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Four groups of five non-lactating and non-pregnant Belgian Blue double-muscled (BBDM) cows were used to investigate the effect of energy level (E) on digestion, and blood and urine metabolites. The energy levels of the groups, applied indoors during a 140-day restriction period, were 100%, 90%, 80% or 70% of their energy requirements (E100, E90, E80, E70) respectively. Afterwards, animals grazed on the same swards for 203 days (re-alimentation period). Balance trials were conducted at the end of the restriction period (BT1) and at the end of the re-alimentation period (BT2). Blood was sampled at the end of these trials. Diets consisted of maize silage and straw (80/20 on a dry matter basis) and a mineral-vitamin premix, fed at the appropriate E during BT1, or maize silage and a mineral-vitamin premix, fed at 125% of the maintenance requirements, during BT2. Significant increases of the digestibility coefficients were found during BT1 when E decreased, resulting in a better net energy capture of 7% for E70 compared with E100 (p < 0.05). Slightly, but non-significantly higher digestibility coefficients were observed for decreasing E during BT2. Plasma concentrations of glucose and creatinine did not differ between treatments during BT1, while differences were found for triacylglycerols and alpha-amino nitrogen. A tendency for a linear increase was observed for non-esterified fatty acids with decreasing E. Differences in blood metabolite concentrations disappeared in BT2. Urinary creatinine excretion was not affected by E, while body nitrogen loss increased linearly with energy restriction in BT1. No differences were found during BT2, suggesting that non-lactating and non-pregnant BBDM cows are able to adapt to a cyclic change of body weight and body reserves. These data show that restricted cows mobilized body fat as well as body protein. It is concluded that the qualitative aspects of metabolism during energy restriction are comparable in double-muscled cows with those in non-double-muscled animals, although the magnitude of the effects may be different.

Milk intake data were collected at 4-week intervals from Belgian Blue double-muscled (BBDM) suckling calves up to 16 weeks after birth. Dams were fed at 100%, 90%, 80% or 70% of their energy requirements during a 140-day indoor period from the beginning of December to the end of April (restriction period). Afterwards, cows were turned out on pasture (re-alimentation period). Mean calving date was 3 June, but parturitions were spread over the year. A total of 521 individual milk intake (IMI) and 120 average daily milk intake (AMI, mean of IMI) records were collected. IMI amounted to 7.0 ± 2.2 kg/day and was not affected by energy level during the indoor period. It was highest in May and June. Calves born out of multiparous cows consumed more milk than those born out of primiparous cows (7.4 v. 6.2 kg per day; P = 0.001), while intake tended to be higher in female than in male calves (7.2 v. 6.8 kg per day; P = 0.044). Dam age at calving, parity, post partum weight and body condition were only weakly correlated with AMI (r 0.4). AMI was correlated with pre-weaning live-weight gain (r = 0.807) and weaning weight (r = 0.783), with a slightly higher correlation for male than for female calves. Daily live-weight gain during the suckling period was increased by 79 g per extra kg daily milk intake on average, and by 86 and 74 g, respectively, for male and female calves. Calf solid feed intake was low, even when milk intake was low. In terms of net energy intake, milk was only substituted for solid feed by 29%. It can be concluded from the calf intake that milk production in BBDM cows is comparable with that of cows from other beef breeds, but its variation is considerable, complicating an accurate estimation.

-The relationship between the body condition in Belgian Blue double-muscled cows and the performance of cows and calves has been studied over a 5-year period. One hundred and twenty-six cows, with a mean initial parity of 1.6 ± 1.1 were involved. During each winter, they were fed 100, 90, 80 or 70% of their energy requirements (140-day restriction period). At the end of April, all cows were turned out on pasture in identical circumstances (re-alimentation period). Half of the cows were suckled by their offspring; the other cows were dried off following calving and colostrum collection. Body condition score (BCS; scale 0 to 5) was determined at the start and end of the restriction period and the re-alimentation period, at monthly intervals and at calving. Two hundred and thirteen parturitions were involved, of which 63% occurred during the first half of the year. BCS (mean of monthly observations) was lower (P < 0.001) in primiparous (1.45) cows than in cows with two (1.69) or more parturitions (1.81). BCS (mean of monthly observations) was lower in suckling cows (1.51) than in dry cows (1.79; P < 0.001). BCS (mean of monthly observations) was reduced by energy restriction from 1.75 to 1.56 (P < 0.001). BCS-change during the restriction and re-alimentation periods was related to body weight change (R 2 = 0.538). BCSchange was negative during the restriction period, but it was more than compensated for during the re-alimentation period. BCS at calving was not related to the length of the subsequent calving interval. Cows with a BCS less than 1.5 at calving, yielded less milk and calf performance was reduced when compared with those with a BCS over 1.5. The dams of calves that died at birth had a lower BCS at calving (1.45) than the dams of surviving calves (1.75; P = 0.044). Open cows at 9 months postpartum had a higher BCS at calving (1.78) than cows that became pregnant within 9 months postpartum (1.50; P < 0.001). Consequently, it is difficult to define a universal optimum BCS for double-muscled cows, resulting in a maximal milk production and calf growth, a low calf loss and cow culling rate and a calving interval of approximately one year. (140 jours ; période de restriction). Toutes les vaches ont été mises au pâturage dans des conditions identiques à partir de la fin avril (période de compensation). La moitié des vaches ont allaité leur veau, tandis que les autres vaches ont été taries après collection du colostrum. La NEE (0-5) était déterminée au début et à la fin de la période de restriction et de la période de compensation, chaque mois et aussi au moment du vêlage. Il y avait 213 vêlages, dont 63 % pendant la première moitié de l'année. La NEE (moyenne des observations) était plus faible (P < 0,001) chez les primipares (1,45) que chez les vaches à deux (1,69) ou plus de vêlages (1,81). La NEE (moyenne des observations) était plus faible chez les vaches allaitantes (1,51) que les vaches taries (1,79 ; P < 0,001). La NEE (moyenne des observations) a été réduite de 1,75 à 1,56 par une restriction ...