Economic Value and Produced Milk Quality in Holstein Lactating Cows in Organic System

Document Type: Research Articles

Authors

1 Department of Animal Science, Faculty of Agriculture, University of Tabriz, Tabriz, Iran

2 Department of Animal Science, Faculty of Agriculture and Natural Resources, University of Tehran, Karaj, Iran

3 Department of Management and Accounting, Farabi Compus University of Tehran, Qom, Iran

Abstract

In the past decade, a global demand for products from organic agriculture has increased rapidly. Milk quality is of major interest for all parties. Therefore, the objective of this study was to compare cow performance and product quality in conventional and organic system. Twenty Holstein dairy cows were allotted to one of 2 diet groups, which including: a conventional diet (CON), and an organic system with high forage (OHF). Multiparous cows (3rd and 4th parity) were randomly assigned to the treatments. Range forages were used as part of diets and cows were offered concentrate and silage two times a day. Dry matter intake (DMI) and milk yield were measured across 200 d. Furthermore, somatic cell count, feed cost and feed efficiency were determined at 20 day intervals. The milk yield was different for cows that treated with the OHF (22.5 kg/d) and CON (28.9 kg/d) systems, respectively. Body weights were not affected by treatments; however, differences in body condition scores (P<0.05) were observed. Although energy corrected milk, milk urea nitrogen, cortisol and β-hydroxybutyrate acid were higher in cows fed CON system; milk fat, phytanic acid, hippuric acid and profit to cost ratio were higher (P<0.05) in cows fed organic system. Additionally, lower feed efficiency, feed cost and blood urea nitrogen were observed in cows fed organic diets (P<0.05).

Keywords


INTRODUCTION

In recent years the market for organic products has grown considerably and along with this the consumer’s awareness of the production process. Therefore, organic farming using domestic livestock has recently become widespread around the world. Clearly, crucial prerequisites in order to produce high quality milk are healthy cows fed with feed free from unusual feeds. Organic farming defines clear rules for feeding of livestock, health management, and housing of animals (Mullen et al. 2015). With the transition from conventional to organic dairy farming, milk yield and its composition change drastically (Ellis et al. 2006; Prandini et al. 2009; Slots et al. 2009; Butler et al. 2011). There is a growing body of research comparing organic and conventional farming systems. In a critical review, Mullen et al. (2015) demonstrated that the benefits of organic systems are more influenced by specific farm management policies than by production system itself. Although organic systems may reduce milk yield and growth rates (Slots et al. 2009; Butler et al. 2011), organic production methods may improve animal health and welfare, human health and improve the environment (Ellis et al. 2006; Slots et al. 2009; Prandini et al. 2009; Mullen et al. 2015). Milk yield on organic dairy farm is lower than milk yield on conventional farms (Adler et al. 2013). The reasons for lower milk yield in organic dairy herds may be due to differences in genetics, management, feeding practices, and increased subclinical mastitis (Mullen et al. 2015). In addition to differences in feeding and milk yield, reproductive efficiencies may also be different in organic method. Organic milk is produced in rural and nomadic breeders of Iran for many years, and organic dairy products are available in villages and cities humid climate area (without a dry season and with temperate summers and winter) in Iran (Sharifi et al. 2015). However, the high demand for organic milk in recent years asks for production on a larger scale. No published studies have evaluated the effect of organic systems on the performance of dairy cows in Iran. Therefore, the objective of this study was to evaluate the use of organic systems in different levels of forage and their effects on body weight, body condition score, milk production, and milk quality of Holstein dairy cows in Iran.

 

MATERIALS AND METHODS

Animals, diets and experimental design

The study was conducted at Valfajr Agricultural Research Center farm, located in the central Alborz range lands of Noshahr region of Mazandaran Province, Iran. All activities were performed under the guidelines approved by the Standard Committee of the Ministry of Agriculture and Veterinary Organization of Iran. Of 20 selected Holstein dairy cows for this study the average (Mean±SD) initial body weight (BW) was 495.5 ± 39.6 kg and the previous year daily milk yield (MY) was 27.5 ± 1.1 kg/d. Cows (as a group) were held at all times freely in the farm and pasture except when being milked. A completely randomized block design with 2 treatments was used and cows were randomly distributed into groups, and blocked by average body weight (BW), MY and parity (3rd and 4th parity). The two treatments during the study were: a conventional system (CON) and an organic system with high forage (OHF). Daily amounts of diet in CON were offered at morning (05:00), mid-day (13:00) and evening (21:00) and the non-consumed feed were collected and subtracted from the provided amount of feed. Organic cows were fed according to the rules of Bystrom et al. (2002) and offered ad libitum forage. For the OHF the requirements were calculated from a predicted forage intake (2.0-2.25 kg DM/100 kg live weight) and predicted milk yield, while, in conventional system CON the requirements were calculated based on milk yield. All cows received concentrate, minerals and vitamins in relation to the expected nutritional needs for MY. Cows were milked 3-time a day at 04:00, 12:00 and 20:00 hours and had ad libitum access to fresh water. The concentrate component and amount in diets are in Table 2. The rangeland forages (in spring, summer and autumn) used in diets contained mainly Hordeum bulbosum (35%), Lolium perenne (27%), Prangos ferulacea (22%), Poa pratensis (10%) and others species (6%).

 

Range management

The rangeland area was 20.33 hectares of grassland from the Noshahr region of Mazandaran Province, Iran. Furthermore, 8.92 hectares of agricultural land was used for production of conventional feed (Table 1).

 

Table 1 Tillable land and major crops in organic and conventional farm

 

DM: dry matter; OHF: organic system with high forage and CON: conventional system.

 

For grazing in rangeland, a paddock was divided into 4 sections and forage was grazed every 50 days. The range areas were not irrigated and the yearly average rainfall amounted to about 1205 mm with 16.7 ˚C of average yearly temperature. The soil structures were classified as loam and/or sandy-loam, with a neutral pH (6.83-7.19) and 2.99%-4.75% organic matter. During each 50-day, botanical characterisation was performed using the method of Sharifi et al. (2016b) and the percentage of each species in the samples were recorded. Pasture samples were also collected at the same time and used for chemical analysis.

 

Data collection

Forages and other feeds were evaluated according to the association of official analytical chemists (AOAC, 1991) method. Samples of sun-dried forages were packaged and sent to the laboratory for analysis of dry matter, crude protein, crude fiber, ether extract, Ash and neutral detergent fiber measurements.

 

Table 2 Estimation of intake for Holstein cows (n=10 per group)

 

1 Mineral composition: Ca: 180 g/kg; P: 60 g/kg; Mg: 50 g/kg; Na: 50 g/kg; Cu: 1.3 g/kg; Zn: 6.0 g/kg; Mn: 3.5 g/kg; I: 0.06 g/kg; Co: 0.032 g/kg; Se: 0.02 g/kg; vitamin A: 600000 IU/kg; vitamin D3: 120000 IU/kg and vitamin E: 1300 IU/kg.

OHF: organic system with high forage and CON: conventional system.

 

The BW of cows was recorded at 20-day intervals prior to the morning feed allotment. Cows were weighed when leaving the milking parlor using a digital scale. A scale of 1 to 9 for body condition score (BCS) (Khadem et al. 2009) was estimated for cows by the same person throughout experiment. The scoring scale ranged from 1 for very thin to 9 for very fat. The BCS values were recorded 4 times which included the dry period (pre-calving), post-calving, and the early and mid lactation. Data for daily dry matter intake (DMI) was recorded from the beginning to the end of the experiment. With data spanning 200 days, cows had DMI records for 10 periods (d 1 to d 20, d 21 to d 40, d 41 to d60, etc.). Also, milk yield for each period was recorded as the average milk produced by cows in each day of the 20-day periods. Additionally, milk fat and protein contents were measured once a week and somatic cell count (SCC) and milk urea nitrogen (MUN) were analyzed every 20 days. The fat content of milk was measured using the Smart-Trac rapid fat analyzer (CEM, Matthews, NC.). The Lacti-Check ultrasound milk analyzer (P&P International Ltd., Hopkinton, MA) was used to measure the protein contents, while the SCC was determined with Fossomatic 90 (Foss electric). For the MUN measurement, samples were collected every 20 days. A concentration of MUN was determined in all trials using the same diacetyl monoxime colorimetric assay adapted to a continuous flow analyzer (Khadem et al. 2009). Hippuric and phytanic acid were determined with a gas chromatograph (GC-2010, Shimadzu Co., Japan) equipped with a 100 m capillary column (0.25 mm i.d., 0.20 mm film thickness) and a flame ionization detector. Furthermore, feed efficiency (FE) was estimated by dividing energy-corrected milk (ECM) by the daily DMI of cows (Sharifi et al. 2016a). For blood metabolite and urea nitrogen, blood samples (20 mL) were collected from the tail vein of cows at 20-day farm visits using evacuated tubes containing EDTA at a level of 1.8 g/L of blood. Samples were kept on ice for 15 min after collection and then centrifuged at 1000 × g for 20 min. Plasma was harvested and stored frozen in plastic tubes at −20 ˚C until further analysis. The plasma urea concentration was determined using the method described by Chaney and Marbach (1962). β-hydroxybutyrate acid and non esterified fatty acids were assayed by colorimetric method (Ranbut®, Ireland). Cortisol of serum was measured by hormonal cortisol kit using Gama counter (Kon. Pron.) system.

 

Statistical analyses

For statistical analysis, the dependent variables were BW, BCS, MY, milk components, DMI, feed efficiency (FE), MUN, blood urea nitrogen (BUN) and feed cost, the fixed effects were dietary treatment, parity and 20-d period nested within dietary treatment. The MIXED linear model procedure of SAS (SAS, 2004), in which cow was the random variable and sample sequence was the repeated measures, was used. The autoregressive covariance [AR (1)] structure was used because it resulted in the lowest Akaike’s information criterion (Littell et al. 1998). The GLM PROC model was also used when necessary. Results are presented as least square means and statistical differences were considered significant at (P<0.05). Trends towards significance were considered at (0.05≤P<0.10).

 

RESULTS AND DISCUSSION

Body weight and body condition score

The change of BW over time is shown in Table 3. There were no statistically significant differences for BW between treatment groups; however, the CON cows lost slightly more BW than the organic cows during experiment because of higher energy density. Pre-calving BCS were not different between treatment groups (Table 3); but, significant differences were observed between treatments after calving (P<0.05) and early (P<0.001) and mid-lactation (P<0.01). Although trends for BW change in CON cows was higher than organic system, results showed that organic system can improve body condition in cows. Across all periods CON cows had higher BCS than organic system except in early lactation. Also, dry cow BCS was similar for all treatment groups. Similar results were reported by Roesch et al. (2005) but their finding that BCS was not different between cows fed organic compared to conventional system is in contrast with our results.

 

Table 3 Estimation of body condition score, body weight, dry matter intake and milk yield of cows fed organic and conventional systems in Holstein lactating

OHF: organic system with high forage; CON: conventional system; ECM: energy-corrected milk and DMI: Dry matter intake.

* (P<0.05); ** (P<0.01) and *** (P<0.001).

SEM: standard error of the means.

 

Bystrom et al. (2002) found that cows fed organic system weighed less at the end of lactation compared to cows fed conventional system although BW and BCS change was greater for conventional cows compared to organic cows. Furthermore, Trachsel et al. (2000) reported changes in body condition score of cows fed organic systems was lower than cows fed conventional system.

 

Dry matter intake and feed efficiency

Table 3 show the DMI intake for treatment groups over the 200 day of lactation. For the mean of all periods, cows fed CON system had a higher (P<0.05) DMI than cows fed OHF system (21.2 kg/d vs. 17.8 kg/d, respectively). Normally, DMI reduction can be a result of bulkier feed intake and fewer digestibilities in OHF system. Table 3 show the change in FE during the trial period. Cows fed CON system had higher (P<0.01) FE than cows fed OHF system (1.41 vs. 1.33, respectively). It may be difficult to determine how cows in different treatments partitioned consumed energy into alternative components of production (i.e., body maintenance and growth or restoration of body reserves); however, it is possible to determine how treatment groups utilized energy from consumed feed to restore of body reserves. Our observation of relatively lower DMI in organic system is in line with many reports in the literature (Prandini et al. 2009; Butler et al. 2011; Adler et al. 2013; Stiglbauer et al. 2013). However, organic cows in the current study consumed more forage than conventional cows (Table 2); but conventional cows consumed more concentrates than organic cows. In contrast to our study, Bystrom et al. (2002) found that feed efficiency was not different between animals fed conventional vs. organic systems. In contrast, Thomassen et al. (2008) reported that feed efficiency was greater for cows fed organic systems compared to conventional system, because of the higher forage consumption of organic cows compared to conventional cows.

 

Milk yield and composition

In the Table 3 means and standard error of means for MY for each period and across to the 200 days is given. Changes in DMI and MY of cows were similar from beginning to the end of the experiment. Also, the changes of milk fat and protein, ECM, SCC, hippuric and phytanic acid in the study periods are shown in Table 4. Milk yield was different among treatment groups, especially early lactation periods (P<0.001). Across the lactation period, cows fed CON system had higher (P<0.01) MY than cows fed OHF system (28.9 kg vs. 22.5 kg/d, respectively). Fat percentage was higher for cows fed OHF system compared to the CON system (3.73% vs. 3.56%, respectively). For protein content, cows fed CON diets had higher (P<0.05) value than OHF diet (3.51% vs. 3.36%, respectively). Furthermore, Table 4 shows that CON system was associated with significantly (P<0.05) higher SCC than other system at early and mid-lactation periods with a tendency for CON system to have fairly higher (P<0.10) SCC than organic system for mean of periods.

 

Table 4 Estimation of milk composition of cows fed organic and conventional systems in Holstein lactating

 

OHF: organic system with high forage and CON: conventional system.

(P<0.10) * (P<0.05); ** (P<0.01) and *** (P<0.001).

SEM: standard error of the means.

 

The milk yield and milk composition of the current study are in agreement with finding of others Roesch et al. (2005), Prandini et al. (2009), Butler et al. (2011), Stiglbauer et al. (2013) and Kuhnen et al. (2015) which all reported that MY was higher for conventional cows than organic cows. While in contrast with our results Thomassen et al. (2008) reported that milk yield was not significantly different for cows fed organic or conventional systems. No difference could be related to the same rate of forage or energy density in both treatments. Roesch et al. (2005), Butler et al. (2011) and Kuhnen et al. (2015) reported that percentages of milk protein was equal between groups, but a higher fat percentage was seen with organic feeding compared to the conventional feeding because of more forage intake. Conversely, Adler et al. (2013) showed that conventionally kept cows had higher milk, fat and protein content in milk than organically managed cows. Muller and Helga (2010) reported that SCC was not significantly different between an organic vs. conventional feeding. In contrast, Kuhnen et al. (2015) reported that average individual cow SCC levels were significantly higher in organic herds compared to conventional except in winter. Moreover, Table 4 indicated that consumption of organic system did statically (P<0.01) higher phytanic acid than CON system. Similarly, content of hippuric acid was increased (P<0.001) by OHF system than CON system (31.3 vs. 18.9 mg/L). Cows on organic system consume more forage than CON system. Therefore, they consume more phytol (part of chlorophyll) which is broken down in ruminant’s stomachs to phytanic acid. In agreement to our study, Larsen et al. (2010) and Adler et al. (2013) founds that, on average, organic milk had double the phytanic acid levels than conventional. Dietary intake of phytanic acid have been suggested to be involved in both health and disease promoting processes, thus some researchers have suggested that it can prevent diabetes and metabolic diseases, while others have suggested that it promotes development of prostate cancer (Werner et al. 2011). The potential health-promoting properties is based on the fact that animal and in vitro studies have shown that phytanic acid might have preventive effects on metabolic dysfunctions, since in animal studies it increases expression of genes involved in fatty acid oxidation, enhances glucose uptake and metabolism in hepatocyte and potentially reduce metabolic efficacy through increased differentiation of brown adipocyte differentiation and expression of uncoupling protein-1 (Werner et al. 2011). Hippuric acid such as phytanic acid could be a marker to distinguish organic milk from cows fed on different feeding system. However, it is necessary to check if the hippuric acid content comes from fresh forage or from organic handling.

 

Milk urea nitrogen and blood urea nitrogen

Across the 200 days, CON cows had higher (P<0.01) MUN than OHF cows (19.0 vs. 15.0 mg/dL) groups respectively (Table 4). Similarly, CON cows had higher (P<0.05) BUN (Table 4) than OHF cows (4.79 vs. 4.28 mmol/L, respectively). This finding is in accordance to the works of Bystrom et al. (2002), Roesch et al. (2005) and Adler et al. (2013) who found that high forage diets compared to high concentrate diets appear to significantly decrease MUN levels. Furthermore, results of this study are similar to those reported by Trachsel et al. (2000) and Roesch et al. (2005) who reported BUN levels were greater in CON cows compared to organic cows. BUN reduction in the OHF cows can be due to the lower crude protein in diets. It can lead to a decreased ammonia production in the rumen and consequently decreased urea production in the liver. Our study provide support to other study that the participating systems adequately reflect the performance level for the two management systems and are not due to biased selection of systems. Consequently, MUN a fraction of milk protein that is derived from BUN may be one the useful tools (for quality of milk) that may help monitoring of any change required in the feeding and management of a herd.

 

Blood metabolite

Regarding the blood serum parameters, non esterified fatty acids (NEFA) showed the highest levels at 10 days of parturition for organic system (Figure 1), whereas CON cows had higher (P<0.01) NEFA concentration on days 60 and 90. Blood serum β-hydroxybutyrate acid (BHBA) increased in CON cows after 20 days of parturition above 0.4 mmol/L and reached maximum levels at 20-day in OHF (Figure 1). NEFA serum concentration is an indicator of the lipid mobilization degree from reserve adipose tissue and, in conclusion, of the negative energy balance in ruminants (Ellis et al. 2006). Altogether, studies demonstrate that organic system is not more prone to develop a negative energy balance than conventional system (Roesch et al. 2005; Muller and Sauerwein, 2010; Stiglbauer et al. 2013). Contrary to our results, Fall et al. (2008) showed that the profiles of all tested metabolic variables NEFA, and BHBA were very similar between organic and conventional systems. Roesch et al. (2005) compared NEFA and BHBA at 30-day post-partum without discovering any differences. But, there have been concerns that the high energy demands of early lactation cannot be satisfied in organic management.

 

Figure 1 Time courses of non esterified fatty acids (NEFA), β-hidroxy butyrate acid (BHBA), and cortisol in an organic system with high forage (OHF) and conventional system (CON) during the observation periods. Means of NEFA, BHBA and cortisol were significantly diferent (P<0.05) detect among treatments for all periods. Overall SEM for NEFA= 0.08, BHBA= 0.03 and cortisol= 0.06

 

 

The results showed that the cortisol level on days 10 was higher in CON cows than OHF cows (1.86 vs. 1.18 ng/mL, respectively, Figure 1) and that the cortisol levels on days 20, 30, 60 and 90 were significantly different for all treatments. Cortisol, often referred to as the “stress hormone”, is a glucocorticoid secreted by the hypothalamic-pituitary-adrenal axis (Katharina et al. 2015). Levels of cortisol are known to increase in response to physical or psychological stress. Cortisol plays an important role in the body and primarily affects metabolic and immune function (Katharina et al. 2015). Improved animal welfare is considered one of the key benefits of converting to the organic system (Mullen et al. 2015) which logically should equate to reduce cow stress.

 

Feed cost (FC) and income over feed cost (IOFC)

Across the 200 days, cows fed CON system had significantly higher FC than cows fed OHF systems (7.81 vs. 6.09 $/day, respectively). Cows fed CON system had higher IOFC compared to cows fed OHF system (Table 5). On the other hand, the average cost of production for each of the 2 treatments with organic and conventional systems is listed in Table 5. Production costs were higher in the CON system than other group because of the higher use of transport, chopping silage, worker, harvesting and electricity costs. The results of this study indicate that the highest profit to cost ratio (PCR=total revenue/total expenses) was related to the dairy cow of OHF system. Economy of animal production is closely associated with the efficiency of breeding. It is generally understood as the company’s ability to change the material inputs (expressed as costs) into the marketable product under the common production conditions (Michalickova et al. 2014). High level of milk yield which finally reduced the unit cost per kg of milk was the main determinant of difference in this case.

 

Table 5 Estimation of feed cost, income over feed cost (IOFC) and profit to cost ratio of cows fed organic and conventional systems in Holstein lactating

 

1 Income, minus income from calf production has been reported.

2 Aggregation of income from the sales of farm outputs (GR=∑N RxiYi).

3 Profit to cost ratio (PCR): PCR= total revenue/total expenses.

4 Fixed costs included: maintenance costs of farm.

OHF: organic system with high forage and CON: conventional system.

* (P<0.05) and ** (P<0.01).

SEM: standard error of the means.

 

Michalickova et al. (2014) noted comparable value for the profit to cost ratio in milk production in spite of extremely low milk yield per cows reared in mountain and foothill regions.

 

CONCLUSION

By focusing on different levels of evaluation, we conclude that Holstein cows fed on organic system differ from conventional system. DMI and MY were higher in cows fed CON system compared to those in cows fed the other system. However, profitability is likely to be higher for cows fed OHF system, because cows fed CON system had significantly higher FC and IOFC than OHF system. Therefore, despite the lower MY in OHF system, this system is deemed more appropriate due to the lower cost with the same profit to cost ratio compared with conventional system. Feed efficiency was the greatest for CON cows compared to organic cows. Furthermore, the results indicate that the maximum BUN and MUN in CON system can be effective in reducing milk quality. Moreover, cows of OHF system had higher phytanic and hippuric acids contents than cows of CON system during experiment.

 

ACKNOWLEDGEMENT

We gratefully thank the team at the experimental dairy farm at the company PAK for financial support. Moreover, University of Tehran is grateful for the support of research.

Adler S.A., Jensen S.K., Govasmark E. and Steinshamn H. (2013). Effect of short term versus long term grassland management and seasonal variation in organic and conventional dairy farming on the composition of bulk tank milk. J. Dairy Sci. 96, 5793-5810.

AOAC. (1991). Official Methods of Analysis. Vol. I. 15th Ed. Association of Official Analytical Chemists, Arlington, VA, USA.

Butler G., Stergiadis S., Seal C., Eyre M. and Leifert C. (2011). Fat composition of organic and conventional retail milk in northeast England. J. Dairy Sci. 94, 24-36.

Bystrom S., Jonsson S. and Martinsson K. (2002). Organic versus conventional dairy farming studies from the Ojebyn project. Pp. 179-184 in Proc. Orga. Res. Conf. Aberystwyth, UK.

Chaney A.L. and Marback E.P. (1962). Modified reagents for determination of urea and ammonia. Clin. Chem. 8, 130-132.

Ellis K.A., Innocent G., Grove-White D., Cripps P., McLean W.G., Howard C.V. and Mihm M. (2006). Comparing the fatty acid composition of organic and conventional milk. J. Dairy Sci. 89, 1938-1950.

Fall N., Grohn Y., Forslund K., Essen-Gustavsson B., Niskanen R. and Emanuelson U. (2008). An observational study on early lactation metabolic profiles in Swedish organically and conventionally managed dairy cows. J. Dairy Sci. 91, 3983-3992.

Katharina G., Sigl T., Meyer H.H.D. and Wiedemann S. (2015). Cortisol levels in skimmed milk during the first 22 weeks of lactation and response to short-term metabolic stress and lameness in dairy cows. J. Anim. Sci. Biotechnol. 6, 31-38.

Khadem A.A., Sharifi M., Afzalzadeh A. and Rezaeian M. (2009). Effects of alfalfa hay or barley flour mixed alfalfa silage contained diets on feeding behavior, productivity, rumen fermentation and blood metabolites of lactating cows. Anim. Sci. J. 80, 403-410.

Kuhnen S., Stibuski R.B., Honorato L.A. and Machado Filho L.C.P. (2015). Farm management in organic and conventional dairy production systems based on pasture in Southern Brazil and its consequences on production and milk quality. Anim. 5, 479-494.

Larsen M.K., Nielsen J.H., Butler G., Leifert C., Slots T., Kristiansen G.H. and Gustafsson A.H. (2010). Milk quality as affected by feeding regimens in a country with climatic variation. J. Dairy Sci. 93, 2863-2873.

Littell R.C., Henry P.R. and Ammerman C.B. (1998). Statistical analysis of repeated measures data using SAS procedures. J. Anim. Sci. 76, 1216-1231.

Michalickova M., Krupova Z. and Krupa E. (2014). Determination of economic efficiency in dairy cattle and sheep. Slovak J. Anim. Sci. 47, 39-50.

Mullen K.A.E., Dings E.H.A., Kearns R.R. and Washburn S.P. (2015). A comparison of production, reproduction and animal health for pastured dairy cows managed either conventionally or with use of organic principles. Prof. Anim. Sci. 31, 167-174.

Muller U. and Sauerwein H. (2010). A comparison of somatic cell count between organic and conventional dairy cow herds in West Germany stressing dry period related changes. Live. Sci. 127, 30-37.

Prandini A., Sigolo S. and Piva G. (2009). Conjugated linoleic acid (CLA) and fatty acid composition of milk, curd and Grana Padano cheese in conventional and organic farming systems. J. Dairy Res. 76, 278-282.

Roesch M., Doherr M.G. and Blum J.W. (2005). Performance of dairy cows on Swiss farms with organic and integrated production. J. Dairy Sci. 88, 2462-2475.

SAS Institute. (2004). SAS®/STAT Software, Release 9.1. SAS Institute, Inc., Cary, NC. USA.

Sharifi M., Hosseinkhani A., Sofizade M. and Mosavi J. (2016a). Effects of fat supplementation and chop length on milk composition and ruminal fermentation of cows fed diets containing Alfalfa silage. Iranian J. Appl. Anim. Sci. 6, 293-301.

Sharifi M., Khadem A.A., Heins B.J., Pahlavan R. and Safdari M. (2015). The effect of weaning age on performance and economics of Holstein calves reared under organic farming system. Iranian J. Appl. Anim. Sci. 5, 29-33.

Sharifi M., Taghizade A. and Hosseinkhani A. (2016b). Organic Production in Livestock. Education and Agricultural Promoti-on Press, Tehran, Iran.

Slots T., Butler G., Leifert C., Kristensen T., Skibsted L.H. and Nielsen J.H. (2009). Potentials to differentiate milk composition by different feeding strategies. J. Dairy Sci. 92, 2057-2066.

Stiglbauer K.E., Cicconi-Hogan K.M., Richert R., Schukken Y.H., Ruegg P.L. and Gamroth M. (2013). Assessment of herd management on organic and conventional dairy farms in the United States. J. Dairy Sci. 96, 1290-1300.

Thomassen M.A., Van Calker K.J., Smits M.C.J., Iepema G.L. and De Boer I.J.M. (2008). Life cycle assessment of conventional and organic milk production in the Netherlands. Agric. Syst. 96, 95-107.

Trachsel P., Busato A. and Blum J.W. (2000). Body condition scores of dairy cattle in organic farms. J. Anim. Physiol. Nutr. 84, 112-124.

Werner L.B., Hellgren L.I., Raff M., Jensen S.K., Petersen R.A., Drachmann T. and Tholstrup T. (2011). Effect of dairy fat on plasma phytanic acid in healthy volunteers a randomized controlled study. Lipids. HealthDisease. J. 10, 95-102.