Seasonal Dynamics of Serum Mineral Profiles in Indigenous Nagavali Sheep

Introduction

Sheep contribute significantly to India's agriculture, rural employment, and GDP, with Andhra Pradesh ranking second nationally at 17.6 million sheep (20th Livestock Census). The resilient Nagavali breed, reared primarily for meat, constitutes roughly 4.5% of the state's population across the north coastal districts. However, climate change poses a severe threat to livestock productivity. Rising Temperature-humidity Index (THI) levels which peak during summer can adversely effect the health of the animal by increasing the physiological parameters of rectal temperature (RT), respiration rate (RR), and pulse rate (PR) in Munjal sheep reared in a subtropical climate (Kumar S et al., 2025) [2] . Consequently, prolonged heat stress elevates disease incidence and significantly impairs growth, meat production, and reproductive performance (Habeeb, et al., 2018) [4] , (Al-Ghareebawi et al., 2026) [3] . Serum biochemical tests are widely utilized to diagnose diseases and evaluate nutritional status in animals. This study aims to establish a baseline mineral profile for Nagavali sheep and evaluate seasonal variations in rams and ewes. Ultimately, these reference parameters will serve to assess the long-term impact of climate change on the mineral status of this breed.

Materials and Methods

The present investigation was carried out on Nagavali sheep of Andhra Pradesh maintained at Livestock Research Station, College of Veterinary Science, Garividi, S.V.V.U, Vizianagaram, Andhra Pradesh. Blood collection was done in the months of May, August and December for the seasons Summer, Monsoon and Winter respectively. Experimental Design: A total of 100 apparently healthy Nagavali sheep, aged one year and older and exhibiting similar physiological status, were randomly selected for the study.

Statistical Analysis

Results are expressed as mean ± Standard error (SE). Data were analyzed using a Student's t-test in Microsoft Excel 2007 following the statistical methods described by Snedecor and Cochran (1989) [1] .

Results and Discussion

The average Temperature-Humidity Index (THI)

The mean values of the Temperature-Humidity Index (THI) recorded during the experimental period are presented in [7] , Finocchiaro et al., (2005) [8] noted a distinct impact of high THI values on dairy sheep. One effective approach for studying animal responses to heat stress is evaluating the correlation between bioclimatic indicators such as the THI and production and reproduction traits (Serradilla et al., 2018). According to Srikandakumar et al., (2003) [10] , a THI value of 72 or below represents a lack of heat stress, 73 to 77 indicates mild heat stress, 78 to 89 denotes moderate heat stress, and values above 90 signify severe heat stress.

Our findings indicate that while the summer season experienced moderate heat stress, the monsoon and winter seasons remained stress-free. This observation is consistent with Silanikove (2000) [11] , who confirmed that a THI score of 70 or less constitutes a comfortable thermal zone for animals. Furthermore, Rathwa et al., (2017) [6] concluded that the THI is a sensitive indicator in indigenous sheep. [12] who studied thermoregulatory and physiological responses of Najdi sheep exposed to environmental heat load prevailing in Saudi Arabia and reported that calcium levels are reduced under heat stress conditions. Similar recordings were observed by Ramana et al., (2013) [13] who examined the productivity and physiological responses of sheep exposed to heat stress and showed lower levels of calcium in heat stress group. The current experiment's results are consistent with those of Nazifi et al., (2003) [14] in Iranian sheep and Srikandakumar et al., (2003) [10] in sheep. A decrease in blood calcium concentration in summer might be related to a reduction in food intake, which has been recorded under heat stress conditions (Al Haidary et al., 2012) [12] . Low calcium levels may be caused by hypoproteinemia resulting in reduced calcium transporters which is due to decreased feed intake linked with heat stress (Srikandakumar et al., 2003).

Phosphorus

In the present study, mean values of Phosphorus in ewes, and rams of sheep could not show significant difference but elevated, winter than summer. The results of the present study are in accordance with Al-Eissa et al., (2012) [15] who aimed to investigate the effects of seasonal variations on the composition of blood in Nubian Ibex goats and reported non-significant difference in phosphorus level in summer and winter. Although there was no significant difference, lower levels of phosphorus were noticed in summer in rams.

The stidies were incontrast to findings were reported by Nazifi et al., (2003) [14] in Iranian sheep and by Ramana et al., (2013) [13] who studied the productivity and physiological responses of sheep exposed to heat stress. The lower level of inorganic phosphorous recorded during the summer season may be attributed to a decrease in feed intake, whereas the greater level of inorganic phosphorous found during the winter season may be related to a higher basal metabolic rate, which leads to increased feed consumption (Vasava, 2017) [16] . Additionally, less availability of green roughage in the summer compared to the winter season may result in decreased serum phosphorous levels in sheep.

Mangnisium

Magnesium is indispensable for numerous enzymatic activities, is important for maintaining the electrolytic balance and is of fundamental importance for normal neuromuscular function as well as for the transport of calcium and potassium. The mean ± SE value of Serum Magnesium was higher during hot-humid in comparison to winter season but the effect was non-significant (p>0.05).

The elevated Serum Magnesium levels in present study during hot-humid season were similar to the results of Gottam G.S. (2020) [17] in Pugal Sheep. Stress related changes were observed by Healy and Falk (1974) [18] in the values of magnesium, whereas, stress effect was not observed on the mean value of serum magnesium in Merino sheep by Parker et al. (2003). These results were contrary to the findings of Nazifi et al. (2003) Serum calcium concentrations demonstrated significant seasonal fluctuations, with markedly higher levels recorded in rams, ewes, and the total herd during winter compared to summer. This increase is primarily attributed to enhanced dry matter intake (DMI) during cooler months and higher dietary calcium concentrations in seasonal vegetation. Conversely, serum phosphorus and magnesium concentrations did not exhibit statistically significant variations across the rainy, winter, and summer seasons. However, both minerals showed a consistent numerical trend toward higher serum levels during winter, aligning with increased pasture biomass availability and superior forage quality that enhance total daily mineral ingestion and absorption.

Author's Contribution Sai Srinivas and Gangu Naidu performed experiments and analysis, K Aswani kumar, A Sampath Ganesh and T Srinivasa rao conceptualized and organized the research.

Declaration of Competing Interest:

The authors declare no competing or financial interests

Acknowledgement

Acknowledgments:The authors thank Department of Veterinary Physiology and Biochemistry, College of Veterinary Science, Garividi, for providing the infrastructure to conduct the study.

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