Abstract
The purpose of this study was to study the effect of different levels of crude protein (CP) in the diet of Kazakh white-headed bull calves on their growth, development, feed efficiency and reproductive qualities using the digital Intergado system. The study involved 21 animals aged 7-8 months, divided into three groups: control (CP 11%), experimental 1 (CP 13%) and experimental 2 (CP 14.5%). The results showed that in the experimental groups, the consumption of metabolic energy increased significantly (up to 2.61±0.01 Mcal/lb) and crude protein (up to 0.92±0.03 kg; p = 0.006), as well as protein decomposed in the rumen (RDP up to 0.70±0.02 kg). This led to an improvement in the nitrogen balance, which became positive in experimental group 2 (0.01±0.01 kg d-1; p < 0.001). The most significant effect was observed on the productivity of animals. The experimental groups showed significantly higher average daily gains: 1.20±0.08 kg (CP 13%) and 1.26±0.07 kg (CP 14.5%) versus 0.87±0.14 kg in the control (p < 0.05). The absolute weight gain was 53.00±2.98 kg (experimental 2) and 50.43±3.36 kg (experimental 1), significantly exceeding the control group (36.57±5.79 kg; p < 0.05). The feeding efficiency improved significantly: the feed conversion rate in the group of CP 14.5% was 5.17 versus 8.54 in the control. Meat quality indicators included an increase in the area of the muscular eye in Experimental group 1 (39.81±1.59 cm2; p < 0.05). It is important to note that the studied protein levels did not negatively affect the indicators of reproductive function, where the scrotum circumference ranged from 28.14±1.32 cm in the control to 30.14±0.80 cm in the experimental group 1, and the ejaculate score ranged from 7.66±0.51 points in the control to 7.79±0.61 points in the experimental group 1, without statistically significant There were no significant differences (p = 0.388 and p = 0.693, respectively). However, an increase in methane emissions was recorded in the experimental groups (up to 14.75±0.01 g/kg DM; p < 0.001). Thus, the level of 13-14.5% crude protein in the diet provides a significant improvement in the growth, digestibility and bioavailability of nutrients without impairing reproductive functions, and can be recommended for intensive fattening of bull calves using digital feeding control technologies.