Impact of glucogenic additive in transition dairy cow diets of varying ruminal starch degradability on yield and composition of milk and reproductive parameters

A two-factorial experiment was carried out on 6 groups (10 animals each) of Polish Black and White Holstein-Friesian cows in the transition period to determine the effect of glucogenic additive (GA) to the diets containing grains of varied ruminal starch degradation on cow performance. The animals from 3 control groups (C-groups) were fed the diets without any additive, whereas 3 other, experimental ones (A-groups) received the diets with additive of glucogenic preparation (450 g per head/day) comprising calcium propionate and loose propylene glycol (1 : 1). In the control groups as well as in the experimental ones, three analogical treatments, differing in concentrate composed of grain species of varying ruminal degradability of starch, i.e. maize (M) - low ruminal degradability, barley and wheat (BW) - high ruminal degradability and marriage of them (MBW) were conducted. Finally, the treatments were: C-M, C-BW, C-MBW, A-M, A-BW, and A-MBW. The rations of all groups based on maize silage, haylage, and meadow hay were mixed at 69 : 19 : 12 ratio (dry matter (DM) basis) and given ad libitum. Besides, all the animals received adequate concentrate rations to satisfy their nutritional requirements. The experiment started two weeks before the expected parturition and lasted till the 6th lactation week. Neither GA nor a type of grain in the diets showed significant negative influence on DM intake. A glucogenic additive has positively affected some basal nutrient digestibility, elevating significantly DM and crude protein (CP) coefficients of the apparent total tract digestibility (CATTD), by about 3 percentage points. The GA × grain interactions (P ≤ 0.05) in CATTD of CP and nitrogen-free extract (NFE) were stated, with the peak values reported in the A-BW treatment. GA increased (P ≤ 0.05) daily milk yield by nearly 5% in comparison with the control treatments. GA × grain interaction was noted with the best effect in the treatment where GA was given along with maize-barley-wheat-based concentrate. Besides, the glucogenic additive decreased (P ≤ 0.05) protein (PDI) expenditure per 1 kg of fat-corrected milk (FCM) by ca. 6% and raised (by 0.15 percentage point in week 6) protein content, while lowered the urea milk level in weeks 3 and 6 of lactation by approximately 15%. It showed beneficial effect on cow reproductive indicators reducing the time interval from calving to successful insemination and improving insemination index.