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Influence of production level, number, and stage of lactation on milk quality in compost barn systems

Abstract

This study evaluated the influence of milk production, number of lactations, and days in milk (DIM) on the quality and composition of milk from dairy cows housed in a compost barn (CB) system. The study was carried out using a six-year database, counting 31,268 observations from 2,037 cows of European breeds. Multiparous cows showed higher fat and protein production. Lactose showed high levels for primiparous and the initial stage of lactation (4.65%) and was negatively influenced by somatic cell count (SCC). Milk urea nitrogen was higher (14.01%) from 106 to 205 days in milk, and the other components were higher at >305 days. Therefore, the solids content was higher in the first and second lactations due to the high contents of lactose, fat, and milk protein, but lactose was reduced over lactations. In contrast, high DIM increased SCC and concentrated solids due to lower milk production. The effect of milk production, stage, and lactation order on the composition and milk quality of herds housed in CB showed the same pattern as in other production systems.

Key words
Compost bedded pack barn; confinement; dairy cows; lactation physiology

INTRODUCTION

Rearing cows in compost barns (CB) has become common on dairy farms and has been seen as a promising system (Fernández et al. 2020FERNÁNDEZ A, MAINAU E, MANTECA X, SIURANA A & CASTILLEJOS L. 2020. Impacts of compost bedded pack barns on the welfare and comfort of dairy cows. Anim 10: 1-11., Llonch et al. 2021LLONCH L, GORDO C, LÓPEZ M, CASTILLEJOS L, FERRET A & BALANYÁ T. 2021. Agronomic characteristics of the compost-bedded pack made with forest biomass or sawdust. Processes 9: 546., Emanuelson et al. 2022EMANUELSON U, BRÜGEMANN K, KLOPČIČ M, LESO L, OUWELTJES W, ZENTNER A & BLANCO-PENEDO I. 2022. Animal health in compost-bedded pack and cubicle dairy barns in six European countries. Anim 12: 396.). It is partially due to an increase in milk production, welfare, lifespan, better use of the land area, efficient use of labor, and improved quality of life for farmers (Barberg et al. 2007BARBERG AE, ENDRES MI, SALFER JA & RENEAU JK. 2007. Performance and welfare of dairy cows in an alternative housing system in Minnesota. J Dairy Sci 90: 1575-1583., Mota et al. 2017MOTA VC, CAMPOS AT, DAMASCENO FA, RESENDE EAM, REZENDE CPA, ABREU LR & VAREIRO T. 2017. Confinamento para bovinos leiteiros: histórico e características. Pubvet 11: 433-442., Vilela et al. 2017VILELA D, DE RESENDE JC, LEITE JB & ALVES EA. 2017. A evolução do leite no Brasil em cinco décadas. Revista de Política Agrícola 26: 5-24., Piovesan & Oliveira 2020PIOVESAN SM & OLIVEIRA DS. 2020. Fatores que influenciam a sanidade e conforto térmico de bovinos em sistemas compost barn. Revista Vivências 16: 247-258., Vieira et al. 2021VIEIRA FMC, SOARES AA, HERBUT P, VISMARA EDS, GODYŃ D, DOS SANTOS ACZ, LAMBERTES TDS & CAETANO WF. 2021. Spatio-thermal variability and behaviour as bio-thermal indicators of heat stress in dairy cows in a compost barn: A case study. Anim 11: 1-19.).

Brazil and the United States lead the ranking of the most scientific productions about compost barn systems (Silva et al. 2022SILVA GGBS, FERRAZ PFP, DAMASCENO FA, ZOTTI MLAN & BARBARI M. 2022. Compost Barns: A Bibliometric Analysis. Anim 12: 2492.). In Brazil, studies have focused on CB characteristics (Oliveira et al. 2019OLIVEIRA VC, DAMASCENO FA, OLIVEIRA CEA, FERRAZ PFP, FERRAZ GAS & SARAZ JAO. 2019. Compost-bedded pack barns in the state of Minas Gerais: architectural and technological characterization. Agron Res 17: 2016-2028., Radavelli et al. 2020aRADAVELLI WM, DANIELI B, ZOTTI MLAN, GOMES FJ, ENDRES MI & SCHOGOR ALB. 2020a. Compost barns in Brazilian Subtropical region (Part 1): facility, barn management and herd characteristics. Res Soc Dev 9: e445985198., b, Guesine et al. 2023GUESINE GD, SILVEIRA RMF & DA SILVA IJO. 2023. Physical and environmental characteristics of the compost barn system and its effects on the physical integrity, reproduction and milk production of dairy cattle: a scoping review. J Anim Behav Biometeorol 11: 2023010.), healthy, welfare, and animal behavior (Pilatti & Vieira 2017PILATTI JA & VIEIRA FMC. 2017. Environment, behavior and welfare aspects of dairy cows reared in compost bedded pack barns system. J Anim Behav Biometeorol 5: 97-105., Costa et al. 2018COSTA JH, BURNETT TA, VON KEYSERLINGK MAG & HÖTZEL MJ. 2018. Prevalence of lameness and leg lesions of lactating dairy cows housed in southern Brazil: Effects of housing systems. J Dairy Sci 101: 2395-2405., Mota et al. 2019, Piovesan & Oliveira 2020PIOVESAN SM & OLIVEIRA DS. 2020. Fatores que influenciam a sanidade e conforto térmico de bovinos em sistemas compost barn. Revista Vivências 16: 247-258., Yameogo et al. 2021YAMEOGO B, ANDRADE RR, TELES JÚNIOR CGS, LAUD GS, BECCIOLINI V, LESO L, ROSSI G & BARBARI M. 2021. Behavioural patterns of cows housed in two different typologies of compost-bedded pack barns. Agron Res 19: 1205-1215.), microclimate and heat stress (Vieira et al. 2021VIEIRA FMC, SOARES AA, HERBUT P, VISMARA EDS, GODYŃ D, DOS SANTOS ACZ, LAMBERTES TDS & CAETANO WF. 2021. Spatio-thermal variability and behaviour as bio-thermal indicators of heat stress in dairy cows in a compost barn: A case study. Anim 11: 1-19., Frigeri et al. 2023FRIGERI KDM, KACHINSKI KD, GHISI NDC, DENIZ M, DAMASCENO FA, BARBARI M, HERBUT P & VIEIRA FMC. 2023. Effects of heat stress in dairy cows raised in the confined system: a scientometric review. Anim 13: 1-21.), milk composition (Weber et al. 2020WEBER CT, SCHNEIDER CLC, BUSANELLO M, CALGARO JLB, FIORESI J, GEHRKE CR, CONCEIÇÃO JM & HAYGERT-VELHO IMP. 2020. Season effects on the composition of milk produced by a Holstein herd managed under semi-confinement followed by compost bedded dairy barn management. Semin Cienc Agrar 42: 1667-1678., Nogara et al. 2021NOGARA KF, BUSANELLO M, HAYGERT-VELHO IMP, ZOPOLLATTO M, FRIGERI KDM & ALMEIDA PSG. 2021. Characterization and relationship between bulk tank milk composition and compostbedded variables from dairy barns in Rio Grande do Sul state, Brazil. Turkish J Vet Anim Sci 45: 890-900.), mastitis, and udder health (Fonseca et al. 2023FONSECA M, MENDONÇA LC, SOUZA GN, CESAR DE, CARNEIRO JC, BRITO EC, MENDONÇA JF, PAIVA E BRITO MAV & GUIMARÃES AS. 2023. Epidemiology of mastitis and interactions of environmental factors on udder health in the compost barn system. Arq Bras Med Vet Zootec 75: 14-26., Freu et al. 2023FREU G, GARCIA BLN, TOMAZI T, DI LEO GS, GHELLER LS, BRONZO V, MORONI P & DOS SANTOS MV. 2023. Association between mastitis occurrence in dairy cows and bedding characteristics of compost-bedded pack barns. Pathogens 12: 1-13.).

On the other hand, questions related to the bed material used in CB and how the bed could affect the comfort and production of cows have been lesser researched (Damasceno et al. 2020DAMASCENO FA, MONGE JL, NASCIMENTO JAC, ANDRADE RR, BARBARI M, SARAZ JAO & FERRAZ GAS. 2020. Estimate of manure present in compost dairy barn systems for sizing of manure storage. Agron Res 18: 1213-1219., Valente et al. 2020VALENTE DA, SOUZA CF, ANDRADE RR, TINÔCO IFF, SOUSA FC & ROSSI G. 2020. Comparative analysis of performance by cows confined in different typologies of compost barns. Agron Res 18: 1547-1555.). Moreover, there is scarce information about how cow characteristics (milk production, period of lactation, and number of lactations) affect milk quality and composition in CB. These cow characteristics have a significant impact, especially on the udder health of cows housed on CB and the dairy activity profitability (Breitenbach 2018BREITENBACH R. 2018. Economic viability of semi-confined and confined milk production systems in free-stall and compost barn. Food Sci Nutr 9: 609-618., Biasato et al. 2019BIASATO I, D’ANGELO A, BERTONE I, ODORE R & BELLINO C. 2019. Compost bedded-pack barn as an alternative housing system for dairy cattle in Italy: Effects on animal health and welfare and milk and milk product quality. Ital J Anim Sci 18: 1142-1153., Marcondes et al. 2020MARCONDES MI, MARIANO WH & DE VRIES A. 2020. Production, economic viability and risks associated with switching dairy cows from drylots to compost bedded pack systems. Anim 14: 399-408.). Thus, our objective was to analyze the influence of milk production, number of lactations, and days in milk (DIM) on the quality and composition of milk from dairy cows housed in a CB system, using a six-year database.

MATERIALS AND METHODS

This study is characterized as an observational descriptive research, a type of longitudinal retrospective study based on data obtained by consulting the records of a database.

The dataset contained information on the composition and quality of milk from four different herds, 208±94 cows, respectively, located in the municipality of Castro/PR, Brazil (24°47’32” South and 50°00’42” West, at 996 meters above sea level, humid subtropical climate according to the Köppen classification, and mean temperature of 17 °C, Alvares et al. 2014ALVARES CA, STAPE JL, SENTELHAS PC, GONÇALVES JLM & SPAROVEK G. 2014. Köppen’s climate classification map for Brazil. Meteorol Z 22: 711-728.). The data were provided by the Paraná Association of Cattle Breeders of the Holstein Breed (APCBRH) of Curitiba/PR and comprised 60 months of evaluation, between 2016 and 2021. The year 2019 contained the least amount of information relating to these herds. All farms had similar breeding conditions, where the animals were confined in a CB system with sawdust and shaving bedding. Dairy cows belonged to breed groups of European origin, with a predominance of Holstein animals. The animals received a total mixed diet, consisting of corn silage, commercial concentrate, wet brewery residue, pre-dried oats and ryegrass, soybean hulls, corn meal, minerals, additives, and water.

The analyzed milk variables consisted of fat (%), protein (%), lactose (%), milk urea nitrogen (MUN, mg/dL), and SCC (cells/mL), together with the productive level of the herds, DIM, and number of lactations. Table I shows the descriptive statistics of the data. An analysis via infrared spectrophotometry was used to determine milk fat, protein, lactose, and MUN (Bentley model 2000, Bentley Instruments Inc., Chaska, MN, USA). SCC was determined using an electronic counter (Somacount 500, Bentley Instruments Inc., Chaska, MN, USA).

Table I
Descriptive statistics of the distribution of data regarding milk production.

After tabulating all data, the initial sample included 46,423 observations from 2,200 cows. However, some exclusions were made to eliminate biased effects, which could influence the final results. This cut-off point was defined based on the 90th percentile of the coefficient of variation of the data and, therefore, the 10% with the highest variation in the number of cows tested was excluded.

Some extreme data were categorized for these exclusions, such as very advanced lactations (> 7 lactations), milk production (from < 5 to > 80 liters daily), days in milk (< 5 to ≥ 500 days), milk fat (< 2.00 to ≥ 6.00%), protein (< 2.00 to ≥ 6.00%), lactose (< 3.00 to ≥ 6.00%), total solids (TS) (< 8.00 to ≥ 16.00%), MUN (< 7.00 to ≥ 25.00 mg/dL), and SCC (< 1,000 to ≥ 5,000,000 cells/mL). A total of 31,268 observations from 2,037 cows were left after all the exclusions (Figure 1).

Figure 1
Data distribution and exclusion of extreme data from the analysis.

Categorizations were made for DIM, number of lactations, and milk production (MP). Lactations were considered as 1, 2, 3, and > 3, while MP was categorized as < 25 liters, 25 to 40 liters, and > 40 liters, and DIM as ≤ 105 days, 106 to 205 days, 206 to 305 days, and > 305 days. A mixed generalized linear model was used for data analysis. The number of lactations, milk production categories, and DIM were included as fixed components for modeling, and the cows were considered as repeated measures of random effects for the same animal analyzed in different months. Only the model for SCC used a lognormal distribution, whereas a normal distribution model was used for the other variables. The general statistical model used is shown below:

y i j k l m = µ + L a c t i + M P j + D I M k + C o w l + ɛ i j k l m

where yijklm is the measure of the response variable for the n-th observation, µ is the constant common to all observations, Lacti is the fixed effect of the number of lactations with = 4, MPj is the fixed effect of the milk production category with = 3, DIMk is the fixed effect of days in lactation with = 4, Cowl is the random effect of repeated measurement of the cow over the months, ɛijklm is the random error associated with the observation.

All the data were analyzed using PROC GLIMMIX of the SAS University Edition (SAS Institute 2012SAS Institute Inc. 2012. Cary, NC, USA. Disponível em: https://odamid.oda.sas.com/SASStudio/. Acesso em: 16 mar. 2022.
https://odamid.oda.sas.com/SASStudio/...
), considering statistically significant differences at the level of < 0.05 (5%) probability.

RESULTS

Fat

No statistical difference was observed in the fat content among the second and third lactations (3.65 and 3.64%, respectively), with the highest levels of this component being verified in these lactations compared to the first (3.59%) and over three lactations (3.58%) (Table II). Furthermore, the highest fat content (3.95%) was found in milk productions < 25 liters and > 305 DIM (3.79%).

Table II
Influence of lactation, milk production and DIM variables on milk fat content.

Protein

The milk protein content presented a statistical difference among the studied lactations (p<0.0001), with a higher value in the second lactation (3.41%) and lower values in cows with more than three lactations (3.30%) (Table III). Milk protein showed a similar pattern to that of the fat component, being higher in productions < 25 liters (3.53%) and with > 305 DIM (3.54%).

Table III
Influence of lactation, milk production and DIM variables on milk protein content.

Lactose

The lactose content presented a difference among lactations, in addition to decreases of 5.07% between the first lactation and above three lactations. The highest levels of lactose (4.66% and 4.64%, respectively) were observed in milk productions > 40 liters and ≤ 105 DIM (Table IV).

Table IV
Influence of the variables lactation, milk production and DIM on the lactose content of milk.

Total solids

The total solids content of milk presented no difference between the first and second lactations (12.65 and 12.62%, respectively) and decreased in productions > 25 liters. The DIM period that provided the highest solids content was > 305 DIM (12.80%) (Table V).

Table V
Influence of lactation, milk production and DIM variables on milk total solids.

Milk urea nitrogen

MUN was higher in the first lactation (14.08 mg/dL) compared to the other lactations, showing a drop of 5.82%. Lower levels of MUN were observed in productions < 25 liters (13.28 mg/dL). However, MUN was higher between 106 and 205 DIM (14.00 mg/dL) (Table VI).

Table VI
Influence of lactation, milk production and DIM variables on milk urea nitrogen.

SCC

SCC was higher in cows with a higher number of lactations (>3) and with > 305 DIM (174,013 and 117,300 cells/mL, respectively). Cows with productions > 40 liters also had a higher mean SCC (159,465 cells/mL) than the other production categories (Table VII).

Table VII
Influence of lactation, milk production and DIM variables on milk SCC.

DISCUSSION

Milk fat and protein contents were higher in multiparous cows. These components and the produced volume were also higher in multiparous cows (4.14%, 3.18%, and 22.47 liters, respectively) than in primiparous cows (3.82%, 3.01%, and 19.26 liters, respectively), according to data from Sitkowska (2008)SITKOWSKA B. 2008. Effect of the cow age group and lactation stage on the count of somatic cells in cow milk. J Cent Eur Agric 9: 57-62..

Reductions of 8.35% in fat content were observed in daily milk productions above 25 liters. It occurs through the dilution effect, favored by the increase in milk production (Galvão Júnior et al. 2010GALVÃO JÚNIOR JGB, RANGEL AHN, MEDEIROS HR, SILVA JBA, AGUIAR EM, MADRUGADA RC & LIMA JÚNIOR DM. 2010. Efeito da produção diária e da ordem de parto na composição físico-química do leite de vacas de raças zebuínas. Acta Vet Bras 4: 25-30.). The milk fat content is less expressive in the Holstein breed due to its significant milk production (Ludovico et al. 2019LUDOVICO A, TRENTIN M & RÊGO FCA. 2019. Fontes de variação da produção e composição de leite em vacas Holandesa, Jersey e Girolando. Arch de Zootec 68: 236-243.). The higher the production level of the animal, the lower the percentage of milk fat (> 25 liters = 3.11%), and the lower the daily milk production (< 15 liters) and the higher the DIM (> 316 days), the higher the concentration of total solids, fat, and protein (Cabral et al. 2016CABRAL JF, SILVA MAP, CARDOSO TS, BRASIL RB, GARCIA JC & NASCIMENTO LEC. 2016. Relação da composição química do leite com o nível de produção, estádio de lactação e ordem de parição de vacas mestiças. Rev Inst Laticínios Cândido Tostes 71: 244-255.), which is not beneficial. A high number of lactations is associated with higher milk production (Kappes et al. 2020KAPPES R, KNOB DA, THALER NETO A, ALESSIO DRM, RODRIGUES WB, SCHOLZ AM & BONOTTO R. 2020. Cow’s functional traits and physiological status and their relation with milk yield and milk quality in a compost bedded pack barn system. R Bras Zootec 49: e20190213.), but an inverse effect occurs when the value exceeds five lactations (Zafalon et al. 2005ZAFALON LF, NADER FILHO A, AMARAL LA, OLIVEIRA JV & RESENDE FD. 2005. Alterações da composição e da produção de leite oriundo de quartos mamários de vacas com e sem mastite subclínica de acordo com o estágio e o número de lactações. Arq Inst Biol 72: 419-426.).

The lactose content showed a decrease of 3.01% as the DIM progressed and 5.07% when the number of lactations increased in the evaluated herds of the European breed. Sabek et al. (2021)SABEK A, LI C, DU C, NAN L, NI J, ELGAZZAR E, MA Y, SALEM AZM & ZHANG S. 2021. Effects of parity and days in milk on milk composition in correlation with β-hydroxybutyrate in tropic dairy cows. Trop Anim Health Prod 53: 270. reported that the increase in the number of lactations of cows and the DIM favor changes in milk characteristics, including a reduction in the lactose content. Lactose has a negative correlation with SCC and the number of lactations of animals, and the increase in SCC led to a reduction in the lactose content and, consequently, lower milk production. Kappes et al. (2020)KAPPES R, KNOB DA, THALER NETO A, ALESSIO DRM, RODRIGUES WB, SCHOLZ AM & BONOTTO R. 2020. Cow’s functional traits and physiological status and their relation with milk yield and milk quality in a compost bedded pack barn system. R Bras Zootec 49: e20190213. observed similar data in the CB system, in which lactose was affected by the number of lactations, SCC, and udder depth.

Milk lactose is an important osmotic regulator, as it is related to water in the mammary gland, thus contributing to the produced milk volume. In the present study, the highest lactose content (4.66%) was found in milk productions above 40 liters. This fact justifies the high correlation (0.98) between lactose and milk production (Miglior et al. 2007MIGLIOR F, SEWALEM A, JAMROZIK J, BOHMANOVA J, LEFEBVRE DM & MOORE R. 2007. Genetic analysis of milk urea nitrogen and lactose and their relationships with other production traits in Canadian Holstein cattle. J Dairy Sci 90: 2468-2479.). The same authors also verified a moderate to high magnitude of heritability (0.48 to 0.51) for this component.

Factors such as DIM, milk production, number of lactations, animal age, and breed contribute to the variation in lactose content (Galvão Júnior et al. 2010GALVÃO JÚNIOR JGB, RANGEL AHN, MEDEIROS HR, SILVA JBA, AGUIAR EM, MADRUGADA RC & LIMA JÚNIOR DM. 2010. Efeito da produção diária e da ordem de parto na composição físico-química do leite de vacas de raças zebuínas. Acta Vet Bras 4: 25-30.). According to Ludovico et al. (2019)LUDOVICO A, TRENTIN M & RÊGO FCA. 2019. Fontes de variação da produção e composição de leite em vacas Holandesa, Jersey e Girolando. Arch de Zootec 68: 236-243., Holstein cows have a higher lactose content (4.56%) compared to Jersey (4.47%) and Girolando (4.52%) animals. Regarding the Girolando genotypes (1/2 HG, 5/8 HG, and ¾ HG), the lactose content in milk was higher as the presence of Holstein genes increased (Ludovico et al. 2019LUDOVICO A, TRENTIN M & RÊGO FCA. 2019. Fontes de variação da produção e composição de leite em vacas Holandesa, Jersey e Girolando. Arch de Zootec 68: 236-243.). The comparison of data from 32 ½ blood Brown Swiss and Holstein cows in the initial third of lactation showed no variation in the lactose content between the genetic groups, with an average content of 4.61% (Deitos et al. 2011DEITOS AC, MAGGIONI D & ROMERO EA. 2011. Produção e qualidade de leite de vacas de diferentes grupos genéticos. Campo Digital 5: 26-33.). These data reinforce that milk lactose has low variability (Kaskous 2018KASKOUS S. 2018. The effect of using quarter individual milking system “MultiLactor” on improvement of milk performance and milk quality of different dairy cows breeds in different farms. Emir J Food Agric 30: 57-64.). Lactose is the component that most contribute to the total solids content (> 4.3%) (Santos & Fonseca 2019SANTOS MV & FONSECA LFL. 2019. Controle de mastite e qualidade do leite - Desafios e soluções. 1º ed., Pirassununga: Edição dos Autores, 301 p.) and, possibly for this reason, it favored the higher levels of total solids during the first and second lactations (12.65 and 12.62%, respectively).

Quantifying solids content is important to assess the nutritional quality of milk. Some components are used in payment programs and/or quality bonuses in the dairy industry (Cabral et al. 2016CABRAL JF, SILVA MAP, CARDOSO TS, BRASIL RB, GARCIA JC & NASCIMENTO LEC. 2016. Relação da composição química do leite com o nível de produção, estádio de lactação e ordem de parição de vacas mestiças. Rev Inst Laticínios Cândido Tostes 71: 244-255.) to stimulate specialization in dairy activity and reach higher levels of competitiveness in this sector (Monteiro Junior et al. 2021). Auldist et al. (2007)AULDIST MJ, BRIEN GO, COLE D, MACMILLAN KL & GRAINGER C. 2007. Effects of varying lactation length on milk production capacity of cows in pasture-based dairying systems. J Dairy Sci 90: 3234-3241. also highlighted the influence of extensive lactations (> 16 months) on the reduction in solids content in milk, as losses were smaller from 10 to 16 months. However, we found in our study that high levels of total solids (TS) were observed in DIM above 305 days (12.80%), possibly due to the lower milk production of cows in this period of lactation, which leads to TS concentration.

Urea production in the liver via the urea cycle comes from the excess protein in the diet of dairy cows (or the lack of synchronism in the rumen environment due to low dietary starch content), which reaches other tissues such as the mammary gland via blood circulation, which can be measured in the milk (Televičius et al. 2021TELEVIČIUS M, ANTANAITIS R, JUOZAITIENĖ V, PAULAUSKAS A, MALAŠAUSKIENĖ D, URBUTIS M & BAUMGARTNER W. 2021. Influence of calving ease on in-line milk urea and relationship with other milk characteristics in dairy cows. Agric (Switz) 11: 1-13., Vlizlo et al. 2021VLIZLO VV ET AL. 2021. Functional state of the liver in cows with fatty liver diasease. Ukr J Ecol 11: 167-173., Wang et al. 2021WANG D, CAI J, WANG B, DING S, GUAN LL & LIU J. 2021. Integrative network analysis revealed molecular mechanisms of urine urea output in lactating dairy cows: Potential solutions to reduce environmental nitrate contamination. Genomics 113: 1522-1533.). In the present study, a 4.14% increase was observed in MUN from daily productions of 25 liters, a fact that can be explained because MUN is positively associated with milk production (Doska et al. 2012DOSKA MC, SILVA DFF, HORST JA, VALLOTO AA, ROSSI JUNIOR P & ALMEIDA R. 2012. Sources of variation in milk urea nitrogen in Paraná dairy cows. R Bras Zootec 41: 692-697.). MUN is a component of milk that reflects the nutritional management of the herd, being a direct indicator of protein intake and metabolism, that is, the nutritional condition of the cow, energy, and protein balance, in addition to indicating the occurrence of metabolic disorders (Eicher et al. 1999EICHER R, BOUCHARD E & BIGRAS-POULIN M. 1999. Factors affecting milk urea nitrogen and protein concentrations in Quebec dairy cows. Prev Vet Med 39: 53-63., Vlizlo et al. 2021VLIZLO VV ET AL. 2021. Functional state of the liver in cows with fatty liver diasease. Ukr J Ecol 11: 167-173.).

There is a negative association between the pregnancy rate and MUN levels in bulk milk, with MUN values above 19 mg/dL promoting reductions in reproductive performance (Televičius et al. 2021TELEVIČIUS M, ANTANAITIS R, JUOZAITIENĖ V, PAULAUSKAS A, MALAŠAUSKIENĖ D, URBUTIS M & BAUMGARTNER W. 2021. Influence of calving ease on in-line milk urea and relationship with other milk characteristics in dairy cows. Agric (Switz) 11: 1-13.). Almeida et al. (2021)ALMEIDA R, DOSKA MC, HORST JA, VALLOTO AA, SANTOS GT & LIMA LS. 2021. Associations of days open with milk urea nitrogen and other herd traits in dairy cows. R Bras Zootec 50: e20200081. studied three dairy herds housed in free stalls in southern Brazil and found that individual cow MUN concentration (not from bulk tank milk) should not exceed 15.5 mg/dL before conception, as it can negatively impact future milk production and cow fertility. Considering this limit, we can state that the analyzed herds had adequate MUN levels (13.26 to 14.08 mg/dL).

The highest MUN levels in milk were positively associated with the first lactation (14.08%), followed by a decrease of 5.82% in cows with more than three lactations. High MUN levels were also observed in the first lactation (16.16 mg/dL) in dairy herds in the state of Paraná, Brazil (Doska et al. 2012DOSKA MC, SILVA DFF, HORST JA, VALLOTO AA, ROSSI JUNIOR P & ALMEIDA R. 2012. Sources of variation in milk urea nitrogen in Paraná dairy cows. R Bras Zootec 41: 692-697.), probably due to the oversupply of protein for this category. However, changes in MUN may be a consequence of the physiological state of the animals, as high MUN levels were still verified in both the first and second lactations even providing the same feed (single diet) to the cows in a tie-stall system (Sabek et al. 2021SABEK A, LI C, DU C, NAN L, NI J, ELGAZZAR E, MA Y, SALEM AZM & ZHANG S. 2021. Effects of parity and days in milk on milk composition in correlation with β-hydroxybutyrate in tropic dairy cows. Trop Anim Health Prod 53: 270.). Additionally, the same authors also verified that the highest MUN levels (17.01 and 16.95 mg/dL) were found between the DIM of 101 to 200 and 201 to 305 days, respectively.

Younger cows in the herd had better mammary gland health, as they are temporarily less exposed to environmental and contagious risks than multiparous cows. For this reason, primiparous and early-lactating cows showed lower SCC values (54,480 and 73,325 cells/mL, respectively) in this study, which indicates good management during the dry period. The number of lactations influences the increase in milk SCC, as 764 (with ≥ 3 lactations) out of 2,657 animals, that is, 28.75% of the cows, had an intramammary infection (Souza et al. 2009SOUZA GN, BRITO JRF, MOREIRA EC, BRITO MAVP & SILVA MVGB. 2009. Variação da contagem de células somáticas em vacas leiteiras de acordo com patógenos da mastite. Arq Bras Med Vet Zootec 61: 1015-1020.). Cows with a higher number of lactations are more likely to have subclinical mastitis verified by their increased individual SCC (Schunig 2021SCHUNIG R. 2021. Risk factors associated with the increase of somatic cells count in milk at cow-level. 56 f. Dissertação (Mestrado em Zootecnia) – Setor de Ciências Agrárias, Universidade Federal do Paraná, Curitiba. (Unpublished).).

High SCC (considering cows with SCC ≤ 200,000 cells/mL as healthy) is an indicator that inflammation is occurring in the mammary gland (Dohoo & Leslie 1991DOHOO IR & LESLIE KE. 1991. Evaluation of changes in somatic cell counts as indicators of new intramammary infections. Prev Vet Med 10: 225-237., Botton et al. 2019BOTTON FS, ALESSIO DRM, BUSANELLO M, SCHNEIDER CLC, STROEHER FH & HAYGERT-VELHO IMP. 2019. Relationship of total bacterial and somatic cell counts with milk production and composition – multivariate analysis. Acta Sci Anim Sci 41: e42568., Schunig 2021SCHUNIG R. 2021. Risk factors associated with the increase of somatic cells count in milk at cow-level. 56 f. Dissertação (Mestrado em Zootecnia) – Setor de Ciências Agrárias, Universidade Federal do Paraná, Curitiba. (Unpublished).), which may progress to clinical or subclinical mastitis. Subclinical mastitis can increase the total protein content of milk, even without a quality improvement (Zafalon et al. 2008ZAFALON LF, NADER FILHO A, CARVALHO MRB & LIMA TMA. 2008. Influência da mastite subclínica bovina sobre as frações protéicas do leite. Arq Inst Biol 75: 135-140.). In the primiparous cows, losses from SCC were lower because the animals had less contact with pathogens that cause mastitis. The animals are more exposed and more susceptible to infection with advancing lactations and increasing age (Magalhães et al. 2006MAGALHÃES HR, EL FARO L, CARDOSO VL, PAZ CCP, CASSOLI LD & MACHADO PF. 2006. Influência de fatores de ambiente sobre a contagem de células somáticas e sua relação com perdas na produção de leite de vacas da raça Holandesa. R Bras Zootec 35: 415-421.). The seasons of the year also affect this variable, as there is a higher incidence of mastitis in the summer and fall (SCC 404,000 and 438,000 cells/mL, respectively) than in the spring and winter (341,000 and 308,000 cells/mL, respectively), considering the CB system (Weber et al. 2020WEBER CT, SCHNEIDER CLC, BUSANELLO M, CALGARO JLB, FIORESI J, GEHRKE CR, CONCEIÇÃO JM & HAYGERT-VELHO IMP. 2020. Season effects on the composition of milk produced by a Holstein herd managed under semi-confinement followed by compost bedded dairy barn management. Semin Cienc Agrar 42: 1667-1678.).

In addition, high SCC values from cows with extensive lactations contribute to lower lactose content (4.36%) (Kappes et al. 2020KAPPES R, KNOB DA, THALER NETO A, ALESSIO DRM, RODRIGUES WB, SCHOLZ AM & BONOTTO R. 2020. Cow’s functional traits and physiological status and their relation with milk yield and milk quality in a compost bedded pack barn system. R Bras Zootec 49: e20190213.). This is due to the damage caused to milk-secreting cells, decreasing lactose synthesis and, consequently, lowering milk and total solids production (Harmon 1994HARMON RJ. 1994. Symposium: mastitis and genetic evaluation for somatic cell count. J Dairy Sci 77: 2103-2112., Coelho et al. 2014COELHO KO, MESQUITA AJ, MACHADO PF, LAGE ME, MEYER PM & REIS AP. 2014. Efeito da contagem de células somáticas sobre o rendimento e a composição físico-química do queijo muçarela. Arq Bras Med Vet Zootec 66: 1260-1268., Alessio et al. 2016ALESSIO DRM, NETO AT, VELHO JP, PEREIRA IB, MIQUELLUTI DJ, KNOB DA & SILVA CG. 2016. Multivariate analysis of lactose content in milk of Holstein and Jersey cows. Semina Ciênc Agrár 37: 2641-2652., Ludovico et al. 2019LUDOVICO A, TRENTIN M & RÊGO FCA. 2019. Fontes de variação da produção e composição de leite em vacas Holandesa, Jersey e Girolando. Arch de Zootec 68: 236-243.). Thus, the percentage of lactose in the milk has a negative correlation with SCC, ranging from 0.41 to 0.49 (Eckstein et al. 2014ECKSTEIN II, POZZA MSS, ZAMBON MA, RAMOS CECO, TSUTSUMI CY, FERNANDES T, ECKSTEIN EI & BUSANELLO M. 2014. Qualidade do leite e sua correlação com técnicas de manejo de ordenha. SAP 13: 143-151., Silva et al. 2018SILVA JE, BARBOSA SBP, ABREU BS, SANTORO KR, SILVA EC, BATISTA AMV & MARTINEZ RLV. 2018. Effect of somatic cell count on milk yield and milk components in Holstein cows in a semi-arid climate in Brazil. Rev Bras Saude Prod Anim 19: 391-402., Silva & Antunes 2018SILVA JC & ANTUNES RC. 2018. Efeito do tipo de ordenha e do ambiente sobre a qualidade do leite cru com base na contagem de células somáticas. Cienc Anim Bras 19: 1-16.). The reduction in lactose in cases of mastitis occurs because this component is consumed by bacteria, forming lactic acid and leading to casein instability (Santos & Fonseca 2019SANTOS MV & FONSECA LFL. 2019. Controle de mastite e qualidade do leite - Desafios e soluções. 1º ed., Pirassununga: Edição dos Autores, 301 p.).

The influence of the number of lactations and DIM on SCC has already been reported in the literature. A low mean SCC during the first lactation can be attributed to the health of the mammary gland in primiparous cows (Cabral et al. 2016CABRAL JF, SILVA MAP, CARDOSO TS, BRASIL RB, GARCIA JC & NASCIMENTO LEC. 2016. Relação da composição química do leite com o nível de produção, estádio de lactação e ordem de parição de vacas mestiças. Rev Inst Laticínios Cândido Tostes 71: 244-255.). The higher the number of lactations, the greater its risk of becoming a source of infection and disease transmission within the herd (Zafalon et al. 2005ZAFALON LF, NADER FILHO A, AMARAL LA, OLIVEIRA JV & RESENDE FD. 2005. Alterações da composição e da produção de leite oriundo de quartos mamários de vacas com e sem mastite subclínica de acordo com o estágio e o número de lactações. Arq Inst Biol 72: 419-426.). Additionally, negative effects on SCC are also observed in cows with advanced DIM (Schunig 2021SCHUNIG R. 2021. Risk factors associated with the increase of somatic cells count in milk at cow-level. 56 f. Dissertação (Mestrado em Zootecnia) – Setor de Ciências Agrárias, Universidade Federal do Paraná, Curitiba. (Unpublished).). Dias et al. (2017)DIAS MBC, LEÃO KM, CARMO RM, SILVA MAP, NICOLAU ES & MARQUES TC. 2017. Milk composition and blood metabolic profile from holstein cows at different calving orders and lactation stages. Acta Sci Anim Sci 39: 315-321. also reported that number of lactations and DIM influence milk production and composition.

Information regarding management and nutrition is scarce although the database has a considerable number of observations. Additionally, the literature lacks studies demonstrating the effect of milk production, DIM, and number of lactation on the pattern of milk quality and composition in CB, as well as the incidence and prevalence of mastitis in these herds. Thus, further discussions on this topic are still necessary. In CB, monitoring the temperature of the bed is essential to control its humidity, as 31% of the variation in the tank components is explained by variables related to the compost barn (Nogara et al. 2021NOGARA KF, BUSANELLO M, HAYGERT-VELHO IMP, ZOPOLLATTO M, FRIGERI KDM & ALMEIDA PSG. 2021. Characterization and relationship between bulk tank milk composition and compostbedded variables from dairy barns in Rio Grande do Sul state, Brazil. Turkish J Vet Anim Sci 45: 890-900.).

CONCLUSION

The effect of milk production and stage and number of lactation on the composition and milk quality of herds housed in CB shows the same pattern as in other production systems. Milk production affected total milk fat, protein, and solids as a function of the dilution effect in productions above 40 liters per day and with advanced DIM, with higher levels of total solids being observed during the first and second lactations of dairy cows. Both, lactose and MUN, were higher in primiparous cows. Although milk SCC tends to increase as the number of lactations increases due to the higher exposure to mastitis-causing agents, compromised milk quality and composition are only verified after five lactations. Thus, the good health of the mammary gland could be verified in this study, as the highest mean of SCC obtained was 159,465 cells/mL, which characterizes a healthy cow. These data reinforce that the analyzed farms manage to obtain quality milk, adding potential bonuses for quality to their remuneration.

ACKNOWLEDGMENTS

The authors would like to thank the Paraná Association of Cattle Breeders of the Holstein Breed (APCBRH) for the availability of the database. This study was partially funded by the Coordenação de Aperfeiçoamento de Pessoal de Nível Superior – Brazil (CAPES; Finance Code 001), which granted a scholarship to Karise Fernanda Nogara in the Master’s program in Animal Production and Environment at UFPR.

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Publication Dates

  • Publication in this collection
    07 June 2024
  • Date of issue
    2024

History

  • Received
    4 Dec 2022
  • Accepted
    18 Nov 2023
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