Effects of vaccination against 18 immunogens in beef replacement heifers at weaning.

Humoral immune responses to vaccination, mean daily body-weight gains, morbidity, and mortality were compared in groups of beef replacement heifers from weaning to 4 months after weaning. The only difference in management among groups of heifers was the number and type of vaccines they received. Heifers were vaccinated at weaning (mean age, 205 days) and again 28 days later against 0, 1, 9, 10, 17, or 18 antigens, using commercially available monovalent and multivalent vaccines. The common vaccine component in all treatment groups was a modified-live bovine respiratory syncytial virus. Mean daily gain, morbidity, mortality, and serum neutralization antibody titers to bovine respiratory syncytial virus did not differ among treatment groups. Although the study revealed the safety of vaccinating beef heifers against 18 antigens at weaning, our data emphasized the need for serial vaccination to induce a measurable serum antibody response.     

Body weights at weaning and 18 months of Zebu, Brown Swiss, Charolais and crossbred heifers in south-east Mexico

The objective of this study was to evaluate the body weights up to 18 months of age of 12 breed groups of Zebu (Z), Brown Swiss (BS) and Charolais heifers (CH), and their crosses under tropical conditions. A total of 1434 data on weaning weights adjusted to 240 days (WW8), average daily gain to 240 days (ADG8) and 1025 body weights adjusted to 550 days (BW18) and average postweaning daily gain (ADG18) of heifers born from 1981 to 1995 were used. Cows and calves remained together from birth to weaning and grazed on Guinea grass (Panicum maximum). Years of birth were grouped in three periods, because of the small numbers of observations per year (1981–85, 1986–90 and 1991–95). Similarly, months of birth were grouped in three seasons: dry (February to May), rainy (June to September) and windy and rainy (October to January). Ages of dams were classified in six groups (≤3, 4, 5, 6, 7 and ≥8 years). Breed groups were animals with 12.5%, 25.0%, 50.0%, 62.5%, 75.0% and 100% BS genes and 25.0%, 50.0%, 75.0% and 100% CH genes and also Z and undefined crossbred animals. Data were analysed using a fixed model that included effects of period, and season of birth, age of dam and breed group of heifer. Analyses of variance showed significant (p < 0.05) effects of period, season and breed group for all traits. However, parity was significant (p < 0.05) only for WW8 and ADG8. Interactions among main factors were not significant (p > 0.05). Z heifers gained the least weight to weaning but were similar to BS at 18 months of age. CH were heavier at 18 months of age than BS heifers, but not at weaning. Body weights at 18 months of age of 1/8 and 1/4 BS crossbred heifers were similar (p > 0.05) and lower than F₁ (BS × Z) (p < 0.05); however, the later and higher grades of BS had the highest body weights at 18 months of age and were similar to CH and 1/4 CH × 3/4 Z heifers. Undefined crossbred heifers had better performance than the Z breed group. Environmental factors were important sources of variation for pre‐ and postweaning traits. Under the conditions of this study, crossbred heifers generally performed better than Z heifers up to 18 months of age.     

Dynamics and diagnostic use of ALP activity in the blood of cattle exposed to a temperature of 56 degrees C

Possibilities of the diagnostic utilization of determined thermostable portion of the ALP activity in bovine serum were studied. The work is based on the finding that the total ALP activity is formed by two fractions with different sensitivity to the temperature of 56 degrees C. Dynamics of the loss of ALP activity during serum heating was of an equal character in all four tested groups. The loss was always highest during the first minutes of heating, after 15 to 20 minutes it became equal. A period of 15 minutes of the serum heating is sufficient for obtaining information on the size of the ALP thermostable fraction. The ALP activity and its residue after 15-minute thermal inhibition (thermostable portion) were tested in the sera of 163 head of cattle divided into seven groups. The size of this residue was related to the age of animals, degree of gravidity did not affect the residue. The thermostable portion in 6 to 10 months old bullocks was 14.86 +/- 4.93%, in 2.5 to 5 years old heifers 41.20 +/- 20.37% and in clinically healthy dairy cows 54.35 +/- 18.26%. In a group of calved breeding cows 44.13 +/- 19.74% of the initial activity remained. Determination of the thermostable ALP fraction can be applied with certain limitation in pre-clinical diagnostics of disorders of mineral metabolism in bones of cattle. In herds of healthy dairy cows the value of thermostable portion should not be lower than 45% of the original ALP activity. In 2.5 to 3 years old heifers this level is considered to be 35%.     

Effect of management factors and blood metabolites during the rearing period on growth in dairy heifers on UK farms

Growth rates during rearing affect the age and body weight (BW) of replacement heifers at first calving. Diet and disease can affect growth via altered metabolic hormone concentrations, but are difficult to monitor accurately on commercial farms. This study investigated the effect of management and metabolic indices (IGF-I, insulin, glucose and urea) on the growth rate of 509 Holstein-Friesian heifers on 19 UK dairy farms. Size (BW, heart girth, height and crown-rump length) was measured at approximately 1, 6 and 15 months. The mean daily weight gain up to 6 months for all calves was 0.77 kg/day, with extreme variability both between cohorts of calves (range 0.49–1.02 kg/day) and between individual calves within farms (range 0.45–1.13 kg/day). Growth was enhanced by supplemental colostrum, by milk replacer as opposed to whole milk and by ad libitum milk feeding and was reduced by gradual weaning and dehorning after weaning. Larger group size slowed growth before weaning (>6 calves) but increased it post-weaning (>20 calves). These management differences were reflected in altered plasma IGF-I concentrations, which were positively associated with growth throughout the rearing period. Larger calves at 1 month had a greater weight gain up to 6 months. Sub-optimum growth of some heifers within each cohort was established at an early age and resulted in animals reaching the start of breeding at an inadequate size (BW range 209–498 kg at 15 months). This could be alleviated by altered management strategies and improved monitoring of growing heifers.     

Relative calving date of first-calf heifers as related to production efficiency and subsequent reproductive performance

Relative date of first calving of beef heifers was studied in relation to production efficiency and subsequent reproductive performance. Crossbred heifers were managed in a drylot environment for 1 yr with feed intake measured through weaning of the first calf. Mean heifer age at entry into drylot was 572 d. Production traits were evaluated by calving group (CG), where CG1 included records of heifers calving (and calves born) in the first 21 d of the calving season for a particular year, CG2 included those calving from 22 through 42 d and CG3 included those calving after 42 d. Calving groups did not differ significantly for preweaning calf ADG, but weaning age differences resulted in heavier weaning weights for CG1 compared with CG2 and CG3. An earlier relative calving date was associated with increased cumulative feed energy intake of heifers and their calves during the 1-yr test period. In terms of production efficiency, the weaning weight advantage of earlier calving was offset only partly by the increased feed energy intake of the dam-calf unit, resulting in 6.3 Mcal (12.4%) less ME per kg calf weaning weight for CG1 vs CG3 for the 1-yr period. Within a limited calving season, earlier calving dams tended to be biologically and economically more efficient because a greater proportion of their annual production cycle was in a productive (lactating) mode, diluting maintenance costs as a fraction of all costs. Heifers in CG1 also tended to calve earlier than CG3 heifers for the second calf. Calving interval was a biased measure under the management conditions of a limited breeding season and culling of open cows.     

Effect of rate and time of gain after weaning on the development of replacement beef heifers

Three experiments were conducted during three consecutive years to compare rate and time of gain of weaned heifer calves on growth, reproductive development and future calf production. Three groups of Angus X Hereford heifers were fed in one of the following regimens from 45 d after weaning until breeding: (1) no gain the first one-half of the development period followed by .91 kg x head-1 x d-1 gain the last one-half; (2) .45 kg x head-1 x d-1 gain the entire trial and (3) .91 kg x head-1 x d-1 the first one-half of the development period and no gain the last one-half. The same diet was fed to all heifers, but the intake was varied to meet weight gain requirements. Wither height and heart girth increased (P less than .05) during the periods the heifers were fed to gain weight. By the end of the feeding trials, there were not differences (P greater than .05) in any of the growth measures. There were no differences (P greater than .05) in age at puberty, conception rate or calf production the following year. Adequate growth and development of replacement heifers is necessary, but much latitude exists in the rate and time of growth between weaning and breeding.     

Beef heifer development within three calving systems

A 3-yr study was conducted to evaluate the effects of calving system, weaning age, and postweaning management on growth and reproduction in beef heifers. Heifer calves (n = 676) born in late winter (average birth date = February 7 +/- 9 d) or early spring (average birth date April 3 +/- 10 d) were weaned at 190 or 240 d of age, and heifers born in late spring (average birth date May 29 +/- 10 d) were weaned at 140 or 190 d of age. Heifers were managed to be first exposed to breeding at approximately 14 mo of age. After weaning, the calves were randomly assigned to treatments. Heifers on the constant gain treatment were fed a corn silage- and hay-based diet. Heifers on delayed gain treatments were placed on pasture but were fed grass hay or a supplement, or both, depending on the forage conditions. Three months before their respective breeding seasons, delayed gain heifers were moved to drylot and fed a corn silage- and barley-based diet (late winter or early spring) or moved to spring rangeland (late spring). The data were analyzed using mixed model procedures with calving system, weaning age, and postweaning management options creating 12 treatments. Average daily gain was 0.36 +/- 0.05 (SED) kg/d less (P < 0.001) for delayed gain heifers during the initial phase, whereas these heifers gained 0.44 +/- 0.03 kg/d more (P < 0.001) than constant gain heifers during the last 90 d before breeding. Body weights at the beginning of the breeding season did not differ (P = 0.97) between constant gain and delayed gain heifers but were affected by calving system and weaning age, reflecting some of the differences in initial BW. Prebreeding BW for heifers weaned at 190 d of age were 36 +/- 6.4 kg heavier (P < 0.001) for those born in late winter and early spring compared with late spring and were 388, 372, and 330 kg for heifers weaned in October at 240, 190, or 140 d of age (linear effect, P < 0.001). The proportion of heifers exhibiting luteal activity at the beginning of the breeding season was not affected (P = 0.57) by treatment. Approximately half of the heifers were randomly selected for breeding. Treatment had no effect (P = 0.64) on pregnancy rates. In conclusion, heifers from varied calving systems and weaning strategies can be raised to breeding using either constant or delayed gain strategies without affecting the percentage of heifers cycling at the beginning of the breeding season. These results suggest that producers have multiple options for management of heifer calves within differing calving systems.     

Correlation of serum alkaline phosphatase activity with the healing process of long bone fractures in dogs

BACKGROUND: Bone healing is monitored mainly by physical and serial radiologic examinations of the fracture site. However, it is sometimes difficult to distinguish a delayed union from a nonunion, and advanced imaging techniques may not be available. Serum biochemical markers of bone formation, such as alkaline phosphatase (ALP) activity, may be clinically useful in evaluating the progress of healing. OBJECTIVE: The purpose of this study was to correlate serial values of serum ALP activity with the process of fracture healing in dogs and to assess its potential as a postsurgical prognostic indicator. METHODS: Changes in serum ALP activity were studied in 83 dogs with closed long bone diaphyseal fractures treated surgically. Physical and radiologic examinations of the fracture site and determination of serum ALP activity and calcium (Ca) and phosphate (P) concentrations were performed on admission (day 0); postoperatively on days 10, 20, and 30; and subsequently on a monthly basis until bone union was completed or signs of nonunion were evident. The dogs were allocated into 3 groups with respect to the fracture healing progress as documented by physical and serial radiologic examination. RESULTS: Group A dogs (n=35) developed a medium-sized callus that led to bone union within 2 months. Group B dogs (n=36) had a hypertrophic callus and delayed union, within 3-5 months. Group C dogs (n=12) had slow progress in fracture healing, with minimal callus formation during a 2-month period. Changes in mean serum ALP activity followed the same pattern in groups A and B, reaching a maximum level on day 10. Group A values returned to normal within 2 months, at which point bone union was complete, whereas group B values remained increased and returned to normal within 3-5 months, thus correlating with delayed union. In Group C, mean serum ALP activities showed no significant changes during the 2-month follow-up period, consistent with failure of bone union (nonunion). Serum P and Ca changes followed a proportional and inverse pattern to ALP changes, respectively. CONCLUSION: Serial determination of serum ALP activity during fracture healing could be an additional tool in predicting fractures at risk of developing a nonunion, helping the clinician to choose the appropriate intervention.     

Housing, feeding and management of calves and replacement heifers in Swedish dairy herds

A questionnaire was sent to 1500 randomly selected dairy herds in Sweden, asking for general information about the herds, including routines from birth to first calving and also routines at breeding, calving and during the grazing period. Fifty-eight percent of the questionnaires were returned. The preweaned calves were kept in individual calf pens in 68% and in group housing systems in 28% of the herds. Pens with slatted floors were the main housing system for replacement heifers from weaning to breeding, and tie stalls from breeding to first calving. Whole milk was used in 44% and milk replacements in 42% of the herds. The calves received, as a median, 2.5 litres of milk per meal and 2 meals per day. The median age at weaning was 8 weeks. Age was the single most common criteria used for deciding both weaning and breeding time. The median age when the heifers were first turned out to pasture was 6 months. Prophylactic anthelmintic treatment was used by 65% of the herds. The most common diet for replacement heifers before calving was a combination of grain, hay and silage.     

The effect of parasite control on fertility in beef heifers

The effect of anthelmintic treatment on the growth and conception rate in beef heifers was studied in southwestern Virginia, USA. Forty mixed-breed heifers were divided into two groups at weaning and placed on experimental pastures. Control heifers did not receive anthelmintic treatment, while animals in the treatment group were given ivermectin (200 μg kg⁻) at the time of allocation to groups in October and again in April the following year. Supplemental feed was provided throughout the winter to ensure adequate weight gains. In May, the heifers were exposed to bulls for natural breeding for a period of 6 weeks. Weight gains, fecal egg counts, serum pepsinogen levels and pasture larvae counts were monitored throughout the experiment. No difference in conception rate was observed between the two groups, although the cumulative weight gain was significantly greater in treated than non-treated animals. Serum pepsinogen levels and fecal egg counts were also generally lower in treated than non-treated heifers.     

断奶应激对犊牛血液生化、免疫和内分泌的影响

选择体质量和出生日期接近的26头犊牛,其中6头母犊,20头公犊。10日龄开始补充苜蓿干草、精饲料自由采食,60日龄断奶。分别在断奶前（-1d）和断奶后1,3,5,7,14d采集血液,测定血清中代谢物、激素及免疫球蛋白含量的变化情况。结果表明,断奶影响犊牛的消化代谢,血清中葡萄糖、总蛋白、尿素氮、甘油三酯含量变化显著（P〈0.01）。断奶造成犊牛血清皮质醇、急性反应蛋白、T3、T4、乳酸脱氢酶、碱性磷酸酶、溶菌酶显著变化（P〈0.01）,使免疫球蛋白、γ-IFN、IL-1含量有不同程度下降（P〉0.05）。因此,断奶不仅降低了犊牛的免疫力,而且对犊牛产生了严重的应激反应。     

Influence of age and sex on serum osteocalcin concentrations in horses at weaning and during physical conditioning

Three experiments were conducted to evaluate serum osteocalcin concentrations in normal weanling and yearling Quarter Horses. In Experiment 1, jugular blood samples were taken at 3 hr intervals for 24 hr to evaluate diurnal changes in serum osteocalcin concentration of foals (n=3) and yearlings (n=5). In Experiment 2, twelve Quarter Horse foals were weaned at 4 months of age to determine the influence of sex, weaning and method of weaning of serum osteocalcin concentration. The third experiment utilized fifteen yearling Quarter Horses (7 geldings, 8 fillies) in a two-phase trial to evaluate normal peripheral osteocalcin concentration in sedentary and exercising horses. In Experiment 1, there was no detectable variation (P>.05) in serum osteocalcin concentration during the 24 hr sample period in either age group. In Experiment 2, colts had greater (P<.05) osteocalcin concentrations than fillies at weaning. Method of weaning did not alter mean serum osteocalcin concentration (P>.1). Serum osteocalcin concentrations declined (P<.05) in all horses following weaning but returned to preweaning levels within one week. In Experiment 3, sedentary horses had similar (P>.1) osteocalcin concentrations on d 0, 45 and 90. Serum osteocalcin concentrations of sedentary horses were not affected by sex (P>.1). During exercise, fillies had greater (P<.05) osteocalcin concentrations than geldings. Serum osteocalcin concentrations of all horses declined linearly (P<.0001) during the 90 d exercise period. Osteocalcin may be useful as a tool to assess bone metabolism during growth and physical conditioning in horses. However, variability in serum osteocalcin concentrations due to age, sex and level of activity suggest that these factors must also be considered.     

The effects of late gestation nutrient restriction of dams on beef heifer intake,metabolites and hormones during an ad libitum feeding trial

This study's objective was to determine if nutrient restriction during late gestation affected beef heifer feed intake, body weight (BW) gain and endocrine regulation during a 10‐week feeding trial. During the last 100 days of gestation, control (CON) dams were fed to increase body condition score (BCS). Whereas, nutrient‐restricted dams (NR) and NR dams protein supplemented 3 days/week (NRS) were fed to decrease BCS by 1.2. After parturition, all cow‐calf pairs were moved to a common pasture and fed in excess of requirements until weaning. At 15 months of age, heifers were randomly sorted into two pens and adjusted to a commercial total mixed ration over a 2‐week period. Blood samples and BW were taken at the initiation of feeding and on a biweekly basis for the duration of the feeding trial. Feed intake was monitored for 10 weeks using a GrowSafe System. After 10 weeks, an intravenous glucose tolerance test (IVGTT) was performed on 21 randomly subsampled heifers. During the feeding trial, NR heifers consumed more feed than CON and NRS heifers. Heifers from NR dams tended to increase BW compared to NRS and CON heifers when adjusted for initial BW. Heifers from NR and NRS dams had a greater increase in BCS compared to heifers from CON dams. Plasma glucose and insulin concentrations during the feeding trial increased in NR heifers compared to the other groups beginning at 2 and 4 weeks respectively. Plasma leptin concentrations were increased in the NR and NRS heifers compared to the CON heifers beginning at week 4 of feeding. During the IVGTT at the conclusion of the feeding challenge, plasma glucose and insulin were increased in NR heifers compared to other treatment groups. These results show that nutrient restriction during late gestation alters appetite and endocrine regulation in heifer offspring.     

Follicular Dynamics in Heifers during Pre-pubertal and Pubertal Period Kept under Two Levels of Dietary Energy Intake

The objective of this study was to characterize follicular dynamics in pre-pubertal, pubertal and post-pubertal periods, as well as the effect of high-energy intake on follicular development and age at puberty in heifers. Thirty-one Nelore (Bos indicus) heifers, 6 months old, were randomly assigned to receive two different diets: one of low (GI) and other of high dietary energy intake (GII). Animals were evaluated in relation to body weight gain by being weighed every 21 days. Heifers were evaluated every other day by real-time linear ultrasonography to characterize ovarian structures development from weaning to post-pubertal period. Blood samples were collected to determine plasmatic concentrations of progesterone by RIA method. The ovulation was determined when progesterone concentrations were >1 ng/mL in three consecutive samples, and by ultrasound images of corpus luteum; and oestrous behaviour in some animals. Age at puberty differed among heifers of GII (17.00 +/- 0.46 months) compared with heifers of GI (19.87 +/- 0.47 months; p < or = 0.05). Maximum size of the dominant follicles at pre-pubertal period was greater in GII heifers than in GI (10.52 +/- 0.33 and 9.76 +/- 0.15 mm, respectively; p < or = 0.05). As heifers approached first ovulation time, size of dominant follicle increased (11.75 +/- 0.37 mm for GI and 12.52 +/- 0.91 mm for GII; p < or = 0.05). Body weight at puberty was not different in both groups (302.33 +/- 27.31 kg for GI and 326.19 +/- 27.78 kg for GII heifers; p > 0.05). We conclude that animals receiving high dietary energy intake attained the puberty earlier and the development of follicles were different than in low dietary energy intake.     

Beef heifer production as affected by indoor feed intensity and slaughter age when grazing semi-natural grasslands in summer

Only limited knowledge exists on how to produce high-quality beef carcasses when the cattle also are grazing semi-natural grasslands for nature conservation purposes. The objectives of the two factorially-designed trials were to determine the effects of indoor feed intensity (low vs. high) and slaughter age (18 vs. 22 months) on performance and carcass quality of beef heifers, raised from weaning until slaughter and grazing semi-natural grasslands during growing seasons. In the first trial, 56 Charolais heifers were used of which 28 were fed only grass-clover silage ad libitum (low; CL), and another 28 heifers were fed 2.0 kg of grain daily in addition to the silage (high; CH). In the second trial, 28 Angus heifers were fed grass-clover silage at 80% ad libitum (low; AL), whereas another 28 heifers were fed silage ad libitum (high; AH). According to a national nature conservation score, the grazing pressure on the semi-natural grassland was classified as having been satisfactory to maintain the floristic diversity as no litter had been accumulated onto the sward. From weaning until slaughter, no difference in average daily gains (ADG) was found between the CH and the CL, whereas the AH had higher ADG than the AL (693 vs. 573 g, P < 0.001). Heifers in both trials had higher carcass weights and more fat, Charolais heifers also had better conformation and Angus heifers had higher dressing percentage at 22 months than at 18 months of slaughter age (P < 0.05). In conclusion, carcass traits in both trials were more affected by slaughter age than by feed intensity and desirable grazing effects were achieved on the pasture.     

Effect of antiparasitic treatment in beef replacement heifers

Two studies were conducted in western Canada to evaluate the impact of antiparasitic treatment on weight gain and reproductive performance in beef replacement heifers from weaning to first breeding. Treatment of heifers at weaning with ivermectin increased the rate of weight gain in comparison to treatment with fenthion. The feed efficiency of ivermectin-treated animals was also significantly better than those treated with fenthion. Increased weight was associated with an increased number of animals in estrus at the end of the feeding period for heifers receiving ivermectin. We concluded that treatment with ivermectin improved feed efficiency and weight gain in heifers from weaning to breeding. In turn, this weight gain appeared to be associated with an increased number of heifers in estrus.     

Postweaning growth and reproduction of beef heifers exposed to calve at 24 or 30 months of age in spring and fall seasons.

Angus and Angus x Hereford heifer calves born in spring or fall seasons were allotted by weight at weaning to be exposed to bulls for calving at either 24 or 30 mo of age. Comparisons were made 1) within birth season--heifers born in the same season were first exposed to bulls at either 14 to 16 or 19 to 22 mo of age and 2) within breeding season--heifers born in different but consecutive seasons (spring-fall or fall-spring) were exposed to bulls during the same season but at different ages. Spring-born heifers exposed for 30-mo calving were heavier (336 vs 302 kg) and taller (P less than .01) at breeding than those exposed for 24-mo calving. Also, more were observed in estrus and became pregnant (P less than .01) during a 21-d AI breeding period, but season-long (63 d) pregnancy rates were not different (86%). Fall-born heifers exposed for 24- or 30-mo calving were similar for weight, hip height, and body condition score (BCS) at breeding, but season-long pregnancy rates were 71 and 94%, respectively (P less than .01). Although fall-born heifers were heavier at weaning (P less than .01), spring-born heifers were heavier, taller, and had higher BCS at breeding (P less than .01), regardless of age. Within spring breeding seasons, breeding weight and initial reproduction were not affected by heifer age. Within fall breeding seasons, older heifers were larger (P less than .01) and had greater reproductive performance (P less than .05) than younger heifers. Age at breeding, irrespective of season, consistently affected (P less than .01) both hip height (116 vs 113 cm) and pelvic area (209 vs 178 cm2) for older vs younger heifers, respectively. These data indicate that heifers exposed for 30-mo first calving are heavier, taller, have larger pelvic area, and have greater reproductive performance than those exposed for 24-mo first calving.     

Dairy-heifer management in the Netherlands

The objective of this study was to describe the Dutch rearing performance of dairy heifers by the evaluation of performance indices at weaning, breeding and calving. The second objective was to determine the extent to which dairy farmers use pre-set rearing targets and data monitoring for the evaluation of their rearing results. A questionnaire was sent to 3000 randomly chosen dairy cattle farmers to survey their heifer-rearing practices. Almost a third of the farmers (n=959) completed and returned the questionnaire. Of the farms responding, 29% realised an age at first calving of < or =24 months, 51% from 25 to 27 months, and 20% of > or =27 months. The farmers indicated that the average body weight after calving was within the range 525-550 kg. Average wither height class was 141-145 cm. Most farmers estimated the body-condition score of their heifers at calving to be 3-3.5. In 29% of the cases, weaning occurred at an age of < or =8 weeks, 35% at 9-10 weeks of age and 36% at > or =11 weeks of age. Most farmers (81%) commenced breeding at an age of > or =15 months.Intermediate evaluation of the rearing policy by means of performance goals and measurements was limited, and many of the reported performance indices on age and body weight were outside the range of the recommended target values. These results indicated that the common Dutch heifer-rearing management system could be improved considerably.     

Hemodynamic responses of the caudal artery to toxic tall fescue in beef heifers

Color Doppler ultrasonography was used to compare blood flow characteristics in the caudal artery of heifers fed diets with endophyte (Neotyphodium coenophialum) infected (E+) or noninfected (E-) tall fescue seed. Eighteen crossbred (Angus x Brangus) heifers were assigned to 6 pens and were fed chopped alfalfa hay for 5 d and chopped alfalfa hay plus a concentrate that contained E-tall fescue seed for 9 d during an adjustment period. An 11-d experimental period followed, with animals in 3 pens fed chopped alfalfa hay plus a concentrate with E+ seed and those in the other 3 pens fed chopped hay plus concentrate with E E- seed. Color Doppler ultrasound measurements (caudal artery area, peak systolic velocity, end diastolic velocity, mean velocity, heart rate, stroke volume, and flow rate) and serum prolactin were monitored during the adjustment (baseline measures) and during the experimental period. Three baseline measures were collected on d 3, 5, and 6 during the adjustment period for comparison to post E+ seed exposure. Statistical analyses compared the proportionate differences between baseline and response at 4, 28, 52, 76, 100, 172, and 268 h from initial feeding of E+ seed. Serum prolactin concentrations on both diets were lower (P <0.001) than baseline beginning at 4 h from the start of the experimental period. However, trends in serum prolactin concentrations for heifers on the E- diet suggested ambient temperature was affecting these concentrations. Caudal artery area in E+ heifers had declined (P <0.10) from baseline by 4 h and was consistently lower (P <0.05) for the remainder of the period. Heart rates for E+ heifers were lower than the baseline rate from 4 (P <0.10) to 100 (P <0.001) h, but were similar (P >0.10) to the baseline for 172 and 268 h measures. Blood flow in E+ heifers was consistently lower than the baseline from 4 (P <0.05) to 172 (P <0.001) h, but was similar to the baseline at 268 h when heart rate was similar to the baseline rate. Caudal artery areas for the E- diet were similar to baseline areas except at 100 h when it was greater than baseline. Heart rates and flow rates for E- heifers did not differ (P >0.10) from baseline measures during the experimental period. Results indicated that onset of toxicosis was within 4 h of cattle exposure to E+ tall fescue and is related to vasoconstriction and reduction in heart rate.     

Evaluation of reproductive traits in Bos taurus and Bos indicus crossbred heifers: effects of postweaning energy manipulation

Reproductive traits were evaluated in Bos taurus and Bos indicus crossbred heifers that were fed different diets during the postweaning period. The study was designed in a 2 x 2 x 2 factorial arrangement of treatments. Angus x Hereford (AH; n = 148) and Brahman x Hereford (BH; n = 148) heifers were sorted after weaning by body weight into light (LW) and heavy (HW) weight blocks. Heifers in each weight block were assigned to diets calculated to reach a target weight of 55% (LE) or 65% (HE) of their projected mature weights by the start of the breeding season. Puberty was determined after a 160-d observation period and characterized by the following criteria: 1) behavioral estrus, 2) presence of a palpable corpus luteum (d 6 to 10; estrus = d 0), and 3) rise in serum progesterone above 1 ng/ml (d 6 to 10). A higher (P = .01) proportion of AH heifers than of BH heifers reached puberty by the breeding season (93% vs 67%). Interactions of breed x weight block and energy level x weight block also contributed to this difference. Weight at puberty was heavier (P = .001) among HE than among LE heifers and greater for heifers in HW than for those in LW blocks (P = .02). Differences in prebreeding weight, body condition, average daily gain, hip height, and pelvic area were influenced selectively by breed, energy level, or weight block. Pregnancy rates were higher (P = .01) among AH than among BH heifers. Incidence and severity of dystocia was influenced by the breed x energy level interaction (P = .01). Brahman x Hereford heifers had less (P = .01) dystocia than AH heifers, HE heifers had less (P less than .02) dystocia than LE heifers, and HE-AH heifers had less (P less than .01) dystocia than LE-AH contemporaries. Subsequent duration of the postpartum interval to estrus was shorter (P = .002) among AH than among BH females. Pregnancy rates at the end of the 2nd yr were higher (P = .02) among LW than among HW females and weights were heavier (P = .001) at weaning among calves weaned from BH dams.