Effects of different amounts of zinc on performance and some blood and ruminal parameters in Holstein suckling calves

Zinc is involved in the regulation of many metabolic processes and zinc deficiency resulting in low appetite, consequently decreased feed intake. Also, zinc deficiency decreases the growth and weight gain of the animal. It has been reported that the daily requirement of zinc for suckling calves is 33 mg/kg DM. While, the amount of this element in cow’s milk is 3-5 mg/kg. Therefore, zinc supplementation may improve the performance of suckling calves. So, this study was performed to investigate the effect of different levels of zinc on performance and some blood and ruminal parameters in Holstein suckling calves.

This study was conducted using 18 newborn Holstein calves from 4 days of age to weaning (70 days) in a completely randomized design. Experimental treatments were treatment 1 (control, basal diet), treatment 2 (basal diet plus 30 mg / kg DM as zinc sulfate) and treatment 3 (basal diet plus 60 mg/ kg DM as zinc sulfate). The calves were housed in individual pens with cement floors and were offered with whole milk (approximately at 10% of weight) in two equal meals daily at 8:00 and 19:00 during the experimental period. They had free access to the pelleted starter and fresh-water. After 15 days, chopped wheat straw (5 %) and alfalfa (5%) were added to their starter. Daily feed and ort were measured to estimate daily dry matter intake and animals were weighed fortnightly to obtain average daily gain. Blood samples were taken from the jugular vein at the end of the trial (day 70) before the morning feeding for measurement of blood mineral (Zn, Ca, P, Fe, and Cu) status and the hematological parameters (hemoglobin concentration, red blood cell count, white blood cell count and hematocrit %). Also, the ruminal fluid samples were collected on day 70, 3 h after the morning feeding, by stomach tube and a vacuum pump for determination of ruminal volatile fatty acids concentrations.

The results showed that the use of different levels of zinc had no significant effect on feed conversion ratio in weaning calves. However, average daily gain in treatments 2 and 3 (724.29 and 765.00 g / day, respectively) and dry matter intake in treatment 3 (1692.41 g / day), were significantly (P<0.05) higher than the control treatment (628.29 and 1532.83 g / day, respectively). Supplementation of zinc significantly increased (P<0.05) serum zinc concentration in treatments 2 and 3 (1.184 and 1.168 mg / l, respectively). However, no significant differences were observed among treatments for the concentration of other minerals in blood serum (calcium, phosphorus, iron and copper). Also, supplementation of zinc had no significant effect on blood hematological parameters. Ruminal total volatile fatty acids, acetic acid, propionic acid, and butyric acid concentrations, and acetic acid: propionic acid ratio were not affected by zinc supplementation.

Generally, the results showed that a basal diet containing 29.68 mg Zn/kg DM can supply the zinc requirement of Holstein suckling calves. But, zinc supplementation improved the performance of these animals.