Large Dairy Farms Research Articles

Impact of Dairy Manure Processing Using Polyacrylamide on Antibiotic-Resistant Bacterial Level

This study investigates levels of bacteria through population indicators as well as the levels of antibiotic-resistance bacteria in dairy manure. Although overall bacteria levels may be reduced during manure processing, it is of interest whether changes in management practices could lead to increased levels of antibiotic-resistance bacteria, which are becoming more prevalent in agricultural soils, groundwater, and surface water. Appropriate manure treatments are needed not only to reduce the potential risk of exporting antibiotic-resistant bacteria to an environment, but also reduce antibiotic-resistant bacteria exposure to animals if processed water is recycled. Results from this research revealed manure separation under relatively low speed centrifuge with 100 ppm polyacrylamide (PAM) emulsion addition reduced bacteria indicators population such as total coliforms and Escherichia coli (E. coli) significantly in the liquid stream compared to no PAM added. However, the percentages of antibiotic-resistant isolates in liquid stream after centrifuge with PAM were higher compared to raw manure and no PAM added. Antibiotic resistance (cephalosporin, florfenicol, penicillin, or tetracycline) was observed or 65.38% of bacterial isolates in manure from a large dairy farm in Wisconsin and 39.29% of isolates demonstrated multidrug resistance. The results from this study strongly suggest that appropriate manure treatment is essential in order to help minimize the abundance of antibiotic resistance in our water environment.

Antimicrobial resistance profiles of 5 common bovine mastitis pathogens in large Chinese dairy herds

The prevalence of antimicrobial resistance (AMR) is increasing in human and animal pathogens, becoming a concern worldwide. However, prevalence and characteristics of AMR of bovine mastitis pathogens in large Chinese dairy herds are still unclear. Therefore, our objective was to determine the AMR profile of bacteria isolated from clinical mastitis in large (>500 cows) Chinese dairy herds. A total of 541 isolates of the 5 most common species, Staphylococcus aureus (n = 103), non-aureus staphylococci (NAS; n = 107), Streptococcus species (n = 101), Klebsiella species (n = 130), and Escherichia coli (n = 100), isolated from bovine clinical mastitis on 45 dairy farms located in 10 provinces of China were included. Presence of AMR was determined by minimum inhibitory concentrations using the microdilution method. Prevalence of multidrug resistance (resistance to >2 antimicrobials) was 27% (148/541). A very wide distribution of minimum inhibitory concentrations was screened in all isolates, including Staph. aureus isolates, which were resistant to penicillin (66%). In addition, NAS (30%) were more resistant than Staph. aureus to oxacillin (84%), penicillin (62%), tetracycline (34%), and clindamycin (33%). Prevalence of resistance to tetracycline was high (59%) in Streptococcus spp. Additionally, prevalence of resistance of both E. coli and Klebsiella spp. was high to amoxicillin/clavulanate potassium (81 and 38%, respectively), followed by tetracycline (only Klebsiella spp. 32%). A high proportion (27%) of isolates were multidrug resistant; the most frequent combinations were clindamycin-cefalexin-tetracycline or enrofloxacin-cefalexin-penicillin patterns for Staph. aureus; enrofloxacin-oxacillin-penicillin-tetracycline patterns for NAS; clindamycin-enrofloxacin-tetracycline patterns for Streptococcus spp.; amoxicillin/clavulanate potassium-ceftiofur-polymyxin B patterns for Klebsiella spp.; and amoxicillin/clavulanate potassium-ceftiofur-polymyxin B patterns for E. coli. Resistance for 4 kinds of antimicrobials highly critical for human medicine, including daptomycin, vancomycin, imipenem, and polymyxin B, ranged from 0 to 24%. In conclusion, prevalence of AMR in mastitis pathogens was high on large Chinese dairy farms, potentially jeopardizing both antimicrobial efficacy and public health. Results of this study highlighted the need for improvements in antimicrobial stewardship and infection control programs in large Chinese dairy farms to reduce emergence of AMR.

Длительность и напряженность пассивного и приобретенного иммунитета к респираторным вирусам у телят на молочных комплексах

Длительность и напряженность пассивного и приобретенного иммунитета к респираторным вирусам у телят на молочных комплексах

Farm records in investigation of epidemiology, symptomatology and causes of clinical mastitis in a dairy farm

Mastitis is one of the most important diseases in dairy cow farms and one of the most common cause for antibiotic treatment. Aims of this study were: to investigate frequency and trends of clinical mastitis in cows on a large dairy farm, describe clinical characteristics of mastitis and investigate causative infectious agents in selected cases alongside antimicrobial resistance. In our study we used farm records for clinical mastitis recorded for period 2016 and 2017. We also used results of the regular on farm testing of the somatic cell count for 2017. Samples of milk from all clinical mastitis cases were taken during November and December 2017 in order to investigate causative agents and their antimicrobial resistance. Occurrence of clinical mastitis was 205 cases (47.7%) in 2017 compared to 93 cases (29.7%) recorded in 2016. In 2017 reoccurrence of clinical mastitis in same animal was recorded for 93 cows (45.4%). In 2016 reoccurrence of clinical mastitis in same animal was recoded for 49 cows (29.7%). Average course of clinical mastitis in 2016 was 3 days, while in 2017 4.5 days (continuous days of recording a case in farm records). Somatic cell count in more than half of tested animals was higher than 200.000 SC/ml according to the measurements from February and July 2017 (number of cows tested 236 and 169, respectively). Out of 23 milk samples, 20 had bacteriological growth. In 9 samples we identified S.aureus, in 6 streptococcus spp., in 4 coagulase negative staphylococci (CNS) and one sample contained E.coli. Most common resistance was found for lincomycin-spectinomycin (100%) gentamicin (92%), followed by cefquinome (65%), linkomycin (53%) and erythromycin (47%). Isolates of S.aureus were resistant on the largest number of investigated antibiotics.

Selection Criteria for Holstein Friesian and Crossbreed Dairy Cattle Objective Traits in Ethiopia

There was no research regarding selection criteria for the economically relevant dairy cattle objective traits in Ethiopia. Therefore, the goal of this paper was to determine the selection criteria for Holstein Friesian and crossbreed dairy cattle economically relevant traits. The research was based on 236 respondents of large, medium and small scale dairy farms from Dire-Dawa, Harar, Bishoftu, Holeta agricultural research center and Mekele. Data were analyzed using statistical analysis software and traits preferences were ranked by calculating index values with the principle of weighted average. For Holstein Friesian preducers, the most preferred breeds were pure Holstein Friesian, Holstein Friesian crossbreeds and local cattle breeds with an overall index value of 0.47, 0.36, and 0.13, respectively. Similarly for crossbreed producers, pure Holstein Friesian (0.46), Holstein Friesian crossbreed (0.37) and local cattle (0.15), respectively, were their main breed preferred. In the present study, both Holstein Friesian and crossbreed producers were used milk yield (0.61, and 0.64) and milk yield composition (0.39, and 0.34), as the main preferred selection criteria for milk composition, respectively. On the other situations, age at first calving (0.45, and 0.39), age at first service (0.38, and 0.37), and service per conception (0.08, and 0.17), were the preferred selection criteria for economically relevant reproduction traits both for Holstein Friesian and crossbreed, respectively.

A Case study about Employee Management in Large Scale Dairy Farms in Hokkaido

A Case study about Employee Management in Large Scale Dairy Farms in Hokkaido

Life-cycle Analysis of Advanced Manure Management Systems for a Wisconsin Confined Animal Feeding Operation (CAFO)

Abstract. Manure management is becoming an increasing burden for large dairy farms in Wisconsin and across the United States due to land application limitations for nutrients and hauling costs. One solution is to install advanced manure management systems, which remove large portions of water from the manure and treat it to a level sufficient for surface water discharge, livestock consumption, or irrigation. These systems can be divided into a pretreatment stage, which consists of solids removal, and a treatment stage, which generally consists of membranes. Not only does this approach reduce the quantity of material that is land applied, it can separate the nutrients into individual manure streams that can be more easily managed. However, there is still limited understanding regarding the costs and operation and maintenance requirements of these systems. To this end, a life-cycle analysis was completed for five commercially available advanced manure management systems based on how they would treat manure from a 3,500-cow dairy farm in Wisconsin, which was concerned only with the drawbacks of hauling and not application limitations. The evaluation included both an economic and non-economic analysis. The economic analysis consisted of a 20-year total present worth life-cycle cost analysis. The non-economic analysis consisted of a comparison of a set of non-economic factors that matched the management goals and strategies identified by the participating farm. Overall, all five systems evaluated addressed nutrient limitations and hauling costs. No treatment system had a payback less than 20 years at a hauling cost of $0.0040 L-1 ($0.015 gal-1). However, two systems had a payback period less than 20 years for a hauling cost of $0.0053 L-1 ($0.02 gal-1). Furthermore, if capital costs were ignored, the cost of recovered water was comparable to hauling costs for four of the alternatives. Still, there was high uncertainty in the estimated costs due to the low number of current installations of these systems on CAFOs. There was also a wide range of responses to the non-economic evaluation metrics, especially regarding performance, nutrient management techniques, chemical usage, and estimated regular operation and maintenance, which was again, likely due to the limited number of farm installations. Future work will verify actual costs and performance of these systems once implemented. Keywords: Advanced Manure Management, CAFOs, Dairy, Life-cycle analysis.

Screening milk for bovine tuberculosis in dairy farms in Central Province, Sri Lanka

Bovine tuberculosis is a chronic bacterial disease caused by Mycobacterium bovis. It can be transmitted to humans through direct contact with infected cattle or consumption of unpasteurized milk and milk products. The current study was performed to assess whether raw milk produced in three large scale dairy farms in Central Province of Sri Lanka contain any M. bovis. Raw milk samples were collected from 330 cows representing 230 single intradermal comparative cervical tuberculin test reactors and 100 none-reactors. All milk samples were cultured on Lowenstein Jensen medium with/ without sodium pyruvate for the isolation of Mycobacterium spp., and slopes were observed for the occurrence of growth daily for the first week and then at weekly intervals for 8 weeks. Direct Polymerase Chain Reaction (PCR) was performed simultaneously on all milk samples to detect M. bovis after extracting DNA with a commercial kit. The minimum detection level of M. bovis for PCR in milk was 200 CFU/mL. Only two milk samples from reactive cows were positive for acid fast bacilli. However, their cultures were confirmed as non-tuberculous mycobacteria by PCR. Consequently, all milk samples were confirmed negative for M. bovis according to direct PCR. It was concluded that the milk samples from three large scale dairy farms in Central Province of Sri Lanka did not contain M. bovis.

Molecular epidemiology and distribution of antimicrobial resistance genes of Staphylococcus species isolated from Chinese dairy cows with clinical mastitis

Staphylococcus species, categorized into Staphylococcus aureus and non-aureus staphylococci (NAS), are frequent causes of mastitis in dairy cattle around the world. Current treatments using antimicrobials are under increasing scrutiny due to rising prevalence of multi-drug resistance in S. aureus. Objectives of this study were to determine: (1) genetic diversity of Staphylococcus species isolated from clinical mastitis in cows from large Chinese dairy farms; and (2) prevalence and distribution of antimicrobial resistance genes (ARG) in these isolates. Staphylococcus aureus (n = 96) were isolated from 26 herds located in 12 provinces of China, whereas NAS (n = 112) were isolated from 59 herds located in 18 provinces of China. The NAS were identified at the species level using a partial 16S rRNA sequencing method, whereas random amplification of polymorphic DNA (RAPD) PCR was done to determine genetic relationships of isolates. Finally, PCR was used to detect resistance and biofilm formation genes. Staphylococcus chromogenes (33%) was the most common NAS species, followed by Staphylococcus sciuri (17%) and Staphylococcus epidermidis (8%). Staphylococcus aureus was grouped in 12 genotypes, of which 2 types represented 56% of isolates. Staphylococcus chromogenes (n = 37) clustered into 8 RAPD types, with 2 prevalent types containing 73% of isolates. The most prevalent ARG in S. aureus isolates was blaZ (95%), followed by tetM (33%), tetK (31%), ermT (26%), and aacA-aphD (23%). The mecA and vanA were detected in 16 and 4% of isolates, respectively. In NAS, blaZ (100%), mecA (73%), tetK (79%), tetM (96%), mphC (63%), and msrA (54%) were frequently detected. Antimicrobial resistance genes mecA, tetK, tetL, tetM, dfrG, ermB, msrA, mphC, aadD, and aphA3 were more commonly detected in NAS than in S. aureus. Biofilm formation genes (icaA and icaD) were frequently detected in staphylococci isolated from bovine clinical mastitis. The existence of predominant RAPD types in S. aureus and S. chromogenes isolates across Chinese dairy farms indicated that specific genotypes had disseminated within herds and become more udder-adapted. High prevalence of ARG, especially in NAS, highlighted the risk of selection of multi-drug resistant staphylococci with potential as a reservoir of ARG.

Are Cows Comfortable in Modern Dairy Facilities?

The main challenge in modern large dairy farms is to achieve maximum milk production while maintaining optimal cow health and welfare. Facilities should be designed to assure that calves, heifers and cows are comfortable and can successfully grow and develop in order to reach peak performance. It is crucial to provide dairy cattle with basic shelter needs and allow farm staff to manage these animals in an effective manner. In addition, cows need to accomplish certain natural behavioral activities daily. Some factors that may decrease or limit the ability of cows to express natural behaviors include but are not limited to resting area and resting behavior, time spent away from pen (i.e. for milking and other management procedures), feed and water access and availability, stocking density, and environmental factors such as heat stress. Understanding cows needs and their natural behaviors allows us to adjust facilities in order to optimize cow comfort and subsequent productivity and profitability.

Comparative assessment of the antigenity of autogenic vaccine against salmonelosis in the RA and RG

The results of the comprehensive approach to the diagnosis, general and special measures for the elimination of the infection center for the outbreak of Salmonella in calves in one of the large dairy farms in the Volyn region are presented. The use of classical diagnostic methods using modern environments and approaches made it possible to isolate and identify two types of Salmonella Typhimurium and S. dublin. Antibiotic therapy of calves for salmonellosis calves was carried out with labeled antibiotics in combination with medicinal products of symptomatic nature. Forced current and final disinfection of cages and whole calf, as well as wicker yards and cows were carried out with a 0.1% solution of the new disinfection preparation “Epydes”, created on the basis of derivatives of polyhexamethylenguanidine (PGMG), at a rate of 0.3 l/m2. For a specific prevention of salmonellosis, we designed our two series of autogenic vaccines from isolated strains of salmonella, the difference between which was the choice of adsorbent. The study of the tension of humoral immunity in cats and calves vaccinated against salmonellosis in agglutination and indirect hemagglutination reactions revealed high levels of antibodies to immunogens that were part of two experimental autopsy series of autogenic vaccines. In this case, the immune response to the antigens of the Tifimurium was higher than that of Dublin antigens. Titres of antibodies from cats and calves vaccinated with a vaccine in which the aerosol was used as an adsorbent were higher than those for a vaccine in which an aluminum hydroxide was used as an adsorbent. The reaction of indirect agglutination showed several times the higher sensitivity to detect salmonella antibodies than the agglutination reaction, which is the basis for recommending it as an immunological method of tension of humoral immunity for animal salmonellosis. The comprehensive approach to diagnosis of disease, modern approaches to the treatment of calves with salmonella, the destruction of the pathogen in the environment and the modern approach to the immunization of the infection, made it possible to improve the economy throughout the year from salmonella caused by two types of salmonella.

The impact of green economy measures on rural employment: Green jobs in farms

In the circular economy concept, besides protecting the environment, green policy measures provide essential economic benefits through resource security, economic stability, and the creation of green jobs. This study centres its attention on the labour use aspect of the circular economy and aims to examine the potential for green economy measures to create green jobs in the agriculture sector. As a methodological approach, we combine “top-down” and “bottom-up” analyses of the green economy experience of Slovenia, where agri-environmental measures (AEM) play an essential role in the Slovenian rural development programme (2007–2014), with the highest amount of subsidies per unit of output among the 10 new European Union Member States. The results show that an AEM adoption of green policy measures by very large dairy and field crop farms significantly increases total labour use: while for field crop farms this increase is in hired labour, for dairy farms this increase is in family labour. While hired and family labour perform as substitutes for very large dairy farms, they perform as complements for very large field crop farms. The present study suggests further steps towards identifying the green economy measures that are needed to create green jobs in the agriculture sector for rural youth.

Exploration of factors determining milk production by Holstein cows raised on a dairy farm in a temperate climate area.

In this study, we examined factors that affected milk production by cows raised in a temperate climate area. We conducted this study on a large dairy farm containing approximately 2000 Holstein cows, located in a temperate climate area. We collected 7803 calving records for 4069 cows from 2012 to 2016. We then assessed the effect of hot weather on milk yield by examining three climate factors: season, maximum temperature (MAX), and the temperature and humidity index (THI). We found that increases in heat stress caused linear decreases in milk yield (P < 0.05). Additionally, the effects of the three climate factors on milk yield varied depending on cow parity and days open (P < 0.05). Thus, management procedures should consider cow parity and lactating stage to minimize the negative effects of heat stress on milk production. We also found that the lowest Akaike information criterion value was obtained in our model when using THI for 305-day milk yield. This suggests that THI is a more accurate variable for evaluating heat stress than MAX or season.

Economic analysis of dairy farming in Bangladesh.

A study was conducted to analyze the dairy farming sector of Bangladesh from an economic viewpoint. Primary data was collected from smallholder dairy farms using survey questionnaires. A Cobb-Douglas production function and multiple regression models were estimated to analyze farm milk productivity and gross margin of the dairy farms. Surveyed dairy farms owned on an average 3.07 milking cows comprising 0.37 indigenous and 2.70 crossbred cows. Average milk productivity was 7.80liter per cow per day, in which indigenous cow milk productivity was 1.91iter per day and crossbred cow milk productivity was 6.48liter per cow per day. The study found that average daily milk production of small, medium, and large dairy farms were 5.45, 32.50, and 59.83liter, respectively. Average monthly revenue and cost of milk production were US$ 79 and US$ 21 per cow, resulting in the average net return of US$ 58 per cow per month. Both quantitative estimation and t test results indicated a positive and statistically significant relationship between farm size and milk productivity and gross margin. The study findings also indicate that crossbred cows are providing higher economic benefits to the dairy farmers compared to the indigenous breeds. Despite being smallholder and subsistence, dairy farming shows potential for increasing returns to scale, and hence, there is a scope for further growth of the sector.

Manure management coupled with bioenergy production: An environmental and economic assessment of large dairies in New Mexico

Consolidation in livestock production generates higher net farm incomes due to economies of scale. However, it also brings manure disposal problems. New Mexico ranks number one in the U.S. in dairy herd size. Dairy manure is a significant source of nitrates, and improper management of manure from large dairy farms can produce adverse environmental and health effects. We use a combination of life-cycle assessment, cost-benefit analysis, and sensitivity analysis to assess environmental and economic impacts of three alternative dairy manure management cases: direct land application (DLA), anaerobic digestion (AD), and anaerobic digestion coupled with microalgae cultivation (ADMC). By modeling a typical large dairy farm in New Mexico, four environmental impacts and the present value of net benefits of each case are evaluated under a baseline scenario and different policy scenarios. Our results show that, for a typical large dairy farm in New Mexico, the DLA case is the least sustainable regarding any of the environmental impacts. AD is most profitable in the baseline, tax credit, and carbon credit scenarios while ADMC is most profitable in the presence of a market for nutrient credits. Policy implications are discussed for dairy manure management coupled with bioenergy production on large dairy farms in arid regions.

What I learned when I became a dairy manager

Working in dairy management changed my perspective on veterinary medicine and the services that veterinarians should provide to clients, especially on larger dairy farms. While the cows are the main income producers on a dairy farm, there is a lot more to running a farm than managing cows. Labor, capital, crops, manure, and feed procurement all need to be managed, along with all of the other tasks connected with running a small business. So cow management may not always be at the top of the owner's mind, and is usually delegated to employees. Veterinary emergencies are not true farm-level emergencies. Clients want good emergency service but a successful intervention only benefits one cow. True emergencies are those that affect the farm's ability to produce and sell its product: a refrigeration failure, a drug residue in a milk tank, equipment failures, labor issues. Vets tend to focus too much on per cow averages and diseases. Profit is determined by the total amount of milk or milk solids the farm sells, not the per-cow average production. Averages tend to have bias and momentum. Management should focus on cows that are not performing well and try to prevent future cows from having the same problem. Monitoring should focus on things that can be changed quickly and promise quick results, like reforming a failing colostrum program. Many traditional veterinary services only benefit one cow. It is better to focus on interventions that help the productive cows in the herd. They have trouble executing those recommendations. Change on a dairy farm is not easy and may affect many people. Advice should come with an implementation plan.

Factors associated with the bovine viral diarrhoea (BVD) status in cattle herds in Northwest Germany

In Germany, all calves are tested for the presence of bovine viral diarrhoea/mucosal disease virus (BVDV) virus since January 1, 2011. The basis for this compulsory investigation is the BVDV Federal Regulation (BVDVV), which demands testing of calves before the age of six months and according to the new regulation of June 2016 within four weeks or before entering another stock. In 2012, a questionnaire was sent to 7250 Lower Saxony cattle farmers to identify potential factors associated with the presence of BVDV. Completed questionnaires were received from 2542 farms for further analysis. For BVD status determination of these farms, the diagnostic results of 425,911 ear notch samples of calves as part of the BVD eradication period from June 2010 to December 2013 were used.For the analysis of the completed questionnaires, a univariable analysis was performed by the chi-square or Wilcoxon test for each variable studied. In addition, a multivariable logistic model was performed. Four potential risk factors remained after a backward selection in the final logistic regression model: the dairy production compared to the suckling and other types of production, the herd size, the purchase of animals and the location in western region in comparison with the central and eastern regions. In summary, according to the results of this study, the farm with the highest probability of a BVDV infection in Lower Saxony is a large dairy farm that purchases cattle and is located in a cattle-dense region. When the complete eradication of the virus will be achieved, the results of the present study may help to conduct a risk-oriented monitoring programme.

Management practices associated with reproductive performance in Holstein cows on large commercial dairy farms

As a result of the increase in herd size and the intensification of production, the complexity of reproductive management has been growing in dairy herds. The aim of our study was to examine the associations of management practices and reproductive performance in Holstein cows on large commercial dairy farms. Management practices applied to cows were surveyed between 22 May and 6 November 2015 in 34 large Holstein-Friesian dairy herds in Hungary. Individual data of 23 784 cows that calved between 1 January 2014 and 31 December 2014 in the surveyed herds were gathered. Associations between the management practices and the reproductive parameters were analyzed by mixed effects models. Regarding heat abatement we found that ventilation with sprinklers was associated with the shortest breeding interval (P<0.01), the shortest calving to conception interval (P<0.01), and the highest odds of being pregnant by 200 days in milk (P<0.01). Solely ventilation showed similar (P>0.05) results to lack of heat stress protection. It was also revealed, that lack of a well-established voluntary waiting period (VWP) or a VWP shorter than 50 days was associated with less days to first service (P<0.01), shorter breeding interval (P<0.01) and calving to conception interval (P<0.05), as well as higher odds of carrying a calf by 200 days in milk (P<0.01) compared with those using a VWP of at least 50 days. Those farms that applied transrectal ultrasonography were more likely to use ventilation with sprinklers (P<0.05), hormonal synchronization (P<0.01) and to perform early pregnancy diagnosis followed by pregnancy recheck (P<0.05). The application of transrectal ultrasonography with one of the aforementioned practices was associated with reduced days to first service (P<0.05), shorter breeding interval (P<0.05) and higher odds of pregnancy at 200 days in milk (P<0.05). Our study highlights the management practices most closely related to improved reproductive performance, which are, therefore, suggested to be applied on dairy farms, considering the local circumstances of the individual farms.

Strategies for increasing fertility in high productivity dairy herds.

Over the years, the dairy cow has been selected and managed for high performance and efficiency in milk production. Thus, different factors influence the fertility of dairy cows of high productivity. It has been observed that genetic selection for large productions and metabolic adaptations may explain the greater requirement to maintain reproduction at satisfactory levels. Also, these animals are more susceptible to environmental factors such as increased temperature and humidity. Studies have shown that heat stress results in reduced estrous expression and impairs ovarian function, interfering with folliculogenesis and steroidogenesis. Likewise, under heat stress conditions, dry matter intake is reduced, prolonging the after calving negative energy balance and calving-conception interval. Thus, suboptimal reproductive performance is one of the main factors responsible for the economic losses in large dairy farms. In this context, numerous management practices have been introduced to improve reproduction in high productivity animals, making reproductive management increasingly complex in dairy farms. Among them, we can mention the implementation of management and nutrition conditions adapted to the periods of heat stress, as well as protocols and biotechniques that improve the quality of the follicles and oocytes. Thus, because genetic selection for better fertility animals is a characteristic of low heritability, the success of reproductive programs in highly productive herds depends on the association of the control of genetic and physiological factors with those of environmental, nutritional and management. This paper aims to discuss reproductive aspects of dairy cows of high productivity, the role of heat stress in this context, and the implementation of management, nutrition and biotechnology conditions, to minimize the adverse effects on the reproduction of these animals.

Factors affecting the milk urea nitrogen concentration in Chinese Holstein cows

AbstractIn order to investigate the factors affecting milk urea nitrogen in Chinese Holstein cows, a large commercial dairy farm participated in a 30-month study. In this study, the mean milk urea nitrogen concentration was 11.75 mg/dl. The milk urea nitrogen reached its maximum value on day 90 of lactation for the first parity and the third or higher parities, but it peaked at the end of lactation for the second parity. The milk urea nitrogen of the first parity was lower than that of other parities. The milk urea nitrogen showed its minimum level in January, and reached its maximum in July. The milk urea nitrogen at the first month of lactation in cows calving in summer was higher than other seasons, while at the fourth month of lactation, the milk urea nitrogen of cows calving in autumn was significantly lower than in cows calving in other seasons. Positive correlations were observed between daily milk yield, net energy for lactation, crude protein and milk urea nitrogen for the first and third parities, but negative correlations were observed in the second parity. The milk urea nitrogen showed significantly positive correlations with fat content, total solid content and daily matter intake for all parities. A negative correlation was observed between milk urea nitrogen and protein content, with the exception of the second parity. For all data, as milk urea nitrogen concentration increased, milk protein content decreased. It has been recommended that milk urea nitrogen concentration should be evaluated in combination with parity, days in milk, season (or month), daily matter intake and dietary nutritional components, in order to improve the management and economic benefits of dairy farm.