D. A. Neuendorff

Effects of naloxone and animal temperament on serum luteinizing hormone and cortisol concentrations in seasonally anestrous Brahman heifers

The effect of endogenous opioid peptides (EOP) and individual animal temperament on serum luteinizing hormone (LH) were investigated in seasonally anestrous Brahman heifers (n = 24). Animals that had shown behavioral estrus in previous months but that had not returned to estrus for at least 30 d were selected. The heifers were ranked by temperament (tame = 1, normal = 2, wild = 3) and randomly allotted into three groups. Blood was collected from one heifer of each group per day. Blood samples were taken via jugular cannula every 15 min for 6 h and every 30 min for another 4 h. After the first hour of sampling, the heifers received intravenous saline (SAL, n = 8); naloxone (LN, 0.5 mg/kg i.v., n = 8); or naloxone (HN, 1.0 mg/kg i.v., n = 8). Three hours after naloxone treatment, each heifer was given gonadotropin releasing hormone (GnRH, 100 microg i.m.). All samples were processed to yield serum and were assayed for LH by radioimmunoassay (RIA). Hourly samples were assayed for cortisol by RIA. The area under the LH curve 60 min postnaloxone treatment was higher in LN and HN than in SAL (57.0 and 40.8 vs 6.1 units; P<0.01); and the area under the 180 min postnaloxone curve remained higher in LN than in SAL (106.2 vs 35.1 units; P<0.05). Cortisol concentrations 60 min postnaloxone administration were above prenaloxone levels(38.2 vs 26.7 ng/ml; P<0.0002). Temperament scores of heifers were positively correlated with cortisol release. The area under the cortisol curve had a negative correlation with mean LH. Serum LH concentrations appear to be suppressed by EOP in seasonally anestrous Brahman heifers, and EOP appear to reduce serum cortisol concentrations. Excitable heifers had higher concentrations of serum cortisol, which negatively affected serum LH concentrations.

Exogenous PGF2α enhanced GnRH-induced LH release in postpartum cows

This study evaluated the effect of exogenous PGF(2)alpha on circulating LH concentrations in postpartum multiparous (n = 32) and primiparous (n = 46) Brahman cows. The cows were randomly allotted within parity and calving date to receive 0, 1, 2 or 3 mg im PGF(2)alpha (alfaprostol)/100 kg body weight (BW), with or without GnRH on Day 30 after calving. Blood samples were collected at weekly intervals from calving through treatment. Serum progesterone concentrations were determined using RIA procedures to assure that only anestrous cows were treated. Sterile marker bulls were maintained with cows on Coastal bermudagrass pastures until the first estrus was detected. Multiparous cows had a shorter (P < 0.05) interval from calving to estrus than did primiparous cows. Serum LH was affected by time (P < 0.0001), PGF(2)alpha dose (P < 0.0002), GnRH (P < 0.0001), parity by PGF(2)alpha dose (P < 0.0003), PGF(2)alpha dose by GnRH (P < 0.0009), parity by GnRH (P < 0.0008), and by parity by PGF(2)alpha dose by GnRH (P < 0.0005). Multiparous cows not receiving GnRH had higher mean serum LH (P < 0.02), LH peak pulse height (P < 0.03), and area under the LH release curve (P < 0.03) compared with primiparous cows. The number of LH pulses/6 h was greater (P < 0.06) in multiparous than primiparous cows, and was greater (P < 0.02) in multiparous cows receiving 3 mg/100 kg BW than in cows receiving 2 mg/100 kg BW, but not in the controls or in cows receiving 1 mg/100 kg BW. Exogenous GnRH resulted in increased (P < 0.0001) serum LH concentrations in all cows, and LH was enhanced (P < 0.0009) by simultaneous treatment with PGF(2)alpha. Primiparous cows had a greater response (P < 0.0005) to PGF(2)alpha and GnRH compared with multiparous cows. Pituitary release of LH in response to GnRH was enhanced by simultaneous exposure to PGF(2)alpha in Day 30 postpartum cows.

Effects of restricted nursing on physiological and behavioral reactions of Brahman calves to subsequent restraint and weaning1

The influence of restricted nursing on physiological and behavioral reactions to later restraint and weaning was examined in Brahman (Bos indicus) calves. The calves were blocked for sex and randomly assigned at birth to one of two treatments: restricted nurse (RN), or ad libitum nurse (ALN). The RN calves were separated from their dams at 21 days of age and allowed to nurse once daily (2-h duration) for 19±3 days. The ALN calves remained with their dams from birth until weaning. The ALN calves were brought in and worked through handling facilities for the same amount of time each day as the RN calves. At 192±4 days of age each calf was restrained while blood samples (5) were taken and heart rate monitored via telemetry. Two weeks later, the calves were weaned and blood samples and behavioral observations were taken. Mean plasma cortisol concentration (MC) increased over time for both treatments (P<0.004) in response to restraint, but was greater for RN than for ALN calves after 15 min of restraint (P<0.03). In response to restraint, RN calves had overall greater heart rates than did ALN calves (P<0.02). In response to weaning, ALN calves tended to travel more (P<0.07), and included more calves who ate (P<0.05), and vocalized (P<0.05). The effects of the restricted nursing regimen, which inherently includes handling, appears to alter the calfs later response to restraint and weaning. However, due to the lack of a uniform response further research is required to determine the meaning of and causal factors for this alteration.

Seasonal variations in characteristics of estrous cycles in pubertal Brahman heifers.

A group of pubertal Brahman heifers (n = 16) was monitored from October through March to investigate the seasonal changes in estrous cyclicity. The heifers had a mean age of 16.7 +/- 0.3 mo at the initiation of the experiment. They were kept on pasture with vasectomized marker bulls. Supplemental feed to meet NRC requirements was provided. Estrus occurrence was checked once a day and blood samples were taken weekly by tail venipuncture from heifers that had been in estrus 7 to 14 d earlier. Samples were processed to yield serum and were assayed for serum progesterone by radioimmunoassay. A high proportion of heifers (88%) had abnormalities such as estrus without the formation of a functional corpus luteum (CL) or anestrus, with a distribution of the two abnormalities as follows: October 0 and 0, November 50 and 25, December 0 and 50, January 0 and 50, February 18 and 31 and March 0 and 7%, respectively. Mean serum progesterone concentrations during the luteal phase differed by month: 4.26, 1.50, 3.25, 2.27, 2.65 and 3.70 ng/ml for October, November, December, January, February and March, respectively (P<0.001). Heifers that went into anestrus had lower mean serum progesterone concentrations than heifers that had regular estrous cycles throughout the study period (1.35 vs 2.22 ng/ml; P<0.0005). The months with the shortest daylengths (December and January) had the highest incidence of anestrus. Transitional periods (November and February) seemed to occur before and after the months with the highest occurrence of anestrus. During this transitional period a high incidence of estrus without the formation of a functional CL was detected. Serum progesterone concentrations were lower in all heifers during the months with high occurrence of abnormal estrous cycles.

Effect of alfaprostol on postpartum reproductive efficiency in brahman cows and heifers

Brahman cows (n=54) and heifers (n=18) were randomly allotted by calving date, sex of calf and age to one of four treatment groups. Group 1 received no treatment (control), Group 2 received 5 mg alfaprostol (AP) i.m. on Day 21 postpartum, Group 3 received 5 mg AP i.m. on Day 32 postpartum and Group 4 received 5 mg AP i.m. on both Days 21 and 32 postpartum. Blood samples were collected via tail vessel puncture at 30 min-intervals for 8 h from half the animals in each group on Days 21 and 32 postpartum, with AP injection administered 2 h after sampling had begun. All cows were bled at weekly intervals. Samples were processed to yield serum and stored at -20 degrees C until assayed for luteinizing hormone (LH) or progesterone (P4). All cattle were maintained with epididymectomized marker bulls and were artificially inseminated (A.I.) at first estrus. Serum P4 was below 1 ng/ml prior to AP treatment in all animals and did not differ (P>0.10) between treatments. Alfaprostol treatment affected mean postpartum interval (from parturition to return to standing estrus and subsequent corpus luteum formation with serum progesterone concentrations>1 ng/ml; P<0.08). The control group (84.8+/-7.9 d) did not differ from Group 2 (86.3+/-11.1 d) or Group 3 (66.7+/-5.5 d) but did differ (P<0.09) from Group 4 (65.1+/-6.4 d). Cattle injected on Day 32 had a shorter (P<0.01) postpartum interval than those not receiving treatment on that day (65.9+/-4.2 vs 85.7+/-6.8 d). Pregnancy rate was affected (P<0.05) by AP treatment. The control group (72.2%) did not differ (P>0.10) from any group but, Group 2 (50.0%) was lower (P<0.04) than Group 3 (83.3%) and (P<0.02) Group 4 (88.9%). Cattle treated on Day 32 (Groups 3 and 4) had a higher (P<0.02) pregnancy rate (86.1%) than those not treated on Day 32 (Groups 1 and 2; 61.1%). Serum LH was affected by day (P<0.0003) and treatment by day (P<0.07) but not by time (P>0.10). Treatment Group 3 (P<0.08) and Group 4 (P<0.0003) mean LH concentrations differed between Days 21 and 32 postpartum. Cattle receiving AP treatment on Day 32 postpartum had a higher (P<0.04) cumulative frequency of return to estrus by 100 days postpartum than nontreated cattle.

Effect of estrus synchronization with Syncro-Mate-B® on serum luteinizing hormone, progesterone and conception rate in Brahman heifers

Twenty-two estrous cyclic, 2-yr-old Brahman heifers were randomly assigned to receive either estrus synchronization with Syncro-Mate-B((R)) (SMB; 11) or no treatment (Control; 11). Blood samples were collected via tail vessel puncture at onset of estrus and daily thereafter until Day 11 after estrus. Blood samples were also collected from five SMB and five Control heifers at 0, 4, 8 and 12 h after the onset of estrus. All samples were processed to yield serum and stored at -20 degrees C until radioimmunoassay. Heifers were inseminated by one technician using semen from a single ejaculate of a Brahman bull 12 h after the onset of estrus. All SMB heifers exhibited estrus within 72 h of implant removal. All heifers had corpora lutea (CL) detected by rectal examination 8 to 12 d following estrus. Serum luteinizing hormone (LH) was not affected by treatment, time (4 - h intervals) or an interaction of treatment by time (P > 0.10). Independent analysis with h indicated that at h 12, SMB (2.2 +/- 0.06 ng/ml) had lower LH than did control heifers (8.9 +/- 2.1 ng/ml). Serum progesterone increased from Day 1 through Day 12 in all heifers, which is indicative of functional CL. Serum progesterone was affected by treatment (P < 0.0001) and time (d intervals; P < 0.10). Progesterone elevation was lower (P < 0.05) and area under the progesterone curve was lower (P < 0.03) in SMB (5.6 +/- 0.5 ng/ml, 32.0 +/- 4.5 units, respectively) when compared with control heifers (7.0 +/- 4 ng/ml, 43.7 +/- 2.4 units, respectively). Conception rate was lower (P < 0.01) in SMB heifers (2 of 11) than in control heifers (8 of 11). The lowered conception rate in SMB treated Brahman heifers may be due to altered timing of LH release following estrus, resulting in an altered time of ovulation.

Genetic parameters of three methods of temperament evaluation of Brahman calves.

The objective of this study was to estimate the heritability of 3 measures of temperament in Brahman and Brahman-influenced calves (n = 1,209). Individual animal pen scores (PS) were determined by a trained observer who evaluated groups of 5 or 4 calves at a time for willingness to be approached by a human. Exit velocity (EV) was the rate (m/s) at which each calf exited a squeeze chute. Temperament score (TS) was calculated individually as (PS + EV)/2. Temperament was evaluated at 5 different times of record (28 d preweaning, weaning, 28 d postweaning, 56 d postweaning, and yearling). Contemporary groups (n = 34) comprised calves of the same sex born in the same season of the same year. There were an average of 36 calves per contemporary group and group size ranged from 3 to 78 calves. Average weaning age (186 d) ranged from 105 to 304 d. Calves were born from 2002 through 2012. Random effects included additive genetic and the permanent environmental variance. The fixed effects analyzed were age of dam, sex of calf, contemporary group, fraction of Brahman (2 levels: 1 and 0.5), age of calf at record, and weaning age. At weaning, the mean PS was 2.68 ± 0.1, the mean EV was 2.41 ± 0.1, and the mean TS was 2.48 ± 0.1. The PS was affected by fraction of Brahman (P = 0.034) and tended to be affected by age of dam (P = 0.06). The EV was affected by contemporary group (P < 0.001) and tended to be affected by weaning age (P = 0.074). Contemporary group affected TS (P < 0.001). All 3 methods of temperament evaluation were affected by time of record (P < 0.001). The regression coefficients for PS, EV, and TS were 0.0023 ± 0.0014, 0.0022 ± 0.0012, and 0.0015 ± 0.0012 m·s(-1)·d(-1) of age, respectively. Estimates of maternal genetic effects were always 0 and omitted from final models. Estimates of heritability were 0.27 ± 0.1, 0.49 ± 0.1, and 0.43 ± 0.1 for EV, PS, and TS, respectively. Estimates of permanent environmental variances as proportions of phenotypic variance were 0.33 ± 0.1, 0.23 ± 0.1, and 0.33 ± 0.1 for EV, PS, and TS, respectively. There appears to be sufficient additive genetic variance for selective improvement of temperament characteristics in Brahman cattle.

Effect of alfaprostol, lasalocid, and once-daily suckling on postpartum interval in Brahman and Brahman crossbred cattle

Brahman cows (n = 49) and primiparous heifers (n = 11), Brahman x Hereford primiparous F1 heifers (n = 86) and Simmental x Brahman primiparous F1 heifers (n = 13) were randomly allotted by breed, age and date of calving to one of eight treatment groups: 1) control; 2) once-daily suckling; 3) lasalocid (200 mg/hd/d); 4) alfaprostol (5 mg intermuscular injections on Days 21 and 32 post partum); 5) lasalocid + once-daily suckling; 6) alfaprostol + once daily suckling; 7) alfaprostol + lasalocid; 8) alfaprostol + lasalocid + once daily suckling. All animals received 2.3 kg/hd/d of a concentrate (6 corn : 1 cottonseed meal) and lasalocid was mixed and fed in the concentrate. Body weights and condition scores were taken on Day 1 post partum and every 28 d thereafter. All animals were maintained with sterile marker bulls with Brahman and Simmental x Brahman cattle artificially inseminated at first estrus. Blood samples were collected at weekly intervals starting on Day 21 post partum until estrus and at nine to twelve days post estrus when the ovaries were palpated for corpora lutea. After the first postpartum estrus with a corpora lutea, cows were placed with fertile bulls. Mean serum progesterone concentrations were below 0.5 ng/ml prior to treatment. Calf weight gains to 90 d were not affected by age (P > 0.10) but were lower in the once-daily suckling group (P < 0.05). Treatment did not affect cow weight or condition score (P > 0.10). Cows had a shorter postpartum interval (P < 0.0001) than heifers. Once-daily suckling shortened postpartum interval (P < 0.0001) and positively influenced the cumulative frequency of return to estrus by 40 d post partum (P < 0.02). Alfaprostol did not affect postpartum interval (P > 0.10) but did increase the cumulative frequency of return to estrus by 90 d post partum (P < 0.03). Lasalocid did not affect postpartum interval or cumulative frequency of return to estrus (P > 0.10). Both once-daily suckling and alfaprostol were effective in increasing the numbers of animals inseminated by 90 d post partum. The once-daily suckling + alfaprostol treatment resulted in the shortest postpartum interval.

Testicular and epididymal function during the peripuberal period in Brahman bulls receiving various amounts of protein degradable in the rumen.

Thirty-nine Brahman bulls with an initial age and weight of 301.7 +/- 4.1 d and 202.7 +/- 4.7 kg, respectively, were randomly allocated to 1 of 2 dietary treatment groups within age, weight and sire in order to study the influence of source of protein and stage of peripuberal period on testicular and epididymal function. In the soybean meal treatment the amount of protein undegradable in the rumen averaged 47%, while it was 72% in the fish meal treatment. The supplements were isocaloric and isonitrogenous. Bulls were electroejaculated, and castrations were performed randomly in a predetermined order when the first ejaculate with the first motile sperm cells (Stage 1), 10 to 25 million (Stage 2), and 50 million or more sperm cells (Stage 3 - puberty) was obtained. Testicular and epididymal traits were analyzed for a single testicle and epididymis. Daily sperm production, daily sperm production per gram of testicular parenchyma, testicular weight and testicular parenchyma weight were not affected by treatment. Bulls receiving fish meal had heavier (P < 0.01) epididymis than soybean meal-fed bulls (6.6 +/- 1.0 vs 3.9 +/- 0.6 g) but similar (P > 0.05) epididymal sperm reserves. Daily sperm production (1 testicle) was 115.2 +/- 0.1, 447.4 +/- 0.1, 792.7 +/- 0.1 million sperm cells, and daily sperm production per gram of testicular parenchyma was 1.5 +/- 0.5, 3.2 +/- 0.6 and 6.4 +/- 0.6 million sperm cells for bulls at Stage 1, 2 and 3, respectively. Sire and amount of undegradable intake protein had significant (P < 0.05) affects on the distribution of epididymal sperm reserves, with soybean meal-fed bulls having the higher proportions of epididymal sperm reserves in the cauda epididymis.

The effect of aspirin administration and parity on plasma salicylate concentrations and postpartum reproductive parameters in Brahman cows

Forty pluriparous (M) and 20 primiparous (P) suckled Brahman cows were used to evaluate the effect of aspirin and parity on plasma 13,14-dihydro-15-keto-prostaglandin F2alpha (PGFM) and progesterone (P4) concentrations and some reproductive parameters. On Day 7 after calving (PP), the cows were allocated within parity into 2 groups: the aspirin group received concentrate containing aspirin at a rate of 100 mg/kg of body weight every 12 h until Day 13 PP; and the control received concentrate every 12 h for the same interval. Blood samples were collected after first and last aspirin feeding and daily from Day 1 PP to Day 6 PP and from Day 14 PP to Day 21 PP, twice daily from Day 7 PP to Day 13 PP, and weekly until first non-return to estrus. Plasma salicylate concentrations in the aspirin group cows were affected by parity (P < 0.01) and time after feeding (P < 0.0001). P cows showed higher plasma salicylate concentrations with a later peak and slower decrease than M cows. Aspirin-treated P cows had longer PP intervals than either control P, control M, or aspirin-treated M cows. Cows receiving aspirin had a lower pregnancy rate, an increased incidence of abnormal estrous cycles, and a decline in the presence of corpora lutea after estrus. Cows that formed a corpora lutea and had received aspirin had higher P4 release between Day 6 and 14 after estrus. Aspirin-treated cows that did not form corpora lutea had lower P4 release between Days 9 and 14 after estrus. A treatment by parity interaction affected mean PGFM proportions (P < 0.01) during the treatment period. Aspirin-fed P cows increased PGFM release as measured by mean proportion of Day 6 PP values. Aspirin-fed M cows showed a decrease in mean PGFM proportions. Aspirin feeding during the early PP showed different effects on some reproductive parameters in P and M Brahman cows, indicating differences in PP physiology between parities.