Cwr Compton

A review of prevention and control of heifer mastitis via non-antibiotic strategies.

Clinical and subclinical mastitis is a significant problem in primiparous dairy cattle (heifers) with a higher prevalence and incidence in heifers than cows, especially early in lactation. Differences in management (e.g. nutrition, pasturing, no use of dry cow therapy) as well as differences in physiological status (e.g. continuing growth in heifers) are likely contribute to the observed differences between heifers and cows. These differences may result in the requirement for different approaches for mastitis management in heifers than for cows. Mastitis is a multifactorial disease, hence control requires an understanding of the risk factors before effective interventions can be defined. Control strategies are aimed at reducing the incidence of new intramammary infections and eliminating existing infections. Potential strategies can include improved environmental and animal hygiene, application of internal and external teat sealants, prepartum application of teat antiseptics, prepartum milking and control of horn fly in environments where it acts as vector. Other less well-proven strategies to control heifer mastitis include management of heifers as a physically separate group from older cows and not feeding mastitic milk to calves. It is concluded that several well-proven strategies are available to manage heifer mastitis. However, further research is likely to improve understanding of heifer mastitis and lead to novel managerial approaches to mastitis control in this age group.

Relationships between endometritis and metabolic state during the transition period in pasture-grazed dairy cows

The primary objective of this study was to identify relationships between endometritis and metabolic state during the calving transition and early lactation periods. A subset of mixed age and breed dairy cows (n=78) from a seasonal, pasture-grazed herd of 389 cows was examined. The selected cows were grouped as having endometritis at d 42 postpartum or being unaffected by endometritis. Endometritis was defined as >6% (upper quartile) of uterine nucleated cells being polymorphonuclear cells (H-PMN; n=38); unaffected by endometritis was defined as ≤1% of nucleated cells being polymorphonuclear (L-PMN; n=40). Milk yield was determined at each milking, and milk composition (fat and protein) was determined at 2-wk intervals. Blood samples collected on d -14, 0 (d of calving), 4, 7, 14, 28, and 42 were analyzed for indicators of energy status (nonesterified fatty acids, glucose, and urea), liver function (albumin, globulin, glutamate dehydrogenase, and aspartate aminotransferase), inflammation (haptoglobin), and mineral status (Ca and Mg). Samples collected weekly from d 21 to 63 or 70 were analyzed for progesterone content. The postpartum anovulatory interval was defined to end on the first day postpartum that plasma progesterone concentration was ≥1 ng/mL. A greater percentage of H-PMN cows failed to ovulate before d 63 or 70 (34%) compared with L-PMN cows (10%), although the proportions of cows ovulating within either polymorphonuclear group was similar through d 56 postpartum. Plasma concentrations of albumin and the albumin:globulin ratio were consistently lower in H-PMN cows. Plasma Mg was lower, whereas glutamate dehydrogenase and aspartate aminotransferase were higher, in H-PMN cows during early lactation compared with L-PMN cows. Circulating metabolites indicative of energy status (nonesterified fatty acids, glucose, and urea) were not different between polymorphonuclear groups. Among 3- to 5-yr-old cows, daily milk yield for the first 42 d after calving was lower for H-PMN cows than for L-PMN cows. Among cows >5 yr old, protein percentage was lower in H-PMN cows compared with L-PMN cows. In summary, endometritis at 42 d postpartum in the herd studied was associated with an increased likelihood of remaining anovulatory. These cows had lower albumin concentrations throughout the calving transition period, perhaps indicating impaired liver function, with lower plasma Mg and evidence of hepatocellular damage in early lactation. Similar profiles of nonesterified fatty acids and glucose indicated that energy status was not a risk factor for endometritis.

Invited review: A systematic literature review and meta-analysis of mortality and culling in dairy cattle

Dairy industries and individual farmers are concerned about mortality and culling of dairy animals. This is because the timing and fates of animals that exit dairy farms have important animal welfare and economic consequences that reflect the conditions under which they are farmed and the efficiency of their production systems. Reports from a few countries have indicated increased incidence of mortality, and occasionally culling, of dairy animals in recent decades, and these changes have been associated with intensification of production systems. Dairy industries and farmers need benchmarks for culling and mortality against which they can compare themselves, as well as improved understanding of the extent of any change and of any associated factors. We reasoned that a systematic literature review and meta-analysis of scientific articles published between 1989 and 2014 would allow us to determine whether these reports were universal, to quantify any change over time, and to investigate whether production systems or study factors were associated with culling and mortality. From 3,275 articles retrieved from databases and manual searching of cited articles, 118 articles were appraised independently by 2 assessors, and 51 articles representing 54 studies were determined to be eligible for review and meta-analysis. We estimated that both the annual incidence risk (IR) and incidence density of mortality of cows had increased significantly from 0.02 per cow and 2.32 per 100 cow-years, to 0.04 per cow and 3.75 per 100 cow-years, an increase per decade of 0.02 per cow and 1.42 per 100 cow-years, respectively. We also estimated that the annual IR of culling attributed to low production had declined significantly from 0.07 to 0.05 and that the IR of perinatal, but not neonatal, mortality had increased significantly from 0.04 to 0.06 per decade. We found no evidence of change in overall annual IR of culling of cows over time or any association between study design factors and the IR or incidence density of culling or mortality. These findings provide benchmarks for describing culling and mortality, and should encourage farmers and researchers in countries with modern dairy industries to discover and implement management strategies to reduce the animal welfare and economic costs associated with these changes.

Factors influencing antimicrobial prescribing by veterinarians and usage by dairy farmers in New Zealand

Abstract AIMS: To determine the factors associated with the selection of antimicrobials by dairy veterinarians, and the attitudes of those veterinarians and dairy farmers to antimicrobial usage and resistance. METHODS: Facilitated focus groups of dairy farmers (n=22) and an anonymous online survey of dairy cattle veterinarians (n=206 respondents) were used to determine prescribing behaviour, factors affecting prescribing of antimicrobials, and the attitudes of veterinarians and farmers to the use of antimicrobials and the risk of antimicrobial resistance (AMR). RESULTS: Amongst the 22 farmers, the most common primary reason for choosing an antimicrobial was veterinary advice (87%) followed by personal experience (68%). Farmers had limited knowledge or concern about the risk of AMR, particularly outside their farm, with only 47% and 26% agreeing or strongly agreeing that use of antimicrobials on their farm would increase the risk of resistance in their herd and in humans, respectively. Prescribing of antimicrobials by veterinarians was predominantly based on diagnosis (168/206; 82%), and response to previous therapy (134/206; 65%), while duration above the minimum inhibitory concentration (43/206; 21%) was also considered important. Non-clinical factors such as withholding period (52/206; 25%) and farmers’ preferences (45/206; 22%) also influenced prescribing. Antimicrobial culture and susceptibility testing was not widely used, with 126/166 (76%) having culture results for less than four of the last 10 clinical mastitis cases for which they prescribed antimicrobials. Attitudes about prescribing and AMR varied with years of practice, gender and employment status. CONCLUSIONS: Veterinarians primarily considered technical reasons when prescribing antimicrobials. However non-technical factors did influence prescribing, in particular client feedback about perceived efficacy and perceptions of cost/benefit. Farmers stated that veterinarians were the most credible source of advice for selection of antimicrobials, but that personal experience on their farm was also important. CLINICAL RELEVANCE: Farmers’ perception of efficacy of antimicrobials, based on clinical outcomes, is an important determinant of their preferred choice of product. Hence, where changes in on-farm use patterns are required, clear communication by veterinarians about prudent antimicrobial choice and usage will require initial education around classes of antimicrobials and risk of resistance, as well as information around assessing efficacy of antimicrobial usage. Many veterinarians are in businesses that do not have practice prescribing policies. Such policies would likely lead to more consistent and judicious use of antimicrobials.

Reproductive performance in the subsequent lactation of dairy cows previously treated for failure to be detected in oestrus

Abstract AIM: To describe the effect of treatment of cows not detected in oestrus (NDO) with progesterone (P4) and oestradiol benzoate (ODB) in one lactation, on the reproductive and productive performance in the subsequent lactation. METHODS: Cows (n=770 from nine herds) which were NDO 10 days before the planned start of the seasonal breeding programme (PSM) were blocked by herd, age (2 or >2 years old) and ovarian status (i.e. with or without a palpable corpus luteum; CL), and treated either with an intravaginal progesteronereleasing device and ODB and resynchrony, or were left as untreated controls. In the following lactation, data were collected on the occurrence of endometritis, NDO, breeding dates, pregnancy test results and milk production. The effect of treatment and ovarian status in the previous lactation on the incidence of disease, and the proportions submitted for service, conceived and pregnant in the subsequent lactation were analysed. Calving dates and intervals from start of breeding to first insemination and conception were analysed using Kaplan Meier survival analysis. Additional multivariate analyses were undertaken to include known confounders such as age, breed, herd, calving date and milk production, as well as the cyclic status (i.e. previously cycling, NDO, or ‘late-calving’) in the previous lactation, to examine the potential ‘carryover’ effects of previous status on the reproductive performance in the subsequent lactation. RESULTS: Treatment of NDO cows resulted in an earlier calving date (Julian calving date 214, 95% CI=207–221, vs 224, 95% CI=220–228; p=0.005), more female calves reared (31.4% vs 23.3%; p=0.01), and reduced risk of being NDO (33.9% vs 46.1%; p=0.002) in the subsequent lactation compared with controls. There were no differences in the incidence of peripartum disease, or the proportion of cows submitted, conceived or pregnant between the Treatment and Control groups in the subsequent lactation (p>0.2). Previously CL-positive (+ve) NDO cows were less likely to produce a female calf that was reared (19.0% vs 29.9%; p=0.005), more likely to be treated as NDO (26.4% vs 18.6%; p=0.02), less likely to conceive by the end of the subsequent lactations breeding programme (82.2% vs 87.8%; p=0.09), and took longer to conceive (41 vs 33 days from the PSM to conception) than cows that were NDO-CL-negative (-ve) in the previous lactation. There was no interaction between ovarian status and treatment for any of the outcome variables (p>0.05). Cows that were NDO or late-calving in the previous lactation were more likely to be NDO (p<0.005), treated as NDO (p<0.005), and have longer PSM Animal Health Centre, PO Box 21, Morrinsville, New Zealand. Author for correspondence. Email: smcdoug@ahc.co.nz to conception intervals (p<0.005) in the subsequent lactation than cycling herdmates, despite inclusion of factors known to confound reproductive performance in analyses. CONCLUSIONS: Treatment of NDO cows resulted in more female calves reared, earlier calving and a reduced risk of being NDO in the subsequent lactation. Status (i.e. NDO-CL+ve or NDO-CL-ve) affected some reproductive measures in the subsequent lactation, and the effect of treatment in the subsequent lactation differed between the two groups for some measures. Reproductive performance in the subsequent lactation was not improved despite the earlier calving date and longer calving to PSM intervals. Additionally, the previous seasons status was still important in the subsequent seasons reproductive performance, despite adjusting for known confounders of fertility. CLINICAL RELEVANCE: The economic benefits from treatment of NDO cows are likely limited to effects of an earlier calving date and potential for longer lactation and increased milk yield, increased number of calves derived from artificial insemination and from a reduced number of NDO cows in the subsequent lactation. Effects of improved reproductive performance in the subsequent lactation were not demonstrated and hence should not be included in any economic analysis of therapy of NDO cows.

Serological and necropsy findings for rams infected with Brucella ovis which were not identified by the complement fixation test

The eradication of Brucella ovis from a commercial flock of 36 Romney rams was complicated by four infected rams remaining undetected despite four successive flock examinations using the complement fixation test. These four rams were subsequently tested using an enzyme-linked immunosorbent assay and a gel diffusion test and shown to be infected by semen culture. All four rams could have been identified as infected at the initial test if the enzyme-linked immunosorbent assay had been used in addition to the complement fixation test. Although gross evidence of epididymitis was found in only one ram at necropsy, three had histological lesions of epididymitis and all four had a seminal vesiculitis.

Randomised controlled trials demonstrate efficacy of a novel internal teat sealant to prevent new intramammary infections in dairy cows and heifers

Abstract AIMS: The main aim was to investigate the effectiveness of a novel internal teat sealant (ITS) formulation containing bismuth subnitrate and the antiseptic chlorhexidine, in adult cows (Trial A) and nulliparous heifers (Trial B), to reduce the incidence of new intramammary infection (IMI) between treatment and calving and reduce the prevalence of IMI within 6 days following calving. METHODS: In Trial A dairy cows (n=326) without history of clinical mastitis and with a maximum composite milk somatic cell count <200,000 cells/mL during the current lactation were enrolled from three spring-calving mainly pasture-based herds immediately following the final milking. In Trial B all heifers (n=166) were enrolled from two herds approximately 3 weeks before the start of calving. Glands were randomly assigned to controls or treatment with ITS, and mammary secretion samples were taken from all glands prior to treatment, and on two occasions 0–4 and 3–6 days post-calving to determine the incidence of new IMI and the prevalence of IMI immediately post-calving. Additionally, cows in Trial A were monitored for cases of clinical mastitis (CM) in the non-lactating period and animals in both trials were monitored for cases of CM within 30 days of calving. RESULTS: The ITS reduced the estimated incidence of new IMI with both major and any pathogens compared to control glands in cows (6.2 vs. 14.2% and 14.7 vs. 32.8%, respectively) and in heifers (3.0 vs. 13.1% and 13.4 vs. 25.3%, respectively) (p<0.001). The ITS reduced the estimated prevalence of a major or any pathogen compared to untreated controls at both 0–4 and 3–6 days post-calving, in both cows and heifers. Additionally, the ITS reduced the incidence of CM in the non-lactating period in cows (−1.0%, p=0.01) and in the 30 days following calving in heifers (−2.0%, p=0.06), and tended to reduce the estimated incidence of CM in cows post-calving (−1.7%, p=0.10). CONCLUSIONS: The novel ITS reduced the incidence of new IMI, and the prevalence of IMI at calving in both adult cows and heifers, and reduced the incidence of CM in the non-lactating period of cows and in the first 30 days after calving in heifers. CLINICAL RELEVANCE: The results of these trials demonstrate the efficacy of a novel ITS for the control of mastitis in likely uninfected dairy cows over the non-lactating period and in heifers in late pregnancy.

Subclinical ketosis in post-partum dairy cows fed a predominantly pasture-based diet: defining cut-points for diagnosis using concentrations of beta-hydroxybutyrate in blood and determining prevalence

AIMS: Firstly, to define, in dairy cows in the first 5 weeks post-calving fed a predominantly pasture-based diet, cut-points of concentrations of beta-hydroxybutyrate (BHBA) in blood, above which there were associations with purulent vaginal discharge (PVD), reduced pregnancy rates (PR) and decreased milk production, in order to better define subclinical ketosis (SCK) in such cattle; and secondly, to determine the prevalence, incidence and risk factors for SCK. METHODS: An observational field study was conducted in 565 cows from 15 spring-calving and predominantly pasture-fed dairy herds in two regions of New Zealand during the 2010– 2011 dairy season. Within each herd, a cohort of randomly selected cows (approximately 40 per herd) was blood sampled to determine concentrations of BHBA on six occasions at weekly intervals starting within 5 days of calving. The key outcome variables were the presence/absence of PVD at 5 weeks post-calving, PR after 6 weeks (6-week PR) and after the completion of the breeding season (final PR), and mean daily milk solids production. RESULTS: Two cut-points for defining SCK were identified: firstly concentration of BHBA in blood ≥1.2 mmol/L within 5 days post-calving, which was associated with an increased diagnosis of PVD (24 vs. 8%); and secondly concentration of BHBA in blood ≥1.2 mmol/L at any stage within 5 weeks post-calving, which was associated with decreased 6-week PR (78 vs. 85%). The mean herd-level incidence of SCK within 5 weeks post-calving was 68 (min 12; max 100)% and large variations existed between herds in peak prevalence of SCK and the interval post-calving at which such peaks occurred. Cows >8 years of age and cows losing body condition were at increased risk of SCK within 5 weeks of calving. CONCLUSIONS: Cows with concentration of BHBA in blood ≥1.2 mmol/L in early lactation had a higher risk of PVD and lower 6-week PR. Cow and herd-level prevalence of SCK varied widely in early lactation. CLINICAL RELEVANCE: Subclinical ketosis is common and is significantly associated with reproductive performance in mainly pasture-fed New Zealand dairy cattle. Controlling SCK may therefore result in improvements in herd reproductive performance. However considerable variation exists among herds in the incidence of SCK and in the timing of peak prevalence which means that herd-specific monitoring programmes are required to define herd SCK status accurately.

Prevalence of subclinical ketosis in mainly pasture-grazed dairy cows in New Zealand in early lactation

AIMS: The main aim of this study was to describe the prevalence of primary subclinical ketosis (SCK) in mainly pasture-grazed dairy cows in three dairy-farming regions of New Zealand 7–12, and 35–40 days post-calving. A second aim was to investigate herd- and cow-level factors associated with the prevalence of SCK. METHODS: A cross-sectional longitudinal prevalence survey was undertaken in 1,620 dairy cows from 57 herds. A random sample of cows without disease in the prior 30 days were enrolled at one farm visit within 5 days of calving, and blood samples were collected 7 and 28 days later (7–12 and 35–40 days post-calving) for measurement of beta-hydroxy butyrate (BHBA) concentrations using an electronic cow-side meter. SCK was defined as blood BHBA concentration ≥1.4 mmol/L. RESULTS: Mean cow-level prevalence of SCK varied with interval post-calving (16.8 and 3.2% at 7–12 days and 35–40 days post-calving, respectively) and age (13.0 and 13.1% of 2-year olds and ≥8-year olds, respectively, compared to 7.2% of 3–4-year-old cows). Mean herd-level prevalence of SCK was 14.3 (min 0, max 60.0)% and 2.6 (min 0, max 24.4)% at 7–12 days and 35–40 days post-calving, respectively, and was greater in Southland (13.3%) than Waikato and Canterbury herds (6.9 and 4.7%, respectively). CONCLUSIONS: This is the first population-based report of the prevalence of SCK in New Zealand dairy herds and demonstrates that age and interval post-calving are important risk factors determining prevalence; and that there is wide variation in prevalence between herds. CLINICAL RELEVANCE: Subclinical ketosis may be unrecognised but common in many New Zealand dairy cows in the first 2 weeks of lactation.

Evaluation of three synchrony programs for pasture-based dairy heifers

The objective was to evaluate the efficacy and economic benefits of three synchrony programs in 1137 heifers from 10 pasture-based dairy herds. Heifers were randomly assigned to one of three treatments within each herd on Day -13 (Day 0 = start of the breeding program). They were treated with: (1) PGF(2α) on Days -13 and -2, with AI after detection of estrus between Days 0 and 3 (Double PG); (2) GnRH, PGF(2α), and GnRH on Days -9, -2, and 0, respectively, with placement of an intravaginal progesterone (P4)-releasing device between Days -9 and -2, and set time AI on Day 1 (GPG + P4); or (3) same as the GPG + P4 group but with the set time AI on Day 0 (Cosynch + P4). Plasma P4 concentrations were determined on Days -20 and -13 to determine pubertal status. The Cosynch + P4 treatment had a higher (P < 0.05) conception rate to AI (57% vs. 47% vs. 48% for Cosynch + P4, GPG + P4, and Double PG, respectively), 21-day in-calf rate (76% vs. 72% vs. 63% for Cosynch + P4, GPG + P4, and Double PG), and a shorter median interval from the start of the breeding program to conception (0, 14, and 19 days for Cosynch + P4, GPG + P4, and Double PG). Heifers that had reached puberty before breeding, compared with those that had not, had higher (P < 0.05) in-calf rates to AI (53% vs. 47%) at 21 days (74% vs. 64%) and at 42 days (91% vs. 84%). Pubertal status was associated with herd, breed, age, and body condition score at the start of mating (P < 0.05). A partial budget model demonstrated that, compared with the Double PG program, there was an economic benefit from the Cosynch + P4 (mean, NZ