The impacts of several hormonal growth promotants (HGP) on Warner-Bratzler Shear Force (WBSF), desmin degradation ratio (DDR) and collagen content (COLL) were assessed. Treatments within feedlot and pasture finished steer carcasses (n = 60, n = 40, respectively) were control (CON-100-F and CON-400-P), oestradiol HGPs (OES-100-F and OES-400-P) and trenbolone acetate/oestradiol HGPs (TBA+OES-100-F only). The longissimus lumborum (LL), gluteus medius (GM), infraspinatus (IS), semitendinosus (ST,) and the LL and biceps femoris (BF) were collected from feedlot and pasture finished steers, respectively. All muscles were aged between 3 and 35 days. The LL from TBA+OES-100-F carcasses had increased WBSF and decreased DDR, which varied in magnitude with ageing (P < 0.05). The GM from OES-100-F steers also had lower DDR (P < 0.05). The feedlot HGP treatments had no impact on the WBSF of the IS, ST or GM and no impact on COLL in the LL. The OES-400-P had no impact on WBSF, DDRor COLL for both muscles (P > 0.05).

Carcass value is a complex relationship with varying contributions between eating quality (MSA Index) and lean cut yield (LCY%). Bone-out data from 112 Bos taurus steer carcasses, grain finished for 100 days with a hormonal growth promotant were analyzed. Carcass values were calculated using 1) flat cut prices, 2) cut prices weighted for MSA grades, and 3) cut prices weighted for MSA grades for four high value primals. To extend the range in eating quality, analyses were re-run assuming no HGP implants. When all cuts were valued according to eating quality grade, the impact of the MSA Index and LCY% varied in their importance in determining carcass value. However, if only four high value cuts were harvested, carcass value was largely a function of LCY%. The importance of eating quality and carcass yield in determining carcass value was dependent upon the type of cattle, the cuts being harvested and the grade premiums/discounts realized.

Problems associated with muddy pens have been identified as some of the most serious animal welfare issues related to outdoor feedlot beef production, but there is relatively little work examining the use of woodchip bedding for lot-fed beef cattle under conditions of cold, wet, but non-freezing winters on soil under-bases. This study examined the effects of graded levels of woodchip on the performance and behaviour of feedlot cattle housed in wet pen conditions. Bos taurus steers (n = 300" 379.1 ± 24.1 kg) were blocked by weight and breed and randomly assigned to 30 10-steer feedlot pens provided with either no woodchip bedding (Control, n = 10) manure interface only, or 15 cm depth of woodchip bedding (W15, n = 10) or 30 cm depth of woodchip bedding (W30, n = 10). The steers were housed in these treatment pens for 109 days on a feedlot ration, and the pens were irrigated so that approximately 74 mm of total precipitation (irrigation + natural rainfall) fell onto the pen surface every 30 days. Temperatures were mostly <20 C maximum and 1 to 5 C minimum. Steers were weighed on five occasions. Animal position and posture in pen were recorded once a week over an 8-hour day-time period. Carcase characteristics were measured, and adrenal gland weights were recorded. Providing woodchip bedding increased liveweight gain (P < 0.001) and gain:feed (G:F, P = 0.012) after day 28, increased DM intake (DMI) after day 92 (P = 0.049), and increased carcase weight (P = 0.001) and dressing percentage (P = 0.023). There was no additional benefit of W30 over W15 for liveweight gain or DMI, but the benefit of W15 for G:F was lower than that of W30 by the end of the feeding period (P = 0.012). There were no effects of bedding on other carcase quality traits. Steers in Control pens utilised the front of the pen for lying and standing more than the W15 and W30 steers (P < 0.001) suggesting the steers in the Control pens perceived the front of the pen as less aversive, potentially due to increased drainage compared to rest of the pen and proximity to feed bunk. Adrenal gland weight/kg and carcase weight tended to be higher in the Control treatment group than the W30 steers (P = 0.077). This research has demonstrated that for a 109-day feeding period in cold, wet conditions, steer performance and welfare can be improved by providing a minimum of 15 cm woodchip bedding.

Hormonal Growth Promotant (HGP) implants have been used to increase productivity and profitability of beef production for over 40 years. The use of HGPs can improve average daily liveweight gain by 10-30% and feed conversion efficiency by 5-8%. Whilst HGP implants have a positive impact on beef production, their negative impact on beef eating quality has been an important industry and research topic over the past two decades.

The Meat Standards Australia (MSA) beef grading model predicts muscle by cooking method eating quality outcomes, based on inputs from production, carcass and processing variables, which have been correlated to untrained consumer sensory scores. A body of Australian research conducted in the mid-2000s identified that the use of HGP implants, results in a decrease in consumer sensory scores and objective measures of tenderness, such as shear force. This resulted in a common HGP adjustment introduced to the MSA model in 2008 to account for the negative impact on eating quality. However, there was concern from industry stakeholders that a single HGP adjustment in the MSA model may not account for the different HGP formulations used in Australia, particularly oestradiol only (OES) formulations used in northern Australia for pasture growing and finishing cattle. This formed the basis of this research and the hypothesis that OES implants have minimal or no impact on eating quality when assessed by the MSA consumer sensory protocols.

The feedlot experiment allocated 300 cross-bred steers to three HGP treatment groups; untreated control (CON-100-F), 100 day oestradiol only HGP implant (OES-100-F) and a combination trenbolone acetate and oestradiol HGP implant (TBA+OES-100-F), which were finished on a grain ration for 73 days. The use of a stronger anabolic formulation (TBA+OES100-F) significantly increased live weight gain but had negative impacts on carcass traits such as ossification and marbling, when compared to CON-100-F treatment. Similarly, the use of the TBA+OES-100-F implant resulted in a marked decrease in consumer sensory eating quality points (MQ4) of the m. longissimus lumborum (LL, ~8 MQ4 points), as well as an increase in shear force, though ageing for 35 days mitigated much of these impacts. The OES100-F treatment significantly increased liveweight gain when compared to the CON-100-F treatment and had moderate effects on carcass traits. The OES-100-F treatment impact on consumer sensory scores and shear force in the LL, was not different from that of the use of CON-100-F at five or 35 days ageing. However, m. gluteus medius (GM) samples at 35 days ageing were significantly different among treatments for consumer sensory scores. The HGP treatment impact was greater in the LL than in the GM, which supports previous findings that HGP implants have the greatest impact on muscles that have the greatest ageing potential. There was an increase in the inhibitor of post-mortem proteolysis, calpastatin, in both HGP treatments, and the TBA+OES-100-F treatment was significantly different from the CON-100-F. This inhibition of post-mortem proteolysis assisted in explaining part of the reduced eating quality. Further analysis of a subset of the carcasses and muscles, indicated that the TBA+OES decreased desmin degradation post-mortem in the LL. The OES-100-F treatment only decreased desmin degradation in the GM, which possibly explains the consumer sensory score impact at 35 days ageing. None of the HGP treatments had an impact on shear force for the GM, m. infraspinatus (IS), or m. semitendinosus (ST), or the LL sarcomere length or collagen content in the LL from these subsets of animals.

For the pasture experiment, 200 Bos taurus/Bos Indicus composite steers were allocated to two HGP treatment groups; untreated control (CON-400-P) or a 400 day oestradiol only HGP (OES-400-P), and finished on pasture for 386 days. The OES-400-P treatment increased liveweight gain, carcass weight and ossification when compared to the CON-400-P treatment. The HGP treatment had a large negative impact on consumer sensory scores in the LL (~10 MQ4 points) and increased shear force. This negative impact of the OES-400-P treatment was reduced by ageing for 35 days, though still significantly different from the CON-400-P treatment. The OES-400-P impact was greater in the LL, when compared to the GM. The OES-400-P treatment increased calpastatin activity, which explained part of the negative impact on eating quality. On further analysis of a subset of carcasses, the OES-400-P treatment had no impact on shear force, desmin degradation, sarcomere length or collagen content, in the LL andm. biceps femoris (BF). This means that consumers in the pasture experiment detected a significant impact on eating quality, which could not be explained by reduced desmin degradation in this subset of animals

The MSA model uses both the common HGP adjustment combined with the indirect effects on carcass traits such as marbling, ossification and hump height, to account for differences in HGP formulation impacts on eating quality. To test the accuracy of the MSA model for predicting the eating quality of different HGP formulations, residual consumer MQ4 scores were generated (predicted MQ4 minus actual MQ4) for all muscle samples across the two experiments and ageing periods. The MSA model accurately predicted (5/18), or under predicted (11/18), the majority of the HGP treatment samples. The majority of the underprediction was predominately for 35 day ageing and the GM HGP treatment samples. This could be seen as a safeguard for the consumer, as it would ensure that the beef eating experience was as expected or better than expected. Some over-prediction was observed in the CON-100-F and TBA+OES-100-F treatment samples, which may be due to factors such as the genetic propensity for the cross-bred cattle used in this experiment to have tougher LL muscles than the population in the MSA model. As a result, it was decided by the MSA Pathways Committee, an independent scientific reference group, that the use of a common HGP adjustment, combined with the indirect effects on carcass traits, provided a reasonable prediction of eating quality of different HGP formulations. There was an intention to further examine the HGP muscle ageing algorithms in the MSA model, as it was not fully accounting for these improvements. Similarly, consumers scored GM samples higher than the MSA model accounted for. Additional research GM sample data generated in future eating quality experiments may increase the accuracy of prediction GM samples in the model.

The results of these experiment concluded that different HGP formulations had different impacts on eating quality when steers were finished in a feedlot or on pasture. However, the MSA provides a reasonable prediction of eating quality for these different formulations through a common HGP adjustment, combined with the different impacts on carcass traits. One of the mechanisms that explains the negative HGP impact on eating quality is through an increase in calpastatin, and therefore a decrease in muscle degradation post-mortem.