Impacts of incorporation of follicle stimulating hormone into an estrous synchronization protocol for timed artificial insemination of crossbred beef cattle.

One-hundred-eighty crossbred beef cows and 66 crossbred beef heifers across three locations were stratified by body weight (BW), body condition score (BCS), and age (within location) to evaluate administration of follicle stimulating hormone (FSH) on Day 2 using a modified 7-day CO-Synch plus CIDR(®) protocol (Day 0=CIDR insertion) with timed-artificial insemination (TAI) at 72 h (cows) or 54 h (heifers) following CIDR removal. Estrous response following CIDR removal was determined using an Estrotect patch and TAI and final pregnancy rates were determined by transrectal ultrasonography 42-45 days following TAI and ≥ 45 days following removal of clean-up bulls. Estrous response rate, TAI and final pregnancy rates for cows were not affected (P ≥ 0.65) by treatment. Cows that exhibited estrus had greater (P<0.01) TAI pregnancy rate (66%) than cows not exhibiting estrus (38%). There was an estrous response by postpartum length interaction (P=0.02) where cows exhibiting estrus and ≥ 55 days postpartum had greater TAI pregnancy rates (75%) compared to cows not exhibiting estrus and < 55 days postpartum (39%) or ≥ 55 days postpartum (28%). For heifers, timed AI (P=0.46) and final pregnancy rates (P=0.45) were similar across treatments and estrous response had no effect (P=0.30) on TAI pregnancy rates. In conclusion, the addition of FSH to the CO-Synch plus CIDR estrous synchronization protocol did not increase TAI pregnancy rates in beef cows or heifers. However, a positive estrous response to the synchronization protocol was associated with increased TAI pregnancy rates in cows.

Impact of cow size on dry matter intake, residual feed intake, metabolic response, and cow performance.

Thirty-eight Angus-cross beef cows were used to evaluate differences in DMI, residual feed intake (RFI), and endocrine markers on the basis of cow size and RFI ranking during 2 stages of production. Cows housed in individual pens (2.2 × 9.1 m) were fed, over a 70-d feeding period, 30% Bermuda grass hay and 70% ryegrass baleage diet during lactation (LACT) and a 100% ryegrass hay diet during postweaning (NOLACT). Individual daily feed intake, BW, and BCS were recorded, and hip height was used to determine frame score (FS). Feed intake was used to calculate RFI for each cow, and cow was the experimental unit. Blood samples were obtained on d 0 and 70 and were analyzed for glucose, insulin, leptin, triiodothyronine (T3), and thyroxine (T4). Cows were assigned to a light (LIT) or heavy (HEV) BW groups on the basis of mean BW at the beginning of the LACT period. On the basis of RFI values for each feeding period, cows were placed into a negative (NEG; RFI < 0.00) or positive (POS; RFI > 0.00) RFI group and into a low (LOW; ≤0.2 SD mean RFI), medium (MED; within ±0.19 SD), or high (HI; ≥0.2 SD mean RFI) RFI group. During LACT, DMI was 4.8% greater (P = 0.03) and FS was greater (P < 0.01; 6.4 and 5.5 ± 0.16) for the HEV compared with LIT BW cows. No RFI by day interaction or RFI group main effect occurred for endocrine markers during LACT; however, a negative relationship (P = 0.04) existed between BW group and combined T3 data, and a positive relationship (P = 0.04) existed between RFI and combined insulin data. For both LACT and NOLACT, RFI was similar (P > 0.05) among BW groups; however, DMI was 6.5% and 8.9% greater (P < 0.01) for POS compared with NEG RFI in the LACT and NOLACT periods. In LACT, DMI was greater (P < 0.01) for HI and MED RFI compared with LOW RFI, and in NOLACT, DMI was greater (P < 0.01) for the HI compared with MED and LOW RFI cows and MED compared with LOW RFI cows. During NOLACT, DMI was 8.9% greater (P < 0.01) for the HEV (12.4 ± 0.22 kg) compared with LIT (11.3 ± 0.19 kg) BW cows. Change in BCS was greater (P ≤ 0.03) in higher RFI cows in both RFI groups only in the NOLACT period. Differences in T3 and T4 on d 0 and 70 were 25% and 15% greater (P ≤ 0.04) for the LIT BW group compared with the HEV BW group. A negative correlation existed (P ≤ 0.04) between BW group and T3 and T4, as well as leptin and RFI (P = 0.03). Although cow BW was independent of RFI and T3 and T4 levels tended to be greater in lighter BW cows, DMI was consistently greater for cows with heavier BW and higher RFIvalues.

The effect of exogenous follicle stimulating hormone (FSH) and endogenous plasma leptin concentrations on the pregnancy rate of beef heifers subjected to fixed-timed artificial insemination (FTAI).

In this study, 53 crossbred beef heifers were used to test the hypotheses that administration of exogenous FSH 2 days following CIDR insertion and administration of estradiol would increase the pregnancy rate in heifers synchronized for FTAI and that plasma leptin concentrations in beef heifers would be higher for heifers that became pregnant to FTAI. The heifers used in this study had a median age of 440 days, an average weight of 324 kg, an average body condition score of 5.1 and a mean reproductive tract score of 3.1. Heifers were stratified by weight and BCS into two groups and then treatments were randomly allotted to each group: (1) control (n=28) or (2) FSH (n=27). Both groups were administered 200mg estradiol benzoate (EB) and received an intravaginal controlled internal drug-releasing device (CIDR) on day 0. On day 2, females in the FSH treatment group were administered 20 mg of FSH, while the control group received 1 ml of saline. On day 7 all females were administered 25 µg PGF2α and the CIDR was removed. Then 24h following CIDR removal all females were administered 1mg EB and 24h later were subjected to FTAI. Pregnancy diagnosis was performed via transrectal ultrasonography 43 days following insemination. Blood samples were collected via jugular venipuncture on days 2, 6-10, 13 and 52 and plasma leptin concentrations were determined by radioimmunoassay. Pregnancy rates were higher (P=0.01) for FSH-treated females (60%) compared with females not receiving FSH (25%). Circulating plasma leptin concentrations were higher (P=0.0051) for pregnant females compared with females that did not become pregnant following FTAI during the experiment. Mean plasma leptin concentration was also higher (P=0.04) from day 2 to day 9 during the synchronization protocol in heifers that became pregnant compared with heifers that did not become pregnant from FTAI. There was no difference (P=0.38) in reproductive tract scores for heifers that became pregnant compared with heifers that did not become pregnant from FTAI. Circulating leptin concentrations were not different (P=0.11) for females receiving FSH compared with females in the non FSH-treated group. Circulating leptin concentrations were affected by sampling day (P<0.0001). However, there was no interaction between sampling day and pregnancy status (P=0.80), treatment and pregnancy status (P=0.14) or treatment and sampling day (P=0.12). These results indicate that the administration of FSH on day 2 of the synchronization protocol may increase pregnancy rates in beef heifers and that increased circulating concentrations of plasma leptin during the synchronization protocol may be indicative of subsequent pregnancy outcome.

The effect of equine chorionic gonadotropin (eCG) on pregnancy rates of white-tailed deer following fixed-timed artificial insemination.

Control of the white-tailed doe's reproductive cycle is not well documented. The objective was to determine the effects of giving equine chorionic gonadotropin (eCG) at progesterone device removal on fixed time artificial insemination (FTAI) pregnancy rates in white-tailed does. All does (n = 74) were synchronized with a vaginal progesterone implant (CIDR; 0.3 g progesterone), inserted on Day 0 (without regard to stage of estrous cycle), removed 14 days later, and subjected to FTAI, on average, 60 h post-CIDR removal. Of these, 34 were given 200 IU (im) of eCG at CIDR removal. Overall, FTAI pregnancy rate was 50% across 2 yrs (effect of year, P = 0.35). Administration of eCG at CIDR removal did not affect (P = 0.16) pregnancy rate (eCG = 59%; no eCG = 43%). Pregnancy rates were not affected by vulva score or doe disposition. Does that were ≤ 4 yrs old were more likely (P = 0.01) to become pregnant than does > 4 yrs of age. Does inseminated ≥ 60.5 h after CIDR removal were 22 times more likely (P = 0.002) to become pregnant to FTAI than does inseminated < 60.5 h. When frozen-thawed semen was deposited in the cervix or uterus, does were 17 times more likely (P = 0.005) to become pregnant compared with those receiving intravaginal insemination. Fecundity was not different (P = 0.73) across treatment groups (1.6 ± 0.11; no eCG vs. 1.7 ± 0.10; eCG). Furthermore, fecundity of does pregnant to FTAI was not different (P = 0.72) compared with does pregnant to clean-up bucks (1.7 ± 0.08; AI does vs. 1.7 ± 0.09; clean-up bucks). In summary, white-tailed does were successfully inseminated using a 14 days FTAI protocol, eCG may not be essential for acceptable pregnancy rates, and increased pregnancy rates may result when FTAI is done ≥ 60.5 h after progesterone device removal.

Comparison of the permeability properties and post-thaw motility of ejaculated and epididymal bovine spermatozoa.

There are very few experimental reports on the comparative water transport (membrane permeability) characteristics of ejaculated and epididymal mammalian spermatozoa during freezing. In the present study, we report the effects of cooling ejaculated and epididymal bovine sperm from the same males with and without the presence of a cryoprotective agent, glycerol. Water transport data during freezing of ejaculated and epididymal bovine sperm suspensions were obtained at a cooling rate of 20 degrees C/min under two different conditions: (1) in the absence of any cryoprotective agents, CPAs and, (2) in the presence of 0.7 M glycerol. Using values published in the literature, we modeled the spermatozoa as a cylinder of length 39.8 microm and a radius of 0.4 microm with an osmotically inactive cell volume, V(b), of 0.61 V(o), where V(o) is the isotonic cell volume. The subzero water transport response is analyzed to determine the variables governing the rate of water loss during cooling of bovine spermatozoa, i.e. the membrane permeability parameters (reference membrane permeability, L(pg) and activation energy, E(Lp)). The predicted best-fit permeability parameters ranged from, L(pg)=0.021-0.038 microm/min-atm and E(Lp)=27.8-41.1 kcal/mol. The subzero water transport response and consequently the subzero water transport parameters are not significantly different between the ejaculated and epididymal bovine spermatozoa under corresponding cooling conditions. If this observation is found to be more generally valid for other mammalian species as well, then in the future the sperm extracted from the testes of a postmortem male could be optimally cryopreserved using procedures similar to those derived for ejaculated sperm.

Control of horn flies (Haematobia irritans) and gastrointestinal parasites and its relation with cow-calf performance.

The objective of this study was to assess the effects of horn fly and gastrointestinal (GI) nematode control on cow-calf performance with a spring-calving system. A total of 508 cow-calf records from two locations in Louisiana were available for study over two trials (2005 and 2006). Cow and calf pairs were stratified by cow age, calf sex, calf age, calf sire breed and calf sire and randomly assigned to three replicate treatment groups across the two locations. The treatments were: (1) no horn fly or GI nematode control; (2) horn fly control administrated to cows with insecticidal ear tags applied in late-May (start of trial); (3) GI nematode control administrated to calves in late-May, mid-July and late-August (each calf received fenbendazole at the rate of 5 mg kg(-1) body weight); and (4) horn fly and GI nematode control as stated above. Length of the trials ranged from 115 to 124 days (late-May to weaning in late-September or early-October). Cows and calves were weighed at the start of the trial, mid-July and weaning. Weekly horn fly counts were conducted. Individual calf fecal samples were collected in late-May, mid-July, late-August, weaning and 10-14 days after late-May and late-August collections. Cows treated for horn flies had lower (P<0.05) fly counts compared with untreated cows for each trial; however, overall fly counts for the treated cows at one location exceeded over 70 flies per side. Calves treated with fenbendazole had lower (P<0.01) GI nematode fecal egg counts (FEC) for the 10-14 day post-treatment collections. Calves treated GI nematodes and whose dams were treated for horn flies had numerically higher or greater (P<0.05) total calf gains (8.6 kg and 11.8 kg) in both trials than untreated calves. Weight gain differences for fenbendazole-treated calves compared with untreated calves were of greater magnitude from mid-July to weaning than weight gain differences from late-May to mid-July in both trials. There were no treatment differences for any of the cow response traits. In conclusion, improvement in calf growth from both horn fly and GI nematode treatments were realized even with marginal levels of fly control and a greater response in calf growth resulted when deworming of spring-born calves occurred when they were 4 months of age or older.

Influence of Angus and Belgian Blue bulls mated to Hereford x Brahman cows on growth, carcass traits, and longissimus steak shear force.

Steers and heifers were generated from Angus (A) and Belgian Blue (BB) sires mated to Brahman x Hereford (B x H) F(1) cows to characterize their growth, carcass traits, and LM shear force. A total of 120 B x H cows purchased from 2 herds and 35 bulls (14 A and 21 BB) produced calves during the 5-yr project. After the stocker phase, a representative sample of A- and BB-sired heifers and steers were transported to the Iberia Research Station to be fed a high-concentrate diet. The remaining cattle were transported to a commercial feedlot facility. Each pen of cattle from the commercial feedlot was slaughtered when it was estimated that heifers and steers had 10 mm of fat or greater. The BB-sired calves were heavier at birth (P < 0.01) than the A-sired calves. During the feedlot phase, the A-sired calves gained more BW (P < 0.05) than the BB-sired calves. The BB-sired calves had heavier (P < 0.01) carcass weights than the A-sired calves. This was due to a combination of a heavier final BW and greater dressing percent. Because of their greater muscling and reduced (P < 0.01) fat, carcasses from BB-sired calves had greater yield (P < 0.01) compared with carcasses from A-sired calves. Carcasses from A-sired calves had a greater (P < 0.01) marbling score and greater (P < 0.01) USDA quality grade than carcasses from BB-sired calves. Tenderness, as measured by shear force of the steaks aged for 7 d, was similar for A- and BB-sired calves. However, steaks aged for 14 d from the A-sired calves had a reduced shear force (P < 0.01) compared with steaks from the BB-sired calves. Steer calves were heavier (P < 0.01) at birth and weaning, and had more total BW gain in the feedlot, which resulted in a heavier final BW and HCW compared with the heifers. Steer carcasses also had greater marbling scores and quality grades, whereas the heifer carcasses had larger LM area per 100 kg of carcass weight. In conclusion, the BB-sired calves had heavier carcass weights and greater cutability, whereas the A-sired calves had a greater degree of marbling and greater quality grade, and steaks from carcasses of A-sired calves were more tender as measured by shear force at 14 d.

The relationship between body condition, leptin, and reproductive and hormonal characteristics of mares during the seasonal anovulatory period.

An experiment was conducted to determine the effects of high vs low body condition scores (BCS) produced by restricted feeding on reproductive characteristics, hormonal secretion, and leptin concentrations in mares during the autumnal transition and winter anovulatory period. Mares with BCS of 6.5 to 8.0 were maintained on pasture and/or grass hay, and starting in September, were full fed or restricted to produce BCS of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) by December. All but one mare with high BCS continued to ovulate or have follicular activity during the winter, whereas mares with low BCS went reproductively quiescent. Plasma leptin concentrations varied widely before the onset of restriction, even though all mares were in good body condition. During the experiment, leptin concentrations gradually decreased (P < 0.0001) over time in both groups, but were higher (P < 0.009) in mares with high vs low BCS after 6 wk of restriction, regardless of initial concentration. No differences (P > 0.1) between groups were detected for plasma concentrations of LH, FSH, TSH, GH, glucose, or insulin in samples collected weekly; in contrast, plasma prolactin concentrations were higher (P < 0.02) in mares with high BCS, but also decreased over time (P < 0.008). Plasma IGF-I concentrations tended (P = 0.1) to be greater in mares with high vs low BCS. The prolactin response to sulpiride injection on January 7 did not differ (P > 0.1) between groups. During 12 h of frequent blood sampling on January 12, LH concentrations were higher (P < 0.0001), whereas GH concentrations (P < 0.0001) and response to secretagogue (EP51389; P < 0.03) were lower in mares with high BCS. On January 19, the LH response to GnRH was higher (P < 0.02) in mares with high BCS; the prolactin response to TRH also was higher (P < 0.01) in mares with high BCS. In conclusion, nutrient restriction resulting in low BCS in mares resulted in a profound seasonal anovulatory period that was accompanied by lower leptin, IGF-I, and prolactin concentrations. All but one mare with high BCS continued to cycle throughout the winter or had significant follicular activity on the ovaries. Although leptin concentrations on average are very low in mares with low BCS and higher in well-fed mares, there is a wide variation in concentrations among well-fed mares, indicating that some other factor(s) may determine leptin concentrations under conditions of high BCS.

High versus low body condition in mares: interactions with responses to somatotropin, GnRH analog, and dexamethasone.

Mares that had previously been fed to attain body condition scores (BCS) of 7.5 to 8.5 (high) or 3.0 to 3.5 (low) were used to determine the interaction of BCS with the responses to 1) administration of equine somatotropin (eST) daily for 14 d beginning January 20 followed by administration of GnRH analog (GnRHa) daily for 21 d and 2) 4-d treatment with dexamethasone later in the spring when mares in low BCS had begun to ovulate. The majority of mares with high BCS continued to cycle throughout the winter, as evidenced by larger ovaries (P < 0.002), more corpora lutea (P < 0.05), greater progesterone concentrations during eST treatment (P < 0.04), and more (P < 0.05) large- and medium-sized follicles. Treatment with eST alone or in combination with GnRHa had no effect (P > 0.05) on ovarian activity or ovulation. Plasma leptin concentrations were greater (P < 0.002) in mares with high BCS; however, there was no effect (P > 0.10) of eST treatment. Plasma IGF-I concentrations were greater (P < 0.0001) in mares treated with eST compared with mares given vehicle, and mares with high BCS had greater IGF-I (P < 0.02) and LH concentrations (P < 0.02) than mares with low BCS. Plasma leptin concentrations in mares with high BCS were increased (P < 0.001) within 12 h of dexamethasone treatment; the leptin response (P < 0.001) in mares with low BCS was greatly reduced (P < 0.001) and transient. Glucose and insulin concentrations also increased (P < 0.0001) after dexamethasone treatment in both groups, and the magnitude of the response was greater (P < 0.0001) in mares with high BCS than in mares with low BCS. In summary,low BCS in mares was associated with a consistent seasonal anovulatory state that was affected little by eST and GnRHa administration. In contrast, all but one mare with high BCS continued to experience estrous cycles and(or) have abundant follicular activity on their ovaries. The IGF-I response to eST treatment was also reduced in mares with low BCS, as was the basal leptin concentration and leptin response to dexamethasone. Although low BCS and leptin concentrations were associated with inactive ovaries during winter and early spring, mares with low BCS eventually ovulated in April and May while leptin concentrations remained low.