Lifetime growth pattern and beef eating quality

A total of 72 Limousin crossbred (LIMx) cattle of suckler herd origin were used (12 steers & 12 heifers) for each of the three growth paths and started the trial at approximately 12 months of age. The short duration growth path animals were finished indoors on an intensive concentrate based finishing system and slaughtered at 12-16 months of age. The medium duration growth path animals were turned out to graze a high quality grass reseed from 12-17 months of age and finished indoors during the subsequent winter feeding period when offered a mixed forage:concentrate (F:C) finishing diet. They were slaughtered at 18-24 months of age when judged to have achieved commercially acceptable carcass characteristics (target R4L). Finally, the long duration growth path animals were grazed for two summer periods on poor quality, unimproved grassland with the intervening winter period being a store period where the animals were offered forage based diets. The final finishing diet was a mixed F:C diet offered during their 2nd winter prior to slaughter at 25-36 months of age. All animals completed their respective growth paths as planned.

Average days on trial were 86, 286 and 622 (P<0.001) for the short, medium and long duration growth paths respectively with mean slaughter ages of 15.1, 21.8 and 32.9 (P<0.001) months. Similarly, mean slaughter liveweights were 528, 624 and 671 kg (P<0.001) and average lifetime daily liveweight gains were 1.58, 0.96 and 0.54 kg/d (P<0.001) respectively. Mean carcass weights were 298, 356 and 378 kg (P<0.001) with average slice shear force measurements of 10.8, 10.4 and 11.9 kg (P<0.05) for the short, medium and long GPs respectively indicating that the long growth path finishing systems produced beef of poorer tenderness than either the short or medium growth path systems. The proportional content of gristle in the striploin section samples was also significantly higher (P<0.001) in the long growth path system at values of 1.63, 1.62 and 1.96 % of the longissimus dorsi muscle respectively. Human taste panel assessments of beef eating quality showed increased levels of toughness (38.7, 42.5 & 46.9; P<0.05) between the short, medium and long growth paths respectively. Despite these differences, the long growth path system could still produce beef eating quality parameters that were considered acceptable for the human food chain.

From a financial perspective, the average total feeders margin (£/head) was 301, 523 and 570 (P<0.001) for the short, medium and long growth path systems respectively. Despite this however, when these values were expressed on a daily basis (i.e. total FM/days on the growth path system) the mean values were 3.72, 1.86 and 0.91 (£/head/day) across the same three growth path systems. Once variable costs were deducted, Gross Margin figures were 36, 86 and 65 £/head whilst further deducting fixed cost estimates reduced Net Margin figures to -27, -34 and -209 £/head for the short, medium and long growth path systems respectively. Total variable costs were 265, 437 and 505 £/head whilst estimated fixed costs were 63, 120 and 274 £/head for the short, medium and long growth path systems respectively. Examining the quadratic relationships between feeders margin and the costs incurred either here or from industry estimates revealed that the greatest potential for profit was to be found when animals were slaughtered at younger, rather than older ages.

It is concluded that commercial beef finishers be advised to adopt efficient, short to medium duration (12-20 months) finishing systems that deliver higher quality beef to the human food chain whilst offering producers the greatest opportunity for commercial profit.

The Challenge

One of the means that beef farmers can reduce their greenhouse gas emissions (per kg of beef produced) and improve their profitability is to increase growth rates and thus reduce age at slaughter.  Therefore the AHDB B&L R&D strategy includes the objective of improving animal growth through better feeding methods.  Furthermore, there is evidence that younger animals at slaughter produce more tender meat and the AHDB B&L Quality Standard Mark standards include restrictions on animal age at slaughter.  Nevertheless the correct age limit for quality beef production from steers and heifers is often debated.  This project was established to examine the validity of the age threshold.

The Project

The three objectives of this proposed work were to:

1. Produce finished steers and heifers at a wide range of ages between 12 – 36 months of age according to alternative lifetime growth patterns which will include a period of growth check for the older animals using typical production systems used on-farm in England and Wales
2. Evaluate effects of lifetime growth patterns on overall productive output, carcass and meat eating quality parameters (particularly including toughness attributes) assessed by both laboratory and trained taste panel methods
3. Communicate the results to EBLEX, the wider farming community and associated industry practitioners

Deliverables

1. Establishment of the effects of lifetime growth pattern on carcass and eating quality parameters for alternative finishing systems typical of those used in the UK
2. Demonstration of production system principles to maintain the consistency of beef quality
3. Engagement of beef producers, processors and retailers in understanding the importance of production methods and their effects on enhancing consistency of eating quality
4. Dissemination of improved production principles and benefits to levy payers
5. Enhanced uptake of these principles across the wider beef industry

Approach

The overall project approach was to establish a continuous randomised block experiment with a 3x2 factorial design investigating three main treatments (three alternative lifetime growth patterns) and two cattle sexes (steers and heifers) and to study their effects on carcass and meat eating quality. 

The project had four main components as follows:

1. To establish six (3x2) experimental cattle groups of finishing cattle (steers and heifers) finished according to three typical production systems in operation across industry.  These production systems were: (i) a short duration finishing system with steers and heifers slaughtered at 12 - 16 months of age using high quality diets, (ii) a medium duration finishing system including a grazing phase with steers and heifers slaughtered at 18 – 26 months of age, and (iii) a long duration finishing system including at least two periods of grazing with steers and heifers slaughtered at 28 – 36 months of age; this third group of cattle was managed to include at a winter feeding period where there was a definite interruption in growth (animals were simply fed for maintenance)
2. Complete animal finishing. Diets using a combination of forage, concentrates and where appropriate grazing, were be formulated to achieved desired growth patterns and animal performance was monitored frequently (liveweights taken every fortnight) throughout their lifetime to accurately define alternative growth patterns during key periods of each production cycle
3. Assess the major aspects of meat eating quality over each of the respective cattle groups using a combination of both laboratory tenderness measures and taste panel assessment procedures
4. Communicate the outcomes to AHDB and any associated industry-wide practitioners