Review: Role of early life nutrition in regulating sexual development in bulls.

The availability of high-quality semen from genetically elite bulls is essential to support continued genetic gain and the sustainability of cattle production worldwide. While reducing the age at which usable semen is available also reduces the generation interval, it is dependent on timely onset of puberty in young bulls. There is now good evidence that hastened sexual development in bulls is achieved through enhancing nutrition in early life. This review will cover the physiological and molecular-based response to prevailing diet in key organs that orchestrate the ontogeny of sexual development in the bull calf. Given the central importance of the interaction between metabolic status and neuronal function to the progression of sexual development, we will discuss how communication between metabolic organs, reproductive organs and the brain are mediated via molecular and physiological processes. The availability of high-throughput nucleic acid and protein sequencing technologies and innovative data analytics have allowed us to improve our understanding of molecular regulation of puberty and sexual development. Analysing data from a number of organs, simultaneously, allows for a better understanding of the underlying biology and biochemical interactions that are influencing sexual development. Specifically, we can determine how early life nutritional interventions augment changes in potential key molecules regulating sexual development. Ultimately, a greater understanding of the inherent regulation of postnatal sexual development in the bull calf and how strategically targeted nutritional management can advance the ontogeny of this process, will facilitate the timely availability of high-quality semen from genetically elite animals, thus supporting more economically and environmentally sustainable beef and dairy production systems.

Enhancing early life nutrition alters the hepatic transcriptome of Angus × Holstein-Friesian heifer calves.

Early life nutrition has a major influence on subsequent lifetime performance in cattle. The aim of this experiment was to investigate the effect of plane of nutrition from 3 to 21 weeks of age on the liver transcriptome. Holstein-Friesian × Angus heifer calves with a mean (±SD) age and BW of 19 (±5) days and 51.2 (±7.8) kg, respectively, were assigned to either a high-energy diet to support a mean average daily gain (ADG) of 1.2 kg/day (HI; n = 15) or a moderate diet (MOD; n = 15) to support a mean ADG of 0.5 kg/day. At 145 ±â€¯3 days of age, all calves were euthanised, liver tissue samples collected and flash-frozen in liquid nitrogen. Following RNA sequence analysis, the total number of differentially expressed genes (DEGs) (at false discovery rate (FDR) > 0.05) was 537; 308 upregulated and 229 downregulated in HI compared to MOD. The number of DEGs mapped to IPA (at FDR > 0.05) was 460; 264 upregulated and 196 downregulated. There was greater expression of genes associated with cellular development and metabolism in heifers on the HI compared to the MOD diet. The genes (fold change) of the somatotrophic axis; IGF1 (3.7), IGFALS (2.6) and GHR (1.5) were upregulated in the HI compared to MOD diet. The cytokine receptor genes, IL17RB (1.7) and IL20RA (3.3), were upregulated in the HI heifers, which were detected in a network interacting with metabolically regulated genes. The potential enhanced cell-to-cell communication evident from DEGs would increase the calves' ability to combat health challenges. The findings of this study indicate that enhancing the early life plane of nutrition in heifer calves results in the upregulation of genes that are associated with increased metabolic activity and thus metabolic capacity. Moreover, the interaction between metabolic and immune communication genes indicates that enhanced nutrition has the potential to improve the immune response in the liver which will play a central role in ensuring optimal lifetime performance.

Increasing the frequency of ejaculate collection in young dairy bulls increases semen production and field fertility.

Younger bulls typically produce lower volumes of semen per ejaculate with a lower sperm concentration than older more mature, bulls and often fail to meet semen demand using standard collection frequency schedules. The objective of this study was to assess the effect of ejaculate collection frequency on semen output, sperm quality and field fertility in young bulls under commercial conditions. Holstein Friesian bulls aged 366 ± 8 days (mean ± SEM) were assigned one of two ejaculate collection frequencies: (i) HF (n = 14 bulls), where ejaculates were collected twice a day, five days in each two-week period or (ii) LF (n = 12 bulls), where ejaculates were collected once a day, two days per week. The trial period continued until each bull reached both 20 ejaculates and 1000 marketable frozen semen straws. Subjective motility was assessed on all ejaculates pre-freeze and post-thaw (at 0 and 2 h). A subset of ejaculates were assessed post-thaw by computer-assisted sperm analysis for motility, kinematics and morphological defects and by flow cytometry for viability, membrane fluidity, acrosome integrity, reactive oxygen species and DNA fragmentation. A total of 13,846 inseminations (9,541 for HF and 4,305 for LF) were carried out on dairy cows and heifers. HF reached the 1000 straw threshold 41 days earlier than LF (P < 0.01) with the same number of ejaculates. Ejaculate volume and sperm concentration were not affected by treatment but the first ejaculate of the day (HF only) had a greater volume (P < 0.001) and sperm concentration (P < 0.05) than the second ejaculate. HF had higher pre-freeze total (P < 0.01) and gross (P < 0.05) motility than LF. HF had higher post-thaw (2 h) total and gross motility than LF (P < 0.05). Ejaculate rejection rates did not differ between treatments. There was no effect of treatment, week or ejaculate number of the day (HF only) on post-thaw motility and kinematic parameters or sperm viability, membrane fluidity, acrosome integrity and DNA fragmentation. However, HF had lower superoxide production than LF (P < 0.05). Pregnancy per artificial insemination was 64.5 ± 1.0% and 59.9 ± 1.1% for the HF and LF bulls, respectively (mean ± SEM; P = 0.05). In conclusion, collecting ejaculates more frequently from young bulls significantly reduced the number of days required to obtain 1000 straws, increased semen quality in terms of lower superoxide production and increased field fertility.

Fatty acid concentration of plasma, muscle, adipose and liver from beef heifers fed an encapsulated n-3 polyunsaturated fatty acid supplement.

Increasing the content of polyunsaturated fat in the human diet is a priority for reducing cardiovascular disease and cancer risks. Beef has the potential to contribute to the polyunsaturated fat content in the human diet; however, ruminants cannot synthesise many long-chain fatty acids de novo; they require dietary supplementation. The objectives of the current study were to evaluate (i) the effect of a partially rumen protected n-3 long-chain polyunsaturated fatty acid (LC-PUFA) dietary supplement on the fatty acid composition of muscle (Longissimus dorsi), adipose and liver tissues of beef heifers and (ii) the usefulness of blood plasma as a predictor of tissue concentrations of specific fatty acids. Charolais crossbred heifers (n = 20) were assigned to one of two isolipid dietary treatments namely palmitic acid (control) or an n-3 LC-PUFA supplement for a 91-day period. Blood plasma and adipose tissue samples were taken to determine the temporal effect of these diets on fatty acid composition (days 0, 10, 35 and 91), while liver and muscle samples were taken following slaughter. Dietary lipid source did not influence animal growth rate or body condition score. At day 91, the percentage differences between control and n-3 LC-PUFA heifers in concentrations of eicosapentaenoic acid were +61, +176 and +133 % in liver, muscle and adipose, respectively. For docosahexaenoic acid, at the same time point, the percentage differences were +57, +73 and +138 % for liver, muscle and adipose, respectively. Medium-to-strong positive correlation coefficients were evident for liver and plasma fatty acids, in particular, there were positive relationships with concentrations of total saturated fatty acid (SFA), total n-6 PUFA and total n-3 PUFA. This trend also extended to both the ratio of PUFA to SFA (slope (ß1) = 0.56 ±â€¯0.167, intercept (ß0) = 0.56, R2 = 0.61, P < 0.05) and the ratio of n-6 to n-3 PUFA (ß1 = 0.15 ±â€¯0.054, ß0 = 0.24, R2 = 0.52, P < 0.05). A strong correlation was also detected in the ratio of n-6 to n-3 in plasma and muscle tissue of heifers fed the n-3 LC-PUFA diet (ß1 = 0.53 ±â€¯0.089, ß0 = -0.31, R2 = 0.83, P < 0.001). The results of this study show that the n-3 LC-PUFA can be readily increased through targeted supplementation and that plasma concentrations of n-3 LC-PUFA are useful predictors of their concentrations in a number of economically important tissues.

Ewe breed differences in cervical anatomy and cervicovaginal mucus properties: An international study.

In sheep, cervical artificial insemination (AI) involves depositing semen at the cervical opening, as it is not possible to traverse the cervix due to its complex anatomy. However, internationally this method yields low pregnancy rates when frozen-thawed semen is used. An exception to this is in Norway, in which vaginal deposition of frozen-thawed semen to a natural estrus yields pregnancy rates around 70%. As the cervix and its secretions are the principal factors influencing sperm transport to the site of fertilization the aim of this study was to characterise the differences in the cervical anatomy as well as the cervicovaginal mucus properties of six European ewe breeds across three countries known to have differences in pregnancy rates following cervical AI with frozen-thawed semen. These were Suffolk and Belclare in Ireland, Fur and Norwegian White Sheep (NWS) in Norway and Ile de France and Romanov in France (n = 28-30 ewes/breed). Cervicovaginal mucus was collected at the follicular and luteal phases of both a synchronized and natural cycle and assessed for mucus weight, viscosity and colour. The anatomical characteristics of the cervix (length of the cervix, number of cervical rings and the appearance of the external os) were assessed post-mortem. There was a type of the cycle by ewe breed interaction represented by no differences in mucus production between ewe breeds at the natural cycle for both the follicular and luteal phases of the cycle. However, there were differences between ewe breeds at the synchronized cycle (P < 0.05). Belclare had the lowest mucus production at the follicular phase while NWS had the lowest amount of mucus at the luteal phase of the synchronized cycle. Overall, across all ewe breeds, mucus production was higher at the follicular than at the luteal phase (P < 0.05). Despite reports of Suffolk and NWS having the most divergent pregnancy rates following cervical AI with frozen-thawed semen, both breeds had the lowest overall mucus viscosity at the follicular phase of both types of cycle with no differences between both ewe breeds (P > 0.05). The length of the cervix, number of cervical rings and the external os type were affected by ewe breed (P < 0.05). Suffolk ewes had longer cervices but lower number of cervical rings than NWS and Fur ewes (both with higher pregnancy rates). In conclusion, while mucus production and mucus viscosity was affected by breed, these changes are not consistent with the known differences between ewe breeds in their pregnancy rates following cervical AI with frozen-thawed semen.

The Role of DNMT and HDACs in the Fetal Programming of Hypertension by Glucocorticoids.

The causes of hypertension are complex and involve both genetic and environmental factors. Environment changes during fetal development have been linked to adult diseases including hypertension. Studies show that timed in utero exposure to the synthetic glucocorticoid (GC) dexamethasone (Dex) results in the development of hypertension in adult rats. Evidence suggests that in utero stress can alter patterns of gene expression, possibly a result of alterations in the topology of the genome by epigenetic markers such as DNA methyltransferases (DNMTs) and histone deacetylases (HDACs). The objective of this study was to determine the effects of epigenetic regulators in the fetal programming and the development of adult hypertension. Specifically, this research examined the effects of the HDAC inhibitor valproic acid (VPA) and the DNMT inhibitor 5-aza-2'-deoxycytidine (5aza2DC) on blood pressure (BP) and gene expression in prenatal Dex-programmed rats. Data suggest that both VPA and 5aza2DC attenuated the Dex-mediated development of hypertension and restored BP to control levels. Epigenetic DNMT inhibition (DNMTi) or HDAC inhibition (HDACi) also successfully attenuated elevations in the majority of altered catecholamine (CA) enzyme expression, phenylethanolamine N-methyltransferase (PNMT) protein, and elevated epinephrine (Epi) levels in males. Although females responded to HDACi similar to males, DNMTi drove increased glucocorticoid receptor (GR) and PNMT expression and elevations in circulating Epi in females despite showing normotensive BP.

Effect of Early Calf-Hood Nutrition on the Transcriptional Regulation of the Hypothalamic-Pituitary-Testicular axis in Holstein-Friesian Bull Calves.

The aim of this study was to investigate the effect of early calf-hood nutrition on the transcriptomic profile of the arcuate nucleus of the hypothalamus, anterior pituitary and testes in Holstein-Friesian bulls. Holstein-Friesian bull calves with a mean (±S.D.) age and bodyweight of 19 (±8.2) days and 47.5 (±5.3) kg, respectively, were offered a high (n = 10) or low (n = 10) plane of nutrition in order to achieve an overall growth rate of 1.2 and 0.5 kg/day. At 126 (±3) days of age, calves were euthanized, hypothalamus (arcuate region), anterior pituitary and testicular parenchyma samples were harvested and RNAseq analysis was performed. There were 0, 49 and 1,346 genes differentially expressed in the arcuate nucleus, anterior pituitary and testicular tissue of bull calves on the low relative to the high plane of nutrition, respectively (P < 0.05; False Discovery Rate <0.05). Cell cycle processes in the anterior pituitary were down regulated in the low relative to the high plane of nutrition; there was no differential expression of genes related to reproductive processes. Gene expression involved in cholesterol and androgen biosynthesis in the testes were down regulated in animals on the low plane of nutrition. This study provides insight into the effect of early life plane of nutrition on the regulation of the HPT axis.

Role of early life nutrition on regulating the hypothalamic­anterior pituitary­testicular axis of the bull

The objective of this study was to examine the effect of nutrition during the first 18 weeks of life on the physiological and transcriptional functionality of the hypothalamic (arcuate nucleus region), anterior pituitary and testes in Holstein­Friesian bull calves. Holstein­Friesian bull calves with a mean (±S.D.) age and bodyweight of 19 (±8.2) days and 47.5 (±5.3) kg, respectively, were assigned to either a HIGH (n = 10) or LOW (n = 10) plane of nutrition, to achieve an overall target growth rate of 1.2 or 0.5 kg/day, respectively. At 126 ± 1.1 days of age, all calves were euthanised. Animal performance (weekly) and systemic concentrations of metabolic (monthly) and reproductive hormones (fortnightly) were assessed. Testicular histology, targeted gene and protein expression of the arcuate nucleus region, anterior pituitary and testes were also assessed using qPCR and immunohistochemistry, respectively. The expression of candidate genes in testicular tissue from post pubertal 19-month-old Holstein­Friesian bulls (n = 10) was compared to that of the 18-week-old calves. Metabolite and metabolic hormone profiles generally reflected the improved metabolic status of the calves on the HIGH (P< 0.001). Calves offered a HIGH plane of nutrition were heavier at slaughter (P < 0.001), had larger testes (P < 0.001), larger seminiferous tubule diameter (P < 0.001), more mature spermatogenic cells (P < 0.001) and more Sertoli cells (P < 0.05) in accordance with both morphological and transcriptional data. Overall, testicular gene expression profiles suggested a more mature stage of development in HIGH compared with LOW and were more closely aligned to that of mature bulls. Ghrelin receptor was the only differentially expressed gene between LOW and HIGH calves in either the anterior pituitary (P < 0.05) or arcuate nucleus region of the hypothalamus (P < 0.10) and was upregulated in LOW for both tissues. This study indicates that an enhanced plane of nutrition during early calfhood favourably alters the biochemical regulation of the hypothalamus­anterior pituitary­testicular axis, advancing testicular development and hastening spermatogenesis.

Review: The effect of nutrition on timing of pubertal onset and subsequent fertility in the bull.

The advent of genomic selection has led to increased interest within the cattle breeding industry to market semen from young bulls as early as possible. However, both the quantity and quality of such semen is dictated by the age at which these animals reach puberty. Enhancing early life plane of nutrition of the bull stimulates a complex biochemical interplay involving metabolic and neuroendocrine signalling and culminating in enhanced testicular growth and development and earlier onset of sexual maturation. Recent evidence suggests that an enhanced plane of nutrition leads to an advancement of testicular development in bulls at 18 weeks of age. However, as of yet, much of the neuronal mechanisms regulating these developmental processes remain to be elucidated in the bull. While early life nutrition clearly affects the sexual maturation process in bulls, there is little evidence for latent effects on semen traits post-puberty. Equally the influence of prevailing nutritional status on the fertility of mature bulls is unclear though management practices that result in clinical or even subclinical metabolic disease can undoubtedly impact upon normal sexual function. Dietary supplements enriched with various polyunsaturated fatty acids or fortified with trace elements do not consistently affect reproductive function in the bull, certainly where animals are already adequately nourished. Further insight on how nutrition mediates the biochemical interaction between neuroendocrine and testicular processes will facilitate optimisation of nutritional regimens to optimise sexual maturation and subsequent semen production in bulls.

Plane of nutrition before and after 6 months of age in Holstein-Friesian bulls: I. Effects on performance, body composition, age at puberty, and postpubertal semen production.

The aim of this study was to examine the effect of plane of nutrition (1) during the first 6 mo of life and (2) from 6 mo of age to puberty on early growth characteristics, age at puberty, and postpubertal semen production in Holstein-Friesian bulls. Holstein-Friesian bull calves (n = 83) with a mean (standard deviation) age and body weight of 17 (4.4) d and 52 (6.2) kg, respectively, were assigned to a high (Hi) or low (Lo) plane of nutrition for the first 6 mo of life. The Hi and Lo calves received 1,200 and 450 g of milk replacer, respectively; Hi calves were fed concentrate ad libitum and Lo were fed a maximum of 1 kg concentrate daily, and concentrate allowances remained the same after weaning. At 24 wk of age, bulls were reassigned within treatment to either remain on the same diet or to switch to the opposite diet until puberty, resulting in 4 treatment groups: Hi-Hi, Hi-Lo, Lo-Lo, and Lo-Hi. After puberty, all bulls were fed a moderate plane of nutrition until 60 wk of age; thereafter, the diet was ad libitum concentrates until slaughter at 72 wk of age. Bulls were weighed weekly before weaning and every 2 wk after weaning. Scrotal circumference (SC) was measured every 2 wk, beginning at 15 wk of age. Beginning at a SC of 24 cm, electro-ejaculation was carried out every 2 wk to establish the onset of puberty. Semen collection continued monthly after puberty. Thermal images of the scrotum were taken monthly from 28 to 36 wk of age. Scrotal skin thickness (SST) was measured monthly (from 16 wk of age to puberty) using a digital calipers. Bulls on the Hi diet had a higher scrotal temperature and SST at each time point than those on the Lo diet. Average daily gain (ADG) was greatest in Hi-Hi bulls, with Hi-Lo and Lo-Hi having similar ADG but both being greater than Lo-Lo. Bulls on the Hi diet pre-6 mo of age were younger at puberty, regardless of diet offered post-6 mo of age. Bulls offered a Hi diet post-6 mo were heavier at puberty. Neither scrotal temperature nor dietary treatment affected postpubertal semen production variables. In conclusion, a high plane of nutrition during the first 6 mo of age hastened the onset of puberty and the availability of saleable semen, regardless of plane of nutrition post-6 mo of age.

Plane of nutrition before and after 6 months of age in Holstein-Friesian bulls: II. Effects on metabolic and reproductive endocrinology and identification of physiological markers of puberty and sexual maturation.

The aim of this study was (1) to examine the effect of plane of nutrition during the first and second 6 mo of life on systemic concentrations of reproductive hormones and metabolites in Holstein-Friesian dairy bulls, and (2) to establish relationships with age at puberty and postpubertal semen production potential. Holstein-Friesian bull calves (n = 83) with a mean (standard deviation) age and body weight of 17 (4.4) d and 52 (6.2) kg, respectively, were assigned to a high or low plane of nutrition for the first 6 mo of life. At 24 wk of age, bulls were reassigned, within treatment, either to remain on the same diet or to switch to the opposite diet until puberty, resulting in 4 treatment groups: high-high, high-low, low-low, and low-high. Monthly blood samples were analyzed for metabolites (albumin, urea, total protein, ß-hydroxybutyrate, glucose, nonesterified fatty acid, triglycerides and creatinine), insulin, insulin-like growth factor-1, leptin, adiponectin, FSH, and testosterone. A GnRH challenge was carried out at 16 and 32 wk of age (n = 9 bulls per treatment). Blood was collected at 15-min intervals for 165 min, with GnRH administered (0.05 mg/kg of body weight, i.v.) immediately after the third blood sample. Blood samples were subsequently analyzed for LH, FSH, and testosterone. Stepwise regression was used to detect growth and blood measurements to identify putative predictors of age at puberty and subsequent semen quality traits. Metabolic hormones and metabolites, in general, reflected metabolic status of bulls. Although FSH was unaffected by diet, it decreased with age both in monthly samples and following GnRH administration. Testosterone was greater in bulls on the high diet before and after 6 mo of age. Testosterone concentrations increased dramatically after 6 mo of age. Luteinizing hormone was unaffected by diet following GnRH administration but basal serum LH was greater in bulls on a high diet before 6 mo of age. In conclusion, the plane of nutrition offered before 6 mo of age influenced metabolic profiles, which are important for promoting GnRH pulsatility, in young bulls.

Effect of breed, plane of nutrition and age on growth, scrotal development, metabolite concentrations and on systemic gonadotropin and testosterone concentrations following a GnRH challenge in young dairy bulls.

The onset of puberty in the bull is regulated by the timing of early GnRH pulsatility release from the hypothalamus, which has been demonstrated to be affected by plane of nutrition during calf-hood. The aim of this study was to determine the effect of plane of nutrition on growth rate, scrotal development, metabolite concentrations and exogenous gonadotrophin (GnRH) induced release of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone (TT) in pre-pubertal bulls of two contrasting dairy breeds. Holstein-Friesian and Jersey bull calves were assigned to either a high or low plane of nutrition from 3 to 49 weeks of age. Intensive blood sampling was conducted at 16, 24 and 32 weeks of age, every 15 min from 30 min prior to intravenous administration of exogenous GnRH to 135 min after. Monthly blood samples were also collected and analyzed for insulin like growth factor 1 (IGF-1), insulin, leptin, adiponectin and metabolite concentration. Insulin and IGF-1 were higher in bulls on a high plane of nutrition (P < 0.001) but were not affected by breed (P > 0.05). Leptin was not affected by plane of nutrition or breed (P > 0.05). Adiponectin tended to be higher in bulls on a high plane of nutrition (P = 0.05), but was not affected by breed (P > 0.05). Bulls on a high plane of nutrition had a greater concentration of LH in response to GnRH (P < 0.05) but there was no effect of breed (P > 0.05). FSH concentration was not influenced by breed or plane of nutrition but FSH concentrations did decrease with age (P < 0.01), while, LH was not affected by age (P > 0.05). Jersey bulls, particularly those on a high plane of nutrition, had higher TT production in the pre-pubertal period (P < 0.001). Using 28 cm as a proxy for age at puberty, bulls on a high plane of nutrition were predicted to reach puberty earlier than bulls on a low plane. In conclusion, the data clearly demonstrate that a high plane of nutrition positively affects several key nutritional and reproductive hormones which are critical to the endocrinological functionality of the hypothalamic-pituitary-testicular axis in dairy-bred bull calves.

Population pharmacokinetics of teicoplanin and attainment of pharmacokinetic/pharmacodynamic targets in adult patients with haematological malignancy.

OBJECTIVES: To describe the population pharmacokinetics of teicoplanin in adult patients with haematological malignancies receiving higher than standard doses, and to perform Monte Carlo simulations to determine dosing regimens associated with optimal teicoplanin concentrations. METHODS: This was a hospital-based clinical trial (EudraCT 2013-004535-72). Nine blood samples were collected on Day 3, plus single trough samples on Days 7 and 10, and 24 and 48 hours after the last dose. Teicoplanin minimum inhibitory concentrations were determined for Gram-positive isolates from study patients. Population pharmacokinetic analyses and Monte Carlo dosing simulations were undertaken using Pmetrics. RESULTS: Thirty adult haematological malignancy patients were recruited with a mean (SD) loading dose, age, total body weight, and creatinine clearance of 9.5 (1.9) mg/kg, 63 (12) years, 69.1 (15.8) kg, and 72 (41) mL/min, respectively. A three-compartment linear pharmacokinetic model best described the teicoplanin concentration data. Covariates supported for inclusion in the final model were creatinine clearance for clearance and total body weight for volume of the central compartment. The median (IQR) area under the concentration-time curve from 48 to 72 hours (AUC48-72h) was 679 (319) mg.h/L. There was a strong correlation between the AUC48-72h and trough concentration at 72 hours (Pearson correlation coefficient 0.957, p <0.001). Dosing simulations showed that administration of five loading doses at 12-hourly intervals, stratified by total body weight and creatinine clearance, increased the probability of achieving target concentrations within 72 hours. CONCLUSIONS: To increase the number of patients achieving optimal teicoplanin concentrations an individualized dosing approach, based on body weight and creatinine clearance, is recommended.

Effect of milk replacer and concentrate intake on growth rate, feeding behaviour and systemic metabolite concentrations of pre-weaned bull calves of two dairy breeds.

Early-life nutrition affects calf development and thus subsequent performance. The aim of this study was to examine the effect plane of nutrition on growth, feeding behaviour and systemic metabolite concentrations of artificially reared dairy bull calves. Holstein-Friesian (F; n=42) and Jersey (J; n=25) bull calves with a mean±SD age (14±4.7 v. 27±7.2 days) and BW (47±5.5 v. 33±4.7 kg) were offered a high, medium or low plane of nutrition for 8 weeks using an electronic feeding system which recorded a range of feed-related events. Calves were weighed weekly and plasma samples were collected via jugular venipuncture on weeks 1, 4 and 7 relative to the start of the trial period. The calves offered a high plane of nutrition had the greatest growth rate. However, the increased consumption of milk replacer led to a reduction in feed efficiency. Holstein-Friesian calves offered a low plane of nutrition had the greatest number of daily unrewarded visits to the feeder (P<0.001). ß-hydroxybutyrate (BHB) concentrations were greater in F calves on a low plane of nutrition (P<0.001). Although there was no effect of plane of nutrition, BHB concentrations in F calves increased before weaning, concomitant with an increase in concentrate consumption. Urea concentrations were unaffected by plane of nutrition within either breed. Jersey calves on a low plane of nutrition tended to have lower triglycerides than those on a high plane (P=0.08), but greater than those on a medium plane (P=0.08). Holstein-Friesian calves offered a high plane of nutrition tended to have greater triglyceride concentrations than those on a medium plane (P=0.08). Triglycerides increased from the start to the end of the feeding period (P<0.05), across both breeds. A medium plane of nutrition resulted in a growth, feeding behaviour and metabolic response comparable with a high plane of nutrition in pre-weaned bull calves of both F and J breeds.

Dietary polyunsaturated fatty acid supplementation of young post-pubertal dairy bulls alters the fatty acid composition of seminal plasma and spermatozoa but has no effect on semen volume or sperm quality.

The aim of this study was to examine the effects of dietary supplementation with rumen protected n-6 or n-3 polyunsaturated fatty acids (PUFA) on the quantity and quality of semen from young post-pubertal dairy bulls. Pubertal Holstein-Friesian (n = 43) and Jersey (n = 7) bulls with a mean ± s.e.m. age and bodyweight of 420.1 ± 5.86 days and 382 ± 8.94 kg, respectively, were blocked on breed, weight, age and semen quality (based on the outcomes of two pre-trial ejaculates) and randomly assigned to one of three treatments: (i) a non-supplemented control (CTL, n = 15), (ii) rumen-protected safflower (SO, n = 15), (iii) rumen-protected n-3 PUFA-enriched fish oil (FO, n = 20). Bulls were fed their respective diets, ad libitum for 12 weeks; individual intakes were recorded using an electronic feeding system for the initial 6 weeks of the feeding period. Semen was collected via electro-ejaculation at weeks -2, -1, 0, 7, 10, 11 and 12 relative to the beginning of the trial period (week 0). On collection, semen volume, sperm concentration and progressive linear motility (PLM) were assessed. On weeks -2, -1, 0, 10, 11, 12, semen was packaged into 0.25 mL straws and frozen using a programmable freezer. On weeks -1, 7 and 11; a sub-sample of semen was separated into sperm and seminal plasma, by centrifugation and stored at - 20 °C until analysis of lipid composition. Semen from 10 bulls per treatment were used for post-thaw analysis at weeks 10, 11 and 12 (3 straws per ejaculate). Sperm motility was analysed by computer assisted semen analysis (CASA). In addition, membrane fluidity, acrosome reaction and oxidative stress were assessed using flow cytometry. Sperm from bulls fed SO had a 1.2 fold higher total n-6 PUFA content at week 11 compared to week -1 (P < 0.01) while bulls fed FO had a 1.3 fold higher total n-3 PUFA content, in sperm by week 11 (P < 0.01). There was no effect of diet on semen volume, concentration or PLM of sperm when assessed either immediately following collection or post-thawing. Membrane fluidity and oxidative stress of sperm were also not affected by diet. The percentage of sperm with intact-acrosomes was lower in CTL bulls compared to those fed SO (P < 0.01). In conclusion, while the lipid composition of semen was altered following dietary supplementation with either n-6 or n-3 based PUFA, this did not lead to measurable improvements in the quantity or quality of semen produced by young post-pubertal dairy bulls.

Early onset of puberty in cattle: implications for gamete quality and embryo survival.

Advancing the age at which puberty and subsequent sexual maturation is attained in cattle is central to the reproductive and economic efficiency of both beef and dairy production systems worldwide. Onset of puberty in both male and female cattle is regulated by a complex network of biochemical processes and involves interaction among many key metabolic, neuroendocrine and reproductive tissues. Although our understanding of the biochemical interplay that conditions and eventually triggers the pubertal process has improved in recent years, much of the intricate mechanistic detail still eludes us. Environmental factors, such as nutritional management, as well as the genetic makeup of the animal undoubtedly affect the timing of puberty in cattle. In particular, there is now overwhelming evidence to support the importance of early life nutrition in regulating the timing of puberty in both bulls and heifers. For both genders, there is significant evidence that an improved metabolic status, early in calfhood, advances maturation of the hypothalamic-pituitary-gonadal axis, therefore facilitating earlier sexual development. Although advancing sexual maturation is a desirable goal, it is important that any strategy used does not impinge upon normal gametogenesis or postpubertal fertility potential. To this end, the aim of this review is to discuss the underlying biology of puberty in cattle with particular emphasis on the role of nutritional management during early calfhood in: (1) advancing the maturity of the hypothalamic-pituitary-gonadal axis; and (2) implications for the quality of gametes and subsequent fertility.

Utilization of brown trout Salmo trutta by Acanthocephalus clavula in an Irish lake: is this evidence of a host shift?

The population biology of the fish acanthocephalan Acanthocephalus clavula was described from 161 wild brown trout, Salmo trutta sampled over a two-year period in Clogher Lake in the west of Ireland. Overall prevalence of the parasite was 86% and the mean abundance was 53 worms per fish. Despite the presence of large numbers of worms in the trout very few females (2%) attained full reproductive maturity. This suggests that trout is an accidental host. A sample of yellow eels, Anguilla anguilla was examined at a different time from the same lake. The prevalence of A. clavula was 97% and the average abundance was 8 worms per fish. In contrast to the situation in trout, the proportion of female worms attaining full reproductive maturity was 61% fulfilling the expected characteristic of a preferred definitive host. The possible explanations for the very high abundance of A. clavula in trout are discussed and include the influence of fluctuations in host populations, host diet and the absence of a potential competitor.

Interspecific interactions between Acanthocephala in the intestine of brown trout: are they more frequent in Ireland?

The aim of this paper was to test the hypothesis that when the 2 species of Acanthocephalan Pomphorhynchus laevis and Acanthocephalus clavula are found concurrently within the intestine of brown trout under field conditions, they have the potential to interact negatively. Evidence has shown that Acanthocephala are more likely to exhibit negative interactions with their own and other species, under both field and experimental conditions. Furthermore, the likelihood of these interactions is increased in Ireland because of the absence of certain definitive hosts and the fact that concurrent infections by two or more species of Acanthocephala are more commonly observed in fish. Data collected from wild and stocked brown trout and from 2 lakes provided an opportunity to compare the 2 potentially interacting helminth species in their fundamental and realized niche and several pieces of convincing evidence are provided here to support the hypothesis. A significant negative association between the numbers of each species found in individual fish was reported and this was consistent for both wild and stocked trout. Furthermore, an analysis of the proportions of low, moderate and high intensity infections in single and concurrent infections revealed a significant reduction in increasing intensities in concurrent infections compared to single infections. Finally, strikingly different patterns of niche inhabitation were observed, particularly for P. laevis in the presence of A. clavula in wild trout. Results from the niche width analysis also support the observations on average position in single and concurrent infections. The niche width of P. laevis when it co-occurred with A. clavula decreased markedly in high intensity infections compared to low intensity infections.

Comparison of the macroparasite communities of wild and stocked brown trout (Salmo trutta L.) in the west of Ireland.

The aim of the present study was to compare the helminth infra and component communities of wild and stocked brown trout in Lough Feeagh, in the west of Ireland, and also to examine the establishment and development of helminth communities in stocked brown trout. Fish were sampled in May, August and November 1997 and 1998 and an additional sample of wild brown trout was examined in April 1997. In total 217 wild trout and 122 stocked trout were examined. The acanthocephalans Acanthocephalus clavula and Pomphorhynchus laevis were the first parasite species to infect stocked trout in May 1997. In May 1998 both acanthocephalan species along with the trout specialists Eubothrium crassum and Crepidostomumfarionis were the first to infect trout. Mean species richness values for stocked trout increased from May to November, in 1997 and 1998. For wild trout, mean species richness values increased from April to November, in 1997 and decreased from May to November in 1998. The parasite communities of wild trout were richer than those of stocked trout in May of both years. In August the parasite communities recorded for wild and stocked trout were similar in terms of the number of species present but differed in terms of structure, and in November the parasite communities of stocked trout were richer than those of wild trout.

Parasite community similarity between four Irish lakes.

A total of 140 trout were examined from four lakes in north west Ireland, Loughs Craghy, Waskel, Meela and Owennamarve. Eleven species of metazoan parasite were recorded, ten of which were of freshwater origin and Anisakissp. was the only marine species. No acanthocephalan species were found. Diphyllobothrium ditremum, D. dendriticum and Anisakissp. were the only allogenic species. Lough Owennamarve had the largest component community with nine species recorded. Lough Meela, the only brackish water lake had the smallest component community with six species recorded. Lough Waskel and Craghy had intermediate component community values. Lough Meela showed the lowest levels of similarity to any of the other lakes. Values for the Shannon-Wiener diversity index were highest for Lough Owennamarve and lowest for Lough Meela and intermediate for the other two lakes. Lough Meela had the highest values for the Simpson's dominance index and the Berger-Parker index. Lough Owennamarve had the highest Brillouin's index and Lough Meela had the lowest. The use of multiple regression techniques to control for the potentially confounding effect of geographical distance as a predictor of community similarity was discussed. No parasite species found could be considered as regionally and locally abundant and therefore described as a core species. The helminth community appears to have some degree of predictability, but chance colonization events are also important.