Effects of reducing crude protein concentration in starter feed containing constant rumen undegradable protein on dairy calves performance.

Abstract

This study aimed at investigating the effects of decreasing crude protein (CP) in diets with constant rumen undegradable protein (RUP) content on dry matter (DM) intake, growth, feed efficiency (FE) and blood parameters in calves in a randomized complete block design. Dietary treatments included: (a) a calf starter containing 200g/kg CP (62g/kg RUP, based on DM), (b) a starter containing 180g/kg CP (65g/kg RUP, based on DM) and (c) a starter containing 160g/kg CP (65g/kg RUP, based on DM). A total 42 newborn male and female Holstein calves were fed 8L milk/day until day 45, after which they were weaned and continued the experiment until day 75. Solid feed intake and total DM intake were measured daily, and body weight and skeletal growth parameters including withers height and heart girth were recorded weekly. Blood samples were collected on days 45 and 75. Solid feed intake, total DM intake, weaning weight, average daily gain from birth to weaning and from birth to 75days, final weight and FE were not affected by the experimental treatments. In addition, skeletal growth parameters were similar among groups. Glucose concentration was similar among treatments; however, calves fed the starter containing 160g/kg CP had significantly lower plasma concentrations of albumin and urea nitrogen compared with those fed starters containing 180 and 200g/kg CP. These results indicate that CP level in the calf starter could be decreased to 160g/kg DM if RUP levels stay at 65g/kg DM, without negatively affecting feed intake and calf performance.