Effect of an energy restriction followed by a re-alimentation period on efficiency, blood metabolites and hormones in Belgian Blue double-muscled cows

The aim of the present study was to determine to what extent an energy restriction, followed by a re-alimentation, affects body weight (BW), feed efficiency and concentrations of blood metabolites and IGF-1 (insulin-like growth factor 1). Two experiments were conducted with 20 (initial BW 621±18 (SE) kg) and 13 (initial BW 613±29 kg) non-pregnant dry Belgian Blue double-muscled cows, respectively. A similar diet was fed in both experiments, consisting of maize silage, 0.5 kg per day of a vitamin-mineral premix, and urea to prevent a negative rumen degradable nitrogen balance. In experiment 1, cows were divided into 2 groups and fed an energy level (EL) corresponding to their requirements (EL100; 224 days), or 0.7 of their requirements (EL70-130) during the first 112 days (Phase 1), and 1.3 times the requirements during the next 112 days (Phase 2). Cows were weighed, scored for body condition, and blood samples were collected at 8-week intervals. Glucose, non-esterified fatty acids (NEFA), creatinine, IGF-1, IGFBP (IGF Binding Protein)-2 and IGFBP-3 were analysed. EL70 resulted in a larger BW change compared to EL100 (-10.2% of the initial BW; P < 0.001) during phase 1, but BW loss was completely compensated during phase 2. Efficiency of nutrient use (gain/intake) for the restriction and the re-alimentation period as a whole was similar for both treatments (P > 0.10). Blood concentrations of metabolites and IGF-1, IGFBP-2 and IGFBP-3 were not affected by energy restriction (P > 0.10). Concentrations of glucose, NEFA, creatinine and IGFBP-3 were affected by sampling day, while a treatment x sampling day interaction was found for NEFA. In experiment 2, cows were fed at 0.8 or 1.0 of their energy requirements during 140 days, followed by a 70-day re-alimentation period, where all cows were fed ad libitum. EL80 resulted in a BW loss of 7.9% of the initial BW during phase 1. Average growth rate for the restriction period and the re-alimentation period together remained lower (P = 0.014) in comparison with cows fed according to their requirements. Furthermore, efficiency of nutrient use for the whole period was adversely affected P < 0.05). Therefore, feeding Belgian Blue double-muscled cows below their energy requirements should be discouraged.