The objective of this study was to determine the effects of different weaning ages on the performance and behavior of dairy calves reared in paired houses. For this purpose, the present study using forty-eight female Holstein calves (42 ± 0.5 kg) in the form of a completely randomized design with treatments: 1) weaning age 9 weeks or 63 days (control), 2) weaning age 11 weekly or 77 days and 3) weaning age was 13 weeks or 91 days. The method of milking for all 3 treatments was that one week before milking, 1 liter of milk was reduced daily until the end of the seventh day, the calf stopped milking completely. The milk feeding pattern was increasing-decreasing and from 3 to 14 days old 5 liters daily and from 14 to one week before weaning 7 liters of pasteurized raw milk with a temperature of 38.5 degrees in two times (5 in the morning and 3 in the evening) was available to the calves. Calves had free access to drinking water and starter pellet feed with 7% straw forage mixed from the beginning to the last day of the experiment, and daily dry matter intake and health scores were calculated and recorded. Body weight was measured by a digital scale and skeletal growth with a special meter at the beginning (30 days old), weaning time (according to the weaning age of the treatment) and at the end of the experiment. In order to eva‎luate stress behavior during milking, 10 days after milking, head and vocalization behavior was visually recorded during two hours of milk feeding in the morning and evening, and the number of behaviors per minute was recorded (2 hours of morning and evening feeding each day). Finally, all the collected data were analyzed by SAS statistical analysis software with appropriate procedures. Based on the obtained results, the BW of the calves at the age of 105 days (P<0.01) and the whole period (P<0.03) was affected by the experimental treatments, so that the experimental treatment 3 had the highest BW. The effect of time on BW was significant (P<0.01), but it was not influenced by the interaction of treatment and time. The Average Daily Gain on the 105th day and the entire period was affected by the effect of the experimental treatments, so that treatments 2 and 3, which were weaned on the 77th and 91st days, respectively, had the highest ADG on the 105th day and the entire period (P < 0.03). ADG was affected by time and interaction between time and treatment (P<0.01). Treatment 1 had the highest Starter Intake at 60, 70 and 80 days. Also, the calves of treatment 2 along with treatment 1 had the highest SI at 80 days old. Treatment 3 on days 90 and 100 along with treatment 2 had the highest amount of SI (P<0.05). The analysis of the measured data showed that treatment 1 had the lowest intake and treatment 3 had the highest intake of total dry matter (P<0.05) and the effect of time and the interaction of time with treatment had an effect on the TDMI (P<0.01). Vocal production in the morning, evening and whole for treatment 1 had the highest amount and for treatment 3 it had the lowest amount (P<0.01). Also, treatment 1 at the age of 105 days compared to the other two treatments had the lowest Wither Height (P<0.05). In the parameters of Hip Height, Hip Width and Pin Width, treatment 1 had the lowest value compared to the other two treatments on days 105, 300 and the whole period, and this significant difference can be seen in the whole experimental period as well (P<0.05). 0P<). Treatment 3 at 105 days had the highest Pin Height (P<0.01). Time had a significant effect on the Fecal Score so that the stool score decreased with the increase of time (P<0.01) and finally the calves of treatment 1 had the highest Respiratory Score (P<0.05). Based on these results, it can be said that increasing the age of weaning calves in paired houses is very beneficial for them.

غلامرضا قرباني خراجي , فرزاد هاشمزاده

حسن رفيعي يارندي

مهدي قريشي , حسن كريم مجني