Evaluation of the quality of tank milk for herds of Guzerat and F1 Guzolando cross

Rodrigo Coutinho Madruga¹, Adriano Henrique do Nascimento Rangel¹, Stela Antas Urbano¹, Luciano Patto Novaes², Luís Henrique Fernandes Borba¹, Danielle Cavalcanti Sales¹, Jean Berg Alves da Silva² and Edine Roberta de Lima¹

Universidade Federal do Rio Grande do Norte, Campus Universitário, Lagoa Nova, Natal, Rio Grande do Norte, Brazil, Postal code 59078-970.
stela_antas@yahoo.com.br
¹ Campus Universitário, s/n, Natal, Rio Grande do Norte, Brazil, Postal code 59078-970
² Av. Francisco Mota, 572, Mossoró, Rio Grande do Norte, Brazil, Postal code 59.625-900

Abstract

The objective of this study was to evaluate the composition and sanitary quality of the milk in cooling tanks for commercial herds of Guzerat and F1 Guzolando cross in climatic seasons in the state of Ceará. The study was conducted in two private farms located in Madalena-CE. During 15 months, milk samples were collected directly from milk storing tanks, after mechanical homogenization agitation of the stored milk. The milk samples were refrigerated and sent to the Clínica do Leite, Universidade de São Paulo – ESALQ, Piracicaba, SP, Brazil, to analyse for fat, protein, lactose, somatic cell count (SCC) and total bacterial count (TBC). The data were submitted to variance analysis and "F" Fischer testing and the differences between averages were compared using the Tukey test.

The following average composition was found for Guzerat and Guzolando milk, respectively: 4.57% and 4.05% fat; 3.71% and 3.39% protein; 4.67% and 4.61% lactose. The milk fat content did not vary according to the year or seasons. A higher percentage of protein was found in the 2012 year of milk without changes according to the seasons. The lactose content was higher during 2012 and during the winter and spring. With regard to climatic season’s stations, SCC and TBC showed the lowest values during the spring, with variations in other seasons. Guzerat cows produce milk with a higher fat, protein and lactose. In the Guzolando cattle studied, the composition and sanitary quality of the milk were influenced by the years and by the seasons.

Key words: Bos indicus, Bos taurus, dairy cattle, livestock, semi-arid

Introduction

The production of cow's milk has high social and economic importance in Brazil for substantially constituting the Gross Domestic Product (GDP) of agribusiness and is an activity which is conducted in almost all Brazilian municipalities. However, the low productivity of most Brazilian herds combined with the exponential increase in human population and hence the increased consumption of milk and dairy products to meet the demand for animal protein for human consumption has increasingly pushed farmers to seek more production systems adapted to Brazilian conditions and greater economic efficiency of the activity (Mello Lima 2011).

The improvement of production conditions in tropical regions depends on several factors related to the animal, the environment and production technology. In the context of the animal and based on the sustainability of production systems, an alternative has emerged by cross-breeding Zebu animals ( Bos indicus) with specialized dairy breeds (Bos taurus), mainly Holstein, exploiting the advantages of the heterosis effect. Several studies have confirmed the advantages of using Bos taurus x Bos indicus in tropical conditions (Ordaz 2009), and especially the result of such breeding is raising of animals with high productivity and high adaptability to the conditions in Brazil, especially in the Northeast (Mello Lima 2011).

Our objective was to evaluate the composition (fat, protein, lactose) and sanitary conditions (SCC, TBC) of milk in milk cooling tanks of commercial herds of Guzerat and F1 Guzolando cross (½ Guzerat : ½ Holstein) breeds in the climatic seasons in the state of Ceará, Brazil.

Material and methods

The study was conducted at the Fazenda Potrinha (Farm I) and São Carlos (Farm II) farms, both private farms located in the municipality of Madalena-CE, latitude 04° 51'25'' South and longitude 39° 34'37'' West, with an average altitude of 299 meters above sea level, in the Sertões Cearenses mesoregion of Ceará State belonging to the micro region of Quixeramobim backcountry. The climate is classified as AS (tropical with dry season), by the Köppen-Geiger classification. The average rainfall ranges from 600 mm to 1000 mm per year.

Due to the low rainfall during the experimental period (July 2012 to September 2013), animals were kept in confinement, receiving sorghum or corn silage as forage and a concentrate: soybean meal (18.2%), ground corn grain (75.80 %), limestone (2.80%), common salt (1.00%), mineral salt (1.70%) and livestock urea (0.50%).

The cows were milked twice a day (5am and 2pm) by milking machines at both properties. The milking parlor was equipped with a single file double-six milking machine, with a milk line channeled to the expansion tank. In 2012, the herd from Farm I was exclusively composed of 813 pure Guzerat cattle, registered by the Brazilian Association of Zebu Breeders (Associação Brasileira dos Criadores de Zebu - ABCZ), and evaluated in the Genetic Improvement Program of Zebu breeds (Programa de Melhoramento Genético das Raças Zebuínas – PMGZ, Milk control at farm and Performance Growth Control (PGC). For Farm II, the herd in 2012 and 2013 consisted of Guzolando (½ Guzerá x ½ Holstein), totaling 2,180 milking cows, which were registered at ABCZ in the category of Certified Genealogy Control (CGC).

It is important to note that during the experimental period, the average milk production was 8.36 kg/day for Guzerat cows and 15.02 kg/day for Guzolando cows.

For Farm I, only samples and analyzes carried out in 2012 were considered valid. In 2013, the Guzolando herd was introduced at the farm, leading to a mixture of milk coming from the two genetic groups in the milk tank and forcing us to ignore samples.

Data relating to 15 months of samples from July 2012 to September 2013 were analyzed. The milk sampling procedure was performed directly from the milk tank after homogenization by mechanical agitation. 214 samples were collected: 107 in 40 mL vials containing the preservative Bronopol®; and 107 in 40 mL vials with Azidiol®. Samples were identified, refrigerated between 2°C and 6°C, and sent to the Clínica do Leite, Universidade de São Paulo – ESALQ, Piracicaba, SP, Brazil, and milk components were analyzed for fat, protein and lactose, as well as for somatic cell count (SCC) and total bacterial count (TBC).

Milk composition analyzes were performed electronically by infrared absorption and somatic cell count (SCC) was determined using electronic counting by Fourier transform infrared spectroscopy (FTIR) with MILKO SCAN™ (Foss Eletric A/S, HillerØd, Denmark). TBC was analyzed by flow cytometry method, using Bactocount® (BENTLEY Instruments Inc., Chasca MN, USA). To ensure reliability of the records, null values for bacterial count and somatic cell count were excluded, as well as fat values below 2.0% and above 5.0%. For the characteristic of SCC, statistic W Shapiro-Wilk and statistic D Kolmogorov-Smirnov tests were used to check whether the observed values followed a normal distribution. As the data did not follow the normal distribution, linear score was then calculated (ECS) from the SCC data using the formula proposed by Dabdoub & Shook (1984), in which the ECS = [Log2 (SCC/100,000) + 3].

Climatic seasons and year were defined as experimental variables. Summer (Season 1), comprised of the months of January, February and March, being the start of the rainy season; Autumn (Season 2), comprising April, May and June, and the end of the rainy season; Winter (Season 3), comprised of July, August and September; and Spring (Season 4), comprising October, November and December. Data were tabulated and later submitted to variance analysis and "F" Fischer test. The differences between averages were compared using the Tukey test, at 5% probability. Statistical procedures were performed using the SAS program (Statistical Analysis System, SAS Institute, version 9.3).

The general mathematical model used was:

Where:

Y_jk = milk composition characteristics and the hygienic and sanitary quality of the milk of the j-th year (j=1,2), k-th season of the year (k=1, 2, 3, 4);

j-th year (j=1,2), k-th season of the year (k=1, 2, 3, 4);

Results and discussion

The averages for milk composition from the two experimental groups studied are arranged in Tables 1 and 2.

Data concerning fat, protein and lactose levels are similar to those described by Ribeiro et al (2009) for Guzerat, showing the influence of the breed in milk composition, especially in fat and protein and the relationship between these components.

Ribeiro Neto et al (2012) also studied crossbred cattle in the Northeast, and found lower average values for fat (3.66 ± 0.53), protein (3.16 ± 0.22) and lactose (4.41 ± 0.18) components, and higher average values for SCC (564.95 ± 653.56) and TBC (1,190.68 ± 1,384.61), compared to the evaluated herds in this study.

Minimum and maximum SCC values for Guzerat are consistent with the findings of Langoni et al (2011) who worked with raw stored milk and found values between 200,000 and 586,000 cells/ml.

Table 2 presents values that describe the quality of milk from Guzolando cows (½ Guzerat : ½ Holstein). Data are similar to those reported by Signoretti et al. (2013), when evaluating the composition of milk from crossbred cows kept in irrigated pasture of grass and supplemented with concentrate, wherein the following levels were present: fat (4.46% ± 0.06), protein (3.40% ± 0.03), lactose (4.41% ± 0.02) and SCC (360 ± 34).

Fat content levels obtained in this study are higher than those reported in the literature for animals specialized in milk production. Indeed, Zebu cows have a higher fat content in milk compared to Holstein cows (Fonseca and Santos, 2000). Mello Lima (2011) found 3.00% of milk fat in the Holstein cows and 3.98% in milk from Jersey cows. It is possible that the fat content found can be explained by the dilution effect of the milk components in the volume of milk produced. This effect was highlighted by Venturini et al (2007), who pointed out that milk fat content in general is inversely proportional to the milk yield. Reis et al (2013) also found fat content in milk for crossbred Bos indicus x Bos taurus to be between 3.43% and 3.63%.

Table 3 shows the tank milk composition for the Guzolando cows according to the collection years and the seasons. Milk fat content did not vary according to the year or seasons. Higher percentages of protein were found in milk in 2012 without changes according to the season. Lactose content was higher during 2012 and during winter and spring. Regarding SCC and TBC levels, it was observed in 2012 that they were well below those achieved during 2013. Concerning the seasons, SCC and TBC showed the lowest values during the spring, with variations in other seasons.

It is known that the milk fat content varies according to genetic and environmental factors (Ribeiro et al 2009), highlighting nutrition management and stressing that the quality of forage and forage to concentrate ratio interfere in milk fat percentage (Venturini et al 2007; Rosa et al 2012; Rangel et al 2014; Taffarel et al 2015).

Therefore, as there was no change in the genetic composition of the herd, and since the animals were kept in confinement during the experiment consuming silage and concentrate, it is possible to understand the lack of fat effect on farm II’s tank milk.

Regarding milk protein content, the lack of effect of seasons on this variable could also be explained by the nutrition management, which did not change throughout the sample collection period. According to Rosa et al (2012), the effects of diet balance on protein levels are less apparent than changes in fat content. Thus, considering there were no changes in fat content, the variation in protein content was not expected. It is possible that this small variation in protein levels observed in accordance with the years elapsed secondary factors such as milk production and calving order (Galvão Junior et al 2010). High production values influence lower levels of fat and protein in milk (Peres et al 2001; Kgole et al 2012).

Lactose levels found in this study (Guzerat and Guzolando) are consistent with the values reported in the literature for Zebu cows (Ribeiro et al 2009; Galvão Junior et al 2010; Rangel et al 2014.) Few studies report variations in milk lactose level because there is not usually much variation in this component according to genetic and environmental factors (Signoretti et al 2013). However, in this study it is clear that variations in milk lactose level followed variations in SCC. This occurrence could be explained by the idea advocated by Silva et al (2014), who mentioned that lactose is the primary substrate for mesophilic bacteria that colonize the milk in the cooling milk tank, making it possible that the reduction and/or increased SCC has caused an increase and/or decrease in milk lactose content. The reduction could also be explained by the loss of lactose from the mammary gland to blood due to changes in the permeability of the dividing membrane, caused from the inflammatory condition of mastitis (Rangel et al 2009; Ruegg 2011; Akers and Nickerson 2011; Ballou 2012).

According to Normative Regulation 62 of the Ministry of Agriculture, Livestock and Supply (MAPA 2011), as of July 1, 2015, for the Northeast of Brazil, the maximum allowable values for SCC and CBT in refrigerated raw milk is 500,000 cells/mL and 300,000 CFU/ml, respectively. The values contained in Table 3 for such parameters are much higher than those allowed by the regulation and must be reviewed by the farmer to meet the NR 62 recommendation.

However, it is important to clarify that an infection problem of Staphylococcus aureus on farm II in dairy arrays was detected during the experimental period. Staphylococci are important causative agents of mastitis, highlighting S. aureus among them as a pathogen of mastitis classified as infectious (Sá et al 2004). This fact may justify the high values obtained for SCC, since according to Müller (2002), the extent of SCC increase is directly related to the surface of the mammary tissue affected by the inflammatory reaction. For the values of TBC, an infection in the herd also justifies the high values, because according to Beloti et al (2011), practices that prevent mastitis are largely the same that prevent contamination of the milk, so that the SCC and TBC are positively correlated.

It is worth mentioning that the results for the hygienic and sanitary parameters of milk reinforce the idea that management used in obtaining the milk can influence quality (Ruegg 2011; Silva et al 2013; Cicconi-Hogan et al 2013), particularly at farms that use machine milking. Vallin et al. (2009) found that the average TBC found at farms with machine milking was around three times higher than the average found at farms with hand milking. This situation becomes even more serious when there are highly contagious infectious agents such as S. aureus, , making it necessary to devote more attention in these cases to the process of cleaning and sanitizing the milking machines and all instruments involved in the process of collection and preservation of milk.

Conclusion

• Guzerat cows produce milk with a higher concentration of fat, protein and lactose, contributing to higher total solids that are positively reflected in the industrial yield of dairy.
  
  
• The composition and sanitary conditions of milk from F1 Guzolando cross cows are influenced by years and by seasons.

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Received 8 April 2016; Accepted 7 July 2016; Published 1 August 2016

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