A total of 18 Friesian calves having one month of age was used in 3 dietary

treatment groups to study the effect of feeding protected protein or protected fat diets,

from 1 up to B months of age, on histological characteristics of the rumen of Friesian

calves. The 1 group (control) was fed untreated concentrate feed mixture (CFM), the

was fed CFM, 5% of it was replaced by protected fat (PF) and the 3 was fed CFM

treated with 1% formaldehyde on the basìs of its total CP (PP). All groups were fed

plus berseem hay beside the CFM. Thickness of all ruminai wall tunicae, mucosal

lamìnae and stratum (st.) corneum was estimated. Also, density and dimensions of

ruminai papillae were measured to calculate papillary surface area. Results indicated

that tunica mucosa was thicker (Pc0.05) in PP than in PF and control groups.

Thickness of lamina epithelialis mucosa (LEM) did not differ significantly among

treatment groups. However, it was thicker (P'0.O5) in PF than ¡n PP group (0.30 vs.

0.27 mm). As overall mean, st. corneum tended to be thicker ¡n control (44.3 pm) than

in PF (42.9 pm) and PP (43.2 sim) group. Lamina propria was thicker (P<005) in PP

than ¡n PF and control groups (1.20 vs. 0.96 and 1.02 mm). Subrriucosa was thicker

(P<0.05) in PF and PP groups than in control group. Total thickness of tunica

musculosa was higher (P'cO.05) ¡n PP and PP than ¡n control group. Generaly,

thickness of all previous traits varied significantly between different ruminai sacs as

affected significantly by dietary treatments. Ventral ruminai sac showed significantly

the highest thickness in calves of all groups. Papillary length was affected (P'cO.05) by

dietary treatment, but each of PF or PP group did not differ significantly from that of

the control one. Papillary length ¡n was shorter (P<0.05) in PP than in PP group.

Treatment group did not affect papillary width. Density of papiHae was lower (PcO.05)

in PF and PP groups than in control one. Surface area of each papilla was lower

(Pc005) in PF than in PP and control groups, which did not differ significantly.

Papillary surface area per cm2 was lower (P
showed in9nificantly [ower values compared with the control. Inter-papillary surface

area per cm showed negative relationship with papillary density and was significantly

affected by dietary treatments, ruminai sac and their interaction. Total surface area

per cm of different ruminai sacs mainly affected by surface area of papillae within

each cm2. So, total surface area/cm2 showed the same trend of surface area of

papillaelcm2 as affected by dietary treatment and ruminai sacs. On the basis on the

foregoing results, it could be conclude from the nutritional point of view that feeding

calves on the tested diets esuIted had beneftcìat effects on histological and

histometric characteristics of rumen of Friesiari calves during suckling period and

arly post-weaning ages.