Dados do Trabalho

Título

Milk composition and fatty acid profile analysis from a large Holstein herd from Paraná State

Titulo em português

Análise da composição e do perfil de ácidos graxos do leite em um grande rebanho Holandês do Estado do Paraná

Contribuição para a sociedade (opcional)

Monthly milk FA profile analysis is currently available in Brazilian commercial laboratories, and milk analysis from individual cows can bring valuable information to dairy producers and their technicians. From this innovative study, we highlight the importance of analyzing the milk FA profile and particularly De Novo FA for precise nutrition of dairy cows.

Introdução (obrigatório)

Analysis of the milk fatty acid (FA) profile can be relevant for dairy cattle nutrition. FAs in milk come from de novo synthesis and preformed FA. The ratio between these sources can vary with the physiological state of the cow. The milk FA profile is also impacted by the cow's diet. More recently, studies have investigated the variation in milk fat content and its FA profile to improve herd feeding planning.
This study aimed to evaluate milk samples collected monthly from a large Holstein herd in the state of Paraná from nine uninterrupted months to better understand milk composition and the FA profile of milk. A new approach to milk analysis was adopted, focusing on the reliability of laboratory results to obtain accurate and robust data.

Material e métodos (obrigatório)

A total of 12,772 milk samples (1,419 samples per month) were collected in a single dairy herd in Paraná State. This high-producing herd is comprised only of Holstein animals, milked 3x daily, and under a confined free-stall system. Test-days took place between September 2023 and May 2024, through official milk recording, with milk samples being collected from the first daily milking (from 04:00AM to 11:00AM). The milk composition and fatty acid profile analyses were carried out by the Milk Analysis Laboratory – PARLEITE from the APCBRH, using the NexGen® automated spectrometer (Bentley Instruments®) through mid-infrared spectrometry with Fourier Transform Infrared Spectroscopy (FTIR). The analysis included 17 milk variables, covering general milk composition (milk fat, protein, lactose, total solids, and casein contents), somatic cell count (SCC), and milk urea nitrogen (MUN). The FA profile was evaluated considering de novo (C4:0 to C14:0), mixed (C16:0), and preformed FA (>C16:0), and also it was categorized into saturated, unsaturated, monounsaturated, and polyunsaturated FA. Lastly, the contents of the three main milk FA were also reported; palmitic acid (C16:0), oleic acid (C18:1), and stearic acid (C18:0). The results were compiled and analyzed monthly using descriptive statistics, such as mean, standard deviation (SD), coefficient of variation (CV%), and minimum and maximum values. Variables were expressed in g/100g of milk, while FA concentrations were also converted to g/100g of fat. Fat content discounted for glycerol linked to FA was estimated, assuming that 5.5% of the TAG molecule is glycerol. For data analysis, the MEANS and CORR procedures from SAS were applied. The MEANS provided basic descriptive statistics and CORR assessed Pearson correlations among all variables with fat and protein contents, offering an overview of the characteristics and interrelationships of the data.

Resultados e discussão (obrigatório)

The descriptive means and SD of 12,722 milk samples are presented in Table 1, and the results agree with the ones described by Fleming et al. (2017). Focusing on de novo FA, only 6.4% of the samples were below the threshold 23 g/100g FA, and 22.1% of the samples were below the threshold 0.8 g/100g milk. In fact, in a dairy herd with milk fat contents above 4.0%, we expect a lower proportion of milk samples with low de novo FA. Pearson correlations between milk fat content and de novo FA (g/100g of milk) were high and positive (r=0.97; P<0.01), indicating that increases in milk fat content are associated with higher de novo FA concentrations. Positive and high-magnitude correlations were also found between milk fat content and preformed FA (r=0.92), mixed FA (r = 0.97), SFA (r=0.98), UFA (r=0.86), and MFA (r=0.84), and a moderate correlation was found for PFA (r=0.51). FA C16:0 showed a strong positive correlation (r=0.95; P<0.01) with milk fat, whereas C18:0 and C18:1 showed moderate correlations (r=0.79 and 0.76, respectively). When we express the milk FA profile at g/100g of fat, most FA traits showed negative correlations with total milk fat content, except de novo FA (r=0.59; P<0.01), reemphasizing de novo FA association with rumen health. Regarding milk protein content and its association with milk FA profile, the FA category with higher correlations with milk protein content was again de novo FA (r=0.50 g/100g of milk and r=0.46 g/100g of fat). The results suggest a strong association between some milk FA categories and milk fat content, especially de novo and saturated FA, with weaker correlations for milk protein content. De novo FA, synthesized in the mammary gland from ruminal fermentation precursors (acetate and butyrate), has high correlations with milk fat content and moderate correlations with milk protein content, indicating adequate ruminal health.    Table 1: Milk composition and FA profile analyzed by FTIR spectrometry. Variable g/100g milk g/100f fat Fat 4.29 - Fat corrected for glycerol 4.05 - Protein 3.46 - Lactose 4.67 - Total solids 13.37 - Casein 2.75 - Milk urea nitrogen 16.95 - Soamtic cell count 205.1 - De Novo FA 1.04 27.4 Mixed FA 1.30 34.9 Preformed FA 1.41 37.7 Saturated FA 2.54 66.2 Unsaturated FA 1.29 33.8 Monounsaturated FA 1.13 26.7 Polyunsaturated FA 0.17 4.00 Palmitc acid 1.20 29.7 Oleic acid 0.96 23.8 Stearic acid 0.43 10.7  

Conclusão (obrigatório)

We described milk composition and FA profile over nine months on a large farm in the state of Paraná, under an official milk recording program. Milk FAs are strongly correlated with fat content, especially de novo and saturated FA. The distinct correlations between milk fat content and FA categories reflect the complex biology of fat synthesis, evidencing the influence of ruminal and dietary conditions on milk composition. Furthermore, we highlight the importance of analyzing the milk FA profile and de novo FA for precise nutrition of dairy cows.