Determination of colostrum quality in sheep using a brix refractometer and colostrometer

Introduction

Colostrum is formed by the accumulation of breast secretions and proteins passed from the blood during the last few weeks of pregnancy. Colostrum, the first milk produced by mammary glands, is secreted just before and during the first week after birth (Güngör, 2006) [1] . Since colostrum is the sole nutritional source of newborns, it is the second most important factor affecting survival after body reserves. Nutrient-rich colostrum contains high levels of immunoglobulins, enzymes, hormones, growth factors and neuroendocrine peptides (Nowak and Poindron, 2006) [2] . The first day after birth is crucial for lambs, as inadequate colostrum intake or poor quality can result in insufficient passive immunity (Tsiligianni et al., 2012) [3] . In ruminants, syndesmochorial placentation prevents the in utero transmission of immunoglobulins, resulting in low serum IgG levels at birth. Therefore, it is crucial for neonatal lambs to absorb maternal immunoglobulins from colostrum at an early stage to acquire passive immunity and survive (Koyuncu et al., 2018) [4] . Immunoglobulins, which play an important role in establishing passive immunity in newborns, are present in high levels in colostrum (Jaster, 2005) [5] . The ability of the newborn to transfer adequate passive immunity depends on the age at colostrum intake and the immunoglobulin concentration in the colostrum. Therefore, it is important to be able to measure the quality of colostrum produced by the mother (Perez-Marin et al., 2023) [6] . Colostrum quality is directly related to immunoglobulin concentration (Ahmann et al., 2021) [7] . Various methods, such as electrophoresis (Lopreiato et al., 2017) [8] , radial immunodiffusion (Akköse et al., 2025) [9] , and the enzyme-linked immunosorbent assay (ELISA) (Schoen et al., 2025) [10] , were used to determine immunoglobulin levels in sheep colostrum. These methods are the gold standard for determining levels of immunoglobulin G (IgG), immunoglobulin G1 (IgG1), immunoglobulin G2 (IgG2), immunoglobulin M (IgM), and immunoglobulin A (IgA). However, these analyses require laboratory equipment and expertise and take a lot of time. Rapid on-site assays, such as colostrometer and refractometer, effectively assess the quality of colostrum and correlate well with the gold standard methods (Lemberskiy-Kuzin et al., 2019) [11] . On-farm testing studies using colostrometer (Karakuş and Atmaca, 2016) [12] and Brix refractometer (Hamer et al., 2023 [13] ; Sarica and Aydoğdu, 2024 [14] ; Akköse, 2025) [15] were also conducted to estimate immunoglobulin values. The colostrometer estimates colostrum quality by measuring specific gravity, which reflects total solids. Since protein is 64% of total solids and globulins are 47% of protein, specific gravity correlates well with immunoglobulin content (Nava-Cruz et al., 2024) [16] . The Brix refractometer also provides a rapid and simultaneous estimation of colostrum's total solids concentration (Akköse, 2025) [15] . Studies on colostrum quality and its influencing factors have generally been conducted on cows. Additionally, few studies have compared the Brix refractometer and colostrometer methods for assessing the quality of colostrum in sheep. The aim of this study was to evaluate the quality of sheep colostrum using a digital Brix refractometer and a colostrometer.

Materials and Methods

The study was conducted in 2025 at the Research and Application Farm of Yüzüncü Yıl University in Van, Türkiye. The study examined 30 pregnant Norduz sheep raised under semi-intensive conditions. The ewes were fed a diet consisting of alfalfa hay, barley straw, and a concentrate feed. Approximately 250 ml of colostrum were collected by hand milking from both udders of each ewe within the first six hours after birth. The birth weight, birth type, gender of the lambs, and dam age were recorded. Colostral specific gravity was measured using a colostrometer (KRUUSE) designed for bovine colostrum, with a range of 1.025-1.075 at a temperature of 20°C. The quality of colostrum is categorized by specific gravity (SG) into poor (red zone, <1.035), intermediate (light-green zone, 1.035-1.045), and good (dark-green zone, >1.045) (Karakuş and Atmaca, 2016) [12] . The Atago PAL-1 Digital Refractometer (0-53 Brix) was used in the digital refractometer analysis. After cleaning the sample chamber with distilled water and obtaining a value of zero, a few drops of the colostrum sample were added, and the measurement was taken. Measurements were performed at room temperature. The results were confirmed by repeating the digital refractometer analysis. Descriptive statistics of the obtained data were performed using the SAS (2022) [17] package program.

Results and Discussion

Factors affecting Brix values (%) of Norduz ewe colostrum are given in Table 1. Colostrum with a Brix percentage below 22% is considered poor quality. In contrast, colostrum with a Brix value of 22-26% is considered medium quality, while those above 26% are considered high quality (Kara and Şenel, 2025) [18] . Of the colostrum samples examined in this study, 16 were below 22% Brix, 11 were between 22% and 26%, and three were above 26% (Figure 1). The average Brix value of Norduz ewe colostrum samples was found to be 21.31%, ranging from 15.40% to 29.70%. The%Brix value obtained in the study was found to be similar to the 21.02% reported by Todaro et al. (2023) [19] , but lower than the 27.69% reported by Sarica and Aydoğdu (2024) [14] and the values of 24.39% and 24.30% reported by Övet (2024) [20] for sheep and goats, respectively. Uysal et al. (2024) [21] reported that the Brix percentages of colostrum varied according to sheep breeds and ranged from 21.6-44.7% at 0 hours postpartum, 15.1-45.3% at 4 hours, and 12.0-40.4% at 24 hours. These differences in the literature may stem from many factors, primarily breed, as well as the ewes' feeding regimen, year of birth, season of lambing, vaccination status during pregnancy, and the method used to analyze colostrum quality. Although no statistically significant differences were found among the dam age groups, the highest average Brix values were found in colostrum samples from two-and three-yearold dams. Akköse (2025) [15] found no difference in colostrum quality between ewes and yearling lambs, as determined by the Brix refractometer.

The colostrum Brix value of ewes giving birth to single lambs was 21.42%, while that of ewes giving birth to twins was 20.33 (p>0.05). However, Sarica and Aydoğdu (2024) [14] found that the optical and digital Brix values of the colostrum from ewes that gave birth to twins were significantly higher (p≤0.05) than those from ewes that gave birth to a single lamb. Similar to birth type, no statistically significant difference was found in the Brix values of colostrum between ewes that gave birth to female and male lambs. Of the colostrum samples collected in the study, five were found to be of poor quality (<1.035), eight were found to be of moderate quality (1.035-1.045), and 17 were found to be of good quality (>1.045) (Figure 2). The average specific gravity of Norduz ewe colostrum was found to be 1.049 (Table 2). This value was the same as the value reported for Norduz breed by Karakuş and Atmaca (2016) [12] . Because this value was greater than 1.045, it was classified as good-quality colostrum, and its immunoglobulin level was above the reported threshold of 20 mg/mL for sheep (Eğdir, 2023) [22] . Although factors such as fat and solids content, colostrum temperature, have been reported to affect colostrometer readings, colostrometers can still be useful for distinguishing high-quality colostrum from low-quality colostrum (Godden, 2008) [23] . The effects of dam age and gender on colostrum specific gravity were not significant. On the other hand, the specific gravity of the colostrum was determined to be 1.051 and 1.028 for dams with single and twin lambs, respectively. The difference was found to be significant (p<0.001). The specific gravity of the colostrum produced by ewes that gave birth to twins was within a much narrower and lower range. This situation showed that colostrum was systematically less concentrated (lower in solids) compared to single-birth ewes.

Conclusion

According to the study results, the quality of colostrum in Norduz sheep was determined to be high by a colostrometer. It was also evaluated as slightly below the 22% threshold value by a digital Brix refractometer. However, since a definitive threshold value for quality colostrum has not yet been established for sheep, as it has for cattle, more studies are needed to make an accurate assessment.

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