Effect of different forms of chromium on feed intake, rumen parameters, and blood metabolites of Afshari ewes during transition period and their lambs under the influence of heat stress

During the time around parturition, animals make many metabolic adjustments to support the transition from pregnancy to lactation. Before giving birth, animals are subjected to a lot of metabolic effects, to prepare the physiological conditions of the body in the time after giving birth and during lactation. In addition, dairy cattle produce milk more than their ability to consume energy, as a result, they are in a negative energy balance at the beginning of lactation, which may reduce the longevity of the cattle in the herd and increase the rate of elimination of dairy cattle. Heat stress in late pregnancy is aggravated by energy restriction. In such conditions, the use of management and nutritional methods will reduce the problems during the transfer period and heat stress. One of the ways to optimize the productive and reproductive conditions of livestock, through improving the metabolism of nutrients and eliminating or reducing stress conditions, is to use chromium as a metabolic improver. According to scientific sources, the chromium requirement for sheep is three to five mg per day, and for dairy cows is 15 to 50 mg per day. Inorganic chromium has a bioavailability of about 0.5%. Organic chromium has more than 25% intestinal absorption, and therefore, consumption of inorganic chromium is not recommended due to its low bioavailability and toxic effects. Among the sources of organic chromium, chromium-methionine has been recognized by important global food and drug organizations as a compound with high bioavailability, impressive metabolic responses, and no toxicity complications. This experiment was conducted to investigate the effect of using different forms of chromium around calving on feed consumption, nutrient digestibility, nutritional behavior of Afshari ewes, and the performance of their lambs under the influence of heat stress.
Forty pregnant Afshari ewes were assigned to four experimental treatments with 10 replicates from 42±5 days before the expected birth in a completely randomized design. Experimental treatments include 1) a basic diet without chromium supplementation (control), 2) a basic diet containing three mg of chromium in mineral form per kg of dry matter, 3) a basic diet containing three mg of chromium in the form of chromium-methionine per kg of dry matter, and 4) a basic diet contained three mg of chromium in the form of chromium nanoparticles per kilogram of dry matter. The length of the test period was 84 days. Weighing of ewes was done at the beginning, at the time of calving, and the end of the period. The rest of the feed is weighed every day and the daily feed consumption was calculated by deducting from the provided feed. Sampling of the rumen fluid was done on the 14th day after birth. The rumen fluid was taken before feeding in the morning (zero hour), and at three and six hours after feeding by esophageal tube, then the pH amount of rumen contents was measured and recorded immediately after extraction by a mobile digital pH meter (Metrohm laboratory pH meter-691) which was calibrated at the same place. To measure rumen liquid ammonia nitrogen, samples were used three hours after morning feeding. To measure the concentration of volatile fatty acids, five mL of rumen fluid samples were prepared and 1 mL of metaphosphoric acid 25% was added to them and kept at -20ºC until the experiment. On the 10th day after birth, blood samples were taken from the jugular vein of ewes and lambs three hours after morning feeding. To measure blood metabolites including glucose, insulin, cholesterol, triglyceride, urea, creatinine, total protein, albumin, and globulin, Pars Azmoun chemical kits and auto-analyzer (Spain BT 3500) were used.
The results showed that, from the third to the sixth weeks after birth, dry matter consumption in ewes receiving chromium-methionine and chromium nanoparticles had an upward trend compared to the other two treatments (P<0.05). The addition of chromium to the diet of ewes had no significant effect on rumen pH, volatile fatty acids, and rumen ammonia nitrogen concentration. The addition of chromium supplement to the diet of ewes caused a significant decrease in the rumen protozoa population compared to the control group (P<0.05). Adding different forms of chromium to the diet of sheep caused a decrease in glucose concentration, and an increase in chromium, insulin, total protein, albumin, and serum globulin compared to the control group (P<0.05). No significant difference was observed between experimental treatments on blood cholesterol, triglyceride, urea, and creatinine concentrations. Also, different forms of chromium did not have a significant effect on the blood parameters of the born lambs.
In general, the use of chromium, especially in the form of chromium-methionine and chromium nanoparticles, is recommended during the transfer phase of sheep under the influence of heat stress.