Effect of supplemental trace mineral level and form on peripubertal bulls.

Objectives were to determine if supplemental trace mineral levels and/or forms (sulfate and metal amino acid complexes) influence age at puberty, semen quality, endocrine status, and scrotal circumference in peripubertal bulls. Fifty peripubertal bulls were blocked by age and scrotal circumference and assigned to one of five treatments: (1) 1x sulfate form (1S); (2) 1x complexed form (1C); (3) 1S+1C (2SC); (4) 1S + 2 × 1 C (3SCC); and (5) 3 × 1S (3S). Each 1x supplementation level contained 360 mg Zn, 125 mg Cu, 200mg Mn and 12.5mg Co. Liver biopsies were collected on d -21 and 100, and scrotal circumference, semen, and blood samples were collected on d -14, 14, 42, 70, and 98. All bulls were deficient in Cu yet adequate in Zn on d -21. Following 100 d on treatment, liver Zn concentrations decreased (P<0.01) and liver Cu concentrations increased (P<0.01) in bulls regardless of treatment. Day 100 liver Zn concentrations were similar (P=0.50) across treatments, but liver Cu concentrations were greater (P=0.07) in 3SCC and 3S bulls compared to 1C and 1S bulls, whereas 2SC bulls were intermediate. Bulls fed complexed minerals tended to reach puberty after fewer (P=0.11) days on treatment (43.9 ± 5.7 d) than bulls fed only sulfate minerals (58.5 ± 6.7 d). Supplementing complexed Cu and Zn to prepubertal bulls may lower the age at puberty, however, no differences (P ≥ 0.40) in semen characteristics or scrotal measurements (P ≥ 0.11) were observed.

Estrus synchronization systems involving prostaglandin F(2alpha) and progesterone pretreatment in beef heifers.

Two trials were conducted to evaluate treatments combining progesterone pretreatment and prostaglandin F(2alpha) (PGF(2alpha)) on estrus response, pregnancy and calving rate in heifers. Treatments in Trial 1 were 1) control (T(1); n=59), 2) 25 mg PGF(2alpha) on Day 0 (T(2); n=58), 3) 150 mg progesterone (P(4), i.m.) in corn oil on Day -24 plus PGF(2alpha) (T(3); n=61), and 4) 150 mg P(4) on Day -5 plus PGF(2alpha) (T(4); n=59). Trial 2 had T(2) and T(4) only. Heifers were artificially inseminated 8 to 16 h after detection of estrus for 10 and 5 d in Trials 1 and 2, respectively. In Trial 1 more heifers in T(3) and T(4) showed estrus by 72 h compared to T(1) and T(2). In T(3), percentages were greater at 84 and 96 h than in T(1) and T(2). There were no differences between T(3) and T(4) or T(1) and T(2) over time. Cumulative distributions of responses showed that more heifers in T(3) and T(4) were in estrus by 84 h after PGF(2alpha) than after other treatments, while T(3) showed the greatest total number of heifers in estrus by 84 h; this difference persisted for 180 h. In Trial 2, percentages of heifers observed in estrus for T(1) and T(4) were not different. Average interval from PGF(2alpha) to estrus was shorter in Trial 1 for T(3) heifers compared to other treatments. No difference was observed in interval to estrus for T(2) and T(4) in Trial 2; this interval averaged 58 h. Artificial insemination pregnancy rates were not different among treatments in either trial and averaged 67.4%. In Trial 1, a greater proportion of heifers in T(2), T(3) and T(4) calved by 35 days into the calving season compared to T(1), but in Trial 2 calving rates for T(2) and T(4) were not different. Progesterone pretreatment combined with PGF(2alpha) appeared to enhance estrus synchronization without influencing either pregnancy or calving rates.

Synchronization of estrus in beef heifers using either melengesterol acetate (MGA)/prostaglandin or MGA/Select Synch.

The objective of this study was to evaluate synchronization, conception, and pregnancy rates of yearling beef heifers synchronized with either the Select Synch protocol preceded by 7 days of MGA feeding (MGA/Select Synch) or the traditional MGA/PGF protocol. Heifers in the MGA/Select Synch group (n = 402) were fed MGA (0.5 mg/day/head) for 7 days, received an injection of GnRH (100 microg) the day following the last MGA feeding and an injection of PGF (25 mg) 7 days after GnRH. Heifers in the MGA/PGF group (n = 394) received MGA (0.5 mg/day/head) for 14 days, followed by an injection of PGF (25 mg) 17 days later. Synchronization rates tended (P = 0.08) to be higher for the MGA/Select Synch (82%) compared to the MGA/PGF (77%)-treated heifers. Conception and pregnancy rates to AI were similar (P > 0.10), 57 and 46% for the MGA/Select Synch heifers and 61 and 47% for the MGA/PGF heifers, respectively. Mean estrous response (h) was earlier (P < 0.05) for the MGA/Select Synch versus MGA/PGF treatment, 56 versus 61 h post-PGF treatment, respectively. In summary, short-term (7 days) MGA feeding preceding the Select Synch protocol produced similar synchronization, conception, and pregnancy rates as the traditional MGA/PGF protocol.

The influence of timing and the addition of urea to supplements containing DL-methionine on ruminal fermentation and cow weight change in beef cows.

A study was conducted to determine an optimal time for supplementation of DL-methionine in relation to time of forage intake by mature British breed-type crossbred cows, and two other experiments were conducted to determine whether ruminal ammonia concentration limited changes in disappearance rates in situ and ruminal functions caused by supplements containing DL-methionine. Experiments 1 and 2 used 4 x 4 Latin square designs with four cows in each experiment. Treatments in Exp. 1 were no supplement (CON), DL-methionine at feeding (0800), DL-methionine 4 h after feeding (1200), and DL-methionine 7 h after feeding (1500). Treatments in Exp. 2 were .5 kg of beet pulp (CON), .5 kg of beet pulp plus 16.5 g of DL-methionine (MET), .5 kg of beet pulp plus 16.5 g of DL-methionine and 55 g of urea (METU), and .4 kg of soybean (SOY). Experiment 3 was conducted in a 326-ha pasture with treatments of no supplement (CON), .5 kg of beet pulp plus 12.5 g of DL-methionine and 30 g of urea (METU), and .4 of kg soybean meal (SOY). In Exp. 1, in situ NDF disappearance rates of cows supplemented at 1200 and 1500 were greater (P less than .01) than those of cows supplemented at 0800. In Exp. 2, ruminal ammonia concentration was greatest (P less than .001) for METU (5.2 mg/dl) and least for CON (1.5 mg/dl). Disappearance rates in situ for DM differed (P less than .01) among treatments; METU was similar (P greater than .2) to SOY but faster (P less than .01) than MET. Disappearance rates of NDF were greatest (P less than .001) for METU-supplemented cows. In Exp. 3, DM and NDF disappearance rates were faster (P less than .10) for SOY than for METU. Cow BW change was positive for METU and SOY, and decrease in condition score was least (P less than .10) for METU- and SOY-treated cows. These studies indicate favorable ruminal responses to DL-methionine supplementation; however, the response depended on time of supplementation and ruminal ammonia concentration.

Effects of milk intake on forage intake and performance of suckling range calves.

A study to examine the relationships between milk intake, forage intake, and performance of Hereford-Angus suckling range calves was conducted during July, August, and September of 1984 and 1985. Twenty calves were used each year. The study was conducted at the Red Bluff Research Ranch located 56 km west of Bozeman, Montana. Average daily gain, milk intake (MI), forage digestibility, and fecal output (FO) were measured at 28-d intervals, beginning when the average calf age was 66 +/- 4 d. Milk intake was estimated using weigh-suckle-weigh techniques. Total fecal collections were used to measure FO. Forage digestibility and rates of passage were determined using nylon bag in situ techniques and external markers in ruminally cannulated calves of the same age. Fecal output by calves increased as body weight and age increased. Milk intake was higher (P less than .05) in 1985 than in 1984, but FO was higher (P less than .01) in 1984 than in 1985. Fecal output by calves was negatively correlated to MI in July (r = -.62; P less than .05) and August (r = -.56; P less than .05). No significant correlations were detected between MI and ADG (P greater than .10). Forage intake estimates were derived from FO, rate of passage, and in situ digestibility values. During July, calves consumed .3 kg more forage for each kilogram of reduction in fluid MI (P less than .05). In both August and September, calves consumed .6 kg more forage for each kilogram of reduction in fluid MI (P less than .10). Calves maintained similar digestible energy (DE) intake both years, although the source of DE varied.

Production from first-calf beef heifers fed a maintenance or low level of prepartum nutrition and ruminally undegradable or degradable protein postpartum.

Two experiments were conducted in consecutive years to determine the effects of prepartum nutrient level and postpartum ruminally undegraded protein intake on nutrient status, milk production, subsequent calf production, and reproductive performance of 126 crossbred, primiparous beef heifers. Prepartum treatments were low nutrient intake (LN) (approximately 2.5 kg of TDN, .5 kg of CP animal-1.d-1 and maintenance nutrient intake (MN) (5 kg of TDN, 1 kg of CP animal-1.d-1), which were fed for 75 d before parturition. Two postpartum protein supplements were formulated to provide 250 g/d of ruminally degradable protein (RD) and one to supply ruminally undegraded protein (UD) at 250 g/d of additional UD CP compared to the RD supplement. Cholesterol was lower (P less than .01) in heifers given UD than in heifers given RD. Blood urea nitrogen was higher (P less than .01) for UD-fed heifers than for RD-fed heifers and was higher in LN heifers (P less than .06) than in MN heifers. Milk production did not differ (P greater than .11) as a result of LN, MN, UD, or RD. Postpartum cow weight gain was greatest (P less than .01) for UD and LN heifers. The percentage of heifers bred during the first estrous cycle of the breeding season was greater (P less than .02) for UD than for RD. Overall, prepartum nutrition did not interact with postpartum protein supplement, nor did it have any effect on postpartum interval, whereas UD increased cow weight gain postpartum and reduced postpartum interval.

Influence of biostimulation by mature bulls on occurrence of puberty in beef heifers.

The objective of this study was to determine if biostimulation of prepuberal beef heifers by mature bulls would alter proportions of heifers exhibiting puberty, or age or weight at puberty. Angus (A), A X Hereford (H) and Tarentaise X HA heifers (n = 103) were stratified by age and weight within breed-type and location of birth and allotted randomly to the following treatments: 1) heifers exposed to mature bulls (T1; n = 52) or 2) heifers isolated from bulls (T2; n = 51). At the start of the experiment, heifers in T1 and T2 were 287 +/- 2 and 286 +/- 2 d of age, respectively. Male-to-female ratio for T1 was 1:26. Heifers in T1 and T2 were maintained in drylots separated by .5 km. Heifers were observed for estrus twice daily for 152 d. Puberty was characterized by the following criteria: 1) behavioral estrus, 2) presence of a palpable corpus luteum (d 9; estrus = d 0) and 3) a rise in serum progesterone above 1 ng/ml (d 9). Proportions of heifers reaching puberty by 11, 12, 13, 14 and 15 mo of age did not differ (P greater than .10) between treatments. Percentages of heifers reaching puberty by the end of the experiment were 84 and 89% for T1 and T2, respectively. Age and weight at puberty did not differ (P greater than .10) between treatments and averaged 370 +/- 7 d and 293 +/- 4 kg, respectively. Results from this experiment indicated that presence of mature bulls did not alter proportions of beef heifers reaching puberty, or age and weight at puberty.

The effects of degradable and undegradable intake protein on the performance of lactating first-calf heifers.

Two 60-d experiments were conducted to evaluate the effects of supplementing degradable (DIP) and(or) undegradable (UIP) intake protein on the performance of lactating first-calf heifers. Diets were formulated to meet the requirements for either DIP, metabolizable protein (MP), or both when diets contained low-quality grass hay and an efficiency of microbial protein synthesis estimate of 10%. In Exp. 1, 32 individually fed first-calf heifers (avg 395 kg) were allotted to a 2 x 2 factorial arrangement of treatments (main effects of DIP, MP, and DIP x MP interaction) 1 d after calving. Cows consumed a basal diet of chopped crested wheat grass hay (4.3% CP, 67% DIP) ad libitum. Supplemental DIP and UIP were supplied by varying the ratios of soybean meal (75% DIP) and a heat-treated, protected soybean meal (70% UIP). Cow weight gain was better (P < 0.01) when adequate DIP was supplied than when DIP was deficient. However, calf weight gain was not increased by supplementing the cow with DIP. Supplemental UIP did not (P > 0.40) improve cow or calf weight gain. Blood urea N levels were higher (P < 0.01) for cows receiving supplemental DIP and UIP. However, milk production estimates were similar among treatments, as were digestibilities of OM and ADF. Nitrogen digestibility was greater when supplemental DIP was fed, but providing additional UIP did not (P = 0.15) change N digestibilities. Experiment 2 evaluated similar supplements using the same experimental design to determine changes in cow and calf weight gain, body condition score, and pregnancy rate. Seventy-two first-calf heifers (avg 441 kg) were allotted to supplement treatments 1 d after calving and were fed grass hay (5% CP, 53% DIP, 10% microbial efficiency) for ad libitum consumption for 60 d. Supplements were individually fed three times/week. Varying the ratios of soybean meal, heat-treated soybean meal, and corn gluten meal provided additional DIP and UIP. Unlike in Exp. 1, supplemental UIP improved (P < 0.05) cow weight gain. Calves from dams supplemented with DIP gained 5 kg more weight after 60 d than calves from dams deficient in DIP. Pregnancy rates in the fall were similar (P = 0.90) among treatments. These data suggest that DIP was more limiting in Exp. 1 than was UIP. Supplementing UIP in Exp. 2 improved cow weight gains but did not improve calf gains. Data suggest that the efficiency of microbial protein synthesis for this forage-based diet was probably less than 10%.

Effects of supplementing combinations of inorganic and complexed copper on performance and liver mineral status of beef heifers consuming antagonists.

Performance, immune response, and liver trace mineral status were measured in growing heifers supplemented with different copper (Cu) concentrations and sources when diets contained the Cu antagonists Mo, S, and Fe. Sixty Angus x Hereford heifers were managed in two groups for 112 d and were either individually fed diets and mineral treatments using individual feeding stalls (Stall) or pen-fed grass hay and individually supplemented mineral treatments (Pen). The basal diet of grass hay, rolled barley, and soybean meal was analyzed to contain 6 mg Cu/kg DM. The treatments consisted of 1) no supplemental Cu (Control); 2) 49 mg Cu/kg DM from Cu sulfate (i.e. approximately five times NRC recommendation for Cu from CuSO4) (5X-SO4); 3). 22 mg Cu/kg DM from CuSO4 (2X-SO4); 4). 22 mg Cu/kg DM from a combination of 50% CuSO4 and 50% Cu-amino acid complex (50-50); and 5). 22 mg Cu/kg DM from a combination of 25% CuSO4, 50% Cu-amino acid complex, and 25% Cu oxide (CuG) (25-50-25). All heifers were supplemented with the Cu antagonists Mo (10 mg/kg DM), S (2,900 mg/kg DM), and Fe (500 mg/kg DM). These diets resulted in dietary Cu:Mo ratios that averaged 0.5:1 for Control, 4.5:1 for the 5X-SO4, and 2.4:1 for 2X-SO4, 50-50, and 25-50-25. Rate and efficiencies of gain and cell-mediated immune function were not different (P > 0.10) among treatments. Data suggest supplements containing combinations of inorganic and complexed Cu interacted differently in the presence of Mo, S, and Fe. Heifers consuming the 25-50-25 supplement in the Stall group initially lost hepatic Cu rapidly but this loss slowed from d 50 to d 100 compared to the Control (P = 0.07), 50-50 (P < 0.05), and 2X-SO4 (P < 0.05) heifers and was similar (P > 0.10) to that in the 5X-SO4 heifers. In the Pen group, total hepatic Cu loss tended to be greater for 25-50-25 and 2X-SO4 compared to 5X-SO4 heifers (P = 0.09 and P = 0.06, respectively); Cu loss in the 50-50 heifers was similar (P > 0.10) to that in the 5X-SO4 heifers. This suggests that supplementing combinations of inorganic and amino acid-complexed Cu was as effective in limiting hepatic Cu loss during antagonism as was increasing dietary Cu levels to five times the NRC recommendation. A combination of 25% CuSO4 , 50% Cu-amino acid complex, and 25% CuO limited liver accumulation of Mo compared to supplements without CuO and could provide a strategic supplementation tool in limiting the systemic effects of Cu antagonism in beef cattle.

The effects of ruminally undegradable protein, propionic acid, and monensin on puberty and pregnancy in beef heifers.

Two hundred ten spring-born English crossbred beef heifers were used in two experiments in consecutive years using a randomized complete block design. The objectives were to determine the effects of increasing dietary intake of ruminally undegradable protein or propionic acid on the occurrence of puberty and to elucidate the mechanism by which monensin decreases age of puberty in beef heifers. Diets were fed for 120 d beginning in mid-November and consisted of mature grass hay and barley straw with .45 kg.animal-1 x d-1 supplement (CON) formulated to obtain .4 kg.animal-1 x d-1 of BW gain; .5 kg of supplement similar to CON and containing an additional 250 g of ruminally undegradable intake protein supplied from blood and corn gluten meal (UIP); .45 kg of supplement similar to CON composition and containing 400 g.animal-1 x d-1 of a 50% water and 50% propionic acid mixture (PROP); or .45 kg of supplement similar to CON supplying 200 mg.animal-1 x d-1 of monensin (MON). The hay:straw ratio in each diet was adjusted biweekly, to maintain similar BW gains for heifers fed each dietary treatment. As planned, BW gains were similar (P > .1) for all heifers. The heifers fed MON were 21 d younger (P < .05) at first estrus than heifers fed UIP; CON and PROP were intermediate and similar to heifers fed MON and UIP. The heifers fed UIP were 7 to 8 kg heavier (P < .05) at puberty than CON- or PROP-treated heifers. The heifers fed PROP were 6 kg heavier (P < .1) at puberty than heifers fed MON. Heifers that received UIP required less (P < .05) TDN than did heifers that received CON or PROP to achieve similar gain. Pregnancy rate was similar for all treatment groups. Feeding UIP in excess of NRC CP requirements may improve energy utilization of heifers fed mature roughages but may delay the onset of puberty compared with heifers fed monensin. This study demonstrated that nutrient composition of the diet may influence age of puberty independent of growth rate.

Reproductive efficiency of range beef cows fed different quantities of ruminally undegradable protein before breeding.

Two studies, using 128 crossbred, multiparous beef cows grazing native winter and spring rangeland, were conducted to determine effects of protein supplementation on nutrient status and subsequent calf and reproductive performance. Postparturient cows (body condition score [BC] = 3.9) were fed 1.82 kg of one of two supplements (54% CP at 490 g of CP/d) per cow on alternate days. Supplements were formulated to contain 50% (245/490 g of CP) ruminally undegradable (UD) CP (RU50) or 25% (119/490 g of CP) UD CP (RU25) and were fed until breeding (BC = 4.2). Late-calving cows (Study 1) were individually fed supplement while grazing native range. Early-calving cows (Study 2) were group-fed supplement on alternate days while grazing native range and were daily fed approximately 5.4 kg of medium-quality grass hay (10.5% CP). Late-calving cows had similar (P > .22) BW losses postpartum, whereas early-calving cows fed RU50 lost 39 kg less (P < .01) BW than did cows fed RU25. Cows that received RU25 returned to estrus sooner (P < .02), in the late-calving study, than cows fed RU50 (47 vs 56 d, respectively). The percentage of cows serviced in the first 21 d of breeding (96 and 100% for late- and early-calving studies, respectively) and pregnancy rates (88 and 86% for late- and early-calving studies, respectively) did not differ regardless of postpartum protein supplement. When adequate CP was provided in the diet for optimum function of the rumen, addition of ruminally undegraded CP decreased weight loss of mature, postpartum beef cows grazing native range.(ABSTRACT TRUNCATED AT 250 WORDS)

Zinc and copper status in ewes supplemented with sulfate- and amino acid-complexed forms of zinc and copper.

Thirty 6-yr-old Targhee ewes were randomly allotted to one of five supplemental treatments to evaluate supplementation effects on liver and fecal Zn and Cu concentrations and serum alkaline phosphatase activity: 1) control, 2) Zn complex, 3) Zn and Cu (ZnCu) complex, 4) Zn sulfate, and 5) ZnCu sulfates. Supplements were administered daily in gelatin capsules for 56 d. Liver biopsies and serum samples were collected every 14 d starting on d 0. Supplemental Zn and Cu levels were formulated to provide 90 mg/kg Zn and 10 mg/kg Cu, respectively, on a daily dry matter intake basis. Form (complex vs sulfate) x type (Zn vs ZnCu) interactions were not detected (P > 0.35). Therefore, contrast statements were used to make the following treatment comparisons: 1) control vs supplement, 2) Zn vs ZnCu, and 3) complex vs sulfate. Ewe BW at the end of the study (P = 0.09) and ewe BW change from beginning to end of the study (P = 0.07) were greater for supplemented than control ewes. Body weight and BW change did not differ between sulfate and complex (P > 0.39) or Zn- and ZnCu- (P > 0.40) supplemented ewes. Liver Cu concentrations did not differ (P = 0.41) between control and supplemented ewes. Liver Cu concentrations were higher (P < 0.10) for ewes supplemented with ZnCu than Zn and complex than sulfate forms of supplement. Liver Zn concentration tended (P = 0.13) to be higher in ZnCu than Zn-supplemented ewes. Liver and fecal Zn concentration were higher (P < 0.06) in ewes fed complex than sulfate supplements. However, serum alkaline phosphatase activity tended (P = 0.12) to be greater in ewes fed sulfate than complex supplements. Supplementing mature ewes with complexed minerals resulted in higher concentrations of Zn and Cu in the liver. In addition, supplemental Cu tended to increase concentrations of Zn in the livers of ewes; however, high levels of supplemental Zn did not negatively impact liver Cu concentrations.

Effects of flunixin meglumine on pregnancy establishment in beef cattle.

The objective of this research was to determine effects of a single injection of the PG synthesis inhibitor flunixin meglumine (FM; 1.1 mg/kg of BW, intramuscularly) approximately 13 d (range 10 to 15 d) after AI on pregnancy establishment. Three experiments were conducted using estrus-synchronized heifers and cows. Technicians and AI sires were equally represented across treatments within locations and experiments. Bulls were introduced on the day of FM treatment. Pregnancy to AI was diagnosed 28 to 50 d after AI using ultrasonography. In Exp. 1, beef heifers (n = 1,221) were divided within 5 locations to receive FM or no further treatment (control). At insemination, heifers were divided into 2 similar pastures or pens, and approximately 13 d later, 1 group of heifers within each location was processed through an animal handling facility to administer FM treatment. There was no location x treatment interaction (P = 0.62) on AI pregnancy rates, so data were pooled. Pregnancy rates to AI were reduced (P = 0.02) among heifers receiving the FM treatment procedure (66%) compared with control heifers (72%). In Exp. 2, suckled beef cows (n = 719) were assigned within 2 locations to receive FM or no further treatment (control) approximately 13 d after AI. At insemination, control and FM cows were divided into separate pastures, and only FM cows were handled after AI for the FM treatment procedure. There was no location x treatment interaction (P = 0.75), so data were pooled. Pregnancy rates to AI did not differ (P = 0.80) between FM (57%) and control cows (59%). In Exp 3, beef heifers (n = 247) and suckled beef cows (n = 335) from 1 location received no injection (control) or injection of FM approximately 13 d after AI when all cows and heifers were processed through a working facility. Pregnancy rates to AI were not different (P = 0.37) between FM (45%) and control (42%) cows or between FM (56%) and control (55%) heifers. We conclude FM administration at 1.1 mg/kg of BW approximately 13 d after AI did not improve pregnancy establishment in beef cows and heifers and that the effects of handling heifers at this time may decrease pregnancy establishment.

Effects of flunixin meglumine and transportation on establishment of pregnancy in beef cows.

Objectives of these studies were to determine the effects of flunixin meglumine (FM) administration on early embryonic mortality and circulating PG and cortisol concentrations in transported and non-transported cows. Cows (n = 483) from 3 locations were used to evaluate the effects of transportation and FM approximately 14 d after AI on the establishment of pregnancy and serum concentrations of progesterone, PGF metabolite (PGFM), and cortisol. Treatments were transport (n = 129), transport + FM (n = 128), no transport (n = 130), and no transport + FM (n = 96). Multiparous cows (n = 224) were used at 2 locations, and nulliparous cows (n = 259) were used at 1 location. The no transport + FM treatment was used at only 2 locations. Flunixin meglumine (approximately 1.1 mg/kg of BW; i.m.) was administered before the cows were separated into transportation groups. Transportation included 4 to 6 h of transportation, without calves, via semitractor trailer. Nontransported cows remained penned, with their calves in adjacent pens, during the same period as the transported cows. Blood samples were collected from all cows before and after treatment and, at 2 locations, approximately 3 h after the onset of treatment. Location affected AI pregnancy rate (P < 0.01). Treatment effects, although not significant (P = 0.16), were of a magnitude to be considered practically important. Cows that received transportation + FM tended (P = 0.07) to have greater AI pregnancy rates (74%) than those that did not receive FM (66%), irrespective of transportation. Cortisol concentration was greater (P < 0.05) for transported cows than for nontransported cows. Cows receiving FM had greater (P < 0.05) AI pregnancy rates than non-FM cows (71 vs. 61%, respectively). Cows receiving transportation had lower (P < 0.01) mean PGFM concentrations than nontransported cows (45.4 vs. 54.6 pg/mL, respectively), and cows receiving FM had lower (P < 0.01) mean PGFM concentrations than non-FM cows (39.4 vs. 60.6, respectively). We conclude that transportation of cows approximately 14 d after AI increased serum cortisol concentrations but did not affect AI pregnancy rates. However, treatment of cows with FM increased AI pregnancy rates, irrespective of whether they were transported.

Synchronization of estrus and artificial insemination in replacement beef heifers using gonadotropin-releasing hormone, prostaglandin F2alpha, and progesterone.

We evaluated whether a fixed-time AI (TAI) protocol could yield pregnancy rates similar to a protocol requiring detection of estrus, or detection of estrus and AI plus a clean-up TAI for heifers not detected in estrus, and whether adding an injection of GnRH at controlled internal drug release (CIDR) insertion would enhance fertility in CIDR-based protocols. Estrus in 2,075 replacement beef heifers at 12 locations was synchronized, and AI was preceded by 1 of 4 treatments arranged as a 2 x 2 factorial design: 1) Estrus detection + TAI (ETAI) (n = 516): CIDR for 7 d plus 25 mg of prostaglandin F2alpha (PG) at CIDR insert removal, followed by detection of estrus for 72 h and AI for 84 h after PG (heifers not detected in estrus by 84 h received 100 microg of GnRH and TAI); 2) G+ETAI (n = 503): ETAI plus 100 microg GnRH at CIDR insertion; 3) Fixed-time AI (FTAI) (n = 525): CIDR for 7 d plus 25 mg of PG at CIDR removal, followed in 60 h by a second injection of GnRH and TAI; 4) G+FTAI (n = 531): FTAI plus 100 microg of GnRH at CIDR insertion. Blood samples were collected (d -17 and -7, relative to PG) to determine ovarian status. For heifers in ETAI and G+ETAI treatments, a minimum of twice daily observations for estrus began on d 0 and continued for at least 72 h. Inseminations were performed according to the a.m.-p.m. rule. Pregnancy was diagnosed by transrectal ultrasonography. The percentage of heifers exhibiting ovarian cyclic activity at the initiation of treatments was 89%. Pregnancy rates among locations across treatments ranged from 38 to 74%. Pregnancy rates were 54.7, 57.5, 49.3, and 53.1% for ETAI, G+ETAI, FTAI, and G+FTAI treatments, respectively. Although pregnancy rates were similar among treatments, a tendency (P = 0.065) occurred for pregnancy rates in the G+ETAI treatment to be greater than in the FTAI treatment. We concluded that the G+FTAI protocol yielded pregnancy rates similar to protocols that combine estrus detection and TAI. Further, the G+FTAI protocol produced the most consistent pregnancy rates among locations and eliminated the necessity for detection of estrus when inseminating replacement beef heifers.