A review of thermal stress in cattle

Cattle control body temperature in a narrow range over varying climatic conditions. Endogenous body heat is generated by metabolism, digestion and activity. Radiation is the primary external source of heat transfer into the body of cattle. Cattle homeothermy uses behavioural and physiological controls to manage radiation, convection, conduction, and evaporative exchange of heat between the body and the environment, noting that evaporative mechanisms almost exclusively transfer body heat to the environment. Cattle control radiation by shade seeking (hot) and shelter (cold) and by huddling or standing further apart, noting there are intrinsic breed and age differences in radiative transfer potential. The temperature gradient between the skin and the external environment and wind speed (convection) determines heat transfer by these means. Cattle control these mechanisms by managing blood flow to the periphery (physiology), by shelter-seeking and standing/lying activity in the short term (behaviourally) and by modifying their coats and adjusting their metabolic rates in the longer term (acclimatisation). Evaporative heat loss in cattle is primarily from sweating, with some respiratory contribution, and is the primary mechanism for dissipating excess heat when environmental temperatures exceed skin temperature (~36°C). Cattle tend to be better adapted to cooler rather than hotter external conditions, with Bos indicus breeds more adapted to hotter conditions than Bos taurus. Management can minimise the risk of thermal stress by ensuring appropriate breeds of suitably acclimatised cattle, at appropriate stocking densities, fed appropriate diets (and water), and with access to suitable shelter and ventilation are better suited to their expected farm environment.

Farm economic impacts of bovine Johne's disease in endemically infected Australian dairy herds

OBJECTIVE

To determine the farm economic impact of bovine Johne's disease (BJD) infection and controls in commercial Victorian dairy herds.

DESIGN

Benefit-cost analysis of BJD and various control methods in a Victorian dairy herd.

RESULTS

Farm losses from BJD occurred from clinical disease. Clinical cases occur on average in 5-year-old cows, resulting in losses of A$1895 in the year of culling and A$221 in the year preceding culling, giving a total loss of A$2116. Early removal also resulted in loss of future profit equating to A$375 per year. This is the annualised value of foregone future income and costs expressed as a net present value (NPV). The total loss from removal of a clinical case was estimated as A$2491. The average clinical incidence in infected dairy herds prior to entry into the Victorian Bovine Johne's Test-and-Control Program (TCP) was 1.8% and the average Victorian dairy herd size was 262 cows in 2013-14, resulting in annual losses of 4.7 clinical cases if infected and implementing no BJD control. Farm annual loss of profit was estimated as A$11,748 ($44.84 per cow/year). Control of BJD using vaccination, test-and-cull or combined approaches was economical but the cost of implementation in initial years would exceed disease costs. Vaccination-based control provided minimal long-term losses and was the most cost-effective control over a 10-year planning horizon.

CONCLUSION

Endemic BJD resulted in modest but persistent losses in typical infected dairy herds. Control of disease using test-and-cull, vaccination or combined test-and-cull with vaccination was cost-effective.

Efficacy of inclusion of equine chorionic gonadotrophin into a treatment protocol for anoestrous dairy cows

AIM

To compare the performance of intravaginal devices containing 1.0 g (DIB) or 1.38 g (CIDR) progesterone and to determine the efficacy of inclusion of equine chorionic gonadotrophin (eCG) into progesterone-based anoestrous cow treatment protocols for New Zealand dairy cows.

METHODS

Anoestrous cows (n = 1,906) from 12 herds were randomly assigned to four treatments: 100 μg gonadorelin (GnRH) at Day -10; 500 μg cloprostenol at Day -3; 100 μg GnRH at Day -1 and fixed time artificial insemination (FTAI) on Day 0 (gonadotrophin-prostaglandin-gonadotrophin [GPG] group, n = 475); GPG with CIDR device (1.38 g progesterone) inserted between Day -10 and Day -3 (CIDR group, n = 477); GPG with DIB device (1.0 g progesterone) inserted between Day -10 and Day -3 (DIB group, n = 477); and DIB with 400 IU eCG at Day -3 (DIB + eCG group, n = 477). Conception rates to FTAI and pregnancy at Day 28 were analysed using generalised estimating equations (GEE). Time to conception and time to return to oestrus were analysed using Kaplan-Meier survival analysis and Cox's proportional hazards regression.

RESULTS

The proportion of cows conceiving to FTAI was 0.34 (95%CI = 0.29-0.37), 0.38 (95%CI = 0.34-0.43), 0.38 (95%CI = 0.33-0.42) and 0.41 (95%CI = 0.37-0.46) for GPG, CIDR, DIB and DIB + eCG groups, respectively. The proportion of cows pregnant by Day 28 was 0.55 (95%CI = 0.51-0.60), 0.57 (95%CI = 0.52-0.61), 0.56 (95%CI = 0.52-0.60) and 0.63 (95%CI = 0.59-0.67) for GPG, CIDR, DIB and DIB + eCG groups, respectively. There was an interaction between treatment and number of days calved (p < 0.05). Cows more than 60 days calved and treated with DIB + eCG had higher FTAI conception and 28-day pregnancy rates than cows treated with GPG (p < 0.001). Median interval to conception did not differ between treatments (p > 0.05). There were no differences between DIB and CIDR groups for any parameter (p > 0.05). The range of the relative risk distribution among herds comparing DIB + eCG to DIB groups was greater than that comparing CIDR to DIB groups for conception to FTAI and pregnancy at Day 28.

CONCLUSIONS

The inclusion of eCG into progesterone-based anoestrous cow treatment protocols improves conception to FTAI and 28-day pregnancy rates in cows >60 days calved at treatment compared with a GPG protocol. There was no difference in clinical performance between DIB and CIDR devices.

CLINICAL RELEVANCE

The combination of a low payload (1.0 g) progesterone releasing intravaginal device with eCG treatment at device removal within a GPG treatment is a clinically effective treatment for anoestrous in New Zealand dairy cows.

The characterization of lactic acid producing bacteria from the rumen of dairy cattle grazing on improved pasture supplemented with wheat and barley grain

AIMS

To identify and characterize the major lactic acid bacteria in the rumen of dairy cattle grazing improved pasture of rye grass and white clover and receiving a maize silage and grain supplement with and without virginiamycin.

METHODS AND RESULTS

Eighty-five bacterial isolates were obtained from the rumen of 16 Holstein-Friesian dairy cows. The isolates were initially grouped on the basis of their Gram morphology and by restriction fragment length polymorphism analysis of the PCR amplified 16S rDNA. A more definitive analysis was undertaken by comparing the 16S rDNA sequences. Many of the isolates were closely related to other previously characterized rumen bacteria, including Streptococcus bovis, Lactobacillus vitulinus, Butyrivibrio fibrisolvens, Prevotella bryantii and Selenomonas ruminantium. The in vitro production of L- and/or D-lactate was seen with all but five of the isolates examined, many of which were also resistant to virginiamycin.

CONCLUSION

Supplementation of grain with virginiamycin may reduce the risk of acidosis but does not prevent its occurrence in dairy cattle grazing improved pasture.

SIGNIFICANCE AND IMPACT OF THE STUDY

This study shows that lactic acid production is caused, not only by various thoroughly researched types of bacteria, but also by others previously identified in the rumen but not further characterized.

Manipulation and control of the estrous cycle in pasture-based dairy cows

Treatments designed to synchronize luteolysis, preovulatory follicular development, and ovulation, and resynchronize estrus after a first AI have improved responses to synchronization treatments. Protocols based only on the use of PGF result in variable onset of estrus. Concentrations of progesterone prior to administering PGF have affected submission rates and fertility while administration of estradiol benzoate (EB) after inducing luteolysis has improved the synchrony of estrus and ovulation in some studies. In pasture-based dairy cows, GnRH-based protocols have generally resulted in one-third of both anestrous and cycling cows conceiving following synchronization of ovulation and timed AI. Protocols which use intravaginal progesterone releasing inserts (IVP4) are effective in inducing estrus in over 90% of treated dairy cows. Resynchronization of estrus after reinsertion of an IVP4 also improves the synchrony of returns to estrus, but pregnancy rates to the first AI have been reduced in some studies, and submission rates at a resynchronized estrus are less than at the first synchronized estrus. Administration of EB can be used to synchronize follicle wave emergence in resynchronized cows with intervals to new wave emergence comparable to that in cows synchronized for a first AI, but plasma concentrations of progesterone following treatment may be reduced. Synchronization of estrus and ovulation can be enhanced by administration of EB or GnRH during proestrus, but dose, timing and stage of follicular development at the time of treatment can affect outcomes.

A comparison of performance of the Ovsynch treatment program between cycling and non-cycling cows within seasonally-calving dairy herds

OBJECTIVE

To compare performance of the Ovsynch program on reproductive performance between cycling and non cycling cows in seasonally-calving herds.

PROCEDURE

An Ovsynch mating program (100 mg Gonadorelin on day 1 and day 9, 500 mg of Cloprostenol on day 7 with fixed time artificial insemination on day 10) was administered to 3,559 cows from 14 herds in Australia and New Zealand. Cycling status before planned start of mating was determined. All cows were treated and artificial insemination continued for at least 25 days after fixed time artificial insemination. Pregnancy testing was performed 75 to 100 days after fixed time artificial insemination. Multivariable modelling examined the impact of the Ovsynch program and other risk factors upon reproductive performance.

RESULTS

Thirty percent of cows were classified as no visible oestrous (NVO). Odds of being NVO increased significantly for cows that were young, recently calved, and in low body condition. The fixed time artificial insemination conception rate was 35.7% and 33.2%, 21-day pregnancy rate was 54.5% and 48.4% and 42-day pregnancy rate was 69.7% and 62.6% for cycling and NVO cows respectively. Odds of pregnancy increased significantly for cows calved more than 40 days by planned start of mating, in greater body condition, and cycling, and there was a significant interaction between body condition and cycling status in both models. The return-to-service rates by 24-days were 67.6% and 55.9% and by the end of the AI period were 86.9% and 81.5% for cycling and NVO cows respectively. Odds of return to service increased significantly for cows in greater condition score in both models. Odds of return were increased for cycling cows in the 24-day multivariable model.

CONCLUSION

The Ovsynch program may provide a useful treatment option for NVO cows within seasonally-calving pasture-based dairy herds.

The sensitivity and specificity of single manual examination tests for detection of corpora lutea in the ovaries of non-cycling cows

OBJECTIVE

To evaluate the sensitivity and specificity of single manual examination of ovarian surface structures and of ovarian size as tests for the detection of corpora lutea in non-cycling cows

DESIGN

Non cycling cows were dichotomously classified for the presence of palpable corpora lutea and for ovarian size. The performance characteristics of the palpable corpus luteum test and the ovarian size test were estimated using Bayesian analysis. Previously published information on prevalence and test performance was combined with observed data using the Gibbs Sampler to derive posterior distributions for prevalence and test parameters.

RESULTS

Prior distributions for the prevalence of corpora lutea in cows not detected on heat before mating within seasonal herds were centred on 25%, and for the corpus luteum test sensitivity were centred on 70%. No prior assumptions for any other test parameter were made. From a total of 650 cows, 144 were found to have at least one corpus luteum, and 156 were found to have two small ovaries. The posterior estimate obtained for prevalence was 0.30 (95% Cl 0.22 to 0.43), for corpus luteum test sensitivity was 0.71 (95% Cl 0.49 to 0.93), and for corpus luteum test specificity was 0.98 (95% Cl 0.49 to 1.00). For the ovarian size test, the posterior estimate for size test sensitivity was 0.98 (95% Cl 0.95 to 1.00) and for size test specificity was 0.34 (95% CI 0.28 to 0.43). Sensitivity analysis indicated that corpus luteum test sensitivity ranged from 0.60 to 0.70 in most herds.

CONCLUSIONS

Errors associated with pre-mating heat detection are likely to result in between 15 to 30% of cycling cows not detected in oestrous before mating, resulting in the inclusion of cycling cows within the population of non-cycling cows. This mixed population of cows is then subjected to manual examination by veterinarians in order to assign cows to treatment groups. The corpus luteum test has modest sensitivity and high specificity and the size test has high sensitivity and low specificity. Therefore the use of a single examination of the ovaries of cows not detected on heat before the mating period, in order to classify them as anovulatory anoestrous cows with or without a corpus luteum, is not sufficient to accurately classify them and thus to recommend treatment.

A comparative field trial of cephalonium and cloxacillin for dry cow therapy for mastitis in Australian dairy cows

OBJECTIVE

To investigate and compare the therapeutic efficacy of dry cow agents containing either cephalonium or cloxacillin within Australian dairy herds.

DESIGN

A treatment-control trial.

METHODS

Milk from infected quarters of cows with high somatic cell counts in milk on eight Australian dairy farms was cultured to identify bacterial pathogens. Cows were randomly assigned to treatment groups and one group was treated with cephalonium at drying off and the other group was treated with cloxacillin at drying off. Milk samples from infected quarters were collected immediately after calving and were cultured for pathogens. The effect of treatment on bacteriological cure was examined and somatic cell counts from infected cows from the first two herd tests after calving were examined for a treatment effect. On four farms, milk samples were collected for culture from all cases of clinical mastitis identified within the first 7 days after calving. The effect of treatment upon incidence of clinical mastitis after calving was examined.

RESULTS

There was no significant difference between treatments on quarter cure rates for new infections, for chronic infections and for infections with Staphylococcus aureus, Streptococcus agalactiae and Streptococcus uberis. Infected quarters treated with cephalonium had a significantly higher cure rate than quarters treated with cloxacillin when Corynebacterium bovis and Staphylococcus epidermids were included as pathogens combined (80.3% versus 70.7%). There was no significant difference between the treatments on somatic cell counts of infected cows at the first two herd tests after calving. There was no difference between treatments on the incidence of clinical mastitis in the first 7 days after calving.

A clinical trial to evaluate the effectiveness of antibiotic treatment of lactating cows with high somatic cell counts in their milk

OBJECTIVE

To determine the effectiveness of treatment of lactating cows with high somatic cell counts in milk.

DESIGN

Randomised clinical trial.

METHODS

Single pooled quarter samples of milk were obtained from cows with somatic cell counts above 500,000 cells/mL on fifty farms. Milk samples were cultured for known mastitis bacterial pathogens. Cows were randomly allocated to treated and untreated groups. Treated cows received both intramammary cloxacillin and parenteral erythromycin. Single pooled quarter milk samples were obtained at 6 weeks after treatment and were cultured for the presence of pathogenic bacteria. The percentage of samples with no growth at the post-treatment culture was used as an estimate of the bacteriological cures for each pathogen type and for each treatment group. Somatic cell counts of cows were compared between treatment groups and within pathogen group. The number of cows that completed a full lactation were compared between each treatment group and within each pathogen group.

RESULTS

Treatment had no effect upon bacteriological cures, irrespective of pathogen present or the presence of bacteria during the previous lactation. There was no effect of treatment upon somatic cell count except for cows infected with Streptococcus dysgalactiae in which treatment caused a significant lowering of cell counts. This effect was not present in the subsequent lactation. Treatment of chronically infected cows did not alter the probability of a cow completing a full lactation but did improve the probability of newly infected cows being retained for the next lactation. Twenty-eight of 214 treated cows developed clinical mastitis in more than one quarter after treatment, thus indicating a poor technique by farmers for the insertion of intramammary antibiotics.

CONCLUSIONS

Treatment during lactation of cows with high somatic cell counts in milk is ineffective in reducing bacterial infections and in reducing somatic cell counts to acceptable numbers.