Dietary cation-anion difference
In a meta-analysis undertaken by Santos et al (2021) (Journal of Dairy Science10.3168/jds.2018-14628) the literature was systematically reviewed, searching randomised experiments with transition cows that manipulated the prepartum dietary cation-anion difference (DCAD) or experiments with acidogenic diets in which dietary Ca, P, or Mg were manipulated. Forty-two experiments, including 134 treatments and 1803 cows, were included in the meta-analysis. Of those, five experiments with 15 treatments reported responses for 151 nulliparous cows. Data collected included the mineral composition of prepartum diets, parity group prepartum, breed, days on treatment, and means and respective measure of variance for urine pH, dry matter intake (DMI), bodyweight, body condition, productive performance, concentrations of minerals and metabolites in blood, and incidence of diseases. Reducing the prepartum DCAD reduced intake prepartum but improved intake postpartum in both parity groups. Interactions between DCAD and parity group occurred for yields of milk, fat-corrected milk (FCM), fat, and protein because reducing the DCAD improved those responses in parous cows; however, reducing the DCAD either had no effect on yields of milk and protein or reduced the yield of FCM and fat in nulliparous cows. The equations from the statistical models predicted that reducing the DCAD from +200 to −100 mEq/kg would increase blood total Ca on the day of calving from 1.86 to 2.04 +/− 0.05 mM, DMI postpartum 1.0 kg/day, and milk yield 1.7 kg/day in parous cows. The increased concentrations of blood total Ca at calving and postpartum explained the marked reduction in risk of milk fever in parous cows with a reduction in DCAD. As the DCAD decreased, the risk of retained placenta and metritis also decreased, resulting in fewer disease events per cow in both nulliparous and parous cows. Dietary concentrations of Ca, P, or Mg prepartum had no effect on DMI or yields of milk and FCM; however, increasing dietary Ca within the study range of 0.16 to 1.98% of dry matter tended to increase the risk of milk fever in parous cows regardless of DCAD fed. Collectively, results support the recommendation of feeding prepartum acidogenic diets to result in a negative DCAD to parous cows. However, with nulliparous cows, productive performance was either depressed or unaffected and there was insufficient evidence to recommend DCAD for this group.
Measuring antimicrobial use
Antimicrobial use on UK dairy farms is measured for surveillance purposes, with veterinary sales data as a proxy for use. Two other methods of recording use have been used commonly onfarm: medicine waste bins and farm medicine records. The objective of this research by Rees et al (2021) (Journal of Dairy Science10.3168/jds.2020-18690) was to assess agreement between the three most common methods for measuring on-farm antimicrobial use with a predetermined reference method on UK dairy farms. Antimicrobial use was measured prospectively on 26 farms using medicine waste bins into which participants placed all discarded medicine packaging for a 12-month period. At the end of 12 months farm medicine records and veterinary sales data were obtained retrospectively for participating farms. The reference method used was based on pre- and post-study inventories combined with veterinary sales data. The systematic difference between the mean on-farm antimicrobial use measured by each of the three methods and a reference method was investigated. When compared with the reference method, veterinary sales data had excellent reliability for injectable antimicrobials and intramammary antimicrobials and moderate to excellent reliability for other antimicrobials. Medicine waste bins had good to excellent reliability for injectable, and intramammary products and no agreement for other forms of antimicrobial. Farm medicine records did not agree for any form of antimicrobial when compared with the reference method. The use of veterinary sales data as a proxy for on-farm antimicrobial use in the UK represented excellent statistical reliability and offered clinically good agreement with the reference method when used to measure injectable antimicrobials. These results have research and policy implications, both nationally and internationally, and their application may be essential in accurately quantifying antimicrobial use on dairy farms.
Attitudes of UK students towards farm animal careers
Within the production animal sector, it has long been forecast that demand for veterinary services could outstrip supply. A study by Payne et al (2021) (The Veterinary Record10.1002/vetr.455), which is also discussed in the editorial of this journal, aims to identify factors influencing veterinary undergraduates' attitudes towards a career in farm animal veterinary practice and how those factors may be influenced by their experiences during their time as undergraduates. An online survey was distributed to all vet schools in the UK and Ireland. Thematic analysis and descriptive data analyses were performed on the 1146 responses received. Seven themes were identified: relationships, preferences and interest, fit, direct experience, fear, ethics and values and lifestyle. When considering first job choice, extra mural studies (EMS) and personal interest (60% and 75% of respondents respectively) were very influential. Factors that appeal or put off respondents from a career with farm animals varied dependent on anticipated first job, but working hours and out-of-hours work were consistently identified as barriers to embarking on a production animal orientated career. EMS presents an excellent opportunity for veterinary surgeons to open discussion around undergraduate concerns (hours, salary, lone working, support etc) and to encourage and reassure students with positive experiences and up-to-date information on the working conditions in the sector.