Puberty In Heifers Research Articles

Nutrition, Growth, and Age at Puberty in Heifers

Puberty onset and age at first calving have a critical impact on livestock production for good reproductive efficiency of the herd and to reduce the duration of the non-productive stage of the growing heifer. Besides genetic factors, sexual maturation is also affected by environmental factors, such as nutrition, which can account for up to 20% of the observed variability. The rate of body weight gain during growth is considered the main variable influencing the age at puberty, dependent on planes of nutrition in growing animals during the prepubertal-to-pregnancy stage. This paper reviews current knowledge concerning nutrition management and attainment of puberty in heifers, considering the relevance of some indicators such as body measurements and hormones strictly linked to the growth and puberty process. Puberty onset is dependent on the acquisition of adequate subcutaneous adipose tissue mass, as it is the main source of the hormone leptin. Until a certain level, body condition score and age at puberty are negatively correlated, but beyond that, for fatter animals, such correlation is gradually lost. Age at puberty in heifers was reported to be negatively related to IGF-1. Future research should be planned considering the need to standardize the experimental animals and conditions.

Genome-wide association and expression quantitative trait loci in cattle reveals common genes regulating mammalian fertility

Most genetic variants associated with fertility in mammals fall in non-coding regions of the genome and it is unclear how these variants affect fertility. Here we use genome-wide association summary statistics for Heifer puberty (pubertal or not at 600 days) from 27,707 Bos indicus, Bos taurus and crossbred cattle; multi-trait GWAS signals from 2119 indicine cattle for four fertility traits, including days to calving, age at first calving, pregnancy status, and foetus age in weeks (assessed by rectal palpation of the foetus); and expression quantitative trait locus for whole blood from 489 indicine cattle, to identify 87 putatively functional genes affecting cattle fertility. Our analysis reveals a significant overlap between the set of cattle and previously reported human fertility-related genes, impling the existence of a shared pool of genes that regulate fertility in mammals. These findings are crucial for developing approaches to improve fertility in cattle and potentially other mammals.

24 Effects of Gestational and Postweaning Nutrition on Brain Development and Puberty in Beef Heifers

Abstract Approximately 5 million beef heifers enter the U.S. cow herd annually, and their lifetime productivity is largely dependent upon their ability to attain puberty and produce a calf by 24 mo of age. However, a considerable proportion of heifers within existing U.S. production systems fail to achieve these goals, particularly in southern regions where Bos indicus-influenced cattle predominate. Consequently, managerial approaches are needed that employ nutritional programming of the reproductive neuroendocrine axis, while minimizing feeding costs and optimizing the consistent attainment of puberty by approximately 14 mo of age. Our previous research has clearly demonstrated that increased BW gain between 4 and 8 mo of age facilitates pubertal development by programming hypothalamic centers that regulate gonadotropin releasing-hormone (GnRH) secretion. Among the different metabolic hormones, leptin has a critical role in conveying nutritional information to the hypothalamus and controlling puberty. Two hypothalamic neuronal populations that express the orexigenic peptide neuropeptide Y (NPY) and the anorexigenic peptide alpha melanocyte-stimulating hormone (αMSH; a product of the POMC gene) are key components of afferent pathways that convey inhibitory (NPY) and excitatory (αMSH) inputs to GnRH and kisspeptin neurons. Our studies have demonstrated that short-term increases in dietary energy intake after early weaning at 4 mo of age result in epigenetic, structural, and functional modifications in these hypothalamic pathways to promote high-frequency, episodic release of GnRH and luteinizing hormone. However, integrating the foundational knowledge of metabolic imprinting of the brain for early puberty with issues related to lifetime performance is complex. One approach has been to employ a novel stair-step nutritional regimen involving alternating periods of dietary energy-restriction and re-feeding during juvenile development. This approach is designed to support early onset of puberty by imprinting functional alterations in the hypothalamus during key periods of brain development while optimizing other aspects of growth and performance. Finally, while several key processes of fetal brain development occur during late gestation, neither maternal undernutrition (BCS 3.0-3.5) nor maternal obesity (BCS 7.5-8.0) during the last two trimesters of gestation impacted the organization of hypothalamic neurocircuitries controlling GnRH/LH secretion or age at puberty in the heifer offspring. Collectively, these results indicate that the adult reproductive phenotype in Bos indicus-influenced females is resilient to significant degrees of nutritional stress imposed during prenatal development, particularly if early gestation (first trimester) is avoided. These findings are in contrast with reports in Bos taurus females in which late gestation nutritional extremes result in delayed puberty in heifer offspring, suggesting that potential genotype-specific differences may exist. Research support: USDA-NIFA-AFRI (2018-67015-27595 and 2021-67015-33676).

Effect of sires' expected progeny difference for scrotal circumference and juvenile ADG on the puberty of crossbred beef heifers.

The early attainment of puberty in heifers is essential for the profitability of the cow-calf farm. This study aimed to evaluate the impact of juvenile average daily gain (ADG) and sire's expected progeny difference (EPD) on puberty of crossbred beef heifers. Sixty Angus × Nellore heifers early weaned (age = 102 ± 4.3 d; initial BW = 103 ± 4.7kg) were used in a 2 × 2 factorial arrangement. The factor 1 was the sire's EPD for scrotal circumference, in which heifers born from sires with positive EPD were considered precocious (P), and heifers born from sires with negative EPD were considered non-precocious (NP). The factor 2 was the high (HG; ADG = 0.9kg; ad libitum) and medium ADG (MG; ADG = 0.7kg) from 3rd to 7th month of age (1st phase). After 1st phase until puberty, all heifers were fed ad libitum (2nd phase). Statistical analysis was performed by SAS. There was an interaction between factors for DMI in the 1st phase (P = 0.02), which PHG heifers had higher DMI than NPHG. There was no effect on puberty rate, BW, age and BCS at puberty comparing HG vs. MG. However, favorable sires' EPD for scrotal circumference induced a higher proportion of puberty (P 87% vs. NP 59%) at 15months of age. Thus, the ADG in juvenile age did not affect puberty rate, but sires with positive EPD increased puberty rate of Angus × Nellore heifers in heifers fed a high gain diet.

Role of Date Palm Pollen on Heifer's Puberty and Maturity in Iraq.

The use of herbal remedies has played a crucial role throughout medicine, and human beings have always used these valuable resources to treat their health problems and diseases. Phoenix dactylifera (Palm) is one of the most famous medicinal plants. Therefore, this study was designed to investigate the possible effects of date palm pollen supplementation on the heifer's puberty. This study was conducted in Najaf- Iraq, on 10 crossbred heifers 6 months old, from December 1st, 2021, to August 1st, 2022. The animals were divided randomly into two groups: T1 was supplemented with 2g of date palm pollen (DPP) plus the main ration, while T2 was supplemented only with the main ration. The results revealed a significant effect (P<0.05 and P<0.01) in T1 over T2, accelerating the heifer's puberty and sexual maturity. The results also showed a significant effect (P<0.01) between T1 and T2 at the level of the hormones FSH, LH and estrogen in the age of puberty, as well as the presence of a significant difference (P<0.01) and (P<0.05) between T1 and T2 at the level of the hormones FSH and estrogen in the age of sexual maturity. The results also showed a significant effect (P<0.05) for T1 and T2 in weight at puberty and maturity. This study aimed to accelerate puberty and sexual maturity in the heifers.

81 Effects of Hurricane-Related Stress During Gestation on Replacement Heifer (Bos Taurus) Development in a Limited-Resource Beef cow-Calf System

Abstract In a limited resource cow-calf operation, obtaining puberty in heifers is one of the main concerns for long-term productivity. Although nutritional factors have a large role in heifer development, environmental factors are sometimes overlooked until a catastrophic event such as a hurricane occurs. For this project, two heifer groups, born in the same herd at different intervals, were compared: Group 1(experienced catastrophic hurricane event in 3rd trimester of their fetal development) and Group 2 (no adverse event during gestation). The groups were weighed four similar time points during development: at 12 months of age (Period 1, pre-pubertal), 13-14 months (Period 2, puberty), pre-breeding (Period 3), and at the end of breeding (Period 4). The blood cortisol, glucose, and progesterone concentrations were compared between the groups during their pre-pubertal period. Group comparisons were performed using mixed procedures of SAS. Data are presented as means ±SEM. Group mean differences were declared significant at P &amp;lt; 0.05. We observed a significant (P &amp;lt; 0.01) Group by Period effect on heifer body weight (655.2± 14.2 vs. 747.3 ±15.4, for Groups 1 and 2, respectively). Overall, Group 1 was lighter than Group 2 in periods 1 and 2, but there was no difference thereafter. There were significant group differences in glucose (60.5± 8.8 vs 95.3±11.5, mg/dL for groups 1 and 2 respectively, P&amp;lt; 0.01) and progesterone (62.2±12.6 vs 124.0± 13.8, pg./mL for groups 1 and 2, respectively, P&amp;lt; 0.01). However, there was no significant difference in cortisol concentrations (P&amp;lt; 0.48). Therefore, catastrophic weather events such as hurricanes that are common throughout the world might have a negative impact on heifer development, as observed in this project. This observation warrants further investigation. Funding agency: USDA- NIFA CBG #2021-38821-34599

The influence of weaning age and biocholine supplementation to post-weaning growth and puberty in Brangus heifers

This experiment was conducted to determine the effect of earlier weaning in addition to biocholine supplementation on age at puberty of Brangus heifers. Brangus calves were randomized and divided into three weaning ages groups, at 30 (Hyper-early weaning; HW), 75 (Early weaning; EW) and 180 days (Conventional weaning; CW). Then, calves were supplemented using the additive Biocholine (BIO) or not (CON). Animals were subjected to puberty induction and the presence of estrus was observed for 7 days. In addition, transrectal ultrasonography was performed to assess the ovarian activity and the presence of corpus luteum to determine heifer puberty. We also evaluated the body weight (BW; Kg), hip height (HH; cm), thoracic perimeter (TP; cm) and BW:HH ratio during the experimental period. BIO group showed higher ADG (>226 g/day) when the animals were exposed to ryegrass pasture compared to CON (P < 0.05). We observed an interaction between weaning x biocholine and CW-BIO heifers showed greater HH more compared to CW-CON (P < 0.05). Overall, animals that have reached puberty at day 8 after puberty induction showed 331.0 ± 5.04 kg BW, 122.0 ± 0.56 cm HH and 165.4 ± 0.75 cm TP and 2.7 ± 0.03 BW:HH. At the time of ovulation detection, the heifers from the HW group had 32.1 kg BW, 3.93 cm HH and 0.18 cm BW:HH greater compared to CW (P < 0.05). The BIO supplementation together with ryegrass pasture, led to an increase in ADG weight throughout the evaluated period. We concluded that HW heifers showed an adequate body development throughout the experimental period until puberty appearance at the same age as others weaned groups.

Early juvenile but not mid-to-late prenatal nutrition controls puberty in heifers but neither impact adult reproductive function†.

Objectives were to test the hypothesis that pre- and post-natal nutrition in the bovine female, independently or interactively, affect age at puberty and functional characteristics of the estrous cycle of sexually mature offspring. Brangus and Braford (n = 97) beef cows bearing a female fetus were fed to achieve body condition scores of 7.5-8 (H, obese), 5.5-6 (M, moderate), or 3-3.5 (L, thin) by the start of the third trimester and maintained until parturition. Heifer offspring were weaned and fed to gain weight at either a high (H; 1 kg/day) or a low (L; 0.5 kg/day) rate between 4 and 8 months of age, then fed the same diet during a common feeding period until puberty, which resulted in compensatory growth of heifers in the L group. Heifers (n = 95) from the H postnatal diet reached puberty 2 months earlier (12 ± 0.4 months; P= 0.0002) than those from the L postnatal diet (14 ± 0.4 months). Estrous cycles of a subgroup of postpubertal heifers (n = 53) were synchronized to evaluate antral follicle count (AFC), rate of growth and size of the pre-ovulatory follicle, size of corpus luteum and ovary, endometrial thickness, and plasma concentrations of progesterone and estradiol-17β (E2). Although there was a trend for postnatal H heifers to have greater AFC and plasma concentrations of E2 compared to L heifers, neither pre- nor post-natal nutrition affected any other physiological or hormonal variables, including short-term fertility. Postnatal nutritional effects on pubertal age remained the dominant observed feature.

PSI-7 Evaluating the Relationship of Puberty Status at 10 Months of Age with Heifer Characteristics

Abstract The objective was to evaluate the relationship of heifer puberty status at 10 months of age with body weight (BW), hair shedding score (HSS), and dam age. Puberty status was assessed at 10 months of age on 177 fall-born, Simmental × Angus heifers (birth date 9/26/2020 ± 18.7 d) using fabric heat patches (Estrotect; Hermitage, Tennessee) for 22 d. Patches were scored as 0, 50, or 100% activated with heifers scored 50 or 100% considered pubertal. Heifers with missing patches (n = 10) were excluded from the analysis. Heifers grazed endophyte-infected tall fescue pastures from 6 to 12 months of age. Heifers were assigned HSS at 10, 11, and 12 months of age. A HSS of 1 indicates a slick summer coat and a 5 is a full winter coat. The MIXED procedure of SAS 9.4 was used to analyze data. Heifers classified as pubertal at 10 months of age had greater (P = 0.01) birth BW than prepubertal heifers (33.1 kg vs. 30.8 kg, respectively). Heifers that were pubertal at 10 months of age also had greater (P ≤ 0.05) BW at 6, 8, 10, and 12 months of age than prepubertal heifers. Additionally, pubertal heifers had greater (P = 0.01) ADG from 6 to 12 months of age while grazing. Pubertal heifers tended (P = 0.10) to have a lesser, more desirable HSS at 10 months of age and had a lesser (P &amp;lt; 0.01) HSS at 11 and 12 months of age compared with prepubertal heifers. Dam age was not different (P = 0.60) between heifer puberty status at 10 months of age. In conclusion, pubertal heifers were heavier at birth, heavier from 6 to 12 months, and had more desirable HSS compared with prepubertal heifers at 10 months of age.

PSXIII-17 Supplementing organic-complexed or inorganic Co, Cu, Mn, and Zn to beef cows during gestation: post-weaning responses of offspring reared as replacement heifers or feeder cattle

Abstract Beef cows and their progeny were used to evaluate the effects of supplementing organic-complexed or inorganic Co, Cu, Mn, and Zn during gestation: on offspring reared as replacement heifers or feeder cattle. Non-lactating, pregnant beef cows (n = 190) were ranked by parity, pregnancy type, body weight (BW) and body condition score (BCS), at 117 ± 2.2 d of gestation (d 0) and assigned to receive a supplement containing: 1) sulfate sources of Cu, Co, Mn, and Zn (INR; n = 95) or 2) an organic complexed source of Cu, Mn, Co, and Zn (AAC; Availa®4; Zinpro Corporation, Eden Prairie, MN; n = 95). From d 0 to calving, cows were maintained in a single pasture and individually offered treatments three times a week. Calves were weaned at 6 mo of age (d 367) and preconditioned for 45-d. Heifer puberty status was verified weekly (d 437 to d 619) based on plasma progesterone concentrations. Steer calves were shipped to a commercial feedlot on d 493, where they were managed as a single group until slaughter (d 724). Plasma cortisol concentration was greater (P = 0.05) in AAC calves at weaning but tended to be less (P = 0.10) on d 370 compared with INR calves. Mean plasma haptoglobin concentration was greater (P = 0.03) in INR vs. AAC calves during preconditioning, and no treatment effects were noted (P = 0.76) for preconditioning average daily gain (ADG). Puberty attainment was hastened in AAC heifers during the experiment (treatment × day; P &amp;lt; 0.01), despite similar (P = 0.39) ADG between treatments from d 412 to 620. No treatment effects were detected (P ≥ 0.24) for steer ADG from d 412 until slaughter, nor for carcass quality traits. Therefore, supplementing Co, Cu, Zn, and Mn as organic complexed instead of sulfate sources to beef cows during the last 5 mo of gestation did not improve performance of steer progeny until slaughter, but hastened puberty attainment in female progeny reared as replacement heifers.

PSXIII-19 The influence of weaning age and biocholine supplementation to post-weaning growth and reproductive development in Brangus heifers

Abstract This experiment was conducted to determine the effect of earlier weaning in addition to biocholine supplementation on age at puberty of Brangus heifers. Brangus calves were randomized and divided into three weaning ages groups, at 30 (Hyper-early weaning; HW), 75 (Early weaning; EW) and 180 days (Conventional weaning; CW). Then, calves were supplemented using the additive Biocholine (BIO) or not (CON). Animals were subjected to puberty induction and transrectal ultrasonography was performed to assess the ovarian activity and the presence of corpus luteum to determine heifer puberty. We also evaluated the body weight (BW; Kg), hip height (HH; cm), thoracic perimeter (TP; cm) and BW:HH ratio during the experimental period. BIO group showed higher ADG (&amp;gt;226g/day) when the animals were exposed to ryegrass pasture compared to CON (P &amp;lt; 0.05). We observed an interaction between weaning x biocholine and CW-BIO heifers showed greater HH more compared to CW-CON (P &amp;lt; 0.05). Overall, animals that have reached puberty at day 8 after puberty induction showed 331.0±23.14kg BW, 122.0±2.58cm HH and 165.4±3.45cm TP and 2.7±0.14 BW:HH. At the time of ovulation detection, the heifers from the HW group had 32.1kg BW, 3.93cm HH and 0.18cm BW:HH greater compared to CW (P &amp;lt; 0.05). The BIO supplementation together with ryegrass pasture, led to an increase in ADG weight throughout the evaluated period. We concluded that HW heifers showed an adequate body development throughout the experimental period until puberty appearance at the same age as others weaned groups.

Supplementing organic-complexed or inorganic Co, Cu, Mn, and Zn to beef cows during gestation: postweaning responses of offspring reared as replacement heifers or feeder cattle.

One hundred and ninety nonlactating, pregnant beef cows (¾ Bos taurus and ¼ Bos indicus; 138 multiparous and 52 primiparous) were assigned to this experiment at 117 ± 2.2 d of gestation (day 0). Cows were ranked by parity, pregnancy type (artificial insemination = 102, natural service = 88), body weight (BW) and body condition score, and assigned to receive a supplement containing: (1) sulfate sources of Cu, Co, Mn, and Zn (INR; n = 95) or (2) an organic complexed source of Cu, Mn, Co, and Zn (AAC; Availa4; Zinpro Corporation, Eden Prairie, MN; n = 95). The INR and AAC provided the same daily amount of Cu, Co, Mn, and Zn, based on 7 g of the AAC source. From day 0 to calving, cows were maintained in a single pasture and segregated 3 times weekly into 1 of 24 individual feeding pens to receive treatments. Calves were weaned on day 367 (200 ± 2 d of age), managed as a single group for a 45-d preconditioning period (days 367 to 412), and transferred to a single oat (Avena sativa L.) pasture on day 412. Heifer calves were moved to an adjacent oat pasture on day 437, where they remained until day 620. Heifer puberty status was verified weekly (days 437 to 619) based on plasma progesterone concentrations. Steer calves were shipped to a commercial feedlot on day 493, where they were managed as a single group until slaughter (day 724). Plasma cortisol concentration was greater (P = 0.05) in AAC calves at weaning but tended to be less (P = 0.10) on day 370 compared with INR calves. Mean plasma haptoglobin concentration was greater (P = 0.03) in INR vs. AAC calves during preconditioning, and no treatment effects were noted (P = 0.76) for preconditioning average daily gain (ADG). Puberty attainment was hastened in AAC heifers during the experiment (treatment × day; P < 0.01), despite similar (P = 0.39) ADG between treatments from days 412 to 620. Expression of myogenin mRNA in the longissimus muscle was greater (P = 0.05) in INR vs. AAC heifers on day 584. No treatment effects were detected (P ≥ 0.24) for steer ADG from day 412 until slaughter, nor for carcass quality traits. Hepatic mRNA expression of metallothionein 1A was greater (P = 0.02) in INR vs. AAC steers on day 586. In summary, supplementing Co, Cu, Zn, and Mn as organic complexed instead of sulfate sources to beef cows during the last 5 mo of gestation did not improve performance and physiological responses of the steer progeny until slaughter, but hastened puberty attainment in the female progeny reared as replacement heifers.

Heifers with positive genetic merit for fertility traits reach puberty earlier and have a greater pregnancy rate than heifers with negative genetic merit for fertility traits

This study investigated the hypothesis that dairy heifers divergent in genetic merit for fertility traits differ in the age of puberty and reproductive performance. New Zealand's fertility breeding value (FertBV) is the proportion of a sire's daughters expected to calve in the first 42 d of the seasonal calving period. We used the New Zealand national dairy database to identify and select Holstein-Friesian dams with either positive (POS, +5 FertBV, n = 1,334) or negative FertBV (NEG, -5% FertBV, n = 1,662) for insemination with semen from POS or NEG FertBV sires, respectively. The resulting POS and NEG heifers were predicted to have a difference in average FertBV of 10 percentage points. We enrolled 640 heifer calves (POS, n = 324; NEG, n = 316) at 9 d ± 5.4 d (± standard deviation; SD) for the POS calves and 8 d ± 4.4 d old for the NEG calves. Of these, 275 POS and 248 NEG heifers were DNA parent verified and retained for further study. The average FertBV was +5.0% (SD = 0.74) and -5.1% (SD = 1.36) for POS and NEG groups, respectively. Heifers were reared at 2 successive facilities as follows: (1) calf rearing (enrollment to ∼13 wk of age) and (2) grazier, after 13 wk until 22 mo of age. All heifers wore a collar with an activity sensor to monitor estrus events starting at 8 mo of age, and we collected weekly blood samples when individual heifers reached 190 kg of body weight (BW) to measure plasma progesterone concentrations. Puberty was characterized by plasma progesterone concentrations >1 ng/mL in at least 2 of 3 successive weeks. Date of puberty was defined when the first of these samples was >1 ng/mL. Heifers were seasonally bred for 98 d starting at ∼14 mo of age. Transrectal ultrasound was used to confirm pregnancy and combined with activity data to estimate breeding and pregnancy dates. We measured BW every 2 wk, and body condition and stature at 6, 9, 12, and 15 mo of age. The significant FertBV by day interaction for BW was such that the NEG heifers had increasingly greater BW with age. This difference was mirrored with the significant FertBV by month interaction for average daily gain, with the NEG heifers having a greater average daily gain between 9 and 18 mo of age. There was no difference in heifer stature between the POS and NEG heifers. The POS heifers were younger and lighter at puberty, and were at a lesser mature BW, compared with the NEG heifers. As a result, 94 ± 1.6% of the POS and 82 ± 3.2% of the NEG heifers had reached puberty at the start of breeding. The POS heifers were 20% and 11% more likely to be pregnant after 21 d and 42 d of breeding than NEG heifers (relative risk = 1.20, 95% confidence interval of 1.03-1.34; relative risk = 1.11, 95% confidence interval of 1.01-1.16). Results from this experiment support an association between extremes in genetic merit for fertility base on cow traits and heifer reproduction. Our results indicate that heifer puberty and pregnancy rates are affected by genetic merit for fertility traits, and these may be useful phenotypes for genetic selection.

41 Diet-induced alterations in the hypothalamic and arcuate nucleus transcriptome in prepubertal heifers

Early onset of puberty is a key trait underpinning economically efficient cattle production systems. Although prepubertal plane of nutrition has been positively associated with earlier onset of puberty, the underlying biochemical mechanisms remain unknown. The hypothalamus, and particularly the arcuate nucleus (ARC), has a pivotal role during this developmental stage because it is a central regulator of homeostasis, mediating various neuroendocrine and physiological functions, including feed intake and reproduction. Thus, we hypothesised that a high plane of nutrition during early calfhood would affect the transcriptional profile of hypothalamic tissue, and in particular, elicit differential expression of biochemical pathways consistent with earlier sexual development in beef heifers. Angus×Holstein-Friesian heifer calves (19±5 days of age, 51.2±7.8kg, mean±s.d.) were offered a high (HP, n=14) or moderate plane of nutrition (MP, n=15) from 3 to 21 weeks of age to achieve target growth rates of 1.2 and 0.5 kg/d, respectively. At 21 weeks of age, calves were killed and the brain recovered. The ARC region was separated from the remainder of the hypothalamus, with both tissues flash frozen and subsequently used for RNA sequencing. Differential expression of genes (DEGs) was determining using R Bioconductor package EdgeR (version 3.20.9). The resultant list of DEGs was then submitted to Ingenuity Pathway Analysis and Weighted Gene Co-expression Network Analysis (WGCNA). At slaughter, bodyweight was higher in HP calves (189.6 vs. 113.0 kg; P&amp;lt;0.001). Compared with calves on MP, a high plane of nutrition altered the expression of 39 and 80 transcripts in the hypothalamus and ARC, respectively (P&amp;lt;0.05). COL15A1, CDH17, and IL20RA were among the most upregulated transcripts in both hypothalamic tissue sections. The HP treatment induced downregulation of AGRP and NPY and upregulation of POMC in the ARC, which have previously been associated with early onset of puberty in heifers. Functional analysis highlighted the importance of DEGs in the hypothalamus and ARC related to diets, with stress-signalling pathways among the most highly dysregulated pathways in both tissues. Through pathway analysis of the ARC DEGs, a total of 7 networks were derived, including one involved in organ morphology, reproductive system development and function, and developmental disorder. Interestingly, CGA, the most upregulated DEG in the ARC and a potential upstream regulator in this brain region, was one of the most connected genes within this network. Furthermore, WGCNA revealed that expression of some hub genes in networks of co-expressed genes, previously associated with puberty in cattle, was affected by diet in the ARC (POMC, CBLN2, and CHGA) and the remainder of the hypothalamus (PENK). The results of this study indicate that an enhanced plane of nutrition during early calfhood alters the biochemical regulation of the hypothalamus consistent with advanced sexual development in the prepubertal heifer. This research was funded by Irish Department of Agriculture, Food and the Marine (RSF 13/S/515).

106 In Utero Exposure of Ergot Alkaloids does not Impact Heifer Growth and Reproductive Performance

Abstract In utero exposure to toxins can alter fetal development and postnatal performance. The objective of this study was to investigate the effects of in utero exposure of ergot alkaloids via endophyte-infected (EI) fescue diets during gestation on heifer growth, onset of puberty, ovarian characteristics and AI pregnancy rates. Pregnant Angus and SimAngus cows grazed either endophyte-free (EF) or EI pastures on d90-180 of gestation. Assessment of puberty of heifer (n = 40) via measurement of BW, BCS, reproductive tract scores (RTS), pelvic area (PA) and weekly blood sample for progesterone (P4) analysis started at 10 mo of age. At 14 mos of age, all heifers were synchronized using the CoSynch+7d CIDR protocol and inseminated to examine reproductive measurements, follicle mapping and AI pregnancy rate. Data were analyzed using a MIXED procedure of SAS and examined for effects of EI, sire, and age. Statistical significance was determined at P &amp;lt; 0.05 and a tendency at 0.05 &amp;lt; P &amp;lt; 0.10. In utero exposure to EI did not affect ADG, BW, or BCS (P &amp;gt; 0.05) however, there was a sire by treatment interaction for ADG during onset of puberty (P &amp;lt; 0.05). While EI did not affect PA or RTS (P &amp;gt; 0.05), sire significantly influenced RTS and PA (P &amp;lt; 0.05) thus impacting of onset of puberty. Based on P4 concentrations, only 55% of all heifers were cyclic by 14 months of age and there was a sire by treatment interaction for onset of puberty (P &amp;lt; 0.05). No differences were observes in AI pregnancy rate between heifer groups (EF 39.5±7; EI, 43.7±7; P &amp;gt;0.05). While EI did not affect follicle counts or luteal area (P &amp;gt; 0.05), sire significantly influenced the percentage of preselected (2-4mm) and selected (&amp;gt;9mm), but not transitional (5-8mm), ovarian follicles at breeding age (P &amp;lt; 0.05). While consumption of EI fescue during gestation impacts cow performance and onset of puberty in heifers, it has minimal effect on heifer growth and reproductive development and performance.

To What Extent Does Photoperiod Affect Cattle Reproduction? Clinical Perspectives of Melatonin Administration – A Review

Abstract The seasonality of reproduction in most mammals is dictated by photoperiod, temperature and nutrition. Melatonin, mainly synthesized in the pineal gland, is generally accepted as the active mediator of photoperiod responses including reproduction. While non-pregnant heifers and cows show continuous sexual activity and are therefore not seasonal breeders, it has been suggested that photo-periodicity may influence the appearance of puberty in heifers and the onset of parturition. Further, the light/dark ratio may influence endocrine patterns of gestation and a shorter light period correlates with the incidence of twin pregnancies. This review considers specific aspects of the effects of photoperiod and melatonin on reproduction in dairy cattle and discusses the clinical applications of melatonin.

Feed supplementation affect age and weight at puberty in Girolando (Bos taurus x Bos indicus) heifers in the tropics

The effect of feed supplementation (FS) on age and weight at puberty, ovarian follicular population and blood progesterone concentrations was determined in 80 Girolando heifers. Heifers were distributed in four treatments: T1) 8-month-old heifers that received FS (n = 20); T2) 8-month-old heifers that received no FS (n = 20); T3) 10-month-old heifers that received FS (n = 20); and T4) 10-month-old heifers that received no FS (n = 20). Body weight was recorded at the beginning of the study and then every 21 days. Daily weight gain, total weight gain and weight at puberty were then determined. Heifers in T1 and T3 received each 2 kg of feed supplement daily until the onset of puberty. Ovarian structures were examined by transrectal ultrasonography to determine the population of medium size (4.1–8 mm) and large size (≥8.1 mm) follicles, growth of dominant follicles, ovulation and to confirm the presence of a corpus luteum (CL). Blood progesterone (P4) concentrations were determined on days 7 and 14 post-ovulation, using solid phase enzyme-linked immunosorbent assay (ELISA). Puberty was reached at an earlier age and heavier body weight in feed supplemented heifers. Follicular population, growth of the dominant follicle and blood P4 concentrations were higher (P<0.05) in the heifers given FS. Feed supplementation reduced the age at puberty in heifers by 4 to 5 months in both age groups. In conclusion, FS should be offered to heifers at 10 instead of 8 months of age, because this will shorten by 2 months the duration of the FS period.

205 Neuroendocrine pathways and the nutritional control of puberty in heifers

Abstract Approximately 5 million beef heifers enter the U.S. cow herd annually, and their lifetime productivity is heavily-dependent upon their ability to attain puberty and produce a calf by 24 mo of age. However, a significant proportion of heifers within existing U.S. production systems fail to achieve these objectives. Therefore, approaches are needed that facilitate nutritional programming of the reproductive neuroendocrine axis, while minimizing feeding costs and optimizing the consistent establishment of puberty by 14–15 mo of age. Accelerated rates of BW gain during early calfhood, particularly between 4 and 9 mo of age, facilitate pubertal development by programming hypothalamic centers that regulate GnRH secretion. Among the different metabolic hormones, leptin plays a critical role in conveying nutritional information to the brain and controlling pubertal progression. Two hypothalamic neuronal populations that express the orexigenic peptide neuropeptide Y (NPY) and the anorexigenic peptide alpha melanocyte-stimulating hormone (αMSH) are key components of afferent pathways that convey inhibitory (NPY) and excitatory (αMSH) inputs to GnRH neurons. Our studies have demonstrated that short-term increases in dietary energy intake during juvenile development result in epigenetic, structural, and functional modifications in these hypothalamic pathways to promote high-frequency, episodic release of GnRH/LH. However, integrating the foundational knowledge of metabolic imprinting of the brain for early puberty with issues related to lifetime performance is complex. One approach has been to employ a novel stair-step nutritional regimen involving alternating periods of dietary energy-restriction and re-feeding during juvenile development. This approach is designed to support early onset of puberty by imprinting genomic, biochemical and morphologic alterations in the hypothalamus during key periods of brain development while optimizing other aspects of growth and performance. Finally, our recent findings suggest that maternal nutrition during gestation can also induce neuroendocrine changes that are likely to persist long after puberty and influence reproductive performance throughout adulthood in cattle.

Body Weight and Blood Biochemical Changes Following Nutritional Supplementation in Prepubertal Jaffrabadi Buffalo (Bubalus bubalis) Heifers

The high plan of nutrition right from an early age is believed to enhance ovarian activity and early onset of puberty in heifers. This study was therefore conducted to know the body weight, ovarian and blood biochemical changes in nutritionally supplemented and control groups of prepubertal Jaffrabadi buffalo (Bubalus bubalis) heifers. A total of 12 animals of 30 ± 2 month's age and the identical body weight of 380–410 kg from Cattle Breeding Farm, JAU, Junagadh were utilized for this study. They were randomly divided into two equal groups of 6 animals in each treatment and control groups. The heifers of the treatment group were supplemented with bypass fat (100 g), bypass protein (950 g) and chelated mineral mixture (50 g) over the routine farm feeding practices of control group, and its effect on body weight gain and blood biochemical profiles were studied at a monthly interval during 6 months of experimental period. The overall effect of nutritional supplementation on animals body weight, blood glucose and total cholesterol over the control group was statistically non-significant (p greator than 0.05) yet beneficial. The plasma total protein levels in the supplemented group increased with a duration of supplement and levels were significantly (p less than 0.05) higher over the control group. The ovarian dynamics evaluated by transrectal ultrasound during last three months of the study revealed an increasing number of growing follicles greator than 4 mm in diameters (5.00 ± 0.13 to 6.67 ± 0.40), without significant variation in diameters of largest follicles (9.14 ± 0.45 to 10.27 ± 0.85 mm) between groups or periods. However, none of the heifers exhibited behavioral signs of estrus during 6 months study, in spite of the establishment of cyclicity with the presence of developed follicles, or CLs suggesting silent ovulation, at 36 ± 2 months of age in this breed.

Endocrine basis for puberty in heifers and ewes

Maturation processes that culminate in puberty and sexual maturity are initiated before birth, continue through prepuberty (> 50 days before puberty) and peripuberty (50 days before puberty) and are completed early after puberty. The hypothalamus is the primary site of change during transition to sexual maturity. Maturation of the hypothalamus results from decreased negative feedback of oestradiol that leads to increased frequency of release of LH pulses. Increased tonic release of LH pulses during sexual maturation is the primary endocrine factor that regulates the onset of puberty in ewe lambs and heifers. Increased frequency of release of LH pulses enhances development of ovarian follicles which produce enough oestradiol to induce behavioural oestrus and a preovulatory surge of gonadotrophins. In later stages of peripuberty, ovulation or luteinization of follicles results in transient increases in progesterone for shorter periods than is typical for luteal phases of the oestrous cycle of mature ewes and cows. Transient increases in progesterone are not generally preceded by behavioural oestrus. After the demise of the transient luteal structures, puberty is attained with occurrence of the first behavioural oestrus that is accompanied by ovulation and development of a corpus luteum with a typical lifespan. At puberty, all components of the hypothalamic-pituitary-ovarian axis are in place for oestrous cycles to be expressed. Factors that can influence the pubertal rise in release of LH pulses are genotype, gender, season of year when pubertal age is attained, growth or nutritional intake, social cues or treatment with exogenous progestins. Sexual maturation continues after puberty with an enhanced probability of pregnancy occurring from actions of ovarian steroids at the uterus.