- During the peripartum period (3 weeks before through 3 weeks after calving, a.k.a. “transition”), high producing dairy cows experience, among others, , oxidative stress and immune suppression that compromise performance and increased incidence of diseases.Among trace minerals, supplementation of Selenium (Se) can help to improve the transition by enhancing glutathione peroxidase (GPx) activity and boosting the immune system. Thus, cows during the transition period would benefit from a high amount of Se. Among ways to supplement Se to dairy cows, use of biofortified plants (i.e., the soil is fertilized by inorganic Se that is then incorporated in plant proteins as Se-methionine and Se-cysteine) has proven to be effective in increasing the Se status and improve animals’ health and performance, including their offspring, when fed topregnant beef cows at 2.5 % BW. Different from beef cows, high-producing dairy cows need a more precisely balanced ration that requires a more complex diet; thus, it is not possible to feed only hay. Thus, it remains to be determined if feeding an increased level of Se biofortified hay can be effective in improving the Se status in peripartum high-producing dairy cows.
The present dissertation aimed to assess if feeding Se biofortified hay at a level that is more typical for a ration of high-producing dairy cows is an effective way to improve the transition from pregnancy to lactation in high-producing dairy cows. To accomplish the aim, we tested if supplementing high producing dairy cows with 1 kg/100 kg BW (1% BW) of Se biofortified hay was effective in improving 1) Se status (Part 1) and 2) the transition from pregnancy to lactation (Part 2). For the experiment, we used 10 Jersey and 8 Holstein pregnantdairy heifers that were supplemented with 1% BW of Se biofortified (TRT; n=9; 3.2 mg/kg DM Se) or non-biofortified (CTR; n=9; 0.4 mg/kg DM Se) alfalfa hay mixed with the TMR from approx. 40 days prior- to 2 weeks post-partum.
The objectives of Part 1 of the experiment were to assess if the aforementioned treatment improved 1) the Se concentration in whole blood, liver, milk, and colostrum; 2) the amount of Se that is transferred into the calves; and 3) the antioxidant activity of cows and calves through the determination of GPx activity. For Part 1, we hypothesized that supplementing primiparous dairy cows with a relatively low amount of Se biofortified hay during the dry period and early lactation enhances the Se concentration and antioxidant status in cows and their calves. Se concentration and other trace minerals in whole blood of cows and claves and liver, milk, and colostrum of cows were measured by using ICP-MS, and GPx activity in samples was measured via a commercial kit. Se concentration in blood was 2-fold higher (P<0.05) in TRT vs. CTR (204.5 vs. 95.0 ng/ml) which resulted in higher Se in liver (1.24 vs 0.62 µg/g dry weight) and colostrum (99.1 vs. 27.2 ng/ml) but not milk. Higher GPx activity in plasma (92.8 vs. 77.9 nmol/min/ml) and erythrocytes (549.2 vs. 260.0 nmol/min/ml) were detected, but not in milk. GPx activity in plasma samples was also higher in TRT vs. CTR (92.8 vs. 77.9 nmol/min/ml) and erythrocytes (549.2 vs. 260.0 nmol/min/ml) but not in milk. Compared to CTR, calves from TRT had higher Se in the blood (215.5 vs. 161.22 ng/ml) but only a numerically (P=0.09) larger GPx activity in plasma. A positive correlation was detected between Se in blood and GPx activity in erythrocytes and plasma in cows. Our results proved that feeding pregnant primiparous dairy heifers with one % BW of Se biofortified alfalfa hay is an efficient way to improve Se status in cows and their calves. Se supplementation increased antioxidant activity via GPx in cows and, numerically, in calves. Feeding Se biofortified hay raised Se level in colostrum but not in milk.
Part 2 of the experiment aimed to examine the effect of the treatment on performance, metabolism, oxidative status, and immune response of transition primiparous dairy cows. We hypothesized that supplementing primiparous dairy cows with a relatively small amount of Se biofortified hay during the dry period and early lactation improves performance, metabolism, oxidative status, and immune response. Cows were monitored daily for health status, dry matter intake (DMI), activity, weekly for body weight, and body condition score (BCS). Blood samples were also collected to measure hematocrit (HMC) and metabolic, oxidative, and inflammatory biomarkers. Phagocytosis, white blood cell differential count, and carrageenan skin test (CST) were measured in primiparous cows. Milk yield and components, including fatty acid profile (FA), were determined. Supplementation of primiparous cows with 1% BW of Se-biofortified hay did not affect milk yield or milk components, including fatty acid profile, body weight or DMI. Se biofortified hay affected only a few of the measured parameters in the blood. Albumin level increased, and haptoglobin and urea tended to be increased by supplementation of Se-biofortified hay, indicating a better liver status, especially post-partum. The treatment increased advanced oxidation protein products (AOPP), which is a marker of protein oxidation. An improved antioxidative function of albumin by Se-biofortified hay supplementation was supported by the negative correlation of AOPP with myeloperoxidase and parameters related to inflammation but a positive association with albumin. Se biofortified hay increased hematocrit indicating either a positive effect on erythropoiesis or in lifetime of erythrocytes that could be reduced around calving and/or per effect of severe inflammations. Treatment did not affect any of the measured parameters associated with the immune system. Feeding 1% BW of Se biofortified hay had little effect on metabolic, inflammatory, and oxidative status parameters with no effect on cow’s performance or immune response. Supplementation with Se biofortified hay possibly enhanced liver function, promoted the antioxidant role of albumin, and improved level of red blood cells.