Effects of dietary phosphorus concentration during the transition period on plasma calcium concentrations, feed intake, and milk production in dairy cows

Environmental sustainability and ruminant production: A UK veterinary perspective

Environmental sustainability is an issue of growing importance within the livestock industry, particularly for farmed ruminants. Changes to farming practices made to improve sustainability can have an impact on the health and welfare of animals, and so become the concern of veterinary practitioners. This review outlines the metrics used to measure sustainability and how sustainability interacts with ruminant health and welfare, allowing practitioners to incorporate environmental considerations into their existing livestock work. Topics covered include nutrition, disease control, genetics and stocking density.

A new system of phosphorus and calcium requirements for lactating dairy cows

Accurately predicting phosphorous (P) and calcium (Ca) dietary requirements is critical for optimizing dairy cattle performance, and minimizing mineral excretions and ecosystems eutrophication. This study provides a new factorial system to determine net and dietary P and Ca requirements for maintenance and lactation, derived from a meta-regression of mineral trials involving lactating dairy cows. A comprehensive global database was constructed from 57 peer-reviewed articles of mineral balance trials, with a wide range of dietary and animal performance data. We estimated the net requirements for maintenance from the intercept of a nonlinear equation between mineral intake and the sum of total fecal and urinary excretions, which is an estimate of endogenous mineral loss. Mineral secreted in milk was used to obtain net requirements for lactation. The mineral metabolizable coefficient was quantified through observed (treatment means) mineral intake and total fecal and urinary excretions, discounting the estimated endogenous excretions from our proposed models. The nonlinear models of total fecal and urinary mineral excretion were evaluated (observed versus predicted values) using a 5-fold cross validation approach. The models to estimate the sum of endogenous fecal and urinary excretions of P (0.135±0.043 g P/kg BW0.75) and Ca (0.360±0.144 g Ca/kg BW0.75) exhibited suitable precision and accuracy; r = 0.89 and 0.79, concordance correlation coefficient = 0.85 and 0.77, and root mean square prediction error = 24.1 and 20.5% observed means, respectively. Dietary variables (forage level, fiber, starch, crude protein, and ether extract) did not affect the metabolizable coefficient (MC) of P and Ca; therefore, an overall dietary MC of P (0.69±0.01) and Ca (0.65±0.02) were proposed. Our new system estimates lower net and dietary P requirements for lactating dairy cows compared to the NASEM-2021 and NRC-2001 models, but slightly higher Ca requirements than NASEM-2021.This proposed system holds potential to reduce the use of phosphorus in diets for dairy cows, and thus to enhance economic efficiency and environmental sustainability of the dairy industry.

Acidified diet is not effective in preventing hypocalcemia in dairy cows on French commercial farms

The objective of this study was to assess, in the context of typical dairy farms in western France, the preventive effects of prepartum diet acidification (AcD) and mineral intake during late gestation on the incidence of subclinical hypocalcemia (SHC) and subclinical hypophosphatemia (SHP) after calving. We conducted a longitudinal study that followed a cohort of 371 Holstein cows from 26 French dairy farms; of these, 235 cows (15 farms) were supplied with anionic salts during late gestation, and 136 cows (11 farms) were not. Blood samples were collected from 1 to 22 cows per farm (average of 14.3 cows per farm) between 24 and 48 h after calving. Total calcium and inorganic phosphorus concentrations in plasma were then quantified by inductively coupled plasma - optical emission spectrometry. The effects of AcD on the incidence of SHC and SHP were assessed using mixed linear models that evaluated the cow-level factors parity, milk yield index, and individual health events/treatments, and the farm-level factors diet calcium and magnesium content, dietary phosphorus intake, vitamin D supply, diet crude protein content, and duration of AcD, with farm as a random effect. Approximately 55% of cows were diagnosed with SHC (calcium < 2.0 mmol/l, n = 203) and 37% with SHP (inorganic phosphorus < 1.3 mmol/l, n=136). The first model confirmed earlier findings that the risk of SHC is higher with increased parity (P ≤ 0.0001) and revealed a higher risk associated with high milk yield (P = 0.0005), high phosphorus intake (40–60 g/cow per day, OR = 3.5; ≥ 60 g/cow per day, OR = 7.3; P = 0.0003) and high vitamin D supply (≥ 19950 IU/cow per day, OR = 3, P = 0.007). The second model highlighted a greater risk of SHP with increasing parity (P = 0.03) and showed trends for the preventive effects of AcD (OR = 0.4, P = 0.07) and moderate amounts of phosphorus in the diet (OR = 0.4, P = 0.10). Overall, our results do not support the effectiveness of AcD in preventing SHC or SHP under field conditions examined here, probably resulting from insufficient diet acidification.

Implementation of hypocalcaemia prevention programmes in commercial dairy herds: From theory to practice

Hypocalcaemia prevention programmes have been widely studied in experimental settings, but their feasibility has not been assessed under field conditions. The main objective of this study was to evaluate, in the context of small dairy farms in western France, whether and how dairy farmers implement prevention programmes and manage the feeding of dry cows to prevent hypocalcaemia. Seventy-nine commercial Holstein dairy farms in Brittany (France) were enrolled in a qualitative study in 2019. We conducted in-person interviews with the farmers to 1) understand the rationale behind the type and seasonality of prevention programmes they implemented and 2) assess how closely they followed common recommendations when implementing them. Most farmers (80 %) used at least one prevention programme, especially supplying a mineral mix formulated to meet the needs of dry cows in late gestation (53 %), acidifying the diet in late gestation (37 %), and supplying calcium at calving (oral or injectable form, 37 %). The use of programmes depended on whether the diet composition varied throughout the year. Among farmers who provided an acidified diet, 25 % did not supply a specific mineral mix to dry cows to ensure an adequate amount of P, Ca, and Mg, which could decrease the effectiveness of the acidification programme. A lack of reliability in feeding practices, such as not weighing feed or not delivering feed frequently enough, was identified for 61 % of contributing farms. Management practices could result in supplying an unsuitable amount of P, Ca, or Mg immediately before calving; for example, inappropriate batching practices around calving were identified for 22 % (cows) to 32 % (heifers) of farms. In addition, nearly all contributing farmers had no processes in place to monitor the effectiveness of the programmes implemented. Reasons for this overall lack of compliance should be explored.

Potential of ESBL-producing Escherichia coli selection in bovine feces after intramammary administration of first generation cephalosporins using in vitro experiments

Selection and spread of Extended Spectrum Beta-Lactamase (ESBL) -producing Enterobacteriaceae within animal production systems and potential spillover to humans is a major concern. Intramammary treatment of dairy cows with first-generation cephalosporins is a common practice and potentially selects for ESBL-producing Enterobacteriaceae, although it is unknown whether this really occurs in the bovine fecal environment. We aimed to study the potential effects of intramammary application of cephapirin (CP) and cefalonium (CL) to select for ESBL-producing Escherichia coli in the intestinal content of treated dairy cows and in manure slurry, using in vitro competition experiments with ESBL and non-ESBL E. coli isolates. No selection of ESBL-producing E. coli was observed at or below concentrations of 0.8 µg/ml and 4.0 µg/ml in bovine feces for CP and CL, respectively, and at or below 8.0 µg/ml and 4.0 µg/ml, respectively, in manure slurry. We calculated that the maximum concentration of CP and CL after intramammary treatment with commercial products will not exceed 0.29 µg/ml in feces and 0.03 µg/ml in manure slurry. Therefore, the results of this study did not find evidence supporting the selection of ESBL-producing E. coli in bovine feces or in manure slurry after intramammary use of commercial CP or CL-containing products.