Composition, cellularity and biochemical profile of milk from primiparous and pluriparous Holstein cows during the stages of lactation

[Composição, celularidade e perfil bioquímico do leite de vacas Holandesas primíparas e pluríparas durante as fases da lactação]

ABSTRACT

The aim of the study was to verify the influence of calving order and stage of lactation on milk composition, SCC and biochemical profile of whey from Holstein cows. Two hundred negative milk samples in strip cup test and in CMT and with SCC < 200,000 cells/mL were allocated into three groups: milk samples from females with one lactation (G1; n=76), milk samples from females with two or three lactations (G2; n=73) and milk samples from females with four to six lactations (G3; n=51) according with the phase of lactation (initial, intermediate and final). GGT and ALP activities, and total protein, albumin, total Ca, P, Mg, Fe, Cl, Na, K and ionized Ca concentrations were determined. There was an influence of calving order and stage of lactation on SCC in all groups, while milk composition (fat, protein, lactose and total solids) was influenced only by order of calving. The lactation stage influenced all biochemical parameters evaluated of whey. Calving order also influenced biochemical profile, except the iron concentration. More detailed knowledge of the physiological variations that influence milk composition can contribute to the establishment of more accurate and specific ranges of normal values to monitor the health of mammary gland.

Keywords:
SCC; CMT; stage of lactation; calving order; whey

RESUMO

O objetivo deste estudo foi verificar a influência da ordem de parto e do estágio da lactação na composição e na CCS do leite e no perfil bioquímico do soro lácteo de vacas da raça Holandesa. Duzentas amostras de leite negativas no teste da caneca de fundo escuro e CMT e com CCS < 200.000 células/mL foram alocadas em três grupos: amostras de leite de fêmeas de primeira lactação (G1; n=76), amostras de leite de fêmeas com duas ou três lactações (G2; n=73) e amostras de leite de fêmeas com quatro a seis lactações (G3; n=51) e em três momentos, de acordo com a fase da lactação (inicial, intermediária e final). Foram determinadas as atividades das enzimas GGT e ALP e as concentrações de proteína total, albumina, Ca total, P, Mg, Fe, Cl, Na, K e Ca ionizado. Houve influência da ordem de parto e da fase da lactação na CCS do leite em todos os grupos, enquanto a composição do leite (teor de gordura, proteína, lactose e sólidos totais) foi influenciada apenas pela ordem de parto. O estágio de lactação influenciou todos os parâmetros bioquímicos avaliados no soro lácteo. A ordem de parto também influenciou o perfil bioquímico do soro lácteo, exceto a concentração de ferro. O conhecimento mais detalhado das variações fisiológicas que influenciam a composição do leite pode contribuir para o estabelecimento de intervalos de valores de normalidade mais precisos e específicos para monitorar a saúde da glândula mamária.

Palavras-chave:
CCS; CMT; estágio da lactação; ordem de parto; soro lácteo

INTRODUCTION

The milk production chain is one of the country's main economic activities, with a strong effect on generating employment and income. Brazil is the fourth largest producer of milk in the world (36 billion liters/year), with emphasis on the states of MG, PR, RS, SC, GO and SP, behind only the United States of America, India and China (Rocha et al., 2020; Faostat…, 2022; Pesquisa…, 2022).

The bovine mammary gland is composed of four distinct mammary quarters and its ejection out of the udder is a complex process and dependent on a neurohormonal mechanism (Reece, 2008; Dias et al., 2020). From a physiological point of view, milk is a biological fluid obtained from the secretion of the mammary glands of female mammals for the purpose of feeding their offspring (Vidal and Saran Netto, 2018). Legally, milk is defined as the product resulting from the complete and uninterrupted milking, under hygienic conditions, of healthy, well-fed and rested cows (Brasil, 2017). From a physicochemical point of view, milk is an aqueous solution in which colloidal particles of casein, fat globules, lactose, water-soluble proteins, mineral salts and vitamins are dispersed (Fox and McSweeney, 1998; Fonseca and Santos, 2000).

Currently, milk quality is the most important factor in selecting animals for dairy production. In addition to the microbiological quality of milk and somatic cell count (SCC), the volume of total solids, represented mainly by fat and protein content, and the quantity produced by lactation are also considered (Vidal and Saran Netto, 2018; Fonseca, 2021b). In this context, the black and white Holstein breed stands out for its high production, quality and ease of management (Silva et al., 2023).

Bovine milk is generally composed of 87% water and 13% total solids (or total dry extract) and one of the factors that has the greatest effect on the production, composition and quality of milk is mastitis (Fonseca and Santos, 2000; Fox, 2009). However, physiological and environmental factors, such as breed, female age, number of offspring, days in lactation, nutrition and seasonality, can also affect the composition of bovine milk and must be considered (González, 2001; Fonseca, 2021b).

With the present study it is expected to better understand the influence of physiological factors (order of calving and stage of lactation) on the composition of milk from cows without changes in the physical examination of the mammary gland and whose milk remained negative in strip cup test and CMT and with CCS < 200,000 cells/mL.

MATERIAL E METHODS

Milk samples from lactating cows belonging to a dairy farm located in the municipality of Taiaçu, state of São Paulo, were evaluated. The herd consisted of around 440 Holstein animals, with 232 lactating cows, raised intensively and mechanically milked three times a day, producing, on average, 28 kg milk/cow/day. The milking parlor was a side-by-side type with a high vacuum line. Before milking, the teats were disinfected by immersion in a pre-dipping solution (Prevent Pré Dipping, Revtec Bioquímica, Vargem Grande do Sul, SP) and drying with disposable paper towels. After milking, the teats were immersed in a post-dipping solution (Atomic Pós Dipping, Revtec Bioquímica, Vargem Grande do Sul, SP). The cows received a diet based on concentrate, corn silage, millet silage, wet grain, barley and cottonseed, in accordance with NASEM recommendations (Nutrient…, 2021).

The study was approved by the Ethics Committee on the Use of Animals (CEUA) of the Faculdade de Ciências Agrárias e Veterinárias - FCAV/UNESP/Câmpus de Jaboticabal (Protocol nº 7758/23).

Before the first morning milking, and in a single day, 236 mammary quarters were screened, from 68 females, primiparous and multiparous, with 16 to 290 days in lactation, without changes in the physical examination of the mammary gland (Feitosa, 2020) and negative in strip cup test and the California Mastitis Test (CMT).

After antisepsis of teats with cotton soaked in 70% alcohol, 30 mL of milk samples were collected by manual milking in sterile plastic bottles containing bromonate preservative, for somatic cell counting (SCC) and evaluation of milk composition, and 20 mL samples of milk in sterile plastic bottles without preservative, to evaluate the biochemical profile. All milk samples were packaged and transported in isothermal boxes with ice to the laboratory.

Somatic cell counting was performed using flow cytometry method in an automatic counter (Somacount 300, Bentley Instruments Incorporated, Minnesotta, USA) and the evaluation of fat, protein, lactose, total solids and defatted dry extract contents of milk, by infrared method at the Laboratório de Fisiologia da Lactação “Lair Antônio de Souza” (LAFLA), Clínica do Leite, Departamento de Produção Animal, Escola Superior de Agricultura “Luiz de Queiroz” - ESALQ/USP, Piracicaba-SP.

Of the 236 milk samples collected, 36 samples showed SCC ≥ 200,000 cells/mL and were excluded from the study.

Thus, the 200 selected milk samples, coming from 58 lactating females, were allocated into three groups, according to the animals' lactation number: milk samples from first lactation females (G1; n=76), milk samples from females with two or three lactations (G2; n=73) and milk samples from females with four to six lactations (G3; n=51) and at three moments, according to the lactation stage: milk samples collected in the initial phase (first to the third month of lactation), milk samples collected in the intermediate phase (fourth to seventh month of lactation) and milk samples collected in the final phase of lactation (eighth to tenth month of lactation).

Whey was obtained after milk coagulation by adding renin (Coalho Estrella, Chr. Hansen Brasil Ind. e Com. Ltda, Valinhos, São Paulo, Brazil), using the technique recommended by Sant´Ana and Birgel (2003). After the addition of renin, the samples were placed in a water bath at 37°C for 20 minutes and then centrifuged for 20 minutes at 4,500 x g at 4ºC.

To evaluate biochemical profile of whey, enzymes activities of gamma-glutamyltransferase - GGT (modified Szasz method), and alkaline phosphatase - ALP (modified Bowers and McComb method) were determined, as well as total protein (biuret method), albumin (bromocresol green method), total calcium (CPC method - cresolphthalein), phosphorus (modified Daly and Ertinghausen method), magnesium (sulfonated Magon method), chlorides (mercuric thiocyanate method), and iron (modified Goodwin method) concentrations, using a set of commercial reagents (Labtest Diagnóstica, Lagoa Santa, MG, Brazil). Sample readings were performed in a semi-automatic spectrophotometer (Labquest, Labtest Diagnóstica, Lagoa Santa, MG, Brazil), with light of appropriate wavelength for each test. Additionally, sodium, potassium, and ionized calcium contents were determined using ion selective method in an automatic analyzer (9180 Electrolyte Analyzer, Roche, Mannheim, Germany).

The data obtained, expressed as mean and standard deviation, were subjected to analysis of variance (ANOVA) and Tukey’s test for comparison between pairs of means, at a 5% level of significance, after checking the homogeneity of samples.

RESULTS

The results of milk composition and SCC from primiparous and pluriparous cows in the initial phase (first to third month of lactation), intermediate phase (fourth to seventh month of lactation) and final phase of lactation (eighth to tenth month of lactation) are presented in Table 1.

Regarding milk composition, no significant variations were observed in fat (FAT), protein (PROT), lactose (LACT), total solids (TS), and defatted dry extract (DDE) contents in different stages of lactation in any of three experimental groups (p>0.05) (Table 1), however, significant differences were observed between primiparous cows (G1) and multiparous cows (G2 and G3), in at least one phase of lactation, with higher FAT levels, PROT and TS in G1 (p<0.05) (Table 1) and higher LAC levels in G2 and G3 (p<0.05) (Table 1). No significant differences were noted in DDE levels between the groups evaluated (p>0.05) (Table 1).

On the other hand, significant variations in SCC were found between the three experimental groups throughout lactation, with higher counts in primiparous cows group (G1), and a significant reduction in SCC throughout lactation in all groups evaluated (p<0.05) (Table 1).

Table 1
Mean ± standard deviation of milk composition and somatic cell count of Holstein cows with one lactation (G1), with two or three lactations (G2) and with four to six lactations (G3) during initial, intermediate and final stages of lactation

Variables / Groups	Lactation Stages
	Initial	Intermediate	Final
FAT (g/100g)
G1	1.63 ± 0.60 Aa	1.56 ± 0.68 Aa	1.33 ± 0.49 Aa
G2	1.16 ± 0.44 Ba	1.29 ± 0.63 ABa	1.06 ± 0.37 Aa
G3	1.05 ± 0.31 Ba	0.89 ± 0.22 Ba	1.07 ± 0.39 Aa
PROT (g/100g)
G1	3.37 ± 0.29 Aa	3.38 ± 0.32 Aa	3.45 ± 0.32 Aa
G2	3.24 ± 0.34 ABa	3.34 ± 0.38 Aa	3.25 ± 0.20 Aa
G3	3.13 ± 0.25 Ba	3.30 ± 0.32 Aa	3.26 ± 0.17 Aa
LACT (g/100g)
G1	4.62 ± 0.35 Aa	4.55 ± 0.93 Aa	4.76 ± 0.19 Aa
G2	4.86 ± 0.19 Ba	4.93 ± 0.14 Ba	4.87 ± 0.13 ABa
G3	4.93 ± 0.12 Ba	4.94 ± 0.16 ABa	5.00 ± 0.09 Ba
TS (g/100g)
G1	10.58 ± 0.70 Aa	10.69 ± 0.81Aa	10.53 ± 0.74 Aa
G2	10.25 ± 0.60 ABa	10.53 ± 0.87 ABa	10.16 ± 0.52 Aa
G3	10.06 ± 0.56 Ba	10.06 ± 0.55 Ba	10.29 ± 0.45 Aa
DDE (g/100g)
G1	8.96 ± 0.47 Aa	9.13 ± 0.40 Aa	9.19 ± 0.40 Aa
G2	9.09 ± 0.41 Aa	9.24 ± 0.41 Aa	9.10 ± 0.32 Aa
G3	9.02 ± 0.35 Aa	9.17 ± 0.43 Aa	9.22 ± 0.32 Aa
SCC (cells/mL)
G1	138.265 ± 28.208 Aa	77.263 ± 8.523 Ab	41.783 ± 9.606 Ac
G2	26.348 ± 2.058 Ba	18.788 ± 2.655 Bb	13.353 ± 1.498 Bc
G3	9.143 ± 854 Ca	7.444 ± 511 Cb	5.083 ± 996 Cc

• FAT: fat content; PROT: protein content; LACT: lactose content; TS: total solids content; DDE: defatted dry extract; SCC: somatic cell count.
• Means followed by equal capital letters in same column and equal lowercase letters in same line do not differ from each other using Tukey’s test (p>0.05).

The composition, SCC, and total bacterial count (TBC) of bulk milk sample from the property is presented in Table 2. These results refer to the monthly analysis of the property, carried out in the same month as the milking samples for the present study. All evaluated parameters in bulk milk sample were within normal values and/or in compliance with the requirements of Brazilian legislation.

Table 2
Composition, somatic cell count (SCC), total bacterial count (TBC) of bulk milk sample from dairy farm located in the municipality of Taiaçu-SP

Components	Bulk milk sample	Average milk composition (min-max)	Normative Instruction nº76
FAT (g/100g)	3.57	4.0 (2.5-5.5)	min. 3.0
PROT (g/100g)	3.29	3.3 (2.3-4.4)	min. 2.9
LACT (g/100g)	4.63	4.6 (3.8-5.3)	min. 4.3
TS (g/100g)	12.40	12.9 (11.3-14.7)	min. 11.4
DDE (g/100g)	8.81	8.9 (7.9-10.0)	min. 8.4
SCC (cells/mL)	313,000	-	500,000
TBC (CFU/mL)	6,000	-	300,000

• FAT: fat content; PROT: protein content; LACT: lactose content; TS: total solids content; DDE: defatted dry extract.
• Source: adapted from Walstra et al. (2005) e Brasil (2018).

The average daily milk production of 58 females, whose samples were selected for the study, is presented in Table 3. Greater daily milk production was observed in multiparous cows with a greater number of lactations, but without significant differences in relation to production of females with a lower number of lactations (p>0.05).

Table 3
Average daily milk production (kg) of primiparous and multiparous Holstein cows (n=58) from dairy farm located in the municipality of Taiaçu-SP

Category	Average daily milk production (kg)
primiparous (n=20)	27.56 ± 7.94 A
multiparous with 2 or 3 lactations (n=21)	30.24 ± 11.33 A
multiparous with 4 to 6 lactations (n=17)	34.36 ± 7.42 A

• Means followed by equal capital letters in same column do not differ from each other using Tukey’s test (p>0.05).

The results of biochemical profile of whey from primiparous and pluriparous cows in the initial phase (first to third month of lactation), intermediate phase (fourth to seventh month of lactation) and final phase of lactation (eighth to tenth month of lactation) are presented in Table 4.

Significant variations were observed in all biochemical parameters evaluated in different lactation phases in at least one of the experimental groups (p<0.05) (Table 4). Significant differences were also observed in relation to calving order, except for iron concentration (Table 4).

Regarding GGT activity, there was a significant increase in whey of all females from beginning to end of lactation and significantly higher activities in multiparous group (G2: 3,804 U/L and G3: 3,570 U/L) in final stage of lactation (p<0.05) (Table 4). A significant increase in ALP enzymatic activity was also observed throughout the lactation phases (p<0.05) and significantly lower values of this enzyme activity in whey from multiparous females of G2 at beginning of lactation (28.12 U/L) (Table 4).

Furthermore, there was a significant increase in total proteins concentration from initial to final phase of lactation in whey of all animals (p<0.05), with lower concentrations being observed in G3 at beginning of lactation (1.06 g/ dL) and higher values in G2 at end of lactation (1.48 g/dL) (Table 4). Similar behavior was noted for albumin concentration throughout lactation. However, the increase was only significant (p<0.05) in whey from G2, which also presented the highest value for this protein at end of lactation (0.08 g/dL) (Table 4).

In relation to mineral content of whey, a significant reduction in total calcium concentration was observed during lactation in whey of primiparous (G1) (p<0.05). The lowest value of this element was found in whey from G2 in final stage of lactation (30.88 mg/dL) (Table 4).

On the other hand, a significant increase in magnesium concentration in whey of G1 was observed from initial to final phase of lactation (p<0.05), with pluriparous cows from G2 having the lowest concentrations of this mineral in intermediate stage (6.62 mg/dL) and in final stage of lactation (6.86 mg/dL) (Table 4).

Primiparous females (G1) had significantly higher phosphorus concentrations (p<0.05) in whey at all stages of lactation compared to pluriparous females (G2 and G3). Regarding the stage of lactation, a significant increase was observed in whey of G1 between initial and intermediate phase and a significant reduction in G3 between intermediate and final phase (p<0.05) (Table 4).

Although no significant differences were noted in iron concentration in whey of primiparous (G1) and multiparous (G2 and G3) females (p>0.05), a significant increase in the concentration of this element in whey was observed in G3 between intermediate phase and final phase of lactation, when the highest iron level was observed (6.02 ug/dL) (Table 4).

In relation to electrolytes concentrations in whey, there was a significant increase in chlorides in whey of multiparous females of G2 and G3 from beginning to end of lactation (p<0.05), with the highest levels being found in these two groups in end of lactation (G2: 122 mMol/L and G3: 125 mMo/L) (Table 4).

Table 4
Mean ± standard deviation of biochemical parameters of whey from Holstein cows with one lactation (G1), with two or three lactations (G2) and with four to six lactations (G3) during initial, intermediate and final stages of lactation

Parameters / Groups	Lactation Stages
	Initial	Intermediate	Final
GGT (U/L)
G1	2,592 ± 313 Aa	3,237 ± 432 ABb	2,881 ± 521 Ac
G2	2,711 ± 534 Aa	2,970 ± 471 Aa	3,804 ± 738 Bb
G3	2,558 ± 298 Aa	3,400 ± 881 Bb	3,570 ± 809 Bb
ALP (U/L)
G1	51.95 ± 27.34 Aa	102 ± 37.18 Ab	147 ± 74.69 Ac
G2	28.12 ± 11.66 Ba	90.97 ± 40.49 Ab	150 ± 33.85 Ac
G3	53.29 ± 19.37 Aa	83.84 ± 47.58 Aa	144 ± 94.18 Ab
TP (g/dL)
G1	1.13 ± 0.09 ABa	1.13 ± 0.06 Aa	1.24 ± 0.07 Ab
G2	1.16 ± 0.13 Aa	1.20 ± 0.10 Ba	1.48 ± 0.20 Bb
G3	1.06 ± 0.08 Ba	1.23 ± 0.07 Bb	1.34 ± 0.18 ABc
Alb (g/dL)
G1	0.05 ± 0.02 Aa	0.05 ± 0.01 Aa	0.06 ± 0.01 Aa
G2	0.05 ± 0.01 Aa	0.06 ± 0.01 Ba	0.08 ± 0.02 Bb
G3	0.06 ± 0.01 Aa	0.05 ± 0.01 ABa	0.06 ± 0.03 ABa
tCa (mg/dL)
G1	39.14 ± 4.64 Aa	31.78 ± 3.18 Ab	34.73 ± 3.95 Ab
G2	32.59 ± 5.01 Ba	32.72 ± 2.40 Aa	30.88 ± 5.00 Ba
G3	37.26 ± 3.53 Aa	36.67 ± 3.65 Ba	37.61 ± 4.85 Aa
Mg (mg/dL)
G1	7.04 ± 1.04 Aa	6.86 ± 1.07 Aa	7.77 ± 1.25 Ab
G2	7.03 ± 1.00 Aa	6.62 ± 0.60 Aa	6.86 ± 0.91 Ba
G3	7.35 ± 1.11 Aa	7.74 ± 0.78 Ba	8.00 ± 0.76 Aa
P (mg/dL)
G1	41.12 ± 5.00 Aa	44.87 ± 2.42 Ab	41.32 ± 3.15 Aa
G2	36.33 ± 2.99 Ba	35.71 ± 3.21 Ba	36.30 ± 4.90 Ba
G3	36.89 ± 5.22 Bab	37.23 ± 4.70 Ba	32.18 ± 6.62 Bb
Fe (ug/dL)
G1	3.17 ± 2.42 Aa	1.97 ± 2.81 Aa	3.50 ± 2.75 Aa
G2	3.86 ± 2.10 Aab	3.54 ± 2.70 Aa	6.02 ± 3.68 Ab
G3	3.78 ± 2.81 Aa	3.63 ± 2.71 Aa	5.98 ± 3.60 Aa
Cl (mMol/L)
G1	116 ± 9.34 Aa	116 ± 5.30 Aa	111 ± 9.40 Aa
G2	114 ± 9.33 Aa	116 ± 8.44 Aab	122 ± 10.41 Bb
G3	112 ± 8.36 Aa	111 ± 12.45 Aa	125 ± 13.43 Bb
Na (mMol/L)
G1	139 ± 5.52 Aa	144 ± 4.74 ABb	137 ± 9.17 Aa
G2	144 ± 10.05 Ba	140 ± 10.31 Aa	140 ± 18.71 Aa
G3	132 ± 5.65 Ca	147 ± 7.90 Bb	157 ± 24.02 Bb
K (mMol/L)
G1	40.74 ± 2.59 Aa	42.65 ± 0.97 Ab	41.61 ± 2.35 Aab
G2	39.47 ± 3.21 ABa	39.20 ± 2.51 Ba	32.72 ± 4.22 Bb
G3	37.73 ± 1.98 Ba	36.45 ± 4.02 Cab	33.33 ± 7.25 Bb
iCa (mMol/L)
G1	3.35 ± 0.28 Aa	2.64 ± 0.21 Ab	2.73 ± 0.24 Ab
G2	3.19 ± 0.28 ABa	2.80 ± 0.25 Ab	2.52±0.48 Ac
G3	3.06 ± 0.22 Ba	3.10 ± 0.29 Ba	3.06 ± 0.55 Ba

• GGT: gamma-glutamyltransferase; ALP: alkaline phosphatase; PT: total protein; Alb: albumin; tCa: total calcium; P: phosphorus; Mg: magnesium; Cl: chlorides; Fe: iron; Na: sodium; K: potassium; iCa: ionized calcium.
• Means followed by equal capital letters in same column and equal lowercase letters in same line do not differ from each other using Tukey’s test (p>0.05).

There was a significant increase in sodium concentration in whey of primiparous females (G1) from initial to intermediate phase of lactation and in whey of pluriparous females in G3 from intermediate to final phase (p<0.05). Significantly higher values of this electrolyte were observed in G3 in intermediate (147 mMol/L) and final (157 mMol/L) stage of lactation (Table 4).

Significantly higher potassium levels were noted in whey of females from G1 at all stages of lactation compared to pluriparous females (G2 and G3). Regarding the lactation stages, significant increases (p<0.05) of this electrolyte were observed in whey of G1 between initial and intermediate stage and significant reductions in whey of G2 and G3 between initial and final stage of lactation (p<0.05) (Table 4).

There was a significant decrease in ionized calcium concentration in whey of primiparous females of G1 and multiparous females of G2 from initial to final stage of lactation (p<0.05). Regarding the order of calving, higher levels of this electrolyte were found in whey of G1 in initial phase of lactation (3.35 mMol/L) and in whey of G3 in intermediate (3.20 mMol/L) and final phase (3.06 mMol/L) of lactation (Table 4)

DISCUSSION

In addition to changes in milk composition related to health factors, it is also important to better understand factors related to animals, since several organoleptic properties and the yield of dairy products in industry vary depending on milk composition.

Bovine milk is composed mainly of water (87%) and total solids, which include fat (3-4%), protein (3.5%), lactose (5%), and minerals (1.2%) (Walstra et al., 2005; Souza et al., 2021) and its composition varies according to factors such as breed, age, mammary gland health, stage of lactation, nutritional management and seasons (Dobranić et al., 2008).

There was no influence of lactation stages (initial, intermediate and final) on any milk components of primiparous (G1) and multiparous (G2 and G3) cows, despite reports of lower concentrations of fat and proteins in milk at beginning of lactation, followed by an increase after second half of lactation, and a decrease in lactose levels throughout lactation (Fox and McSwenney, 1998).

On the other hand, there was an influence of number of lactations on milk constituents, with higher levels of fat, protein and total solids being found in bovine females with one lactation (G1). As primiparous cows have a lower milk production than cows with more calving, as they are still undergoing body and mammary development (Fonseca, 2021a), it may be that there was a concentration of these components in milk of this animal category.

Multiparous cows (G2 and G3) had higher lactose levels. Lactose is the main carbohydrate in milk and the majority component of milk solids and, in technological terms, just like fat, milk protein is one of the main constituents of greatest economic relevance, even serving as a criterion for payment of milk for quality to rural producers for dairy products. This is because protein is extremely important in production of dairy products, mainly due to quality and yield (Vidal and Saran Netto; 2018; Souza et al., 2021).

In relation to current legislation, FAT and DDE contents of primiparous (G1) and pluriparous (G2 and G3) cows were below the minimum values established by Normative Instruction nº76 (Brasil, 2018). Milk fat is one of the main components in terms of value, flavor, and nutrition and also the one most subject to variations (Fonseca and Santos, 2000; Souza et al., 2021). Bovine milk normally contains 3.5% fat, but the level varies greatly depending on several factors, including the point during milking when sample is collected, being lower at beginning of milking and gradually increasing in percentage as milk is removed from mammary gland (Fox and McSwenney, 1998; González, 2001).

Thus, the values obtained, below the values of bulk milk from studied property (FAT: 3.57 g/100g and DDS: 8.81 g/100g) are probably related to the moment and method of milk sampling: before beginning of milking and only a mammary quarter, to meet the criteria established by study (negative milk sample in strip cup test and CMT), and not a representative sample of entire milking taken from meter/sampler.

Somatic cells found in milk are mainly composed of epithelial desquamation cells and blood leukocytes and the factor that most contributes to an increase in SCC values is mastitis. Thus, SCC is an important indicator of health of dairy cow's mammary gland and counts above 200,000 cells/mL indicate the occurrence of subclinical mastitis (Smith et al., 2001; Santos, 2002; Langoni et al., 2011; Chamilete et al., 2022). Milk SCC is also influenced by cow productivity, number of calving, stage of lactation, and animal breed (Fonseca and Santos, 2000; Alhussien and Dang, 2018).

Several studies indicate higher SCC in multiparous females compared to primiparous females and an increase in SCC throughout lactation as milk production decreases (Batra, 1986; Breen et al., 2009; Fox, 2009; Sebastino et al., 2020), however, in the present study, the highest SCC were observed in primiparous females and in all groups, there was a decrease in SCC throughout lactation.

The transition period is a critical time for dairy cows, and this is aggravated in heifers, as primiparous condition is new for animals, causing intense levels of stress (Collet, 2018). Furthermore, daily milking routine exposes the animal to the risk of transmitting contagious pathogens, and milking vacuum has an adverse impact on the ends of teats (Fonseca and Santos, 2000; Fox, 2009), which may have influenced the SCC of milk from primiparous cows in study.

The decrease of SCC of milk of primiparous (G1) and multiparous (G2 and G3) cows throughout lactation may be related to good management practices on dairy farm, as SCC and TBC of bulk tank of property (313,000 cells/ mL and 6,000 CFU/mL) are below the values established by current legislation (Brasil, 2018) and the fact that lactating females are already more adapted to milking routine as days of lactation progress.

The stage of lactation influenced all biochemical parameters evaluated in whey, with an increase trend in GGT and ALP enzyme activities and in total calcium, phosphorus, sodium, potassium and ionized calcium concentrations, and a decrease in total protein, albumin, magnesium, iron and chlorides concentrations, as the lactation stage progresses. The order of calving also influenced the biochemical profile of whey, except iron concentration. Whey of primiparous females from G1 showed a higher concentration of magnesium. Whey from pluriparous females in G2 exhibited greater GGT and ALP enzyme activities and higher levels of total protein, albumin and iron, while whey of pluriparous females from G3 showed a higher concentration of chlorides.

Although mammary gland infection is the most important factor that causes changes in milk composition, due to changes related to inflammatory process, such as increased permeability of blood capillaries and changes in ionic pumping systems (Zafalon and Nader Filho, 2007; Vidal and Saran Netto; 2018), more detailed knowledge of physiological variations can contribute to the establishment of more accurate and specific ranges of normal values to monitor the health of mammary gland.

CONCLUSIONS

There was an influence of calving order and lactation stage in SCC and the biochemical profile of whey of primiparous and pluriparous Holstein cows, while milk composition was influenced only by order of calving. It is noteworthy that sampling methodology used in the study, per mammary quarter and before milking, negatively influenced the results of milk fat content.

ACKNOWLEDGEMENTS

This study was financed in part by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) - Finance Code 001.

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Publication Dates

• Publication in this collection
  27 Jan 2025
• Date of issue
  Jan-Feb 2025

History

• Received
  22 Jan 2024
• Accepted
  18 June 2024