D.W. Forrest

Phenotypic and genetic relationships of residual feed intake with performance and ultrasound carcass traits in Brangus heifers.

The objective of this study was to characterize residual feed intake (RFI) and to estimate phenotypic and genetic correlations with performance and ultrasound carcass traits in growing heifers. Four postweaning feed efficiency trials were conducted using 468 Brangus heifers. The complete Brangus pedigree file from Camp Cooley Ranch (Franklin, TX), which included 31,215 animals, was used to generate genetic parameter estimates. The heifer progeny from 223 dams were sired by 36 bulls, whereas the complete pedigree file contained 1,710 sires and 8,191 dams. Heifers were individually fed a roughage-based diet (ME = 1.98 Mcal/kg of DM) using Calan gate feeders for 70 d. Heifer BW was recorded weekly and ultrasound measures of 12th- to 13th-rib fat thickness (BF) and LM area (LMA) obtained at d 0 and 70. Residual feed intake (RFIp) was computed as actual minus predicted DMI, with predicted DMI determined by linear regression of DMI on mid-test BW(0.75) (MBW) and ADG with trial, trial x MBW, and trial x ADG as random effects. Overall means for ADG, DMI, and RFI were 1.01 (SD = 0.15), 9.51 (SD = 1.02), and 0.00 (SD = 0.71) kg/d, respectively. Stepwise regression analysis revealed that inclusion of gain in BF and final LMA into the base model increased the R(2) (0.578 vs. 0.534) and accounted for 9% of the variation in DMI not explained by MBW and ADG (RFIp). Residual feed intake and carcass-adjusted RFI (RFIc) were strongly correlated phenotypically and genetically with DMI and FCR, but not with ADG or MBW. Gain in BF was phenotypically correlated (P < 0.05) with RFIp (0.22), but not with FCR or RFIc; however, final BF was genetically correlated (P < 0.05) with RFIp (0.36) and RFIc (0.39). Gain in LMA was weakly phenotypically correlated with FCR, but not with RFIp or RFIc; however, gain in LMA was strongly genetically correlated with RFIp (0.55) and RFIc (0.77). The Spearman rank correlation between RFIp and RFIc was high (0.96). These results suggest that adjusting RFI for ultrasound carcass composition traits will facilitate selection phenotypically independent of growth, body size, and carcass composition; however, genetic relationships may still exist between RFI and carcass composition.

Methods for collecting follicular oocytes from mares

A series of experiments was conducted to develop a procedure for consistent, repeatable collection of oocytes from the preovulatory follicle of the mare. In one experiment, in situ follicular aspiration with a needle and syringe was performed on 19 mares. From 37 aspirations, four oocytes were recovered (10% recovery rate). In a second experiment, ovaries were visualized via standing flank laparotomy during which two different aspiration techniques were used. Use of a needle and syringe as in the first experiment resulted in successful oocyte recovery in one of seven (14%) attempts. Aspiration via a continuous irrigation vacuum system (CIV), developed for use during laparotomy, resulted in collection of oocytes from six of 10 (60%) attempts. In the third experiment, oocytes were recovered from seven of 18 (38%) attempts at in situ follicular aspiration using a double-lumen needle attached to the CIV. In each experiment, some mares were subjected to stimulation of follicular maturation by exogenous hormones. Oocyte recovery was significantly increased in treated mares as compared with nontreated mares. Results indicate that collection of equine follicular oocytes by in situ aspiration is possible with moderate success. Oocytes apparently are not physically damaged by the procedure, as most retained either the corona radiata or the entire cumulus cell mass.

Dexamethasone acutely down-regulates genes involved in steroidogenesis in stallion testes.

In rodents, livestock and primate species, a single dose of the synthetic glucocorticoid dexamethasone acutely lowers testosterone biosynthesis. To determine the mechanism of decreased testosterone biosynthesis, stallions were treated with 0.1mg/kg dexamethasone 12h prior to castration. Dexamethasone decreased serum concentrations of testosterone by 60% compared to saline-treated control stallions. Transcriptome analyses (microarrays, northern blots and quantitative PCR) of testes discovered that dexamethasone treatment decreased concentrations of glucocorticoid receptor alpha (NR3C1), alpha actinin 4 (ACTN4), luteinizing hormone receptor (LHCGR), squalene epoxidase (SQLE), 24-dehydrocholesterol reductase (DHCR24), glutathione S-transferase A3 (GSTA3) and aromatase (CYP19A1) mRNAs. Dexamethasone increased concentrations of NFkB inhibitor A (NFKBIA) mRNA in testes. SQLE, DHCR24 and GSTA3 mRNAs were predominantly expressed by Leydig cells. In man and livestock, the GSTA3 protein provides a major 3-ketosteroid isomerase activity: conversion of Δ(5)-androstenedione to Δ(4)-androstenedione, the immediate precursor of testosterone. Consistent with the decrease in GSTA3 mRNA, dexamethasone decreased the 3-ketosteroid isomerase activity in testicular extracts. In conclusion, dexamethasone acutely decreased the expression of genes involved in hormone signaling (NR3C1, ACTN4 and LHCGR), cholesterol synthesis (SQLE and DHCR24) and steroidogenesis (GSTA3 and CYP19A1) along with testosterone production. This is the first report of dexamethasone down-regulating expression of the GSTA3 gene and a very late step in testosterone biosynthesis. Elucidation of the molecular mechanisms involved may lead to new approaches to modulate androgen regulation of the physiology of humans and livestock in health and disease.

Effect of suckling manipulation on postpartum reproduction in primiparous Brahman-cross cows

Abstract The effect of suckling manipulation on postpartum reproductive performance was investigated in 106 primiparous Brahman-cross cows. Suckling manipulation treatments were 1) suckling ad libitum (SAL, n = 52) and 2) once-daily suckling (ODS, n = 54) beginning at 30 d after parturition. By 60 d after parturition, 57% of the ODS and 29% of the SAL groups, respectively (P

Cloprostenol inouced luteal regression in the beef cow. I. Ovarian response and endocrine changes

Forty-two cycling, multiparous beef cows (percentage-Brahman) were given two injections of 500 ug Cloprostenol (CLP) 11 days apart. Cows were randomly allocated to be ovariectomized at 0, 12, 24, 36, 48, 60 or 72 hr after the second CLP injection. Mean CL weight declined within 36 hr after CLP. Mean concentration of P4 in luteal tissue increased between o and 60 hr, while mean P4 content per CL declined by 12 hr after CLP. There was a precipitous decrease in mean serum P4 by 12 hr following CLP injection. Serum E2 was elevated until 24 hr and then declined through 72 hr after CLP. Follicular T concentration increased from 0 to 48 hr and then decreased by 60 hr. We conclude that CLP caused rapid diminution of luteal function which was accompanied by a reduction in P4 content but not in P4 concentration. Futhermore, the concentration of E2 in large follicles decreased by 72 hr post-CLP which is consistent with an alteration of the steroidogenic pathway in the periovulatory follicle.

Clinical observations on changes in concentrations of hormones in plasma of two stallions with thermally-induced testicular degeneration

Summary To investigate effects of thermally-induced testicular degeneration on hormonal and seminal parameters in stallions, the scrotum was insulated for 36 hours in two mature (5-year-old mixed breed and 11-year-old Throughbred) stallions. Semen was collected daily for 10 days (DSO) prior to, and at intervals after, scrotal insulation. When DSO determinations were not being made, semen was collected 3 times weekly. Jugular blood samples were collected at 15-minute intervals for 6 hours from each stallion prior to, and at intervals after, scrotal insulation. A mouse interstitial cell testosterone assay was modified to quantify biologic activity of equine luteinizing hormone (BLH) in plasma samples. Immunoactive luteinizing hormone (ILH) and testosterone (T) concentrations were determined in plasma samples by routine RIA procedures. Percentages of progressively motile and morphologically normal spermatozoa began to decrease by 1 to 2 weeks postinsulation, reached nadir values at 3 to 3-1/2 weeks postinsulation, and returned to preinsulation values by 7 weeks postinsulation. Total number of spermatozoa and total number of progressively motile, morphologically normal spermatozoa in ejaculates at DSO returned to normal by 8 weeks postinsulation in stallion 2 and 12 weeks postinsulation in stallion 1. Concentrations of BLH and ILH increased, and while T concentrations decreased, immediately postinsulation. The increase in ILH concentrations was greater than the increase in BLH concentrations, resulting in a decrease in the BLH:ILH (B:I) ratio. Following the peak in LH secretion immediately postinsulation, LH concentrations gradually decreased while T concentrations increased. The B:I ratio was elevated from 1 to 13 weeks postinsulation compared to immediately postinsulation. In addition to changes in spermatozoal quality in ejaculates, stallion response to scrotal insulation included increased secretion of luteinizing hormone and impaired Leydig cell function (as determined by reduced testosterone concentration in circulating plasma). The proportion of biologically active LH secreted in response to thermal testicular injury increased during the recovery phase.

Ontogeny of ovarian inhibition of pulsatile luteinizing hormone secretion in postnatal holstein heifers

The hypotheses that pulsatile secretion of luteinizing hormone (LH) increases in heifers between 3 and 9 weeks of age and that ovarian inhibition of pulsatile LH release is first established between 3 and 9 weeks of age were tested in Holstein heifers. Heifers were bilaterally ovariectomized at 3 (n=5), 6 (n=4) or 9 (n=4) weeks of age. Blood samples were collected via indwelling jugular cannulae at 10-min intervals for 8 hr 1 week before and 1 and 4 weeks after ovariectomy. During the preovariectomy sampling period, no LH pulses were detected in the 3- or 6-week-old heifers, while one LH pulse occurred in three of four heifers in the 9 week age group. Both mean plasma LH concentration and number of LH pulses increased (P<0.01) by 1 week after ovariectomy only in the 6 and 9 week age groups. Between 1 and 4 weeks following ovariectomy, mean LH concentration increased (P<0.01) in all age groups, while number of LH pulses increased (P<0.01) only in the 3 week group. When the data from the three age groups were combined, amplitude of LH pulses increased (P<0.01) between 1 and 4 weeks following ovariectomy. Mean plasma levels of corticoids did not differ among age groups within sampling periods. We conclude that ovarian inhibition of pulsatile LH secretion is established by 6 weeks of age in Holstein heifers and that the initial increase in mean LH concentration following ovariectomy is mainly due to an increased frequency of LH pulses and the subsequent increase is due to a greater amplitude of LH pulses. Furthermore, the delayed development of pulsatile LH secretion following ovariectomy in the 3-week-old heifers provides a basis for further studies to determine the integrity of the hypothalamic-pituitary axis in postnatal heifers.

Effects of early pregnancy diagnosis by palpation per rectum on pregnancy loss in dairy cattle

OBJECTIVE To determine the effect of palpation per rectum (PPR) by use of 1 or 2 fetal membrane slips (FMSs) for pregnancy diagnosis during early gestation on pregnancy loss in dairy cattle. DESIGN Controlled, randomized block design. ANIMALS 928 healthy pregnant cattle. PROCEDURES All cattle were determined to be pregnant by use of transrectal ultrasonography at approximately day 31 after estrus and randomly allocated into 2 groups (control group [n = 476 cows] and palpation group [452]). The control group was not subjected to pregnancy diagnosis via PPR. The palpation group was subdivided into 2 groups (PPR FMS 1 [n = 230 cows] and PPR FMS 2 [222]), which involved PPR and pregnancy diagnosis via 1 or 2 FMSs, respectively, during the same examination, which was performed by 1 veterinarian between days 34 and 43 after estrus. All cattle were reevaluated by use of transrectal ultrasonography on days 45 and 60 to determine viability of the embryo and fetus, respectively. RESULTS Overall pregnancy loss between days 31 and 60 was 14.1%. Pregnancy loss for the control, PPR FMS 1, and PPR FMS 2 groups from days 31 to 60 was 14.5%, 12.6%, and 14.9%, respectively. Embryonic pregnancy loss for the control, PPR FMS 1, and PPR FMS 2 groups was 12.4%, 9.1%, and 9.5%, respectively. Fetal pregnancy loss for the same groups was 2.4%, 3.8%, and 5.9%, respectively. CONCLUSIONS AND CLINICAL RELEVANCE Pregnancy diagnosis via 1 or 2 FMSs performed during PPR in early gestation did not increase pregnancy loss in dairy cattle.

Ratios of serum concentrations of testosterone and progesterone from yearling bulls with small testes

Thirty crossbred bulls, 12 to 13 mo of age, were used to examine the relationship of testosterone and progesterone concentrations and testosterone: progesterone ratio to measurements of testicular function. Bulls were allotted to 1 of 2 groups based on scrotal circumferences (SC) as follows: the Small SC (n=20) group had scrotal circumference less than 28 cm while the Large SC (n=10) group had scrotal circumference greater than 28 cm. All bulls were administered GnRH (100 mug, im), and blood was obtained immediately prior to injection (t=0), 30 min after injection (t=30) and 2 to 3 h after injection (t=150). Serum was assayed for concentrations of testosterone and progesterone. Semen was evaluated for the percentage of morphologically normal spermatozoa. Testicular parenchyma was sectioned and stained, and 300 cross sections per testis of seminiferous tubules were examined under a light microscope and classified as either active (spermatocytes and spermatids present) or inactive (no spermatocytes or spermatids present). Although progesterone concentrations varied widely (range: 21 pg/ml to 1070 pg/ml), repeated measurements from individual bulls were highly correlated (r(2)=0.74) and did not change significantly (P > 0.1) in response to GnRH treatment. Small SC bulls had a higher percentage of inactive seminiferous tubules (P < 0.001) and a lower percentage morphologically normal spermatozoa (P < 0.001) than Large SC bulls, but no differences in testosterone or progesterone concentrations or in the ratio of testosterone: progesterone were detected. Mean serum testosterone concentration increased (P < 0.0001) by 30 min after GnRH treatment and continued to increase (P < 0.0001) through t=150 but did not differ (p > 0.1) between groups. Normal testosterone secretion in response to GnRH injection suggested that no biochemical lesions in the testosterone production pathway were present in bulls with very small scrotal circumference.

Correlation of in vivo testicle and seminal vesicle size with post mortem dimensions in bulls

This study was conducted to quantify the relationships between in vivo measurements of testicular and seminal vesicle size and post mortem size of these organs in 30 Santa Gertrudis bulls. The in vivo measurements of testicles were obtained by transrectal ultrasonography and palpation per rectum, while scrotal circumference was measured by scrotal tape. Linear post mortem dimensions were obtained by direct measurements of the excised organs. Volume was assessed by water displacement while the testicles were weighed. Seminal vesicle length, determined by palpation, had the highest correlation with post mortem measurements (r = 0.70; P = 0.0001). Accurate estimation of the thickness of the vesicles (1.47 vs 1.55 cm for in vivo and post mortem, respectively) was performed by ultrasonograph. Of all seminal vesicle linear measurements, width had the highest correlations with volume measured by water displacement (r = 0.67; P = 0.0001 and r = 0.38; P = 0.04 for post mortem and in vivo, respectively). Testicular diameter was accurately measured by ultrasonography (5.54 vs 4.58 cm in vivo and post mortem, respectively) and was highly correlated (range r = 0.84 to 0.89; P = 0.0001) with post mortem measurements of testicular volume, weight and circumference. The correlation between scrotal circumference and diameter of the testicle was 0.75 (P = 0.0001). The correlations of testicular diameter measured by ultrasound with the post mortem measurements of testicular weight and circumference were similar to the correlations between scrotal circumference and those 2 post mortem measurements. We conclude that palpation of vesicle length is highly correlated with volume of the seminal vesicle in situ. Individual linear measurements do not seem to be an accurate predictor of the relativ size of the seminal vesicle. Furthermore, ultrasonography does not seem to be a more accurate measure of testicular size than scrotal circumference for evaluation of breeding soundness.