Allan John Gunn

Context: Compost-bedded pack (CBP) barns are increasingly used to house cows worldwide. They are loose housing facilities where an organic bedding base is mixed daily to remove faeces and urine from the bedding surface and oxygenate the pack, allowing composting to occur. These facilities face challenges in maintaining low moisture percentages within the bedding to ensure cow comfort and good udder health. Aims: To investigate current methods of managing CBP barns to maintain compost moisture and temperature at the recommended levels and assess the effectiveness of a bacterial and enzymatic treatment on bedding characteristics and cows’ preference. Methods: A 5-week multisite replicated exposure study was conducted on 40 areas of five commercial CBP barns in Australia from late autumn to early spring in 2023 and 2024. The packs were randomly divided into alternating control (n = 20) and treatment (n = 20) areas. All areas were monitored over 1 week to obtain a baseline before the treatment was applied in the 20 treatment areas at the start of Weeks 2 and 4, as per manufacturer recommendations. Compost temperature (°C), area per cow per study area (log m2/cow), and aerial ammonia concentrations (ppm) were assessed as outcome variables every 2 ± 1 day across all five farms. Three farms had additional outcome variables of compost moisture percentage and carbon to nitrogen ratio assessed weekly. Local weather conditions were measured daily, whereas the cultivation rate of the pack (m2/min) was recorded as a covariable for three farms. Multilevel mixed models were used to analyse the effects of treatment, covariables, and the interaction of treatment over time. Key results: There was no effect of treatment on bedding conditions. Aerial ammonia concentrations were detected only on 6 days. Reducing the cultivation rate (increasing the time spent per m2) of the pack was effective at increasing compost temperature. Conclusions: The product tested was not effective at improving bedding conditions nor did it change cow preference in the packs studied. Management of cultivation rate is important for maintaining bedding conditions. Minimal ammonia detection is a positive finding for human and cattle health in these barns. Implications: The product tested needs further evaluation under different bedding conditions if it is to be recommended for use. Australian CBP can be successfully managed to house dairy cows.

Age at first breeding (AFB) was investigated by breeding heifers from 5 commercial farms at >330 kg at younger or older than 13 mo of age. Heifers were weighed, and body condition scored at recruitment. Where the farmer elected to breed heifers 13 mo had a higher BW at enrolment and increased odds of abortion in their nulliparous year compared with the heifers with an AFB 13 mo an increased hazard of exit from the herd, a decreased risk for medical treatment and produced 891 L less milk over 305 d per enrolled heifer when compared with the heifers with an AFB 24 mo when compared with those with an AFC of 24 mo compared with 330kg) heifers to 10-13 mo of age may therefore be of benefit as a management strategy, though risks of increased medical treatment and stillbirth must be considered.

This study aims to determine the effects of feeding, management, and reproductive strategies used to reduce age at first calving (AFC) on production and reproductive performance through meta-analytic methods. A literature search using 3 search engines was conducted to identify prospective studies that evaluated AFC for data extraction. Inclusion criteria included specific dairy breeds, a treatment group with an AFC below 26 mo of age, and prospective enrollment of heifers. There were few prospective studies suitable for meta-analysis, with 16 studies containing 35 appropriate experiments. There was substantial heterogeneity, likely due to differences in study design and interventions used to induce an AFC difference. Outcomes were assessed using classical multilevel random effects meta-analytic models with standard mean difference, effect sizes, or risk ratios being evaluated where appropriate. Meta-regression was performed using the difference in AFC. There was a loss of production for first-lactation milk (-2.06 L/d of earlier calving), fat (-0.12 kg/d of earlier calving), and protein (-0.08 of kg/d earlier calving) yield for heifers calving at a younger age than their peers. There were no differences in second- and third-lactation milk yield, calving difficulty, heifer reproductive performance, survival to calving, and survival to the end of first lactation. Although the production in first lactation is decreased, this may be offset by fewer days to first calving without compromising the heifers' ability to calve, become pregnant for the first time, or survive to the end of first lactation. Given the lack of prospective studies, more randomized controlled experiments over multiple lactations, including health, production, and reproductive data, are needed to evaluate this topic further.

The sperm plasma membrane is of the utmost importance to the structural integrity and fertilising ability of the spermatozoon. Without a functional membrane, a spermatozoon cannot be expected to survive the arduous journey from testes to oviduct, particularly when its journey is disrupted by assisted reproductive technology (ART). In this study, we endeavoured to characterise a more complete bull sperm membrane-associated proteome through reanalysing publicly available RAW mass spectrometer data files from three previously published studies. Individually, these studies have utilised differing software platforms and inclusion criteria for their identification of membrane-associated proteins. The reanalysis of these datasets with standardised search criteria against up-to-date databases has identified 742 proteins. Amongst the proteins identified, 378 overlap with those reported in earlier studies, whereas we describe 364 previously unreported bovine sperm membrane-associated proteins linked to key functions, including zona pellucida binding. Next, the bovine proteome was mapped to human homologues (humanised), with a 96.8% conversion rate, allowing us to perform a more advanced functional analysis of the identified membrane-associated proteins, highlighting roles in energy metabolism, sperm motility, actin polymerisation, and protein ubiquitination. This deeper understanding of the bull sperm membrane-associated proteome will inform biomarker discovery for evaluating bull fertility and guide strategies to preserve sperm integrity during storage and ART procedures. Lay summary: In this study, we combined and reanalysed publicly available data files from three previously published studies to generate an updated list of the proteins associated with the membrane of bull sperm cells. We identified 742 proteins in total, of which 364 were not reported previously in the original studies. Membrane proteins are important because they sit on the surface of the sperm and control how it recognises and communicates with the egg. Our functional analysis of these proteins revealed roles in sperm motility, energy production, and key fertilisation events, such as binding to the egg. This study highlights the value of depositing data in public repositories so that older datasets can be reanalysed as analytical tools improve. A greater understanding of sperm membrane-associated proteins will improve knowledge of bull fertility with important implications for breeding and livestock production industries.

Objective: To determine if Intraperitoneal fluid therapy (IPFT) is an effective rehydration therapeutic option for dehydrated neonatal calves. Perceived risks and unknown efficacy have limited IPFT implementation into practice. It is hypothesized that IPFT will be an efficient and safe method of fluid administration to healthy neonatal calves. Methods: 4 L of isotonic saline was administered IP to healthy calves (n = 4). Control animals received no treatment (n = 2). Clinical and blood parameters were collected before and after fluid administration in all animals. Results: Girth diameter and transabdominal ultrasonographic fluid depth changes indicated fluid absorption from the abdominal cavity following IPFT. Total plasma protein, chloride, and sodium concentration changes demonstrated fluid absorption into the systemic circulation. Clinical parameters and serum amyloid A concentrations indicated the absence of inflammation during or following IPFT administration. Conclusions: This study indicates that IP saline was effectively absorbed into the systemic circulation within a clinically useful timeframe. Intraperitoneal fluid therapy is a viable treatment option for moderately dehydrated calves. Clinical Relevance: Fluid therapy is indicated in dehydrated calves primarily for volume replacement and when more than 8 days old for correcting acid-base aberrations. Those that are recumbent and unable to suck will likely require IV fluid therapy. The animals likely to benefit from IPFT are those that are able to suck and ambulate but are likely to require more than oral rehydration therapy.

Summary: Fungal endometritis and placentitis have been reported as a rare but important cause of infertility in the mare. There are no reported clinical cases of fungal endometritis causing embryonic loss in the mare. This case report aims to highlight the potential of fungal endometritis as an aetiological agent in embryonic loss in the mare; an incidental diagnosis of a case of fungal endometritis and embryonic loss while undertaking routine pregnancy assessments in a Standardbred mare. After a positive pregnancy diagnosis after 13 days post‐ovulation, a mare was diagnosed with endometritis and pregnancy loss associated with the growth of an unusual fungus, likely of the Acremonium spp., 28 days post‐ovulation. While fungal embryonic loss is rare, it should be considered a potential reason for pregnancy wastage in the mare.

Testicular heat stress is a well described phenomenon that occurs in mammals that possess a scrotum. Different models to induce testicular hyperthermia, such as surgical cryptorchidism, hot water bath, scrotal insulation or increased environmental temperature have all shown that spermatocytes and spermatids are unambiguously affected by high temperature, resulting in poor sperm production weeks later. Furthermore, a body of evidence suggest the involvement of oxidative stress is either a major or contributory pathway, which gives rise to the potential to overcome this condition. Whilst experimental models conclusively show the deleterious effect of testicular heat on sperm quality, the physiological relevance of the work is still debated. Herein we summarise a cohort of studies that report the effect of “season” on sperm quality. The data show season can affect sperm production, motility and morphology depending on where the work was performed. In countries where temperatures drop below zero, there is evidence showing summer conditions tend to improve semen quality. However, in sub-tropical countries, some studies show a decrease in summer, whilst others show no change. Herein we offer a reasonable explanation for this apparent controversy and present a range of antioxidant supplements that may offer some protection against testicular hyperthermia.

Our previous studies showed that microinjection into the median eminence of the sheep of glucagon-like peptide- 1 (GLP-1) or its receptor agonist exendin-4 stimulates luteinising hormone (LH) secretion, but it is unknown whether the same effect may be obtained by systemic administration of the same. The present study measured the response in terms of plasma LH concentrations to intravenous (iv) infusion of exendin-4. A preliminary study showed that infusion of 2 mg exendin-4 into ewes produced a greater LH response in the follicular phase of the oestrous cycle than the luteal phase. Accordingly, the main study monitored plasma LH levels in response to either 0.5 mg or 2 mg exendin-4 or vehicle (normal saline) delivered by jugular infusion for 1 h in the follicular phase of the oestrous cycle. Blood samples were collected at 10 min intervals before, during and after infusion. Both doses of exendin-4 increased mean plasma LH concentrations and increased LH peripheral pulse amplitude. There was no effect on inter-pulse interval or timing of the preovulatory LH surge. These doses of exendin-4 did not alter plasma insulin or glucose concentrations. Quantitative PCR of the gastrointestinal tract samples from a population of ewes confirmed the expression of the preproglucagon gene (GCG). Expression increased aborally and was greatest in the rectum. It is concluded that endogenous GLP-1, most likely derived from the hindgut, may act systemically to stimulate LH secretion. The present data suggest that this effect may be obtained with levels of agonist that are lower than those functioning as an incretin.