Helen Marie Golder

Context: Evaluating diets to reduce methane production in calves. Aims: To determine whether diets with different combinations of pyromellitic diimide (PMDI), monensin, and fumaric acid would reduce methane concentrations and provide a production benefit without adverse outcomes in calves in a pilot study. Methods: Individually housed Holstein and Angus × Holstein calves, at a mean of 4.6 months of age, were block-randomised to the following four groups (n = 3 calves/group): (T1) no feed additives (negative control), (T2) monensin (20 mg/kg dry-matter intake, DMI) + fumaric acid (2.5 g/kg DMI) (positive control), (T3) PMDI (90.5 mg/kg DMI), and (T4) PMDI (90.5 mg/kg DMI) + monensin (20 mg/kg DMI) + fumaric acid (2.5 g/kg DMI). Treatments were mixed with dried distillers grain and fed once daily in a total mixed ration. The study included adaptation (8 days), treatment (27 days), and post-treatment (3 days) periods. Methane and carbon dioxide concentrations were measured during feed visitation for each calf for two consecutive days in adaptation and nine treatment days, by using air continuously collected from a semi-confined feeder in 4 of the 12 calf pens. Feed intake and health were recorded daily, and bodyweight (BW) weekly. Key results: Final BW and production measures did not differ among groups. The proportion of feed consumed in both the adaptation and treatment periods had treatment by day interactions but did not differ among treatments. Repeated measures of BW and average daily gain were not influenced by treatment. Methane concentration in the treatment period was 75.2% and 72.9% lower in both PMDI-containing treatment groups (T3 and T4 respectively) and 45.8% lower in the positive control (T2), than in the negative control (T1). Mean methane concentration decreased 25.6%, 38.4%, 82.0%, and 78.7%, for T1–T4 respectively, from the adaptation to treatment periods. Conclusions: Supplementation with combinations of PMDI, monensin, and fumaric acid all markedly reduced methane concentration during feeding without negative outcomes. Further studies are required to evaluate rumen degradation, long-term methane reduction, rumen fermentation, health, and productivity responses. Implications: Supplementation with PMDI has potential as a feed additive to reduce methane in ruminants.

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.

Dairy farming systems can be broadly classified as either housing-based dairy (HOUSED) or pasture-based dairy (PASTURE) systems. System-level differences in diet, housing, management, and milk production may influence health and reproduction of cows and the interaction of parity with these outcomes. This multi-site prospective, observational study investigated risks of pregnancy, mastitis, and lameness for different parities and housing systems (HOUSED and PASTURE). There were 15 HOUSED and 14 PASTURE Australian dairy farms enrolled, with health, reproduction, and production data collected from each farm between Feb 2022 to Jan 2026. Linear regression, logistic regression, and Weibull parametric survival models were used to assess the effects of parity, production system, and season on measures of pregnancy, mastitis and lameness. Robust sandwich estimators controlled within-farm correlation. The 100 d in-calf rate (100DICR, logistic regression) was not significantly different between PASTURE (34.0%; 95%CI: 28.0, 40.0) and HOUSED (32.9%; 95%CI: 28.9, 36.9) farms. The hazards of pregnancy (HPREG) assessed with a Weibull model were not different between PASTURE (1.04 HR, 95%CI: 0.82, 1.25) and HOUSED [1.08 hazards ratio (HR); 95%CI: 0.70, 1.45] farms. There was a monotonic decrease in the 100DICR and HPREG with increasing parity regardless of system. Cows breeding during Summer or Spring in PASTURE farms and Spring in HOUSED farms had reduced reproductive efficiency compared with other seasons. The effect of season was greater in PASTURE compared with HOUSED. There were 34,890 mastitis events across 129,039 lactation records. The crude incident rate of mastitis in HOUSED was 42.6 per 100 cows per 365 cow-days (95%CI: 41.9, 43.3) and 34.9 (95%CI: 33.7, 36.3) in PASTURE. The hazard of mastitis was numerically greater in HOUSED (2.85 HR, 95%CI: 1.10, 4.61) compared with PASTURE (2.13 HR, 95%CI: 1.62, 2.64) farms. The hazard of mastitis increased monotonically with parity. There were 9,495 cases of lameness across 125,362 lactation records. The crude incident rate was 8.75 per 100 cows per 365 cow-days (95%CI: 8.43, 9.07) in HOUSED and 10.7 (95%CI: 9.97, 11.4) in PASTURE. The hazard of lameness was similar in HOUSED (1.04 HR, 95%CI: 0.24, 1.84) and PASTURE (1.19 HR, 95%CI: 0.92, 1.44) farms. The hazard of lameness were unchanged in the first 3 (PASTURE) and 2 (HOUSED) parities but increased with parity thereafter. The association of increasing parity was far greater on health and reproductive outcomes than that of housing system. These results suggest that to support cow health and longevity we must address the impact of increased parity on health and reproduction of cows.

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.

This review examines the role glycerophospholipids ( PL ) in dairy cow health, with specific focus on phosphatidylcholine ( PC ), phosphatidylethanolamine ( PE ), phosphatidylinositol ( PI ) and phosphatidylserine ( PS ). Increasing parity of cows is associated with lower concentrations of plasma PL that contain very long-chain omega-3 fatty acids, including docosahexaenoic acid and eicosapentaenoic acid, which are precursors for prostaglandin synthesis, and have anti-inflammatory roles. Low concentrations of these PL could plausibly contribute to the increased risk of disease, reproductive failure and mortality in older cows. The bioavailability and metabolism of fatty acids may differ among supplements that are predominately neutral lipids, such as triacylglycerol-rich oils, and those bound to PL including pasture, whole or ground oilseeds and fish meal. Hepatic lipidosis can occur during the transition period if there is insufficient very-low density lipoproteins ( VLDL ) production in the liver to transport lipids into blood circulation. The PC are the primary PL of VLDL and are produced by two main pathways in the liver, the cytidine diphosphate-choline pathway that uses choline as a substrate, and the PE N -methyltransferase pathway that uses PE and methyl-donors as substrates. Co-supplementation strategies that target both pathways may increase PC production over a one-pathway supplementation strategy. The PIs are phosphoinositides precursors, which have broad physiological roles including regulating inflammatory processes and may offer targets for novel treatment and management of disease. Both the PI and PE are precursors to endocannabinoids, important regulators of energy metabolism, immune function and reproduction in mammals. Early findings on the endocannabinoid system in transition dairy cows yielded results that diverge from non-ruminant models. The PS expression on cytoplasmic membranes signals apoptosis, coagulation and contributes to sperm–oocyte recognition. As lipidomic diagnostics become increasingly available, understanding the metabolism of PL will continue to develop and promises to offer novel strategies for optimising cattle health and longevity.

Identifying physiological determinants of dairy cow survival and their potential modulation by parity may reveal opportunities to improve herd health and longevity. This multisite, prospective, observational study investigated culling and mortality hazards using targeted lipidomic and standard metabolite assays. Blood samples, stratified by parity, were collected from 2 cow cohorts (1) dry and (2) peak-milk, from across 29 commercial Australian farms (14 pasture-based, 15 confinement-based). There were 717 nonlactating, late-pregnant, dry cows (∼27 d prepartum) and 794 peak-milk cows (∼58 DIM) sampled. A total of 186 lipid species (including glycerophospholipids, sphingomyelin, and triacylglycerols) and 11 routinely measured metabolites were evaluated. Sample cows were followed for an average of 693 d and exit reasons recorded. Competing risk survival models were used to estimate the cumulative incidence of culling and mortality by parity and cohort. Blood analytes were autoscaled within cohort and farm, controlling for farm-level effect on metabolites. Survival analysis was performed using an adaptive least absolute shrinkage and selection operator (LASSO) Cox full likelihood model that explored associations among blood analytes and hazards of removal, with a shared frailty of farm (accounting for farm-level baseline hazards), and 2 removal outcomes considered: culling (censoring: death, cull from farm accident, end of follow-up) and mortality (censoring: cull, death from farm accident, end of follow-up). Separate models were used to estimate survival outcome by cohort and parity groupings (first, second and third, and greater than third) or with parity as a categorical covariate. Due to high correlations, analyte data were reduced to 25 clusters using Ward's hierarchical clustering criterion. Bootstrapping of the LASSO variable selection procedure identified clusters with high selection frequency for use in the final model. The hazards and cumulative incidence of culling and mortality increased with parity. Glycerophospholipids with very-long-chain n-3 fatty acids were associated with reduced hazards of culling in parity 1 peak-milk cows (0.39 hazard ratio [HR]), whereas glycerophospholipids with n-3 α-linolenic acid were associated with reduced hazards of culling in parity >3 peak-milk cows (0.18 HR). Sphingomyelin with >C18 fatty acyl chains was associated with increased hazards of culling in parity >3 peak-milk cows (2.02 HR). Clusters containing the routinely evaluated analytes albumin, globulin, urea, magnesium, glucose, triglycerides, β-hydroxybutyric acid, bilirubin, and nonesterified fatty acid were associated with culling and mortality, consistent with their roles in health and reproduction. Lipids collected from dry cows were poor predictors of survival. Many novel plasma lipid targets for future research into survival of cattle were identified, with proinflammatory lipid profiles associated with increased risk of culling and mortality.

Dairy cow housing and management can be broadly described as either intensive confinement-based (CONFINE) or extensive pasture-based (PAST) systems. The diets between systems typically differ in their forage base, with CONFINE farms often utilizing maize silage in a TMR. Consequently, the lipid composition of diets differs between systems. The influence of housing system on blood lipidomics is currently unknown, but due to the bioactive role of lipids in influencing overall health and productivity, differences in diet may have consequences for reproduction, health, and aging of cows. The objective of this cross-sectional, multisite study was to investigate blood lipids and metabolites from cows in PAST and CONFINE systems, in the dry period (∼27 d prepartum) and at peak milk (∼58 DIM). After exclusions, blood samples from 303 PAST and 398 CONFINE dry-period cows and 350 PAST and 431 CONFINE peak-milk cows from 15 PAST and 15 CONFINE farms were analyzed. A total of 185 lipid species (including glycerophospholipids, sphingomyelins, and triacylglycerols) were evaluated using targeted liquid chromatography-MS, as were 11 routinely measured metabolites. Dry and peak-milk cohorts were analyzed separately throughout. Lipids and metabolites associated with housing system were selected using a variable stabilization approach that was achieved by calculating the frequency of inclusion in categorical (housing system) penalized models using bootstrapping. Variables were retained if inclusion frequency exceeded a false-positive threshold. Five different statistical models were used with variable stabilization. Dry cows in CONFINE systems had decreased globulin, urea, and glycerophospholipids associated with n-3 fatty acids. The highest total inclusion rates in the dry cohort were phosphatidylcholine (PC; 36:5), which mostly comprises palmitic acid (C16:0) and eicosapentaenoic acid (EPA; 20:5n-3), then phosphatidylethanolamine (PE; 38:5, 16:0/22:5n-3 or 18:0/EPA) and PC(34:3; 16:0/18:3 α-linolenic acid [ALA]). No lipids were increased in more than one stabilized model in CONFINE dry cows. Peak-milk CONFINE cows had increased glycerophospholipids associated with n-6 fatty acids. The highest total inclusion-rate lipids in the peak-milk cohort were phosphatidylinositol (PI; 38:3; 18:0/20:3n-6 dihomo-γ-linolenic acid), PC(34:2; 16:0/18:2 linoleic acid [LA]), PC(40:7; 18:2/22:5n-6), PC(34:1; 16:0/18:1), and PE(34:2; 16:0/LA). The CONFINE peak-milk cows also had decreased PC(34:3; 16:0/ALA). This study identified specific lipids that were strongly associated with housing systems, findings that have not been reported elsewhere. Given the important biological functions of omega fatty acids, the pattern of glycerophospholipids with increased n-6 and decreased n-3 in CONFINE cows may indicate housing systems create different risk profiles for reproduction, health, and aging.

Context: How to improve integration of male dairy calves into red meat supply chains. Aims: To evaluate the effects of two diets differing primarily in starch, antimicrobial content and milk replacer volume on: (1) short- and long-term rumen adaptation; and (2) lifetime production in Holstein steers. Methods: Holstein males, 3–7 days old (n = 72; 36 steers/treatment; six per replicate), were randomised to control (CON; 6 L milk replacer/calf.day; 38.2% of DM lifetime dietary starch; 50 ppm monensin, 20 ppm flavophospholipol) or treatment (TRT; 4 L milk replacer/calf.day; 47.5% of DM lifetime starch diets with yeast products) strategies. Calves were fed milk replacer twice daily for 42 days, but different pre-starter (Days 0–24), starter (Days 25–99) and finisher diets (Days 100–452). Ruminal fluid was collected at 104, 200 and 438 days old (14 days pre-slaughter) from 24 steers (2 per replicate). Fermentation, production and carcass measures were analysed by mixed models; ruminal bacterial genera were centre log transformed and subjected to redundancy analysis. Key results: The CON group had a higher risk of subclinical ruminal acidosis at Day 438 than the TRT group (P < 0.001). Liver abnormalities were 17.1% (CON) and 31.3% (TRT). The CON group had greater fermentation, with 138.4 ± 5.6 mM of total volatile fatty acids versus 111.6 ± 5.6 mM (TRT), and 8.4 mM higher acetate and 18.1 mM higher propionate, but pH was 0.31 units less (P < 0.050). Shannon diversity increased over time (P < 0.001) and was greater for the TRT group at Day 200, compared with the CON group (P = 0.013). Bacterial composition differed at each treatment by time comparison (P ≤ 0.01), with variation increasing over time from 8.6 to 19.2%, suggesting the different diets lead to different microbial successions. The CON steers finished with 12 kg heavier carcasses than the TRT steers, with 0.8% greater dressing percentage, 1.5 mm more fat at P8 and 1.7 mm more rib fat (P < 0.050). Conclusions: CON diets produced better carcass weights, P8 and rib fat, and had more fermentability than the TRT diets, likely reflecting better long-term adaptation. Implications: Both diets enabled integration of dairy calves into the red meat supply chain, but with differing lifetime rumen adaptations.