Effect of organic zinc, vitamin A and vitamin E supplementation on morphometric changes, NEFA and BHBA during the transition period of crossbred cows

Introduction

The "transition period," the period from three weeks before to three weeks after calving, is extremely stressful for dairy cows or any other livestock species. The period is characterised by negative energy balance, fat mobilisation, and elevation of circulating non-esterified fatty acids and ketone bodies (Seifi, et al. 2007) [11] . The degree of changes in body reserves of a cow as assessed by periodical body condition score (BCS) and body weight changes during this period are the effective management tools. Besides BCS and body weight, NEFA and BHBA concentrations in the serum also act as internal indicators (metabolic) during transition period. Oxidative stress leads to peroxidative damage of lipids and other macromolecules with consequent alteration of cell membranes and other cellular components, and can also lead to the modification of important physiological and metabolic functions. There is pressing need to optimize the feeding strategies and managemental aspects during this period. There was lack of reports on the effect of organic compounds in roughage-based diets and only a limited number of studies have investigated the importance of organic zinc supplementation in transition cows. Most of the fat soluble antioxidant vitamins such as retinol, α-tocoferol and β-carotene decrease at the time of parturition are reported to be associated with several health problems (Weiss, 1990) [12] . Besides zinc as the important trace mineral supplementation, other micronutrients especially fat-soluble vitamins.

Materials and Methods

The protocols adopted in this experimental study were approved by the Institutional Animal Ethics Committee (IAEC), College of Veterinary Science, Hyderabad and is in accordance with the guidelines for the care and use of Laboratory animals with IAEC vide approval No.22/25/ C.V.Sc, Hyd. IAEC. Forty advanced pregnant multiparous crossbred cows (about one-month pre-partum) with an average body weight of 530±20 kg were selected from farmers of nearby villages of Korutla, Jagityal district located in central Telangana and the town lies at 18.8 o N latitude and 78.93 o E longitude and rises to an average height of 258 m above the sea level. The animals were allotted randomly into 4 groups of 10 animals each. All the cows were housed in well-ventilated hygienic stalls and stall fed throughout the experimental period. The animals were treated for both ecto and endo parasites well before the initiation of the study. The proximate analysis of feeds was performed as per the procedures described by AOAC (2019) [2] .

Mineral estimation:

The di-acid digestion method is the most frequently used procedure for feed minerals like Cu, Zn, Fe, Mn, Co, Mg estimations by atomic absorption spectrophotometer using Air/Acetylene gas. 0.5g of sample was taken in a conical flask and 10 ml of nitric acid (concentrated) was added and kept overnight. The next day, 10 ml nitric acid was added again to the same conical flask along with and 2 to 3ml of perchloric acid. The sample was digested by using hot plate until it developed the colour less solution or 1 to 2 ml of solution was remained in conical flask. The digested sample was cooled and added 10 ml of 2N HCl. The digested solution was filtered by using 42 no. filter paper and volume was made to 50 ml by adding double distilled water. The mineral concentration was recorded by using atomic absorption spectrophotometer (AAS). The Tri-acid digestion method is the mostly used procedure for serum minerals like Cu, Zn, Fe, Mn, Co, Mg estimations by AAS. Reagents used are of tri-acid mixture: 9:3:1 Nitric acid. Perchloric acid, Sulfuric acid. 1ml serum was taken in 100 ml conical flask and 10ml of tri-acid mixture was added. It developed pale yellow color. The sample was digested by using hot plate at 60 o c until colorless or 1 ml sample remained in the conical flask. Cooled the sample and made volume to 25 ml by using double distilled water. Read the sample by using AAS for minerals.

Experimental Rations and Feeding Regimen

Conventional practice of feeding concentrates and roughages separately was followed throughout the experiment. Chopped green super Napier (Pennisetum purpureum) (around 25 kg) and paddy straw (around 5 kg) were used as sources of roughage for feeding of experimental animals in all the groups. Concentrate feed ingredients were maize (average 3.5 kg), wheat bran (average 1.75 kg), cotton seed cake (average 1kg), moong dal chunni (1.75kg), mineral mixture and salt. The cows had free access to fresh and wholesome clean drinking water all the time.

Four different rations were fed to four treatment groups during the dry period as mentioned below *All the forms of Zn were supplemented as per NRC (2001) [8] nutrient requirements for dairy cattle. During the lactation period zinc requirement was 1261 mg/day/animal in high yielders and during the late gestation additional zinc requirement of 274 mg/day/animal was supplemented. Zinc supplementation was done through oral route by feeding the animals individually by preparing the mineral mixture. This mineral mixture was prepared with pre mixer at feed plant, Department of Animal Nutrition, College of Veterinary Science, Rajendranagar, Hyderabad. The mineral mixture was prepared separately for four treatments by adding different sources of zinc and as per zinc bioavailability.

Addition of different zinc sources to the mineral mixture

All the cows were fed basal diet (roughages and concentrates) in accordance with the ICAR (2013) [6] nutrient requirements for the experimental period of 150 days i.e., 1-month before calving to 4-months after calving. Fifty grams of mineral mixture per day per animal was fed individually. Zinc was supplemented to the mineral mixture prepared, as per NRC (2001) [8]

Body Condition Scoring (BCS)

The BCS of the animals was recorded five times during experiment period, first at start of the experiment (pregnant stage of the animal), second at the time of calving and thereafter at monthly intervals. The score for individual animal was given with visual appraisal based on observing five important points as short ribs, backbone, hook and pin bones, thurl (area over pelvis) and tail head as per Homestead and miniature cattle directory (Ferguson et al., 1994) [5] . [10] on periparturient dairy animals, suggesting a transient shift in mineral metabolism during parturition. The higher serum zinc concentrations observed in cows supplemented with organic zinc sources, particularly zinc methionine and zinc glycinate, indicate superior bioavailability compared to inorganic zinc, thereby enhancing systemic zinc status. Body weight changes across the transition period followed a typical pattern, with maximum values before calving and a decline during early lactation. This reduction is primarily associated with negative energy balance (NEB), reduced dry matter intake, and increased energy demands for milk production. However, cows supplemented with organic zinc sources exhibited relatively higher body weights, suggesting improved nutrient utilization and metabolic efficiency. These findings are consistent with earlier reports indicating that organic trace minerals support better growth performance and reduce body weight loss during early lactation Antari et al., 2021) [1] . Body condition score (BCS) declined during the postpartum period, reflecting mobilization of body reserves to meet energy demands. The lack of significant differences in BCS among treatment groups suggests that while zinc supplementation improves metabolic parameters, its direct influence on body reserve mobilization may be limited. Nevertheless, the observed trend aligns with previous studies Chandra et al. (2013) [4] indicating that BCS changes during transition are largely governed by energy balance rather than mineral supplementation alone. Non-esterified fatty acids (NEFA), an important indicator of lipid mobilization, were significantly elevated around calving, confirming intensified fat mobilization during this period. The reduced NEFA concentrations in zinc-supplemented groups, especially with zinc methionine, indicate improved energy balance and reduced lipolysis. This suggests that organic zinc supplementation may enhance metabolic adaptation by improving feed intake and insulin sensitivity. These are in accordance with Chandra et al. (2013) [4] . Elevated NEFA levels have been associated with increased risk of metabolic disorders; hence, their reduction in supplemented groups indicates better health status and metabolic stability. Similarly, beta-hydroxybutyric acid (BHBA) concentrations increased after calving, reflecting enhanced ketogenesis due to NEB. However, lower BHBA levels in zincsupplemented groups suggest improved hepatic metabolism and reduced ketone body formation. This may be linked to improved insulin activity, which promotes lipogenesis and inhibits excessive fat mobilization (Barletta et al., 2017) [3] . The observed relationship between NEFA and BHBA further supports the role of energy balance in regulating metabolic health during the transition period. The decrease in serum vitamin A Oliveira et al. (2015) [9] and E Maurya et al. (2014) [7] concentrations at calving can be explained by their transfer into colostrum, which is essential for neonatal immunity. Supplementation of these vitamins resulted in higher circulating levels, indicating effective dietary absorption and utilization. Their antioxidant properties likely contributed to reduced oxidative stress and improved immune function, thereby supporting overall metabolic health during the transition period.The combined supplementation of zinc methionine with vitamins A and E showed synergistic effects in improving body weight, reducing NEFA and BHBA concentrations, and enhancing metabolic stability. These findings suggest that integration of organic trace minerals with antioxidant vitamins can effectively mitigate the adverse effects of NEB and oxidative stress during the transition period. Overall, the study highlights the importance of mineral form and vitamin supplementation in modulating metabolic responses in transition dairy cows. The improved performance observed with organic zinc sources, particularly zinc methionine, underscores their potential role in enhancing productivity and health during this critical physiological phase.

References

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