Serum thyroid hormones and lipid profile levels and their correlation at different lactation stages of Murrah buffalo

Introduction

Pregnancy and lactation are physiological periods that result in an increased metabolic demand that, if not satisfied, could provoke a threat to homeostasis (Fiore., (2018) [10] . Periparturient period as well as during the first stage of lactation, increased mammary gland activity results in energy deficiency and increased lipid mobilization from body reserves (Arfuso et al., 2016) [1] . Despite the action of homeostatic mechanisms to maintain blood parameters within physiologic levels, changes in metabolites and hormones occur as a result of increased metabolic demands during both pregnancy and lactation (Arfuso et al., 2016., Ashmawy NA, 2015) [1,2] . The peripartum period represents a critical life phase in buffaloes as well (Abdulkareem TA, 2013., Fiore et al., 2017) [9,3] . The peripartum period and lactation are accompanied by marked changes in some biochemical variables and thyroid hormone values in buffaloes. Moreover, the relationship found between TSH values and milk yield seems to suggest a possible role of the thyroid gland in the maintenance of lactogenesis (Fiore., 2018) [10] . Thyroid gland hormonal activity has an important role in the peripartum period for determining the cell metabolism intensity, the metabolism of lipids and carbohydrates, and the lactation course. (Huszenicza et al., 2002) [16] . Thyroid hormones induce HMG-CoA reductase, which is the first step in cholesterol biosynthesis. Triiodothyronine (T3) upregulates LDL receptors by controlling the LDL receptor gene activation and significantly affects lipid and lipoprotein metabolism. It can influence HDL metabolism by increasing cholesteryl ester transfer protein (CETP) activity. (Rizos, et al., 2011) [23] . The hormonal activity of the thyroid gland has an important role in ruminants for the modulation of metabolic variables. (Fiore, et al., 2017) [9] . Thyroid hormones are important regulators of mammary gland function. In the absence of thyroid hormones, growth and differentiation of the mammary epithelium are reduced (Vonderhaar and Greco, 1979) [31] . Thyroid hormones and lipid profile changes during the postpartum period are extensively studied in cows but the information is scanty in buffalo.

Materials and Method Experimental animals & Collection of samples

The study was conducted on 24 healthy lactating buffaloes from Kokani Dairy Farm, located at Wadalagaon, Dist. Nashik, Maharashtra, India. Blood samples were collected by jugular venipuncture from each buffalo during morning hours between 8:00 am to 10:00 am. About 10 ml of a blood sample from these animals was collected during the Early (15-45 days), Mid (100-130days), and Late (200-230days) stages of lactation in a clot activator gel tube. A total of 6 samples were collected from each buffalo during the early, mid, and late lactation period at monthly interval and clear serum was separated and used for analysis. The average maximum, minimum atmospheric temperature and humidity during the experimental period were 33.13±0.32 ºC, 22.72±0.30 ºC and 61.31±2.15% respectively.

Estimation of thyroid hormones and lipid profile

To measure the circulating levels of total triiodothyronine (T3), thyroxine (T4) and fT4 in the collected serum samples radioimmunoassay was conducted by implying ready to use kits supplied by Board of Radioisotope Technology (BRIT), Bhaba Atomic Research Centre. The radioimmunoassay was carried out at Radiation Medicine Centre (RMC), Parel, Mumbai -400 012. The lipid profile viz. total cholesterol, triglyceride, HDL cholesterol, LDL cholesterol, VLDL cholesterol, estimated using standard biochemical kits and spectrophotometry.

Statistical Analysis

Analysis of variance of the data of the concentration of triiodothyronine, thyroxine, free thyroxine and lipid profile were done using 'R' software and according to Snedecor and Cochran (1994) [25] using one way ANOVA.

Results & Discussion

Thyroid Hormones Mean ± SE serum thyroid hormones profiles during different stages of lactation in Murrah buffaloes is presented in Table1. The levels of TT3 remained almost same during early and mid-stage of lactation and the levels increased significantly (P < 0.002) during late stage of lactation. Similar trend and range were found in the study of Tiirats (1997) [27] in dairy cows, Tajik et al. (2010) [26] in water buffalo, Fiore et al. (2017) [9] in buffalo, Dalvi et al. (2013) [28] in Pandharpuri buffalo, Vala et al. (2020) [29] in lactating Jafarabadi buffalo and Cincovic et al. (2015) [7] in dairy cows. However, Kolbeisy and shetaewi (1992) found the higher levels of T3 values in water buffalo as compare to our study during early stage of lactation. Blood levels of thyroid hormones in peripartum cows decreased, particularly in early lactation, when body reserves are mobilized for high milk production (Bonczek et al., 1988; Tiirats, 1997; Huszenicza et al., 2002) [6,27,16] . Ronge et al. (1988) [24] has also reported lower circulating levels of T3 during early lactation and suggest their role in the partitioning of nutrients. There was no significant variation in the levels of T4 during early and late lactation but the levels decreased significantly (P < 0.005) in mid lactation stage. The mean and range of levels of thyroxine during different stages of lactation agreed with the study of Galdhar et al. (2021) in buffalo, Cincovic et al. (2015) [7] in cows, and Fiore et al. (2017) [9] in postpartum dairy cows. Also, Hassan et al., (1984) in buffaloes and Pichaicharnarong et al. (1982) [20] observed that, as lactation stage advances reduction in plasma T4 in Swamp buffalo. The lower levels of T4 during mid stage of lactation may be because of peak of milk production. It is supported by the observations of Vanjonack and Johnson (1976) [30] that, the thyroid hormones are excreted by the mammary gland and with high milk production lose greater amounts of these hormones through the udder thus resulting in lowered plasma concentration. Also, may be due to considerable mammary drain of iodine during lactation (Premachandra and Turner, 1961; Ayoub, 1966) [22,4] . Nixon et al. (1988) [19] recorded levels of fT4 during three stages of lactation in four seasons in serum of Holstein cows which was higher than the findings of present study. Only the free fractions of serum thyroid hormones are available for utilization by peripheral tissues (Bantle et al., 1980) [5] and only the free fractions control the rates of secretion of thyroid releasing hormone (TRH) and thyroid-stimulating hormone (Faglia et al., 1979) [11] . In our study the levels of fT4 also fall significantly (P < 0.005) during the mid stage of the lactation.

Lipid Profile

As regards to the lipid profile, the Mean ± SE serum levels of triglycerides, total cholesterol, HDL-C, LDL-C and VLDL-C during different stages of lactation in Murrah buffaloes is presented in Table 2. All the lipid profile parameters viz. Triglycerides, Total Cholesterol, HDL-c, LDL-c and VLDL-c have shown significant increased (P < 0.005) during mid-lactation and then levels fall during late lactation. The levels of total cholesterol and triglycerides increased significantly during the mid and late stage of lactation. Similar trend was observed in study of Tripathi et al. (2010) [28] , Hagawane et al. (2009) [14] , Polat et al. (2002) [21] in lactating and Grasso et al. (2004) [12] in water buffalo. The higher level of cholesterol and triglycerides with advancement of lactation may be the physiological adjustment to meet the lactation requirement (Lone et al. 2003) [18] for lactogenesis. The lipoprotein profile viz. HDLc, LDL-c and VLDL-c has shown similar trend of that of triglyceride and total cholesterol. There levels significantly increased during mid lactation and remained higher levels during late lactation than that of early lactation.

Correlation of thyroid hormones and lipid profile

The triiodothyronine hormone in serum was positively correlated with triglyceride (r=0.18), VLDL cholesterol (r= 0.17 and negatively with total cholesterol (r= -0.069), HDL cholesterol (r= -0.039), LDL cholesterol (r= -0.1). However, all the relation were statistically nonsignificant. The thyroxine and free thyroxine hormone in serum was negatively correlated with total cholesterol (r= -0.025), triglyceride (r= -0.17), LDL cholesterol (r= -0.064), VLDL cholesterol (r= -0.16) while positively with HDLcholesterol. However, all the relation were statistically nonsignificant.

Conclusion

There was significant increase in the levels of total triiodothyronine (TT3) during late stage of lactation. However, the levels remained almost same during the early and mid-lactation. The levels of total thyroxine (TT4) remained same during early and late lactation but the values decreased significantly in mid lactation stage. Free thyroxine (fT4) has followed the similar trend of TT4. There are no reports of the levels of serum fT4, in lactation buffaloes and it is reported first time in the present study. The triiodothyronine hormone in serum was positively correlated with triglyceride, VLDL cholesterol and negatively with total cholesterol, HDL cholesterol, LDL cholesterol however, all the relation were statistically nonsignificant. Barring HDL-cholesterol thyroxine and free thyroxine hormone in serum was negatively correlated with total cholesterol, triglyceride, LDL cholesterol, VLDL cholesterol. However, all the relation were statistically nonsignificant.

Acknowledgement

AcknowledgementAuthors are thankful to Manager, Kokani Dairy Farm, Wadalagaon, Nashik, Maharashtra, India, for providing facility for collection of blood samples of lactating buffaloes. Also, we are thankful to Board of Radioisotope Technology (BRIT), Bhabha Atomic Research Centre, Mumbai. For providing thyroid hormones RIA kits and laboratory facility for analysis. The authors are also grateful to the Associate Dean, Mumbai Veterinary College, Mumbai for providing facilities & fundings.

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