The fattening of cull Charolais cows : effect of linseed meal on fattening performance and meat quality

Abstract

Two experiments were carried out to investigate the effects of protein supplementation on the finishing of cull Charolais cows. The objectives of the two studies were to compare the effects of using linseed meal, containing 2.5 % crude fat, or soybean meal as protein sources for cull cows.

Two different levels of protein supplementation were also compared. The daily gain, feed efficiency, carcass traits, composition of carcass gain and meat characteristics were evaluated to assess the effects of the different diets.

In each experiment, 45 cows, average age 5.5 years, were divided into five groups according to body condition, age and liveweight. A group of five cows was slaughtered at the start of the feeding period in order to estimate initial carcass composition.

Four groups of 10 cows were then fed iso-energetic diets composed of maize silage, desiccated beet pulp and either soybean meal or linseed meal. The levels of protein supplementation fed daily were 0.65 kg DM or 3.5 kg DM for soybean meal and 1.4 or 4 kg DM per head for linseed meal. The four diets had the same concentrate level and they contained 90 or 160 g PDI per UFL for soybean and 90 or 110 g PDI per UFL for linseed. All four groups were slaughtered at the same average feeding time : after 80 days in experiment 1 and 58 days in experiment 2.

Daily liveweight gains were high (1.5 kg). These could be explained by the DM intake, 14.1 kg and 14.5 kg per head in experiments 1 and 2 respectively. They did not significantly vary for either the protein source or the protein level. At slaughter, the average liveweight was 710 kg and the average carcass weight was 392 kg. The ratio of cold carcass weight to pre-slaughter liveweight was 54.2% and the ratio of hot carcass weight to empty pre-slaughter liveweight was 65.1%. Whatever the protein level, feeding linseed meal or soybean meal resulted in similar values for empty liveweight, carcass weight, killing-out percentage and conformation score. For a similar carcass weight and length of feeding time, linseed meal increased fattening. At a daily level of 1.4 kg DM per head, the subcutaneous fat increased by 13%. At a daily level of 4 kg DM, subcutaneous fat, fifth-quarter fat, carcass fat and intra-muscular lipids increased by 25%, 12%, 10% and 7 to 19% respectively (depending on the muscle). When the protein level was 90g PDI per UFL, the muscle carcass gain was 22 to 24 kg whatever the protein source. Increasing protein level with linseed meal resulted in increasing carcass fat (+ 6 to 9 kg). This contrasted with soybean meal where an increase resulted in a muscle increase. Linseed meal versus soybean meal had no influence on the acceptability of the final meat.