factors in estrous cycling beef heifers.

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.

Effect of neuropeptide Y on GnRH-induced LH release from bovine anterior pituitary cell cultures derived from heifers in a follicular, luteal or ovariectomized state.

Objectives were to determine if neuropeptide Y (NPY) had direct effects GnRH induced secretion of LH from the anterior pituitary gland, and if endogenous steroids modulated the effect of NPY. To accomplish these objectives, 15 Hereford heifers were assigned to one of three ovarian status groups: follicular, luteal, or ovariectomized. One animal from each of the three ovarian status groups was slaughtered on each of 5 days and anterior pituitary gland harvested. Anterior pituitary gland cells within ovarian status were equally distributed and randomly assigned to one of three cell culture treatments: no NPY or GnRH (control), 10 nM GnRH, or 100 nM NPY+10 nM GnRH. Anterior pituitary cell cultures were incubated with or without NPY for 4 h and further incubated for an additional 2 h with or without GnRH and supernatant collected for quantification of LH. Treatment of anterior pituitary cell cultures with GnRH or GnRH+NPY did not affect LH release in cultures obtained from follicular (S.E.=5%; P=0.58) or ovariectomized (S.E.=7%; P=0.22) heifers. Both GnRH and GnRH+NPY increased LH release from anterior pituitary cell cultures from heifers in the luteal phase (S.E.=14%; P < or = 0.05) compared to control cultures. Cultures from luteal phase heifers treated with GnRH did not differ from those treated with GnRH+NPY (P=0.34). These data provide evidence to suggest that effects of NPY on LH release may occur primarily at the level of the hypothalamus.

Effects of varying levels of undegradable intake protein on endocrine and metabolic function of young post-partum beef cows.

Twelve Hereford x Angus heifers, 2.5 year, 492 +/- 17 kg (BCS = 5 +/- 0.5), were randomly assigned to one of three supplements, stratified by calving date and calf sex. Treatments consisted of a daily equivalent of: (1) low undegradable intake protein (UIP) (L: 908 g per cow per day; 36% CP, 108 g UIP), (2) middle UIP (M: 908 g per cow per day; 36% CP, 165 g UIP), and (3) high UIP (H: 908 g M + 243 g feather meal per cow per day; 46% CP, 335 g UIP). Cows were fed sudan grass hay (7.3% CP, as fed) daily at 2% BW (as fed). Supplement was individually fed twice weekly from Week 2 to Week 11 post-partum. Cow body weight (BW), backfat (BF) and rumpfat (RF) thicknesses decreased in all cows, (P < 0.05) yet did not differ among treatments (P > 0.10). There were no differences among treatments in calf BW (P > 0.10). Serum insulin, blood urea nitrogen (BUN), milk components and yield did not differ among treatments (P > 0.10). Area under the curve (AUC) for serum LH was greater (P = 0.07) in H versus L and M (809 versus 599 and 607 +/- 69 U, respectively). No differences were observed in FSH AUC or mean serum concentrations (P > 0.10). Uterine pH did not differ among treatments or between supplement versus non-supplement days (P > 0.10). Serum progesterone remained below I ng/ml for all cows indicating absence of return to estrus. Under the conditions of this study, BW, BF, RF, serum insulin, BUN, milk components, and yield, uterine pH and serum FSH were not affected by level of UIP. However, supplement containing high levels of UIP enhanced GnRH-induced LH release.

Reproductive outcomes for dairy heifers treated with combinations of prostaglandin F2alpha, norgestomet, and gonadotropin-releasing hormone.

We conducted three experiments to test various protocols for synchronizing estrus, ovulation, or both before insemination of heifers. In experiment 1, 23 controls received two PGF2alpha injections; 23 heifers were treated like the controls plus a norgestomet implant for 8 d, with the second PGF2alpha injection 24 h before implant removal; and 23 heifers were treated like the previous group plus 100 microg of GnRH 54 h after the second PGF2alpha injection. Although norgestomet and GnRH altered some estrual characteristics, conception rates in experiment 1 (n = 69) and experiment 2 (278 heifers receiving the same treatments as those in experiment 1) generally were not different among treatments. Reproductive outcomes were not improved by adding norgestomet and GnRH to a standard PGF2alpha protocol. In experiment 3, control heifers received PGF2alpha and were inseminated after detected estrus or at 72 to 80 h after a second injection of PGF2alpha given 14 d after the first injection. Select Synch heifers, treated with GnRH either 6 or 7 d before PGF2alpha were inseminated after detected estrus, whereas Ovsynch heifers were treated like Select Synch heifers but also received a second GnRH injection approximately 36 h after PGF2alpha and were inseminated 18 h later. Estrus detection and pregnancy rates after Ovsynch were less than those of controls, whereas conception and pregnancy rates did not differ between control and Select Synch heifers. Therefore, the Select Synch protocol was equivalent to a standard PGF2alpha protocol, whereas Ovsynch was inferior to both of those protocols.

Genetic differentiation among geographically isolated populations of Criollo cattle and their divergence from other Bos taurus breeds.

The microsatellites HEL5, HEL9, INRA063, and BM2113 were used to analyze genetic similarities and differences of geographically isolated Criollo cattle herds in Mexico. Criollo cattle from five counties within the state of Chihuahua and one county from the state of Tamaulipas (n = 60) were sampled. The five counties in Chihuahua included Cerocahui (n = 14), Chinipas (n = 10), Guachochi (n = 15), Morelos (n = 30), and Temoris (n = 9). Samples of DNA were amplified by PCR and separated on a 7% polyacrylamide gel. Microsatellite size was established by comparison to M13mp18 DNA ladder and a documented set of four bovine controls. Allele frequencies and genotypic deviations from Hardy-Weinberg equilibrium were tested using the GENEPOP program. Eleven alleles were generated at HEL5 for the populations sampled (149 to 169 bp). Allele frequencies were greatest for the 163-bp allele in Criollo cattle from Cerocahui, Chinipas, Moralos, and Tamaulipas (0.23 to 0.5). Cattle from Guachochi had an allele frequency of 0.38 for the 151-bp allele, and cattle from Temoris had an allele frequency of 0.25 for the 149- and 167-bp alleles, with no 163-bp allele. Amplification with HEL9 produced 12 alleles (145, 149 to 169 bp) and showed common high-frequency alleles at 149, 157, and 159 bp for animals from all regions. The Chinipas population showed a moderate allele frequency at 145 bp; no other regions contained this allele. For INRA063 there were five alleles with 182 and 184 bp in low frequency. For BM2113 there were 10 alleles in the Criollo cattle (125 to 143 bp), with an equal distribution of frequencies for all alleles. In two regions, Guachochi and Morelos, genotypic frequencies deviated from Hardy-Weinberg equilibrium. Cattle from the Temoris region were genetically most distant from Criollo cattle of the other five regions.

Insertion of Inhbb into the Inhba locus rescues the Inhba-null phenotype and reveals new activin functions.

The activins (dimers of betaA or betaB subunits, encoded by the genes Inhba and Inhbb, respectively) are TGF-beta superfamily members that have roles in reproduction and development. Whereas mice homozygous for the Inhba-null allele demonstrate disruption of whisker, palate and tooth development, leading to neonatal lethality, homozygous Inhbb-null mice are viable, fertile and have eye defects. To determine if these phenotypes were due to spatiotemporal expression differences of the ligands or disruption of specific ligand-receptor interactions, we replaced the region of Inhba encoding the mature protein with Inhbb, creating the allele Inhbatm2Zuk (hereafter designated InhbaBK). Although the craniofacial phenotypes of the Inhba-null mutation were rescued by the InhbaBK allele, somatic, testicular, genital and hair growth were grossly affected and influenced by the dosage and bioactivity of the allele. Thus, functional compensation within the TGF-beta superfamily can occur if the replacement gene is expressed appropriately. The novel phenotypes in these mice further illustrate the usefulness of insertion strategies for defining protein function.

Effect of subacute swainsonine (locoweed; Oxytropis sericea) consumption on immunocompetence and serum constituents of sheep in a nutrient-restricted state.

The subacute dose-response effects of swainsonine (SW) consumption on immunocompetence and serum constituents of sheep in a nutrient-restricted state were investigated. Sheep (23 wethers, 5 ewes) were assigned to 1 of 5 SW treatments (0, 0.2, 0.4, 0.8, or 1.6 mg swainsonine/ kg bw/d). Swainsonine was delivered by feeding locoweed (Oxytropis sericea) with grama grass and alfalfa hays for a 28-d treatment period followed by a 21-d recovery period without locoweed. Body weights were measured weekly and behavioral changes were monitored for clinical signs of SW toxicity. Venous blood was collected weekly for lymphoblastogenesis and serum constituent analyses. Clinical signs (sluggishness, decreased responsiveness) of swainsonine toxicity were observed from d 14 to 35 in the 0.8 and 1.6 mg treatments. Subacute oral exposure did not appear to affect lymphoblastogenic analyses. Acute and subacute alterations in various serum constituents did indicate subclinical effects of SW ingestion. Linear, quadratic and cubic dose-response relationships were detected for some serum constituents (e.g., alkaline phosphatase, aspartate aminotransferase). Subacute SW consumption at the levels investigated does not seem to affect the immunocompetence of nutrient restricted sheep. The lack of change in serum alkaline phosphatase at the 0.2 mg SW/kg bw/d dose indicates the potential for a no adverse effect level of SW consumption in nutrient restricted sheep. In combination with measurable SW in serum, rises in serum alkaline phosphatase and aspartate aminotransferase activities, and declines in serum Fe and cholesterol during subacute exposure to SW establish these markers as potential indicators of subclinical SW toxicosis.

Effect of glucose administration during the estrous cycle on serum hormone profiles, mRNA for steroidogenic enzymes, and breeding performance of ewes.

Thirty mature Debouillet ewes were used to examine effects of exogenous glucose on endocrine, ovarian, and reproductive responses. Treatments were administered from d 5 through 15 of a normal estrous cycle (d 0 = estrus). Fifteen ewes received daily i.p. injections containing 100 mL of saline (.9%, control), and 15 ewes received daily i.p. injections containing 50 g of glucose (100 mL of 50% dextrose). Ovaries were removed from five ewes per group on d 15, and luteal mRNA encoding steroidogenic enzymes and follicular fluid progesterone (P4) were determined. Serum glucose in treated ewes increased rapidly after injection and remained elevated (P < .01) for 4 h after treatment on d 10 and 14 compared with control values. Serum insulin concentration was also greater (P < .01) after glucose treatment on d 10 and 14, but serum growth hormone concentration was similar (P > .10) in both groups on these days. Serum LH concentration and pulsatility were not altered by glucose injection (P > .15). Serum P4 remained elevated longer (P < .05) during the estrous cycle in treated than in control ewes. Corpora lutea from treated ewes also had more (P < .10) mRNA encoding for cytochrome P450 side-chain cleavage enzyme, but mRNA for 3 beta-hydroxysteriod dehydrogenase/delta 5- delta 4 isomerase and follicular fluid P4 were similar (P > .40) between groups. Glucose-treated ewes conceived later (P < .10) and produced fewer lambs (P < .10) than did controls. These data indicate that exogenous glucose and(or) the subsequent increased serum insulin resulted in ovarian changes associated with elevated luteal P4 production.

Semen traits and metabolic and gonadotropic hormone profiles in ram lambs treated with glucose.

Two experiments were conducted to examine reproductive and endocrine responses of ram lambs to exogenous glucose. In Experiment 1, three ram lambs (6 mo of age) received 100 ml ip of saline (0.9%) daily and three animals received 50 g glucose (100 ml 50% dextrose) daily for 18 d. In Experiment 2, ten lambs (5 per group) were treated similarly for 10 d. Serum samples were collected intensively before and after GnRH treatment on the last day of both experiments. After 15 d of glucose treatment in Experiment 1, treated rams weighed 58 kg compared with 68 kg for the controls (P = 0.08). A similar numerical trend was observed in Experiment 2, suggesting that intraperitoneal glucose decreases feed intake. In both experiments, 50 g of glucose induced a rapid elevation in serum glucose to greater than 120 mg/dl compared with 70 to 80 mg/dl for the controls (P < 0.05). Serum insulin rose to over 6 ng/ml in both trials in lambs receiving glucose compared with values of about 2 ng/ml for the controls (P < 0.01). Serum growth hormone was not altered (P > 0.10) by glucose in either experiment and IGF-1 was similar (P > 0.20) between groups in Experiment 2. Although serum concentrations of prolactin tended (P = 0.14) to be reduced by glucose treatment (64 +/- 21 ng/ml) compared with that of the controls (120 +/- 21 ng/ml) in Experiment 1, the opposite trend (P = 0.20) was observed in Experiment 2. Serum thyroxine was elevated (P = 0.08) in glucose-treated rams compared with that in controls in Experiment 2 but triiodothyronine concentrations were similar (P > 0.80) between groups. In Experiment 1, area under the curve (AUC) for LH after a GnRH challenge tended (P = 0.14) to be greater in glucose-treated (1,351 units) than in control (999 +/- 139 units) animals. The AUC for FSH (Experiment 1) did not differ (P = 0.30) between groups. The LH AUC in Experiment 2 was about 2,500 units for both groups (P = 0.80). The AUC for testosterone in Experiment 1, was 5,452 and 2,597 (+/- 1051) units for rams treated with 0 and 50 g glucose/d (P = 0.13), but testosterone AUC in Experiment 2 was similar between groups (P > 0.70). No effect of exogenous glucose was evident in either experiment for semen traits. Results suggest that 50 g ip glucose daily for 10 or 18 d induced large increases in serum insulin but other metabolic and reproductive hormones were not greatly influenced.

An increase in serum lipids increases luteal lipid content and alters the disappearance rate of progesterone in cows.

To determine whether an increase in serum lipids alters the area occupied by lipid droplets in steroidogenic luteal cells and(or) clearance rates of progesterone from serum, pregnant beef heifers received control (n = 6) or treatment (n = 5) diets. To increase serum lipids, the treatment diet contained calcium soaps of fatty acids. Control and treatment diets were formulated to be isocaloric and isonitrogenous. Feeding of diets was initiated approximately 100 d before parturition and continued through the third postpartum estrous cycle. On d 12 or 13 of the third postpartum cycle, corpora lutea were collected by ovariectomy and a center slice was processed for electron microscopy. Eight samples from each slice were sectioned, stained, and examined at a magnification of 2,500x. Five micrographs per sample were analyzed for area occupied by small (SLC) and large (LLC) luteal cells, percentage of the area of each steroidogenic cell type occupied by lipid, and total steroidogenic area (SLC + LLC) occupied by lipid. Jugular blood was collected before and after ovariectomy, and progesterone, cholesterol, high-density lipoprotein (HDL), and low-density lipoprotein (LDL) were quantified. Cows consuming treatment diets had approximately twice (P < .05) the concentration of cholesterol, HDL, and progesterone in serum that controls had. The percentage of the area of SLC, LLC, and total area occupied by lipid was greater (P < .05) in treated than in control cows. The average time required for serum concentrations of progesterone to decrease by 50% after ovariectomy was greater (P < .05) in treated than in control cows (170 +/- 16 vs 113 +/- 15 min).(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of cytochrome P450scc synthesis and activity in the ovine corpus luteum.

The rate-limiting step in luteal biosynthesis of progesterone consists of cleavage of the side chain of cholesterol by mitochondrial cytochrome P450 side-chain cleavage enzyme (P450scc) to form pregnenolone. Luteal mRNA encoding P450scc, quantitated on selected days of the 16-day ovine estrous cycle, was similar on days 3 and 6, increased by 2-fold on day 9 (P < 0.05) and remained elevated on day 15. Levels of P450scc mRNA on day 15 of pregnancy were not different from those found on any day of the cycle (P < 0.05). To determine whether levels of mRNA encoding P450scc are hormonally regulated, ewes on day 10 of the estrous cycle were injected with hCG or prostaglandin F2 alpha (PGF2 alpha). P450scc mRNA was not increased for up to 36 h after injection of hCG, nor decreased within 8 h after injection of PGF2 alpha (P < 0.05). An assay for P450scc activity was developed which utilized ovine small and large luteal cells in the presence of 22R-hydroxycholesterol and ovine high density lipoprotein. Enzyme activity was quantitated by measurement of progesterone production. In small luteal cells activation of the protein kinase A (PKA) second-messenger system by treatment with LH resulted in 910% increase in progesterone production without altering activity of P450scc. Activation of the protein kinase C (PKC) second-messenger system with phorbol 12-myristate 13-acetate caused a 51% reduction in progesterone secretion from large luteal cells but did not alter activity of P450scc. These findings suggest that in mature luteal tissue steady state levels of mRNA encoding P450scc, and enzyme activity are independent of acute regulation by activation of PKA or PKC second-messenger systems.

Regulation of messenger ribonucleic acid encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase in the ovine corpus luteum.

Three experiments were conducted to determine how steady-state levels of mRNA encoding 3 beta-hydroxysteroid dehydrogenase/delta 5-delta 4 isomerase (3 beta-HSD) in the ovine corpus luteum vary 1) between the two steroidogenic luteal cell types, 2) during the estrous cycle, and 3) during prostaglandin F2 alpha (PGF2 alpha)-induced luteolysis. In the first experiment, RNA (10 micrograms) was isolated from purified preparations (n = 4) of large or small steroidogenic luteal cells. Large luteal cells contained 42% more (p < 0.05) message for 3 beta-HSD per microgram RNA than did small luteal cells, while the amount of mRNA for tubulin did not differ between the two types of luteal cells. To determine whether luteal levels of mRNA for 3 beta-HSD differ during the estrous cycle, corpora lutea were collected from cycling ewes (n = 3/day) on Days 3, 6, 9, 12, and 15 postestrus. Levels of mRNA for 3 beta-HSD were similar on Days 3, 6, 9, and 12 but were lower (p < 0.05) on Day 15 postestrus, while levels of mRNA for tubulin were unchanged. In the final experiment, ewes were treated on Day 10 postestrus with two injections of PGF2 alpha (5 mg each) or saline (control) at a 4-h interval. Corpora lutea were collected from ewes (n = 4/treatment) 1 h or 8 h after the second injection of PGF2 alpha or 8 h after the second saline injection.(ABSTRACT TRUNCATED AT 250 WORDS)

Performance of Bos indicus-influenced bulls in serving capacity tests and multiple-sire breeding groups.

Three experiments were conducted with Santa Gertrudis (SG) or F1 (Gelbvieh x SG or Red Angus x SG) bulls to assess factors that influence copulatory activity and fertility of Bos indicus-influenced genotypes. In Exp. 1, 3-yr-old SG bulls (n = 20) with sexual experience and 20-mo-old virgin SG bulls (n = 34) were allotted in a split-plot design (age, bull within age group, test day, and heifer treatment). Number of mounts (Mt), intromissions (I), and ejaculations (E) were measured 14 d apart during two 30-min serving capacity (SC) tests. Estrus was either induced via progesterone+estradiol cypionate (PE) injections or synchronized with Syncro-Mate B (SMB). There were more (P less than .05) I and E on Test d 2 than on Test d 1. Heifers treated with SMB received more (P less than .001) Mt, I, and E than did heifers treated with PE. Sixteen 20-mo-old bulls from Exp. 1 were allotted to breeding pastures at a bull:heifer ratio of 4:119 +/- 3 for 50 d in Exp. 2. Breeding pasture treatments either included or excluded low-SC bulls. Neither pregnancy rate nor least squares mean day of conception differed between treatments. Experiment 3 evaluated copulatory activity with a 2 x 2 factorial arrangement (breed and test day) in 14- to 16-mo-old SG (n = 45) and F1 (n = 16) bulls. The F1 bulls had more Mt, I, and E than did the SG bulls (P less than .05).(ABSTRACT TRUNCATED AT 250 WORDS)