The effect of different levels of concentrate supplement on wight gain, growth performance and blood parameters of weaned Ghezel lambs under grazing conditions

The lamb rearing system in the pasture can provide a better growth rate when the diet is accompanied by concentrate supplements. Supplementary feeding can compensate the limitation of natural feed by replacing part of pasture fodder with concentrate especially in low rainfall seasons. However, availability and high costs of concentrate diets have caused their limited use by many small farmers. The purpose of this research was to investigate the effect of different levels of concentrate supplement on weight gain, growth performance, blood parameters and grazing behavior of weaned Ghezel lambs under grazing conditions.

This experiment was conducted by using 32 male Ghezel lamb (average weight = 29±2.7) in a completely randomized design with 4 treatments and 8 replications. The experimental treatments were 1) a control treatment consisting of free access to pasture grazing, 2) free access to pasture grazing with 150 g of concentrate supplement per day per head, 3) free access to pasture grazing with 250 g of concentrate supplement per day per head and 4) free access to pasture grazing with 350 g of concentrate supplement per day per head. In order to determine the daily weight gain, the lambs were weighed at the beginning and end of the period in the morning before the start of grazing. The grazing behavior of lambs in the pasture were recorded by direct observation every 10 minutes during access to the pasture. At the end of the experiment, blood samples were taken at noon from jagular vein and the samples were evaluated to determine glucose, urea, total protein, albumin, cholesterol and triglyceride. Feces samples were collected using special fabric bags that were tied to the animal's tail.

The results of the present study showed that concentrate supplement improved the daily weight gain, but no significant difference was observed between different levels of feeding with concentrate supplement. Among growth traits, body length and body height were significantly affected by experimental treatments. The amount of time lambs spent grazing in the pasture was not affected by feeding with different levels of concentrate supplementation. Supplemental feeding of concentrate increased the digestibility of organic matter. Changes in blood glucose of lambs during the experimental period were significant between the control group and the groups receiving the supplemental concentrate. Net profit per lamb also increased due to feeding with concentrate supplement.

The results of the present study showed that feeding Ghezel lambs with concentrate supplement in pasture conditions caused a significant increase in growth performance and it will be economical due to more net profit. Based on the obtained results, it is recommended to feed at least 150 grams to 350 grams of concentrate supplement daily when rearing Ghezel lambs in pasture grazing conditions