Composition and somatic cell count of milk in conventional and agro-ecological farms: a comparative study in Depressão Central, Rio Grande do Sul state, Brazil

C J Olivo, L I Beck, A Mossate Gabbi, P Santini Charão, M F Sobczak, L F Gomes Uberty, J W Dürr* and  R Araújo Filho

Departamento de Zootecnia, Universidade Federal de Santa Maria (UFSM) - Campus,
Camobi, 97119-900, Santa Maria, RS, Brazil
clairo@ccr.ufsm.br   ;   amgabbi@mail.ufsm.br
*Faculty of Agronomy and Veterinary, UPF, Brazil

Abstract

This study had the objective to analyze the composition and the somatic cell count (SCC) of milk in farms managed by conventional and agro-ecological systems of production, localized in Depressão Central, Rio Grande do Sul State, south region of Brazil. Three agro-ecological farms were identified in the region and were compared with five conventional farms.  Samples of milk were taken in the autumn-winter and spring-summer periods and analyzed for protein, fat, lactose, total solids and SCC.

Milk yields and contents of fat and protein in the milk were higher in the conventional system, while lactose was higher and SSC lower,  in the agro-ecological system.

The main difference between the farms was the use of organic manure on the grassland, a greater number of grazing paddocks, higher level of concentrate feeding, less time spent in in the pens where roughages were fed, and use of  homeopathic and phytoterapic products for control of mastitis and parasites, in the agro-ecological compared with conventional farms.

Key words: agro ecology, milk composition, small-farms, somatic cell count, systems of production.

Introduction

In Brazil, there has been a significant increase in the number of farms involved with agro-ecological systems, but most of these are dedicated to crop production. In livestock, especially dairy production, such increases are minor. The greater part of the information about agro-ecology in livestock has originated in regions with a temperate climate (Aroeira and Fernandes 2001). As most regions of Brazil are localized under tropical conditions, the farmers argue that the absence of technical advice and research about agro-ecological systems is a major constraint to the adoption of such systems.

A comparative analysis of  milk production systems shows that the peak of the curve of lactation is rarely detected in cows submitted to an organic production system. Persistence of lactation, however, was superior, compared with cows in conventional systems (Kristensen and Kristensen 1997). In milk production per cow, research has demonstrated only minor differences between organic and conventional systems (Allard and Pellerin 1998; Aroeira and Fernandes 2001; Weller et al 2002). It is important to know, in these comparisons, the amounts of concentrate offered. According to Jonsson (1996), when the amounts are equal, the performance of cows in the organic system may be slightly better than in the conventional system

In relation to milk composition, most research showed no differences in major constituents of milk (fat, protein and lactose)  (Allard and Pellerin 1998; Toledo et al 2002; Steinshamn et al 2000). One study indicated higher levels of protein and fat in milk produced by cows submitted to the organic system (Weller et al 2002)., In contrast, Pabst (1994) and Weber et al (1993) reported higher levels of protein and fat for the conventional system. Several factors, independent of the system, tend to influence milk composition, such as genetic merit, volume of milk produced, diet, season of year, lactation stage, milking management and health status. In relation to season, research conducted in countries of temperate climate showed higher values of SCC during summer (Bodoh et al 1976; Harmon 1998; Petkow et al 2001). This fact coincides with increased of cases of clinical mastitis in summer months. This condition has been attributed to environmental contamination. Studies have confirmed the association between levels of clinical mastitis and bacterial count in the floor of the housing and milking installations (Harmon 1998). In this respect, cows submitted to conditions of a feedlot presented higher risk of contamination in the mammalian gland compared with those managed in a pasture system (Nickerson 1998).

Working in Florida (USA) with conventional systems of dairy production, Fontaneli (1999) showed that SCC was 654,000, 223,000 and 364,000 cells/ml, respectively, in cows managed in feedlot, barley-ryegrass-clover/pearl millet grazing and barley-ryegrass/Bermuda grass grazing.

In Brazil, the research on SCC is relatively new. Data observed from Paraná (south Brazil) by Ribas (1998), with a large number of controlled animals, between 1994 and 1997, demonstrated that monthly SCC averaged 500,000 cells/ml. In herds localized in Minas Gerais and São Paulo (southeastern Brazil), Machado et al (2000) recorded in 4,787 samples that 65% presented up to 500,000 cells/ml. In Minas Gerais (southeastern Brazil), Brito and Brito (1998) found values between 200,000 and 300,000; 232,000 and 623,000 and up to 1,000,000 cells/ml in three herds evaluated. In Santa Catarina (Brazil), Mitidiero (2002) analysed milk from cows submitted to treatment with homeopathy and phytoterapic products in comparison with cows submitted to conventional management. SCC was 779,067 and 463,567 cells/ml, respectively.

High levels of SCC reduce production and also interfere with milk composition. Nickerson (1998) and Harmon (1998) affirmed that there is a linear inverse relation between SCC and milk production. SCC values which already characterize some infection, result in a reduction of lactose between 5 and 20%, of protein between 6 and 18% and total solids betrween 3 and 12%. There are also diminished levels of calcium and potassium, an increase in sodium, chloride and passage of blood protein to milk (Dürr 2001). Overall, an increase of SCC leads to reduction of milk quality and in the value of the byproducts of manufacturing (Schäellibaum 2000). Comparing systems in relation to SCC, the results are contradictory (Aroeira and Fernandes 2001; Kristensen and Kristensen 1997). However, a tendency was observed to a better index in herds submitted over time to an organic system (Toledo et al 2002; Kristensen and Kristensen 1997).

The increasing interest in agro-ecological products and the absence of research with livestock in Brazil under this system, was the motive for conducting the present study. The general objective was to analyze and to compare agro-ecological milk farms in the Depressão Central, Rio Grande do Sul State, Brazil, in comparison with conventional farms. The specific objective was to analyze milk composition and SCC.

Materials and Methods

The comparative study was done in farms localized in the region of Depressão Central, Rio Grande do Sul State, south of Brazil. Initially, a survey was carried out with the objective to identify the presence of rural establishments involved in production of agro-ecological milk. Three farms were identified that had been certified by the Brazilian Ministry of Agriculture (Brasil 1999) as producing organic, agro-ecological, biological and biodynamic products.

For a comparison of systems, five conventional dairy farms were chosen in the same region, which presented similar characteristics (use of family labor, Holstein herds and average production between 9 and 11 kg/cow/day).  The study to characterize the farms and to collect milk samples was done in the period 2001-2002.

Agro-ecological and conventional farms had, on average, 21 ha and 49 ha, respectively. The area devoted to dairy production was 10 ha in the agro-ecological farms and  23 ha in the spring-summer period and 30 ha in the autumn-winter period for the conventional farms. The herds were  constituted by animals of the Holstein breed both systems, with an average of  23 animals in the agro-ecological system and 58 animals in the conventional system.  During the autumn-winter period, the feeding strategy in the agro-ecological system was based on annual and natural pastures submitted to rotational grazing (day and night periods), with fertilization by organic manure. The conventional system utilized similar type of pastures but with application of chemical fertilizers. The agro-ecological farms had, on average, eight paddocks, while the conventional system had, on average, six paddocks. The supplementation with roughage was with maize silage and whole plant cassava for the agro-ecological farms and chopped sugarcane and maize silage in the conventional farms. At milking time, the agro-ecological farms supplemented the cows with concentrate, on average, 3.16 kg/cow/day while on the conventional farms this was an average of 2.6 kg/cow/day. To control mastitis and ecto-and endo-parasites, agro-ecological farmers utilized homeopathic and phytoterapic products, respectively, while in the conventional system, synthetic chemical products were used.  In two of the agro-ecological and in three of the conventional farms, milking was by hand. In one agro-ecological and two conventional farms, milking was by mechanical means (bucket milker). In the milking routine, teats were washed but teat dipping after milking was not practiced in  both systems. Only on the conventional farms did the routine include drying the teat after washing.

Comparatively, it was observed that the cows in the conventional system stayed more time, after each milking, next to the installations. In this period, while the animals received the roughage supplements,  the mean time observed near to installations was two hours and three hours/day, approximately, for agro-ecological and conventional farms, respectively.

Milk samples were collect individually from the cows in the second and fifth month of lactation, in two seasons (autumn-winter and spring-summer.  After milking, the individual production was recorded and a sample of 100 ml was conserved and later analyzed for levels of total solids, protein, fat and lactose by infra-red meter (Bentley 2000). SCC analysis was done electronically by flux cytometer (Bentley Somacount 500) in the Food Research Center of Universidade de Passo Fundo, Brazil.

222 samples were collected, 102 in the agroecological system and 120 in the conventional system. 55% of samples were taken in the autumn-winter period and 45% in the spring-summer period. The data were submitted to ANOVA, adapted to an entirely randomized design with variable number of repetitions. The treatments were conventional and agro ecological systems. A variable number of animals within farms were analyzed, and considered as sub-samples of the experimental unit. The mathematical model was:

U_ijkl = m + a_i + b_j (a_i) + g_k + (ag)_jk + (gb(a_i))_kj + e_ijk,

where:

Y_ijk are estimated parameters;
m is a general mean;
a_i is the effect of system of production (agro ecological/conventional);
b_j is the effect of farm;
g_k is the effect of period (autumn-winter/spring-summer);
(ag)_jk is the interaction between system of production and period;
(gb(a_i))_kj is the interaction between farm, system and period
e_ijk is the experimental error.

Tukey's test, with level of significance of 5%, was used for comparisons of means. Linear correlations were made among some of the variables.

Results and Discussion

Measurement of milk yield was not a major feature of this comparative study, but it was utilized to relate different associations of composition and quality of milk. It was higher for the ecological farms as was percent of lactose in the milk (Table 1). Other attributes of milk (fat, protein and SCC) were higher in the conventional farms. Total solids was the same in both.

 

The most important finding was the higher lactose content , and lower SSC, in milk from the agro-ecological farms, the two parameters being negatively correlated (r= -0.54 and -0.33 for conventional and agro-ecological farms, respectively) (Table 2).  The implication is that incidence of mastitis was lower, or treatment of mastitis was more effective, in the ecological farms. Similar relationships between lactose level and SSC have been observed by Nickerson (19980),  Harmon (1998) and Schäellibaum (2000).

 

These results are in disagreement with data reported from British herds (Aroeira and Fernandes 2001),  but agree with conclusions of Toledo et al (2002) and Weller and Davies (1998), who found SCC to be lower in herds managed on the organic system in comparison with those on the conventional system. Krutzinna et al (1996) reported there were no differences among herds submitted to organic and conventional strategies.

 

Although not the objective of this study , it was observed that on the conventional farms, the animals stayed more time next to the installations.  In research conducted by Fontaneli (1999), it was fond that  confined cows had approximately twice the SCC in milk compared with animals in a grazing system.  In the agro-ecological farms, the longer time spent in the pasture probably improved the hygienic conditions of the system.

Conclusions

Milk produced in agro-ecological farms had higher levels of lactose and lower SSC than milk from conventional farms, implying the productionof a more hygienic product

Acknowledgment

This research was partially supported by FAPERGS.

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