محمد شمس الهی

The aim of this researach was to investigate the effect of starter fatty acid (FA; n-3 or n-6) type and crude protein (CP; 18 or 21%) on growth performance, skeletal growth indices, plasma metabolites, urinary purine derivatives and microbial protein synthesis of growing calves. A total of 40 Holstein calves (20 males and 20 females; average BW = 39 kg) were randomly divided into 4 groups (n = 12 animals/group) and assigned to experimental diets in a complete randomized block design to a 2 × 2 factorial arrangement. Experimental diets were as follow: (1) starter diet with calcium salt of n-6 FA and 18% CP, (2) starter diet with calcium salt of n-6 FA and 21% CP, (3) starter diet with calcium salt of n-3 FA and 18% CP and (4) starter diet with calcium salt of n-3 FA and 21% CP. Milk feeding value was similarly based on a constant protocol across experimental treatments and calves had ad libitum access to water and starter diets throughout the study. All calves were weaned on d 63 of age and remained in the study until d 83 of age. Results showed that starter diet dry matter intake (DMI), milk DMI, total DMI, daily weight gain, body weight (BW) and feed efficiency (FE) did not influence by the interaction between dietary FA type and CP level (P>0.05). Starter DMI, milk DMI and total DMI were not affected by starter FA type or CP level (P>0.05). BW at weaning and at the end of study and pre-weaning and entire period FE was greater in calves fed starter diet containing n-3 FA compared to those fed n-6 FA (P<0.05). Skeletal growth indices including heart girth and hip height at weaning and at the end of study and withers height at weaning was greater in calves starter diet containing n-3 FA and 21% CP compared to other groups (P<0.05). Calves fed starter diet with n-3 FA supplement had higher withers height at weaning compared to those fed n-6 FA (P<0.05). Plasma glucose and insulin concentrations in pre-weaning period were greater in calves fed starter diet containing n-3 FA and 21% CP compared to other groups (P<0.05). The greatest plasma urea nitrogen (PUN) concentration was observed in calves fed starter diet containing n-6 FA and 21% CP compared to other groups (P<0.05). Experimental diets had no effect on urinary excretion of allantoin (AL), uric acid (UA) and total purine derivatives (PD) and microbial protein synthesis (MPS; P<0.05). Increasing starter diet CP level from 18 to 21% increased urinary excretion of AL and total PD and MPS (P<0.05). In summary, these results showed that feeding starter diet with n-3 FA and 21% CP improved growth performance and skeletal growth indices of Holstein calves. Keywords: Growing calf, n-3 fatty acid, n-6 fatty acid, crude protein, growth performance.