Empty body chemical composition estimated from non-carcass parts in Belgian Blue double-muscled bulls

Phase-feeding to optimize performance and quality of Belgian Blue double-muscled bulls

To optimize performance and carcass quality of Belgian Blue double-muscled bulls four phased feeding regimens were evaluated. All diets were offered ad libitum and consisted of 650 g concentrates and 350 g maize silage per kg dry matter (DM). Total period was divided into three phases (ca. 360 to 460, 460 to 570 and 570 to 680 kg). All four groups received the same maize silage but the different energy and protein densities were applied using different concentrates. During the three phases, the negative control (NC) group constantly received a diet with a low protein and a moderate energy density; the second group (DP) received with each phase diets with decreasing protein density while the energy density remained moderate; the third group (IE) received diets with increasing energy density at a constantly high protein density and the last group (DPIE) received diets which decreased in protein and increased in energy density.

The NC group grew significantly slower during the first interval (1·37 v. 1·62 kg/day for the other groups), resulting in a significantly longer total finishing period. During the third period IE had the slowest growth. The NC group needed 21 and 20 days more than the DP and DPIE groups, respectively, to reach the same slaughter weight. The NC group had the lowest DM intake during the first interval, the IE group during the third interval. No significant differences (P > 0·05) were found for food conversion, when expressed as DM or NEF (net energy for fattening). IE had the worst protein conversion while NC had the best, with the two other groups being intermediate.

The only important significant difference concerning carcass quality was the improved dressing proportion of the IE and DP groups. Although significant, differences in the fat content of the m. longissimus thoracis are of minor importance. These results proved that for Belgian Blue double-muscled bulls, protein density of the diet can be decreased with increasing live weight, while energy should be increased to give optimal performance.

Double-muscled and conventional cattle have the same net energy requirements if these are related to mature and current body protein mass, and to gain composition

The hypothesis tested in this paper is that double-muscled (DBM) and conventional cattle, considerably differing in body composition, have similar NE requirements when: a) NE(m) is scaled as a function of current (P(i)) and adult (P(m)) protein mass; and b) ME for gain (ME(g)) is estimated from protein (Pr) and lipid (Lr) retention and their partial ME use efficiencies, the k(p) and k(l) values, respectively. First, 2 databases were examined: 1 was developed combining well known literature information from comparative slaughter trials conducted on British beef steers; the other was based on a trial conducted using extremely lean DBM Piemontese bulls. From the first database, NE(m) was calculated to be 1.625 × P(i) ÷ P(m) × P(m)(0.73) (MJ/kg(0.73)). From the second database, the daily ME(g) was determined as 22.8 MJ × Pr ÷ k(p) + 38.74 MJ × Lr ÷ k(l), assuming (from prior reports) that k(p) = 0.20 and k(l) = 0.75. Thereafter, ME(m) was defined as ME intake minus ME(g), and, hence, NE(m) was predicted as 1.625 × P(i) ÷ P(m) × P(m)(0.73) (where 1.625 was the value obtained from the first dataset). The resulting k(m) (NE(m)/ME(m)) averaged 0.67. This k(m) value did not differ from that (0.65; P = 0.12) predicted by Garrett's equation, which uses dietary ME content as the only predictive variable. Second, the procedure was tested for the ability to detect effects on k(m) caused by increasing BW and dietary factors not estimable from the dietary ME content only. Data were gathered from a trial involving 48 DBM Piemontese bulls divided into 4 groups fed 1 of 4 diets differing in CP content (145 or 108 g/kg DM), with or without addition of 80 g/d of rumen-protected CLA (rpCLA). Bulls were examined at 3 consecutive periods of growth, corresponding to 365, 512 and 631 kg of average BW. All energy balance items were influenced by increasing BW, except k(m) (P = 0.61), in agreement with the expectation that NE(m) requirement depends on the degree of maturity (P(i)/P(m)) and the P(m)(0.73) of an animal, whereas k(m) reflects characteristics of the feed provided. The k(m) value was also influenced by the CP × rpCLA interaction (P = 0.013). We conclude that DBM and British beef steers have similar NE requirements when these are scaled as a function of P(i) and P(m), and gain composition, considering Pr, k(p), Lr and k(l). The proposed procedure will be useful to predict the energy requirements and feed use in cattle of different types that vary in BW, provided that body and gain compositions are known or accurately predicted.