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AbstractThe study examined effects of thyroid manipulation with propylthiouracil (PTU) on the metabolic adaptability of transitional dairy cows to early lactation. The study included 30 primiparous Holstein-Friesian cows, which were divided into two groups: PTU+ (n = 15; received orally 4 mg/kg PTU during 20 days before expected calving) and PTU− (n = 15; did not receive orally PTU). Blood was sampled from each cow consecutively from − 20, − 17, − 13, − 5, − 4, − 3, − 2, and − 1 days before the expected term of calving, calving day (0), and + 1, + 2, + 3, + 4, + 5, + 10, + 15, + 30 and + 60 days after the calving to measure thyroid stimulating hormone (TSH), triiodothyronine (T3), thyroxine (T4), insulin, glucose, beta-hydroxybutyrate (BHB), bilirubin, total protein and albumin concentrations. Liver samples were biopsied at −7 ± 2 and +7 day relative to calving from both groups of cows to determine deiodinase (DIO) expressions and fat and glycogen content. Additionally, milk yield was monitored during the first 60 days of lactation. PTU successfully induced thyroid suppression by significantly reducing T3 and T4 concentrations and hepatic DIO1 expressions and caused PTU+ cows to have significantly higher insulin and glucose concentration in the precalving period. After calving, PTU+ cows had higher insulin and glucose concentration, liver glycogen content and overall milk production, lower BHB concentration, BCS loss, and liver fat deposits. Accordingly, cows treated with PTU have a more favourable energy balance and metabolic adaptation to early lactation.

The study aimed to determine the concentration of energy-related hormones in cow’s milk and to consider them from a public health perspective. Fourteen Holstein cows were subjected to milk and blood sampling on the following days in lactation (DIL): 10, 30, 60, 90, 150, 180, 210, 250 and 280 to determine milk hormones, fat and protein content and blood biochemical parameters. For the same purpose, bulk-tank milk was sampled and samples of retail m ilk with 1.5% (CM1.5) and 3.2% (CM3.2) fat was purchased. Milk insulin-like growth factor-1 (IGF-1) values were significantly lower at 90, 150, 180, 210 and 250 and significantly higher at 10, 30 and 60 DIL than lactation average (LA). Milk insulin concentrations were significantly lower at 30, 60 and 90 and higher at 210, 250 and 280 DIL than LA. Free thyroxine (fT4) level in the milk was higher at 250 DIL, while milk free triiodothyronine (fT3) concentrations were lower at 30, 60, 90 and 280 DIL, and significantly higher at 10 and 180 DIL than respective LA. Milk cortisol levels were lower at 60 and 280 DIL than LA. All measured milk hormones were significantly lower in CM1.5compared to CM3.2, bulk-tank milk and LA. An exception was the LA of IGF-1, which was significantly lower than the IGF-1 content in CM1.5. Blood biochemical parameters fluctuated evenly during lactation and were within the reference range. Hormone concentrations in cow’s milk fluctuate during lactation, giving milk an important role in the context of public health.

The aim of our study was to investigate if the thyroid axis of newborn calves is affected by prenatal application of propylthyouracil (PTU). The study included 20 late pregnant Holstein cows. One group (n=10) was treated with PTU (4 mg/kg of BW daily) from day 20 before expected calving until the day of calving. The other group (n=10) was non-treated. Placental samples of dams were obtained for measuring mRNA expression of iodothyronine deiodinases type I (D1), type II (D2) and type III (D3). After parturition calves were separated from the dams and included in the study. Blood samples were taken daily from each calf starting on the day of birth until day 7 of age. Blood T3, T4and TSH concentrations were measured. PCR analysis of the placental tissue revealed an abundance of all three types of placental deiodinases in non-treated cows, and a significant elevation of mRNA levels for all three types of deiodinases after PTU treatment. Calves that originated from dams treated with PTU had significantly lower T3and T4and significantly higher TSH concentrations compared to non-treated calves during the first 2 days of life. Starting from day 4 until day 6 of life the opposite effect was observed meaning that calves prenatally exposed to PTU had significantly higher T3and T4and slightly lower TSH. Our study, for the first time, provides information related to iodothyronine deiodinases mRNA expression in bovine placenta, and confirm that PTU treatment of pregnant dams provokes depression of thyroid function in newborns during the first days of life.