Randomized, noninferiority trial evaluating the efficacy of a novel teat sealant in pasture grazed dairy cows.

The intramammary infusion at the end of lactation of a bismuth subnitrate internal teat sealant (ITS), with no antibiotic component has been shown to be an effective means of reducing new intramammary infections over the dry period. There has, however, been very few comparative studies between different brands of ITS under grazed pasture conditions. The objectives of this study were, therefore, to determine if a new bismuth subnitrate internal teal sealant (ShutOut, MSD Animal Health) was noninferior to Teatseal (Zoetis) regarding end-points such as (a) detection of the ITS product after calving, (b) clinical mastitis during the dry period and early lactation, and (c) subclinical mastitis at 30 to 60 d in milk. A total of 1,105 mixed-age cattle were enrolled across 2 farms comparing 2 ITS products for detection of the ITS at calving and prevention of clinical and subclinical mastitis. Both ITS contained 65% (2.6 g) bismuth salts emulsified in ≤ 1.4 g of mineral oil (ShutOut as investigational product, IVP; Teatseal as control product, CPT). At dry-off, treatment was allocated to every second cow. All cows met industry best practice criteria for using ITS treatment without antibiotics. Outcomes included detection of ITS at first stripping of the udder by the farmer, clinical mastitis (CM) from dry-off to 30 d following calving and subclinical mastitis at 30 to 60 d following calving. For ITS detection, a generalized mixed linear regression model was used to model the data, with clustering of quarters within cow accounted for by including cow as a random intercept. Clinical mastitis was analyzed at the cow-level using a Fisher's exact test, and SCC was modeled using a negative binomial distribution. The IVP was noninferior to the CPT for ITS detection following calving. There were 1344/1800 (71.5%) of quarters with ITS detection in the IVP in comparison to 1076/1604 (67.1%) of quarters in the CPT treated group. The quarter-level CM incidence risk was low (45 cases out 4,324 quarters; 1.04%). The overall cow-level CM risk was 4.1% (44/1081), with 20/540 (3.7%) cases in animals in the IVP group and 24/541 (4.4%) cases in animals in the CPT group. The IVP was noninferior to the CPT for cow-level mastitis incidence. The median SCC for all animals was 23,000 cells/mL, with a mean of 92,000 cells/mL. The back-transformed estimated marginal mean estimated SCC was 84,800 (95% CI 75,200-95,600) cells/mL for animals in the IVP group, and 98,800 (95% CI 87,600-111,300) cells/mL for animals in the CPT group. The IVP was, therefore, noninferior for all outcomes measured.

Changes in the metabolic profiles of dairy cows before and after calving that were mainly fed fodder beet (Beta vulgaris vulgaris L.) during the dry period.

Case history: Two commercial pasture-based farms within the North Canterbury district of New Zealand were feeding fodder beet (Beta vulgaris vulgaris L.) as a large proportion of the diet to cows during the dry period. On each farm 25 multiparous cows were blood sampled up to six times from 28 days before, to 21 days after calving (Day 0). Plasma samples were analysed for concentrations of ß-hydroxybutyrate (BHBA), non-esterified fatty acid (NEFA), Ca, Mg and P, and aspartate aminotransferase (AST) activity. The first sampling visit was performed when cows were being fed their maximum intake of fodder beet. Clinical findings: The mean body condition score (BCS) of cows on Farm 1 was 5.4 (95% CI = 5.3-5.6) and on Farm 2, 5.4 (95% CI = 5.3-5.6) at first sampling. Mean concentrations of BHBA increased between Days -15 and Day -8 then decreased postpartum on Day 2 before increasing again on Day 21. On Farm 2, concentrations remained low (<1.2 mmol/L) on all days of sampling. Mean concentrations of NEFA in plasma remained low during the periparturient period on Farm 1, then increased on Day 2. On Farm 2, concentrations were elevated above 0.3 mmol/L between Days -28 and -17 then decreased on Day -10, before increasing on Day 2. Mean concentrations of Ca, Mg and P were higher than threshold values on both farms prepartum. However on Day 2, there were 8/23 (35%) cows on Farm 1 and 6/23 (26%) cows on Farm 2 with concentrations of Ca in plasma <2.0 mmol/L, and 10/23 (44%) cows on Farm 1 and 8/23 (35%) cows on Farm 2 with concentrations of P in plasma <1.3 mmol/L. Mean AST activities remained relatively constant and below 130 IU/L on both farms at all sampling times. Clinical relevance: On both farms, post-partum hypocalcaemia and hypophosphataemia were common after calving despite differing fodder beet feeding and mineral supplementation regimes. There was more variation in energy status, especially prior to calving. More research is required on factors affecting mineral and energy status in dry cows fed fodder beet.

Vitamin B12 status and the effects of vitamin B12 supplementation during the first year of life of spring calves from pasture-fed dairy herds.

AIMS: To determine the vitamin B12 status of dairy calves during their first year of life, and to evaluate the benefits of vitamin B12 supplementation. METHODS: In Experiment I, 20 17-day-old heifer calves from the AgResearch Flock House herd were monitored until 198 days old. On Days 0 and 90 of the study, half of the animals received an injection of microencapsulated vitamin B12 at 0.12 mg/kg bodyweight. All received colostrum, milk replacer and calf meal, with ad libitum access to pasture. At regular intervals the calves were weighed and serum collected for vitamin B12 measurement. In Experiment II at Flock House and the adjacent Landcorp Tangimoana station, 80 150-day-old heifer calves were monitored until 342 days old. On Days 0 and 97, half of the animals received vitamin B12 as per Experiment I. At regular intervals samples were collected from 12 calves per group, to determine concentrations of vitamin B12 in serum. RESULTS: Mean concentration of vitamin B12 in milk replacer was 63 (SE 4) µg/kg dry matter (DM). Cobalt concentrations in calf meal were 0.45-1.58 and 0.07-0.28 mg/kg DM in pastures. From 17 to 198 days of age (Experiment I) mean concentrations of vitamin B12 in serum of the control group decreased from 119 (SE 8) to 57 (SE 5) pmol/L. From 150 to 342 days of age (Experiment II), overall mean concentrations of the control groups at Flock House and Tangimoana were 90 (SE 2) and 96 (SE 3) pmol/L, respectively. Vitamin B12 injections increased (p<0.001) serum concentrations for at least 90 days, with peak concentrations of 323 (SE 23) (Experiment I) and 520 (SE 22) (Experiment II) pmol/L reached 28-35 days after each injection. Liveweight gain was not increased by supplementation and there was no difference in final liveweight between groups. CONCLUSIONS: Concentrations of vitamin B12 in serum of unsupplemented calves prior to weaning indicated their vitamin B12 status was adequate due to the vitamin B12 and Co content of the milk replacer, and calf meal. Concentrations decreased during the transition to a pasture-based diet. Supplementation increased concentrations of vitamin B12 in serum but did not improve liveweight gains. CLINICAL RELEVANCE: Under this calf rearing system, vitamin B12 deficiency is unlikely to occur prior to weaning, and vitamin B12 supplementation is unlikely to increase growth rates of grazing calves when concentrations of vitamin B12 in serum are > 90 pmol/L.

Diagnosis of the Cu and Se status of dairy cattle in New Zealand: how many samples are needed?

AIM: To determine the minimum number of samples required to obtain a robust estimate of the Cu and Se status of dairy herds, as assessed by determining liver Cu and serum Se concentrations. METHODS: Results were collated from analyses of samples of liver from 18 dairy herds and serum from 19 herds, for concentrations of Cu and Se, respectively. All herds were in either the Manawatu or Rangitikei regions of the North Island of New Zealand. Data were used to determine the required sample size for each herd; firstly to estimate the population mean with 90% confidence with a precision of 27.5 nmol/L for Se in serum, and 100 µmol/kg fresh weight (FW) for Cu in liver; and secondly to ensure that the 90% CI of the sample mean did not include specified thresholds for concentrations of Se or Cu. RESULTS: For Se concentration in serum, the SD of each batch varied from 0.5-147 nmol/L, and for Cu concentration in liver, the SD varied from 173-829 µmol/kg FW. For Se, the minimum sample size required to estimate the population mean to within 27.5 nmol/L with 90% confidence was >10 for 13/19 batches. For Cu, the minimum sample size required to estimate the population mean to within 100 µmol/kg FW was >10 for 17/18 batches. When estimating required sample size based on 90% CI and a threshold value, the minimum sample size to confirm the population mean of Se was >140 nmol/L was four in 17/18 batches where the sample mean was>140 nmol/L. For concentrations of Cu in liver, ≤8 samples would have been sufficient for a threshold of 45 µmol/kg FW in 16/18 batches. For the 95 µmol/kg threshold, the minimum required was 12. For the threshold of 300 µmol/kg FW, 6/17 batches with a mean >300 µmol/kg FW required ≤ 20 samples. CONCLUSIONS: From this dataset of 21 herds, the sample size recommendation for ensuring that the population mean of Se concentration was not below the marginal threshold was similar to previous recommendations. For Cu concentrations in liver, the estimated sample size recommendations for ensuring that the population mean was not below the marginal threshold was much larger than currently recommended. CLINICAL RELEVANCE: In dairy cattle, five to six blood samples per group should be taken to determine Se status, and to effectively monitor Cu status a minimum of 12 liver samples should be taken, preferably in the autumn.