R. B. Staigmiller

Folliculogenesis in the bovine

Abstract During the follicular phase of the estrous cycle in the cow, there is a rapid turnover in large (ovulatory size) follicles with the ovulatory follicle being identifiable by size not more than 3 days prior to estrus. Characteristics of the ovulatory follicle have been described in terms of steroid production and, to a lesser extent, gonadotropin receptors. It remains yet to be determined which factors permit development of these characteristics rather than leading to the onset of atresia.

Use of bovine FSH for superovulation and embryo production in beef heifers

Abstract A biologically active dimeric glycoprotein gonadotropin (bFSH) produced by recombinant DNA technology was used to determine superovulation response and embryo production in Hereford F 1 and Brahman F 1 heifers. Heifers received a total dose of either 18- or 24-mg bFSH administered intramuscularly and given twice daily over a 3-d period. Luteal regression was induced with either dinoprost (Lutalyse ® or cloprostenol (Estrumate ® ) administered immediately before the fifth bFSH injection. Blood samples were obtained just prior to the first and fifth bFSH injection and 12 h after the last injection. Progesterone concentrations were determined by radioimmunoassay. Embryos were collected by routine nonsurgical procedures. Superovulatory response (P 1 than Hereford F 1 heifers. No significant differences were found due to luteolytic agent or bFSH dosage. Serum progesterone concentration in the initial sample was higher (P 1 than in Brahman F 1 heifers, and there were interactions in progesterone concentrations between heifer breed and bFSH dose (P

Superovulation of cattle with equine pituitary extract and porcine ESH

Superovulation has been practiced in cattle for more than 50 years but the results have been highly variable. Scientists at six locations compared a horse pituitary extract (HAP) with a single batch of porcine FSH (pFSH) to determine the efficacy of these hormones to induce superovulation and to test for variability in the superovulatory response. Acetone-dried equine pituitaries were suspended in 40% ethanol containing 6% ammonium acetate, and the supernatant was mixed with 2.5 volumes of cold ethanol. The resulting precipitate was washed with cold ether and dried. Total doses of 18 mg of HAP and 36 mg of pFSH were injected intramuscularly (i.m.) over 4 days, two injections per day, and prostaglandin (PGF(2)alpha; 25 mg, i.m.) was administered on Day 3. Injections were begun on Days 6 to 13 of the estrous cycle. The overall ovulation rates (mean +/- SEM) for HAP and FSH were 8.8 +/- 0.7 and 15.1 +/- 1.0, respectively (n=231; P<0.01). Location interacted (P<0.01) with the type of gonadotropin for the ovulation rate. When expressed as a proportion of the number of corpora lutea, the total number of embryos recovered was greater (P=0.03) for pFSH than for HAP, but there was no difference in the number of Quality 1 and 2 embryos. The results show that HAP can induce a satisfactory superovulatory response, but there was no evidence of reduced variability of response to HAP compared with pFSH.

Negative Feedback Control of Luteinizing Hormone Secretion in Prepubertal Beef Heifers at 60 and 200 Days of Age

Prepubertal beef heifers at 60 and 200 d of age, born in the fall or spring, were assigned randomly to one of three treatment groups: (1) intact = 1; (2) bilateral ovariectomy (OVX); or (3) OVX plus estradiol-17 beta(E2) administered in silastic implants (OVX + E2). Luteinizing hormone (LH) was measured in serum samples collected at 20-min intervals for 4 h from heifers on -1, +7, +21, +35 and +49 d after OVX. Luteinizing hormone concentrations increased in the serum by 7 d after OVX in heifers at both 60 and 200 d of age (P less than .001; time X treatment). Prior to OVX, the LH patterns were characterized by low levels and infrequent episodic pulses. By 49 d after OVX, the mean LH concentrations increased and the pattern changed to one of rhythmic LH pulses with a periodicity of 1 h (P less than .001; time X treatment). Estradiol-treated OVX heifers did not exhibit a postovariectomy rise in serum LH concentrations. Serum E2 concentration 49 d after OVX in OVX heifers was threefold greater than in 1 or OVX heifers, thus demonstrating that E2 exerted negative feedback on pituitary LH secretion in prepubertal heifers. There was no measurable difference in serum E2 concentrations between I and OVX heifers; however, the contrast in the concentration and pattern of serum LH between the two groups was dramatic and suggested gonadal factors in addition to E2 are involved in controlling LH secretion.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple linear and nonlinear regression analyses of factors causing calving difficulty

Calving difficulty (CD) was analyzed as the dependent variable from observations on 592 first-calf, 2-year-old heifers that were either Angus X Hereford (AH), Charolais X AH or Simmental X AH. Independent variables were birth weight (BW), pelvic area (PA), BW.(33), PA.(5), cow weight (CW), cow condition score (CS) and sex of calf (S). CD was analyzed as score (1 = no difficulty through 4 = extreme difficulty) CD-I, % CD (1 vs 2 + 3 + 4 , CD-II) or % high CD (1 + 2 vs 3 + 4 , CD-III). R(2) values from CD-II and CD-III multiple correlation (R) analyses were consistently lower (.10 to .13) than from the CD-I analysis. When only BW and PA were included in the model, R(2) values for CD-I were .36, .39 and .39 for the linear, quadratic and cubic analyses, respectively. When BW, PA, CW, CS and S were included in the model, the R(2) values for CD-I were .40 and .42 for the linear and quadratic analyses (cubic effects were not tested). In the linear analysis with BW.(33) and PA.(5), the R(2) for CD-I was .36. In all analyses, the order of importance of the factors studied was BW and PA, with a much lower contribution from CW and S. CS did not account for a significant increase in R(2) in any analysis. CD remained below 50% whenever the PA BW ratio exceeded 8.4. This ratio is a convenient practical method to relate PA and BW to CD. Conclusions are that the linear effects of BW and PA account for the majority of the identified variation in CD (R(2)) and that small increases in R(2) can be obtained by adding CW, CS and S to the model and/or by expanding the model to include quadratic effects.

Influence of sire, sex of fetus and type of pregnancy on conceptus development.

Estrus was synchronized in 93 crossbred cows 3 to 7 yr old which were then superovulated with 10 mg FSH-P and bred artificially to either a Jersey or Charolais bull. Females pregnant to the Jersey sire were slaughtered at 95, 180 or 250 d of gestation; low pregnancy rate from the Charolais sire resulted in enough dams for slaughter and valid comparisons at 95 d only. Conceptus tissue and organ weights and dam carcass weights and measurements were collected at slaughter. At 95 d of gestation, sire differences were not significant; type of pregnancy (single vs multiple) had significant effects on placentome and membrane weight; fetus sex had highly significant effects on fetus weight and crown-rump length. Fetal brain and heart weights showed little effect of sire, fetus sex or type of pregnancy, indicating these early differentiating tissues are highly competitive for available nutrients for growth. Fetal data at 180 and 250 d of gestation showed highly significant effects of gestation stage on placentome, membrane and fetus weights, crown-rump and metatarsal lengths, and liver, kidney, heart and total brain weights. Type of pregnancy had greater effects on the conceptus traits than did fetus sex at these stages. Nonorthogonal analyses of data from the Jersey-sired pregnancies indicated growth of fetuses in multiple pregnancies was suppressed, and the reduction in fetus weight became more pronounced as gestation progressed. Correlations among conceptus traits and dam carcass data showed different relationships within single and multiple pregnancies. We suggest that the genetic contribution for fetal growth has a positive effect on fetal size throughout gestation while the importance of metabolite availability may change during gestation depending on the genetic growth potential of the fetus and on whether the pregnancy is single or multiple. We speculate that these fetus-dam relationships involve systems controlling fetus growth that arise from the fetus genetic growth potential interacting with positive and negative dam effects that are linked or related to the carcass skeletal-fat-muscle endpoints studied.