Under this study, effect of stair-step nutritional regimen compared to the standard NRC recommended energy levels on growth rate, nutrient utilization, some selected blood metabolites, pubertal age, conception rate and economic analysis in ili- Ravi buffalo heifers were measured. Study lasted for 18 months during the years 2008- 20 I O. Twenty-two heifers, 6-8 month old, 98.57±5.07 kg average ody weight were divided into two equal groups and randomly assigned either control or stair-step nutritional regimen (SSNR) diets. The SSNR was designed in three phase program each having 6 months duration i.e., postweaning (7 to 13 month age), repubertal (13 to 19 month age) and pubertal/breeding (19 to 25 month age). In each phase, the treatment group during step 1, was fed on low energy diet (80% ME of NRC) for 4 months followed by high energy diet (120% ME ofNRC) for 2 months in step 2. The heifers in ontrol group were fed according to NRC (200 I) requirements of Holstein Friesian heifers continuously for 6 months. For both the groups individual feeding was carried out. Daily feed intake and fortnightly fasting weights were recorded. Nutrients digestibility and N balance trials were conducted during last week of each step during each phase. Blood samples were collected at the end of each low or high energy diets for blood metabolites analysis. Oestrus detection was done with the help of a teaser bull at age of 15-16 months. Transrectal ultrasonography was done to assess uterus and ovarian structures development. Measured blood serum progesterone concentration collected every 10 days interval at 09.00-10.00 hours during 18-20 months age by ELISA using commercial kit. The age and live weight at onset of puberty was recorded when heifer tood to be mounted by the bull first time in her life. The heifers detected in oestrus were bred by natural mating at approximately 12-15 hours of the onset of oestrus activity. Heifers not returning to oestrus were examined for pregnancy diagnosis through rectal alpation of uterus at 70-90 days post breeding. Data of feed onsumption during postweaning, prepubertal and pubertallbreeding phases were used to calculate the feed cost used per kg gain between the SSNR and control heifers.

During postweaning phase, heifers fed SSNR low energy diet (2.03 Meal/kg) ained significantly (PO.OS) between the heifers of two groups. Feed conversion ratio (FCR) was poorer (P
During prepubertal phase, there was no difference (P>O.OS) in weight gain between the heifers fed SSNR low energy diet (1.89 Meal/kg) and control diet (2.3S Meal/kg). But on high energy diet (2.80 Meal/kg) weight gain was higher (PO.OS) between the heifers of two groups. On low energy diet there was no difference (P>O.OS) in FCR between the two groups. But on high energy diet FCR was significantly (PO.OS). During pubertal/breeding phase, similar trend of weight gain, DMI and FCR was found in SSNR versus control group as reported in prepubertal phase.

Intake of DM, organic matter (OM) and crude protein (CP) as percent body weight were statistically non-significant (P>O.OS) differet between the SSNR versus ontrol groups during all phases. Metabolizable energy (ME) consumption was significantly PO.OS).

In all phases, apparent DM and OM digestibility did not differ (P>0.05) between the heifers fed SSNR (either low or high energy) and control diets. Neutral detergent fibre (NDF) digestibility was higher (P<0.05) when SSNR heifers fed low energy diet, but on high energy diet NDF digestibility was significantly (P<0.05) lower compared to control, respectively, during all phases with the exception of step I in the prepubertal phase and step 2 in pubertal phase where the differences were non-significant (P>0.05) between the groups. Acid detergent fibre (ADF) digestibility with SSNR low energy diet was significantly (P<0.05) higher than the heifers fed control diets during three phases. But on high energy diet, ADF digestibility was not different (P>0.05) between the two groups. Also N intake was not different (P>0.05) between the heifers fed SSNR (either low or high energy) diets and control diets, respectively, with the exception of step 2 in the postweaning phase when the control group showed a significant (P<0.05) increase in intake of N compared to the SSNR group. Faecal N as well as Urinary N losses in heifers fed SSNR (either low or high energy) versus control diets did not differ significantly (P>0.05).

All heifers have shown haematological values which are almost similar in heifers of two groups. Except total cholesterol, concentration of urea N, glucose and macro minerals in serum did not differ between the two groups.

There was no significant (P>0.05) differences in age and weight at onset of puberty and number of services per conception between the two groups. Pregnancy rate in heifers fed on SSNR diet was 50% while on control diet was 57%. Fifty percent of heifer fed SSNR and 60% of heifers fed control diet as per NRC requirement had serum progesterone concentrations> 1.0 ng/ml in two samples collected 10 days apart before reaching puberty.

The overall feed costs incurred (42660.88 vs 44509.96 Rs./animal) on SSNR heifers was significantly (P<0.05) less than the control heifers fed according to NRC recommendations from weaning to breeding age.