A combination of nutrition and genetics is able to reduce age at puberty in Nelore heifers to below 18 months

Nelore heifers usually begin their reproductive life at ⩾24 months of age mainly due to suboptimal nutritional conditions and genetics. This study aimed to determine the effect of expected progeny difference (EPD) for age at first calving and average daily gain (ADG) on puberty in Nelore (Bos taurus indicus) heifers. A total of 58 weaned heifers (initial BW=174±6 kg; age=9±1 months) were allocated into 28 feedlot pens. Heifers were born from four sires, of which two had low EPD for age at first calving (L; n=33) and two had high EPD for age at first calving (H; n=25). Then, heifers of each EPD were randomly assigned to high ADG (HG; 0.7 kg) or low ADG (LG; 0.3 kg), resulting in four treatments: heifers from L sires were submitted to either HG (LHG; n=17) or LG (LLG; n=16), and heifers from H sires were submitted to either HG (HHG; n=12), or LG (HLG; n=13). The HG heifers were fed a 75% grain diet, whereas the LG heifers received 93% of forage in their diet. Blood samples were collected at 9, 14, 18, 24 and 28 months of age for IGF1 and leptin determination. There was a treatment effect (P<0.01) on the proportion of heifers that attained puberty by 18 (62%, 0%, 0% and 0%), 24 (100%, 6%, 54% and 0%) or 36 (100%, 100%, 100% and 38%) months of age for LHG, LLG, HHG and HLG treatments, respectively. In addition, mean age at puberty was different across treatments (P<0.01). Heifers from the LHG achieved puberty at the earliest age when compared with cohorts from other treatments (18.1, 28.9, 23.9 and 34.5 months for LHG, LLG, HHG and HLG, respectively). Serum IGF1 concentrations were higher for L heifers compared with H cohorts at 9, 14, 18, 24 and 28 months of age (P<0.01; treatment×age interaction), whereas circulating leptin concentrations were higher (P<0.01; age effect) as heifers became older, regardless of the treatments. In conclusion, only Nelore heifers with favorable genetic merit for age at first calving were able to attain puberty by 18 months of age. In heifers with unfavorable genetic merit for age at first calving, supplementary feeding to achieve high ADG was unable to shift the age at puberty below 24 months.     

Impacts of stocking density on development and puberty attainment of replacement beef heifers

In all, 60 Angus×Hereford heifers were ranked by age and BW (210±2 days and 220±2 kg) on day 0, and assigned to: (a) one of three drylot pens (10×14 m pens; 10 heifers/pen) resulting in a stocking density of 14 m²/heifer (HIDENS; n=3), or (b) one of three pastures (25 ha pastures; 10 heifers/pasture), resulting in a stocking density of 25 000 m²/heifer (LOWDENS; n=3). Pastures were harvested for hay before the beginning of this experiment, and negligible forage was available for grazing to LOWDENS heifers during the experiment (days 0 to 182). All heifers received the same limited-fed diet, which averaged (dry matter basis) 4.0 kg/heifer daily of hay and 3.0 kg/heifer daily of a corn-based concentrate. Heifer shrunk BW was recorded after 16 h of feed and water withdrawal on days −3 and 183 for BW gain calculation. On day 0, heifers were fitted with a pedometer behind their right shoulder. Each week, pedometer results were recorded and blood samples were collected for puberty evaluation via plasma progesterone. Plasma samples collected on days 0, 28, 56, 84, 112, 140, 161 and 182 were also analyzed for cortisol concentrations. On days 0, 49, 98, 147 and 182, hair samples were collected from the tail switch for analysis of hair cortisol concentrations. On days 28, 102 and 175, blood samples were collected for whole blood RNA isolation and analysis of heat shock protein (HSP) 70 and HSP72 mRNA expression. Heifers from LOWDENS had more (P<0.01) steps/week compared with HIDENS. No treatment effects were detected (P=0.82) for heifer BW gain. Plasma cortisol concentrations were greater (P⩽0.05) in LOWDENS compared with HIDENS heifers on days 84, 140, 161 and 182 (treatment×day interaction; P<0.01). Hair cortisol concentrations were greater (P<0.01) in HIDENS compared with LOWDENS heifers beginning on day 98 (treatment×day interaction; P<0.01). Heifers from LOWDENS had greater (P=0.04) mean mRNA expression of HSP72, and tended (P=0.09) to have greater mean mRNA expression of HSP70 compared with HIDENS. Heifers from HIDENS experienced delayed puberty attainment and had less (P<0.01) proportion of pubertal heifers on day 182 compared with LOWDENS (treatment×day interaction; P<0.01). In summary, HIDENS altered heifer stress-related and physiological responses, and delayed puberty attainment compared with LOWDENS.     

Creep-feeding to stimulate metabolic imprinting in nursing beef heifers: impacts on heifer growth,reproductive and physiological variables

This experiment compared growth, physiological, and reproductive responses of beef heifers with (MI) or without (CON) access to a creep-feeder, as a manner to stimulate metabolic imprinting while nursing their dams. On day 0, 60 Angus×Hereford heifers were ranked by BW and age (140±3 kg and 68±3 days), and assigned to pairs so all ranking criteria were similar between heifers within each pair. On day 1, pairs were randomly assigned to MI (n=15) or CON (n=15). From day 1 to 51, MI pairs and their dams were allocated to 15 drylot pens where heifers had ad libitum access to a corn-based supplement through a creep-feeder. The CON pairs and their dams were maintained in an adjacent single drylot pen. From day 52 to 111, treatments were managed as a single group on a semiarid range pasture. On day 111, heifers were weaned and allocated to two pastures (one pasture/treatment), receiving hay and a corn-based concentrate until day 326. Heifer BW was recorded before and at the end of the creep-feeding period (day 1 to 51), and on days 112 and 326. On days 0, 51, 111, 187, 261, and 325, jugular blood was collected and real-time ultrasonography for longissimus muscle depth and backfat thickness assessment was performed. Blood was also collected every 10 days from days 113 to 323 for puberty evaluation via plasma progesterone. Liver and subcutaneous fat biopsies were performed on days 51, 111, 261 and 325. Average daily gain was greater (P<0.01) for MI than CON from day 1 to 51, tended (P=0.09) to be greater for CON than MI from day 112 to 326, while BW on day 326 was similar between treatments. On day 51, MI had greater (P⩽0.01) plasma IGF-I and glucose concentrations, as well as mRNA expression of hepatic pyruvate carboxylase and adipose fatty acid synthase than CON. On days 261 and 325, plasma insulin concentrations were greater (P⩽0.03) in CON than MI. Mean mRNA expression of hepatic IGF-I and adipose peroxisome proliferator-activated receptor gamma were greater (P⩽0.05) in MI than CON. No treatment effects were detected for puberty attainment rate. In conclusion, supplementing nursing heifers via creep-feeding for 50 days altered physiological and biochemical variables suggestive of a metabolic imprinting effect, but did not hasten their puberty attainment.     

Genetic variability of the length of postpartum anoestrus in Charolais cows and its relationship with age at puberty

Fertility records (n = 1 802) were collected from 615 Charolais primiparous and multiparous cows managed in an experimental herd over an 11-year period. The objectives of the study were to describe the genetic variability of the re-establishment of postpartum reproductive activity and the relationship with body weight (BW) and body condition score (BCS) at calving and age at puberty. The length of postpartum anoestrus was estimated based on weekly blood progesterone assays and on twice daily detection of oestrus behaviour. The first oestrus behaviour was observed 69 days (± 25 days s.d.) post-calving and the first positive progesterone measurement (≥ 1 ng mL^-1) was observed at 66 days (± 22 days s.d.) for the group of easy-calving multiparous suckling cows. Estimates of heritability and repeatability were h² = 0.12 and r = 0.38 respectively, for the interval from calving to first oestrus (ICO). Corresponding values were h² = 0.35 and r = 0.60 for the interval from calving to the first positive progesterone test (ICP). The genetic correlation between both criteria was high (r_g = 0.98). The genetic relationships between postpartum intervals and BW and BCS of the female at calving were negative: the genetic aptitude to be heavier at calving and to have high body reserves was related to shorter postpartum intervals. A favourable genetic correlation between age at puberty and postpartum intervals was found (r_g between 0.45 and 0.70). The heifers which were genetically younger at puberty also had shorter postpartum intervals.     

Serum thyroid hormone concentrations during growth and puberty in Carora dairy heifers of Venezuela

The aim of this study was to characterize changes in serum concentrations of triiodothyronine (T(3)) and thyroxine (T(4)) in relation to growth and the onset of puberty in Carora heifers, a Venezuelan dairy breed. Heifers aged 7 to 16 months were grouped retrospectively according to puberty status into 4 groups: Pubertal (control group; n = 12) and nonpubertal (n = 8) contemporary (born during the same week) heifers, pubertal (n = 7.) and nonpubertal (n = 7) noncontemporary (born in different months) heifers. A split-plot model with repeated measures over Months 7 to 16 of age was used. Control heifers attained puberty at 290 +/- 5 kg body weight (BW) between 13 and 14 months of age. Significant (P < 0.01) interactions of birth time of year and puberty status were detected in BW and serum concentrations of T(3), but only interaction of birth time of year was found in T(4). A transient but significant (P < 0.05) decrease in T(3) secretion was seen in pubertal contemporary and noncontemporary (101 +/- 4 and 113 +/- 4 ng/d1, respectively) heifers at Month 12 of age, a change which could be critical to the onset of puberty. Significant (P < 0.05) positive correlation was found between BW and T(3). In summary, thyroid hormone secretion changed across the months of growing and around the onset of puberty in Carora heifers.     

Influence of age,body weight and body condition score before mating start date on the pubertal rate of maiden Holstein–Friesian heifers and implications for subsequent cow performance and profitability

The aim of this study was to assess the influence of age, body weight (BW) and body condition score (BCS) of maiden Holstein–Friesian heifers before mating start date (MSD) on the rate of puberty, subsequent production and longevity and their implications with regard to farm profitability. Data were available on 871 Holstein–Friesian heifers from 48 herds. BW was recorded electronically and BCS was recorded by a single operator on a scale of 1 to 5. Heifer age was calculated as the number of days from birth to the day of visit. All of the independent variables of interest were grouped into three or four categories. Three age categories (thirtiles), four BW categories (quartiles) and four BCS categories (⩽2.75, 3.00, 3.25 and ⩾3.50) were formed. Heifers with an identifiable corpus lutuem (CL) in the presence or absence of large follicles and peri-ovulatory signs and with a plasma progesterone (P4) concentration ⩾1 ng/ml were classified as pubertal. In addition, heifers without an identifiable CL in the presence or absence of large follicles and peri-ovulatory signs but with a P4 concentration ⩾1 ng/ml were also classified as pubertal. Age, BW and BCS at MSD were all found to be significantly associated with pubertal rate (P < 0.05). Age was shown to have no practical implications on subsequent cow performance. BW at MSD was favourably associated with subsequent calving date (P < 0.05), subsequent cow BW (P < 0.001) and potential (305 days) milk fat plus protein yield (P < 0.001). BCS at MSD was found to be favourably associated with milk fat plus protein yield potential (P < 0.05) and BCS (P < 0.001) during lactation. The economic analysis undertaken indicated that larger, well-grown heifers will be more profitable because of superior production potential, all else being equal. However, because of the finding of poorer reproductive efficiency in heifers grown to more than 343 kg at MSD, heifers at ∼330 kg at MSD are deemed optimal. This will correspond to mature cow BW of ∼550 kg.     

Effects of temperament on growth,plasma cortisol concentrations and puberty attainment in Nelore beef heifers

Excitable temperament disrupts physiological events required for reproductive development in cattle, but no research has investigated the impacts of temperament on growth and puberty attainment in Bos indicus females. Hence, this experiment evaluated the effects of temperament on growth, plasma cortisol concentrations and puberty attainment in B. indicus heifers. A total of 170 Nelore heifers, weaned 4 months before the beginning of this experiment (days 0 to 91), were managed in two groups of 82 and 88 heifers each (mean ± SE; initial BW=238±2 kg, initial age=369±1 days across groups). Heifer temperament was evaluated via exit velocity on day 0. Individual exit score was calculated within each group by dividing exit velocity into quintiles and assigning heifers with a score from 1 to 5 (1=slowest; 5=fastest heifer). Heifers were classified according to exit score as adequate (ADQ, n=96; exit score⩽3) or excitable temperament (EXC, n=74; exit score>3). Heifer BW, body condition score (BCS) and blood samples were obtained on days 0, 31, 60 and 91. Heifer exit velocity and score were recorded again on days 31, 60 and 91. Ovarian transrectal ultrasonography was performed on days 0 and 10, 31 and 41, 60 and 70, 81 and 91 for puberty evaluation. Heifer was declared pubertal at the first 10-day interval in which a corpus luteum was detected. Exit velocity and exit score obtained on day 0 were correlated (r⩾0.64, P<0.01) with evaluations on days 31, 60 and 91. During the experiment, ADQ had greater (P<0.01) mean BCS and BW gain, and less (P<0.01) mean plasma cortisol concentration compared with EXC heifers. Temperament × time interactions were detected (P<0.01) for exit velocity and exit score, which were always greater (P<0.01) in EXC v. ADQ heifers. A temperament × time interaction was also detected (P=0.03) for puberty attainment, which was delayed in EXC v. ADQ heifers. At the end of the experiment, a greater (P<0.01) proportion of ADQ were pubertal compared with EXC heifers. In summary, B. indicus heifers classified as EXC had reduced growth, increased plasma cortisol concentrations and hindered puberty attainment compared to ADQ heifers. Moreover, exit velocity may serve as temperament selection criteria to optimize development of B. indicus replacement heifers.     

Influence of perioestrous suprabasal progesterone levels on cycle length,oestrous behaviour and ovulation in heifers

In order to induce suprabasal plasma concentrations of progesterone after luteolysis and to determine their effect on oestrous behaviour and ovulation, heifers subcutaneously received silicone implants containing 2.5 (n = 4), 5 (n = 4), 6 (n = 3), 7.5 (n = 3) or 10 (n = 4) g of progesterone, or an empty implant (controls, n = 5) between days 8 and 25 of the cycle (ovulation designated Day 0). Growth of dominant follicles and time of ovulation were determined by ultrasound, and signs of oestrus were recorded and scored. Blood was collected at 2–4 h intervals from Days 15 to 27 and assayed for progesterone concentration. In all heifers, plasma concentrations of progesterone sharply decreased during Days 16–18. Control heifers had their lowest progesterone levels on Days 20.5 and 21, standing oestrus on Day 19.5 ± 0.4 (mean ± SEM), and ovulated on Day 20.7 ± 0.4. A similar pattern was observed in heifers treated with 2.5 and 5 g progesterone. Heifers treated with 6, 7.5 and 10 g of progesterone showed an extended (P < 0.05) interovulatory interval. Onset of prooestrus and time of maximum expression of signs of oestrus were not significantly different from those in controls. However, there was an absence of standing oestrus in most of the cases, signs of oestrus lasted longer (P < 0.05) and were weaker in intensity when doses increased. In these groups, the lowest progesterone concentrations were attained shortly after implant removal. Some heifers treated with 6 and 7.5 g of progesterone had standing oestrus and post oestrous bleeding as seen in the controls but ovulation occurred from Days 24.5 to 27. When plasma progesterone concentrations were over 1 nmol 1⁻¹, disturbed oestrus and delayed ovulation occurred. The extended period of prooestrus and oestrus and delayed ovulation were similar to that described in cases of repeat breeding. It is suggested that suprabasal plasma concentrations of progesterone, after luteolysis, may lead to asynchrony between onset of oestrus and ovulation and consequently be a cause of repeat breeding in cattle.     

Treatment with 17β-oestradiol does not influence age and weight at puberty in Bos indicus heifers

The working hypothesis was that treatment of heifers with 17β-oestradiol (E₂) during specific periods of prepuberty would reduce the response of the hypothalamic–pituitary axis to E₂ negative feedback and induce an earlier onset of puberty. The effects of chronic treatment with exogenous E₂ administered at specific maturational phases on the age and weight at puberty were studied in 96 prepubertal Brahman (3/4–7/8 Bos indicus) heifers (187.0±3.3 days of age, mean±SEM), weighing 149.9±2.5 kg. Heifers were randomly assigned to one of six groups (n=16 per group). Groups 2–6 received E₂ implants (Compudose 200®) for 90-day periods starting at 10, 13, 16, 19 and 22 months of age, while animals in group 1 remained untreated. Implants were placed subcutaneously at the base of the ear. Blood was collected for progesterone (P₄) determination by radioimmunoassay (RIA) and the animals were weighed at monthly intervals from 6 to 15 months then weekly from 15 to 28 months of age. Puberty was defined by concentrations of P₄>1 ng/ml in plasma and identification of a corpus luteum (CL) by transrectal ultrasonography (Aloka 210DX:7.5 MHZ probe). Treatment with exogenous E₂ at any of the ages/treatment intervals evaluated in this study did not reduce age or weight at puberty (P>0.7). The mean age and weight at puberty of control heifers was 735.3±19.7 days (range: 597–861) and 299.2±10.2 kg (range: 233–382), respectively, which is greater than the age and weight at puberty of 481 days and 246 kg, that was previously reported for B. indicus heifers [Post, T.B., Reich, M.M., 1980. Puberty in tropical breeds of heifers as monitored by plasma progesterone. Proceedings of the Australian Society of Animal Production 13, 61–62.]. The large variation in age and weight at puberty that was observed in the present study among heifers might indicate an individual animal effect to E₂ treatment among some of the treated animals. The lengthy interval from birth to puberty observed in this study, as compared to other studies, reflects the effects of other factors such as genotype, environmental or nutritional influences on puberty.     

Profiles of growth hormone and insulin secretion, and glucose response to insulin in growing Japanese Black heifers (beef type): comparison with Holstein heifers (dairy type)

Nine Japanese Black and 10 Holstein heifers ranging from 1 week (wk) to 18 months (mo) old received a single bolus intravenous injection of GH-releasing factor (GRF, 0.25-microg/kg BW), glucose (112.5-mg/kg BW) or insulin (0.2-U/kg BW) at various stages through 18 mo of age. The GH secretory response to exogenous GRF in Japanese Black heifers was lower than that in Holstein heifers at all stages of growth. While insulin secretory function was not very different in both breeds from 1 to 12 mo of age, the insulin response was much higher in Japanese Black heifers than in Holstein heifers after sexual maturation. The degree of decrease in plasma glucose following insulin injection was similar in both breeds at each stage of growth. It is concluded that compared with Holstein heifers, Japanese Black heifers have lower GH and higher insulin secretory functions, and that the two breeds have similar glucose response to insulin.     

Age, body weight and backfat thickness at first observed oestrus in crossbred Landrace x Yorkshire gilts, seasonal variations and their influence on subsequence reproductive performance

The objective of the present study was to investigate puberty attainment in crossbred Landrace x Yorkshire (LY) gilts reared under tropical conditions and their subsequent reproductive performance. This study was carried out in a 2400-sow herd over a 1-year period. A total of 696 crossbred LY replacement gilts were included. Faecal samples from 214 gilts were collected to determine the faecal progesterone profiles around the time of first oestrus. Solid-phase 125I-radioimmunoassay was used to determine the progesterone concentrations in the faecal extract. The gilts entered the herd at an average age of 177.5 +/- 12.6 days, 95.7 +/- 10.2 kg body weight (BW) and a backfat thickness (BF) of 12.0 +/- 2.9 mm. On average, the gilts expressed first standing oestrus at 195 days of age, 106 kg of BW and a BF of 13.0 mm. The interval from entry to the gilt pool to the first observed oestrus (EOI) was 24.4 +/- 18.0 days (range 0-88 days). The hormonal profile indicated that the gilts that actually ovulated during the first observed oestrus was 34% (group A), the gilts that had ovulated before the first observed oestrus was 21% (group B) and the gilts that did not ovulate during the first observed oestrus was 45% (group C). During summer the proportion of group A gilts was significantly lower than during the winter and the rainy seasons (P < 0.05). The BW of gilts at entry significantly correlated with the BF at entry (r = 0.31, P < 0.001), the age at entry (r = 0.47, P < 0.001), the BW at first oestrus (r = 0.65, P < 0.001) and the BF at first oestrus (r = 0.33, P < 0.001). An increase of BW at entry of 1 kg resulted in a decrease of EOI of 0.28 days. The age, BW and BF of gilts at the first observed oestrus significantly influenced the total number of piglets born per litter (TB) and the number of piglets born alive per litter (BA) in the first three parities. Gilts expressing their first oestrus between 181 and 200 days had a significantly larger TB than gilts that expressed first oestrus between 150 and 180 days (P = 0.03) and between 201 and 220 days (P = 0.003). Gilts that showed first oestrus between 110.1 and 120.0 kg had a larger TB and BA than gilts that showed first oestrus between 80.0 and 100.0 kg (P < 0.05). Gilts that showed first oestrus with a BF between 13.1 and 15.0 mm had a larger TB and BA than gilts that showed first oestrus with a BF between 11.1 and 13.0 mm (P < 0.05). Group A gilts had a significantly larger TB than group B (10.5 piglets/L versus 9.4 piglets/L, P = 0.02), while farrowing rate (FR) did not differ significantly among groups A, B and C (78.1, 76.9 and 77.6%, respectively). Gilts that farrowed in the summer had a larger TB and BA than gilts that farrowed in the winter (TB, P = 0.03; BA, P = 0.09) and the rainy season (TB, P = 0.006; BA, P = 0.003). In conclusion, LY gilts reared under tropical conditions expressed first standing oestrus at 195 days of age, 106 kg BW and a BF of 13.0 mm. Under field conditions, 21% of the gilts with an observed oestrus had ovulated. The proportion of gilts that showed first oestrus and ovulated normally was lowest during the summer. The age, BW and BF at first observed oestrus influenced subsequent reproductive performance over the first three parities. The mean litter size (TB and BA) in the first three parities were highest in gilts that had a first observed oestrus between 181 and 200 days with 110.1-120.0 kg BW and 13.1-15.0 mm BF.     

Influence of age,weaning, season and body weight on the levels of progesterone,oestradiol-17β and luteinizing hormone in growing buffalo heifers (Bubalus bubalis)

The influence of age, weaning, season of the year and body weight on the peripheral levels of progesterone, oestradiol-17β and luteinizing hormone (LH) were studied during neonatal, perinatal and peripubertal periods in buffalo heifers. The buffalo heifers exhibited oestrus only after 30 months of age and had higher levels of LH and oestradiol-17β and a lower level of progesterone on the day of oestrus. The progesterone concentration was affected significantly (P < 0.01) by different seasons, by weaning (P < 0.05) and varied between pubertal and neonatal periods (P < 0.01), whereas the oestradiol-17β level was affected significantly (P < 0.01) by weaning and varied at different seasons and with body weight. However, the LH concentration was greater during the neonatal period than the pre- and peripubertal periods and changed significantly (P < 0.01) between groups of ages and body weights. The results suggest that increases in the levels of oestradiol-17β and progesterone after 30 months of age are probably indicative of the onset of puberty in buffalo heifers. However, a further increase in oestradiol-17β, LH, and a decrease in progesterone are essential for oestrus and cyclicity to be exhibited in buffalo heifers.     

Effect of supplemental light on growth,prolactin, progesterone and luteinizing hormone in water buffalo (Bubalus bubalis)

Fifty non-pregnant Surti buffalo heifers aged between 17 and 42 months (n=24, <24 months;n=26, >24 months) were randomly assigned to groups subject to either natural daylight +4h supplemental light (n=25) or natural day light (n=25), to study changes in growth, serum prolactin (Prl), progesterone (P₄) and luteinizing hormone (LH) to supplemental lighting. Ambient temperatures (T) and relative humidity (RH) generally were >27° C and <70% during the day-time, respectively. Light-supplemented heifers had 16.2 kg net body weight (BW) gain at 9 weeks compared to 20.8 kg for controls, but higher mean Prl after 6.5 weeks (P<0.01), and higher P₄ (0.41 vs 0.19 ng/ml;P<0.06) than control heifers. Older heifers had 39.7% greater BW (P<0.01), but a net 4.3% BW gain compared to a 10.1% gain for younger heifers at 10 weeks. Older, light-supplemented heifers had higher mean P₄ (0.63 vs 0.19 ng/ml;P<0.07) than the other groups. These weight and hormonal changes suggest that 4 h supplemental light can alter growth and endocrine function in buffaloes under similar planes of nutrition. While light supplementation did not have a positive effect on body wieght during the 10 week study, body weight and endocrine changes due to supplemental light may be important factors for initiation of reproductive cyclicity.     

Metabolic and reproductive characteristics of replacement beef heifers subjected to an early-weaning regimen involving high-concentrate feeding

In an effort to better understand the consequences of early weaning (EW) for replacement beef heifers, a two-phase experiment was conducted investigating the impact on metabolic function and documenting reproductive characteristics. In phase 1, Angus×Simmental heifers (n=35) were stratified by BW and sire, and randomly assigned to either a normal weaning (NW, n=18) or EW (n=17) treatment. EW heifers were weaned at 107±3 days of age and provided access to a concentrate-based ration ad libitum with limit-fed mixed grass hay. NW heifers remained with their dams until 232±3 days of age, at which point heifers from both treatments were comingled and grazed on mixed summer pasture. Following NW, weekly blood samples were collected from all heifers for progesterone analyses used to determine the onset of puberty. Pelvic and ovarian size was measured before breeding. All heifers were subjected to an estrous synchronization protocol with timed artificial insemination (AI) at 437±4 days of age. During phase 2 of the experiment, a subset of pregnant heifers (n=16) were divided into two replicates and subjected to a glucose tolerance test, epinephrine challenge and progesterone clearance analysis. Neither age nor BW at puberty differed between EW and NW heifers. Likewise, no differences in pelvic area or ovarian size were observed. Thus, it appears that the reproductive maturity of EW and NW heifers was similar. Heifers studied during phase 2 of the experiment were restricted to those that had become pregnant to their first AI. Within this cohort, EW heifers tended to have lower overall circulating progesterone concentrations than those that were NW (P=0.14). Aspects of glucose and insulin dynamics were also altered, as EW heifers tended to have lower baseline glucose concentrations (P=0.10) despite similar baseline insulin concentrations. Compared with NW heifers, EW heifers had lower insulin area under the curve (P<0.05), which was partly the result of a tendency for lower peak insulin concentrations (P=0.11). Results of the glucose tolerance test indicate that a lesser insulin response was necessary to properly clear the glucose in the EW heifers, suggesting enhanced insulin sensitivity. Collectively, these results indicate that EW is not detrimental for the growth or reproductive development of replacement beef heifers, although some differences in glucose and insulin dynamics persist into adulthood.     

Effect of dietary energy and protein density on body composition,attainment of puberty,and ovarian follicular dynamics in dairy heifers

The objectives were to examine the effects of dietary energy and protein density on age and body composition at puberty, and on ovarian follicular dynamics during the pre- and peripubertal periods in Holstein heifers. In Phase 1, heifers were randomly allotted (n=10 per diet) at 100 kg body weight (BW) to diets with either low (P1L), medium (P1M) or high (P1H) energy and protein formulated for an average daily gain (ADG) of 0.5, 0.8 or 1.1 kg per day, respectively. During Phase 2 (P2), all heifers were fed ad libitum a common diet formulated for an ADG of 0.8 kg per day. Half the animals within the high (n=5) and low groups (n=5) entered P2 either at 12 months of age (P2H-12; P2L-12) or at 330 kg BW (P2H-330; P2L-330). Heifers fed P1H, P1M, P1L, and P2L-12 diets attained puberty at approximately 9, 11, 16, and 14 months of age, respectively (P<0.01). Urea space estimates of body fat and protein percent, and back-fat thickness, were lower in P1L heifers compared to P1H or P1M heifers at similar chronological ages (P<0.05) but did not differ at puberty (P>0.10). Compared to P1L heifers, P1H heifers had high amplitude LH pulses at 8 months, and high frequency low amplitude LH pulses at 10 months of age (P<0.05). The mean diameter (mm) of the dominant follicle was smaller (P<0.05) in P1L heifers (10.6) compared to P1H (12.8) or P1M (12.2) heifers at 8 months. Maximum size and growth rate of the nonovulatory dominant follicle increased with age (P<0.05) but did not differ between P1H and P1M heifers at puberty. The diameter (mm) of the nonovulatory dominant follicle, and the first and second ovulatory follicles were larger in P2L-12 heifers (14.0, 14.7, and 14.9) compared to P1M heifers (13.1, 12.5, and 11.9), while the peak progesterone levels and CL growth were lower (P<0.05) in the first cycle. In conclusion, dairy heifers attained puberty at a constant body weight and body composition independent of dietary manipulation, the size of dominant follicles increased with age in association with increased LH support, and heifers realimented from a low energy diet developed larger first ovulatory follicles and smaller CL with lower peak progesterone concentrations in the first cycle.     

The effects of dietary protein on age and weight at the onset of puberty in Brown Swiss and Zebu heifers in the tropics

The effects of dietary protein level on age and weight at onset of puberty were studied in the Mexican tropics using 12 Brown Swiss and 12 Zebu heifer calves in a completely randomized block design. The calves were weaned at 3 mo of age. They were confined in individual pens and fed either an adequate protein (12.8%) or a high protein (16.4%) diet ad libitum through the onset of puberty, which was defined as the first ovulation. To detect the first ovulation, heifers were palpated at 8 mo of age and then every 2 wk. At the detection of a developing follicle or any behavioral sign of estrus, they were palpated daily. Ovulation was confirmed by palpation of a corpus luteum. A blood sample for the determination of plasma progesterone concentration was taken with each palpation. There was a significant effect of breed on age at the onset of puberty, which was 9.4 and 12.3 mo for the Brown Swiss and Zebu heifers, respectively. Weight at puberty was 233 kg, independent of breed. Dietary protein had no effect on the onset of puberty. Brown Swiss heifers reach puberty earlier than Zebu heifers. Heifers in the tropics fed according to NRC recommendations reach puberty at ages comparable to those in temperate climate. This suggests that, if managed properly, calving age for Brown Swiss and Zebu heifers can be 24 and 27 mo, respectively. This is a considerable improvement from 36 to 48 mo of age now common in the area of study.     

Effects of active immunization of prepubertal heifers against prostaglandin F2α, on the onset of puberty and subsequent ovarian function

The objective of these two experiments was to determine the effect of immunization of prepubertal heifers against prostaglandin F_2α conjugated to human serum albumin (PGF-HSA) on the onset of puberty and subsequent ovarian function. Heifers that were 2–3 months of age (n=34; mean ± standard error of the mean (SEM) bodyweight 75 ± 1.4 kg) were given a primary immunization (Day 0) and a booster 183 days later using one of two adjuvants; non-ulcerative Freund's adjuvant (NUFA) and diethylaminoethyl-dextran (DEAF-dextran) and one of two doses of PGF-HSA as immunogen (1 and 10 mg), with six to seven heifers per treatment; control heifers (n=7) were untreated. The experiment lasted up to 562 days. Plasma antibody titres every 2–3 weeks and progesterone concentrations two to three times weekly were determined. Oestrous behaviour was observed twice daily. In addition, the follicular status of ovaries of cyclic (n=4), prepubertal (n=6) or prolonged luteal phase ( > 200 days, induced by immunization against PGF) heifers (n=5) were monitored daily for 23 consecutive days by ultrasound examination. Antibody titres were higher (P < 0.05) immediately following booster immunization in heifers immunized with DEAF-dextran than with NUFA. High titres were maintained for longer (P < 0.05) in heifers immunized with NUFA than with DEAF-dextran. The mean number of oestrous periods was decreased (P < 0.05) in PGF-immunized heifers in comparison with control heifers following booster immunization (3.1, 0.5, 0.9, 1.5, 1.1 in control heifers and in heifers immunized with NUFA-1 mg, NUFA-10 mg, DEAE-dextran-1 mg and DEAE-dextran-10 mg, respectively. Puberty was delayed (P < 0.05), relative to control heifers, by 185 and 122 days (pooled standard error of the difference, 89) in heifers immunized with NUFA-1 mg and DEAE-dextran-10 mg, respectively. After first ovulation at puberty, persistent corpora lutea (CL) formed in two of six heifers immunized with NUFA-1 mg, five of seven immunized with NUFA-10 mg, two of seven immunized with DEAE-dextran-1 mg and one of seven immunized with DEAE-dextran-10 mg. The duration of persistence was 103 ± 19, 301 ± 33, 124 ± 23 and 100 days, respectively. The mean (±SEM) number of dominant follicles was not different (P > 0.05) for the three groups of heifers that were examined by ultrasound (3.7 ± 0.2, 3.8 ± 0.3 and 3.2 ± 0.3 for cyclic, prepubertal and persistent CL, respectively); neither was their rate of growth (1.8 ± 0.2, 1.5 ± 0.1 and 1.5±0.2 mm day⁻¹, respectively), rate of atresia (1.3 ± 0.1, 1.6 ± 0.1 and 1.8 ± 0.2 mm day⁻¹, respectively) or the maximum size of dominant follicles (11.2 ± 0.4, 9.6 ± 0.3 and 12.4 ± 1.8 mm, respectively). In summary, immunization of prepubertal heifers against PGF delayed the onset of puberty and reduced subsequent oestrous behaviour due to the formation of persistent CL following first ovulation and there was a similar growth pattern of dominant follicles before first ovulation in prepubertal heifers, cyclic heifers and heifers which have long-term persistent CL.     

Effects of dry season nutritional supplementation on growth, onset of puberty and subsequent fertility in Boran and Boran x Friesian heifers in Ethiopia

Shortly after weaning at 8 months of age, 43 Boran and 46 Boran x Friesian crossbred heifers were randomly divided to either receive a supplementary feed containing 16% crude protein during the dry season or to serve as controls. Heifers were examined monthly, and data on body weight, wither height and body condition score were recorded. Ovarian size and structures were determined per rectum and heifers were kept under continuous observation for standing estrus. Blood samples were collected at 10-day intervals every month for determination of plasma progesterone levels. All heifers were exposed to intact bulls for 4 months after they attained 18 months of age. Average daily weight gain to puberty was significantly (P<0.01) higher in heifers given supplementation than in the controls (360 vs 326 g/day). The average daily weight gain in Boran heifers (296 g/day) was significantly (P<0.01) lower than in crossbred (392 g/day) heifers. Mean age at puberty differed significantly (P<0.001) between heifers given supplementation (573 days) and the controls (627 days). Boran heifers attained puberty at a significantly later age (660 vs 540 days; P<0.001) than crossbred heifers. Body weight at puberty did not differ between supplemented and control heifers (226 vs 222 kg); while the difference between Boran and crossbred heifers was significant (216 vs 232 kg; P<0.01). Pelvic size and body condition score were not influenced by supplementation but differed significantly between genotypes. Pregnancy rate after 4 months of breeding was higher in supplemented (79%) than in control (64%) heifers. Boran heifers had a significantly (P<0.001) lower pregnancy rate than crossbred heifers (52 vs 91%). Mean age and body weight at conception were not affected by supplementation but differed significantly (P<0.05) between genotypes. The results indicate that prepubertal supplementary feeding during the dry season increased growth rate, reduced age at puberty and improved fertility in both Boran and Boran x Friesian heifers.     

Effects of bull exposure and body growth on onset of puberty in Bunaji and Friesian x Bunaji heifers

A total of ninety seven pre-pubertal Bunaji (BJ) and Friesian-Bunaji (FR x BJ) heifers were allotted randomly to two treatments groups for a period of 15 months. The treatment groups consisted of the followings: Mature Bull Exposure (MBE) and No Bull Exposure (NBE). Heifers were body condition scored and their live weights recorded on 28 days consecutive intervals. A heifer tactile stimulation in bull bio-stimulation. was considered to have attained puberty if she displayed oestrus, had a palpable corpus luteum with an associated P4 concentration > 1 ng x mL(-1). The onset of puberty was significantly earlier in MBE heifers (23.1 +/- 0.4 months) than NBE heifers (26.4 +/- 0.4 months). The mean ages at puberty for MBE-BJ, NBE-BJ, MBE-FR x BJ, NBE-FR x BJ were 24.3, 27.8, 22.1 and 25.0 months respectively. More MBE heifers (70.8%) attained puberty between 17 and 24 months of age than NBE heifers (18.3%) and on the same ages, more FR x BJ heifers (62.0%) than BJ heifers (25.5%). The mean live weight of MBE heifers at puberty (224.4 +/- 4.2 kg) was significantly lower than that of the NBE heifers (255.8 +/- 4.2 kg). The FR x BJ heifers attained puberty at a significantly higher live weight (270.2 +/- 4.2 kg) than the BJ heifers (228.6 +/- 4.2 kg). The use of a vasectomised bull especially in some elite farms that rely on artificial insemination services may be an effective management tool that can decrease age at puberty. More work is required to determine the relative contribution of visual, auditory, olfactory, pheromonal and tactile stimulation in bull biostimulation.     

Ensiled biomass of Solaris tobacco variety used as forage: chemical characteristics and effects on growth,welfare, and follow-up of Holstein heifers

This study examined the use of an innovative tobacco variety, Nicotiana tabacum L., cv. Solaris, as forage. The whole plant biomass was ensiled, and the composition of SiloSolaris from bunker-silo and mini-silos was investigated. The effects of dietary inclusion of SiloSolaris on the growth, welfare, and nutritional profile of sixteen Holstein heifers, divided into two groups (n = 8), SiloSolaris (SS) and Control (CTR), were investigated. Heifers were group-fed diets with a 70:30 forage to concentrate ratio (on a DM basis). Both groups received 16.24 kg DM of concentrate mixture daily, including corn meal, wheat middlings and soybean meal. The CTR group was fed 39.43 kg DM of hay daily, and the SS group received 23.00 kg DM of the same hay and 12.69 kg DM SiloSolaris blended with the concentrate mixture. The feeding trial lasted eighty-one days with a thirty-six day adaptation phase. Data on forty-five days of diet administration are reported. At the end of the feeding trial, the plasma constituents of the heifers were studied. Moreover, heifers were monitored during a follow-up period, lasting up to 1 year after calving, for age at first insemination, age at first calving and daily milk yield. The SiloSolaris chemical composition showed an average DM content of 24.1 (±0.65) g/100 g. During ensiling, a decrease in CP and an increase in ammonia nitrogen contents were observed. The lactic acid content was variable (9.00 ± 2.66 g/100 g DM), while the acetic acid concentration was stable (4.27 ± 0.21 g/100 g DM). No butyric acid was detected in SiloSolaris, whose ammonia nitrogen content accounted for 15.7 (±1.86)% of the total nitrogen on average, and the mean pH value was 5.02 (±0.08). The SiloSolaris diet did not affect heifer growth performance. No differences were detected for body condition, fecal consistency, or locomotion scores. All the investigated plasma constituents were within or very close to the ranges reported for heifers; however, significant differences between the experimental groups were observed for triglycerides, cholesterol, albumin, and magnesium. The follow-up results did not differ between the experimental groups. These initial findings suggest that Nicotiana tabacum cv. Solaris is a promising ensiled forage for growing heifers that deserve to be further investigated.