Factors associated with first service conception in artificially inseminated nulliparous Holstein heifers

Animal and management factors associated with first service conception in nulliparous dairy heifers were determined in 601 Holstein heifers from a dairy farm in north central Florida. Animal data collected included body weight, height at the withers and tail head, body condition score at 6 months of age and just prior to first artificial insemination (AI), and pelvimetry measurements taken just prior to first AI. Management data included season of first AI, inseminator, service sire, method of estrus detection, whether the estrus of first insemination was induced using prostaglandin F(2alpha) (PGF(2alpha)), and whether the heifer received a modified live virus (MLV) vaccine within 21 days of first insemination. Data were analyzed using multivariable logistic regression. Heifers inseminated in the summer were more than four times less likely to become pregnant to first insemination than heifers bred during the rest of the year (odds ratio (OR)=0.24; 95% CI=0.14, 0.41). Using secondary signs for estrus detection instead of standing estrus resulted in significantly reduced odds of conception to first service (OR=0.37; 95% CI 0.13, 1.02). Also, heifers inseminated at estrus induced by PGF(2alpha) were approximately one-third less likely to conceive than those heifers inseminated to a naturally occurring estrus (OR=0.66; 95% CI 0.46, 0.95). An interaction between pelvic size and breeding season was found indicating that large pelvic size had a significant positive effect on fertility in the summer, but was not associated with conception to first service in the winter.     

Bovine GDF10 gene polymorphism analysis and its association with body measurement traits in Chinese indigenous cattle

The objective of this research was to detect bovine GDF10 gene polymorphism and analyze its association with body measurement traits (BMT) of animals sampled from 6 different Chinese indigenous cattle populations. The populations included Xuelong (Xl), Luxi (Lx), Qinchuan (Qc), Jiaxian red (Jx), Xianang (Xn) and Nanyang (Ny). Blood samples were taken from a total of 417 female animals stratified into age categories of 12–36 months. Polymerase chain reaction–single strand conformation polymorphism (PCR–SSCP) was employed to find out GDF10 single polymorphism nucleotide (SNPs) and explore their possible association with BMT. Sequence analysis of GDF10 gene revealed 3 SNPs in total: 1 in exon1 (G142A) and 2 in exon3 (A11471G, and T12495C). G142A and T12495C SNPs are both synonymous mutation. They showed 2 genotypes namely respectively (GG, GA) and (PP and PB). A11471G SNP is a missense mutation leading to the change of Alanine to Threonine amino acid. It showed three genotypes namely AA, BB and AB. Analysis of association of polymorphism with body measurement traits at the three locus showed that there were significant effects on BMT in Qc, Jx and Ny cattle population. These results suggest that the GDF10 gene might have potential effects on body measurement traits in the above mentioned cattle populations and could be used for marker-assisted selection.     

Comparison of cloned and non-cloned Holstein heifers in muscle contractile and metabolic characteristics

Muscle contractile and metabolic characteristics were studied on nine cloned and eight non-cloned (control) heifers. The animals were submitted to repeated biopsies of the semitendinosus (ST) muscle at the ages of 8, 12, 18 and 24 months. The contractile type was determined from the proportion of the different myosin heavy chain (MyHC) isoforms separated by electrophoresis. Glycolytic metabolism was assessed by lactate dehydrogenase (LDH) activity, and oxidative metabolism was assessed by isocitrate dehydrogenase (ICDH), cytochrome-c oxidase (COX) and β-hydroxyacyl-CoA dehydrogenase (HAD) activities. In cloned heifers at 8 months of age, there was a greater proportion of MyHC I (slow oxidative isoform) and MyHC IIa (fast oxido-glycolytic isoform), a lower proportion of MyHC IIx (fast glycolytic isoform), greater COX and HAD activity and a lower LDH/ICDH ratio compared with control heifers. Thus, young cloned heifers had slower muscle types associated with a more oxidative muscular metabolism than control heifers. From 12 months of age onwards, no significant differences were observed between cloned and control heifers. A delay in muscle differentiation and maturation in cloned heifers is hypothesised and discussed.     

Induction of LH surges with 17β estradiol in prepuberal beef heifers: An age dependent response

Twenty-four crossbred heifer calves were used to determine the age at which the endocrine mechanisn involving the stimulatory action of estradiol on luteinizing hormone (LH) release becomes competent to function in prepuberal beef heifers.Twelve calves were studied at 3 months of age at an average body weight of 113 kg; and 12 were studied at 5 months of age at an average body weight of 171 kg. Half of the heifers in each age group were injected with 500 μg of estradiol-17β (E₂) in corn oil and half were injected with corn oil (controls). Acute release of LH did not occur in any control heifers of either age nor in any 3-month-old, E₂-treated heifers but did occur in four of the six heifers treated at 5 months of age.The acute release, lasting for 6 to 8 hr, was initiated between 12 and 14 hr after injection of estradiol with LH peaks ranging from 39 to 146 ng/ml. These results suggest that the hypothalamic-hypophyseal mechanism responsible for estradiol-stimulated LH release becomes functional between 3 and 5 months of age in calves that do not ovulate until 12 to 16 months of age.     

Estrogen - Induced release of luteinizing hormone in prepubertal and postpubertal heifers

This experiment was designed to determine the age at which estradiol-17beta (E(2)) first induces a preovulatory-like surge of luteinizing hormone (LH) in prepubertal heifers. Responses of prepubertal animals 3 to 4 and 5 to 6 months of age were compared with those of postpubertal heifers that received 25 mg prostaglandin F(2)alpha at 0800 hr on day 15 of the estrous cycle. E(2) (500mug) induced surges of LH in 1 5 heifers 3 to 4 months of age, 3 3 heifers 5 to 6 months of age and 5 5 postpubertal heifers. Duration of response and interval between E(2) injection and peak of the response were longer in postpubertal heifers than in those 5 to 6 months old (P<0.10). Peak response and total amount of LH released were greater in animals 5 to 6 months old (P<0.10). Only one prepubertal heifer had elevated concentrations of progesterone following an LH surge. Four of 5 postpubertal heifers receiving E(2) and 3 of 4 postpubertal heifers receiving corn oil had corpora lutea and similar patterns of progesterone concentrations. We conclude that ability to release an LH surge in response to E(2) develops in heifers between 3 and 5 months of age, but that this induced surge does not cause ovulation.     

Effects of biostimulation and nutritional supplementation on pubertal age and pregnancy rates of Nelore heifers (Bos indicus) in a tropical environment

To determine effects of biostimulation (BIO) and dietary supplementation (BIO+S) on pubertal age and pregnancy rates, Nelore heifers (n=392) were randomly assigned to one of four treatment groups (n=98/group). All animals were in tropical environmental conditions, in the middle-west region of Brazil, grazing in pastures of Brachiaria brizantha, cv. Marandu; Panicum Maximum, cv. Tanzania and Brachiaria humidícula. The heifers of the BIO group were kept in the presence of bulls while being maintained on pasture; the animals in the BIO+S group were kept in the presence of bulls while being managed on pasture and were fed a diet with greater energy and protein content to produce 0.49 kg of BW gain/day; the animals in control group (the NBIO) were kept away from bulls and under pasture conditions; and the animals in the NBIO+S group were kept away from bulls, were maintained on pasture, and were fed the same diet as the BIO+S group. Heifers were bred at 22-23 months of age, and pregnancy diagnosis was made 45 days after the end of the breeding season. There were differences (P<0.05) between groups regarding pubertal heifers up to 19 months (NPH), final body weight (FBW) and pregnancy rates (P<0.01), with an advantage for the animals in the BIO and BIO+S groups. Although the effect of a diet with greater protein and energy content was not clear in this experiment, the exposure of heifers to a male during the prepubertal period decreased age at the first breeding season, resulting in a significant reduction in age of first pregnancy in Nelore heifers kept under extensive management systems in a tropical environment.     

Applicability of Arginyl-tRNA: Protein Arginyltransferase in Peptide Synthesis

A monoclonal antibody (MAb 1C3) to bovine β-casein was prepared, and a peptide (from 184 to 202 residues of β-casein) that could bind this monoclonal antibody was separated from a tryptic digest of β-casein. Other β-casein fragments, the peptide from 193 to 202 and the one from 1 to 189 residues, were also prepared for comparison. MAb 1C3 belongs to the IgG₁ subclass with a κ chain and its pI was 5.9. The binding affinity of β-casein and β-casein fragments to the monoclonal antibody was investigated by a competitive radioimmunoassay, and the order of affinity was β-casein peptide from 193 to 202 > β-casein > β-casein peptide from 184 to 202 > β-casein peptide from 1 to 189. On the basis of the results, the mechanism for the interaction between MAb 1C3 and β-casein fragments is discussed.     

Puberty and serum concentrations of ovarian steroids during prepuberal period in Friesian heifers artificially infected with Fasciola hepatica

An experiment was conducted to study the effect of fascioliasis on puberty in 13 Friesian heifers divided into a control group (n = 7) and an infected group (n = 6). At 4 m.o. of age each infected heifer received 600 metacercariae of F. hepatica. Blood samples were taken twice a week, at which time permanent heat mount detectors were checked, from 8 m.o. of age until 2 estruses were detected in all heifers. Serum concentrations of progesterone (P4) and estradiol-17 beta (E2) were assayed by ELISA and RIA, respectively. There was a significant delay in the onset of puberty in infected heifers compared with controls. All animals reached puberty at similar body weights but at different ages. First estrus was delayed by 39 d in infected compared with control animals. Serum concentrations of E2 were significantly higher in the infected group than the control group, while P4 concentrations were lower. Fascioliasis alters the serum concentration of E2, which in turn results in an abnormally low concentration of P4, probably due to underdeveloped or absent corpora lutea.     

Influence of slaughter age and carcass suspension on meat quality in Angus heifers

This study investigated the effects of pelvic suspension and slaughter age on longissimus thoracis et lumborum (LTL) from 40 heifers with at least 75% Angus breeding. A total of 20 heifers were slaughtered directly from pasture at 18 months of age, and carcass sides were hung either by the Achilles tendon or the pelvic bone. The other 20 heifers were assigned to an additional winter housing period and slaughtered at 22 months of age; carcass sides were hung only by Achilles suspension. All carcasses were electrically stimulated and assessed according to the EUROP carcass classification system. In addition, the LTL muscles were aged for 7 or 14 days before meat quality was evaluated for intramuscular fat (IMF), drip loss, colour, shear force, compression and sensory analysis. The 22-month-old heifers were heavier, fatter and had more IMF than 18-month-old heifers. Conformation scores (muscling) did not differ between the two slaughter groups. Pelvic suspension reduced both between- and within-animal variation for peak force, total energy and compression peak force. For the 18-month-old heifers, pelvic suspension also decreased peak force, total energy and compression variables for the LTL muscles from both ageing periods, whereas Achilles-suspended samples had lower shear force values only at day 14. Sensory analysis showed that pelvic-suspended sides had greater tenderness, lower bite resistance, less threadiness, higher juiciness and meat flavour and less visible marbling than meat from Achilles-suspended sides. Pelvic-suspended sides at 18 months of age were similar in peak force and total energy values to the 22-month-old heifers. The importance of ageing the Achilles-suspended sides was more obvious for samples from 18-month-old heifers than from the 22-month-old animals. The correlations between the different instrumental measurements and sensory tenderness were considerably higher for carcasses suspended by the Achilles tendon (r = −0.55 to 0.20) than for those hung by the pelvic bone (r = −0.25 to 0.19). More correlations between sensory-evaluated tenderness and shear variables were significant after 7 days (n = 6) of ageing than after 14 days (n = 4) of ageing. This study clearly shows the benefits of pelvic suspension, which reduces the need for additional feeding after pasture.     

Influences of stress, age and sex on serum growth hormone and free fatty acid levels in cattle.

The serum growth hormone (BGH) and free fatty acid (FFA) concentrations of large groups of calves (male and female ranging in age from 8 to 14 days and from 3 to 6 months old), bulls, oxen, heifers and cows under normal conditions were compared with the serum BGH and FFA values of corresponding large groups of animals under stress conditions. Stress was caused by transport, as it routinely occurs, and was further reinforced by a stay of several hours in unfamiliar surroundings. Stress provokes a significant increase in serum FFA in all groups and induced a significant decrease in serum BGH in all groups, with the exception of the non-pregnant heifers. The male and female calves which were 8 to 14 days old, had significantly higher BGH levels than the older animals. The female calves from 3 to 6 months of age, and the heifers had significantly lower BGH levels than the cows. The males had higher serum BGH values than the females, but a significant difference could be demonstrated only between the male and female calves of both age-groups. The oxen, which were 1 to 3 years old, had significantly higher BGH levels than the non-pregnant heifers of the same age. It appeared that gestation had no influence on the serum BGH and FFA levels of both heifers and cows.     

Studies on the Interaction between αs1- and β-Caseins

The interaction of α_s1-casein with β-, dephosphorylated β-,γ- and R-caseins was studied. It was proved by the sedimentation velocity experiments that α_s1-casein formed a complex with each of these components at 25±C in the presence of 3 mm CaCl₂.

In the presence of 10 mm CaCl₂, β- and dephosphorylated β-casein prevented the precipitation of α_s1-casein and gave micelle-like turbid solutions. However, γ- and R-caseins, fragments of β-casein, did not stabilize α_s1-casein. It was concluded from these results that α-casein interacted with α_s1-casein through its hydropholic region corresponding to R-casein and that hydrophilic region of β-casein was responsible for the stabilization of α_s1-casein.     

Development of the magnetic beads for dye ligand affinity chromatography and application to magnetically stabilized fluidized bed system

Magnetic poly(2-hydroxyethylmethacrylate) [mPHEMA] beads were prepared by suspension polymerization of HEMA in the presence of Fe₃O₄ nano-powder. Cibacron Blue F3GA was covalently immobilized to the mPHEMA beads via nucleophilic substitution reaction between chloride of its triazine ring and hydroxyl groups of HEMA under alkaline conditions. The mPHEMA/Cibacron Blue F3GA beads (100–140 μm in diameter) carrying 68.3 μmol Cibacron Blue F3GA per gram polymer were used for β-casein adsorption studies. Adsorption studies were performed under different conditions in a batch system (i.e., pH, β-casein initial concentration, temperature, and ionic strength) and then in a magnetically stabilized fluidized bed (MSFB) system. The swelling ratio of the mPHEMA was 62.1%. The maximum adsorption capacity for batch system was 20.2% lower as compared to the value obtained in MSFB. The mPHEMA/Cibacron Blue F3GA beads could be repeatedly applied for β-casein adsorption without significant losses in the adsorption capacity.     

The conformation and aggregation of bovine β-casein A. II. Thermodynamics of thermal association and the effects of changes in polar and apolar interactions on micellization

A sedimentation analysis has been used to determine the proportion of protein present as monomer and aggregate in 0.5 and 1.0 g/dl solutions of β-casein A in pH 7 phosphate buffer over the temperature range 10–40°C. The amount and molecular weight of the aggregate increase with temperature; under the conditions used, the aggregation number (n) of β-casein is given approximately by n = 0.6t + 2 with t in degrees centigrade. The concentration of β-casein in monomeric and aggregated states at different temperatures is used to calculate the standard enthalpy of aggregation ΔH° (Van't Hoff) by assuming that β-casein undergoes a cooperative, two-state, micellization process; aggregation is an endothermic process and ΔH° = 66.0 ± 2.6 kJ mol^?1. Combination of this ΔH° with the amount of protein calculated to dissociate when 1 g/dl solutions are diluted isothermally to 0.5 g/dl gives the heat of dilution at various temperatures. These calculated heats of dilution are compared with the experimental values obtained by carrying out the same dilutions in a microcalorimeter. The heat of dilution decreases linearly with β-casein concentration, but the extrapolated zero-concentration values of 65.8 ± 1.6 kJ mol^?1 is the same as the Van't Hoff enthalpy. This agreement in the enthalpy values indicates that the micellization of β-casein occurs cooperatively. The effect of modifying the hydrophobic/hydrophilic balance of the system on the micellization of β-casein A has been investigated. The hydrophobic interaction between the protein molecules is decreased by removing the three C-terminal residues (Ileu Ileu Val) with carboxypeptidase-A. This modification drastically reduces the ability of the β-casein molecule to form micelles. Substitution of ²H₂O for H₂O at constant temperature perturbs the monomer–micelle equilibrium in favor of micelles because of enhanced hydrophobic interactions in the former solvent. The results are consistent with β-casein micellization involving a delicate balance of the hydrophobic forces favoring aggregation and electrostatic forces opposing it.     

Pregnancy rate of Nelore females inseminated with male-sexed semen

Pregnancy rates of Nelore females inseminated with male-sexed semen and conventional semen from the same bulls were evaluated. The females included 433 heifers (2 years old) and 230 non-suckling cows, totaling 663 animals. Average body condition score was 3.5 (1-5 scale). Estrus was induced with prostaglandin F2α. The total pregnancy rate of females inseminated with male-sexed semen of bulls A, B and C was 38.8% (131/338) less (P<0.0001) than the total pregnancy rate observed for females inseminated with conventional semen from the same bulls (57.9% [188/325]). Pregnancy rates of non-suckling cows inseminated with male-sexed semen was 43.3% (49/113), which was similar (P≥0.05) to the values found for heifers inseminated with male-sexed semen from the same bulls (36.4% [82/225]). The pregnancy rate of females inseminated with male-sexed semen was less compared with females inseminated with conventional semen. In addition, there was no significant difference in the pregnancy rate of heifers versus non-suckling cows.     

Genetic correlation between heifer pregnancy and scrotal circumference measured at 15 and 18 months of age in Nellore cattle

Data of pregnancy diagnosis from 24,945 Nellore heifers, raised under tropical conditions in Brazil and exposed to breeding at about 14 months of age, were analyzed simultaneously with 13,742 (analysis 1), 36,091 (analysis 2), 8,405 (analysis 3), and 8,405 (analysis 4) scrotal circumference (SC) records of contemporary young bulls in order to estimate heritability (h(2)) for yearling heifer pregnancy (HP) and for SC measured at around 15 (SC15) and 18 (SC18) months of age and to estimate genetic correlation between HP and SC15 (SC18). Heifer pregnancy was considered as a categorical trait, with the value 1 (success) assigned to heifers that were detected as pregnant by rectal palpation approximately 60 days after the end of a 90-day breeding season and the value 0 (failure) otherwise. In analyses 1 and 3, SC was measured at around 15 months of age and in analysis 2 and 4 it was measured at around 18 months of age. Only 8,848 animals from datasets 1 and 2 were common in both files, which means the same animals measured at different ages. Datasets used in analyses 3 and 4 included the same animals, measured at 15 and at 18 months of age, respectively. Heritability estimates for HP were similar in all analyses, with values ranging from 0.66 +/- 0.08 to 0.67 +/- 0.008. For SC15, the estimates were 0.57 +/- 0.05 in analysis 1 and 0.60 +/- 0.07 in analysis 3. For SC18, the estimates were 0.53 +/- 0.03 in analysis 2 and 0.64 +/- 0.06 in analysis 4. The estimates of genetic correlation between HP and SC15 were 0.15 +/- 0.10 in analysis 1 and 0.11 +/- 0.11 in analysis 3. For the correlation between HP and SC18, the values were 0.27 +/- 0.10 in analysis 2 and 0.16 +/- 0.11 in analysis 4. Based on standard errors and confidence intervals, the best heritability and genetic correlation estimates were obtained from analysis 2, which included more data and a better pedigree structure. Pearson correlation between HP and SC breeding values was similar to the genetic correlation estimates obtained from two-trait models, when all animals in the pedigree file were considered for its calculation. If only sires were considered for the calculation, Pearson correlation was higher but the pattern was the same as from two-trait analyses. The high heritability estimates obtained in the present study confirm that expected progeny difference (EPD) for HP can be used to select bulls for the production of precocious daughters and that the low genetic correlation between SC and HP indicates a greater efficacy of selection based on heifer pregnancy EPD than of selection based on scrotal circumference EPD. The results of the present study, although not conclusive, indicate that SC measured at around SC18 would have a higher genetic correlation with HP than would SC measured at around SC15.     

The Primary Structure of Water Buffalo αs1- and β-Casein: Identification of Phosphorylation Sites and Characterization of a Novel β-Casein Variant

The primary structure of water buffalo α_s1-casein and of β-casein A and B variants has been determined using a combination of mass spectrometry and Edman degradation procedures. The phosphorylated residues were localized on the tryptic phosphopeptides after performing a β-elimination/thiol derivatization. Water buffalo α_s1-casein, resolved in three discrete bands by isoelectric focusing, was found to consist of a single protein containing eight, seven, or six phosphate groups. Compared to bovine α_s1-casein C variant, the water buffalo α_s1-casein presented ten amino acid substitutions, seven of which involved charged amino acid residues. With respect to bovine βA₂-casein variant, the two water buffalo β-casein variants A and B presented four and five amino acid substitutions, respectively. In addition to the phosphoserines, a phosphothreonine residue was identified in variant A. From the phylogenetic point of view, both water buffalo β-casein variants seem to be homologous to bovine βA₂-casein.     

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.     

Characterization of β-casein gene in Indian riverine buffalo

The study aimed at characterization of buffalo β-casein gene and its promoter by PCR-SSCP analysis. Complete β-casein exon VII region analysis revealed two SSCP band patterns, with pattern-I representing predominant allele B (85%) present in homozygous (genotype BB) condition and pattern-II representing a rare allele A1 present in heterozygous condition (genotype A1B). Sequencing of two patterns revealed three nucleotide substitutions at codon 68, 151 and 193 of exon VII. The cDNA sequence of buffalo β-casein gene indicated three further nucleotide substitutions between allele A1 and B at codon 10, 39, and 41. Analysis of β-casein proximal promoter region (− 350 upstream to + 32) revealed four SSCP band patterns. These SSCP patterns corresponded to nucleotide substitutions at seven locations within 382 bp 5′ UTR region of β-casein gene. Haplotype analysis suggested pattern-I of exon VII (wild type) was associated with three types of promoters and pattern-II of exon VII (rare type) corresponded to one exclusive type of promoter. The study suggested two haplotypes of exon VII and four haplotypes of promoter for buffalo β-casein.     

Influences of month of birth and age on patterns of luteinizing hormone secretion in prepubertal heifers

An experiment was done to determine if month of birth and age influenced patterns of luteinizing hormone (LH) secretion in prepubertal heifers. Mean concentrations of LH increased linearly (P < .05) in March-born heifers between one and seven months of age. This was partially due to an increase in number of LH pulses. The prepubertal pattern of LH concentrations was quadratic (P < .05) for heifers born in September because concentrations were slightly higher (P = .15) than those in March-born heifers at one month of age. There were no differences between groups during the remainder of the prepubertal period (3 to 7 months). There was a tendency (P = .18) for September-born animals to reach puberty at younger ages than those born in March. September-born heifers also had greater (P = .06) average daily gains, but body weights at puberty were similar for the two groups. These results show that season of birth influenced LH concentrations at one month of age, but did not significantly affect the increase between three and seven months of age.     

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.