Effect of short-term calf removal at three stages of a follicular wave on fate of a dominant follicle in postpartum beef cows.

The hypothesis that ovulation in response to short-term (48 h) calf removal (CR) is dependent on the developmental stage of the dominant follicle was tested in two studies. The objective of Exp. 1 was to characterize the fate of a dominant follicle following 48-h CR on d 2, 4, or 8 of a postpartum follicular wave. Ovaries of 61 beef cows were examined daily by transrectal ultrasonography starting at d 20 to 21 postpartum. Treatments were no CR (n = 14) and CR on d 2 (n = 12), 4 (n = 16), or 8 (n = 10) of first detected follicular wave. Percentage of cows that ovulated a dominant follicle following treatment was not different among groups (P = 0.62). Maximum size of dominant follicles was larger in cows that ovulated (P = 0.002) than in cows that did not ovulate. The objectives of Exp. 2 were 1) to determine whether a follicular wave could be synchronized in anestrous cows following injection of 1 mg of estradiol benzoate (EB) and 200 mg of progesterone (P4; EB + P4); 2) to characterize the fate of dominant follicles following 48-h CR at three stages of a synchronized follicular wave; and 3) to determine whether estrous cycles of normal length followed ovulation in cows pretreated with EB + P4. Ovaries of 50 anestrous beef cows were examined daily as in Exp. 1. Treatments were sesame oil (SO) injected (i.m.) on d 25 postpartum and no CR (n = 9); EB + P4 and no CR (n = 9); EB + P4 and CR on 6 (n = 12), 8 (n = 9), or 12 (n = 11) d after injection. The EB and P4 injections were given on d 25 postpartum. Variability in day of emergence of subsequent follicular waves was lower in cows receiving EB + P4 than in SO-injected cows (P < 0.05). The percentage of cows that ovulated was not different (P = 0.16), but CR increased the percentage of cows that ovulated when groups that received EB + P4 were compared to the EB + P4 group that did not have CR (53.1 vs 11.1%, respectively; P < 0.05). Maximum diameter of dominant follicles was larger (P = 0.05) in ovulatory follicles. The luteal phase was longer (P < 0.03) in cows receiving EB + P4 injection (10.6 +/- 1.2 d) than in cows receiving SO (4.4 +/- 2.2 d). In summary, the maximum size of ovulatory follicles was greater than that of nonovulatory follicles, the ovulatory response of postpartum anestrous cows was maintained through d 8 of a follicular wave, synchronization of follicular waves was accomplished in postpartum cows using EB + P4, and the subsequent luteal phase length was increased in animals that were administered EB + P4.     

The effect of progesterone alone or in combination with estradiol on follicular dynamics, gonadotropin profiles, and estrus in beef cows following calf isolation and restricted suckling

The effects of calf isolation and restricted suckling on LH pulse characteristics and interval to first ovulation (postpartum interval) were studied in 52 multiparous beef cows, with or without exogenous progesterone. At 30 d postpartum, cows were randomly allocated to one of four treatments (n = 13/treatment): 1) Ad lib, ad libitum access of cows to calves; 2) CI/RS, calf isolation/restricted suckling, where suckling was restricted to once daily; 3) CI/RS+P4, same as CI/RS but cows received an intravaginal progesterone-releasing device at calf isolation for 6 d; or 4) CI/RS+P4+E2, as CI/RS+P4 but the intravaginal progesterone-releasing device had a 10-mg estradiol capsule attached. Daily ovarian scanning and twice-daily blood sampling were performed from d 25 postpartum until the day of second ovulation. A random sample of cows from each treatment (n = 31 in total) were blood-sampled at 15-min intervals for 10 h on d 29, 32, 35, and 38. Ovulatory response to treatment was regarded as ovulation of either the dominant follicle growing at d 30 or the subsequent DF. There was a treatment x day effect (P = .09) on LH pulse frequency, but neither progesterone (CI/ RS+P4) nor progesterone and estradiol (CI/RS+P4+E2) treatment suppressed the calf isolation/restricted suckling-induced increase in LH pulse frequency. The estradiol capsule (CI/RS+P4+E2) delivered sufficient estradiol to delay new follicle wave emergence (treatment x stage; P < .001) and the associated preemergence increase in concentrations of FSH (treatment, P < .05) in cows treated at the postselection stage of follicle wave development, prolonging dominance of the dominant follicle present at treatment initiation (P < .001). The number of cows that ovulated in response to treatment was greater (P < .001) in cows with calf isolation/restricted suckling than in cows suckled ad libitum. Hence, cows assigned to the Ad lib treatment had a longer postpartum interval (P < .001) than cows of the other treatments. Exogenous progesterone treatment increased the frequency of cows exhibiting clinical signs of estrus at first ovulation (P < .001) and reduced the frequency of short estrous cycles (P < .001). We conclude that, in beef cows with calves, a 6-d progesterone treatment does not suppress the calf isolation/restricted suckling-induced increase in LH pulse frequency. Hence, on progesterone withdrawal, the LH pulse frequency is sufficient to stimulate first ovulation, accompanied by overt estrous expression and elimination of a short estrous cycle in most cows.     

Effect of dietary energy, body condition and calf removal on pituitary gonadotropins, gonadotropin-releasing hormone (GnRH) and hypothalamic opioids in beef cows

Beef cows (n = 64) were slaughtered to evaluate effects of dietary energy and calf removal (CR) on hypothalamic and adenohypophysial endocrine characteristics. From d 190 of gestation until parturition, cows received maintenance (ME; n = 32) or low (LE; n = 32) energy diets (ME = 100%, LE = 70% NRC recommendations). After parturition, half (n = 16) of each prepartum diet group received low (LE; n = 32) or high (HE = 130% NRC; n = 32) energy diets. At 30 d postpartum, cows were slaughtered 0 or 48 hr after CR. Hypothalami [preoptic area (POA), hypothalamus (HYP), stalk-median eminence (SME)] and pituitaries were collected. Basal and K(+)-induced release of GnRH from SME, and pituitary luteinizing hormone (LH) and follicle stimulating hormone (FSH) did not differ among groups (P greater than .05). Hypophyseal LH was correlated (P less than .01) with body condition score (BCS) at parturition and slaughter (r = .36 and .47, respectively). Prepartum LE diet increased (P less than .05) met-enkephalin in POA compared to prepartum ME (.59 +/- .05 vs. .44 +/- .04 pmol/mg) regardless of postpartum diet or suckling status. Concentrations of beta-endorphin in combined HYP + POA were decreased (P less than .05) by 48 hr CR (15.1 +/- 1.1 vs. 18.1 +/- 0.7 fmol/mg).(ABSTRACT TRUNCATED AT 250 WORDS)     

Cow/calf preweaning efficiency of Nellore and Bos taurus x Bos indicus crosses

The objectives of this study were to determine if percentage Bos taurus (0 or 50%) of the cow had an effect on ME requirements and milk production, and to compare cow/calf efficiency among 3 mating systems. Metabolizable energy requirements were estimated during a feeding trial that encompassed a gestation and lactation feeding trial for each of 2 groups of cows. Cows were 0 or 50% Bos taurus (100 or 50% Nellore) breed type: Nellore cows (NL; n = 10) mated to Nellore bulls, NL cows (n = 9) mated to Angus bulls, Angus x Nellore (ANL; n = 10) and Simmental x Nellore (SNL; n = 10) cows mated to Canchim (5/8 Charolais 3/8 Zebu) bulls. Cows were individually fed a total mixed diet that contained 11.3% CP and 2.23 Mcal of ME/kg of DM. At 14-d intervals, cows and calves were weighed and the amount of DM was adjusted to keep shrunk BW and BCS of cows constant. Beginning at 38 d of age, corn silage was available to calves ad libitum. Milk production at 42, 98, 126, and 180 d postpartum was measured using the weigh-suckle-weigh technique. At 190 d of age, calves were slaughtered and body composition estimated using 9-10-11th-rib section to obtain energy deposition. Regression of BW change on daily ME intake (MEI) was used to estimate MEI at zero BW change. Increase in percentage Bos taurus had a significant effect on daily ME requirements (Mcal/d) during pregnancy (P < 0.01) and lactation (P < 0.01). Percentage Bos taurus had a positive linear effect on maintenance requirements of pregnant (P = 0.07) and lactating (P < 0.01) cows; during pregnancy, the ME requirements were 91 and 86% of those in lactation (131 +/- 3.5 vs. 145 +/- 3.4 Mcal x kg(-0.75) x d(-1)) for the 0 and 50% B. taurus groups, respectively. The 50% B. taurus cows, ANL and SNL, suckling crossbred calves had greater total MEI (4,319 +/- 61 Mcal; P < 0.01) than 0% B. taurus cows suckling NL (3,484 +/- 86 Mcal) or ANL calves (3,600 +/- 91 Mcal). The 0% B. taurus cows suckling ANL calves were more efficient (45.3 +/- 1.6 g/Mcal; P = 0.03) than straightbred NL (35.1 +/- 1.5 g/Mcal) and ANL or SNL pairs (41.0 +/- 1.0 g/Mcal). Under the conditions of this study, crossbreeding improved cow/ calf efficiency and showed an advantage for cows that have lower energy requirements.     

Effects of supplementation with high linoleic or oleic cracked safflower seeds on postpartum reproduction and calf performance of primiparous beef heifers

Primiparous Angus x Gelbvieh (n = 36) rotationally crossed beef cows (initial BW = 487.9 +/- 10.5 kg, body condition score = 5.5 +/- 0.02) were utilized to determine effects of supplemental safflower seeds high in linoleic (76% 18:2) or oleic (72% 18:1) acid on cow BW change, body condition score, milk production and composition, calf weight gain, cow serum metabolites, and metabolic hormones. On d 3 postpartum, cows were randomly assigned to one of three isonitrogenous dietary supplements with equal total quantity of TDN: corn-soybean control supplement (n = 12); high-linoleate safflower seeds (n = 12); or high-oleate safflower seeds (n = 12). Safflower-seed supplements were formulated to provide 5% DMI as fat. Supplements were individually fed from d 3 postpartum through 90 d postpartum. Cows had ad libitum access to native grass hay (7.8% CP), trace-mineralized salt, and water. Date of parturition was evenly distributed across treatments with all cows calving within 14 +/- 0.8 d. There were no differences (P = 0.65) in total OM intake among treatments. Although cow BW change did not differ (P = 0.33) by treatment, supplementation influenced cow body condition score (P = 0.02) with linoleate-supple-mented cows in higher (P = 0.005) condition overall than oleate-supplemented cows (5.1 +/- 0.06 vs 4.9 +/- 0.06). Twenty-four-hour milk production did not differ (P = 0.68) among treatments. Percentage milk fat was not different at d 30; however, at d 60 and d 90 percentage milk fat was greater (P ( 0.05) in control and oleate-supplemented cows than in linoleate-supplemented cows. Calf BW gains (P = 0.27) and adjusted 205-d weights (P = 0.48) were not affected by supplement treatment. Supplementation did not influence serum concentrations of glucose (P = 0.38), NEFA (P = 0.61), GH (P = 0.29), IGF-I (P = 0.81), insulin (P = 0.26), or IGF-I binding proteins (P > or = 0.11). Days to conception did not differ (P = 0.40) among treatments. Although overall productivity of the primiparous cows and their calves was not altered by safflower-seed supplementation, differential effects were noted between supplements. Oleate supplementation increased percentage milk fat at d 60, and cow body condition score was lower than in linoleate-supplemented cows. Linoleate-supplemented cows had greater body condition scores by 90 d postpartum than either corn-soybean- or oleatesupplemented cows.     

Restricted suckling of tropical dairy cows by their own calf or other cows' calves

The objective of this study was to compare restricted suckling of tropical cows by their own or another cow's calf with artificial rearing of the calves and no suckling. In Exp. 1, cows were mechanically milked twice daily, after which for 15 min they were either suckled by their own calf (Treatment O) or multiple-suckled by other cows' calves (Treatment M) or unsuckled, with the calves reared artificially (Treatment A). Machine milk yield was similar for the three treatments, but in the two suckling treatments the additional milk consumed by the calf increased (P = 0.02) total production (2,682, 2,634, and 2,336 kg/lactation for Treatments O, M, and A, respectively). Machine milk fat concentration was reduced (P = 0.05) by suckling (2.90, 3.07, and 3.20% for Treatments 0, M, and A, respectively), but the milk sampled just before suckling (to represent that taken by the calves) had a high fat concentration (mean 7.9%). Machine milk somatic cell count was also reduced (P = 0.05) by suckling, from 106,000/mL (Treatment A) to 85,000/mL (Treatment M) and 95,000 (Treatment O). Cows suckling their own calf lost more weight and body condition than cows whose calves were reared artificially, with multiple-suckled calves intermediate. Cows suckling their own calf had postpartum interval to first estrus increased (P = 0.01) by 31 d and conception rates to first service of 44% compared to 77% for the other two treatments (P = 0.01). The growth of the suckled calves was compared with that of the artificially reared calves, which were given recommended milk allowances. The artificially reared calves consumed more milk and concentrates, which were available ad libitum to all calves, and gained (P = 0.03) 0.07 kg/d more weight than suckled calves. A second experiment determined that suckling once daily did not reduce reproductive performance compared to artificial rearing. We conclude that suckling cows twice daily increases total milk production but reduces body weight in early lactation. Cows suckling their own calves have reduced reproductive performance compared to those suckling other calves or reared artificially.     

Postpartum supplemental fat, but not maternal body condition score at parturition, affects plasma and adipose tissue fatty acid profiles of suckling beef calves

Three-year-old Angus x Gelbvieh beef cows, which were nutritionally managed to achieve a BCS of 4 +/- 0.07 (479 +/- 36 kg of BW) or 6 +/- 0.07 (580 +/- 53 kg of BW) at parturition, were used in a 2-yr experiment (n = 36/yr) to determine the effects of maternal BCS at parturition and postpartum lipid supplementation on fatty acid profile of suckling calf plasma and adipose tissue. Beginning 3 d postpartum, cows within each BCS were assigned randomly to 1 of 3 treatments in which cows were all fed hay and either a low-fat (control) supplement or supplements with either high-linoleate cracked safflower seeds (linoleate) or high-oleate cracked safflower seeds (oleate) until d 61 of lactation. Diets were formulated to be isonitrogenous and isocaloric, and safflower seed supplements were provided to achieve 5% of DMI as fat. Total concentration of fatty acids in plasma did not differ (P = 0.48) due to maternal BCS at parturition. Percentage of 20:5n-3 in plasma tended (P = 0.06) to be greater for calves suckling cows with a BCS of 6 at parturition. No other differences (P = 0.12 to 0.99) were noted in calf plasma fatty acid profile due to maternal BCS at parturition. Likewise, no differences were detected for total fatty acid concentration (P = 0.88) in calf adipose tissue due to maternal BCS at parturition. Weight percentage of 14:1 (P = 0.001) was greatest in adipose tissue of calves suckling cows fed control and oleate; however, the percentages of 14:0, 15:0, 16:0, 16:1, 17:0, and 18:3n-3 were greater (P < 0.001) in adipose tissue from calves suckling cows fed control compared with calves suckling cows fed linoleate or oleate. Percentages of 18:0, 18:1trans-11, 18:2n-6, and cis-9, trans-11 CLA were greater (P < 0.001) in adipose tissue from calves suckling cows fed linoleate compared with calves suckling cows fed control and oleate. Calves suckling cows fed oleate had greater (P < 0.001) percentages of 18:1trans-9, 18:1trans-10, and 18:1cis-9 in adipose tissue than calves suckling cows fed control or linoleate. Calf plasma and adipose tissue fatty acid profiles were reflective of milk fatty acids. Because fatty acids play an important role in metabolic regulatory functions, changes in milk fatty acid profile should be considered when beef cows are fed lipid supplements.     

Performance of beef cows receiving cull beans, sunflower meal, and canola meal as protein supplements while grazing native winter range in Eastern Colorado

A 2-yr grazing performance study was conducted in Eastern Colorado to evaluate the effects of feeding raw cull beans (Phaseolus vulgaris) or canola meal, compared to sunflower meal, to beef cows grazing dormant, native winter range on body weight and body condition score (BCS) change, reproductive performance, and calf performance. Ninety-five pregnant, spring-calving crossbred cows (541 +/- 51 kg) in 1995 to 1996 and 65 cows (602 +/- 60 kg) in 1996 to 1997 were randomly assigned to one of five treatments (19 and 13 cows per treatment in 1995 to 1996 and 1996 to 1997, respectively): 1) unprocessed Great Northern beans to supply 182 g/d of CP (GNB); 2) canola meal to supply 182 g/d of CP (CM); 3) a mixture of Great Northern beans and sunflower meal, each to supply 91 g/d of CP, for a total of 182 g/d of CP (MIX); 4) sunflower meal to supply 182 g/d of CP (SFM+); and 5) sunflower meal to supply 91 g/d of CP (SFM-). Cow weight and body condition performance were broken into a gestation and a lactation phase in 1995 to 1996; calves were weighed at birth, at the end of the lactation phase in April, and at weaning the following September. Only gestation performance was monitored in 1996 to 1997, and subsequent calf birth and weaning weight were recorded. The SFM- group lost more weight during the gestation phase than other treatments (P < .05), yet no differences were detected for gestation phase daily BCS change, calf birth weight, lactation phase daily weight change, lactation phase daily BCS change, first-service conception rate to AI, or overall pregnancy rate. Off-test calf weight was higher in April for calves from dams of the SFM+ and CM treatments than for calves from dams on the GNB or SFM- treatments (P < .05), and calves from cows on the CM treatment were heavier in April than calves from cows on the MIX treatment (P < .05). No differences in calf weight were present at weaning. Consumption of beans by cows on the GNB treatment was low because of palatability problems. Mixing the beans with sunflower meal in the MIX treatment eliminated this problem. Canola meal, Great Northern beans, or a combination of sunflower meal and Great Northern beans were comparable to sunflower meal as protein supplements for beef cows grazing native winter range, despite obvious palatability problems with the beans.     

Winter grazing system and supplementation during late gestation influence performance of beef cows and steer progeny

A 2 x 2 factorial study evaluated effects of cow wintering system and last trimester CP supplementation on performance of beef cows and steer progeny over a 3-yr period. Pregnant composite cows (Red Angus x Simmental) grazed winter range (WR; n = 4/yr) or corn residue (CR; n = 4/yr) during winter and within grazing treatment received 0.45 kg/d (DM) 28% CP cubes (PS; n = 4/yr) or no supplement (NS; n = 4/yr). Offspring steer calves entered the feedlot 14 d postweaning and were slaughtered 222 d later. Precalving BW was greater (P = 0.02) for PS than NS cows grazing WR, whereas precalving BCS was greater (P < 0.001) for cows grazing CR compared with WR. Calf birth BW was greater (P = 0.02) for CR than WR and tended to be greater (P = 0.11) for PS than NS cows. Prebreeding BW and BCS were greater (P 0.32) by PS. Calf weaning BW was less (P = 0.01) for calves from NS cows grazing WR compared with all other treatments. Pregnancy rate was unaffected by treatment (P > 0.39). Steer ADG, 12th-rib fat, yield grade, and LM area (P > 0.10) were similar among all treatments. However, final BW and HCW (P = 0.02) were greater for steers from PS-WR than NS-WR cows. Compared with steers from NS cows, steers from PS cows had greater marbling scores (P = 0.004) and a greater (P = 0.04) proportion graded USDA Choice or greater. Protein supplementation of dams increased the value of calves at weaning (P = 0.03) and of steers at slaughter regardless of winter grazing treatment (P = 0.005). Calf birth and weaning BW were increased by grazing CR during the winter. Calf weaning BW was increased by PS of the dam if the dam grazed WR. Compared with steers from NS cows, steer progeny from PS cows had a greater quality grade with no (P = 0.26) effect on yield grade. These data support a late gestation dam nutrition effect on calf production via fetal programming.     

Effects of supplemental protein type on productivity of primiparous beef cows

Effects of supplemental degradable (DIP) and undegradable (UIP) intake protein on forage intake, BW change, body condition score (BCS), postpartum interval to first estrus, conception rate, milk production and composition, serum metabolites and metabolic hormones, and calf gain were determined using 36 primiparous Gelbvieh x Angus rotationally crossed beef cows. On d 3 postpartum, cows (average initial BW = 495 +/- 10 kg and BCS = 5.5 +/- 0.1) were randomly assigned to one of three dietary supplements (12 cows/treatment). Date of parturition was evenly distributed across treatment (average span of calving date among treatments = 2.4 +/- 2.5 d). Individually fed (d 3 through 120 postpartum) dietary supplements were 0.82 kg of corn and 0.23 kg of soybean meal per day (DIP), the DIP + 0.12 kg of blood meal and 0.13 kg of corn gluten meal per day (DIP + UIP), and 0.82 kg of corn, 0.07 kg of blood meal, and 0.08 kg of corn gluten meal per day in an isonitrogenous replacement of soybean meal (UIP IsoN). Cows had ad libitum access to native grass hay (8.5% CP) and trace-mineralized salt. Total OM intake was greater (P = 0.06) for DIP + UIP than UIP IsoN cows. At 30 d postpartum, DIP + UIP cows produced more milk than UIP IsoN, with DIP being intermediate; however, at 60 d postpartum, DIP + UIP and DIP cows were not different, but both had greater milk production than UIP IsoN (treatment x day interaction; P = 0.08). A treatment x day interaction (P = 0.06) for BCS resulted from DIP + UIP cows having the greatest BCS at 60, 90, and 120 d d postpartum and DIP having greater BCS than UIP IsoN cows only on d 60 postpartum. Serum insulin concentrations were highest (treatment x day interaction; P = 0.09) for DIP + UIP cows at 30 d postpartum but did not differ among treatment thereafter. Serum insulin-like growth factor-binding protein (IGFBP)-2 (34 kDa) and -3 (40 and 44 kDa) were greatest (P < 0.0003) for DIP cows. Serum urea-N concentrations were greater (P < 0.01) in DIP + UIP cows than in either DIP or UIP IsoN cows. However, postpartum interval to first estrus, conception rate, and calf weaning weights were unaffected (P = 0.35, 0.42, and 0.64, respectively) by treatment. Although UIP in addition to or in replacement of DIP affected milk production and blood metabolites, the productivity of these primiparous beef cows was not altered. Thus, the type of supplemental protein does not seem to influence productivity of primiparous beef cows in production systems with conditions similar to our experimental conditions.     

Gonadotropin releasing hormone-induced secretion of luteinizing hormone during the milk-ejection reflex in the postpartum beef cow

A study was conducted to determine the effect of the milk-ejection reflex on exogenous gonadotropin releasing hormone (GnRH)-induced release of luteinizing hormone (LH) after short-term calf removal. Twenty-four postpartum multiparous beef cows were assigned randomly to groups arranged in a 2(3) factorial arrangement. Factors consisted of two levels of suckling [suckled (S) or nonsuckled (NS)], treatment with GnRH [saline (C) or 200 micrograms GnRH] and days postpartum (d 1 and 14). Dams were isolated from their calves for 4 h on d 1 and 14 postpartum. At the end of 4 h dams were reunited with their calves in S + C and S + GnRH groups, while dams of calves in NS + C and NS + GnRH groups remained separated an additional 2 h. Cows were injected iv with saline or GnRH following the 4-h isolation period, 5 min after calves had begun suckling or nuzzling the udder. Sera from jugular blood samples collected 15 min prior to the end of the 4-h isolation period, immediately prior to injection (0 h) and at 15 min intervals thereafter for 120 min were analyzed for LH. Serum concentrations of LH in control cows did not differ due to suckling or stage of the postpartum period and averaged 2.3 +/- .1 ng/ml. Pituitary response to GnRH was determined by computing the rate of LH release. Rate of LH release (ng LH.ml-1.min-1) in response to GnRH on d 14 was greater (P less than .001) than on d 1 in both suckled and nonsuckled groups (S + GnRH, 37.1 +/- 3.9 vs 18.3 +/- 5.0; NS + GnRH, 34.7 +/- 5.9 vs 14.5 +/- 1.1). However, GnRH-induced release of LH did not differ between suckled and nonsuckled cows on either d 1 or 14 postpartum. These data indicate that response of the bovine pituitary to GnRH during the postpartum period is not influenced by the act of suckling but is enhanced with time after parturition.     

Hormonal, estrual, ovulatory and milk traits in postpartum dairy cows following multiple daily injections of oxytocin

Release of oxytocin at suckling or milking may delay onset of estrous cycles in postpartum cows. Twenty lactating Holsteins of mixed parity were given 100 mU oxytocin iv (n = 10) or 2 ml saline (control; n = 10) via jugular catheters at 0530, 0930, 1730 and 2130 daily from calving (d o) until 28 d postpartum. All cows were milked twice daily at 0130 and 1330. Blood was collected thrice weekly (Monday, Wednesday, Friday at 0530) for 12 wk and analyzed by radioimmunoassay for progesterone and 13,14-dihydro-15-keto-prostaglandin F2 alpha (PGFM) in serum. On d 12, blood was collected every 15 min for 6 h via jugular catheters and concentrations of luteinizing hormone (LH), cortisol and PGFM were determined. Rate of involution of the reproductive tract was estimated twice weekly by palpation per rectum. Overall mean, baseline concentrations, number of pulses/6 h, and pulse duration of LH on d 12 were similar among treatment groups. However, oxytocin seemed to reduce (P less than .10) pulse amplitude of LH in multiparous cows (.4 +/- .2 vs .8 +/- .1 ng/ml), but not in primiparous cows. Concentrations of cortisol and PGFM in serum on d 12 were unaffected by treatment. The average intervals from calving to first ovulation, based on changes of progesterone in serum and the intervals to first estrus, were similar between treatment groups. Rates of involution of the cervix and uterus also were similar between treatments. Milk yield, percent protein in milk and somatic cell counts did not differ between treatment groups. However, percent fat in milk tended to be higher (P less than .10) in cows given oxytocin than in controls (3.99 +/- .22 vs 3.68 +/- .21). These data indicate that multiple daily injections of oxytocin did not affect: 1) length of anestrus and anovulation in postpartum dairy cows, 2) LH release and 3) rates of cervical and uterine involution.     

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.     

Relationship of milk production, milk expected progeny difference, and calf weaning weight in angus and simmental cow-calf pairs.

Milk EPD, used to predict the milk production potential of a parent's daughters, have been reported by all major cattle breed associations. Our objectives were to determine the relationship of milk EPD of a dam to actual milk production (both fluid and components) and offspring weaning weight. Angus (AN; n = 114) and Simmental (SM; n = 82) cows were machine-milked at approximately 60, 104, and 196 d postpartum after overnight calf removal. In addition, one herd of AN was also milked at approximately 35 and 145 d postpartum. A lactation curve was fitted to these measurements to estimate total milk production during lactation. Simple correlations between 205-d total milk yields (TMY) and adjusted 205-d calf weaning weight (WW) were .30 (P < .001) and .47 (P < .001) for AN and SM, respectively. Furthermore, milk EPD was positively correlated to adjusted WW (r = .38 P < .001; r = .39, P < .001) and TMY (r = .32, P < .001; r = .44, P < .001) for AN and SM cows, respectively. A 1-kg change in TMY changed WW by .014 +/- .006 kg (P < .001) in AN and by .032 +/- .009 kg (P < .001) in SM. A 1-kg change in milk EPD resulted in a 4.85 +/- 1.14 kg change in WW (P < .001) in AN and a 3.74 +/- 1.73 kg (P < .05) change in SM. Corresponding changes in TMY were 42.1 +/- 16.6 kg (P < .01) and 69.3 +/- 16.0 kg (P < .001) for AN and SM, respectively.(ABSTRACT TRUNCATED AT 250 WORDS)     

Plasma bovine placental lactogen concentration throughout pregnancy in the cow; relationship to stage of pregnancy,fetal mass,number and postpartum milk yield

This study characterized the peripheral plasma placental lactogen (bPL) profile throughout gestation and examined the relationship between the stage of gestation, fetal mass, number, and postpartum lactation with circulating levels of bPL in Holstein cows after nonsurgical embryo transfer. Cows (n = 12) were divided into two groups: Group 1 = single embryo recipient cows (n = 5); Group 2 = twin embryo recipient cows (n = 7). Blood was collected about every third day from Day 0 (Day 0 was defined as the first day of standing estrus), then daily for the last 10 d of gestation, and sampling was stopped 1 d postpartum. The cows were milked twice daily at 0800 and 1800 hr. Two twin-embryo recipient cows had abnormal pregnancies; therefore, their data were excluded from that of the group and reported separately. The time trend concentrations of plasma bPL were significantly affected by the stage of gestation (P < 0.01) but not fetal number (P < 0.21). In both groups bPL levels remained low during the first two trimesters, then increased rapidly (P < 0.01) to peak concentrations between Days 200 and 220, and stabilized at this elevated level until parturition. Postpartum milk yields were indistinguishable between the singleton and twin-bearing cows. Calf birth weight and postpartum lactation were both correlated (P < 0.01) to peripheral bPL concentration in singleton cows, however, this relationship decreased with a subsequent increase in fetal number. Cows giving birth prematurely to stillborn calves or to a schistosomus reflexus calf exhibited a deviating bPL profile. These results indicate that peripheral bPL levels are positively associated with the stage of gestation but not with fetal number. Otherwise, the peripheral pattern of bPL is a valuable index for predicting feto-placental viability.     

Influence of calf removal on the serum luteinizing hormone response to naloxone in the postpartum beef cow

Twelve anestrous, postpartum beef cows were used to determine the effect of calf removal on the effect of naloxone on serum luteinizing hormone (LH) concentrations. On d 1, six cows were injected iv with saline and six with 200 mg naloxone dissolved in saline. Blood samples were taken at 15-min intervals for 2 h before and 2 h after naloxone or saline administration. At the beginning of blood sampling, calves were removed from three cows in each treatment. At 48 h after calf removal (d 3), all cows were injected iv with 200 mg naloxone and blood samples were collected as on d 1. On d 1, naloxone treatment increased (P less than .01) serum LH concentrations from 1.2 +/- .3 ng/ml at time 0 to 4.3 +/- .6 ng/ml and 4.7 +/- .8 ng/ml at 15 and 30 min, respectively. Injection of saline had no effect on serum LH concentrations. Forty-eight-hour calf removal increased (P less than .01) serum LH concentrations in five of six cows (1.7 +/- .8 vs 4.4 +/- 1.2 ng/ml). Naloxone treatment failed to increase serum LH concentrations in these cows. Injection of naloxone increased (P less than .01) serum LH concentrations in the one cow that did not exhibit an LH increase after calf removal and in six cows whose calves were not removed (1.4 +/- .2 vs 4.4 +/- .5 ng/ml). The present study provides additional evidence that endogenous opioids regulate LH in the postpartum beef cow. We hypothesize that suckling stimulates an opioid inhibition of LH secretion and removal of the suckling stimulus removes the opioid inhibitory tone.     

Effects of supplementation of whole corn germ on reproductive performance, calf performance, and leptin concentration in primiparous and mature beef cows

A 2-yr study using primiparous and multiparous, spring-calving, crossbred beef cows was conducted to evaluate the effects of supplemental whole corn germ on reproductive performance, calf performance, and serum leptin concentrations. Each year, cows were blocked by age and BCS and assigned randomly to one of three treatments: PRE (n = 115) cows received 1.14 kg/d (DM basis) of whole corn germ for approximately 45 d before calving; POST (n = 109) cows were fed 1.14 kg/d of whole corn germ for approximately 45 d after calving; and control cows (n = 118) were fed similar energy and protein from dry-rolled corn (1.82 kg of DM/d) for 45 d before and after calving. Additionally, PRE cows were grouped with controls after calving, and POST cows were grouped with control cows before calving, so that corn germ-supplemented cows received the control supplement in the alternate feeding period. Cow BW (538 +/- 13 kg) and BCS (5.4 +/- 0.13) did not differ among treatments at any time during the experiment. Calf birth weight (39 +/- 2 kg), weaning weight (225 +/- 7 kg), and age-adjusted weaning weight (234 +/- 8 kg) did not differ because of dam supplementation regimen. Treatment did not affect the proportion of cows exhibiting ovarian luteal activity before the start of the breeding season (67%) or pregnancy rate (91%). The interval from exposure to bulls until subsequent calving did not differ (P = 0.16) among PRE (298 +/- 2.3 d), POST (303 +/- 2.6 d), and control (304 +/- 2.3 d) cows. Leptin concentrations did not differ among treatments and were 2.15 +/- 0.75, 1.88 +/- 0.76, and 1.91 +/- 0.75 ng/mL for control, POST, and PRE cows, respectively. Age and week relative to calving influenced leptin concentration. Primiparous cows had similar leptin concentrations to 3-yr-old and mature cows for wk -7 and -6 relative to calving, but lower (P < 0.10) concentrations than mature cows for wk -5, and lower (P < 0.05) concentrations than either 3-yr-old or mature cows for wk -4 to +7 relative to calving. Serum leptin was correlated with BCS (P < 0.0001; r = 0.35) at initiation of the feeding period and was correlated with BCS (P = 0.02; r = 0.12) and weight (P < 0.01; r = 0.14) at the completion of the supplement period, but it was not correlated with initial BW or interim BCS. Calving interval was not correlated (P > 0.12) with weekly measures of serum leptin concentration. Supplementing beef cows with whole corn germ had no effect on cow performance, calf performance, or serum leptin concentrations of cows.     

Suckling inhibits release of luteinizing hormone-releasing hormone from the bovine median eminence following ovariectomy

The effect of suckling on depletion of hypothalamic LHRH from the median eminence (ME) following ovariectomy (OVX) was determined in cattle. Multiparous, postpartum Holstein cows were assigned randomly to three groups: intact, nonsuckled (INT, n = 4); ovariectomized (3 to 5 d after parturition), nonsuckled (OVX, n = 4); and ovariectomized (3 to 5 d after parturition) and suckled by three calves (OVX-S, n = 5). Blood samples were collected at three periods (1 to 7 d before parturition and 3 to 5 d and 31 to 37 d after parturition) to determine plasma LH concentration. At 31 to 37 d after parturition, all cows were slaughtered and each ME was collected and mid-sagitally sectioned. The left half of each ME was used to determine content and concentration of LHRH. Concentrations of LH and LHRH were determined by RIA. Plasma LH concentration was similar among the three groups at 1 to 7 d before parturition and 3 to 5 d after parturition; however, at 31 to 37 d after parturition, OVX cows had a greater (P less than .05) concentration of LH (2.25 +/- .64 ng/ml) than either INT (.47 +/- .10 ng/ml) or OVX-S (.92 +/- .14 ng/ml) cows. Content of LHRH in the ME of INT (80.12 +/- 15.0 ng) and OVX-S 109.8 +/- 16.4 ng) cows was similar but was greater (P less than .05) than that in OVX cows (48.95 +/- 5.9 ng).(ABSTRACT TRUNCATED AT 250 WORDS)     

Administration of human chorionic gonadotropin to suckled beef cows before ovulation synchronization and fixed-time insemination: replacement of gonadotropin-releasing hormone with human chorionic gonadotropin

Two experiments were conducted to evaluate whether hCG administered 7 d before initiating the CO-Synch + controlled internal drug release (CIDR) ovulation synchronization protocol (Exp. 1 and 2), or replacing GnRH with hCG at the time of AI (Exp. 1), would improve fertility to a fixed-time AI (TAI) in suckled beef cows. In addition, the effects of hCG on follicle dynamics, corpus luteum development, and concentrations of progesterone (P4) were evaluated. In Exp. 1, cows were stratified by days postpartum, age, and parity and assigned randomly to a 2 × 2 factorial arrangement of 4 treatments: 1) cows received 100 μg of GnRH at CIDR insertion (d -7) and 25 mg of PGF(2α) at CIDR removal (d 0), followed in 64 to 68 h by a TAI plus a second injection of GnRH at TAI (CG; n = 29); 2) same as CG but the second injection of GnRH at the time of insemination was replaced by hCG (CH; n = 28); 3) same as CG, but cows received hCG 7 d (d -14) before CIDR insertion (HG; n = 28); and 4) same as HG, but cows received hCG 7 d (d -14) before CIDR insertion (HH; n = 29). Pregnancy rates were 52, 41, 59, and 38% for GG, GH, HG, and HH, respectively. Cows receiving hCG (39%) in place of GnRH at TAI tended (P = 0.06) to have poorer pregnancy rates than those receiving GnRH (56%). Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows with concentrations of P4 >1 ng/mL at d -7, increased (P < 0.02) concentration of P4 on d -7, and decreased (P < 0.001) the size of the dominant follicle on d 0 and 3, compared with cows not treated with hCG on d -14. In Exp. 2, cows were stratified based on days postpartum, BCS, breed type, and calf sex and then assigned to the CG (n = 102) or HG (n = 103) treatments. Overall pregnancy rates were 51%, but no differences in pregnancy rates were detected between treatments. Pre-CO-Synch hCG treatment increased (P < 0.05) the percentage of cows cycling on d -7 and increased (P < 0.05) concentrations of P4 on d -7 compared with pre-CO-Synch controls. Therefore, pretreatment induction of ovulation after hCG injection 7 d before initiation of CO-Synch + CIDR protocol failed to enhance pregnancy rates, but replacing GnRH with hCG at the time of AI may reduce pregnancy rates.     

Role of prostaglandin F2 alpha in follicular development and subsequent luteal life span in early postpartum beef cows.

In postpartum cows expected to have corpora lutea (CL) of normal (norgestomet-treated) compared to short (control) life spans, function of the largest follicle increases after an increase in concentrations of prostaglandin F2 alpha (PGF). To determine whether PGF alters follicular growth and subsequent life span of the CL, 43 crossbred beef cows (19 to 22 d postpartum) were assigned to one of four treatments: 1) control (C; n = 10), 2) control+PGF (CPGF; n = 10), 3) norgestomet (N; n = 13), 4) norgestomet+flunixin meglumine (NFM; n = 10). Flunixin meglumine inhibits prostaglandin endoperoxide synthase. On day 0, N and NFM cows received a 6 mg implant of norgestomet. From days 3 through 8, CPGF and NFM cows were injected every 8 hr with 10 mg PGF im or 1 g FM iv, respectively. Implants were removed on day 9. On day 11, each cow received 1000 IU of hCG im to induce formation of CL. Follicular growth was monitored by daily ultrasonography from days 6 through 11. In a majority of the cases (25/32), the largest follicle present on day 6 was still the largest on day 11; frequency of persistence did not differ with treatment. Rate of growth of the largest follicle was greater in CPGF than in N cows (.6 +/- .1 vs .3 +/- .1 mm/d, respectively; P less than .05) but did not differ between C and NFM cows (.4 +/- .1 and .5 +/- .1 mm/d, respectively). Concentrations of estradiol in NFM cows were higher (P less than .05) on day 3 and declined to concentrations similar to those of the other treatments on day 9.(ABSTRACT TRUNCATED AT 250 WORDS)