Evaluation of fully oxidised ß-carotene as a feed ingredient to reduce bacterial infection and somatic cell counts in pasture-fed cows with subclinical mastitis.

AIMS: To assess the effect of oral supplementation with fully oxidised ß-carotene (OxBC) on bacteriological cure, the incidence of clinical mastitis, and somatic cell counts (SCC) in pasture-fed cows with subclinical intramammary infection. METHODS: Cows from four dairy herds were enrolled in early lactation if they had quarter-level SCC >200,000 cells/mL and they had a recognised bacterial intramammary pathogen in one or more quarters. They were randomly assigned to be individually fed from Day 0, for a mean of 40 days, with 0.5 kg of a cereal-based supplementary feed that either contained 300 mg of OxBC (treatment; n = 129 quarters) or did not (control; n = 135 quarters). Quarter-milk samples were collected on Days 21 and 42 for microbiology and SCC assessment. Bacteriological cure was defined as having occurred when the bacteria present on Day 0 were not isolated from samples collected on Days 21 or 42. A new intramammary infection was defined as a bacterial species isolated either on Day 21 or 42 differing from that isolated on Day 0. Clinical mastitis was diagnosed and recorded by herdowners up to Day 42. RESULTS: The bacteriological cure rate was greater for quarters from cows in the treatment group (13.9 (95% CI = 4.1-23.7)%) than for cows in the control group (6.9 (95% CI = 4.8-9.1)%; p = 0.02). The percentage of quarters that developed a new intramammary infection at Day 21 or 42 was greater for cows in the treatment group (17.9 (95% CI = 6.7-29.1)%) than for cows in the control group (13.0 (95% CI = 4.3-21.8)%; p < 0.01). The prevalence of quarters that were infected on Day 42 was less in cows in the treatment group (79.9 (95% CI = 62.3-97.6)%) than the control group (88.2 (95% CI = 78.4-97.9)%; p = 0.009). The incidence of quarters diagnosed with clinical mastitis by Day 42 was lower in cows from the treatment group (1/129 (0.78 (95% CI = 0.02-4.24)%)) than in cows from the control group (6/135 (4.44 (95% CI = 1.65-9.42)%; p = 0.03)). Mean quarter-level SCC was not statistically different between treatment groups (p = 0.34). CONCLUSIONS AND CLINICAL RELEVANCE: Feeding 300 mg/cow/day of OxBC resulted in a higher bacteriological cure rate, a lower prevalence of intramammary infection, and a lower incidence of clinical mastitis compared to untreated controls. However new intramammary infections increased in treated cows, and the magnitude of the increased bacteriological cure was low, resulting in 80% of cows remaining infected at Day 42. Therefore treatment with OxBC should be considered as an adjunct to other mastitis control measures.

Risk factors for subclinical hypocalcaemia, and associations between subclinical hypocalcaemia and reproductive performance, in pasture-based dairy herds in New Zealand.

AIMS To estimate the herd-level prevalence of subclinical hypocalcaemia within 3 days of calving, to determine cow and herd-level risk factors for this condition, and associations with reproductive performance, in pasture-based cows in New Zealand. METHODS Between 10 and 15 clinically healthy cows ≥3-years-old (n=1,051) were enrolled from 76 spring-calving dairy herds. Blood samples were collected from all cows on 1 or 2 days within 3 days of calving, and assayed for total concentrations of Ca in serum. Subclinical hypocalcaemia was defined as concentrations of Ca in serum ≤2.14 mmol/L, and herd-level prevalence was the percentage of sampled cows with subclinical hypocalcaemia. Breeding and pregnancy diagnosis data were obtained for each cow to calculate reproductive outcomes. Herd-level data about management practices were collected from farmers at enrolment. Associations between cow-level variables, and reproductive outcomes, and subclinical hypocalcaemia were examined using multivariable logistic regression mixed models. Associations between herd-level variables and prevalence of subclinical hypocalcaemia were examined using a multivariable linear regression model. RESULTS Mean herd-level prevalence of subclinical hypocalcaemia was 52 (95% CI=49-55)%. Risk of subclinical hypocalcaemia at the cow-level was associated with an interaction between age of cow and interval from calving to sampling (p=0.03). Increasing age of cow was associated with increased risk of subclinical hypocalcaemia, and cows sampled on the day of calving had an increased risk compared with cows sampled 1 or 2 days after calving. Increased herd-level prevalence of subclinical hypocalcaemia was associated with feeding grass silage (p=0.06) or maize silage (p=0.004), and feeding increasing amounts of elemental Mg in the form of magnesium oxide (p=0.02). The mean farmer-reported herd-level prevalence of clinical hypocalcaemia was 2.9 (95% CI=2.1-3.8)%. Subclinical hypocalcaemia was not associated with any of the reproductive outcomes measured. CONCLUSIONS AND CLINICAL RELEVANCE There was a high prevalence of subclinical hypocalcaemia in the pasture-fed, spring-calving dairy herds sampled and a large between-herd variation in prevalence. Subclinical hypocalcaemia increased with increasing age, and declined with time postpartum. Herd-level prevalence was associated with feeding grass silage and maize silage to pre-calving cows and with increasing amounts of supplemented magnesium oxide. Subclinical hypocalcaemia was not associated with reproductive outcomes.

Effect of treatment with oral Ca boluses following calving on concentrations of Ca in serum in pasture-based dairy cows.

AIMS To assess the effect of the administration of two oral Ca boluses on concentrations of total Ca, ß-hydoxybutyrate (BHB) and non-esterified fatty acids (NEFA) in serum, and urine pH, in recently calved pasture-fed dairy cows. METHODS Friesian or Friesian cross Jersey cows from one dairy farm were blocked by age and randomly assigned to no treatment (control; n=14), or treatment (n=13) with two oral Ca boluses administered approximately 12 hours apart, with the first bolus being given within 14 hours of calving. Each bolus weighed 198 g and contained 43 g of Ca; 31 g of Ca from calcium chloride and 12 g of Ca from calcium sulfate. Cows were enrolled over three calendar days, and all cows were managed in one group during the 24-hour study period. Blood samples were collected at 0, 1, 2, 4, 8, 12, 13, 14, 16, 20 and 24 hours after the initial treatment. Serum from each time point was analysed for concentrations of total Ca, and from 0, 12, and 24 hours for NEFA and BHB. Urine was collected at 0, 12 and 24 hours for pH measurement and pH was categorised as <7 or ≥7. The effect of treatment on percentage change in concentrations of Ca in serum relative to 0 hours, and concentrations of NEFA, BHB and urine pH, was examined using multivariable repeated measures mixed models with cow as a random effect. RESULTS In the final multivariable model for percentage change in concentrations of Ca, there was an interaction between time and treatment (p=0.004), with the percentage increase being higher in treatment than control cows at 1, 2, 4, 8 and 13 hours. At 12 hours, 5/13 (41%) treated cows had a urine pH <7compared to 0/12 (0%) control cows (p<0.001), and at 24 hours 13/13 (100%) treated cows had urine pH <7 compared to 0/12 (0%) control cows (p<0.001). Over the 24-hour period, mean concentrations of NEFA or BHB in serum were similar in treated and control cows (p>0.3). CONCLUSIONS AND CLINICAL RELEVANCE Oral treatment with two Ca boluses increased concentrations of total Ca in serum and decreased urine pH in pasture-fed cows. This bolus has the potential to reduce the prevalence and duration of subclinical hypocalcaemia in recently calved cows.

Effect of altering the type of dietary carbohydrate early postpartum on reproductive performance and milk production in pasture-grazed dairy cows.

The objective of this study was to assess the effect of increasing dietary starch for approximately 30 d postpartum on reproduction outcomes in pasture-grazed, seasonal-calving dairy cows. Cows (n = 948) from 3 commercial herds were blocked by age (2, 3, and >3 yr), breed, and expected calving date and randomly assigned to 1 of 2 postpartum treatment groups: high starch (34.7 ± 1.9% nonstructural carbohydrate; mean ± SD) or low starch (22.5 ± 0.4% nonstructural carbohydrate). The high-starch group in all 3 farms received 4.0 to 4.5 kg/d of a 75:25 cracked corn:barley grain mixture in the dairy parlor, split evenly between the morning and afternoon milkings. The low-starch cows received 5.0 to 5.5 kg/d of a 50:50 mixture of palm kernel meal:soy hulls (herds 1 and 3) fed in the parlor; low-starch cows in the remaining herd (herd 2) did not receive a concentrate feed. Cows were cograzed on ryegrass-white clover dominant pastures and were offered corn silage (herds 1 and 3) and canola, corn distillers grain, and palm kernel meal (herd 1) throughout the study. At 1 mo before the start of the seasonal breeding period, the high-starch supplement was removed, and within each herd treatment groups were managed similarly through breeding. Presence of purulent vaginal discharge was assessed at 28 DIM, and tail paint was assessed weekly from 2 to 6 wk postpartum for signs of estrus. The interval to first observed estrus was unaffected by treatment (32.7 vs. 33.5 ± 2 d for high and low starch, respectively), but there were tendencies for a herd × treatment interaction for proportion of cows pregnant to first service and for pregnancy within 6 wk. This interaction was significant for the proportion of cows finally pregnant; a lower proportion of high-starch cows were pregnant to first service, pregnant by 6 wk, and pregnant by the end of the seasonal breeding period in herd 1, but diet did not affect these outcomes in the other herds. Our results do not support a positive effect on reproduction from increasing dietary starch in seasonally bred grazing dairy cows. However, the interactions indicate variability in the herd response to dietary starch early postpartum and imply that pregnancy rate could potentially be compromised through the provision of starch to grazing dairy cows in early lactation (i.e., prebreeding). The experiment was not designed to define the reasons for these interactions, but differences should be considered in future research on the subject.

Factors associated with colostrum quality in individual cows from dairy herds in the Waikato region of New Zealand.

AIMS: To examine associations between various cow-level factors and quality of first-milking colostrum (measured as Brix), and to evaluate herd-level associations between vaccination against calf diarrhoea and colostrum quality, in cows from dairy herds in the Waikato region of New Zealand. METHODS: A single colostrum sample was collected, by complete udder evacuation, from each of 20 cows from 29 dairy herds in the Waikato region of New Zealand during the 2016 spring calving period. Vaccination pre-partum with a calf diarrhoea vaccine was used in 15 herds. Each colostrum sample was tested using a digital Brix refractometer. The body condition score of each cow was recorded at the time of sample collection and farmers provided records of clinical mastitis and facial eczema from the previous 12 months, as well as the age and breed of cows. Associations between cow-level variables in non-vaccinated herds and Brix were examined using a multivariable linear mixed model and estimated marginal means obtained for different categories. RESULTS: Mean Brix of 281 samples from cows in non-vaccinated herds was 18.7 (SD 0.26)%; 63/281 (22.4%) samples had Brix ≥22% and 152/281 (54.1%) had Brix ≥18%. Mean Brix of colostrum samples from cows aged ≥6 years (20.2 (95% CI=19.1-21.2)%) was higher than for samples from 2-year-old cows (18.6 (95% CI=17.3-19.9)%) (p=0.005). Colostrum that was collected at the first milking on the day of calving had higher Brix (20.0 (95% CI=19.1-20.9)%) than colostrum collected from cows that calved the previous day (17.5 (95% CI=16.5-18.4)%) (p<0.001). Mean Brix of colostrum samples from cows which produced ≥8 L (18.2 (95% CI=17.1-19.2)%) tended to be lower than from cows which produced <8 L first-milking colostrum (19.1 (95% CI=18.3-20.0)%) (p=0.08). Among vaccinating herds, 9/15 (60%) had ≥60% colostrum samples with Brix ≥18% compared with 4/14 (29%) of non-vaccinating herds (p=0.04). CONCLUSIONS AND CLINICAL RELEVANCE: Colostrum quality, as measured by Brix, was associated with the total volume of first-milking colostrum, interval from calving to colostrum collection and cow age. Vaccination against calf diarrhoea was associated with a higher proportion of colostrum samples with adequate Brix. Careful selection of colostrum donor cows should ensure newborn calves are fed adequate quality colostrum which should be beneficial in preventing failure of passive transfer of IgG. Testing of colostrum from individual cows with a Brix refractometer is advocated for the selection of colostrum for feeding newborn calves.

Associations between management practices and colostrum quality on New Zealand dairy farms.

AIMS: To describe colostrum quality in spring-calving dairy herds in New Zealand, in terms of Brix, pH and total and coliform bacterial counts and to investigate associations between farm management practices and these measures of colostrum quality. METHODS: In June 2015, commercial dairy farms (n=105), located in North and South Islands of New Zealand, were visited shortly after the first cows had calved, and when approximately 50% and 80% of the herd had calved (early, middle and late visits). One litre of pooled colostrum that was being fed to newborn calves was collected at each visit and used to determine Brix, pH, total bacterial and coliform counts. A survey of calf management practices was conducted with the herd manager or calf rearer after the final visit. RESULTS: Of 298 pooled colostrum samples tested 29/298 (9.7%) had Brix >22%. Brix was higher on farms where calves were picked up twice daily compared with once daily (18.2 (95% CI=16.5-19.9)% vs. 15.9% (95% CI=15.2-16.6)%; p=0.012), and was lower where first milking colostrum was combined with colostrum obtained at later milkings (15.0 (95% CI=13.9-16.1)%) compared with where it was not (16.9 (95% CI=16.3-17.6)%; p=0.002). Vaccination of all cows against calf diarrhoeal pathogens was associated with increased Brix compared with no vaccination (18.1 (95% CI=16.6-19.6)% vs. 16.3 (95% CI=15.6-17.0)%; p=0.033). Mean pH of samples tested decreased from 5.97 (95% CI=5.84-6.09) to 5.58 (95% CI=5.45-5.71) for early and late-season visits, respectively (p<0.001). Of 268 samples tested, 23 (8.6%) had bacterial counts below the recommended threshold of 1.00×105 cfu/mL. Mean bacterial counts increased from 2.75 (95% CI=1.80-3.70)×108 to 4.99 (95% CI=3.95-6.03)×108 cfu/mL for early and late-season visits, respectively (p<0.001). Of 259 samples tested, 23 (8.9%) had coliform counts below the recommended threshold of 1.00×104 cfu/mL. CONCLUSIONS AND CLINICAL RELEVANCE: On a large majority of dairy farms included in this study the pooled colostrum fed to newborn calves had sub-optimal Brix and excessive bacterial counts. Farm-level risk factors such as twice daily pick up of calves from the paddocks, herd vaccination and feeding pooled colostrum that did not combine colostrum obtained at later milkings with first milking colostrum were associated with colostrum quality measures.

Influence of preservation methods on the quality of colostrum sourced from New Zealand dairy farms.

AIMS: To assess the effect of two temperatures (ambient temperature and 4°C), three preservation methods (no preservative, yoghurt and potassium sorbate), and two periods of storage (3 and 7 days) on Brix and total bacterial and coliform counts of colostrum collected from New Zealand dairy farms. METHODS: One litre of colostrum destined to be fed to newborn calves was collected from 55 New Zealand dairy farms in the spring of 2015. Six aliquots of 150 mL were obtained from each colostrum sample, with two aliquots left untreated, two treated with potassium sorbate and two with yoghurt, and one of each pair of aliquots stored at ambient temperature and the other at 4°C. All samples were tested for Brix, total bacterial counts and coliform counts before treatment (Day 0), and after 3 and 7 days of storage. The effect of preservation method and storage temperature on the change in Brix, bacterial and coliform counts after 3 or 7 days of storage was analysed using multivariable random effects models. RESULTS: For all outcome variables there was a temperature by preservation interaction. For aliquots preserved with potassium sorbate, changes in Brix and bacterial counts did not differ between aliquots stored at ambient temperature or 4°C, but for aliquots preserved with yoghurt or no preservative the decrease in Brix and increase in bacterial counts was greater for aliquots stored at ambient temperature than 4°C (p<0.001). For aliquots preserved with potassium sorbate, coliform counts decreased at both temperatures, but for aliquots preserved with yoghurt or no preservative coliform counts increased for aliquots stored at 4°C, but generally decreased at ambient temperatures (p<0.001). There was also an interaction between duration of storage and temperature for bacterial counts (p<0.001). The difference in the increase in bacterial counts between aliquots stored at 4°C and ambient temperature after 3 days was greater than between aliquots stored at 4°C and ambient temperature after 7 days. CONCLUSIONS AND CLINICAL RELEVANCE: Use of potassium sorbate to preserve colostrum for 3 or 7 days resulted in little or no reduction in Brix and a lower increase in total bacterial counts than colostrum stored without preservative or with yoghurt added. Colostrum quality was not affected by storage temperature for samples preserved with potassium sorbate, but storage at 4°C resulted in better quality colostrum than storage at ambient temperatures for colostrum with no preservative or yoghurt added.

Postnatal manganese exposure alters dopamine transporter function in adult rats: Potential impact on nonassociative and associative processes.

In the present study, we examined whether exposing rats to a high-dose regimen of manganese chloride (Mn) during the postnatal period would depress presynaptic dopamine functioning and alter nonassociative and associative behaviors. To this end, rats were given oral supplements of Mn (750 microg/day) on postnatal days (PD) 1-21. On PD 90, dopamine transporter (DAT) immunoreactivity and [3H]dopamine uptake were assayed in the striatum and nucleus accumbens, while in vivo microdialysis was used to measure dopamine efflux in the same brain regions. The effects of postnatal Mn exposure on nigrostriatal functioning were evaluated by assessing rotorod performance and amphetamine-induced stereotypy in adulthood. In terms of associative processes, both cocaine-induced conditioned place preference (CPP) and sucrose-reinforced operant responding were examined. Results showed that postnatal Mn exposure caused persistent declines in DAT protein expression and [3H]dopamine uptake in the striatum and nucleus accumbens, as well as long-term reductions in striatal dopamine efflux. Rotorod performance did not differ according to exposure condition, however Mn-exposed rats did exhibit substantially more amphetamine-induced stereotypy than vehicle controls. Mn exposure did not alter performance on any aspect of the CPP task (preference, extinction, or reinstatement testing), nor did Mn affect progressive ratio responding (a measure of motivation). Interestingly, acquisition of a fixed ratio task was impaired in Mn-exposed rats, suggesting a deficit in procedural learning. In sum, these results indicate that postnatal Mn exposure causes persistent declines in various indices of presynaptic dopaminergic functioning. Mn-induced alterations in striatal functioning may have long-term impact on associative and nonassociative behavior.