The effect of different protein levels in the diet of beef cattle on growth and development, as well as on reproductive ability.

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.